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Algal blooms (ABs) can affect the migration of phosphorus (P) among sediments, interstitial water and overlying water. It is important to analyze the characteristics of P and their interactions in the three media during ABs. A 5-month field study (June to October in 2016) was conducted in Zhushan Bay of Lake Taihu. P fractions, P adsorption characteristics and P diffusion fluxes at the sediment-water interface (SWI) were investigated. During the outbreak period of ABs from June to August, labile P concentrations in the sediment measured by diffusive gradients in thin films (DGT-labile P) and its diffusion fluxes across the SWI increased significantly. The equilibrium P concentration (EPC

Human disturbance is one of the essential forces affecting changes in landscape patterns. Studying the relationship between human disturbances and landscape patterns is of significance for regional conservation and ecosystem management. An understanding of this relationship is also crucial for the mitigation of conflicts between socioeconomic development and environmental protection. In this study, using remote sensing data and geographical information system technology, we created a quantitative method to assess the intensity of human disturbance on the landscape by introducing the concept of hemeroby. By means of the measurement of hemeroby and statistical approaches, we quantitatively analyzed the temporal and spatial changes of human disturbances and their effects on landscape patterns in the Jiangsu coastal zone, China, from 1995 to 2013. The results showed that the intensity of human disturbance gradually increased from 1995 to 2013. While the increasing rate of intensity of human disturbance has slowed down from early period (1995–2002) to later period (2002–2013) because of differences in exploitation activities and regional development policies. Spatially, the hemeroby increased most obviously in the southern counties and northern Ganyu County, resulting from port construction and tidal flat reclamation. Depending on the different degrees of human disturbance, landscape patterns showed obvious differences. Compared with low-level and high-level human disturbance, mid-level human disturbance contributed to more fragmented landscape, more complex patch shape, lower connectivity, and higher diversity. A correlation analysis between landscape indices and hemeroby suggested that the landscape patterns in regions with high-level human disturbance were relatively sensitive to changes in the intensity of human activities. The findings in this paper provide additional spatial information and theoretical guidance for regional conservation and ecosystem management in the Jiangsu coastal zone, China.

Characterization of phosphorus (P) pools is vital to understanding the contribution of P to water eutrophication. In this study, dissolved and particulate P classes during an algae bloom in Lake Taihu, as well as their relationships with the main environmental factors, were analyzed based on solution 31P NMR. The results showed that dissolved P was dominated by orthophosphate (Ortho-P) in heavily polluted regions and by orthophosphate monoester (Mono-P) and orthophosphate diester (Diester-P) in lightly polluted regions, indicating that the main dissolved P classes varied with the degree of lake pollution. The difference in the temporal variation patterns of dissolved P classes revealed that dissolved Ortho-P is the preferred class, and its concentration may be affected by major primary producers. It also revealed that dissolved Mono-P is prone to accumulation under the effects of algal blooms, especially in heavily polluted regions. The main particulate P classes were similar to those of dissolved P, but their variation trends were the same in different lake regions. There were significant positive correlations between the major particulate P classes and Chl a during the majority of the sampling period, indicating that living algal cells have a major contribution to particulate P. Obvious temporal variations of P classes may affect the bioavailability and dynamics of P in the water of Lake Taihu, but the particle reactivities of the main inorganic and organic P classes were similar. Therefore, they have little effect on P partitioning between the dissolved and particulate phases.

The need for minimizing water eutrophication makes controlling phosphorus (P) release and/or loss from sediments/soil an urgent matter. This research seeks to develop methods to predict P release in sediments. We first studied the P adsorption in 10 sediments from a sub lake of Taihu Lake, China for 80 days. After adsorption, the sediments were extracted with 0.01 M CaCl 2 and 0.5 M pH 8.5 NaHCO 3 solutions. We found strong linear relationships between the equilibrium concentration and CaCl 2 -P (R 2 = 0.91) and between P adsorbed and NaHCO 3 -P (R 2 = 0.90). This result suggests that: (I) CaCl 2 -P can be used as a proxy for the P concentration between the sediment interface and overlying water when it is difficult to measure P; (II) NaHCO 3 -P is able to evaluate the newly adsorbed P in the sediments which may reflect the enriched process. The results indicate that we could link CaCl 2 -P and NaHCO 3 -P further using common isotherm models. This hypothesis was tested for our sediment data and soil data from published literature. Models derived from Langmuir and Temkin isotherms could successfully fit the data. In more general applications, our models are also capable of describing the relationship of NH 4 Cl-P and TP. They are routine indexes to assess the status of sediment P. The fact that the models predict P loss in soils or P release from sediment well makes them potentially useful in areas of wide P risk assessment.

