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.

Surface sediment in eutrophic lakes is both a destination and a habitat for overwintering cyanobacteria. The resuspension and recovery of viable, overwintering cyanobacteria from the surface sediment during warm spring weather is usually the primary stage of cyanobacterial blooms (CBs) in shallow eutrophic lakes. Therefore, the elimination of overwintering cyanobacteria in sediment is vital to control CBs. In the present study, sediment plow-tillage (PT) was introduced as an innovative technique for eliminating overwintering cyanobacteria in sediments from Lake Chaohu. Four depths of PT (2, 5, 10, and 15 cm) were tested during the 42-day experiment. The results showed that rapid cell death during the first 0–7 d after PT was accompanied by high oxygen uptake rates. The viable cells in deeper sediment died more quickly and at a higher rate after PT. A PT depth of >10 cm effectively eliminated viable cyanobacteria (with a removal rate of 82.8%) from the sediment and prevented their resuspension. The activity of the viable cyanobacteria also decreased quickly as cyanobacteria were eliminated. It appears that the dark, anoxic environment of the deeper sediment after PT was responsible for the elimination of viable cells. Although high release rates of nitrogen and phosphorus were found to accompany the dying and decomposition of cyanobacteria during days 0–7 of the experiment, greater depth of PT was found to decrease nutrient concentrations in the overlying water. In conclusion, we recommend sediment PT as a new technique for eliminating overwintering algae in sediments. However, the release of nutrients from the sediment and the in situ control of CBs in lakes after PT should be further studied.

Sorption mechanisms of an antibiotic sulfamethazine (SMT) to humin (HM) isolated from a peat soil and its subfractions after sequential treatments were examined. The treatments of HM included removal of ash, O-alkyl carbon, lipid, and lignin components. The HF/HCl de-ashing treatment removed a large amount of minerals (mainly silicates), releasing a fraction of hydrophobic carbon sorption domains that previously were blocked, increasing the sorption of SMT by 33.3%. The de-O-alkyl carbon treatment through acid hydrolysis greatly reduced polarity of HM samples, thus weakening the interaction between sorbents with water at the interfaces via H-bonding, leaving more effective sorption sites. Sorption of SMT via mechanisms such as van der Waals forces and π-π interactions was enhanced by factors of 2.04–2.50. After removing the lipid/lignin component with the improved Soxhlet extraction/acid hydrolysis, the organic carbon content-normalized sorption enhancement index Eoc was calculated. The results demonstrated that the Eoc-lipid for SMT (16.9%) was higher than Eoc-lignin (10.1%), implying that removal of unit organic carbon mass of lipid led to a higher increase in sorption strength than that of lignin. As each component was progressively removed from HM, the sorption strength and isotherm nonlinearity of the residual HM samples for SMT were gradually enhanced. The Koc values of SMT by HM samples were positively correlated with their aromatic carbon contents, implying that π-π electron donor-acceptor interactions between the benzene ring of sorbate and the aromatic domains in HM played a significant role in their interactions.

In the situation of increasing agricultural utilization of residues from biogas production (RBP) it is important to determine the concentration of contaminants, which could occur in these materials. The group of contaminants that requires special attention are polycyclic aromatic hydrocarbons (PAH). The objective of the study was to determine the total and freely dissolved (Cfree) of PAHs in RBP from 6 different biogas plants operating under various temperature conditions and without or with the separation into the solid and liquid fractions. The freely dissolved PAHs were determined using polyoxymethylene (POM method). The total content of the Σ16 PAHs in RBP varied from 449 to 6147 μg/kgdw, while that of Cfree PAHs was at the level from 57 to 653 ng/L. No significant differences were noted in the content of the Σ16 PAHs (total) between the solid and the liquid fractions. This indicates that in the course of the separation, the PAHs are distributed proportionally between the fractions. However in the case of Cfree, PAHs content in the solid fraction was over twice as high as in the liquid fraction. This was probably due to the greater affinity of the particles present in the liquid fraction to the analysed PAHs than to the particles of the solid fraction. Higher affinity to liquid fraction was also confirmed by the distribution coefficients KTOC determined on the basis of Cfree.

