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Journal of Geographical Sciences >

2017 , Vol. 27 >Issue 6: 697 - 710

DOI: https://doi.org/10.1007/s11442-017-1401-9

Orginal Article

Simulation on phosphorus release characteristics of Poyang Lake sediments under variable water levels and velocities

  • TONG Yali ,
  • LIANG Tao * ,
  • WANG Lingqing
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  • Key Laboratory of Land Surface Pattern and Simulation, Institute of Geographic Sciences and Natural Resources Research, CAS, Beijing 100101, China

Author: Tong Yali, MS, specialized environmental geography. E-mail:

*Corresponding author: Wang Lingqing, E-mail:

Received date: 2016-06-15

  Accepted date: 2016-08-20

  Online published: 2017-06-10

Supported by

National Key Project for Basic Research, No.2012CB417004

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Journal of Geographical Sciences, All Rights Reserved
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Abstract

Since the construction of the Three Gorges Dam, the Poyang Lake hydrological characteristics obviously changed. During the impoundment period of the Three Gorges Reservoir, the hydrodynamic factors of Poyang Lake varied. Water level dropped, the velocity decreased and water exchange time lengthened, which changed the release of phosphorous from sediments. In order to investigate how the hydrodynamic factors influence the release of phosphorous from sediments, we used a two-way annular flume device to simulate the release characteristics of phosphorous from sediments under variable water levels and velocities. We found that both water level rising and velocity increasing could enhance the disturbance intensity to sediments, which caused the increase of suspended solids (SS) concentration, total phosphorus (TP) concentration in the overlying water, and the ability that phosphorus released to overlying water from sediments enhanced as well: when overlying water velocity maintained 0.3 m/s, SS concentration increased to 4035.85 mg/L at the water level 25 cm which was about 25 times compared to the minimum value and TP concentration in the overlying water also reached the maximum value at the water level 25 cm which was 1.2 times that of the value at 10 cm; when water level maintained 15 cm, SS concentration increased to 4363.35 mg/L at the velocity of 0.5 m/s which was about 28 times compared to the value of 0 m/s, and TP concentration in the overlying water increased from 0.11 mg/L to 0.44 mg/L. When the water level maintained 15 cm, the phosphorous release rate reached the maximum value of 4.86 mg/(md) at 0.4 m/s. The concentration of total dissolved phosphorous (TDP) and soluble reactive phosphate (SRP) both in overlying water and sediment-water interface were negatively correlated with pH. Using the parabolic equation, the optimum water level at a velocity of 0.3 m/s was calculated to be 0.57 cm, and the optimum velocity at water level of 15 cm was found to be 0.2 m/s.

Key words： hydrodynamic factors; sediment-water interface; total phosphorous; total dissolved phosphorous; soluble reactive phosphate; Poyang Lake

Cite this article

TONG Yali , LIANG Tao , WANG Lingqing . Simulation on phosphorus release characteristics of Poyang Lake sediments under variable water levels and velocities[J]. Journal of Geographical Sciences, 2017 , 27(6) : 697 -710 . DOI: 10.1007/s11442-017-1401-9

1 Introduction

The increase of nutrients in lake is the main reason that why lake eutrophication emerges (Wetzel, 2001; Xing et al., 2005). Generally, when the ration of N/P in lake is larger than 10, phosphorous is the limited element of eutrophication (Chen et al., 2005). Investigations on global lakes have confirmed that 80% of the nutrition level is controlled by phosphorus, another 10% has a direct relationship to phosphorus and nitrogen, and the remaining 10% is influenced by other factors (Reddy et al., 1996; Wetzel, 2001; Kim et al., 2007). The source of phosphorous in lake water body includes internal source and external source, and the internal source of phosphorous in a lake has been proven to be a large proportion of the total phosphorous input (Sundby et al., 1992; Carrick et al., 1993).
The phosphorous in lake can be divided into total phosphorous (TP), total reactive phosphorous (TRP), total dissolved phosphorous (TDP), soluble reactive phosphorous (SRP) and particle phosphorous etc. (Carrick et al., 1993). SRP is basically positive phosphate, and it has long been considered that the phosphate is a biological element that can be directly used by biomass. TP includes dissolved and suspended solid phosphorus, and TDP does not include suspended solid (insoluble) phosphorus. The phosphorus in lake sediments is mainly in the form of adsorption, organic-P, Fe-P, Ca-P, and Al-P (Reitzel et al., 2006; Zhang et al., 2012). When phosphorous enter a lake ecosystem variable physical-chemical processes, including release, decomposition or desorption, will happen, and thus accelerate the extent of eutrophication (Reitzel et al., 2006; Wu et al., 2008; Emily et al., 2014). The migration and transformation of phosphorous in sediment-water interface plays an important role in phosphorous endogenous release, such as the phosphorous in the upper 2 cm sediments in a shallow lake is very easy to diffuse into overlying water through the sediments re-suspension (Xie et al., 2002; Gao et al., 2002; Marcus et al., 2004; Zhang et al., 2013; Testa et al., 2013; Carolina et al., 2012; Wu et al., 2014). The migration and transformation of phosphorus between sediments and overlying water is a dynamic equilibrium process. The release of internal phosphorus in sediments mainly through the following four ways: (1) the release of Fe-P by the change of redox conditions (Reitzel et al., 2006), (2) the release of Fe-P and Ca-P by the variable pH value (Drewry et al., 2009), (3) the degradation of organic matter or mineralization of organic phosphorus (Sun et al., 2007), and (4) the transformation by microbes (Sonderdaard et al., 2003).
In addition, shallow lake is easy to be influenced by hydrodynamic disturbances (Temporetti et al., 2013), which alters the pH, temperature, dissolved oxygen and other environmental factors that can easily influence the processes of phosphorous exchange between lake sediments and overlying water, and therefore, have a significant effect on eutrophication (Xie et al., 2002; Reitzel et al., 2006; Zhang et al., 2013; Tesa et al., 2013). Human activities, especially some water conservancy projects, can critically change the hydrodynamic condition of lakes (Qin et al., 2002). By changing the physical and chemical conditions of sediments and overlying water and even the amount of re-suspended sediments, the sediment transport and release of phosphorus in the sediments are affected, which can aggravate the extent of eutrophication (Qin et al., 2002; Zheng et al., 2004; Temporetti et al., 2013; Li et al., 2013; Huang et al., 2014). Under the strong disturbances, the concentration of SS and TP in the overlying water increased significantly and even several times (Fan et al., 2002; Sun et al., 2007; Pang et al., 2008a; Pang et al., 2008b; Zhang et al., 2008; Jiang et al., 2010). During particle re-suspension, the release of internal phosphorus and absorption of phosphorus in overlying water happened simultaneously (Qin et al., 2004; Liang et al., 2013). Nowadays, the studies of the hydrodynamic disturbance on lake sediments are mainly concentrated in wind waves and velocity, but few studies have been conducted on the disturbance caused by water level. Presently, the simulation of phosphorous release from lake sediments is mainly conducted by three methods: the oscillation method, wave flume method, and annular flume method. The oscillation method and wave flume method have a high cost because they require a mass of samples. The annular flume method simulates an infinite lake surface and the flow field is kept uniform.
Many studies have already shown that the construction of the Three Gorges Dam caused the hydrological conditions of Poyang Lake to change obviously as for the variation of the Yangtze River’s hydrological conditions (Dai et al., 2015; Du et al., 2014; Tang et al., 2015). So, in this study, in order to analyze the associations between hydrodynamic conditions and the release characteristics of internal phosphorous, a two-way annular flume device was used to investigate the effects of variable water levels and velocities on the phosphorus release from lake sediments. The sediments and water sample were sampled from Poyang Lake outlet region where Poyang Lake enters the Yangtze River. Poyang Lake connects to the Yangtze River at Hukou where the variation of Poyang Lake’s hydrological conditions is most apparent. Though the simulation, we want to get helpful data to provide the basic parameters for estimating sediment phosphorus release in a basin scale and afford theoretical basis of eutrophication research and control.

