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Journal of Geographical Sciences >

2016 , Vol. 26 >Issue 1: 83 - 101

DOI: https://doi.org/10.1007/s11442-016-1256-5

Orginal Article

Water level changes in Polish lakes during 1976-2010

  • Dariusz WRZESIŃSKI ,
  • *Mariusz PTAK
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  • Institute of Physical Geography and Environmental Planning, Adam Mickiewicz University, Dzięgielowa 27, 61-680 Poznań, Poland

Author: Dariusz WRZESIŃSKI, e-mail:

*Corresponding author: Mariusz PTAK, e-mail:

Received date: 2015-02-25

  Accepted date: 2015-06-09

  Online published: 2016-01-25

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Journal of Geographical Sciences, All Rights Reserved
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Abstract

The paper presents the analysis of tendencies in water level changes in 32 lakes in Poland during 1976-2010. Series of monthly, seasonal, and annual precipitation and air temperature for 9 meteorological stations were also studied. The trend analysis for all of the studied series of water levels in lakes showed high spatial and temporal variability. Series of annual water levels in the case of 6 lakes showed statistically significant increasing tendencies, and in 7 lakes, significant decreasing trends. Series of annual amplitudes in the majority of lakes (22) showed a decreasing trend, but they were statistically significant only in three cases. The tendencies for air temperature fluctuations are more statistically significant than precipitation. The key role in determining water level changes is played by local factors, particularly including human economic activity, obscuring the effect of natural factors on water level changes. The paper describes cases of changes in water levels in lakes under anthropopressure related to among others: agricultural irrigations, hydropower infrastructure, water transfers, navigation, or mining.

Key words： lake-level trends; lake-level regime; Mann-Kandell Test; climate change; human activity

Cite this article

Dariusz WRZESIŃSKI , *Mariusz PTAK . Water level changes in Polish lakes during 1976-2010[J]. Journal of Geographical Sciences, 2016 , 26(1) : 83 -101 . DOI: 10.1007/s11442-016-1256-5

1 Introduction

Water level changes are among the primary factors affecting the functioning of lakes. The degree of filling lake basins with water is of key importance for the course of a number of processes and phenomena, among others hydrological (Ziverts and Apsite, 2005; Dusini et al., 2009; Rodríguez-Rodríguez et al., 2012), geomorphological (Machowski et al., 2005; Zinke and Bogen, 2013; Castañeda et al., 2015), and biological (Hayashi and van der Kamp, 2007; Nishihiro, 2011). A specific volume of water in a lake and stability of the water table are of high importance from the point of view of human activity. These elements determine the abundance and availability of water resources in lakes, as well as the possibilities of their use in various areas of economy, e.g. industry, agriculture, or tourism. According to Yin et al. (2013), water level changes in lakes are also important for purely technical reasons related to the development of structures along lake shores. Water level changes, their scale, dynamics, and change tendencies depend on natural (Li et al., 2007; Duo et al., 2009; Singh et al., 2010) and anthropogenic (Konatowska and Rutkowski, 2008; Zhuang et al., 2011) factors. In many cases, the determination of their primary cause is very difficult (Jańczak and Choiński, 1988).
In reference to Polish lakes, the issue of water level changes has been undertaken by many researchers on varied sets of objects, i.e. from individual cases to several tens of lakes (Skibniewski, 1954; Pasławski, 1972; Niewiarowski, 1978; Chlost and Cieśliński, 2005; Michalczyk et al., 2011; Kutyła, 2014; Piasecki and Marszelewski, 2014). Depending on the adopted scope of analysis, the papers show variable tendencies in water level changes, and suggest various reasons for the situation. Studies determining the effect of meteorological conditions on water level changes in lakes in Poland conducted to date particularly refer to the course of precipitation. Air temperature, affecting the evaporation volume, is considered less frequently, although as emphasised by Polderman and Pryor (2004), water level changes in lakes are closely correlated with the variability of both precipitation and evaporation. The key role of these two factors is confirmed by e.g. research on lakes in the Tibetan Plateau (Yao et al., 2014).
The objective of the paper is to present tendencies of water level changes in Polish lakes in the years 1976-2010 in relation to precipitation and air temperature fluctuations. The paper determines the scale and direction of water level changes, and the primary causes of such changes.

2 Material and methods

2.1 Study area

The territory of Poland includes more than 7000 natural lakes with an area equal to or exceeding 1 ha. They are particularly located in the northern part of the country within the range of the last glaciation. Data for 32 lakes were used in the study (Figure 1).
Figure 1 Location of the lakes and meteorological stations

2.2 Data collected

Daily observations of water levels provided the basis, for the calculation of monthly, seasonal, annual, maximum, and minimum water levels, and annual amplitudes. Series of mean monthly and annual air temperatures and precipitation totals for 9 meteorological stations from the years 1976-2010 were also used. All of the data come from the collection of the Institute of Meteorology and Water Management.
The paper also uses information concerning hydrotechnical development included in the study of the National Water Management Authority (www.hydrogeoportal.pl), and in the hydrographic maps of Poland at a scale of 1:50,000. The basic parameters of the lakes are presented in Table 1.
Table 1 Morphometric data of the studied lakes (numbering in accordance with Figure 1)
No Lake Area (ha) Volume
(thous m3)		 Average depth (m) Maximum depth (m)
1 Dadaj 978.0 120784.2 12.0 39.8
2 Dejguny 762.5 92617.4 12.0 45.0
3 Drawsko 1797.5 331443.4 17.7 82.2
4 Druzno 1147.5 17352.0 1.2 2.5
5 Hańcza 291.5 120364.1 38.7 106.1
6 Ińsko 529.0 65182 11.0 41.7
7 Jagodne 872.5 82705.2 8.7 37.4
8 Jasień 575.0 48048 8.3 32.2
9 Kalwa 561.0 39468.6 7.0 31.7
10 Lednica 325.0 24397 7.0 15.1
11 Litygajno 154.5 9763.9 6.0 16.4
12 Lubie 1487.5 169880.5 11.6 46.2
13 Łaśmiady 940.0 84607.8 9.6 43.7
14 Mamry 9851.0 1003367.5 9.8 43.8
15 Mikołajskie 424.0 55739.7 11.2 25.9
16 Morzycko 317.5 49826.9 14.5 60.7
17 Necko 400.0 40561.4 10.1 25.0
18 Niesłysz 526.0 34457.6 6.9 34.7
19 Omulew 504.0 22172.7 4.3 32.5
20 Orzysz 1012.5 75326.2 6.6 36.0
21 Powidzkie 1097.5 134776.2 11.5 46.0
22 Raduńskie Górne 362.5 60158.7 15.5 43.0
23 Rospuda Filipowska 323.5 49731.8 14.5 38.9
24 Sasek Wielki 866.0 71194.8 8.2 38.0
25 Selmęt Wielki 1207.5 99463.9 7.8 21.9
26 Serwy 438.5 67181.5 14.1 41.5
27 Sępoleńskie 157.5 7501.6 4.8 10.9
28 Siecino 740.0 104441.7 14.1 44.2
29 Szczytno Wielkie 565.0 51762.5 8.0 21.4
30 Śniardwy 11487.5 660211.8 5.8 23.4
31 Wdzydze 1417.0 220800.0 1.2 69.5
32 Żnińskie Duże 420.5 29492.6 6.8 11.1

2.3 Data analysis

To detect and estimate trends in the time series the Excel template MAKESENS (Mann- Kendall test) developed by researchers of the Finnish Meteorological Institute (Salmi et al., 2002), was used.
The Mann-Kendall test is applicable in cases when the data values xi of a time series can be assumed to obey the model
xi = f (t) +εi, (1)
where f(t) is a continuous monotonic increasing or decreasing function of time and the residuals εi can be assumed to be from the same distribution with zero mean. It is therefore assumed that the variance of the distribution is constant in time.
The Mann-Kendall test statistic S is calculated using the formula:
(2)
where xj and xk are the annual values in years j and k,j >k, respectively, and:
(3)
An upward (increasing) or downward (decreasing) trend can be expressed by a positive or negative value of Z. First the variance of S is computed by the following equation (4) which takes into account that ties may be present:
(4)
where q is the number of tied groups and tp is the number of data values in the pth group.
The values of S and VAR(S) are used to compute the test statistic Z as follows:
(5)
Then, the null hypothesis of no trend, H0, is tested in order to accept or reject it. The xi observations are randomly ordered chronologically, contrary to the alternative hypothesis H1, where there is an increasing or decreasing monotonic trend. The statistic test Z (normal approximation) is computed because all time series are longer than ten. The statistic Z has a normal distribution. The absolute value of Z can be compared to the standard normal cumulative distribution to identify if there is a monotone trend or not at the specified level of significance.

