Nearly a century of road salt use in the snowbelt region of North America has led to substantial increases in salinity levels in freshwater habitats. Salt pollution in lakes and rivers is well characterized. Lacking are broad insights for seasonal ponds. As critical habitats for many endemic species, these small and often poorly flushed surface waters are especially vulnerable to accumulating high levels of salts and other pollutants. Here, we measured salinity in 165 seasonal ponds, characterizing salt pollution patterns across space, through time, and over depth within ponds. We found that 70% of ponds within 37 m of a road contained salinity levels exceeding Canadian federal guidelines. 54% of ponds within 25 m exceeded less conservative US federal guidelines. Within ponds, the water column was stratified due to the combined density effects of salt and temperature. Bottom waters of polluted ponds were about 57% saltier than near-surface waters, though many were much saltier than this. Compared to lakes and rivers, far more seasonal ponds appear to be compromised by deicing salt, and overall, the concentration of salt appears to be substantially higher. Among aquatic habitats, seasonal ponds are experiencing the most severe impacts of freshwater salinization, with consequent impacts on sensitive aquatic organisms.

Inland waters (lakes, reservoirs, and rivers) serve as important regulators of global climate change and carbon (C) cycling. China's inland water systems significantly regulate regional C budgets. However, our understanding of the long-term spatiotemporal patterns and underlying mechanisms of dissolved carbon (DC) storages and fluxes in inland waters remains limited. This study examined lake and reservoir DC storage and river DC flux, quantifying their changes in China over the past three decades. We found that inland water DC stocks in China increased from 96 Tg C in the 1990s to 142 Tg C in the 2010s while DC river flux did not significantly change (13.2 ± 0.4 Tg C/yr). Findings also showed that a combination of climate change, anthropogenic disturbance, and water chemistry collectively drove inland water DC dynamics. River DC was more directly driven by climate and anthropogenic factors (>50%) while lakes and reservoirs were more directly influenced by water chemistry (>70%). Additionally, climate factors can explain changes in dissolved inorganic carbon (DIC) concentrations via water chemistry factors (i.e. electrical conductivity (EC) and pH), while, collectively, climate and the nutrient status can typically explain changes in dissolved organic carbon (DOC) concentrations. This study emphasizes the important role that inland water plays in the global C balance and underscores the necessity of considering it in future C budgets.

Cobalt distribution and speciation were quantified in space and time in the water column of a small, stratified, eutrophic lake, Linsley Pond, North Branford, CT. While scrupulously employing clean techniques, we used ligand exchange with dimethylglyoxime and cathodic stripping voltammetry to evaluate free and complexed forms of Co. Free aquo Co ion concentrations [Co 2+ ] were found in the range from 0.014 to 0.28 nM from June to October 2018. Despite the orthograde distribution for total dissolved Co (0.42–3.34 nM), free Co 2+ was higher in the epilimnion, decreasing with depth. Natural organic ligand concentrations [ L ] were in the span from 0.7 to 8.1 nM, with conditional stability constants (as log K ) in the range from 9.43 to 11.13. Nearly all of the Co was complexed with highly selective ligands, and patterns suggest three controlling processes: (1) Co release from dissolving Mn (and perhaps Fe) oxides, (2) possible limitation by solubility of CoS(s), and (3) stabilization in solution via complexation by strong ligands. No correlation was observed between dissolved organic carbon and [ L ] in this study, suggesting that the ligands are not a simple subset of total dissolved organic matter, but may be specific compounds, perhaps S based. The hypothesis that the biological activity of plankton in Linsley Pond might be limited by micronutrient Co is only weakly supported. Cobalamin (VB 12 ) measured via enzyme-linked immunosorbent assays ranged from 0.033 to 0.048 nM in this lake and does not follow a simple pattern with either total dissolved Co or Co 2+ , or with biological activity as indicated by chlorophyll levels.