2 Materials and methods

2.1 Study site

Poyang Lake is the largest freshwater lake in China, and it exchanges water with the Yangtze River in its drainage basin (Cai et al., 2007). Poyang Lake not only regulates the flood state of the Yangtze River, but also affects material and energy exchange of the Yangtze River (Dai et al., 2015). On the other hand, changes in conditions of the Yangtze River also alter available water resources and the aquatic ecosystem in Poyang Lake. After the construction of the Three Gorges Dam, the hydrodynamic conditions of shallow lakes in the middle and lower reaches of the Yangtze River have been changed significantly, so it is valuable and of practical significance to study the release characteristics of phosphorus in Poyang Lake sediments under variable water levels and velocities. Samples of water and surface sediments were collected from the outlet region of Poyang Lake (P) (29 44'31"N, 116°12'44"E) (Figure 1).
Figure 1 The location and sampling site of Poyang Lake (April 2014>)

2.2 Experimental equipment and principle

The two-way annular flume device is consisted of three parts: upper plate, lower plate and drive control system (Figure 2). The outside diameter was 120 cm, inside diameter was 80 cm, the width of groove was 20 cm, and the depth of groove was 40 cm. The water groove was made of organic glass. The upper plate was covered by the water surface and the height could be adjusted according to the experiment requirements. In order to explore the effects of water level and velocity, water samples were harvested from several holes at different depths of the water groove. The upper plate and lower plate rotated in opposite directions to produce two centrifugal forces in opposite directions. Additionally, a uniform flow field could be formatted by regulating the relative rotating speed of the upper and lower plates. Consequently, the device could simulate release characteristics of phosphorus in sediments of Poyang Lake under variable water levels and velocities.
Figure 2 The structure of two-way annular flume device

2.3 Experiment methods

2.3.1 Sampling and preparation
The experiment was conducted in April 2014 in Nanjing Institute of Geography and Limnology, Chinese Academy of Science. Samples of water (approximately 150 L) and surface sediments (about 100 kg) were collected from the outlet region of Poyang Lake (29°44'31"N, 116°12'44"E). The surface sediments were sampled from the upper 10 cm sediment by Peterson grab (HAD-XDB0201D). The total 150 L of water sample were collected from three layers: the water surface, middle of water volume and 0.5 m above the bottom by Patalas bottle sampler. The average density of sediments was 1.74 g/cm3, and the average moisture content was 44.68%. Sediments and water sample were respectively stored in polyethylene storage tanks at 2℃. The sediment samples were mixed and filled to the bottom of the flume of the two-way annular flume device with a thickness of 6 cm, and then, the water samples were added over the sediment using a siphon. The sediment and water within the device were left for two days in order to restore to a sediment-water interface similar to that in the lake.
2.3.2 Experimental set-up
(1) Simulation of variable water levels
The velocity of the water flow was set to 0.3 m/s. Four water levels, 10, 15, 20 and 25 cm, were studied in order of low to high water levels. Each treatment was applied for 60 min, after which samples were collected from overlying water, sediment-water interface, and pore water. The experiment was designed with two replicates for each treatment.
(2) Simulation for variable velocities
The level of the overlying water was 15 cm. Nine water flow velocities, 0, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4 and 0.5 m/s, were studied in the order of low to high velocities. Each velocity was applied for 60 min, after which samples were collected from overlying water, sediment-water interface, and pore water. Each treatment was studied in duplicate.
The locations of sampling were at depths of 6 cm, 17 cm and 3.5 cm from the bottom of the sink. The samples of 3.5 cm were representative of pore water samples, 6 cm were representative of sediment-water interface water samples, and 17 cm were representative of overlying water samples. Due to the volume limitation of the experiment device, after each sampling, equal amount of deionized water was slowly added to the sink.

2.4 Measurements and statistical analysis

TP and TDP were measured using the molybdenum anti-spectrophotometric method after digestion in alkaline potassium per sulfate. SRP was quantified through spectrophotometry after passing water samples through a GF/C filter. SS were obtained by drying the solid residues collected from the GF/C filtration at 105℃. The pH was measured using a PB-21 precision pH meter (Szmant, 1996). R studio (Server v 0.98.1091) was used to analyze the data and draw figures.
The sediments release equation (Li et al., 2004) is:
$r=\left[ V({{C}_{n}}-{{C}_{0}})+\sum\limits_{j=1}^{n}{{{V}_{t}}({{C}_{j-1}}-{{C}_{a}})} \right]\text{/}A\times t$
where r is the release rate (mg/(m2d), V is the water sample volume in the annular flume (L), Cn is the concentration of nutrients in the nth water sample (mg/L), C0 is the initial nutrient concentration (mg/L), Vt is the volume of water sample (L), Cj-1 is the concentration of nutrients in the (j-1)th water sample (mg/L), Ca is the concentration of nutrients in the original water (mg/L), t is the release time (d), and A is the area of the sediment-water interface (m2).

3 Results and discussion

3.1 The characteristics of sediments and overlying water

Table 1 shows the basic characteristics of sediment and overlying water samples two days after analysis of the mixed sediment samples placed on the bottom of the flume of the two- way annular flume. The average density and moisture content of the sediment samples were 1.74 g/cm3 and 44.68%, respectively. The concentrations of TP in overlying water (17 cm), sediment-overlying interface (6 cm) and pore-water (3.5 cm) were all greater than 0.02 mg/L. These concentrations defined Poyang Lake in a state of eutrophication (Carrick et al., 1993). The concentration of phosphorous in the sediment was much higher than that in overlying water, indicating that the amount of endogenous phosphorous was large and the release of endogenous phosphorous was a potential important source of lake eutrophication.
Table 1 The basic analysis of sediments and overlying water (April 2014)
Sampling site pH SS TP SRP TDP
mg L-1 mg L-1 mg L-1 mg L-1
17 cm (Overlying water) 7.46 52.35 0.1 0.0417 0.0611
6 cm (Sediment-water interface) 7.17 -* 0.459 0.0045 0.0252
3.5 cm (Pore water) 6.69 -* 0.347 0.0419 -*

* represent no measurement.

3.2 The impact of water level on SS concentration in overlying water

At low water levels (10-20 cm), only a small amount of suspended sediments were present, while at high water levels (20-25 cm), many suspended sediments appeared. Within the experimental range of water level, the SS concentration increased as the water level rose. At the low water level disturbance stage (10-20 cm), the concentration of SS increased from 2029.65 mg/L to 2424.15 mg/L, and at the high water level disturbance stage (20-25 cm), the concentration of SS increased from 2424.15 mg/L to 4035.85 mg/L, indicating an approximate 1.7-time increase.
When the water level was low, the finer particles were suspended in a very thin layer near the sediment surface. When the water level further increased, some larger particles began rolling along the sediment surface or became suspended in the overlying water. When the water level increased to 25 cm, the smooth surface of the sediments was severely damaged from constant swirling of the silts on the surface, and the overlying water quickly became completely muddy.

