Effects of low or medium-pressure UV irradiation on the release of intracellular microcystin

UV irradiation could be an alternative growth inhibition treatment against toxic Microcystis blooms in lakes. This study examined the effect of UV irradiation on the release of toxic intracellular microcystin. Conventional algicidal treatment (e.g. copper sulfate) was known to cause rapid release of intracellular microcystin and additional problems, but no studies have examined the case of UV treatment. A pure culture of Microcystis aeruginosa PCC 7806 was exposed to monochromatic low-pressure or polychromatic medium-pressure UV lamps. Irradiated pure culture suspension was subsequently incubated for 14 days under white light fluorescent lamps. During incubation, profiles of the number of cells, intracellular and extracellular microcystin concentration were determined. After the UV exposure, the number of cells gradually diminished; the net log cell reduction after 6 days of incubation was 1.6 log or 2.0 log for 600 mJ/cm2 of LP or MP UV irradiation, respectively. There were three findings for UV irradiation effects on the release of intracellular microcystin. First, because UV exposure can inhibit increases in the number of cells for about 6 days, it inhibited the increase of microcystin concentrations in water. Second, intracellular microcystin was gradually released into the surrounding water through a gradual reduction in the number of cells, preventing a rapid increase of microcystin concentration in water. Microcystin concentration in water was not significantly higher in UV-irradiated samples than non-UV-irradiated sample. Third, UV irradiation was able to degrade intracellular microcystin; it was reduced from 24.6 to 7.06 or 7.16 fg/cell by 600 mJ/cm2 of LP or MP UV irradiation, respectively. This contributed to reduce increases in microcystin concentrations in water. UV treatment can inhibit Microcystis growth and reduce intracellular microcystin content without rapid release of intracellular microcystin.     

Seasonal occurrence and toxicity of Microcystis spp. and Oscillatoria tenuis in the Lebna Dam, Tunisia

Physicochemical and biological water quality, including the total microcystin concentrations, was investigated for the first time from January to December 2005 in the Lebna Dam, Tunisia. Microcystin levels and characterization of the different microcystin variants present were measured by protein phosphatase (PP2A) inhibition assays and by LC/MS/MS, respectively. Nutrient values were high, with total inorganic nitrogen and phosphorus concentrations ranging from 0.05 to 8.4 mg L(-1) and from 0.03 to 1.37 mg L(-1), respectively. However, the chlorophyll-a concentrations were very low with a peak (5.32 microg L(-1)) on 20 September 2005 at 9 m depth water samples. Microscopic examination of the phytoplankton samples showed the dominance in the autumn of three morphospecies of the genus Microcystis and the species Oscillatoria tenuis. The total (particulate and dissolved) microcystin concentrations at the surface and at 9 m depth water samples ranged between 0.008 and 1.73, and 0.005 and 5.57 microg microcystin (MC)-LR equivalent L(-1), respectively, with a peak on 20 September. The presence of the microcystin synthetase genes (mcyA, -B, and -C) in the lysates of the three morphospecies of the genus Microcystis and the species O. tenuis indicated that these species were responsible for the microcystin production in this system. The analysis of the field cyanobacterial sample extract containing these species by LC/MS/MS revealed the presence of two microcystin variants: microcystin-LR (MC-LR) and microcystin-YR (MC-YR).     

Seasonal occurrence and toxicity of Microcystis in impoundments of the Huron River, Michigan, USA

Occurrence and toxicity of Microcystis spp. were measured by ELISA in three impoundments of the Huron River in southeast Michigan, USA. Assays were conducted weekly from June through October 2005. Additional samples were collected to assess microcystin concentrations throughout the drinking water treatment process at the Ann Arbor Water Treatment Facility. Water column stability, nutrient concentrations, and N:P ratios were examined as potential predictors of phycocyanin and microcystin. Microcystin was found in two of the impoundments at seasonally varying concentrations. Microcystis presence was associated with N:P ratios between 40 and 80 by moles, and toxin levels typically peaked one to two weeks after a peak in phycocyanin. The toxin was also detected at low levels at all stages of the drinking water treatment process. Freezing and thawing water samples prior to analysis yielded maximum microcystin assay concentrations. Experiments indicated that the competitive ELISA method is susceptible to false negative reporting. This is the first report of algal toxins in this catchment, and results demonstrate that sensitive and rapid analytical methods offer the chance to link the dynamics of toxin production with environmental conditions.     

