This study aims to establish the relative importance of sediment organic phosphorus (Po) to the total P and the major classes of organic molecules that contribute to sediment Po, determined by measuring their susceptibility to enzymatic hydrolysis, across a suite of lakes ranging from oligotrophic to eutrophic status. The results showed that Po accounted for 21–60% of total P, and bioavailable Po accounted for 9–34% of Po in the sediments. The bioavailable Po includes mainly labile (H2O-Po) and moderately labile (NaOH-Po) P forms. For H2O-Po (accounting for only1.4% of Po), 53% (average) was labile monoester P, 28% was diester P and 17% was phytate-like P. For NaOH-Po (accounting for 9–33% of Po), 32% was labile monoester P, 33% was phytate-like P and 18% was diester P. The composition of bioavailable Po, determined by enzyme assays, was related to the lake nutrient levels, which implies that sediment bioavailable Po could act as an effective indicator for lake eutrophic status. With the increase of lake nutrient levels, bioavailable Po content and alkaline phosphatase activity in the sediment all increased, indicating that Po represents an important and bioavailable source of P that increases with eutrophication, and could contribute to internal loading and resistance of eutrophic lakes to remediation. This implies that eutrophic lakes would maintain long-term eutrophic status and algal bloom phenomena even after the external input of P was controlled and the total P concentration of water has declined. Thus, in order to reduce the release risk of sediment P more efficiently and effectively, sediment P control technique should focus not only on reducing the total P and inorganic P, but should also pay close attention to the removal of bioavailable Po.

A thorough understanding of the labile status and dynamics of phosphorus (P) and iron (Fe) across the sediment-water interface (SWI) is essential for managing internal P release in eutrophic lakes. Fe-coupled inactivation of P in sediments is an important factor which affects internal P release in freshwater lakes. In this study, two in-situ high-resolution diffusive gradients in thin films (DGT) techniques, Zr-Oxide DGT and ZrO-Chelex DGT, were used to investigate the release characteristics of P from sediments in a large freshwater lake (Dongting Lake, China; area of 2691 km2) experiencing a regional summer algal bloom. Two-dimensional distributions of labile P in sediments were imaged with the Zr-Oxide DGT without destruction of the original structure of the sediment layer at four sites of the lake. The concentration of DGT-labile P in the sediments, ranging from 0.007 to 0.206 mg L−1, was highly heterogeneous across the profiles. The values of apparent diffusion flux (Fd) and release flux (Fr) of P varied between −0.027–0.197 mg m−2 d−1 and 0.037–0.332 mg m−2 d−1, respectively. Labile P showed a high and positive correlation (p < 0.01) with labile Fe(II) in the profiles, providing high-resolution evidence for the key role of Fe-redox cycling in labile P variation in sediments.

The worldwide use of pesticides has led to increases in agricultural yields by reducing crop losses. However, increased pesticide use has resulted in pesticide-resistant pest species and recent studies have discovered pesticide-resistance in non-target species living close to farms. Such increased tolerance not only affects the species, but can alter the entire food web. Given that some species can evolve not only resistance to a single pesticide, but also cross-resistance to other pesticides that share the same mode of action, one would predict that cross-resistance to pesticides would also have effects on the entire community and affect community stability. To address this hypothesis, we conducted an outdoor mesocosm experiment comprised of 200 identical aquatic communities with phytoplankton, periphyton, and leopard frog (Lithobates pipiens) tadpoles. To these communities, we added one of four Daphnia pulex populations that we previously discovered were either resistant or sensitive to the insecticide of chlorpyrifos as a result of living close to or far from agriculture, respectively. We then exposed the communities to either no insecticide or three different concentrations of AChE-inhibiting insecticides (chlorpyrifos, malathion or carbaryl) or sodium channel-inhibiting insecticides (permethrin or cypermethrin). We discovered that communities containing sensitive Daphnia pulex experienced phytoplankton blooms and subsequent cascades through all trophic groups including amphibians at moderate to high concentrations of all five insecticides. However, communities containing resistant D. pulex were buffered from these effects at low to moderate concentrations of all AChE-inhibiting insecticides, but were not buffered against the pyrethroid insecticides. These data suggest that a simple change in the population-level resistance of zooplankton to a single insecticide can have widespread consequences for community stability and that the effects can be extrapolated to a wide variety of pesticides that share the same mode of action.