3.3 The impact of water level on TP

As the water levels rose, the TP concentration in the overlying water also increased (Figure 3). The amount of phosphorus released from sediments to the overlying water also slightly increased with the increase of water levels. The lowest TP concentration in the pore water and the highest TP concentration at the sediment-water interface were both found at the water level of 20 cm. Within the experimental range of water level, the TP concentration in the pore water was lower than those in the overlying water and at the sediment-water interface, indicating that the sediment of Poyang Lake was a source of phosphorous, which continuously provided phosphorous.
Figure 3 TP concentrations of pore-water, sediment-water interface, and overlying water at each water level (April 2014)
The variety of TP concentrations represents the comprehensive expression of phosphorous desorption, release, and migration from sediments. At low water levels (10-20 cm), a small amount of phosphorous in the pore water released into the overlying water through the sediment-water interface, while phosphorus in the particles was desorbed into the pore water. This resulted in an apparent increase in TP concentrations in the overlying water and sediment-water interface. As the water level further increased, the amount of phosphorous released into the overlying water increased proportionally. However, at the highest water level, there was a high SS concentration near the sediments leading to phosphorous adsorption by the particles and a decrease in TP concentration in the sediment-water interface.

3.4 The impact of water level on TDP and SRP concentrations

As the water levels increased, the concentrations of both TDP and SRP in the overlying water and sediment-water interface first decreased from depth of 10 cm to 15 cm but then increased from depth of 15 cm to 25 cm (Figure 4). The concentration range of TDP in the overlying water and sediment-water interface was 0.017-0.042 mg/L and 0.010-0.025 mg/L, respectively. The concentration range of SRP in the overlying water and sediment-water interface was 0.008-0.024 mg/L and 0.007-0.018 mg/L, respectively.
Figure 4 Concentrations of SRP and TDP in the sediment-water interface and overlying water at the corresponding water levels (April 2014)
Based on the range of TDP and SRP concentrations in overlying water, we determined 15 cm as the disturbance water level for optimal phosphorus release from sediments since at water levels greater than or less than 15 cm, the concentrations of TDP and SRP varied. Among the different water levels, there were diverse redox environments in sediment-water interface. When the water level was 15 cm, the sediments released the least amount of phosphorous.
The concentrations of TDP and SRP were found to be negatively correlated with pH (Figure 5), with the highest correlation coefficient of 0.70 between SRP and pH. Phosphorus release from sediments is strongly influenced by pH through effects on the formation of Fe-P, Al-P, Ca-P and other elements.
Figure 5 Correlation analysis between concentrations of SRP or TDP and pH

3.5 The impact of velocity on SS concentration in overlying water

When increasing the water velocity from 0 to 0.5 m/s, the SS concentration in the overlying water gradually increased. At the low velocity phase (0-0.2 m/s), the SS concentration increased from 157.5 mg/L to 205.85 mg/L while at the high velocity phase (0.2-0.5 m/s), the SS concentration increased from 642.5 mg/L to 4363.35 mg/L. When velocity increased from zero, the mud in the sediment surface changed from being in a static state to being in a slight suspension, capable of moving into the overlying water. When the velocity was low, a small amount of particles rolled on the sediment surface. Only some of these particles became suspended, causing the water body to become slightly turbid. With the increase in velocity, much more particles moved on the sediment surface and became suspended in the water body, causing much more turbidity.

3.6 The impact of velocity on TP concentrations

When increasing the velocity from 0 to 0.5 m/s, the TP concentration in the overlying water increased from 0.11 mg/L to 0.44 mg/L, about 4 times. The lowest TP concentration at the sediment-water interface (0.18 mg/L) occurred at 0.15 m/s, and the maximum concentration (0.75 mg/L) appeared at the initial velocity of 0 m/s. However, the TP concentration in the pore water changed without trend, and collectively, there was little change (Figure 6).
Figure 6 TP concentrations of overlying water, sediment-water interface and overlying water at corresponding velocities (April 2014)
When velocity increased from 0 to 0.1 m/s, the TP concentrations increased in the pore water, reduced drastically in the sediment-water interface, and rose rapidly in the overlying water. These observations can be explained that phosphorous absorbed by the particles was released into pore water, and phosphorous entered the overlying water through sediment re-suspension at the sediment-water interface. As velocity further increased, phosphorous absorbed by the sediment particles continually released into pore water, and phosphorous from the pore water began moving into overlying water through the sediment-water interface, which was under velocity turbulence. At the velocity of 0.4 m/s, the TP concentrations in the overlying water, at sediment-water interface, and in pore water all reduced, which indicated that the release of phosphorous from sediments had already reached its maximum value. The high velocity of water body caused a great amount of sediment particles to enter overlying water, and these particles adsorbed dissolved phosphorous, leading to a decrease in the TP concentration at the sediment-water interface and in the overlying water.

3.7 The impact of velocity on TDP and SRP concentrations

From the velocities 0 to 0.5 m/s, the TDP concentrations in the overlying water varied between 0.019 and 0.038 mg/L, with an average value of 0.025 mg/L. The minimum concentration of TDP was 0.019 mg/L, found at 0.4 m/s. The TDP concentration at the sediment-water interface changed unpredictably with changes in velocity; however, when considering only 0 to 0.5 m/s, there was an increase (Figure 7).
Figure 7 Concentrations SRP and TDP of overlying water and sediment-water interface at the corresponding velocities (April 2014)
Similarly to the changes of TDP concentrations, the SRP concentrations in the overlying water varied between 0.015 and 0.036 mg/L with an average value of 0.024 mg/L and a minimum concentration of 0.015 mg/L at 0.3 m/s. The SRP concentration at the sediment-water interface also varied unpredictably with increases in velocity. The range of SRP concentrations at the sediment-water interface was 0.013-0.065 mg/L with an average value of 0.024 mg/L.
The concentrations of both TDP and SRP negatively correlated with pH value, as well as water level. TDP and SRP concentrations decreased with increases in velocity during which the amount of phosphorous released from sediments was low and showed a decreasing trend.
Shallow lakes can be easily influenced by hydrodynamic conditions, and the release capability increases with the strong disturbance intensity. When the sediments suspend, phosphorous release from sediments and sorption of particles into the overlying water both occur; this is why there is not a sustaining increase or decrease trend of TDP and SRP. When the disturbance intensity was low, the source of phosphorous in the overlying water mainly came from sediments. When the disturbance intensity enhanced, more particles suspended into overlying water and adsorbed dissolved phosphorous, at the same time, oxygen concentration in the overlying water recovered, and then iron, manganese and other metal elements were oxidized to other forms with high phosphorous adsorption capacity. Increases of TDP and SRP were the results of phosphorous release from sediments and the adsorption of particles and metal elements.

3.8 Effects of water level and velocity on the phosphorous release rate from sediments

Examination of the relationship between the TP concentration and water level as well as that of the phosphorous release rate and water level (Figures 3 and 8) indicated a few points. Firstly, low water level turbulences (10-20 cm) caused a low phosphorous release rate from sediments, and the release rate increased with the increase of water level. Secondly, high water level turbulences (20-25 cm) caused re-suspension of sediments, which in turn released phosphorous into the water body. Finally, high water levels accelerated the release of phosphorous from sediments with the highest release rate of 4.13 mg/(m2d).
Figure 8 Phosphorous release rate from sediments expressed as a function of water level/velocity
By analyzing the relationship between the TP concentration and velocity as well as that of the phosphorous release rate and velocity (Figures 6 and 8), we found that at low velocity turbulences (0-0.2 m/s), sediments barely moved and only a small amount of phosphorous was released into the overlying water. Thus, the release rate was low, and the lowest release rate was 0.43 mg/(m2d). When the velocity turbulence increased, sediments re-suspended and caused the increase of phosphorous release rate, while at the same time, phosphorous absorbed by sediment particles was also desorbed into pore water. At high velocity turbulences (0.2-0.5 m/s), the desorption of sediment particles first reached its maximum value before the TP concentration began to decrease in the pore water and overlying water due to the lack of phosphorous source. At the velocity of 0.4 m/s, the release rate was 4.86 mg/(m2d) and started to decrease. The highest release rate was about 11 times the lowest release rate, similar to the results reported by Pong et al. (2008) and Reddy et al. (1996).
The relationship between the phosphorous release rate from sediments and water level/velocity was modeled using the curve fitting method and the parameters were consistent with the second and third parabolic equations, respectively (Table 2). The first derivative of these two equations was set to zero, and the optimal water level and velocity were calculated.
Table 2 Simulation of phosphorous release rate under variable water levels and velocities
Parameters Independent variables Fitted equations Correlation
coefficients (R2)		 Minimum (cm or m/s)
Release rate Water level (cm) y = 0.0479x2 - 0.0547x + 3.5876 0.99 0.57
Velocity (m s-1) y=-0.0914x3+1.4025x2-5.7575x+7.5701 0.96 0.20