There many materials were used in lake restoration to immobilize phosphorus (P) and reduce the effect of eutrophication. Among them, calcium/aluminum composite (CAC) showed a good capacity of P adsorption. However, a comprehensive of its performance, ecological safety, and the mechanism of P passivation in the aluminum-bound P (Al -P) dominated sediments under varying redox conditions remains incomplete. In the current study, both unwashed CAC (UCAC) and washed CAC (WCAC) showed good P adsorption properties, and the greatest maximum capacity for P adsorption (Qmax) reached 206.8 mg/g at pH 8.5 for UCAC. The SRP and TP in the overlying water of the uncapped sediments showed a decrease-increase-decrease trend in a sequence of transition from aerobic to anaerobic to re-aerobic stages. In contrast, the SRP and TP of the two CACs-capped sediments were maintained low. Phosphorus forms in the uncapped sediment also underwent significant changes during continuous variation of dissolved oxygen (DO) levels. In particular, the decrease in iron-bound P (Fe–P) and Al–P was significantly promoted in the anaerobic phase, and the released P was reabsorbed to form mainly Fe–P in the re-aerobic phase. The CACs-capping promoted the transformation of Fe–P to residual P (Res-P), forming a thick static layer in the surface sediment, thus significantly inhibiting sediment P release. Moreover, the CACs-capping did not induce the Al3+ leaching and significant changes of the microbial community in sediments, and their performances of P immobilization could keep stable to resist the redox variation, which promised to be a good choice for P passivation in eutrophic lake sediments dominated by Al/Fe–P. These findings also confirmed that the risk of P release from Al/Fe–P (mainly Al–P)-dominated sediments was strongly influenced by continuously changing redox conditions, and was probably enhanced by the formation of Fe–P from the resorption of the released P.

Aquatic environment factors often influence and regulate the direction of phosphorus (P) flow at the sediment-water interface (SWI). High pH and low DO, common in eutrophic lakes, would induce large releases of P from sediment, and thus cause the negative effect on the efficiency of some P-passivators. Hence, the development of P passivators that could function over a wide range of pH condition and redox state in the overlaying water with reduced undesirable side effects is critical for the eutrophic lake remediation. In the present study, a calcium (Ca)/aluminum (Al) composite (CA) and a lanthanum (La)/Ca/Al composite (LCA) were prepared for P immobilization in lake sediments, using calcium and lanthanum coprecipitated with aluminum. CA and LCA were shown to have good P sorption performance at pH 4-11, particularly at pH 8-11. Furthermore, CA and LCA have an ability to correct the pH of water that deviates from neutral. The maximum P adsorption (Qmax) of sediment amended by 4 % CA and 4 % LCA increased by 83 % and 103 %, and their equilibrium P concentration (EPC0) decreased by 76 % and 88 %, respectively. Under various pH and DO conditions, the P concentration in overlying water was significantly decreased by CA and LCA amendment, and their addition could effectively counteract the P release from sediments induced by high pH and low DO. The mechanisms of P immobilization in amended sediments under various pH and DO levels are primarily the conversion of reactive P to stable P. The P immobilization performance of CA and LCA could cope with a wide range of pH and redox conditions in eutrophic lakes, and they would help to correct extreme pH values, thus they are expected to be a new generation of commercial P-passivators.

Although the addition of triclosan (TCS) in consumer products has been strictly restricted, its continuous applications in hospitals and other medical facilities and its numerous residues still pose a potential risk to aquatic organisms and aquatic ecosystems. In this study, we investigated the growth, biochemical alterations, and physiological responses of Chlorella vulgaris exposed to different concentrations of TCS. The potential toxicity mechanisms associated with excessive production of reactive oxygen species (ROS) and disruption of photosynthetic system II (PSII) were also analyzed. The results indicated that the growth, cellular ultrastructure, and physiology of C. vulgaris were severely affected by TCS in a dose-effect dependent manner. TCS inhibited the growth of C. vulgaris , leading to mitochondria enlargement, the disordering of the arrangement of thylakoids, cell wall rupture, organelles loss, and the cytoplasm lysis. TCS induced severe oxidative damage characterized by ROS accumulation, elevated malondialdehyde (MDA), and up-regulation of antioxidant enzyme activities. Moreover, in TCS-induced algal cells, the main sites of ROS accumulation were chloroplasts, mitochondria, and cell membranes, with ROS accumulating most in the mitochondria. In addition, TCS caused damage to the reaction center (RC inactivation), donor side (OEC damage), and accepted side (electron transport from Q A to Q B ) of PSII in C. vulgaris , leading to inhibition of photosynthetic activity. These results could provide novel insights into the mechanisms of TCS-induced ROS accumulation and photosynthetic inhibition in C. vulgaris , which would contribute to a deep understanding of TCS toxicity on algae.