The temporal-spatial distributions of DDT-related contaminants (DDXs), including DDT (dichlorodiphenyltrichloroethane), DDE (dichlorodiphenyldichloroethylene) and DDD (dichlorodiphenyldichloroethane), in the sediments of Lake Chaohu and their influencing factors were studied. p,p-DDE and p,p-DDD were found to be the two dominant components of DDXs in both surface and core sediments. The parent DDT compounds were still detectable in sediment cores after the late 1930s. Historical usage of technical DDT was identified as the primary source of DDXs in sediments, as indicated by DDT/(DDD + DDE) ratios of less than one. The residual levels of DDXs were higher in the surface and core sediments in the western lake area than in other lake areas, which might be due to the combined inflow effects of municipal sewage, industrial wastewater and agricultural runoff. The DDX residues in the sediment cores reached peak values in the late 1970s or early 1980s. There were significant positive relationships between DDX residues in sediment cores with annual DDT production and with fine particulate sizes (<4.5 μm). The relationship between the DDXs and TOC in sediment was complex, as indicated by the significant differences among the surface and core sediments. The algae-derived organic matter significantly influenced the amount of residue, composition and distribution of DDXs in the sediments. The DDD/DDE ratios responded well to the anaerobic conditions in the sediments that were caused by algal blooms after the late 1970s in the western lake area. This suggests that the algae-derived organic matter was an important factor and served as a biomarker of eutrophication and also affected the DDX residues and lifecycle in the lake ecosystem.

Addressing the challenge that phosphorus is the key factor and cause for eutrophication, we evaluated the phosphorus release control performance of a new phosphorus inactive clay (PIC) and compared with Phoslock®. Meanwhile, the impacts of PIC and Phoslock® on phytoplankton abundance and community structure in eutrophic water were also discussed. With the dosage of 40 mg/L, PIC effectively removed 97.7% of total phosphorus (TP) and 98.3% of soluble reactive phosphorus (SRP) in eutrophic waters. In sediments, Fe/Al-phosphorus and organic phosphorus remained stable whereas Ca-phosphorus had a significant increase of 13.1%. The results indicated that PIC may form the active overlay at water-sediment interface and decrease the bioavailability of phosphorus. The phytoplankton abundance was significantly reduced by PIC and decreased from (1.0–2.4) × 107 cells/L to (1.3–4.3) × 106 cells/L after 15 d simultaneous experiment. The phytoplankton community structure was also altered, where Cyanobacteria and Bacillariophyceae were the most inhibited and less dominant due to their sensitivity to phosphorus. After PIC treatment, the residual lanthanum concentration in water was 1.44–3.79 μg/L, and the residual aluminium concentration was low as 101.26–103.72 μg/L, which was much less than the recommended concentration of 200 μg/L. This study suggests that PIC is an appropriate material for phosphorus inactivation and algal bloom control, meaning its huge potential application in eutrophication restoration and management.

The internal loading of P is reported to be the main factor initiating algal blooms. However, there are only a few reports on the dynamic variation of labile P in the sediment and overlying water during the decomposition of algal. In addition, the widely perceived relationship between labile P and Fe was not supported by in situ obtained values in freshwater. Consequently, the in situ simultaneous measurement of diffusion gradients in thin-film techniques (DGT) was applied on a large scale to detect the mechanisms of labile P and Fe in a typical shallow lake (Lake Hongze). The newly developed ZrO-DGT and ZrO-Chelex DGT were combined to obtain the concentration of labile P and Fe. Results showed that decomposition of algal might be the main contributor for the concentration dots and peaks of labile P in sediment profiles, as well as for the high values on the horizontal heterogeneity index of labile P at the depth of 0–30 mm of the sediment. Moreover, there existed significant difference between the apparent diffusion fluxes of labile P and Fe across the sediment–water interface which obtained from June sampling and October sampling. The results of apparent diffusion flux in two periods indicated the sediments changed from “sink” to “source” for labile P, especially at Sites 4–8, 10, 13–14, and 18. However, the role of the labile Fe has no significantly variation in the values of the diffusion flux. This phenomenon also contributed to the poor relationship between labile P and Fe in the sediment which obtained from the October sampling. Accordingly, we conclude that algal decomposition might be essential for internal loading of P in this aquatic ecosystem, and that also be the reason for vicious circle of algal occurrence in the following year in the center of Lake Hongze.

