On the successful use of a simplified model to simulate the succession of toxic cyanobacteria in a hypereutrophic reservoir with a highly fluctuating water level

Many freshwater bodies worldwide that suffer from harmful algal blooms would benefit for their management from a simple ecological model that requires few field data, e.g. for early warning systems. Beyond a certain degree, adding processes to ecological models can reduce model predictive capabilities. In this work, we assess whether a simple ecological model without nutrients is able to describe the succession of cyanobacterial blooms of different species in a hypereutrophic reservoir and help understand the factors that determine these blooms. In our study site, Karaoun Reservoir, Lebanon, cyanobacteria Aphanizomenon ovalisporum and Microcystis aeruginosa alternatively bloom. A simple configuration of the model DYRESM-CAEDYM was used; both cyanobacteria were simulated, with constant vertical migration velocity for A. ovalisporum, with vertical migration velocity dependent on light for M. aeruginosa and with growth limited by light and temperature and not by nutrients for both species. The model was calibrated on two successive years with contrasted bloom patterns and high variations in water level. It was able to reproduce the measurements; it showed a good performance for the water level (root-mean-square error (RMSE) lower than 1 m, annual variation of 25 m), water temperature profiles (RMSE of 0.22–1.41 °C, range 13–28 °C) and cyanobacteria biomass (RMSE of 1–57 μg Chl a L^?1, range 0–206 μg Chl a L^?1). The model also helped understand the succession of blooms in both years. The model results suggest that the higher growth rate of M. aeruginosa during favourable temperature and light conditions allowed it to outgrow A. ovalisporum. Our results show that simple model configurations can be sufficient not only for theoretical works when few major processes can be identified but also for operational applications. This approach could be transposed on other hypereutrophic lakes and reservoirs to describe the competition between dominant phytoplankton species, contribute to early warning systems or be used for management scenarios.     

Warmer winters: are planktonic algal populations in Sweden's largest lakes affected?

Winters in Sweden have become warmer in the 1990s, and as a consequence the timing of ice break-up and the growth and decline of spring phytoplankton has shifted, starting earlier. Even spring temperatures have become warmer, leading to an earlier beginning of the summer phytoplankton growth. The spring-ward shift in phytoplankton population growth has resulted in an extension of the growing season by at least one month. Although mean total phytoplankton biomass from May to October has not increased, the spring and early summer biomass of temperature-sensitive phytoplankton groups, such as cyanobacteria and chlorophytes, has increased in the 1990s. No increase was noted for other phytoplankton groups. Considering that some species of cyanobacteria that commonly occur during a summer bloom, such as Anabaena, Aphanizomenon, and Microcystis, can be toxic, the effect of warmer winters on aquatic ecosystems is potentially far-reaching.     

Latitudinal and seasonal capacity of the surface oceans as a reservoir of polychlorinated biphenyls

The oceans play an important role as a global reservoir and ultimate sink of persistent organic pollutants (POPs) such as polychlorinated biphenyls congeners (PCBs). However, the physical and biogeochemical variables that affect the oceanic capacity to retain PCBs show an important spatial and temporal variability which have not been studied in detail, so far. The objective of this paper is to assess the seasonal and spatial variability of the ocean's maximum capacity to act as a reservoir of atmospherically transported and deposited PCBs. A level I fugacity model is used which incorporates the environmental variables of temperature, phytoplankton biomass, and mixed layer depth, as determined from remote sensing and from climatological datasets. It is shown that temperature, phytoplankton biomass and mixed layer depth influence the potential PCB reservoir of the oceans, being phytoplankton biomass specially important in the oceanic productive regions. The ocean's maximum capacities to hold PCBs are estimated. They are compared to a budget of PCBs in the surface oceans derived using a level III model that assumes steady state and which incorporates water column settling fluxes as a loss process. Results suggest that settling fluxes will keep the surface oceanic reservoir of PCBs well below its maximum capacity, especially for the more hydrophobic compounds. The strong seasonal and latitudinal variability of the surface ocean's storage capacity needs further research, because it plays an important role in the global biogeochemical cycles controlling the ultimate sink of PCBs. Because this modeling exercise incorporates variations in downward fluxes driven by phytoplankton and the extent of the water column mixing, it predicts more complex latitudinal variations in PCBs concentrations than those previously suggested.     

