Distribution and bioaccumulation of microcystins in water columns: a systematic investigation into the environmental fate and the risks associated with microcystins in Meiliang Bay, Lake Taihu

For the purpose of understanding the environmental fate of microcystins (MCs) and the potential health risks caused by toxic cyanobacterial blooms in Lake Taihu, a systematic investigation was carried out from February 2005 to January 2006. The distribution of MCs in the water column, and toxin bioaccumulations in aquatic organisms were surveyed. The results suggested that Lake Taihu is heavily polluted during summer months by toxic cyanobacterial blooms (with a maximum biovolume of 6.7x10(8)cells/L) and MCs. The maximum concentration of cell-bound toxins was 1.81mg/g (DW) and the dissolved MCs reached a maximum level of 6.69mug/L. Dissolved MCs were always found in the entire water column at all sampling sites throughout the year. Our results emphasized the need for tracking MCs not only in the entire water column but also at the interface between water and sediment. Seasonal changes of MC concentrations in four species of hydrophytes (Eichhornic crassipes, Potamogeton maackianus, Alternanthera philoxeroides and Myriophyllum spicatum) ranged from 129 to 1317, 147 to 1534, 169 to 3945 and 124 to 956ng/g (DW), respectively. Toxin accumulations in four aquatic species (Carassius auratus auratu, Macrobrachium nipponensis, Bellamya aeruginosa and Cristaria plicata) were also analyzed. Maximum toxin concentrations in the edible organs and non-edible visceral organs ranged from 378 to 730 and 754 to 3629ng/g (DW), respectively. Based on field studies in Lake Taihu, risk assessments were carried out, taking into account the WHO guidelines and the tolerable daily intake (TDI) for MCs. Our findings suggest that the third largest lake in China poses serious health threats when serving as a source of drinking water and for recreational use. In addition, it is likely to be unsafe to consume aquatic species harvested in Lake Taihu due to the high-concentrations of accumulated MCs.     

DEHP enrichment in the surface microlayer of a small eutrophic lake

Investigation of di-2-ethylhexyl phthalate (DEHP) in the surface microlayer (SM) and subsurface water (SSW) of a small eutrophic lake was carried out from April to June 2002. Results obtained from the field samples showed that tens to several hundred mug/L of DEHP was found in each sample of SM and SSW, indicating that the lake has been polluted by DEHP. Linear regression analysis showed that concentrations of DEHP were more strongly correlated with sampling temperature than with chlorophyll a concentrations. Correlation between DEHP concentrations and total phosphor concentrations was also obtained. Enrichment factors (EFs) of DEHP in the SM comparing with the corresponding SSW were ranging over 0.85-2.12 with an average of 1.35. DEHP EFs were significantly related to both enrichment of chlorophyll a in the SM and sampling temperature.     

Nitrate suppresses internal phosphorus loading in an eutrophic lake

The presence of nitrate in the hypolimnion of the eutrophic, dimictic Upper Mystic Lake has been previously shown to suppress the release of arsenic from lake sediments during seasonal anoxia, in large part by oxidizing iron (II) and producing iron oxyhydroxides that sorb inorganic arsenic. Because of the importance of internal phosphorus loading in the phosphorus budget of many eutrophic lakes, the chemical similarities between phosphate and arsenate, and the need to account for internal phosphorus loading as part of many lake restoration strategies, we carried out measurements to determine if the presence of nitrate also suppressed the release of phosphorus from the sediments of this lake during anoxia. Observations showed that this was the case. Arsenic, phosphorus, and iron (II) concentrations were strongly correlated in the water column, as expected, and the depths below which phosphorus and iron concentrations increased relative to epilimnetic values was predicted by the depth at which nitrate concentration approached zero. The results suggest that knowledge of a lake’s nitrogen budget may be a useful tool in the design of lake remediation efforts, even though phosphorus is typically the limiting nutrient.     

Investigation of Lake Sapanca water pollution,Adapazari, Turkey

Lake Sapanca has been the only source of drinking and recreational water for the city of Adapazari, Turkey. This paper reports a study of the variation of nutrient loading and trophic state of the lake, and also water quality parameters of Lake Sapanca compared to those of the neighbouring Lake Iznik. Through one year, samples were taken every three months from 15 different points on the streams feeding and draining off the lake. Nitrate, NO₂‐N, NH₃‐N, TKN, PO₄‐P concentrations on the 12 streams fe and three draining off points were determined. Then, loading, discharge, and accumulation amounts of nitrogen and phosphorus causing eutrophication were calculated and the trophic state of the lake was determined. A simple model was used to analyse the response of Lake Sapanca when the phosphorus loading rate was changed. Through this model, the variation of different parameters (t, M, K, Q, V and A) with respect to phosphorus concentration (C) was studied to identify effects and results. The consequences of an eutrophic state and measures to protect the lake are also discussed.     