4 Conclusions

As the water level and velocity varied, the physicochemical characteristics of the overlying water and sediment-water interface changed. The increase in water level and velocity caused an increase in the SS concentration as well as the pH value in the overlying water while the changes of the sediment-water interface and pore water varied. As well, the TP concentration in the overlying water and phosphorous release rate from sediments both increased with the increase in water level. During the increase in velocity, the phosphorous release rate reached the maximum value at 0.4 m/s. The simulation experiment indicated that the concentrations of both TDP and SRP were negatively correlated with pH value, and the amount of phosphorous release showed a decreasing trend.
The phosphorous release rate with either the water level or velocity was fitted with a best curve fitting method, and water level and velocity were found to be consistent with the second and third parabolic equations, respectively. The optimum water level at the velocity of 0.3 m/s was calculated to be 0.57 cm, and the optimum velocity at the water level of 15 cm was 0.2 m/s.

The authors have declared that no competing interests exist.

References

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DOI

[5]
Du Y L, Zhou H D, Peng W Qet al., 2015. Modeling the impacts of the change of river-lake relationship on the hydrodynamic and water quality revolution in Poyang Lake.Acta Scientiae Circumstantiae, 35(5): 1274-1284. (in Chinese)The hydrological regime condition of Poyang Lake was mainly influenced by watershed runoff and the Yangtze River. In recent 10 years,the relationship of basin,Yangtze river and Poyang lake had been changed greatly. This change not only caused an altered hydrological rhythm,but also affected the water environment in the Lake. The average daily hydrological processes in the period of 2003 —2012 had been compared with those in1956—2002. Results show that seasonal allocations of basin inflow and lake outflow were altered,the highest water level were decreased,and the time of limnetic facies of Poyang Lake were shortened. Furthermore,a 2 dimensional numerical model of hydrodynamic and water quality was applied to study the impacts of the changing river-lake relationship,and the model was validated by the measured data in 2010. The results reveal that water quality became worse due to the drought season coming earlier 21 days during Aug to Nov,and 13 days lagging of flood season during Apr to Jun. The concentration of TN in Poyang lake increased by 10. 6% and 12. 4% during the periods of Apr to Jun,and Aug to Oct,respectively. TP concentration increased by 11. 7%and 13. 6% during the above two respective periods. In the recent 10 years,the separation of dish-shaped lakes at south and west of Poyang Lake from the main lake occurred earlier in the period of Aug to Oct than that in 1956—2002. which increased the risk of eutrophication.

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[6]
Drewry J J, Newham L T H, Croke B F W, 2009. Suspended sediment, nitrogen and phosphorus concentrations and exports during storm-events to the Tuross estuary, Australia.Journal of Environmental Management, 90(2): 879-887.This paper presents a process for estimating pollutant loads from water quality data, to improve catchment-scale modelling in the region for resource management purposes. It describes a program to estimate suspended sediment, total and dissolved nitrogen and phosphorus loads to the Tuross estuary from the Tuross River catchment (1810 km(2)) of coastal southeast Australia. Event-based water quality sampling results obtained during storm events in 2005 are presented. Event 1, during July 2005 was the largest storm event in terms of peak flow for 3.5 years. Other events monitored were also in July, November and December 2005. The early July 2005 event had a flow-weighted mean suspended sediment (SS) concentration during the first 4 days of 63 mg L(-1). Of the events monitored, this was unusual as it was preceded by drought and had the largest SS concentrations (peaking at 180 mg L(-1)) during the rising-stage. In contrast, the November event had a much lower flow-weighted SS mean (28 mg L(-1)), even though peak flow magnitudes were similar. The July and November 2005 events had peak flows of 12,360 and 11,330 ML day(-1). Low-cost rising-stage siphon samplers were used to collect samples during the rapidly rising phase of these events. The use of such samplers and consideration of time-lead/lag flow adjustments, quantified using cross-correlation analysis to account for hysteresis effects, were incorporated into the load estimation techniques. The technique is a potentially useful approach for understanding relationships between water quality concentrations and flow for modelling catchment source strengths and transport processes.

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[7]
Emily K R, Monika I, Paul Het al., 2014. Phosphorus speciation in a eutrophic lake by 31P NMR spectroscopy. Water Research, 62: 229-240.61Variations in time and space indicate major transformations of P-containing compounds.61P-speciation was correlated with temperature, dissolved oxygen, and phytoplankton.61Cyanobacteria biomass was positively correlated to in-lake polyphosphate and phosphonate.

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[8]
Fan C, Zhang L, Yang Let al., 2002. Simulation of internal loadings of nitrogen and phosphorus in a lake.Oceanolgia et Limnologia Sinica, 33(4): 370-378. (in Chinese)On the basis of in situ investigation and analysis of the distribution of sludge and physio chemical characteristics of surficial sediment in Lake Luomahu during 1998, nutrient exchange patterns between sediment water interface were simulated with the soft sediment core samples at different temperatures (due to seasonal changes). The internal source was calculated by means of the release fluxes of nitrogen and phosphorus, together with the representative time section for each experimental temperature, and was compared with the result of concentration diffusion in interstitial water. The result indicates that the internal loadings of N and P in the whole lake are (1113.2卤71.3) t /a and (12.50卤0.95) t /a, respectively. Large differences between N and P contents and relatively high Fe contents in the soft sediment are the main factors that cause higher N release and lower P release.

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[9]
Gao X, Chen Z, Zhang Net al., 2002. Heavy metals and phosphorus in tidal flat sediments of the Yangtze estuary.Journal of Geographical Sciences, 12(4): 472-478.Concentrations of heavy metals (Cu, Pb, Zn, Cr and Cd), and phosphorous (P) were determined in surface tidal flat sediments of the Yangtze estuary and Shanghai coast. Results demonstrate that there were significant differences among the accumulation of the heavy metals in sediments, following the order: Zn > Cu > Cr > Pb > Cd. The spatial distribution and chemical forms of heavy metals in tidal flat sediments were closely related to the distribution of pollution resources (outlet of sewage) and the local sedimentary and hydrodynamic conditions. The dominated form of non-residual heavy metals is bound to Fe/Mn oxides, and the next form is bound to carbonates. Moreover, contents of total P in sediments range from 18.0 μmol.g 611 to 31.4 μmol.g 611 along the coastline, speciation of P in sediments was different, most of P in tidal flat sediments is associated with calcium phases (as Ca-P) similar to marine sediments.