Heavy metals are significant components of industrial wastes and have caused severe environmental pollution and human health problem. Here, solid wastes such as electrolytic manganese residue (EMR), fly ash (FA) and metakaolin (MK) were used as raw materials to prepare EMR-FA-MK geopolymers for efficient immobilization of heavy metals like Pb2+ and Cd2+. The EMR-FA-MK geopolymers can effectively immobilize heavy metals owing to the ion exchange and the mechanism was studied. The effects of calcination temperature on the performances of geopolymers were investigated. The compressive strength of geopolymers after alkaline-thermal activation is improved, and reaches the maximum of 18.3 MPa with calcinated temperature of 600 degrees C. The loading of heavy metals also affects the mechanical properties of EMR-FA-MK geopolymers. Geopolymers with 0.5% heavy metals possess the highest compressive strength of 18.4 MPa after 28 d ambient curing. The leaching test indicates that EMR-FA-MK geopolymers have good immobilization effect on Pb2+ and Cd2+. The leaching concentration of Pb2+ and Cd2+ by the geopolymers are 0.444 mg/L and 0.032 mg/L, both far below the limits in Chinese national standards. Materials characterizations prove that the geopolymer reaction has fully occurred and calcium-silicate hydrate is generated, which could enhance the mechanical properties of the geopolymers. (C) 2021 Elsevier Ltd. All rights reserved.

Berrylium-7 elucidates sediment dynamics (i.e., sources, sinks, deposition, and resuspension) in a Connecticut estuary. Average annual atmospheric deposition of 7 Be is 290 mBq cm −2 year −1 . Sediment samples from 43 locations within the estuary show that 7 Be deposition is spatially complex, but were statistically indistinguishable a year apart. Weekly time series of sediments indicate that levels are nearly constant on this shorter time scale once radioactive decay is taken into account. 7 Be levels in sediments are a balance between steady losses through radioactive decay and periodic pulse inputs following rainstorms. The water column was measured intensively during three rain events, showing that 7 Be is removed rapidly from the water column, with a rate constant averaging 1.00 ± 0.12 day −1 . A mass balance shows that 7 Be is supplied about equally by direct precipitation onto the estuary’s surface and inflow from the watershed. Losses from the water column are split between net sedimentation (43%) and tidal flushing (57%). Variations in sedimentary 7 Be levels at very short (meters) and longer (km) distances, and changes at time scales from hours to years, indicate that a large number of samples are required to capture all the variability in these highly dynamic systems. The current study differs from previous research in that a large number of measurements were conducted on a smaller system, and a full mass balance was developed.

Natural algaecides are more likely to be specific and biodegradable, and may offer an environmentally friendly method for control of cyanobacterial blooms. We explored, for the first time, the potential for watermelon peel aqueous extract (WMPAE) to control the growth of the harmful blue-green alga Aphanizomenon flos-aquae. The growth inhibition and several physiological parameters of A. flos-aquae, in response to WMPAE, were analyzed. Results showed that WMPAE significantly inhibited the growth of A. flos-aquae in a concentration-dependent way. The highest inhibition reached 94 % after 3 days' treatment with 6 g L-1 of WMPAE and a significant effect was obtained with lower doses and shorter times as well. The cell viability decreased quickly, cell shape changed, and intracellular structural damage occurred. At the same time, the antioxidant enzymes (superoxide dismutase SOD, catalase CAT and peroxidase POD) and malondialdehyde (MDA) levels all increased significantly, indicating that WMPAE between 2-6 g L-1 induced severe oxidative stress and damage to A. flos-aquae. Moreover, production of the four pigments chlorophyll a (Chl a), carotenoids, phycocyanin (PC), and allophycocyanin (APC) were all stimulated, though photosynthesis of A. flos-aquae was clearly inhibited. The maximum quantum yield of photosystem II (Fv/Fm) and the effective quantum yield of photosystem II ( Fv'/Fm') declined sharply, suggesting the decreased photosystem capacity of A. flos-aquae to convert light energy into chemical energy. In addition, non-photochemical quenching (NPQ) of A. flos-aquae increased after a very short time exposure to WMPAE, and decreased significantly with prolonged exposure time, which indicated the failure of photo protection mechanisms. These results suggest that the loss of cell viability, and increases in oxidative stress, and damage to intracellular structure and photosynthetic systems might be the mechanisms for the inhibitory effects. Our results suggested that WMPAE could be a novel and effective approach for controlling the growth of A. flos-aquae in aquatic environments.