Concern has increased regarding the adverse effects of polycyclic aromatic hydrocarbons (PAHs) on reproduction. However, limited information is available on the effects of PAHs in crustacean. In order to determine whether benzo[a]pyrene (B[a]P) could cause reproductive toxicity on the swimming crab Portunus trituberculatus, sexually mature female crabs were exposed to environmentally relevant concentrations of B[a]P (0, 0.1, 0.5 and 2.5 μg/L) for 10 days. B[a]P treatments resulted in high accumulation in ovary, and induced oxidative stress in a dose-dependent manner on ovary of crab. Furthermore, the haemolymph estradiol (E2) and testosterone (T) levels were significantly decreased. Histological investigation also revealed the reproductive toxicity caused by B[a]P. The results demonstrated that waterborne exposure to B[a]P caused oxidative damage and disrupted sex steroids in female crab P. trituberculatus, ultimately resulting in histological alternation.

The aim of this study was to identify how hydrologic factors (e.g., rainfall, maximum depth, reservoir and catchment area, and water residence time) and water chemistry factors (e.g., conductivity, pH, suspended particulate matter, chlorophyll-a, dissolved organic carbon, and sulfate) interact to affect the spatial variance in monomethylmercury (MMHg) concentration in nine artificial reservoirs. We hypothesized that the MMHg concentration of reservoir water would be higher in eutrophic than in oligotrophic reservoirs because increased dissolved organic matter and sulfate in eutrophic reservoirs can promote in situ production of MMHg. Multiple tools, including Pearson correlation, a self-organizing map, and principal component analysis, were applied in the statistical modeling of Hg species. The results showed that rainfall amount and hydraulic residence time best explained the variance of dissolved Hg and dissolved MMHg in reservoir water. High precipitation events and residence time may mobilize Hg and MMHg in the catchment and reservoir sediment, respectively. On the contrary, algal biomass was a key predictor of the variance of the percentage fraction of unfiltered MMHg over unfiltered Hg (%MMHg). The creation of suboxic conditions and the supply of sulfate subsequent to the algal decomposition seemed to support enhanced %MMHg in the bloom reservoirs. Thus, the nutrient supply should be carefully managed to limit increases in the %MMHg/Hg of temperate reservoirs.

Increases in water temperature, as a result of climate change, may influence biogeochemical cycles, sediment-water fluxes and consequently environmental sustainability. Effects of rising temperature on dynamics of nitrate, nitrite, ammonium, dissolved inorganic nitrogen (DIN), dissolved reactive phosphorus (DRP), dissolved organic carbon (DOC) and gaseous nitrogen (N2 and N2O) were examined in a subtropical river (the Jiulong River, southeast China) by microcosm experiments. Slurry sediments and overlying water were collected from three continuous cascade reservoirs, and laboratory incubations were performed at four temperature gradients (5 °C, 15 °C, 25 °C and 35 °C). Results indicated: (1) warming considerably increased sediment ammonium, DIN and DOC fluxes to overlying water; (2) warming increased retention of nitrate, and to a lesser extent, nitrite, corresponding to increases in N2 and N2O emission; (3) DRP was retained but released from Fe/Al-P enriched sediments at high temperature (35 °C) due to enhanced coupled transformation of carbon and nitrogen with oxygen deficiency. Using relationships between sediment fluxes and temperature, a projected 2.3°C-warming in future would increase ammonium flux from sediment by 7.0%–16.8%, while increasing nitrate flux into sediment by 8.9%–28.6%. Moreover, substrates (e.g., grain size, carbon availability) influenced nutrient delivery and cycling across cascade reservoirs. This study highlights that warming would increase bioreactive nutrient (i.e., ammonium and phosphate) mobilization with limited gaseous N removal from sediments, consequently deteriorating water quality and increasing eutrophication with future climate change.