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[10]
Huang J, Xu Q, Xi Bet al., 2014. Effects of lake-basin morphological and hydrological characteristics on the eutrophication of shallow lakes in eastern China.Journal of Great Lakes Research, 40(3): 666-674.The Yangtze River floodplain contains numerous oxbow or riverine lakes, all of which were openly connected with the Yangtze River or its major tributaries prior to 1950s. However, stresses resulting from human settlement and utilization of catchment resources have exerted great pressures on these lake ecosystems changing their morphology, connectivity and trophic state lakes. This study examined the interaction of these changes and their impact on eutrophication for 90 shallow lakes in eastern China in 2008 to 2011. TN and TP in the study lakes had negative relationships with mean water depth (Z mean ), but no single lake-basin characteristic was found to dominate chlorophyll-a (Chl-a) growth. Instead, water depth and surface area were found to interactively affect Chl-a concentrations in smaller lakes. That is, Chl-a concentration in the lakes with Z mean >2m and surface area (SA) 25km 2 was significantly higher than that in relatively larger lakes with Z mean >2m and SA>25km 2 (p-value 0.038). Chl-a concentration was higher in the lakes located within the lower Yangtze River basin which had longer retention times, than in the lakes located within the middle Yangtze River basin, where flow velocity is relatively larger. As expected, the water quality was found to be better in the lakes hydraulically connected with rivers than in those isolated from the river. This study revealed that lake-basin morphology and hydrology dominated algal blooms in the highly eutrophic shallow lakes in eastern China.

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[11]
Jiang Y, Li X, Xing Yet al., 2010. Impacts of disturbance on release of total nitrogen and total phosphorus from surficial sediments of Dongping Lake.Environmental Science and Technology, 33(8): 41-44.Surficial sediment samples were collected from Dongping Lake to investigate the impacts of disturbance on release of nutrients elements from surficial sediments.Results showed that no significant impacts could be found for the disturbance on pH of lake water,while the soluble cations increased obviously under the disturbance.There is no significant difference could be found for disturbance intensity of 25 and 50rpm on the accumulative releasing contents and releasing velocity of total nitrogen.Under the disturbance intensity of 100rpm,the accumulative releasing contents and releasing velocity of total nitrogen increased by 5.02mg/kg and 73.5% respectively compared with those of under the static state.Under the disturbance intensity of 25rpm,50rpm and 100rpm,the accumulative releasing contents of total phosphorus increased by 0.185,0.263 and 0.320mg/kg compared to the static state.Releasing velocity of total phosphorus increased by 36.2%,41.7% and 127.6% compared to the static state,which indicated that the disturbance would enhance significantly the release of TN and TP from surficial sediments of lakes.

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[12]
Kim S H, Hwang S J, Shin J Ket al., 2007. Effects of limiting nutrients and N:P ratios on the phytoplankton growth in a shallow hypertrophic reservoir.Hydrobiologia, 581: 255-267.The purpose of this study was to evaluate the effects of limiting nutrients and the N:P ratios on the growth of phytoplankton (mainly cyanobacteria) in a shallow hypertrophic reservoir between November 2002 and December 2003. Nutrient enrichment bioassays (NEBs) were conducted, along with analyses of seasonal ambient nutrients and phytoplankton taxa, in the reservoir. The average DIN:TDP and TN:TP mass ratios in the ambient water were 90 (range: 17–187) and 34 (13–60), respectively, during the study period. The dissolved inorganic phosphorus showed seasonal variation, but less than that of inorganic nitrogen. The TN:TP ratios ranged from 13 to 46 (mean: 27 ± 6) during June–December when the cyanobacteria, Microcystis , dominated the phytoplankton composition. The NEBs showed that phytoplankton growth was mainly stimulated by the phosphorus (all of total 17 cases), rather than the nitrogen concentration (8 of 17 cases). The rapid growth rate of cyanobacteria was evident with TN:TP ratios less than 30. According to the results of the NEBs with different N concentrations (0.07, 0.7 and 3.5 mg l 611 ), but the same N:P ratios and when the nitrogen concentration was highest, the cyanobacterial growth reached a maximum at N:P ratios <1. Overall, the response of cyanobacterial growth was a direct function of added phosphorus in the NEBs, and was greater with increased N concentrations. Thus, cyanobacterial blooms favored relatively low N:P ratios in this hypertrophic reservoir system.

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[13]
Li D, Huang Y, 2013. Phosphorus uptake by suspended sediments from a heavy eutrophic and standing water system in Suzhou, China.Ecological Engineering, 60: 29-36.Phosphorus (P) uptake by suspended sediments, from a heavy eutrophic canal system with high P concentration, was conducted in the lab. Addition of KH 2 PO 4 into the parallel operated experimental units were made similar to the external P input into the canal and carried out periodically. Results of P uptake after 39 days show that added P with the amount of 19.97 mg and 13.61 mg disappeared from the overlying water to 200 g wet sediments under intermittent disturbance and static conditions, respectively. Sequential fractionation indicated that P adsorption by Ox-Fe and Ox-Al might be the dominant P removal mechanism in the system. After P uptake under intermittent disturbance conditions, P adsorption experiment shows that the sediment was saturated with P very slowly (17.49%), compared with the sediment under static conditions (31.60%). Moreover, this sediment exhibited lower values for the constants K and S 0 . It was attributed to the redistribution of different P forms in the sediment. Therefore, the sediment was expected to present a lower P release potential than that under static conditions. After 6 weeks of anoxic incubation, the percentages of the P cumulative release from both sediments to the incorporated P confirmed this. It was suggested that sediment disturbance enhanced P retention in the sediment.

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[14]
Li Y, Pang Y, Lu Jet al., 2004. On the relation between the release rate of TN, TP from sediment and water velocity.Scientia Limnologica Sinica, 16(4): 318-324. (in Chinese)The starting principles of bottom mud in Lake Taihu were simulated in the laboratory in an annular tank; and the different stages of bottom mud movement were analyzed in this paper. The velocity of flow was basically uniformity in this annular tank, the rotation rate of tank and velocity of flow can be converted accurately, the law of sediment suspension and releasing were simulated by different disturbance forces. The sediments from Lake Taihu were used in this experiment, the relational expression between the release rate of TN, TP and water velocity was calculated on the basis of the relationship between the concentration of TN, TP and water velocity. The calculated result was applied in the mathematical model of water flow and water quality in Lake Taihu, and a satisfactory result was obtained.

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[15]
Liang W, Wang Z, Jiao Zet al., 2013. Adsorption of phosphorus in sediment re-suspension under sudden expansion flow conditions.Journal of Hydrodynamics, 25(1): 112-117.Based on the study of hydraulic characteristics of the sudden expansion water flow of an annular flume, this paper determines the vertical velocity distribution and the turbulence intensity distribution in the mainstream and the recirculation regions to analyze the basic features of this flow field. The adsorption of the phosphorus in the sediment is studied by adding the bacteriostatic agent. The results show that the flow speed in the mainstream region is higher than that in the recirculation region. However, the turbulence intensity in the recirculation region increases more than that in the mainstream region. The adsorption of the phosphorus in the sediment includes the physisorption and the biosorption, and the former is stronger than the latter. With the biosorption in the phosphorus removal process, the phosphorus released by the sediment is mainly completed by the poly-P bacteria in the anaerobic condition. The adsorption of the phosphorus in the sediment in the mainstream region of a sudden expansion water flow is strong and stable, whereas the adsorption in the sediment in the recirculation region is largely fluctuated.