Variations in methane (CH4) and carbon dioxide (CO2) emissions in municipal sewer driven by pollution sources are complex and multifaceted. It is important to investigate the role of dissolved organic matter (DOM) components and microbiota to better understand what and how those variations occurred. For this purpose, this study provides a systematic assessment based on short-term in-sewer conditioned cultivations, in conjunction with a field survey in four typical sewers in Shanghai Megacity. The results are as follows: (1) Sediment plays a main role in driving the sewer carbon emission behavior owing to its strong associations with the utilized substrates and predominant microbes that significantly promoted the gas fluxes (genera Bacteroidete_vadinHA17, Candidatus_competibacter, and Methanospirillum). (2) Aquatic DOM in overlying water is an indispensable factor in promoting total carbon emissions, yet the dominant microbes present there inversely correlated with gas fluxes (genera Methanothermobacter and Bacteroides). (3) The total fluxes of both CH4 and CO2 enhanced by pavement runoff were limited. Its high COD-CH4/CO2 conversion efficiencies can be ascribed to its dominant anthropogenic humic-like components and the emerged aquatic tyrosine-like components. (4) Domestic sewage can significantly enhance the total fluxes because of its high concentration of bioavailable DOM. However, these substrates, which were more suitable for supporting microbial growth, as well as the substrate competition caused by sulfate reduction and the nitrogen cycle (revealed by the dominant functional microbes genera Acinetobacter, Pseudomonas, Dechloromona, and Candidatus_competibacter and their correlations with indicators), seemed to be responsible for the low COD-CH4/CO2 conversion efficiencies of domestic sewage. (5) A field survey indicated the distinct features of carbon emissions of sewer sewage discharged from different catchments. An extreme hydraulic condition in a sewer in the absence of influent showed unexpectedly high levels of CO2, while a small amount of CH4 emissions.

Chemicals leached from concrete are an important way that urban stormwater can influence water quality. In this study, we evaluated the weathering properties of sidewalk samples and tested how carbonation (exposure to elevated levels of gaseous CO2) can be used to simulate natural aging of concrete. The experiments focused on acid neutralizing capacity (ANC), which is known to be released by concrete in large amounts, and Cr(VI), because of its established carcinogenicity and prevalence in concrete. Chemical weathering of crushed sidewalk samples was measured with upflow recirculating columns carrying simulated acid rain. The weathering rate of ANC from four different samples was found to decrease after 1 week of exposure to a 5% carbon dioxide atmosphere and to remain constant thereafter through 8 weeks of carbonation treatment. In contrast, weathering of chromium (VI) increased after exposure to a 5% carbon dioxide atmosphere for 1 week, though it also remained stable from then through 8 weeks of carbonation. Almost all ions approached steady state after 2.5 h in the recirculation columns irrespective of carbonation time. The main contributor of ANC was Ca2+ ion, though this was partly balanced by an unexpectedly high amount of SO42−. A notable exception to the temporal leaching pattern was largely un-ionized Si, which continued to increase in concentration for at least 3 days of recirculation. Si levels were also higher than is generally observed for aluminosilicate weathering in small watersheds, a novel finding.