3 Results

3.1 Multiannual water level changes

The trend analysis for all of the studied series of water levels in lakes showed high spatial and temporal variability. Trends in the series of mean monthly water levels from February to July are predominantly increasing, and from September to January-decreasing (Table 2).
Table 2 Results of the Z Mann-Kendall test of monthly and annual water stages in the year 1976-2010
The number of lakes with series of water levels with statistically significant trends is varied. Statistically significant (p<0.05) increasing trends were observed in series from 2 lakes (in the case of series of water levels for January) to 8 lakes (increasing trends in water levels in lakes in March). The strongest increasing trends (p<0.001) are represented by series for two lakes: Lake Jasień (series of water levels from December to June) and Lake Sasek Wielki (series of water levels for June). Statistically significant (p<0.05) negative trends were observed for 4 lakes in series of water levels in February and March, and for 8 lakes in series of water levels in October. The strongest decreasing trends (p<0.001) were observed in the case of 7 lakes. In the case of Lake Powidzkie, this concerns all monthly series of water levels. Mean water levels for Lake Rospuda significantly decrease in the case of series from April to December, for Lake Omulew from July to October, for Lake Siecino from April to June, for Lake Serwy from May to June, and for Lake Łaśmiady in January, May, and June. In the lakes mentioned above, similarly strong negative trends are also observed in series of mean annual water levels, as well as maximum and minimum annual water levels and mean seasonal water levels.
In the studied lakes, series of mean annual water levels for 18 lakes show increasing trends, and for 14 lakes decreasing trends. Statistically significant (p<0.05) decreasing tendencies are observed in the case of 7 lakes, 3 of which show statistical significance of p<0.001. Statistically significant (p<0.05) increasing trends are determined based on annual series of water levels in 6 lakes, including one lake with a trend significant at a level of p<0.001 (Table 2). Selected examples of the course of mean annual water levels in the analysed multiannual are presented in Figure 2.
Figure 2 Multiannual course of mean annual water levels in selected lakes in the years 1976-2010
a. lakes with a significant increasing water level trend; b. lakes with a significant decreasing water level trend;
c. lakes showing no significant water level trends
Series of maximum and minimum annual water levels shows statistically significant (p<0.05) increasing trends for series of minimum water levels for 9 lakes, including one at a level of p<0.001. Seven lakes show statistically significant decreasing trends in the series (p <0.05), including three very significant ones (p<0.001). In the case of series of maximum annual water levels, statistically significant trends are determined for only 2 lakes, and decreasing trends for as many as 8 (Table 2).
The analysis of trends in series of annual water level amplitudes shows the prevalence of decreasing trends, observed in 22 lakes. The trends, however, were statistically significant only in four cases (p<0.05), namely in Lakes Morzycko, Raduńskie Górne, Sasek Wielki, and Selmęt Wielki, for which the significance of the decreasing trend is at a level of p <0.001.

3.2 Changes in trends in annual series of water stages

Because the analysis showed high variability of both the direction and significance of trends in the studied series of water levels from the years 1976-2010, a more detailed analysis were performed regarding shorter 20-year observation terms of mean annual water levels in lakes. A total of sixteen 20-year terms were analysed with a temporal shift of 1 year, beginning from the period 1976-1995, and ending with the period 1991-2010. Figure 3 presents the correlation coefficients of linear regression for each of the 20-year terms with threshold values at a significance level of p=0.05.
Figure 3 Changes in correlation coefficients of water levels in 20-year terms
a. lakes showing an increasing tendency; b. lakes showing a decreasing tendency
Five of the studied lakes showing statistically significant increasing trends in the years 1976-2010 are distinguished by considerable changes in the correlation coefficient in the analysed 20-year terms (Figure 3a). Only 2 lakes (Dejguny and Sasek Wielki) show a similar course of correlation coefficients, and reach statistically significant values only in series after 1988. In the case of Lake Morzycko, periods with significant correlation coefficients are 20-year terms from 1981-2000 to 1985-2004. The course of the correlation coefficient for Lake Hańcza shows that the highest values are obtained at the beginning of the studied multiannual 1976-1995. The correlation coefficient values in consecutive periods successively decrease. In the years 1985-2004 and 1987-2006, they are even negative and statistically significant. The most regular course and constant value is reached by correlation coefficients in the case of Lake Jasień, although in the last two 20-year terms after 1990, they are statistically insignificant.
Lakes with (statistically significant) decreasing trends of annual water levels in the years 1976-2010 show less substantial changes of the correlation coefficient in the studied 20-year terms, and its value is usually statistically significant (Figure 3b). This pattern does not concern Lakes Łaśmiady and Omulew. Their respective series of annual water levels from 1986 and 1987 are distinguished by an increase in the correlation coefficient to positive, although statistically insignificant values.
The remaining lakes not showing statistically significant trends in the studied series of water stages are distinguished by a similar, characteristic, cyclical course of correlation coefficient curves. Correlation coefficients reach low values for series from the years 1978-1997 and 1987-2006, and high in the years: 1976-1995, 1983-2002, and 1991-2010 (Figure 4).
Figure 4 Changes in correlation coefficients of water levels in 20-year terms for selected lakes not showing statistically significant trends in annual water levels

3.3 Meteorological factors contributing to water-level changes

The investigation of the effect of basic climate components determining the conditions of water supply to lakes on their water levels involved the analysis of tendencies in changes in precipitation and air temperature values at 9 meteorological stations, and their correlations with lake water levels.
The analysis of tendencies in monthly, seasonal, and annual sequences of precipitation showed a statistically significant increase in series for February (at 8 stations). In the case of seasonal precipitation, only series of spring precipitation at 3 stations (Chojnice, Łeba, and Poznań) showed a statistically significant increase, and for series of annual precipitation only at the station in Szczecin. The paper only includes results of the Z Mann-Kendall test for annual series of precipitation and air temperature (Table 3).
Table 3 Results of the Z Mann-Kendall test for annual precipitation totals and air temperatures in 1976-2010
Increasing tendencies of air temperatures are considerably stronger. At the majority of stations, a very statistically significant (p<0.001) increase in air temperatures is observed in April, July, and August. Among seasonal temperatures, the highest temperature increase is observed in summer, but a statistically significant increase in temperatures (p<0.05) also occurs at the majority of stations in spring. In series of mean annual air temperatures, a statistically significant increase (p<0.05) was observed at all of the stations except for Szczecin.
The determination of the effect of meteorological conditions on water level changes in lakes involved the analysis of correlations of synchronic and asynchronic (with a temporal shift of one year) series of water levels in lakes with precipitation and air temperature. The correlations of lake water levels with precipitation amounts are positive, and in the case of 13 lakes they proved statistically significant (p<0.05), in the case of 5 lakes even at a level of p<0.001 (Table 4 and Figure 5). The weakest correlations were recorded in the case of lakes with the strongest water level trends resulting from local conditions.
Figure 5 Statistical significance of coefficients of correlation of mean annual water levels in lakes with the annual precipitation total
a. synchronic series; b. asynchronic series
Table 4 Coefficients of correlation of water stages in lakes with precipitation amount and air temperature
The study also confirmed that in the case of many lakes, even stronger correlations occur between precipitation and annual water levels observed in the following year (Table 4 and Figure 5b). This fact was emphasised by among others Vincent et al. (1979) and Chojnowski (1995). As many as 19 lakes show statistically significant correlations of water levels with the precipitation amount observed in the preceding year, including 12 lakes with the significance at a level of p <0.001.
The second meteorological factor determining the water balance of lakes and their water levels is air temperature. An increase in air temperature results in an increase in evaporation, and a decrease in the water level. Therefore, the majority of lakes show negative correlations with air temperature. The correlations, however, are statistically significant only in the case of 4 lakes (p<0.05)-Table 4 and Figure 6a. Due to the observed tendencies of an increase in air temperatures, in the case of lakes where water stages also increase, positive correlations are obtained (Lakes Druzno, Jasień, Hańcza, and Sasek Wielki). In the case of 12 lakes, even stronger negative correlations are observed between annual water levels and the mean temperature observed in the preceding year (Table 4 and Figure 6b). Four lakes (Omulew, Powidzkie, Siecino, and Żnińskie Duże) show statistically significant correlations even at a level of p<0.001. The majority of them, however, are lakes with annual water levels showing a decreasing tendency resulting from human activity.
Figure 6 Statistical significance of coefficients of correlation between mean annual water levels in lakes and mean annual air temperature
a. synchronic series; b. asynchronic series
The analysed multiannual 1976-2010 included 3 periods of draught (in the years: 1982-1983; 1989-1992; and 2003). The strongest draught with the largest range occurred in 1992 (Łabędzki, 2004).
Very low water levels were usually observed in the lakes in these periods, particularly when higher air temperatures were recorded in the same year, e.g. in 1989 and 1992. In some of the lakes, the response of the water level to low water supply from precipitation is delayed. This may be caused by smaller losses to evaporation, observed at lower air temperatures, e.g. in 1996 - Lake Dadaj (Figure 7).
Figure 7 Course of water levels in Lake Dadaj and atmospheric precipitation (a) and air temperature (b) at Mikołajki station in 1976-2010
Responses of lakes are also varied in the case of higher precipitation, when high water supply and low losses to evaporation are observed, and high water levels occur in the following year, e.g. in 1980, 1987, and 2006. When higher precipitation supply is accompanied by high losses to evaporation (high temperature), a high water level in lakes is frequently observed in the same year, e.g. in 1995 and 1999.