Bioassays and the algal populations of Hastings Lake, Alberta, Canada

During summer 1978 an analysis was made of the biomass development and algal species composition of Hastings Lake, a shallow eutrophic lake near Edmonton, Alberta, Canada. The algal growth potential of Hastings Lake water during the period of investigation was of particular interest. Bioassays were carried out using untreated water, water inoculated with Anabaena flos-aquae (competition experiments) and filtered or autoclaved water.The results of bioassays with untreated Hastings Lake water were well correlated with the biomass development in the lake. Bioassays with unialgal cultures in filtered or autoclaved water were carried out to obtain information concerning the nutrient situation in the lake. Iron and/or phosphorus appear to be important limiting factors during the summer period in Hastings Lake.     

大型调水对受水湖体富营养化关键因子的影响

开展了引江济太和引江济巢工程对太湖和巢湖饮用水源地富营养化关键指标TN和TP的影响研究。结果表明,太湖贡湖湾超过Ⅲ类地表水标准的指标为TN、BOD5和TP,引水期长江及入湖的TN和TP浓度基本高于贡湖湾;巢湖东半湖超过Ⅲ类地表水标准的指标为TP,长江水的TP和TN年均浓度均高于巢湖东半湖;在长江现状调水水质下,引长江水入太湖和巢湖不能有效降低两湖水源地TN和TP浓度。可见,外调水源虽增加了水量,却不能从根本上解决富营养化问题,必须坚持水量与水质并重,持之以恒地进行入湖及内源污染治理,从根本上实现湖体及水源地生态恢复。     

Long-term (1956-1999) dynamics of phosphorus in a shallow, subtropical Chinese lake with the possible effects of cyanobacterial blooms.

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.     

Effects of biological activity, light, temperature and oxygen on phosphorus release processes at the sediment and water interface of Taihu Lake, China

Effects of biological activity, light, temperature and oxygen on the phosphorus (P) release processes at the sediment and water interface of a shallow lake, Taihu Lake, China, were investigated. The results show that organisms at the sediment and water interface can stimulate P release from sediments, and their metabolism can alter the surrounding micro-environmental conditions. The extent of P release and its effects on P concentration in the overlying water were affected by factors such as light, temperature and dissolved oxygen. The organism biomass increased as temperature increased, which was beneficial for P release. Dissolved total phosphorus (DTP) and dissolved inorganic phosphorus (DIP) concentrations in the corresponding overlying water were mainly controlled by light. P release occurred in both aerobic and anoxic conditions with the presence of organisms. However in the presence of light , P release in an anoxic environment was much greater than in an aerobic environment, which may stimulate alga bloom and result in an increase in total phosphorus (TP) in the overlying water. This information aids the understanding of P biogeochemical cycling at the interface and its relationship with eutrophication in shallow lakes.     

大型高原湖泊富营养化湖水生态净化工程设计与分析

针对云南省星云湖湖水排放对下游饮用水源地抚仙湖水质的污染日趋严重的问题,采取湖水出流改道措施,改变湖水流向,隔断上游污染,出流改道后的富营养化湖水经生态净化后排放备用水源地。生态净化工程处理规模为20×104 m3/d,主要采用稳定塘/碎石床湿地组合工艺,星云湖原劣Ⅴ类水经生态净化后达到Ⅲ类水质标准。该工程一年多的运行表明,出水水质基本达到设计要求,对保护水源地水质起到巨大作用,也为我国高原湖泊富营养化湖水的治理提供了示范和参考。     

Diurnal variation of dissolved gaseous mercury (DGM) levels in a southern reservoir lake (Tennessee, USA) in relation to solar radiation