Microcystin-LR toxicity on dominant copepods Eurytemora affinis and Pseudodiaptomus forbesi of the upper San Francisco Estuary

This study investigates the toxicity and post-exposure effects of dissolved microcystin (MC-LR) on the dominant copepods of the upper San Francisco Estuary (SFE), where blooms of the toxic cyanobacteria Microcystis aeruginosa coincide with record low levels in the abundance of pelagic organisms including phytoplankton, zooplankton, and fish. The potential negative impact of Microcystis on the copepods Eurytemora affinis and Pseudodiaptomus forbesi has raised concern for further depletion of high quality fish food. Response of copepods to MC-LR (MC) was determined using a 48-h standard static renewal method for acute toxicity testing. Following exposure, a life table test was performed to quantify any post-exposure impacts on survival and reproduction. The 48-h LC-50 and LC-10 values for MC were 1.55 and 0.14 mg/L for E. affinis; and 0.52 and 0.21 mg/L for P. forbesi. Copepod populations recovered once dissolved MC was removed and cultures returned to optimal conditions, suggesting no post-exposure effects of MC on copepod populations. Dissolved microcystin above 0.14 mg/L proved likely to have chronic effects on the survival of copepods in the SFE. Since such high concentrations are unlikely, toxicity from dissolved microcystin is not a direct threat to zooplankton of the SFE, and other mechanisms such as dietary exposure to Microcystis constitute a more severe risk.     

Citizen monitoring: Testing hypotheses about the interactive influences of eutrophication and mussel invasion on a cyanobacterial toxin in lakes

An existing volunteer monitoring network in the state of Michigan was exploited to conduct a statewide survey of the cyanobacterial toxin, microcystin, and to test hypotheses about the interactive influences of eutrophication and dreissenid mussel invasion. A total of 77 lakes were sampled by citizen volunteers for microcystin, total phosphorus (TP) and chlorophyll a. Microcystin was measured in depth-integrated samples collected from the euphotic zone as well as in surface-water samples collected along the shoreline. Average microcystin in samples collected by volunteers was not different from samples collected side-by-side by professionals. Euphotic-zone microcystin was positively related to TP in lakes without dreissenids (uninvaded) but not in lakes with dreissenids (invaded). Regression-tree analysis indicated that euphotic-zone microcystin was eight times higher in the presence of dreissenids for lakes with TP between 5 and 10 μg L⁻¹. In contrast, euphotic-zone microcystin was almost identical in invaded and uninvaded lakes with TP between 10 and 26 μg L⁻¹. Across all lakes, microcystin concentrations at the surface were on average more than double, and in some cases an order-of-magnitude greater than, concentrations in the euphotic-zone. Given these results, it seems prudent to include dreissenid invasion status in forecasting models for microcystin, and to include shoreline sampling in monitoring programs aimed at assessing recreational exposure to cyanobacterial toxins.     

高效液相色谱法测定水中微囊藻毒素

通过对前处理过程中关键环节进行不同水平比较,建立了简便、实用的固相萃取/高效液相色谱/紫外联机(SPE/HPLC/UV)快速测定水样中微囊藻毒素的方法,在微囊藻毒素浓度为0～1.8 mg/L的范围内,HPLC峰面积与藻毒素进样量呈线性关系,方法检测限可达0.01～0.05μg/L.对藻毒素提取方法进行优化后,运用此方法测定了铜绿微囊藻中的藻毒素含量,取得了理想的分析效果,三种藻毒素异构体的回收率均不小于94%.     

Speciation of selected trace elements in three Ethiopian Rift Valley Lakes (Koka, Ziway, and Awassa) and their major inflows

The Ethiopian Rift Valley Lakes (ERVLs) are water resources which have considerable environmental, economic and cultural importance. However, there is an increasing concern that increasing human activities around these lakes and their main inflows can result in increased contamination of these water bodies. Information on total concentrations of some trace elements is available for these lakes and their inflows; however, data on the trace element speciation is lacking. Therefore, the objective of this study was to determine the low molecular mass (LMM) trace element species and also, evaluate the influence of flooding episodes on the LMM trace element fractions. At-site size and charge fractionation system was used for sampling of water from the lakes Koka, Ziway and Awassa and their main inflows during the dry and wet seasons. The results showed that chromium (Cr), manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), and lead (Pb) in Lake Koka and its inflows as well as in Lake Ziway were predominantly present as HMM (high molecular mass, i.e., > 10 kDa) forms, while arsenic (As), selenium (Se), cadmium (Cd) were more mobile during the dry season. In Lake Awassa, all except Cr and Mn were predominantly found as LMM species (low molecular mass, i.e. < 10 kDa) which can be attributed to the high concentrations of LMM DOC (dissolved organic carbon). During the wet season, results from the Lake Koka and its inflows showed that all trace elements were predominantly associated with HMM forms such as colloids and particles, demonstrating that the mobility of elements was reduced during the wet season. The colloidal fraction of elements such as Cr, Ni, and Cd was also correlated with dissolved Fe. As the concentration of LMM trace element species are very low, the mobility, biological uptake and the potential environmental impact should be low.     