This study was focused on the phosphorus mobility among sediments, water and cyanobacteria in eutrophic Lake Dianchi. Four conditions lake water, water and algae, water and sediments, and three objects together were conducted to investigate the effects of cyanobacteria growth on the migration and transformation of phosphorus. Results showed a persistent correlation between the development of cyanobacterial blooms and the increase of soluble reactive phosphorus (SRP) in the lake water under the condition of three objects together. Time-course assays measuring different forms of phosphorus in sediments indicated that inorganic phosphorus (IP) and NaOH-P were relatively more easier to migrate out of sediment to the water and cyanobacteria. Further studies on phosphorus mobility showed that up to 70.2% of the released phosphorus could be absorbed by cyanobacteria, indicating that sediment is a major source of phosphorus when external loading is reduced. Time-course assays also showed that the development of cyanobacterial blooms promoted an increase in pH and a decrease in the redox potential of the lake water. The structure of the microbial communities in sediments was also significantly changed, revealed a great impaction of cyanobacterial blooms on the microbial communities in sediments, which may contribute to phosphorus release. Our study simulated the cyanobacterial blooms of Lake Dianchi and revealed that the cyanobacterial blooms is a driving force for phosphorus mobility among sediments, water and cyanobacteria. The outbreak of algal blooms caused deterioration in water quality. The P in the sediments represented a significant supply for the growth of cyanobacteria.

Tokyo Bay, Ise Bay, and the Seto Inland Sea are the total pollutant load control target areas in Japan. A significant correlation between the incidence of red tides and water quality has been observed in the Seto Inland Sea (Honjo, 1991). However, while red tides also occur in Ise Bay and Tokyo Bay, similar correlations have not been observed. Hence, it is necessary to understand what factors cause red tides to effectively manage these semi-closed systems. This study aims to investigate the relationship between the dynamics of the Red Tide Index and nitrogen regulation as well as phosphorus regulation, even in Ise Bay where, unlike Tokyo Bay, there are few observation items, by selecting a suitable objective variable. The introduction of a new technique that uses the Red Tide Index has revealed a possibility that the total pollution load control has influenced the dynamics of red tide blooms in Ise Bay.

The performances of aluminum chloride modified clay (AC-MC), aluminum sulfate modified clay (AS-MC) and polyaluminum chloride modified clay (PAC-MC) in the removal of Aureococcus anophagefferens were compared, and the potential mechanisms were analyzed according to the dispersion medium, suspension pH and clay surface charges. The results showed that AC-MC and AS-MC had better efficiencies in removing A.anophagefferens than PAC-MC. The removal mechanisms of the three modified clays varied. At optimal coagulation conditions, the hydrolysates of AC and AS were mainly monomers, and they transformed into Al(OH)3(am) upon their addition to algae culture, with the primary mechanism being sweep flocculation. The PAC mainly hydrolyzed to the polyaluminum compounds, which remained stable when added to the algae culture, and the flocculation mainly occurred through polyaluminum compounds. The suspension pH significantly influenced the aluminum hydrolysate and affected the flocculation between the modified clay and algae cells.

The dynamics of nitrogen (N) and phosphorus (P) was studied in mariculture areas around Bolinao and Anda, Philippines to examine its possible link to recurring algal blooms, hypoxia and fish kills. They occur despite regulation on number of fish farm structures in Bolinao to improve water quality after 2002, following a massive fish kill in the area. Based on spatiotemporal surveys, coastal waters remained eutrophic a decade after imposing regulation, primarily due to decomposition of uneaten and undigested feeds, and fish excretions. Relative to Redfield ratio (16), these materials are enriched in P, resulting in low N/P ratios (~6.6) of regenerated nutrients. Dissolved inorganic P (DIP) in the water reached 4μM during the dry season, likely exacerbated by increase in fish farm structures in Anda. DIP enrichment created an N-limited condition that is highly susceptible to sporadic algal blooms whenever N is supplied from freshwater during the wet season.