4 Discussion

The course of water level changes in the analysed lakes suggests a complex character of the process. This fact is reflected in the broad range of tendencies in water level changes. Such a situation is caused by a combination of co-occurring features and factors: meteorological (precipitation, evaporation), individual parameters of lakes (their morphometry and relations with the catchment), and anthropopressure (melioration works, water intake). Their effect on water level changes is emphasised by among others Fathian et al. (2014) based on the example of Lake Urmia (North-western Iran). According to the authors, the observed decreasing tendencies in the lake may be determined by an increase in air temperature, variable precipitation, and intensified human activity.
Shortage of precipitation is one of the potential reasons for a decrease in water levels in lakes. Lack of precipitation or its shortage itself does not result in a decrease in the water level, if it occurs in the season in which the alimentation of lakes from precipitation is not necessary, e.g. due to high retention levels of the catchment, or because it is not the regular lake alimentation season. Shortage or lack of precipitation may trigger a decrease in water levels in lakes, usually when it occurs in the season of lake alimentation with precipitation waters and at high air temperature. The combined effect of two climatic factors, namely atmospheric draught and high temperature disturbs catchment alimentation and causes intensive evaporation of water contained in the soil and surface water bodies. A further decrease in water levels depends only on whether and to what degree the water resources in the lake itself and its catchment can be supplemented. If autumn rainfall is scarce, winter is snowless, and spring meltwater season early, such a combination of conditions does not guarantee the reconstruction of the water resources of the catchment. In such a situation, the water table in a lake at the beginning of a new vegetation season is at a level only slightly higher than in preceding autumn. If the conditions in the new hydrological year are similar as in the preceding one (low precipitation, high temperature), or precipitation even if higher is insufficient, the tendency for decreasing water levels as a result of weak alimentation of lakes may continue. The meteorological conditions of water level changes are therefore strongly varied. An increase in water supply is not always accompanied by higher water levels, and a decrease in water supply by lower water levels. This may result from the effect of air temperature determining higher or lower losses to evaporation. As a consequence, water level changes and precipitation amounts may be synchronic or shifted by one year. Such patterns are particularly clearly observed in lakes with a quasi-natural regime of water levels. Modifications of the observed correlations result from thermal conditions, and their strength from the individual features of the lake and its catchment.
In the case of Polish lakes, human activity is mentioned by Górniak and Piekarski (2002) as important in modifying the natural hydrological cycle in lakes. Dynamic social development in Poland was recorded in the 18th and 19th centuries. During the time, extensive melioration works were conducted, and the obtained areas were adapted for agricultural or settlement purposes. A number of lakes were subject to a considerable water level decrease (Kaniecki, 1991, Kowalewski, 2012) or complete disappearance (Ptak et al., 2013). Over the next decades, the situation regarding water resources in Poland changed radically. Considerable water deficits are currently recorded (particularly in the central part of the country). The water resources of Poland are among the lowest in Europe (Kowalczak et al., 1997), and are comparable to desert countries such as Egypt. The necessity to retain water in catchments in order to reduce extreme hydrological situations (both draughts and floods) has become a priority. In reference to lakes, the direct interference in their hydrological regime concerns among others hydrotechnical development on the outflow, permitting regulation of water levels, and therefore of the accumulated water resources. For example, only in the case of the Wielkopolskie Province, damming of 48 natural lakes with a total area of 3023 ha and volume of 33.008 million m3 is stipulated (www.wzmiuw.pl).
Results obtained for the analysed multiannual suggest the prevalence of the increasing tendency of water levels (recorded for a total of 22 lakes with varied degrees of significance). A similar situation, i.e. prevalence of water level increase in a given group of lakes, was observed in Poland by among others Dąbrowski (2004), where increase was recorded for 16 out of 24 lakes. Other papers (Skibniewski, 1954; Pasławski, 1973; Chojnowski, 1992) record a decrease in water levels in the majority of the analysed cases. In such a situation, it is difficult to synthetically refer the obtained data to earlier papers. In addition to a different time period, they also concern a different number of lakes. This fact, however, proves a certain cyclical character of water level changes in lakes, as confirmed by the analysis of the multiannual 1976-2010 presented in the paper, showing variable character in division into shorter periods. The extrapolation of the obtained data to lakes in other regions of the world is equally complicated. Although the mechanism of water level changes is basically the same, the climatic and morphometric conditions of lakes, and particularly the direction and scale of human activities, can be extremely varied. The territory of Germany, neighbouring to the west, is similar to the study area in a number of aspects. The analysis of water level changes in lakes in the Mecklenburg Lake District by Kaiser et al. (2014) showed that in the years 1999-2008, the majority of them showed a decrease in the water level (23 out of 45 studied lakes), no tendencies of changes were recorded for 15 lakes, and an increase in water level was recorded in seven cases.
Based on a literature review, Bajkiewicz-Grabowska (2001) emphasised that the course of water levels in Polish lakes in the multiannual aspect is primarily determined by local and not climatic conditions. The author confirmed this by analysing 21 lakes from north-eastern Poland in the years 1951-1998. She recorded no statistically significant correlations between precipitation and water levels in the lakes. Determining correlations between water levels and precipitation for 17 lakes located in the catchment area of the Odra River, Kowalik et al. (2008) recorded statistical significance in only two cases. In the multiannual analysed in the paper, such a correlation was observed for 5 lakes. Only 2 lakes (out of 32) showed no positive correlation with precipitation (Lakes Powidzkie and Raduńskie Górne). They are both under strong impact of human activity. Lake Powidzkie is distinguished by the highest decrease in water level (-17.2 cm·dec-1) among all of the lakes. The situation is caused by a disturbance of the groundwater regime over an extensive area as a result of the activity of the nearby brown coal mine. According to Przybyłek and Nowak (2011), mining meliorations caused the development of a depression cone which strongly affected the groundwater supply to Lake Powidzkie (and other lakes in the sequence of the Powidzkie- Ostrowskie channel). This unfavourable situation is not even likely to be reduced by means of the hydrotechnical infrastructure (weir) established on the outflow from Lake Powidzkie. The variability of water levels in Lake Powidzkie and the lake nearest to it (approximately 40 km), namely Lake Lednica in relation to precipitation for Poznań station is presented in Figure 8.
Figure 8 Course of monthly water levels in selected lakes and precipitation in the years 1976-2010
A. Lake Powidzkie; B. Lake Lednica; C. Poznań meteorological station
Lake Raduńskie Górne, included in a larger group of lakes (Raduńskie-Otrzyckie), is important for the economic development of the region. According to Okulanis (1981), who performed a detailed study of the lake, owing to the possibility to artificially regulate discharge, the entire group of the above mentioned lakes constitutes a natural retention reservoir contributing to even discharges of the Radunia River which flows through it. This fact is of importance for the functioning of hydro power plants located on the river (a total of eight power plants with power of 14 MW) as well as other economic infrastructure (e.g. sawmills) located between lakes. In reference to the variability of water levels, the same author determines that the use of lakes for the aforementioned purposes caused a disturbance in the dynamic balance, and the course of changes is of local character. The artificial transformation of the water level regime of Lake Raduńskie Górne resulting from the functioning of the hydro power plant, although considerably varying from other analysed lakes, does not show such an extreme course as a different lake in Poland adapted for energy production. Lake Żarnowieckie (1431 ha) was assumed to serve as a water reservoir for the purposes of a nuclear power plant which was never built. Currently, its southern shore is occupied by a pumping power station (800 MW). Due to this, considerable daily water level changes are observed (approximately 1 m). Based on their observation, Kaźmierski and Jasińska (1996) determined that extreme water stages recorded before the launch of the pump power station in 1983 were exceeded almost every day.
The remaining 25 lakes showing a positive (but statistically insignificant) correlation between water levels and precipitation suggest the predominant role of local factors - blurring the direct correlation between precipitation and water levels. The adaptation of lakes to agricultural purposes is quite a common form of water level regulation (Coe and Foley, 2001, Legesse and Ayenew, 2006, Yildirim et al., 2011). In extreme cases, poorly planned water management in reference to a given lake may result in an irreversible decrease in water level, and as a consequence its disappearance. The most spectacular example of such a situation is Lake Aralskie which was completely dried as a result of irrigation works (Shi et al., 2014, Zmijewski and Becker, 2014). Among the analysed lakes, such activity can be illustrated among others based on the example of Lake Wdzydze, used for irrigation of the nearby meadows. Churski (1961) describes the entire cycle in detail. In the spring season (March-April), irrigation of meadows occurs. During this time, the water level rapidly decreases (by 1 m). At the turn of June and July, the weir regulating the water level is closed (due to haymaking). This is followed by further irrigation of meadows. The weir is closed again in September, when the water level increases by 2 m. After the completion of the second hay harvest, the water level decreases to the average level, and such a situation is maintained throughout winter.
Other examples of water level regulation are encountered in lakes adapted to navigation purposes, e.g. Lakes Necko and Serwy. The former lake is located on the Augustów Canal. The latter, due to the weir regulation, constitutes the primary water reservoir for the summit level of the canal.
The hydrotechnical development on lakes can change its function depending on the character of the prevalent human activity. Murat-Błażejewska et al. (2008) describe the case of Lake Niepruszewskie (242 ha), where the existing weir was used for agricultural irrigations in the first period after its construction (1200 ha), and then was used for the purposes of fisheries. In the recent period, as a result of pressure of owners of land surrounding the lake, its functioning involving increasing retention was reduced.
The depth of lakes and their geological conditions constitute another issue. The location of the lake in efficient aquifers may determine the character and course of the occurring processes (Choiński and Ptak, 2012). In such situations, the course of precipitation does not have to reflect the course of water levels. This fact is confirmed in the case of Lake Jasień (with the highest increase in mean annual water levels among all of the lakes, amounting to 3.8 cm·dec-1), where no significant correlation with precipitation was recorded (although the correlation was positive). According to Borowiak (2000), in this case, surface inflow constitutes a secondary component of water supply, and groundwater alimentation does not only include local aquifers, but exceeds the boundaries of the topographic catchment.
The global increase in air temperature is reflected in the increase of lake waters (Wilhelm and Adrian, 2008, Schmid et al., 2014, Wrzesiński et al., 2015). This translates to an increase in evaporation from water surface. Analysing evaporation from the water surface of Lake Sławskie in the period from May to October 2007, Chmal (2008) recorded its highest value in June, amounting to 114.3 mm. At the multiannual scale, considerable changes in the course of the process are observed for Poland. Kędziora (2010) estimates that in the years 1996-2006, evaporation from water surface for the Wielkopolskie Province increased from 600 to 1000 mm.
Only three of all of the discussed lakes show positive correlations with air temperature. This is a contradiction from the point of view of (undisturbed) water balance. This situation should be interpreted similarly as in the case of precipitation, where the key determinants of water level changes are individual features and local conditions of a given lake. Lake Druzno is an interesting case, where components influencing water level changes include both human activity and natural factors (but not meteorological). According to Fac-Beneda (2013), the main causes include water discharges (by means of pumping stations and discharge pipes) from local polders and water level changes in the Vistula Lagoon (a bay of the Baltic Sea) with which Lake Druzno shares a hydraulic network through the Elbląg River. A similar correlation is described by Zolár and Bengtsson (2006) based on the example of Lake Poopó in Bolivia, where water levels particularly depend on the water levels in Lake Tititaca (connected with Lake Poopó with the Desaguadero River).