Delayed influence of dam storage and discharge on the determination of seasonal proliferations of Microcystis aeruginosa and Stephanodiscus hantzschii in a regulated river system of the lower Nakdong River (South Korea)

This study presents the relationship between the dam hydrology and phytoplankton proliferations in a regulated river system in East Asia. A long-term ecological study reveals that multi-purpose dam regulation on river flow in the Nakdong River (South Korea) affects proliferating patterns of phytoplankton, especially during summer (June-August) and winter (December-next February) as Microcystis aeruginosa and Stephanodiscus hantzschii, respectively, dominate each season by over 80%. Eutrophication was observed in the lower Nakdong River (South Korea) (mean+/-standard deviation: nitrate-N, 2.8+/-0.9 mg L(-1); phosphate-P, 40.3+/-31.3 microg L(-1); chlorophyll a, 45.2+/-84.9 microg L(-1); n=449), and the limnological characteristics responded to climatic variations such as monsoon and summer typhoons. The river basin experiences concentrated rainfall during the rainy season (June-September, over ca. 60% of total annual rainfall). Correlation and cross-correlation for time-delayed relationship revealed the hydrological environments (i.e., quantity of dam storage and discharge) had significantly negative relationship with the population dynamics of the two bloom-forming species for up to the next 2 years. S. hantzschii had clearer relationship with dam storage and discharge, which might be due to the seasonality exhibited by the species. The results support the necessity of "smart flow control" which may enable destruction of bloom formation by the two species with an adequate pulse of discharge generated by upstream dams in the far-east Asian river systems. This would increase the efficiency of water resource management system.     

Analysis of dissolved microcystins in surface water samples from Kovada Lake, Turkey

Dissolved (extracellular) microcystin (MC) concentrations were determined at 3 sampling stations on Lake Kovada, Turkey. The dominant species of cyanobacteria found in August and September of 2006 were Microcystis aeruginosa, Synechococcus sp., Phormidium limosum, Phormidium formosa and Planktothrix limnetica. MC concentrations in water were measured by ELISA and MC variants were examined by HPLC-PDA. Quantitative analysis by HPLC indicated that five MC variants (MC-LR, -RR, -LA, -LW, -LF) were identified in water samples from Kovada Lake. The maximum concentration of dissolved MC-LW was 98.9 µg l^− 1 in October. MC-LR was only detected in May at a concentration of 0.5 µg l^− 1. The cross reactivity of the antibody (MC10E7) to variants such as MC-LA MC-LW & MC-LF was low. Hence the results determined by ELISA were lower than those determined by HPLC in September and October samples due to differences in the specificity of the antibody to MC variants. Total extraceullar MCs was quantified by ELISA and ranged from 0.73 to 48.5 µg MC-LR equivalents l^− 1, which in some cases exceeded the WHO provisional Guideline Value for MC-LR in drinking water. This study confirms that the lakes of Turkey should be monitored for toxic cyanobacteria and for MCs to avoid or reduce the potential exposure of people to these health hazards.     

Benthic cyanobacteria (Oscillatoriaceae) that produce microcystin-LR, isolated from four reservoirs in southern California