Nickel bioavailability is reduced in the presence of dissolved organic carbon (DOC), suspended solids (TSS), and other complexing ligands; however, no studies have examined the relative importance of Ni exposure through different compartments (water, sediment, food). Hyalella azteca and Lymnaea stagnalis were exposed to Ni-amended water, sediment, and food, either separately or in combination. Both organisms experienced survival and growth effects in several Ni compartment tests. The DOC amendments attenuated L. stagnalis Ni effects (survival, growth, and ⁶²Ni bioaccumulation), and presence of TSS exposures demonstrated both protective and synergistic effects on H. azteca and L. stagnalis. ⁶²Ni trophic transfer from food to H. azteca and L. stagnalis was negligible; however, bioaccumulating ⁶²Ni was attributed to ⁶²Ni-water (⁶²Ni flux from food), ⁶²Ni-TSS, and ⁶²Ni-food. Overall, H. azteca and L. stagnalis Ni compartment toxicity increased in the following order: Ni-water >> Ni-sediment >> Ni-all (water, sediment, food) >> Ni-food.

In 2010, an estimate 4.1 million barrels of oil were accidentally released into the Gulf of Mexico (GoM) during the Deepwater Horizon (DWH) Oil Spill. One and a half years after this incident, a set of subtidal and intertidal marsh sediment cores were collected from five stations in Barataria Bay, Louisiana, USA, and analyzed to determine the spatial and vertical distributions and source of hydrocarbon residues based on their chemical composition. An archived core, collected before the DWH oil spill from the same area, was also analyzed to assess the pre-spill hydrocarbon distribution in the area. Analyses of aliphatic hydrocarbons, polycyclic aromatic hydrocarbons (PAHs) and stable carbon isotope showed that the distribution of petroleum hydrocarbons in Barataria Bay was patchy and limited in areal extent. Significant TPH and ΣPAH concentrations (77,399 μg/g and 219,065 ng/g, respectively) were detected in the surface sediments of one core (i.e., core A) to a depth of 9 cm. Based on a sedimentation rate of 0.39 cm yr−1, determined using 137Cs, the presence of anthropogenic hydrocarbons in these sediment core deposited ca. 50 to 60 years ago. The historical background hydrocarbon concentrations increased significantly at the sediment surface and can be attributed to recent inputs. Although the oil present in the bay's sediments has undergone moderate weathering, biomarker analyses performed on core A samples likely indicated the presence of hydrocarbons from the DWH oil spill. The effects of oiling events on Barataria Bay and other marsh ecosystems in this region remain uncertain, as oil undergoes weathering changes over time.

Concentration and spatial distribution of six phthalic acid esters (PAEs) and eight phenols in sediments of urban rivers, namely the Xi River (XR) and Pu River (PR) in Shenyang city, Northeast China were investigated and the ecological risk of these target pollutants was assessed based on the risk quotient (RQ) approach. Target PAEs and phenols were detected in most of sediment samples collected from the XR and PR. The concentrations of total PAEs in sediments varied from 22.4 to 369 μg/g dw in the XR and 3.71–46.9 μg/g dw in the PR. The levels of phenols ranged from 2.72 to 106 μg/g dw in the XR and 0.811–25.0 μg/g dw in the PR, respectively. The dominant pollutants in both XR and PR were DEHP, phenol and 4-methylphnol. The sampling locations XR1-3 in the XR suffered severe contamination from PAEs and phenols. The sites PR1 and PR6 were heavily polluted by phenols and PAEs, respectively. Almost all target PAEs and phenolic compounds in sediment of the XR exhibited medium or high ecological risk to organisms and the ecological risk in the PR mainly originated from PEAs, phenol and 4-methylphenol. These results would provide guidance for individual pollutant control and indicate that it is imperative to take some effective measures to reduce the pollution of those contaminants.