5 Conclusions

The analysis of water level changes in Poland presented in this paper suggests the complex character of the issue.
(1) The analysis of mean annual water levels from the multiannual 1976-2010 suggested the prevalence of increasing trends (for 18 lakes, including 6 statistically significant ones). Out of the remaining 14 lakes with decreasing trends, the correlation was statistically significant for 7 lakes. The study also showed that tendencies of air temperature changes are more statistically significant than those of atmospheric precipitation. Spring, summer, and annual temperature series showed statistically significant increasing trends. The amount of atmospheric precipitation as a revenue value in the water balance should be of key importance in water level changes in lakes. As evidenced in the study, due to the local conditions (morphometric parameters of lakes, their management, etc.), this pattern is ambiguous. Although water levels in 30 (out of 32) lakes showed positive correlations with annual precipitation totals, only five cases were statistically significant. Water levels in lakes show weaker correlations with air temperature. Statistically significant correlations were only determined in the case of 3 lakes. According to the study, for the majority of lakes, their water levels are stronger correlated with asynchronic (shift by 1 year) than synchronic atmospheric precipitation and air temperature series. Correlations of air temperature with water level in the following year are usually negative, and in the case of 12 lakes, statistically significant.
(2) Several centuries of human activity had the strongest impact on hydrological relations in Poland in this respect. At the first stage, it was related to meliorations (aimed at obtaining new land for agricultural and settlement purposes). Over the recent decades (due to the increasing water deficits in Poland), it was involved in the development of hydrotechnical infrastructure aimed at increased retention (of both surface and groundwaters). As evidenced by the analysed examples, in the case of lakes, the interference was both intended and unexpected. In the first case, the interference resulting from precisely controlled water management is aimed at meeting specific economic objectives, e.g. irrigation of the agricultural land in the area (e.g. Lake Wdzydze). In the second case, exploitation of brown coal by means of opencast method resulted in a considerable transformation of a number of components of the natural environment, including a disturbance in hydrogeological relations leading to successive lowering of the water level in Lake Powidzkie.
(3) Due to the large group of factors co-determining water level changes, the process cannot be considered in the regional aspect. As evidenced by the selected examples, the possibility of identification of the primary determinants of water level changes requires individual analysis of each lake. Determining patterns is possible based on multiannual field research. Such an approach referring to individual lakes (de facto constituting study cases) is commonly applied and accepted in the world, as confirmed in the related literature.

The authors have declared that no competing interests exist.

References

Publishing order | Descend order by publishing year | Descend order by cited within
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2
Borowiak D, 2000. Water regimes and hydrological functions of lakes of Polish Lowland. Seria: Badania Limnologiczne, 2, Wyd. KLUG, Gdańsk. (in Polish)

3
Castañeda C, Javier Gracia F, Luna Eet al., 2015. Edaphic and geomorphic evidences of water level fluctuations in Gallocanta Lake, NE Spain.Geoderma, 239/240: 265-279.The pedological implications of lake water level fluctuations are complex, especially in lake margin, where topographical, hydrological, and sedimentary conditions are most variable. Lake water level fluctuations generate landscape elements, which provide insights into the processes involved in soil development and the extent of the zones affected by flooding/desiccation. Coupling information from detailed geomorphological inspections in the field, the mapping of the lakeshore, and the pedogenesis of each landscape element can provide a better understanding of these relationships, which was used to study the saline Gallocanta Lake, NE Spain, a semiarid intramontane lacustrine system that undergoes significant and rapid water level fluctuations. Geomorphic classification of the lake margin forms and environments served as a guide for soil sampling. The geomorphological survey revealed high diversity and contrast in the lake margin environment, from shores affected by coastal erosion to zones characterized by progradation/aggradation. Two soil toposequences and 11 pedons that were on different geomorphic units were studied on two margins of the lake. Following gradients in elevation, moisture, and salinity, soils showed a succession of Inceptisols to Aridisols, with Mollisols developed at intermediate positions and Aquic soils at the lake floor and southern shore. Soils had a sandy, loamy texture and a predominantly carbonatic composition, high variation in CCE (mean=37%), texture, and coarse fragments throughout the soil profiles. Soil salinity was the highest at the lowest topographic position and in the upper soil horizons, where mean ECe=188.6dSm 1 at 25°C. In addition, the highest organic matter (6%) and gypsum (34%) content occurred at the lake floor. Soil color characteristics and concentrations, and depletions of Fe and Mn indicated redox changes associated with soil water saturation under carbonate and or saline conditions. Macro and micromorphological features of oxidized and reduced horizons indicated the alternation between palustrine (reduced) and non-palustrine (detrital, emerged, oxidized) events at different geomorphic and topographic positions, from the lake floor up to 7m above it. Pedogenesis inferred and the littoral/submerged forms located at permanently emerged areas confirmed the past and present trend towards the desiccation of the lake. This study has improved our understanding of how soils form and develop within the context of geomorphic units, and can be used in making land-use decisions in the protected reserve and agricultural surroundings of the lake.

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4
Chlost I, Cieśliński R.2005. Change of level of waters Lake Łebsko.Limnological Review, 5(1): 17-26.ABSTRACT Lake ebsko is one of the numerous coastal lakes of the Polish coastal zone, where a different hydrological regime is observed than in typically inland lakes. Strong influences of the Baltic Sea are recorded here. They cause intense inflow of sea waters into the lake, resulting in raised water stages, during autumn and winter storms or during low water stages in the lake in summer. The changes of water fluctuations in Lake ebsko have a very dynamic and sometimes rapid course. It is manifested not only in annual or monthly distributions but also in daily distributions, where within several hours, water stages can rise by over 20 cm.

5
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6
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7
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8
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9
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10
Coe M T, Foley J A, 2001. Human and natural impacts on the water resources of the Lake Chad basin. Journal of Geophysical Research: Atmospheres, 106(D4): 3349-3356.An integrated biosphere model (IBIS) and a hydrological routing algorithm (HYDRA) are used in conjunction with long time-series climate data to investigate the response of the Lake Chad drainage basin of northern Africa to climate variability and water use practices over the last 43 years. The simulated discharge, lake level, and lake area of the drainage basin for the period 1953–1979 are in good agreement with the observations. For example, the correlation coefficient ( r 2 ) between the simulated and the observed level of Lake Chad for the 288 months of available observations is 0.93. Although irrigation is only a modest portion of the hydrology in the period 1953–1979; representing only 5 of the 30% decrease in simulated lake area for the decade 1966–1975, the simulated lake level and area are in better agreement with the observations when irrigation is included. For the period 1983–1994 the observed water use for irrigation increased fourfold compared to 1953–1979. A comparison of the simulated surface water area, with and without irrigation, suggests that climate variability still controls the interannual fluctuations of the water inflow but that human water use accounts for roughly 50% of the observed decrease in lake area since the 1960s and 1970s.