Cyanobacteria that produce the toxin microcystin have been isolated from many parts of the world. Most of these organisms are planktonic; however, we report on several microcystin-producing benthic filamentous cyanobacterial isolates from four drinking-water reservoirs in southern California (USA): Lake Mathews, Lake Skinner, Diamond Valley Lake (DVL), and Lake Perris. Some samples of benthic material from these reservoirs tested positive for microcystin by an ELISA tube assay, and all the positive samples had in common a green filamentous cyanobacterium 10-15microm in diameter. Seventeen unialgal strains of the organism were isolated and tested positive by ELISA, and 11 cultures of these strains were found to contain high concentrations of microcystin-LR (90-432microgL(-1)). The cultures were analyzed by protein phosphatase inhibition assay (PPIA) and HPLC with photodiode array detector (PDA) or liquid chromatography/mass spectrometry (LC/MS). Microcystin per unit carbon was determined for six cultures and ranged from 1.15 to 4.15microgmg(-1) C. Phylogenetic analysis of four cultures from Lake Skinner and DVL using cyanobacterial-specific PCR and sequencing of the partial 16S rRNA gene suggested the highest similarity to an unidentified cyanobacterium in the oscillatoriales, and to a Phormidium sp. Morphologically, some of the isolates were similar to Oscillatoria, and others resembled Lyngbya. The significance of these organisms lies in the relative scarcity of known toxin producers among freshwater benthic cyanobacteria, and also as a source of cell-bound microcystin in these reservoirs.     

Microcystin analysis in single filaments of Planktothrix spp. in laboratory cultures and environmental blooms

Single filaments of Planktothrix spp. were isolated from laboratory cultures of P. agardhii (NIES 595) and P. rubescens (SL 03) and from four freshwater lakes in England and Turkey. Filament lengths were measured and microcystins were extracted by freeze-thawing and boiling. Microcystin analysis of the isolated single filaments was performed by ELISA using antibodies raised against microcystin-LR with a minimum detection limit (MDL) of 11 pg filament(-1). In some cases a high percentage of the filaments from the environmental samples and laboratory cultures were below the MDL of the assay. Based on the filaments with detectable microcystin contents, P. agardhii from Bassenthwaite Lake (England) had the lowest mean microcystin concentration (0.7 fg microm(-3)), and the highest microcystin concentration (2.9 fg microm(-3)) was measured in P. rubescens from Iznik Lake (Turkey). We investigated the relationship for filaments with microcystin contents above MDL and their biovolume. Relationships varied widely although P. agardhii from Bassenthwaite showed a better (positive) relationship between filament biovolume and microcystin content than P. rubescens from environmental samples. Under culture conditions, P. rubescens showed a good relationship between filament biovolume and toxin content.     

The influence of summer seasonal extremes on dissolved organic carbon export from a boreal peatland catchment: evidence from one dry and one wet growing season

A small peatland catchment in eastern Finland was monitored for runoff and export of dissolved organic carbon. To exemplify the response of a peatland under years of different meteorological conditions, data from one very dry and one wet growing season are presented. Runoff was 194 and 387 mm, and DOC export was 4.2 and 11.3 gC m^− 2 in the dry and wet year respectively. Analysis of the hydrographs showed that in both years most runoff and DOC export was generated during peak flow events, with low baseflow in the intermediate periods. Runoff response to rain events was strongest under a high water table in the spring and autumn, with a summer runoff minimum. The effect of drought on runoff occurred only after mid June when the effects of snowmelt had dissipated. Snowmelt therefore dominated DOC export in the dry year (61%) but contributed much less (29%) in the wet year. The relationship between runoff and the water table was highly similar in both years. Any variation that was observed herein was potentially related to a superficial subsidence of the peat surface under drier summer conditions and to raised spring water levels, causing restricted drainage due to flooding. The observed variation of DOC concentrations in both years generally had a limited impact on DOC export. During peak runoff events, concentrations dropped proportionally to the magnitude of the events. This decrease in available DOC is argued to be caused by a dominance of leaching over supply and production and by the specific hydraulic characteristics of the peatland surface. DOC concentrations were some 25% higher under drought conditions. These elevated concentrations were dispelled by spring snowmelt of the next year, demonstrating that a winter snowpack in boreal regions may be instrumental in limiting the longer term hydrological and biochemical effects of a drought.     

Biodegradation of the cyanobacterial toxin microcystin LR in natural water and biologically active slow sand filters