Variations of dissolved gaseous mercury (DGM) concentrations in a southern reservoir lake (Cane Creek Lake, Cookeville, TN, USA) in relation to solar radiation were investigated consecutively from June 2003 to May 2004. The daytime DGM levels in the lake exhibited a two-phase diurnal trend; the DGM concentrations rose in the morning, peaked around noontime and then fell in the afternoon through the evening; these trends followed the general pattern of diurnal solar radiation variations. The morning and afternoon phases appeared to be asymmetrical with the former relatively steep and the latter gradual. A variety of daytime DGM level variations other than the typical two-phase diurnal patterns were also observed. For the time spans studied, the daytime mean DGM concentrations of the lake ranged from 12 to 68 pg L(-1) (60-340 fM). The daytime mean DGM levels in the summertime (June, July, August) showed values above 30 pg L(-1) (150 fM) in most cases and a large number of peak DGM concentrations above 50 pg L(-1) (250 fM). The summer DGM levels in the lake appear to be comparable to those observed in the large northern lakes for the summertime. The daytime DGM levels in the lake were found to correlate with solar radiation to various degrees (cases of r values above 0.8: approximately 12% and approximately 18% of the total sampling days for correlation with global solar radiation and UVA radiation, respectively). Correlating trends are recognizable between the daytime mean DGM concentration and the corresponding mean global solar radiation (r = 0.66, p < 0.0005) and between the daytime mean DGM concentration and the corresponding mean UVA radiation (r = 0.62, p < 0.0005).     

Phosphorus cycling through phosphine in paddy fields

Phosphine emission fluxes from paddy fields, phosphine ambient levels in air, and the vertical profile of matrix-bound phosphine in soil have been measured throughout the growing season of rice in Beijing, China. It was found that both the seasonal and diurnal emission fluxes and ambient levels fluctuate significantly. During the drainage period, phosphine released from the soil with the highest diurnal average flux on the first period of drainage (approx. 17.7 ng m(-2) h(-1)), whereas its highest ambient level (approx. 250 ng m(-3)) occurred at 06.00 h. During the flooded period, phosphine emission was low, and the peaks of phosphine emissions occurred at midnight. The average flux of PH3 emission for the whole season was found to be approximately 1.78 ng m(-2) h(-1). The mass fraction of matrix-bound phosphine is approximately 0.18 approximately 1.42 x 10(-7) (m/m) part of organic phosphorus or 3.4 approximately 9.2 x 10(-9) (m/m) part of total phosphorus in paddy soil. The amount of phosphine emitted to the atmosphere was only a small fraction of the phosphine that remained in the soil in the matrix-bound form. Soil serves both as the source and the sink of PH3.     

The identification of nutrient limitations on eutrophication in Dianchi Lake,China

Due to rapid urbanisation and economic development, Dianchi Lake has been eutrophic since the 1980s. Control of nutrient loading is regarded as the primary restoration method. Two independent approaches: analysis of 13 years of Dianchi Lake monitoring data using Support Vector Machines (SVM) and a nutrient‐enrichment experiment, identified phosphorus and nitrogen as simultaneously limiting. Total phosphorus (TP) has a clear, stable correlation with chlorophyll‐a (Chl‐a) concentrations in Dianchi Lake. Compared to total nitrogen (TN), TP shows a stronger correlation when Chl‐a concentration is below 0.051 mg/L and an almost equal correlation when it is above this level. An excessive phosphorus to nitrogen ratio may stimulate compensatory fixation of atmospheric N₂ by cyanobacteria; therefore, only reducing the external nitrogen input may not necessarily result in lower total nitrogen and chlorophyll concentrations. We recommend that reducing the lake TP load to the lowest economically‐feasible level is the most cost‐effective restoration measure.     

THE IMPACT OF URBANISATION ON THE WATER QUALITY OF LAKE CHIVERO, ZIMBABWE

This study quantified concentrations of nitrogen and phosphorus in the Lake Chivero catchment area, Zimbabwe. The results showed that sewage effluent is the major source of nutrients in the lake. The lake is hypertrophic, and it was concluded that the current situation is not sustainable. The Vollenweider model was used to predict the acceptable inflow phosphorus concentrations based upon oligotrophic conditions. The predicted value of 10 t/year total phosphorus was considered to be unattainable under the current situation because it is already lower than that from non-point sources. A 1970s value of 75 t/year total phosphorus is recommended as a starting point because it excludes sewage effluent and, for the long-term, it is recommended that pollution prevention and water re-use should be adopted in combination with the recycling of nutrients in controlled urban agriculture.     