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11
Duo B, Bianbaciren, Li Let al., 2009. The response of lake change to climate fluctuation in north Qinghai-Tibet Plateau in last 30 years.Journal of Geographical Sciences, 19(2): 131-142.<a name="Abs1"></a>According to the analysis of the climate materials including the topographic map in 1975, the TM and CBERS satellite remote sensing materials from the 1980s to 2005 as well as the air temperature, precipitation, evaporation rate, maximum depth of snow and the biggest depth of frozen soil in the past 45 years, the water level area of four lakes at the southeast of Nagqu, Tibet including Bam Co, Pung Co, Dung Co and Nuripung Co show a distinct trend of expansion in the past 30 years. In 2005, the water level area of the above four lakes increased by 48.2 km<sup>2</sup> 38.2 km<sup>2</sup> 19.8 km<sup>2</sup> and 26.0 km<sup>2</sup> respectively compared to 1975, with the respective increase rate of 25.6%, 28.2%, 16.2% and 37.6%. That is closely related to the warming and humidified climate change in the recent years such as rise of the air temperature, increase of the precipitation, decrease of the evaporation rate and permafrost degradation.

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12
Dusini D S, Foster D L, Shore J Aet al., 2009. The effect of Lake Erie water level variations on sediment resuspension. Journal of Great Lakes Research, 35(1): 1-12.<h2 class="secHeading" id="section_abstract">Abstract</h2><p id="">Variability in Lake Erie water levels results in variations of the fluid forces applied to the lake bed by free-surface gravity wind-waves. An increase in the bed stress may re-suspend sediment deposited years earlier. This study identifies areas of possible non-cohesive sediment mobilization in response to the forcing conditions and water levels present in Lake Erie. Observations from NOAA buoy 45005 were used to identify wave events generated by a variety of atmospheric forcing conditions. For each event, numerical predictions of significant wave height, wave period, and water level from the Great Lakes Forecasting System (GLFS) were used to characterize the wave event variability over the lake. The Shields parameter was estimated at each 2&nbsp;km&#xA0;&times;&#xA0;2&nbsp;km grid cell with the local wave forcing as predicted by GLFS assuming an estimate of the wave-induced friction factor. In the Cleveland harbor region of the central basin, the Shields parameter was also estimated by assuming uniform wave conditions as observed by NOAA buoy 45005. The &ldquo;contour of incipient motion&rdquo; for both variable and uniform wave events was defined as the offshore contour where the Shields parameter exceeds the critical limit for motion. Comparisons with a radiometrically corrected image from Landsat-7 showed that the spatially varying wave events from GLFS were in qualitative agreement with the satellite observations. A sensitivity analysis of wave height, wave period, and grain size showed the contour of incipient motion to be the most sensitive to wave period. Calculations performed for record high and low water levels showed that the incipient motion of non-cohesive sediments in the relatively flat central basin to be the most sensitive to the historic hydrologic variability present in Lake Erie.</p>

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13
Hayashi M, van der Kamp G, 2007. Water level changes in ponds and lakes: The hydrological processes.Plant Disturbance Ecology, 311-339.Lakes and ponds occur in a wide range of depths, sizes, and permanence rom deep lakes having a permanent body of surface water to shallow ponds having water for only a few weeks each year. These factors also vary within each lake or pond, resulting in diverse communities of aquatic plants growing in various patterns. Certain types of plants require relatively high water levels, while others cannot tolerate standing water. Therefore, water level change is considered to be a disturbance to many aquatic plants. Water level changes in ponds and lakes occur because of the water input exceeding output or vice versa. Because hydrological processes control inputs and outputs, understanding the water level changes and resulting ecological responses requires understanding the individual processes. It is particularly important to realize the intimate link between lakes and their catchments. Disturbance in the catchment, such as major land use change, can cause a dramatic change in hydrological processes, which ultimately affects the lake water level. This fact is clearly demonstrated in this chapter, in the case study of prairie wetlands, where grassing the uplands resulted in the drying out of wetlands. It is expected that collaborative research on ecohydrology is helpful in observing hydrological processes and ecological responses simultaneously, and to develop coupled models for the prediction of ecosystem responses to land use and climate changes.

14
Fac-Beneda J, 2013. The hydrological characteristics of Lake Druzno. In: Lake Druzno Natural Monograph (ed.). Cz. Nitecki, Monografia Przyrodnicza. Wyd. Mantis, Olsztyn, 15-31. (in Polish)

15
Fathian F, Dehghan Z, Eslamian S, 2014. Analysis of water level changes in Lake Urmia based on data characteristics and non-parametric test.International Journal of Hydrology Science and Technology, 4(1): 18-38.ABSTRACT Lake Urmia water level has fluctuated during many years. We investigated water level data (annual maximum, minimum and average series in the period of 1966&ndash;2012) to evaluate changes based on long-term and seasonal patterns over time, data characteristics and temporal change analysis. Our tools for the mentioned analyses included seasonal trend decomposition using loess (STL); normality and independence; change point and trend analysis. The results of STL revealed a sustained decline occurring after the last 1990s and loess trend line confirmed it. The analyses of data characteristics showed that the observed data do not fulfil the assumptions of being independent and identically normal-distributed. Therefore, the non-parametric Pettitt&rsquo;s test was applied to identify an abrupt change point in the data series, followed by trend analysis using the non-parametric Mann-Kendall test. Results showed that there is a significant decreasing trend in water lake level and the beginning of change point is in 1996.

DOI

16
Górniak A, Piekarski K, 2002. Seasonal and multiannual changes of water levels in lakes of northeastern Poland. Polish Journal of Environmental Studies, 11(4): 349-354.Seasonal and multiannual hydrological changes were analysed in seven lakes of northeastern Poland on the basis of a 40-year series of everyday observations of the water level in the years 1961-2000. In the unmodified hydrological lakes occurs an unimodal cycle of variation in the water level with a spring maximum, whose magnitude depends on atmospheric precipitation in the form of snow in the period December- March. In lakes with hydrology transformed by man, seasonal water level changes depend on their economic function in the catchment. An anthropogenic increase in the amplitude of the varying water level in lakes is the factor intensifying the eutrophication of water bodies. Multiannual cycles of variation in lake levels take different spans of time depending on hydrological characters of the lakes.

DOI

17
Jańczak J, Choiński A, 1988. Water level fluctuations in selected lakes in Poland in the years 1956-1985. In: Natural and anthropogenic Transformations of Lakes and Wetlands in Poland, (red. Z. Churski), UMK, Toruń. (in Polish)

18
Kaiser K, Koch P J, Mauersberger Ret al., 2014. Detection and attribution of lake-level dynamics in north-eastern central Europe in recent decades.Regional Environmental Change, 14(4): 1587-1600.The lake-rich glacial landscapes of north-eastern central Europe play an important role in the preservation and use of water resources, including protection of biodiversity, carbon storage and promotion of tourism. With a view to the last c. 20years and the future, a regional ‘syndrome of water shortage’ has been frequently stated, which impairs particularly peatlands, flowing waters and lakes. Accordingly, the overall question addressed in this study is: What can regional and local gauging records tell us about decadal hydrological changes of lakes and their catchments? In the study area, most of the gauging records of lakes begin only in the late 1990s. Forty-five lake-level records were analysed by hierarchical agglomerative clustering, looking for the trend in the 1999–2008 time window. The analyses show that lake levels had varying dynamics, namely a negative, unclear or even a positive trend. The proportional shares of these three groups are 23 (51%) to 15 (34%) to 7 lakes (15%), respectively. In group 1, largely groundwater-fed lakes, lake-level changes depend on groundwater-level changes. These are controlled by decreasing groundwater recharge in the catchments, which are caused by specific seasonal weather conditions in the observation period, and the impact of the dominating pine forests, which consume high quantities of water. In group 2, mainly stream lakes, direct human impact drives the lake levels through the management of weirs and ground sills. Nearly all lakes in group 3, consisting of river, stream and spring lakes, were subject to impoundment measures initiated by local rewetting projects. Thus, an important finding with respect to the impact of climate and land use is the fact that the (‘natural’) lakes of the region, primarily fed by groundwater and precipitation, show a predominantly negative lake-level trend in the period studied. Beyond the 10-year-time window analysed, further regional data show that periodic lake-level fluctuations with amplitudes of c. 1–2(–3) m are characteristic for regional groundwater-fed lakes.