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[16]
Marcus S, Christiane H, 2004. The influence of sorption processes on the phosphorus mass balance in a eutrophic German lowland river. Water, Air, and Soil Pollution, 155: 291-301.Previous studies on sorption processes in running waters lack a quantification of phosphorus sorption in relation to phosphorus mass balances of entire river sections. The present study was designed to investigate the influence of sorption processes on the phosphorus mass balance in a medium-sized lowland river. Riverbed surface sediments were sampled in the lower River Spree in February and in July 2002, and used for sorption shaking experiments. Phosphorus analyses results were evaluated using Langmuir-isotherms. Organic sediments revealed sorption properties that were affected by incubation temperature in a manner opposite to those of clastic sediments. Particulate iron is assumed to be the dominant sorption site of phosphorus in the lower River Spree. Clastic sediments act as phosphorus sinks, especially in summer, when soluble reactive phosphorus (SRP) concentrations in the water body are relatively high. Organic river substrates were found to be a source rather than a sink of phosphorus for the water body, but even in the worst case of a storm event, including complete resuspension of an organic surface layer, the contribution of desorption to the riverine phosphorus load of a eutrophic river was negligible (at maximum 2.5% of SRP load during vegetation period).

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[17]
Pang Y, Yan R, Yu Zet al., 2008a. Suspension-sedimentation of sediment and release amount of internal load in lake Taihu affected by wind.Chinese Journal of Environmental Science, 29(9): 2456-2464.Abstract The water quality in Meiliang Bay of the Taihu Lake was totally tested five times in the four seasons. The suspension samples were obtained by using a sediment trap. The sediment settling flux and resuspended flux were calculated according to the observation data by using Gansith formula, and the relationships between these fluxes and wind speeds were established. Seven experiments were conducted in Laboratory for hydrostatic settling behavior of suspended matter affected by different wind speeds in Lake Taihu. The hydrostatic settling fluxes of suspended matter were calculated and the relationships between the fluxes and suspended matter concentrations were established. Base on these works, the suspension-sedimentation process was decomposed and generalized according to the critical wind speed of 3.7 m/s. Daily sediment resuspended amount and settling amount of the year 2005 was calculated and annual average release amount of internal load in Lake Taihu was estimated using the wind data of nearly 10 years. The results indicate that daily release amount of internal load in Lake Taihu significantly influenced by wind and have the same trend of change with wind, while the release amount of different nutrients in the same condition are different. The Lake Taihu has an annual average release amount of internal load with COD 49,600 t, TN 7773.0 t and TP 275.5 t, of which summer has the markedly highest release amount than other seasons.

PMID

[18]
Pang Y, Zhuang W, Han Tet al., 2008b. Experiment and model simulation of suspended solids in Taihu Lake under wind-wave disturbance.Chinese Journal of Environmental Science, 29(10): 2743-2748.The bottom mud in Taihu Lake was simulated indoors in a wave tank. The rules of starting principle of the bottom mud were analyzed under different kinds of disturbing intensity in this paper. The common wave intensity of Tai Lake could be systematically simulated in the wave tank. The critical sheer stress of bottom mud in Tai Lake is 0.050Pa by the experiment. The calculated result of the flow field and suspended solids from the advanced model of FVCOM conforms to the observation data in Taihu Lake very well, which proves validity of the model. Because the conflict of field observation data in time and space greatly influences the accuracy of model parameters, simulating the suspended solids indoors is very important to the cure of Eutrophication in Taihu Lake.

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[19]
Qin B, Hu W, Gao Get al., 2004. Dynamics of the sediment resuspension and the conceptual schema of nutrient release in the large shallow lake Taihu, China.Chinese Science Bulletin, 49(1): 54-64.正 On the basis of investigations in situ, it was found that mass exchange on the water-sediment interface occurred chiefly on the superficial sediment within 5-10 cm. The spatial physicochemical character of sediment was distributed uniformly. The observation of lake currents and waves indicated that the dynamic sources, which act on the interface of water and sediment, came mainly from waves under strong wind forcing, while the critical shear stresses

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[20]
Reddy K R, Fisher M M, Ivanoff D, 1996. Resuspension and diffusive flux of nitrogen and phosphorus in a hypereutrophic lake.Journal of Environmental Quality, 25: 363-371.ABSTRACT Bottom sediments in shallow lakes can play a major role in releasing nutrients to the overlying water column during wind induced sediment resuspension or by constant flux due to diffusion. internal nutrient loads due to these processes may be equal to or higher than external loads. Laboratory and field experiments were conducted on Lake Apopka, a shallow, hypereutrophic subtropical lake located in central Florida. Ammonium (NH4+) N and soluble reactive P (SRP) flux during sediment resuspension were measured under laboratory conditions using intact sediment cores. Ammonium N and SRP flux due soley to diffusion were assessed using in situ porewater concentrations. Average diffusive flux from sediment to the overlying water was estimated to be 25 mg NH4-N m(-2) d(-1) and 1 mg P m(-1) d(-2). Resuspension hues of NH4+ and SRP were higher than diffusive flux. Soluble reactive P profiles of porewater showed distinct profile differentiation, with the surface 0 to 8 cm sediment depth acting as a P-depletion zone, and the underlying sediment displaying steep gradients in porewater SRP. These results suggest that dissolved NH4+ and SRP transport from the surface 8 cm of sediment was due to sediment resuspension, while below this depth, upward mobility of NH4+ and SRP was regulated by diffusion. Although dissolved N and P flu is upwards (from sediment to water column), during extended periods (annual cycle) tbe lake is functioning as a net sink for N and P by transforming inorganic pools of nutrients into organic forms and depositing them on the sediment surface.

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[21]
Reitzel K, Ahlgren J, Gogoll Aet al., 2006. Effects of aluminum treatment on phosphorus, carbon, and nitrogen distribution in lake sediment: A P-31 NMR study.Water Research, 40(4): 647-654.The effects of aluminum (Al) treatment on sediment composition of carbon (C), nitrogen (N) and phosphorus (P) were investigated in sediment representing pre- and post-treatment years in the Danish Lake S nderby. 31P NMR spectroscopy analysis of EDTA-NaOH extracts revealed six functional P groups. Direct effects of the Al treatment were reflected in the orthophosphate profile revealing increased amounts of Al-P in the sediment layers representing the post-treatment period, as well as changes in organic P groups due to precipitation of phytoplankton and bacteria at the time of Al addition. Furthermore, changes in phytoplankton community structure and lowered production due to the Al treatment resulted in decreased concentrations of sediment organic P groups and total C. Exponential regressions were used to describe the diagenesis of C, N, and P in the sediment. From these regressions, half-life degradation times and C, N, and P burial rates were determined.

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[22]
Sonderdaard M, Jensen J P, Jeppesen E, 2003. Role of sediment and internal loading of phosphorus in shallow lakes.Hydrobiologia, 506(1): 135-145.

[23]
Sundby B, Gobeil C, 1992. The phosphorus cycle in coastal marine sediments.Limnology and Oceanography, 37(6): 1129-1145.Approximately half of the sedimentation flux of particulate phosphorus in the Laurentian Trough in the Gulf of St. Lawrence is mobilized within the sediment and returned to the water column. In the oxidizing surface sediment, a major portion of the sedimentation flux of organic phosphorus is mineralized, and the released phosphate is partitioned between the pore water and surface adsorption sites. Surface-adsorbed phosphate is released to the pore water as needed to replace dissolved phosphate that escapes to the overlying water. Most of the phosphate is released deeper in the sediment column from iron oxides undergoing reduction. The nonmobilized phosphorus, which is buried with the accumulating sediment, appear to consist mostly of stable minerals such as apatite. The concentration of dissolved phosphate in sediment pore waters increases sharply across the sediment-water interface from 2 mol PO4liter-1 in the bottom water to 6卤 3 mol PO4liter-1 in the top centimeter, remains almost constant at this value down to 5-15-cm depth, and then increases rapidly with further depth. In the region of constant concentration, phosphate is buffered by adsorption-desorption equilibria with the sediment. The production rate of phosphate, the buffering capacity of the sediment, and the thickness of the diffusive boundary layer at the sediment-water interface control the shape of the pore-water profile.