Reduction in microcystin concentrations in large and shallow lakes: water and sediment-interface contributions

Blooms of cyanobacteria, or blue-greens, are known to produce chemicals, such as microcystins, which can be toxic to aquatic and terrestrial organisms. Although previous studies have examined the fate of microcystins in freshwater lakes, primary elimination pathways and factors affecting degradation and loss have not been fully explained. The goal of the present study was to explore sources of algal toxins and investigate the distribution and biodegradation of microcystins in water and sediment through laboratory and field analyses. Water and sediment samples were collected monthly from several locations in Lake Taihu from February 2005 to January 2006. Samples were analyzed for the presence of microcystin. Water and sediment were also used in laboratory studies to determine microcystin degradation rates by spiking environmental samples with known concentrations of the chemical and observing concentration changes over time. Some water samples were found to efficiently degrade microcystins. Microcystin concentrations dropped faster in water collected immediately above lake sediment (overlying water). Degradation in sediments was higher than in water. Based on spatial distribution analyses of microcystin in Lake Taihu, higher concentrations (relative to water concentrations) of the chemical were found in lake sediments. These data suggest that sediments play a critical role in microcystin degradation in aquatic systems. The relatively low levels of microcystins found in the environment are most likely due to bacterial biodegradation. Sediments play a crucial role as a source (to the water column) of bio-degrading bacteria and as a carbon-rich environment for bacteria to proliferate and metabolize microcystin and other biogenic toxins produced by cyanobacteria. These, and other, data provide important information that may be applied to management strategies for improvement of water quality in lakes, reservoirs and other water bodies.     

Distribution of organic contaminants in Lake Taihu

Water contamination in Lake Taihu and Lake Wulihu poses a threat to water supply and recreation. Water samples were collected during 1988–1989 for analysis of organic contaminants in the two lakes. Over 800 organic contaminants were detected by GC and GC-MS, and 84 of them were screened by a scoring system as priority contaminants. Results showed that the average concentration was one order of magnitude higher in Lake Wulihu than in Lake Taihu, although the number of contaminants in Lake Wulihu was only double those in Lake Taihu. Concentrations of phthalates, halohydrocarbons, and alkanes in Lake Taihu were close to those in Lake Wulihu, whereas the concentrations of alkylaromatics, anilines, phenols, alcohols, ketones, and polynuclear aromatics in Lake Taihu were lower than in Lake Wulihu by 2–3 orders of magnitude. The average concentration of contaminants in Lake Taihu reaches the highest during the rainy season while this occurs in Lake Wulihu during the dry season because of differences in water flow patterns in the lakes, conditions of the water environment, and physico-chemical properties of contaminants.     

A preliminary modeling analysis of water quality in Lake Okeechobee, Florida: Calibration results

To gain understanding of nutrient and phytoplankton dynamics in Lake Okeechobee, Florida, we developed and applied a deterministic, mass balance, water quality model at the whole-lake spatial scale. The model was calibrated to a comprehensive set of field data for 1985–1986, and then used to simulate the period 1973–1992. The model represented the mean behavior of in-lake total phosphorus, dissolved available phosphorus, total nitrogen and chlorophyll a concentrations reasonably well during the calibration period. The model did not represent dissolved available nitrogen concentrations very well, nor did it capture much of the observed temporal variability during the calibration period. The model results identified important information needs to improve our understanding of the nitrogen cycle including, sediment-water nitrogen fluxes, denitrification and nitrogen fixation. Results from the 1973–1992 simulation indicated that model assumptions and/or calibration parameters were not uniformly applicable over this period. Total phosphorus concentration results from this model were compared with results from two site-specific, empirical loading models for the lake. None of these models represented annual average concentrations uniformly well over the entire 20-year period, and none captured much of the observed inter-annual variability. External total phosphorus loadings and lake hydrology are not sufficient to fully describe total phosphorus dynamics in Lake Okeechobee. Other important factors are diffusive sediment-water fluxes, wind-induced sediment resuspension, and the spatial heterogeneity in the lake.     