DOI

19
Kaniecki A, 1991. Problems of Wielkopolska Lowland drainage over the last 200 years and changes in its water conditions, Materiały konferencji, “Ochrona i racjonalne wykorzystanie zasobów wodnych na obszarach rolniczych w regionie Wielkopolski”, Akademia Rolnicza, Poznań. (in Polish)

20
Kaźmierski J, Jasińska E, 1996. Dynamics and thermal activity of lake waters. in: Majewski W (ed.). The State of the Żarnowieckie Lake after 10 Years of Water Power Station Exploitation). Warszawa: Oficyna Monografie Komitetu Gospodarki Wodnej Polskiej Akademii Nauk, Zeszyt, 11: 21-53. (in Polish)

21
Kędziora A, 2010. Climate changes and their effect on the water conditions of the agricultural landscape. In: Koźmiński C Z, Michalska B, Leśny J et al. Climatic Threats to Agriculture in Poland. (in Polish)

22
Kowalczak P, Farat R, Kepińska-Kasprzak Met al., 1997. Hierarchy of regional requirements of small scale retentio in Poland, Materiały badawcze, Seria: Gospodarka Wodna o Ochrona Wód, 19, Warszawa, IMGW. (in Polish)

23
Kowalewski G, 2012. Over 200 years of drainage practices and lake level drawdown in the Uściwierskie Lowering (Łęczna-Włodawa Lakeland).Limnological Review, 12(4): 179-190.

24
Konatowska M, Rutkowski P, 2008. The changes of the area and of the water-level of Kamińsko Lake (Zielonka Experimental Forestry Division) in the period of recent 150 years.Studia i Materiały Centrum Edukacji Przyrodniczo-Leśnej, 2(18): 205-217. (in Polish)

25
Kowalik A, Grześkowiak A, Nowak B, 2008. Lake’s reaction to extreme changes in their supply.Wiadomości Meteorologii, Hydrologii, Gospodarki Wodnej, 2(3/4): 49-67. (in Polish)

26
Kutyła S, 2014. Characteristics of water level fluctuations in Polish lakes: A review of the literature.Environmental Protection and Natural Resources, 25(3): 27-34.

27
Legesse D, Ayenew T, 2006. Effect of improper water and land resource utilization on the central Main Ethiopian Rift lakes.Quaternary International, 148(1): 8-18.The Ethiopian Rift is characterized by a chain of lakes varying in size, hydrological and hydrogeological setting. Some of the lakes and tributary rivers are used for irrigation, soda abstraction, commercial fish farming and recreation; and they support a wide variety of endemic birds and wild animals. Few lakes shrunk due to excessive abstraction of water; others expanded due to increase in surface runoff and groundwater flux from percolated irrigation water. Excessive land degradation, deforestation and over-irrigation resulted in sedimentation in lakes and increase in soil salinity. The chemistry of some of the lakes has also been changed dramatically. This paper addresses the major environmental changes in the last few decades in the central Main Ethiopian Rift lakes that resulted mainly from anthropogenic factors. The methods employed include field hydrogeological mapping supported by aerial photograph and satellite imagery interpretations, hydro-meteorological data analysis, water balance estimation, catchment hydrological and groundwater flow modelling and hydrochemical analysis. A converging evidence or integrated approach has been adapted to reconstruct the temporal and spatial variations of lake levels and hydrochemistry. The result revealed that the major changes in the rift valley are related mainly to recent improper utilization of water and land resources in the lakes catchment and direct lake water abstraction aggravated intermittently by climatic changes. The terminal lakes show dramatic reduction in level and increase in salinity. These changes appear to have grave environmental consequences on the fragile rift ecosystem, which demands extremely urgent integrated basin-wide water management practice.

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28
Li X-Y, Xu H-Y, Sun Y-Let al., 2007. Lake-level change and water balance analysis at lake Qinghai, West China during recent decades.Water Resources Management, 21(9): 1505-1516.<a name="Abs1"></a>Lake Qinghai, the largest saline lake with an area of 4,260&nbsp;km<sup>2</sup> (2000) and average depth of 21&nbsp;m (1985) in West China, has experienced severe decline in water level in recent decades. This study aimed to investigate water balance of the lake and identify the causes for the decline in lake level. There was a 3.35-m decline in water level with an average decreasing rate of 8.0&nbsp;cm year<sup>&#8722;1</sup> between 1959 and 2000. The lake water balance showed that mean annual precipitation between 1959 and 2000 over the lake was 357&#8201;±&#8201;10&nbsp;mm, evaporation was 924&#8201;±&#8201;10&nbsp;mm, surface runoff water inflow was 348&#8201;±&#8201;21&nbsp;mm, groundwater inflow was 138&nbsp;mm&#8201;±&#8201;9 and the change in lake level was &#8722;80&#8201;±&#8201;31&nbsp;mm. The variation of lake level was highly positively correlated to surface runoff and precipitation and negatively to evaporation, the correlation coefficients were 0.89, 0.81 and &#8722;0.66, respectively. Water consumption by human activities accounts for 1% of the evaporation loss of the lake, implying that water consumption by human activities has little effect on lake level decline. Most dramatic decline in lake level occurred in the warm and dry years, and moderate decline in the cold and dry years, and relatively slight decline in the warm and wet years, therefore, the trend of cold/warm and dry climate in recent decades may be the main reasons for the decline in lake level.

DOI

29
Łabędzki L, 2004. Drought problems in Poland.Woda-Środowisko-Obszary Wiejskie, 1(10): 47-66. (in Polish)

30
Machowski R, Ruman M, Rzętała M, 2005. Water stage fluctuations in selected anthropogenic water reservoirs in the upper part of the Odra catchment.Limnological Review, 5: 145-153.ABSTRACT The aim of this paper is to evaluate fluctuations of water stage in reservoirs, which waters are directly or indirectly used for the needs of inland navigation. There are reservoirs located in the upper part of the Odra catchment: Dzier03no Du03e (50&ordm; 22' N, 18&ordm; 34' E), Dzier03no Ma00e (50&ordm; 23' N, 18&ordm; 34' E), Turawa (50&ordm; 43' N, 18&ordm; 08' E). In hydrological period 1976&ndash;2000 water stages in these reservoirs were characterised by high, unusual under natural conditions fluctuation amplitudes, amounting to 8.18 m (Dzier03no Du03e), 6.73 m (Dzier03no Ma00e) and 6.99 m (Turawa). Water stage fluctuations resulted from influence of natural factors (thawing high water stage, raised-water stage due to rainfall) as well as anthropogenic factors (the necessity to improve navigation conditions, water supply for industrial and municipal purposes, recreation-rest needs). The aim of this paper is to analyse water stage fluc-tuations carried out for some water reservoirs lo-cated in the upper part of the Odra catchment. They are numbered among the group of larger in area and capacity water reservoirs of southern Poland. In res-pect of function they fulfil they are classified as mul-ti-task objects. The common feature of these hydro-logical objects is direct or indirect use of waters stored in reservoir basins for the needs of inland navigation. Post-exploitation water reservoir Dzier03no Du03e (50&ordm; 22' N, 18&ordm; 34' E) exists in the K00odnica catch-ment already since 1964 year and it makes source of water to fulfil navigation conditions at running in the vicinity Gliwice Channel, and indirectly also at the Odra (Fig. 1). With such reservoir function is connected the occurrence of hydraulic structures as inlet cascade of the K00odnica, which releases water surplus from the channel into the reservoir, so-cal-led tower of diversion of water from the reservoir. Apart from &ndash; as M. Rz01ta00a (2000) gives &ndash; it is "na-tural" settlement tank for strongly polluted waters of the K00odnica carrying waters from western part of &ndash; described among others by S. Czaja (1999) &ndash; Katowice conurbation (Rz01ta00a, 2002). Water reservoir Dzier03no Ma00e (50&ordm; 23' N, 18&ordm; 34' E) was created in 1938 through flooding of post-sand excavation (Fig. 1). At normal damming up le-vel (204 m a.s.l.) it occupies the area of 1.1 sq. km, reaching the capacity of 10 hm m 3 and maximum depth of 13 m. It is fed by waters of the Drama &ndash; flowing from the east and by waters of Pni&oacute;wka from the north &ndash; by way of small in area artificial flood lands, so-cal-led water reservoir Dzier03no I. Waters from Dzier03no Ma00e reservoir are used to supply Gliwice Channel. This artificial lake fulfils also recreation purposes.

31
Michalczyk Z, Chmiel S, Turczyński M, 2011. Lake water stage dynamics in the Łęczna-Włodawa Lake District in 1991-2010.Limnological Review, 11(3): 113-122.

32
Micklin P P, 1988. Desiccation of the Aral Sea: A water management disaster in the Soviet Union.Science, 241: 1170-1176.The Aral Sea in the Soviet Union, formerly the world's fourth largest lake in area, is disappearing. Between 1960 and 1987, its level dropped nearly 13 meters, and its area decreased by 40 percent. Recession has resulted from reduced inflow caused primarily by withdrawals of water for irrigation. Severe environmental problems have resulted. The sea could dry to a residual brine lake. Local water use is being improved and schemes to save parts of the sea have been proposed. Nevertheless, preservation of the Aral may require implementation of the controversial project to divert water from western Siberia into the Aral Sea basin.

DOI PMID

33
Murat-Błażejewska S, Zbierska J, Ławniczak Aet al., 2008. Exploitation of water infrastructure in aspect of water resources lowland river catchment.Acta Scientiarum Polonorum Architectura, 7(2): 13-22. (in Polish)

34
Niewiarowski W, 1978. Fluctuations of water-level in the Gopło Lake and their reasons.Polish Archives of Hydrobiology, 25: 301-306.