A bacterium (MJ-PV) previously demonstrated to degrade the cyanobacterial toxin microcystin LR, was investigated for bioremediation applications in natural water microcosms and biologically active slow sand filters. Enhanced degradation of microcystin LR was observed with inoculated (1 x 10(6) cell/mL) treatments of river water dosed with microcystin LR (>80% degradation within 2 days) compared to uninoculated controls. Inoculation of MJ-PV at lower concentrations (1 x 10(2)-1 x 10(5) cells/mL) also demonstrated enhanced microcystin LR degradation over control treatments. Polymerase chain reactions (PCR) specifically targeting amplification of 16S rDNA of MJ-PV and the gene responsible for initial degradation of microcystin LR (mlrA) were successfully applied to monitor the presence of the bacterium in experimental trials. No amplified products indicative of an endemic MJ-PV population were observed in uninoculated treatments indicating other bacterial strains were active in degradation of microcystin LR. Pilot scale biologically active slow sand filters demonstrated degradation of microcystin LR irrespective of MJ-PV bacterial inoculation. PCR analysis detected the MJ-PV population at all locations within the sand filters where microcystin degradation was measured. Despite not observing enhanced degradation of microcystin LR in inoculated columns compared to uninoculated column, these studies demonstrate the effectiveness of a low-technology water treatment system like biologically active slow sand filters for removal of microcystins from reticulated water supplies.     

次氯酸钠对微囊藻毒素释放及降解特性的研究

选用铜绿微囊藻为处理对象,研究了NaClO在藻类处理过程中藻毒素释放和降解的特性。结果表明：NaClO作用于藻细胞后会破坏其完整性,导致藻毒素释放,同时次氯酸钠投加量及藻浓度对藻毒素释放及降解量有较大影响。应避免在藻类大量暴发时（藻浓度〉6．96×10^6个／mL）预氧化中使用次氯酸钠,而在一般藻细胞浓度较低的水厂采用该种预氧化方法除藻,不会造成藻毒素的释放扩散。     

Dynamics of microcystin production and quantification of potentially toxigenic Microcystis sp. using real-time PCR

Cyanobacterial blooms in eutrophied water body are generally composed of various genotypes with or without microcystin-producing genes (mcy gene cluster). Thus there is a need for quantification of potent toxin producing strains. The present study aimed at identifying microcystin variants and its producer strains in Durgakund pond, Varanasi, India, based on quantification of cpcBA-IGS and mcyA (condensation domain) genes using real-time PCR and LC-MS. Increase in microcystin concentrations was correlated with increase in mcyA copy number and the level of pigments (chlorophyll a, phycocyanin and carotenoids). Also, selected environmental factors (water temperature, light irradiance, rainfall, pH, N and P) and the concentration of microcystin variants (MC-LR, -RR and -YR) were also assessed in samples during May 2010 to April 2011 to establish the possible correlation among these parameters. Nutrients favored cyanobacterial bloom but it could not be correlated with the levels of microcystin variants and seemed to be geographically specific. Microcystis sp. dominant in the pond comprised potentially toxigenic cells. The ratio of potentially toxigenic Microcystis sp. to that of total Microcystis sp. ranged from 0% to 14%. Such studies paved the way to identify and quantify the most potent microcystin producer in the tropical aquatic body.     

Impact of sonication at 20 kHz on Microcystis aeruginosa, Anabaena circinalis and Chlorella sp

Blooms of toxic cyanobacteria such as Microcystis aeruginosa periodically occur within wastewater treatment lagoons in the warmer months, and may consequently cause contamination of downstream water and outages of the supply of recycled wastewater. Lab-scale sonication (20 kHz) was conducted on suspensions of M. aeruginosa isolated from a wastewater treatment lagoon, and two other algal strains, Anabaena circinalis and Chlorella sp., to investigate cell reduction, growth inhibition, release of microcystin and sonication efficiency in controlling the growth of the M. aeruginosa. For M. aeruginosa, for all sonication intensities and exposure times trialled, sonication led to an immediate reduction in the population, the highest reduction rate occurring within the initial 5 min. Sonication for 5 min at 0.32 W/mL, or for a longer exposure time (>10 min) at a lower power intensity (0.043 W/mL), led to an immediate increase in microcystin level in the treated suspensions. However, prolonged exposure (>10 min) to sonication at higher power intensities reduced the microcystin concentration significantly. Under the same sonication conditions, the order of decreasing growth inhibition of the three algal species was: A. circinalis > M. aeruginosa > Chlorella sp., demonstrating sonication has the potential to selectively remove/deactivate harmful cyanobacteria from the algal communities in wastewater treatment lagoons.     

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.     