Seeking a compromise between pharmaceutical pollution and phosphorus load: Management strategies for Lake Tegel, Berlin

Lake Tegel (Berlin, Germany) is controlled by two main inflows: inflow #1 (River Havel) is heavily phosphorus-laden, whereas inflow #2 is an artificial confluence that includes discharge from a municipal wastewater treatment plant distinguished by high levels of phosphorus and pharmaceuticals. To reduce the phosphorus load on the lake, a phosphorus elimination plant (PEP) is situated at inflow #2. Moreover, the two inflows are short-circuited by a pipeline that transfers part of the inflow #1 water to the PEP and finally releases it into inflow #2. The pipeline and the PEP have contributed to a continuous reduction in the total phosphorus concentration of Lake Tegel in the past 25 years. We investigate the question of whether the existing lake pipeline can also be used to reduce the amount of pharmaceuticals in Lake Tegel originating from inflow #2 by dilution with water from River Havel, by diverting part of inflow #2 around the lake, or by a combination of both strategies. The circulation pattern of Lake Tegel is complicated by complex bathymetry and numerous islands and is therefore highly sensitive to winds. We tested seven different management scenarios by hydrodynamic modeling for a period of 16 years with the two-dimensional version of the Princeton Ocean Model (POM). None of the scenarios provided a strategy optimal for both pharmaceuticals and phosphorus. Nonetheless, compound regimes, such as alternating the pipe flow direction or adding another pipeline, allowed the most abundant pharmaceutical (carbamazepine) to be reduced while maintaining the current phosphorus level. This study demonstrates the ability of immediate lake regulation measures to maintain water quality. In the case of Lake Tegel, the pipeline can be fully effective with regard to pharmaceuticals only in combination with additional efforts such as advanced pharmaceutical treatment of wastewater and/or phosphorus reduction in the River Havel catchment.     

Phosphorus models for eutrophic lakes

A model is developed for a highly eutrophic lake (White Lake, Michigan) which incorporates both the water and sediment systems and considers two forms of phosphorus—particulate and dissolved. Dynamic interactions of phosphorus between sediments and water are quantified by taking account particulate phosphorus sinking to the sediment-water interface and diffusion of dissolved phosphorus across the interface. Other model mechanisms include vertical eddy diffusion in the water; phosphorus transformation between the particulate form and the dissolved form in both the water and the sediment, diffusion of phosphorus in the interstitial water, and sedimentation in the sediments.

Extensive field data have been used to determine the coefficients and parameters defined in the model formulations. Close agreement between the model calculations and the observed data is obtained, especially for the upper layers of the sediment. Sensitivity analysis for the model further substantiates the model calculations. It is found that two separate forms of phosphorus are necessary to gain detailed insight into the dynamics of phosphorus cycling in White Lake. The model also explains significant releases of phosphorus during anaerobic periods from the sediment to the hypolimnion of White Lake in summer. The general applicability of the model to lakes having different degrees of eutrophication must be determined by an examination and analysis of data from other systems.     

Photo-induced formation of dissolved gaseous mercury in coastal and offshore seawater of the Mediterranean basin

The first measurements on the daily trend of dissolved gaseous mercury (DGM) concentration determined in coastal and offshore waters of the Mediterranean basin are reported. Marked daily behaviour tracking solar radiation has been observed at the coastal sampling station with DGM values ranging from 11.0 to 38.9 pg/l. Contrary to these observations the DGM values in offshore water samples (11.9-20.0 pg/l) were independent of the sampling time, thus identifying the absence of higher levels during the hours of maximum insolation. The availability of Hg2+ substrate necessary for the photo-reaction processes of DGM formation has been evaluated by measuring the reactive mercury concentration. In offshore waters the lower DGM concentrations are attributable to the substrate as a limiting factor. The highest concentration of DOC measured in coastal seawater with respect to the offshore one could moreover enhance the reaction rates of DGM production through the formation of inorganic mercury complexes and weaker organic associations.     

Laboratory investigation of the phosphorus removal (SRP and TP) from eutrophic lake water treated with aluminium

Mechanisms involved in phosphorus (P) removal from eutrophic lake water with aluminium (Al) were assessed by jar tests. For this purpose, eutrophic lake water enriched with soluble reactive phosphorus (SRP), algae or sediments in order to mimic the various conditions found in shallow eutrophic lakes was studied. Total phosphorus (TP) removal was reached after floc settling, the maximal TP removal efficiency (90-95%) was obtained for an Al concentration ranging from 2 to 5 mg L(-1), depending on the organic matter (OM) origin (algae or sediments). Algae appeared to limit macro-floc formation (those able to settle). In contrast, in the presence of sediments, macro-floc formation was favoured at low Al dose (2-3 mg L(-1) Al). High SRP removal was obtained with the lowest Al dose (1 mg L(-1) Al) and remained greater than 60% for an SRP concentration up to 350 microg L(-1). SRP removal was not influenced by the OM origin. The experimental data and literature were used to suggest a hypothetical model for floc formation and P removal with Al under the conditions observed in treated lakes.