Recent changes in trophic state of the Baltic Sea along SW coast of Finland

Drawing reliable conclusions on changes in the trophic state of various subareas of the Baltic Sea is problematic, in large part because the monitoring of productivity parameters exhibiting high natural variability is based on sparse sampling. This emphasizes the importance of long-term data sets. Here we present a 30-year chlorophyll alpha data set from the western Gulf of Finland. The trophic state of the study area showed an increasing trend in the 1970s and 1980s manifested mainly as strengthened vernal blooms. This trend did not continue in the 1990s, and the seasonal phytoplankton biomass maxima since then has begun to show some bias toward the late summer. The changes in seasonal maxima of phytoplankton blooms probably reflect i) decreased availability of N suppressing the magnitude of the vernal bloom, which increases the P reserves for the summer, and ii) enhanced internal P loading, which further increases the summer P reserves.     

Predicting microalgae growth and phosphorus removal in cold region waste stabilization ponds using a stochastic modelling approach

A stochastic ecological model with an integrated equilibrium temperature model was developed to predict microalgae growth and phosphorus removal in cold region waste stabilization ponds (WSPs). The model utilized a Monte Carlo simulation to account for parameter uncertainty. The equilibrium temperature model was parameterized using field data collected from two WSPs in Nunavut, Canada, from 2012 to 2014. The equilibrium temperature model provided good agreement with field data on a daily time step. The full model was run using historic (1956–2005) temperature and solar radiation data from five communities (Baker Lake, Cambridge Bay, Coral Harbour, Hall Beach, Resolute) in Nunavut, Canada. The communities represented a range of geographical locations and environmental conditions. Logistic regression on pooled model outputs showed that mean July temperature and mean treatment season temperature (June 1–September 15, ice-free period) provided the best predictors for microalgae growth. They had a predictive success rate of 93 and 88%, respectively. The modelled threshold (50% probability from the Monte Carlo simulation) for microalgae growth was 8.7 and 5.6 °C for the July temperature and mean treatment season temperature, respectively. The logistic regression was applied to each community (except Sanikiluaq) in Nunavut using historic climate data and a probability of microalgae growth was calculated. Based on the model results, soluble phosphorus concentrations consistent with secondary treatment could be achieved if WSP depth is less than 2 m. The model demonstrated a robust method to predict whether a microalgae bloom will occur under a range of model parameters.     

Interannual variability of phyto-bacterioplankton biomass and production in coastal and offshore waters of the Baltic Sea

The microbial part of the pelagic food web is seldom characterized in models despite its major contribution to biogeochemical cycles. In the Baltic Sea, spatial and temporal high frequency sampling over three years revealed changes in heterotrophic bacteria and phytoplankton coupling (biomass and production) related to hydrographic properties of the ecosystem. Phyto- and bacterioplankton were bottom-up driven in both coastal and offshore areas. Cold winter temperature was essential for phytoplankton to conform to the successional sequence in temperate waters. In terms of annual carbon production, the loss of the spring bloom (diatoms and dinoflagellates) after mild winters tended not to be compensated for by other taxa, not even summer cyanobacteria. These results improve our ability to project Baltic Sea ecosystem response to short- and long-term environmental changes.     

Temperature and nutrients are significant drivers of seasonal shift in phytoplankton community from a drinking water reservoir,subtropical China

Reservoirs are an important source of water supply in many densely populated areas in southeast China. Phytoplankton plays an important role in maintaining the structure and function of these reservoir ecosystems. Understanding of seasonal succession in phytoplankton communities and its driving factors is essential for effective water quality management in drinking-water reservoirs. In this study, water samples were collected monthly at the surface layers of riverine, transitional, and lacustrine zones from May 2010 to April 2011 in Tingxi Reservoir, southeast China. The phytoplankton showed distinct seasonal shifts in community structure at both taxonomic and functional levels. Cyanophyta was the dominant group in summer, especially species of Raphidiopsis in May and Aphanizomenon in June, and cyanobacterial dominance was promoted by both warmer conditions and excessive nutrients loading. Cyanophyta was gradually replaced by Cryptophyta (e.g., Chroomonas caudata) in abundance and by Bacillariophyta (Fragilaria sp. or Synedra sp. and Melosira sp.) in biomass with decreasing temperature. It appeared that seasonal shifts in phytoplankton composition were closely related to climate, nutrient status, and hydrology in this reservoir. Our partial RDA results clearly showed that water temperature and nutrients (TN and TP) were the most critical factors driving phytoplankton community shift in the abundance and biomass data, respectively. Further, with the global warming, cyanobacterial blooms may increase in distribution, duration, and intensity. In our study, the abundance and biomass of cyanobacteria had significant and positive correlations with temperature and phosphorus. Therefore, a stricter limit on nutrient input should be a priority in watershed management to protect drinking water from the effects of cyanobacterial blooms, especially in high-temperature period.     