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[24]
Sun X, Qin B, Zhu Get al., 2007. Effect of wind-induced wave on concentration of colloidal nutrient and phytoplankton in Lake Taihu.Chinese Journal of Environmental Science, 28(3): 506-511.In order to find out the characteristics of colloidal nutrient and phytoplankton under different wind conditions in Lake Taihu, observation were carried out and samples were collected. Colloid was collected by using cross-flow ultrafiltration system. Organic carbon, nitrogen, and phosphorus in colloidal, dissolved and other fractions of water samples were determined, and concentration and biomass of phytoplankton were also determined. The result showed that the concentration of colloidal nitrogen (CN), colloidal phosphorus (CP) increased with the increasing of wind speed when the wind speed was less than 4 m/s , and did not increase or even decreased with the increasing of wind speed when the wind speed was more than 4 m/s . The concentration of Chl-a, phytoplankton, cyanobacteria, and biomass of cyanobacteria increased with the increasing of wind speed when the wind speeds was less than 4 m/s , and decreased with the increasing of wind speeds when the wind speed was more than 4 m/s . It was indicated that the small wind-induced waves are of advantage to the float or growth of cyanobacteria while the big wind-induced waves are of disadvantage to the float or growth of cyanobacteria. Concentration of CN and CP are significantly correlated with concentration of phytoplankton and cyanobacteria, indicating that algae and their production are main sources of CN and CP in summer in Lake Taihu.

PMID

[25]
Szmant A M, Forrester A, 1996. Water column and sediment nitrogen and phosphorus distribution patterns in the Florida Keys, USA.Coral Reefs, 15(1): 21-41.Measurements of the distribution patterns of nutrients (ammonium, nitrate, orthophosphate, total N and total P) and chlorophyll concentrations were conducted under an interdisciplinary program known as SEAKEYS, initiated because of concern that anthropogenic nutrients may be impacting Florida coral reefs. Samples were collected along transects that extended from passes or canals to 0.5 km offshore of the outermost reefs. Seven of the transects were either in the Biscayne National Park (BNP) and Key Largo (upper keys) or Seven Mile Bridge/Looe Key (upper part of lower keys) areas, which have the best present-day reef development; the two in the middle keys off Long Key were in an area of minimal reef development where passes allow estuarine Florida Bay water to flow onto the Florida reef platform. Off the upper keys, water column concentrations of N and chl a were elevated near marinas and canals (1 μM NO 3 , 1 μg/l chl a), but returned to oligotrophic levels (e.g., chl a 81 0.25 μg/l; NO 3 81 0.25 μM; NH 4 81 0.10 μM) within 0.5 km of shore. Phosphorus concentrations, however, were often higher offshore 82 0.2 μM PO 4 ). Sediment interstitial nutrient concentrations decreased from inshore to the offshore reef areas (e.g., 82 100 μM NH 4 inshore to 81 50 μM NH 4 offshore) and were comparable to those of some presumably pristine coastal and reef carbonate sediments. Sediment bulk N was higher nearshore and decreased steeply offshore ( 82 60 μg-at N/gm sediment to 81 20 μg-at N/gm sediment, respectively); bulk P concentrations (81 6 μg- at P/gm sediment) varied little or exhibited the reverse pattern. Sediment N:P ratios were consistently lower offshore (1–10 vs. 20–40 nearshore). Higher offshore P concentrations are attributed to periodic upwelling along the shelf edge. In the middle keys water column nutrients and chl a concentrations were both higher than those in the upper keys, and there was less of an inshore-offshore decrease than that noted in the upper keys. Sediment nutrients were higher also, and nearshore and offshore areas did not differ. Water column and sediment nutrient concentrations and distribution patterns in the upper part of the lower keys were most similar to those measured in the upper keys. Overall, the present data do not support the contention that reef areas in the upper keys are accumulating elevated loads of land-derived nutrients via surface water flow, but does document moderately elevated nutrient and chl a levels in many developed nearshore areas. Most of the anthropogenic and natural nutrients entering the coastal waters from shore appear to be taken up by near shore algal and seagrass communities before they reach patch reef areas. Further work is needed to determine whether nutrient-enriched ground waters reach the reefs, however these would be expected to cause an enrichment of reef sediments, which was not observed.

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[26]
Tang C X, Xiong X, Wu N Het al., 2015. Simulation of the impact of the reverse flow from Yangtze River on the hydrodynamic process of Lake Poyang.Journal of Lake Sciences, 27(4): 700-710. (in Chinese)react-text: 239 Most biochemical processes and associated water quality in lakes depends on their flushing abilities. The main objective of this study was to investigate the transport time scale in a large floodplain lake, Poyang Lake (China). A 2D hydrodynamic model (MIKE 21) was combined with dye tracer simulations to determine residence and travel times of the lake for various water level variation... /react-text react-text: 240 /react-text [Show full abstract]

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[27]
Temporetti P, Snodgrass K, Pedrozo F, 2013. Dynamics of phosphorus in sediments of a naturally acidic lake.International Journal of Sediment Research, 28(1): 90-102.

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[28]
Testa J M, Brady D C, Di T D Met al., 2013. Sediment flux modeling: Simulating nitrogen, phosphorus, and silica cycles.Estuarine Coastal and Shelf Science, 131: 245-263.Sediment-water exchanges of nutrients and oxygen play an important role in the biogeochemistry of shallow coastal environments. Sediments process, store, and release particulate and dissolved forms of carbon and nutrients and sediment-water solute fluxes are significant components of nutrient, carbon, and oxygen cycles. Consequently, sediment biogeochemical models of varying complexity have been developed to understand the processes regulating porewater profiles and sediment-water exchanges. We have calibrated and validated a two-layer sediment biogeochemical model (aerobic and anaerobic) that is suitable for application as a stand-alone tool or coupled to water-column biogeochemical models. We calibrated and tested a stand-alone version of the model against observations of sediment-water flux, porewater concentrations, and process rates at 12 stations in Chesapeake Bay during a 4-17 year period. The model successfully reproduced sediment-water fluxes of ammonium (NH4+,), nitrate (NO3-), phosphate (PO43-), and dissolved silica (Si(OH)(4) or DSi) for diverse chemical and physical environments. A root mean square error (RMSE)-minimizing optimization routine was used to identify best-fit values for many kinetic parameters. The resulting simulations improved the performance of the model in Chesapeake Bay and revealed (1) the need for an aerobic-layer denitrification formulation to account for NO3- reduction in this zone, (2) regional variability in denitrification that depends on oxygen levels in the overlying water, (3) a regionally-dependent solid-solute PO43- partitioning that accounts for patterns in Fe availability, and (4) a simplified model formulation for DSi, including limited sorption of DSi onto iron oxyhydroxides. This new calibration balances the need for a universal set of parameters that remain true to biogeochemical processes with site-specificity that represents differences in physical conditions. This stand-alone model can be rapidly executed on a personal computer and is well-suited to complement observational studies in a wide range of environments. (c) 2013 Elsevier Ltd. All rights reserved.

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[29]
Wetzel R G, 2001. Limnology: Lake and River Ecosystems. 3rd ed. San Diego: Academic Press, USA.

[30]
Wu C, Wang Y, Han Jet al., 2008. Preliminary study on nitrogen and phosphorus release characteristics from sediment in Beigu wetland.Environmental Science and Technology, 31(4): 10-12.The release process of phosphorous and nitrogen from sediment and contaminative degree of the sediment are investigated through continuous test to the concentrations of nitrogen and phosphorus of overlying water body.Results indicated that the disturbance makes a certain degree of increase in the release of nitrogen and phosphorus,therefore changes in external environment conditions can accelerate the release of nitrogen and phosphorus in sediment.There was a high degree of spatial variability of the release of nitrogen and phosphorus in sediment of the wetland in different sampling points,and contribution of the release of nitrogen and phosphorus from sediment to water body should not be overlooked.