Characterization of phosphorus (P) pools is vital to understanding the contribution of P to water eutrophication. In this study, dissolved and particulate P classes during an algae bloom in Lake Taihu, as well as their relationships with the main environmental factors, were analyzed based on solution

Organic phosphorus (P) fractions in surface sediments from a large shallow, eutrophic Lake Taihu, China, were extracted with 0.1 M NaOH after pre-treatment of the sediments with a solution composed of 0.1 M EDTA and 2% (w/v) Na 2 S 2 O 4 . Composition of organic P in the extracts was then characterized by 31 P nuclear magnetic resonance spectroscopy ( 31 P NMR). Several P species, including phosphonates, orthophosphate, orthophosphate monoesters, phospholipids, DNA, pyrophosphate and polyphosphate, were detected in the NaOH extracts. The proportion of extracted organic P to total P in sediments was negatively correlated with total P in the water column, as were the proportions for orthophosphate monoesters and DNA. This implies that the majority of organic P in surface sediments is likely stabilized in some way, and does not directly contribute to the internal loading of P from sediments.

The understanding of organic phosphorus (P) dynamics in sediments requires information on their species at the molecular level, but such information in sediment profiles is scarce. A sediment profile was selected from a large eutrophic lake, Lake Taihu (China), and organic P species in the sediments were detected using solution phosphorus-31 nuclear magnetic resonance spectroscopy (31P NMR) following extraction of the sediments with a mixture of 0.25 mol/L NaOH and 50 mmol/L EDTA (NaOH-EDTA) solution. The results showed that P in the NaOH-EDTA extracts was mainly composed of orthophosphate, orthophosphate monoesters, phospholipids, DNA, and pyrophosphate. Concentrations of the major organic P compound groups and pyrophosphate showed a decreasing trend with the increase of depth. Their half-life times varied from 3 to 27 years, following the order of orthophosphate monoesters > phospholipids > or = DNA > pyrophosphate. Principal component analysis revealed that the detected organic P species had binding phases similar to those of humic acid-associated organic P (NaOH-NRP(HA)), a labile organic P pool that tends to transform to recalcitrant organic P pools as the early diagenetic processes proceed. This demonstrated that the depth attenuation of the organic P species could be partly attributed to their increasing immobilization by the sediment solids, while their degradation rates should be significantly lower than what were suggested in previous studies.

Pretreatment with chemicals such as ethylenediaminetetraacetic acid (EDTA) is often used to improve the analysis of sediment P with solution P-31 nuclear magnetic resonance spectroscopy (35P-NMR), but there is a lack of a comprehensive assessment of the methodology. In this study, the effects of EDTA pretreatment on sediment P extracted using a mixture of 0.25 mol L(-1) NaOH and 50 mmol L(-1) EDTA (NaOH-EDTA) were examined with 45 different sediments. The results showed that EDTA pre-extraction decreased the amount of P extracted by NaOH-EDTA when the concentration ratio of sediment Ca to the sum of sediment Fe and Al [Ca/(Fe+Al), on a wt/vol basis] was lower than 0.4. An increase in total extracted P, coupled with substantial increases in total extracted paramagnetic ions such as Fe and Mn, was observed for another group of sediments with Ca/(Fe+Al) > 0.5, possibly due to the matrix effect. Analysis of 16 representative sediments with 31P-NMR showed that orthophosphate diesters were substantially removed by EDTA pre-extraction for sediments with Ca/ (Fe+Al) between 0.4 and 0.7, reflecting a high risk posed by this pretreatment. Phosphorus diversity and concentration of individual P compounds were markedly improved for sediments with Ca/(Fe+Al) > 0.7, suggesting that EDTA pretreatment was particularly useful for 31P-NMR analysis of calcareous sediments. The present study showed that sediment properties played an important role in determining pretreatment effects. Caution is advised when applying pretreatment methods to different sediments.