Microcystis blooms and their associated microcystins pose a significant health risk to humans. Microcystis normally occurs as colonies in eutrophic water bodies, and its physiological tolerance to algaecides is dissimilar to that of unicellular forms. However, the differences of physiological response to algaecides between unicellular and colonial Microcystis have been poorly explored. The current study investigated the effects of hexane extract of Acorus calamus rhizome (HEACR) on the physiological and photosynthetic mechanisms of unicellular and colonial M. aeruginosa in the laboratory. We analyzed the cell density, reactive oxygen species (ROS) level, malonaldehyde (MDA) content, photosynthetic pigments, capsular polysaccharide (CPS), and photosystem (PS II) parameters of the two morphological forms of Microcystis. Our results show that HEACR suppresses the growth of both unicellular and colonial M. aeruginosa, increases the intracellular ROS level and cause lipid peroxidation, as well as exerting a detrimental effect on chlorophyll a (chl a) content and photosynthetic efficiency. Almost 100% inhibition was observed for unicellular and colonial M. aeruginosa after 3 d exposure to 50 and 100 mg L-1 HEACR, respectively. The ROS level increase, MDA accumulation, the chl a decrease and carotenoid increase in unicellular M. aeruginosa were all more obvious than that in colonial cells. The fall in photosynthetic efficiency of unicellular M. aeruginosa were also more significant than that of colonial cells. After 3d exposure, the maximum quantum yield of PS II photochemistry (Fv/Fm), effective quantum yield of PS II photochemistry (Fv'/Fm') and effective quantum yield of photochemical energy conversion in PS II (YII) of unicellular M. aeruginosa was almost totally inhibited by 20 mg L-1 HEACR, while the Fv/Fm, Fv'/Fm' and YII of colonial M. aeruginosa decreased by 43%, 26% and 66% for 100 mg L-1 of HEACR, respectively. Comparing the two morphological forms of Microcystis, colonies show a greater increase in CPS level to more effectively resist the stress of HEACR and to mitigate ROS generation thereby better defending against oxidative damage. Furthermore, colonial M. aeruginosa shows better photoprotection ability than the unicellular form when exposed to HEACR. The colonies also sustain their maximum electron transport rate, increase their tolerance to strong light, and maintain a higher ability to disperse excess energy. These results demonstrated that HEACR can significantly interfere with the growth and physiological processes of both unicellular and colonial M. aeruginosa, but that colonial M. aeruginosa has a greater ability to adjust physiological tolerance to resist the stresses of HEACR.

Dichlorodiphenyltrichloroethane was used on Cape Cod, Massachusetts (USA), for mosquito and gypsy moth mitigation, from 1948 until the insecticide was banned in the 1970s. There are historical accounts of major spray events, and DDT was expected to have remained immobile in the organic-rich sediments of local ponds. We investigated the potential for sediment cores from lakes on Cape Cod to reveal the depositional history of DDT. This compound and its metabolites dichlorodiphenyldichloroethane and dichlorodiphenyldichloroethylene (ΣDDT) were examined in sediment cores from four kettle lakes on Cape Cod that lie between the towns of Brewster and Harwich, where there is a detailed history of aerial spraying. Sediment cores were dated via 210Pb and analyzed for water content, total carbon, total organic carbon, and organochlorine pesticide concentrations. Use of fallout 137Cs to confirm 210Pb dates was unsuccessful, probably because of post-depositional migration of 137Cs. ΣDDT inventories in each lake were determined to be ~ 10 ng cm−2, which represents about 0.1% on an aerial basis of the quantity known to have been sprayed. Compared to the recorded spraying history, the concentration-depth maxima appear decades later than expected. The overall low quantity and unexpected temporal distribution of pesticide residues are probably explained by natural degradation of DDT in the sediment. A novel mathematical correction to DDT concentrations was applied and yielded adjusted inventories close to expected values, and moved the pesticide concentration maxima to the 1950s and 1960s, when they were expected to have occurred.