35
Nishihiro J, 2011. Effects of lake water-level control on lakeshore plant regeneration. Japanese Journal of Conservation Ecology, 16(2): 139-148.

36
Okulanis E, 1981. Limnological Study of the Lakes Raduńsko-Ostrzyckie. GTN: Gdańsk, Zakład Narodowy im. Ossolińskich: Wrocław, 108. (in Polish)

37
Pasławski Z, 1972. Multiannual water level fluctuations and tendencies in outflow lakes in northern Poland.Przegląd Geofizyczny, 17: 249-259. (in Polish)

38
Pasławski Z, 1973. Long-term fluctuations and trends in water level changes in the outflow lakes in northern Poland.Hydrological Sciences Bulletin, 18(3): 295-301.On the basis of the research completed, it has been stated that long-term fluctuations of mean annual water levels of the lakes under investigation, in spite of the absence of a distinct periodicity, are characterized by a cycle with a 23-year period. The studies of the trends of mean annual water levels revealed a negative tendency ranging from—0·059 to—0·402 cm per annum.

DOI

39
Piasecki A, Marszelewski W, 2014. Dynamics and consequences of water level fluctuations of selected lakes in the catchment of the Ostrowo-Gopło Channel.Limnological Review, 14(4): 187-194.

40
Polderman N J, Pryor S C, 2004. Linking synoptic-scale climate phenomena to lake-level variability in the Lake Michigan-Huron basin.Journal of Great Lakes Research, 30(3): 419-434.<h2 class="secHeading" id="section_abstract">Abstract</h2><p id="">Lake-level change in the mid-latitudes is causally linked to variability in precipitation and evaporation that are dynamically linked to cyclone passages and larger-scale atmospheric variability across temporal scales. Hence, lake-level variability is both a product of and a record of synoptic-scale climate variability. Here, a daily synoptic classification for 1956&ndash;1999 is used to evaluate historical Lake Michigan-Huron water levels in the context of changes in the frequency and intensity of synoptic-scale phenomena. The results demonstrate that both within-type evolution and shifts in the relative frequency of synoptic types contributed to precipitation and evaporation anomalies through the historical period with the former reflecting the importance of the Great Lakes in determining the regional climate. Shifts in the frequency and intensity of synoptic winter types are also demonstrated to be contributing anomalous precipitation and evaporation coincident with phases of lake level associated with the 30-year quasi-periodicity. The synoptic-scale mechanisms of lake-level change over longer time scales illuminated here can be used to infer information about past climate states and improve projections of lake level from model simulations.</p>

DOI

41
Przybyłek J, Nowak B, 2011. Impact of hydrogeological low flows and groundwater drainage by lignite open cast mine on aquifer systems of gniezno Lakeland. Biuletyn - Panstwowego Instytutu Geologicznego, 445(2): 513-528. (in Polish)

42
Ptak M, Choiński A, Strzelczak Aet al., 2013. Disappearance of lake Jelenino since the end of XVIII century as an effect of anthropogenic transformations of natural environment.Polish Journal of Environmental Studies, 22(1): 191-196.This study presents the contribution of reclamation works to the disappearance of Lake Jelenino. On the basis of cartographic materials from the 19th and 20th centuries, as well as historical records, it was possible to establish that the lake of area 495.2 ha disappeared as a result of precise actions aimed at creating new settlements. Reclamation works proceeded in two stages. After the first stage, which took place in 1778-86, the area of Lake Jelenino was reduced by over 360 ha. In the 1970s the reservoir, whose area then amounted to 130 ha, was completely dried. Such a transformation of the natural environment was followed by social and economic changes - inhabitants of Jelenino village, who until then lived by fishing, in a short period of time retrained for agriculture and breeding.

43
Rodríguez-Rodríguez M, Green A J, López Ret al., 2012. Changes in water level, land use, and hydrological budget in a semi-permanent playa lake, Southwest Spain.Environmental Monitoring and Assessment, 184(2): 794-810.Medina playa lake, a Ramsar site in western Andalusia, is a brackish lowland lake of 120 ha with an average depth of 1 m. Water flows into Medina from its 1,748-ha watershed, but the hydrology of the lake has not previously been studied. This paper describes the application of a water budget model on a monthly scale over a 6-year period, based on a conceptual hydrological model, and considers different future scenarios after calibration to improve the understanding of the lake's hydrological functioning. Climatic variables from a nearby weather station and observational data (water-level evolution) were used to develop the model. Comparison of measured and predicted values demonstrated that each model component provided a reasonable output with a realistic interaction among the components. The model was then used to explore the potential consequences of land-use changes. Irrigation of olive groves would significantly reduce both the hydroperiod (becoming dry 15% of the time) and the average depth of the lake (water level <0.5 m 40% of the time). On the other hand, removal of an artificial overflow would double the average flooded surface area during high-water periods. The simulated water balance demonstrates that the catchment outputs are dominated by lake evaporation and surface outflow from the lake system to a creek. Discrepancies between predicted and observed water levels identify key areas of uncertainty for future empirical research. The study provides an improved basis for future hydrological management of the catchment and demonstrates the wider utility of this methodology in simulating this kind of system. This methodology provides a realistic appraisal of potential land-use management practices on a catchment-wide scale and allows predictions of the consequences of climate change.

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44
Salmi T, Määttä A, Anttila Pet al., 2002. Detecting trends of annual values of atmospheric pollutants by the Mann-Kendall test and Sen’s slope estimates: The Excel template application MAKESENS. Air Quality, 31, Finnish Meteorological Institute, 35.

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Schmid M, Hunziker S, Wüest A, 2014. Lake surface temperatures in a changing climate: A global sensitivity analysis.Climatic Change, 124(1/2): 301-315.We estimate the effects of climatic changes, as predicted by six climate models, on lake surface temperatures on a global scale, using the lake surface equilibrium temperature as a proxy. We evaluate interactions between different forcing variables, the sensitivity of lake surface temperatures to these variables, as well as differences between climate zones. Lake surface equilibrium temperatures are predicted to increase by 70 to 85 % of the increase in air temperatures. On average, air temperature is the main driver for changes in lake surface temperatures, and its effect is reduced by ~10 % by changes in other meteorological variables. However, the contribution of these other variables to the variance is ~40 % of that of air temperature, and their effects can be important at specific locations. The warming increases the importance of longwave radiation and evaporation for the lake surface heat balance compared to shortwave radiation and convective heat fluxes. We discuss the consequences of our findings for the design and evaluation of different types of studies on climate change effects on lakes.

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Shi W, Wang M, Guo W, 2014. Long-term hydrological changes of the Aral Sea observed by satellites. Journal of Geophysical Research: Oceans, 119(6): 3313-3326.

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Singh C R, Thompson J R, French J Ret al., 2010. Modelling the impact of prescribed global warming on runoff from headwater catchments of the Irrawaddy River and their implications for the water level regime of Loktak Lake, northeast India.Hydrology and Earth System Sciences, 14(9): 1745-1765.

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Skibniewski L, 1954. Wahania poziomów zwierciadła wody większych jezior Pojezierza Pomorskiego i Mazurskiego.Przegląd Meteorologiczny, VII, 3-4.

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Vincent C E, Davies T D, Beresford A K C, 1979. Recent changes in the level of Lake Naivasha, Kenya, as an indicator of equatorial westerlies over East Africa.Climatic Change, 2(2): 175-189.Lake Naivasha's major level increases occur during May and September. Lake Victoria's level increases mainly in May with a small December increase. East African rainfall is generally during April and November, corresponding with Lake Victoria's changes. Rainfall records from Kenyan highland areas, however, show an August rainfall peak and little rainfall in November. Rainfall amounts from Equator, a highland meteorological station, for July, August and September are highly correlated (at 1% significance level) with the change in Naivasha's level during September. Winds at the highland stations are westerly during August while the lower level stations experience the drier S.E. Trades. The level changes of Lake Naivasha indicate changes in the extent of the penetration of moist air from West Africa between the Trade winds and the 200 mb easterly jet.

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Wilhelm S, Adrian R, 2008. Impact of summer warming on the thermal characteristics of a polymictic lake and consequences for oxygen, nutrients and phytoplankton.Freshwater Biology, 53: 226-237.

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Wrzesiński D, Choiński A, Ptak M, 2015. Effect of the North Atlantic Oscillation on the thermal characteristics of lakes in Poland.Acta Geophysica, 63(3): 863-883. doi: 10.1515/acgeo-2015-0001.This paper presents the effect of the North Atlantic Oscillation (NAO) on the thermal characteristics of lakes in Poland. In the analysis, the use was made of monthly air temperatures recorded at fifteen meteorological stations, water temperatures of twelve lakes, and Hurrell’s winter NAO indices. Over the study period (1971-2010), there was a marked increase in the temperatures of both, air and lake waters. Depending on the NAO phase, water temperatures were observed to depart from mean values, being markedly higher than average (even by 1°C) in the positive winter NAO phase. The differences in water temperatures were statistically significant in the winter-spring season. In turn, in the negative NAODJFM phase lake water temperatures in winter and spring were markedly lower than average (in March even by 1.0°C). The unique response of some lakes depends on their morphometric parameters, including their mean depth.