水力负荷对湖滨带人工湿地除磷效果的影响

分析了湖滨带复合人工湿地的各单元在旱季和雨季的除磷效果。结果表明，在进水TP浓度较高时，沉淀池对TP的去除效果较明显，旱、雨季的不同水力负荷对处理效果几乎没有影响。雨季时潜流人工湿地内发生了不溶性磷的吸附和沉积，实现了对磷的去除；旱季时由于水力负荷极小，水体流动性差，系统内处于厌氧状态，出现了磷的释放。雨季时，表面流人工湿地对磷的去除效果没有沉淀池和潜流人工湿地的理想，旱季的低水力负荷对除磷效果没有显著的影响。     

Priority pollutants in wastewater and combined sewer overflow

Implementation of the European Water Framework Directive and its affiliated directives requires Member States to improve their understanding of priority pollutants (PPs) in urban areas and obviously within wastewater systems. As a direct consequence, this study is intended to furnish data on both PP occurrence and the significance of concentrations in wastewater during dry and wet periods within combined sewers. Various sampling sites within the Paris combined sewer network were selected; for each sample, a total of 66 determinants, including metals, polycyclic aromatic hydrocarbons (PAHs), pesticides, organotins, volatile organic compounds, chlorobenzenes, phthalates and alkylphenols, were analysed. A broad range of PPs was observed in wastewater during dry as well as wet weather periods. Of the 66 elements investigated, 33 and 40 priority substances could be observed in raw sewage and wet weather effluent, respectively. As expected, a majority of metals were present in all samples, reflecting their ubiquitous nature. For both periods, chlorobenzenes and most of the pesticides always remained below the limit of quantification, while the majority of other organic pollutants assessed were identified within the microg l(-1) range. As highlighted by the larger number of substances detected in wet weather samples and the significance of their concentrations, runoff via atmospheric inputs and/or surface leaching was found to induce a wider range of PPs (n=40) and lead to higher concentrations of certain metals, PAHs, pesticides and other individual compounds. The data generated during this survey, which constitutes one of the first studies conducted in Europe to report concentrations for a variety of priority substances in wastewater within combined sewers, may be used in the future to identify PPs of potential significance for dry and wet weather periods and targeted for further investigation.     

Development of predictive models for determining enterococci levels at Gulf Coast beaches

The US EPA BEACH Act requires beach managers to issue swimming advisories when water quality standards are exceeded. While a number of methods/models have been proposed to meet the BEACH Act requirement, no systematic comparisons of different methods against the same data series are available in terms of relative performance of existing methods. This study presents and compares three models for nowcasting and forecasting enterococci levels at Gulf Coast beaches in Louisiana, USA. One was developed using the artificial neural network (ANN) in MATLAB Toolbox and the other two were based on the US EPA Virtual Beach (VB) Program. A total of 944 sets of environmental and bacteriological data were utilized. The data were collected and analyzed weekly during the swimming season (May-October) at six sites of the Holly Beach by Louisiana Beach Monitoring Program in the six year period of May 2005-October 2010. The ANN model includes 15 readily available environmental variables such as salinity, water temperature, wind speed and direction, tide level and type, weather type, and various combinations of antecedent rainfalls. The ANN model was trained, validated, and tested using 308, 103, and 103 data sets (collected in 2007, 2008, and 2009) with an average linear correlation coefficient (LCC) of 0.857 and a Root Mean Square Error (RMSE) of 0.336. The two VB models, including a linear transformation-based model and a nonlinear transformation-based model, were constructed using the same data sets. The linear VB model with 6 input variables achieved an LCC of 0.230 and an RMSE of 1.302 while the nonlinear VB model with 5 input variables produced an LCC of 0.337 and an RMSE of 1.205. In order to assess the predictive performance of the ANN and VB models, hindcasting was conducted using a total of 430 sets of independent environmental and bacteriological data collected at six Holly Beach sites in 2005, 2006, and 2010. The hindcasting results show that the ANN model is capable of predicting enterococci levels at the Holly Beach sites with an adjusted RMSE of 0.803 and LCC of 0.320 while the adjusted RMSE and LCC values are 1.815 and 0.354 for the linear VB model and 1.961and 0.521 for the nonlinear VB model. The results indicate that the ANN model with 15 parameters performs better than the VB models with 6 or 5 parameters in terms of RMSE while VB models perform better than the ANN model in terms of LCC. The predictive models (especially the ANN and the nonlinear VB models) developed in this study in combination with readily available real-time environmental and weather forecast data can be utilized to nowcast and forecast beach water quality, greatly reducing the potential risk of contaminated beach waters to human health and improving beach management. While the models were developed specifically for the Holly Beach, Louisiana, the methods used in this paper are generally applicable to other coastal beaches.