Pollutant removal was compared among subsurface flow constructed wetland (CW) mesocosms used for dairy farm wastewater treatment. Supplemental aeration, flow direction, and the use of phosphorus-reducing filters (PRFs) were varied among the CWs. The following were compared: (1) vertical flow CWs with and without supplemental aeration, (2) aerated CWs with horizontal and vertical flow directions, (3) single-cell and two-cell treatment systems, and (4) wetland-wetland systems (two CWs in series) and wetland-PRF systems (a CW followed by a PRF). The results from this investigation showed that, first, nearly all treatment strategies, either singly or in pairs, substantially reduced almost all the contaminants we tested. Second, supplemental aeration resulted in higher ammonium-nitrogen (NH4-N) removal efficiencies in aerated vertical flow CWs, compared to unaerated CWs. However, it caused no further improvement in dissolved reactive phosphorus (DRP), total suspended solids (TSS), E. coli, or BOD5 removal. Third, there was no difference between aerated horizontal and aerated vertical flow CWs in removal of any of the tested contaminants. Fourth, adding a second stage of treatment significantly improved DRP, TSS, E. coli, and NH4-N removal, but not BOD5. Finally, treatment systems with PRFs showed superior performance in DRP and E. coli removal.

Introducing of earthworms to constructed wetlands (CWs) has been considered as a new approach to solve the clogging problems in the long-established systems. Despite its potential advantage, the correlational researches are still in the stage of preliminary observation and speculation. This paper presents a comprehensive and in-depth research about the positive effects of earthworms (Eisenia foetida) on clog matter (CM) reduction through different pathways, including in vivo metabolism and uptake, conversion, transport, and promotion of microorganism quantities. The results showed that the metabolism and uptake by Eisenia foetida could effectively reduce the CM content at an average removal rate of 0.155 mg g(-1), d(-1), which was obviously higher than the rate of CM decomposition by microorganisms alone. Through the metabolism of earthworms, the amounts of proteins and polysaccharides in CM were decreased, while the amounts of humin and nucleic acids were increased. Simultaneously, the viscosity of CM was reduced by 0.0082 mPa s g(-1) d(-1), and the quantity of microorganisms was increased by 0.0109 mg g(-1) d(-1), which finally made the treated CM can be easily washed away and decomposed. Furthermore, earthworms could reduce the CM content in the clogging layer by transporting the metabolic products out. A regression model was further performed for describing the interaction between earthworm and CM. The simulated value of porosity fitted well with the measured one, suggesting that the earthworms can increase the substrate porosity at a rate of 0.33 mL g(-1) d(-1). This study quantitively depicted the mechanisms of earthworms on the decrement of CM content in CWs, which is of great benefit for the engineering management of constructed wetlands in the future. We also proposed that the density of introduced earthworms should exceed a certain threshold for effectively increasing the substrate porosity and solving the clogging problems. (C) 2018 Elsevier Ltd. All rights reserved.

Recycled tires are often shredded for use in a variety of consumer-related products. The rubber so used may contain a number of compounds known to be deleterious to human and environmental health. We obtained nine samples of shredded tire material sold over the counter to the general public for home use, as well as six samples used for infill in synthetic turf athletic fields. After thorough cleaning and grinding, samples were extracted with either organic solvent (dichloromethane), strong acid, or simulated acid rain, or allowed to degas passively. Compounds released by these multiple methods were then identified, and in some cases quantified. Solvent extraction yielded 92 separate compounds, of which only about half have been tested for human health effects. Of these, nine are known carcinogens and another 20 are recognized irritants, including respiratory irritants that may complicate asthma. Strong acid extraction released measurable amounts of Pb and Cd and relatively large amounts of Zn. These three metals were specifically targeted for analysis, and others may be present as well, but were unmeasured. Simulated acid rain extracted only Zn in significant quantities. Passive volatilization yielded detectable amounts of 11 compounds. Results demonstrate that recycled tire materials contain and can release a wide variety of substances known to be toxic, and caution would argue against their use where human exposure is likely.

We collected seven cores from five coastal ponds in St Thomas, USVI, dated them via 210Pb, and measured their Hg profiles. Levels ranged from 20 to 100ngg−1 and always increased upward to the surface or a shallow mixed zone. Taking into account differences in sediment accumulation rates and the presence or absence of a mixed zone, all sites revealed similar deposition histories. Mercury levels were at low, possibly pristine, values until the early to mid-20th century. Then they then doubled or quadrupled steadily until about 1990, after which Hg became relatively constant. We conclude that Hg in the sediments of these ponds came from long range deposition directly to the ponds and to their watersheds. Constant levels in recent years may be caused by transfer from watersheds, a pathway that is delayed compared to direct deposition from the atmosphere.