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Yao X, Liu S, Li Let al., 2014. Spatial-temporal characteristics of lake area variations in Hoh Xil region from 1970 to 2011.Journal of Geographical Sciences, 24(4): 689-702.lt;p>As one of the areas with numerous lakes on the Tibetan Plateau, the Hoh Xil region plays an extremely important role in the fragile plateau eco-environment. Based on topographic maps in the 1970s and Landsat TM/ETM+ remote sensing images in the 1990s and the period from 2000 to 2011, the data of 83 lakes with an area above 10 km<sup>2</sup> each were obtained by digitization method and artificial visual interpretation technology, and the causes for lake variations were also analyzed. Some conclusions can be drawn as follows. (1) From the 1970s to 2011, the lakes in the Hoh Xil region firstly shrank and then expanded. In particular, the area of lakes generally decreased during the 1970s-1990s. Then the lakes expanded from the 1990s to 2000 and the area was slightly higher than that in the 1970s. The area of lakes dramatically increased after 2000. (2) From 2000 to 2011, the lakes with different area ranks in the Hoh Xil region showed an overall expansion trend. Meanwhile, some regional differences were also discovered. Most of the lakes expanded and were widely distributed in the northern, central and western parts of the region. Some lakes were merged together or overflowed due to their rapid expansion. A small number of lakes with the trend of area decrease or strong fluctuation were scattered in the central and southern parts of the study area. And their variations were related to their own supply conditions or hydraulic connection with the downstream lakes or rivers. (3) The increase in precipitation was the dominant factor resulting in the expansion of lakes in the Hoh Xil region. The secondary factor was the increase in meltwater from glaciers and frozen soil due to climate warming.</p>

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Yildirim Ü, Erdoğan S, Uysal M, 2011. Changes in the coastline and water level of the Akşehir and Eber lakes between 1975 and 2009.Water Resources Management, 25(3): 941-962.The AkAYehir and Eber Lakes, relatively shallow, small freshwater lakes with an area of 361 km(2) and 150 km(2) and average depth of 7 m and 2 m (1998), respectively in southwestern Turkey, have experienced a severe decline in water levels in recent decades. This study aimed to investigate coastline and water level changes of lakes and identify the causes for the decline in lake levels. Nine Landsat images from different times, monthly temperature, precipitation, discharge, lake level records and population data were used to analyze these changes. From 1975 to 2009, the water surface areas of the AkAYehir and Eber Lakes decreased from 356,929 to 126,482 km(2) and from 119,882 to 85,663 km(2), a loss of 64.5% and 28.4% over the 34-year period, respectively. From 1975 to 2004, the AkAYehir Lake level declined by 2.67 m from 956.02 m to 953.35 and the Eber Lake level declined by 2.03 m from 966.75 m to 964.72 m from 1975 to 2004 based on ground lake level data (in situ). The results of the temperature and precipitation analysis showed that although the annual mean climatic factors vary substantially, they show small increasing trend over the record periods. Annual discharge records on the Akar double dagger ay River and its tributaries decreased over the basin during the same period. Irrigation systems, three dams and seven pounds built in recent decades for agricultural irrigation and domestic use, made the major impact on lowering the lake levels because they derive water from the river for human use upstream of the lakes' catchments. Population growth, rising water consumption for agricultural and domestic purposes and building dams has led to lake levels declining. The change of lake levels might depend more on anthropogenic factors than on climatic factors.

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Yin Y, Chen Y, Yu Set al., 2013. Maximum water level of Hongze Lake and its relationship with natural changes and human activities from 1736 to 2005.Quaternary International, 304(5): 85-94.Hongze Lake is the fourth largest freshwater lake in China. The water level of Hongze Lake has changed significantly in the past centuries, and the maximum water level (MWL) is influenced by both natural and anthropogenic factors. This paper explores the changes and driving factors (including natural changes and human activities) of Hongze Lake water level, using the annual MWL data from both historical documents and gauged records, and investigates the relationship between the Hongze Lake MWL and the flood/drought disasters of the Huai River basin, Meiyu length, and human activities. The results shows that during the 1736-1953 period, river changes, such as the Yellow River's capture of the Huai River, contributed substantially to the changes of Hongze Lake water level. The MWL correlated also well with climate changes (e.g. flood/drought changes, Meiyu length) during this period. During 1954-2005, the flood/drought series in the Huai River basin is consistent with the flood season/annual precipitation, but the annual MWL of Hongze Lake is not. This is because a large number of hydraulic projects have been constructed around the Hongze Lake during this period, and thus the MWL is greatly influenced by artificial regulations since the 1950s. The paper comes to the conclusion that the changes of the MWL were mainly driven by natural changes before the 1950s. Anthropogenic activities (especially hydraulic engineering) have played a more and more important role in the MWL changes in the past 50 years.

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Zhuang C, Ouyang Z, Xu Wet al., 2011. Impacts of human activities on the hydrology of Baiyangdian Lake, China.Environmental Earth Sciences, 62(7): 1343-1350.Baiyangdian Lake is the biggest natural freshwater wetland in North China Plain. It provides important ecosystem services such as water regulation and supply, reed production and biodiversity protection. Baiyangdian Lake, however, was threatened by lack of freshwater in recent decades. In this paper, the hydrological changes of the lake were quantified using historical data of water level and groundwater table, and satellite images. In addition, the relationship between water level and socioeconomic development of the basin was investigated. The result revealed a significant decreasing trend of water level in the lake. Water level and groundwater table of Baiyangdian Lake decreased rapidly, caused by the great increase of water withdrawal and consumption due to socioeconomic development in the basin. In particular, population growth and the expansion of irrigated agriculture were two major contributors to the decline of water level and groundwater table. While precipitation was positively correlated with water level, it has less impact on water level and groundwater table than human activities. The diversion of water to the lake raised the water level temporarily and had significant benefits on the wetland ecosystem. The best way to solve ecological problems of Baiyangdian Lake, however, is to control the growth of population, adjust the industrial structure, control land use conversion and improve water use efficiency at the basin scale.

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Zinke P, Bogen J, 2013. Effect of water level regulation on gradients and levee deposits in the Lake Øyeren delta, Norway.Hydrology Research, 44(3): 523-537.Water level changes resulting from a hydropower regulation have influenced water flow, gradients and sediment processes in the Lake Oyeren delta for about 150 years. They are reflected in the morphology of the islands on the delta plain. Under current regulation practices, water levels during the mean annual flood are maintained at about 1 m lower than during the previous regime prior to 1978. As the channels continue to mature, the recently deposited tongues and levees in the southern part will therefore probably maintain a distinctly lower elevation than that of the older islands. The influence of flood regulation on levee deposits during the extreme 1995 flood was estimated by comparing simulated overbank deposits resulting from different flood regulation schemes. The simulations showed that reduced water levels during floods in the presence of older islands extend the period of in-channel flow and promote the development of levee-like deposits in the lower part of the delta plain. This explains some of the characteristics observed in the morphological development, most notably the increased number of lagoons resulting from a higher number of levees.

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Ziverts A, Apsite E, 2005. Simulation of daily runoff and water level for the Lake Butrnieks. Simulation in Wider Europe - 19th European Conference on Modelling and Simulation, ECMS 2005, 633-637.ABSTRACT KEY WORDS Hydrological models, mathematical modelling of hydrological processes, climate changes, reservoir routing, the Lake Burtnieks. ABSTRACT The Lake Burtnieks with around lying areas is one of the unique objects of the nature in Latvia. In this paper the analysis of mathematic modelling results for the rivers' runoff in the Lake Burtnieks watershed and water level of the lake are presented. First time for the Lake Burtnieks is demonstrated possibility to utilise regular observations of meteorological elements and to use mathematical model, which is adapted to natural conditions for the simulation of daily runoff and water level with a high statistical significance. The efficiency criterion R 2 differs from 0.57 to 0.80 but the correlation coefficient r is from 0.8 to 0.9. Changing meteorological data according to the given scenario of climate changes we can obtain different parameters of the predictable hydrological regime in the future. Results of the study are widely applicable including the calculation of nutrient loading from the catchment area as well.

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Zmijewski K, Becker R, 2014. Estimating the effects of anthropogenic modification on water balance in the Aral Sea watershed using GRACE: 2003-12.Earth Interactions, 18(3): 1-16.Not Available

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Zolár P, Bengtsson L, 2006. Long-term and extreme water level variations of the shallow Lake Poopó, Bolivia.Hydrological Sciences Journal, 51(1): 98-114.the big salt fields. Small changes in precipitation and river inflows strongly affect the extent of the lake surface area. For times when there are no satellite images, it is difficult to determine the extent of the lake from observations. Water balance computations were performed to create a water-level series for Lake Poop extending back in time. The dominant water inflow to Lake Poop is from the River Desaguadero, which constitutes the outflow of Lake Titicaca. The water-balance computations confirm the crude peasant knowledge about historical lake status. It is found that if the lake level is less than 1 m during the wet season, there is a risk that this shallow lake dries out in the dry season.

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