[31]
Wu D, Hua Z, 2014. The effect of vegetation on sediment resuspension and phosphorus release under hydrodynamic disturbance in shallow lakes.Ecological Engineering, 69: 55-62.This study was conducted to investigate the effect of vegetation on sediment resuspension and phosphorus release in response to hydrodynamic disturbances in shallow lakes using a unique instrument to simulate wind-driven current. Two common types of vegetation, Vallisneria natans and Acorus calamus of Taihu Lake (a typical shallow lake), were planted in an experiment system. The results indicated that bed shear stress in the presence of vegetation was much less than critical shear stress which led to lower resuspension. Acorus calamus led to a much greater reduction in bed shear stress and better inhibitory effects on sediment resuspension due to its robust stem and better resisting capacity. Additionally, vegetation had a significant inhibitory effect on the release of total phosphorus (TP). The effect was larger for Acorus calamus , especially under hydrodynamic disturbance induced by moderate and high wind speed. TP release by Vallisneria natans was dominated by particulate phosphorus (PP) and that of Acorus calamus was dominated by dissolved total phosphorus (DTP). PP release mechanism was same in flume SV and EV that it was mainly relevant to bed shear stress and SSC. DTP release mechanism was different between plant species.

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[32]
Xie L, Xie P, 2002. Long-term (1956-1999) dynamics of phosphorus in shallow, subtropical Chinese lake with the possible effects of cyanobacteria blooms.Water Research, 36: 343-349.This paper describes the long-term dynamics of phosphorus concentrations in both the lake water and the sediment in a subtropical Chinese lake, Lake Donghu. The total phosphorus (TP) concentration in the lake water experienced an upward trend from the 1950s, and peaked in 1983/1984, but declined obviously afterwards. From the 1950s to thel990s. TP content in the upper 10cm sediment of the lake increased steadily from 0.307 to 1.68mg P gDW(-1) at Station I and from 0.151 to 0.89 mg P g DW(-1) at Station II, respectively. The TP increase in the lake water before mid-1980s was mainly attributed to the massive input of sewage P. The outbreak of cyanobacterial blooms coincided with the peaks of TP and Orthophosphate (PO4-P) in the water in mid-1980s, and the maximum TP of the water reached as high as 1.349mg/l at Station I and 0.757mg/l at Station II (in 1984), respectively. The declines of TP and P04-P in the water after mid-1980s was coincident with the disappearance of cyanobacterial bloom.

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[33]
Xing K, Guo H, Sun Yet al., 2005. Assessment of the spatial-temporal eutrophic character in the Lake Dianchi.Journal of Geographical Sciences, 15(1): 37-43.Water-quality deterioration and eutrophication of the Lake Dianchi have acquired more and more attention in the last few decades. In this paper, the spatial and temporal eutrophication status of the Lake Dianchi was assessed. The comprehensive trophic state index was chosen to assess the trophic status of the Lake Dianchi in the past 13 years. The result reveals that the trophic condition of Caohai is more serious than that of Waihai. Most of time Caohai was in extremely hypereutrophic state from 1988 to 2000. The trophic condition of Waihai had a worsening tendency from 1988 to 2000. Waihai was in eutrophic state before 1995, but it got in a hypereutrophic state after 1995. It was pointed out that TN and TP were the two biggest contributors of CTSIM in both Caohai and Waihai.

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[34]
Zhang K, Cheng P, Zhong Bet al., 2012. Total phosphorus release from bottom sediments in flowing water.Journal of Hydrodynamics, 24(4): 589-594.In this paper, the bottom of the Dianshan Lake was selected as a test sample. The dynamic release of contaminated sediments into the overlying water column was experimentally investigated in an open water channel under different hydrodynamic conditions. The experimental results indicate that the Total Phosphorus (TP) release process can be divided into three stages: rapid release, slow release and equilibration release. In the initial release stage the measured TP concentration changes along the depth. The TP concentration near the sediment-water interface is higher than that near the water surface, but the TP concentration becomes uniform along the depth after 3 h. The dynamic release of re-suspension sediment pollutants is about 6 times higher than the static release of sediment-water interface. There are three main types of release mechanism: diffusion release, re-suspended pore water mixing release and re-suspended particles desorbing release.

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[35]
Zhang L, Fan C, Wang Jet al., 2008. Nitrogen and phosphorus forms and release risks of lake sediments from the middle and lower reaches of the Yangtze River.Scientia Limnologica Sinica, 20(3): 263-270. (in Chinese)Cluster analysis, principal component analysis and correlation matrix analysis were used to analysis the nitrogen and phosphorus release risks from sediments in 18 lakes located in the middle and lower reaches of the Yangtze River, as well as the nitrogen and phosphorus forms and related geochemical parameters from sediments, pore waters and overlying waters. The ecological difference of macrophyte and algae dominated lakes was the main reason of the difference of nitrogen and phosphorus release. The release risks were well correlated with the iron-bound phosphorus (FeP), algae available phosphorus (AAP), total nitrogen (TN), total phosphorus (TP) in sediment, the content of nitrogen and phosphorus in overlying and pore waters, porosity and organic matter content of surficial sediment. The AAP and FeP was the main phosphorus forms deciding the phosphorus release risk and other forms were in less effect on it due to the lower contents or lower transformation ability. The sediment organic phosphorus was not directly related to the phosphorus release risks but remarkably positively correlated to organic matter contents in sediment.

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[36]
Zhang Y, Yang L, Lei Ket al., 2013. Exchange and deposition fluxes of nitrogen and phosphorus across sediment-water interface in lower Yellow River.Journal of Sediment Research, 6: 66-74.This paper studies the exchange and deposition fluxes of nitrogen(N) and phosphorus(P) across the sediment-water interface in the lower Yellow River to estimate the impacts of these two processes on the budget of N and P during river transportation.The results show that the concentrations of total nitrogen(TN)and total phosphorus(TP) in surface water ranged between 2.67 and 5.49mg/L(mean 4.18±0.98mg/L),0.02 and 0.94mg/L(mean 0.39±0.29mg/L) during the study period,respectively,indicating the river water quality was not optimistic.Exchange fluxes of NO-3-N,NH+4-N and PO43--P across the sediment-water interface ranged between- 0.31 and 0.52g /(m2·d),- 0.06 and 0.06g/(m2·d),-1.52 and 0.50mg/(m2·d),with the average values of 0.11±0.24g/(m2·d),-0.01±0.03g/(m2·d),-0.26 ±0.65 mg/(m2·d),respectively.This suggestes that the river sediment acted as a sink of NO-3-N while a source of PO43--P and NH+4-N.Deposition fluxes of TN and TP ranged between 0.57 and 706.55g /(m2·d),2.54 and 1 180.60g /(m2·d),with the average values of 108.72±191.12g/(m2·d) and 256.34±359.39g/(m2·d),respectively.Taking the external loads of N and P into consideration,it is estimated that the impact of exchange process on the riverine budgets of N and P can be neglected.However,about 2.25% of N and3 6.90% of P could be reduced by the process of deposition,which indicates that deposition was the main retention process of P in the lower Yellow River.

[37]
Zheng L, Ye Y, Zhou H, 2004. Phosphorus forms in sediments of the East China Sea and its environmental significance.Journal of Geographical Sciences, 14(1): 113-120.

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