Laboratory studies were conducted and modeled to evaluate whether refractory organic nitrogen in tertiary-treated wastewater effluent could become bioavailable by conversion to mineral forms. Multiday incubations of effluent collected from the Branford and New Haven, Connecticut, waste water treatment plants (WWTP) revealed low but steady conversion of organic nitrogen to nitrate (NO3 −). In Branford, the principal form of organic nitrogen was dissolved, and in New Haven it was particulate. Modeling suggested that in both the cases conversion to NO3 − from organic forms occurred at several per cent per day, and appeared to happen via the intermediary NH4 +. The results suggest that organic nitrogen may be an important source of bioavailable N, contributing to the problem of hypoxia in Long Island Sound and other estuaries.

Vertical distributions of total dissolved phosphorus (TDP), sulfide, chlorophyll, and primary production produced by photosynthetic sulfur bacteria (PSB) were studied in a small stratified, highly productive, and dimictic lake, Linsley Pond, CT, USA. The goal was to understand and model the role of PSB in a lake undergoing trophic transformation as a result of lake management involving reduced phosphorus loading. High levels of sulfide developed in the anoxic hypolimnion, though a decrease was observed compared to earlier years, possibly as a result of lake management under a Total Maximum Daily Load (TMDL) process. A deep chlorophyll maximum was observed, and absorption spectra confirmed that it was the result of photosynthetic sulfur bacteria. The summer chlorophyll maximum occurred at an interface marked by high amounts of sulfide and low, but adequate, levels of light. Primary production by PSB was found at a depth of 7 m in July 2008, and thereafter extended slowly to 9 m until late fall overturn. PSB only contributed a minor portion of total primary production in Linsley Pond that year, but a straightforward biogeochemical phosphorus model reveals that the existence of PSB serves as a significant biological barrier for phosphorus being transported back into the upper mixing zone. A large amount of TDP was trapped in the hypolimnion, and upward transport of TDP from the upper boundary of the hypolimnion to the mixing zone was about 30% of external phosphorus loading from the only tributary during the summer stratification period. By comparison, the amount of TDP assimilated by PSB and settling back to the hypolimnion was comparable to external phosphorus loading to the lake from its tributary. As lake management reduces external P loading and productivity, bottom sulfide is likely to decrease, suppressing PSB activity and having the undesired effect of allowing more TDP to be transported upward to the epilimnion as this biological barrier is suppressed. (C) 2017 Published by Elsevier B.V.

A reliable system simulation to relate socioeconomic development with water environment and to comprehensively represent a watershed's dynamic features is important. In this study, after identifying lake watershed system processes, we developed a system dynamics modeling framework for managing lake water quality at the watershed scale. Two reinforcing loops (Development and Investment Promotion) and three balancing loops (Pollution, Resource Consumption, and Pollution Control) were constituted. Based on this work, we constructed Stock and Flow Diagrams that embedded a pollutant load model and a lake water quality model into a socioeconomic system dynamics model. The Dianchi Lake in Yunnan Province, China, which is the sixth largest and among the most severely polluted freshwater lakes in China, was employed as a case study to demonstrate the applicability of the model. Water quality parameters considered in the model included chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP). The business-as-usual (BAU) scenario and three alternative management scenarios on spatial adjustment of industries and population (S1), wastewater treatment capacity construction (S2), and structural adjustment of agriculture (S3), were simulated to assess the effectiveness of certain policies in improving water quality. Results showed that S2 is most effective scenario, and the COD, TN, and TP concentrations in Caohai in 2030 are 52.5, 10.9, and 0.8 mg/L, while those in Waihai are 9.6, 1.2, and 0.08 mg/L, with sustained development in the watershed. Thus, the model can help support the decision making required in development and environmental protection strategies.