Phytoplankton can bypass nutrient reductions in eutrophic coastal water bodies

The EU-water framework directive aims at nutrient reductions, since anthropogenically induced eutrophication is a major threat for coastal waters. However, phytoplankton biomass in southern Baltic Sea coastal water bodies (CWB) remains high and the underlying mechanisms are not well understood. Therefore, a CWB data set was analysed regarding changes in phytoplankton biomass and nutrient concentration of nitrogen (N) and phosphorus (P) from 2000 to 2014. It was expected to find imbalances between produced phytoplankton biomass and total nutrient concentrations. Inner CWB were cyanobacteria-dominated and showed up to five times higher chlorophyll a-concentrations compared to outer CWB with similar total phosphorus-concentrations. Phytoplankton tended to be P-limited during spring and N-limited during summer. Phytoplankton biomass and nutrient concentrations were even higher during very humid years, which indicated a close coupling of the CWB with their catchment areas. This study suggests that re-mesotrophication efforts need to consider the importance of changed phytoplankton composition and nutrient availabilities.     

Calibration and validation of a dynamic water model in agricultural scenarios

A dynamic aquatic model (DynA model) was previously developed to predict the fate of a chemical in aquatic scenarios characterized by daily or periodic changes in several input parameters. DynA model is here calibrated with data obtained from the literature in specific unsteady state scenarios, such as those of rice fields. The results obtained for two herbicides (cinosulfuron and pretilachlor) in rice paddy scenarios revealed the capability of the model to accurately predict water and sediment concentrations, as shown by some statistical indicators. Modelling efficiency (EF) values of 0.86-0.99 for the water compartment and of 0.77-0.84 for sediment show the good agreement between predicted and measured concentrations. An "external validation" was performed using measured data for a different herbicide (molinate) applied in a Portuguese paddy rice scenario. A sensitivity analysis for this volatile chemical revealed the influence of some climatic parameters (e.g. temperature) to the model outcomes, such as water and sediment concentrations. This confirmed the capability of DynA model as an efficient tool for the pesticide risk assessment in dynamic scenarios.     

Forest Die-Back Modified Plankton Recovery from Acidic Stress

We examined long-term data on water chemistry of Lake Rachelsee (Germany) following the changes in acidic depositions in central Europe since 1980s. Despite gradual chemical recovery of Rachelsee, its biological recovery was delayed. In 1999, lake recovery was abruptly reversed by a coincident forest die-back, which resulted in elevated terrestrial export of nitrate and ionic aluminum lasting ~5 years. This re-acidification episode provided unique opportunity to study plankton recovery in the rapidly recovering lake water after the abrupt decline in nitrate leaching from the catchment. There were sudden changes both in lake water chemistry and in plankton biomass structure, such as decreased bacterial filaments, increased phytoplankton biomass, and rotifer abundance. The shift from dominance of heterotrophic to autotrophic organisms suggested their substantial release from severe phosphorus stress. Such a rapid change in plankton structure in a lake recovering from acidity has, to the best of our knowledge, not been previously documented.     

The carbon budget of Canadian forests: a sensitivity analysis of changes in disturbance regimes, growth rates, and decomposition rates

Ecosystem responses to climate changes will affect the exchange of carbon (C) with the atmosphere, thus providing feedback for future climate response. We have developed a C budget model of Canadian forests and forest sector activities and used sensitivity analysis runs with changes in productivity, decomposition, and disturbance regimes to assess the sensitivity of the Canadian forest sector C budget over the next century. The model operates on data derived from Canada's National Forest Biomass Inventory, from the Oak Ridge National Laboratory global soil C data base, and from Canadian data bases that document areas annually disturbed by fire, insects, and harvesting. It simulates the dynamics of biomass and soil C pools (including detritus and coarse woody debris) as they are affected by growth, decomposition, and disturbances. For the reference run of the model, we assumed unchanging climate and disturbance regimes. Under these conditions, total ecosystem C increased by 2 Gt C (2.3%) over the 100-year simulation period. In the sensitivity analysis, we explored the effects of changes in the area annually disturbed by fire and insect-induced stand mortality (-60 to +300%), growth rates (-10 to +20%), decomposition rates (-10 to +25%), and combined changes in growth and decomposition rates. In every model run, the change of total ecosystem C relative to the reference run was less than 10%. Combined changes to growth and decomposition rates yielded very small deviations from the results of the reference run (-0.8 to +1.2%). Because disturbance regime changes affect forest age-class structure as well as forest dynamics, they are expected to affect C budgets strongly. Total ecosystem C, however, is slightly more sensitive to changes in growth and decomposition parameters than to changes in disturbance regimes. Although the sensitivity analysis results suggest that C budgets are little affected by the range of parameter changes implemented here, we must emphasize that our sensitivity analyses do not account for potentially important processes, such as regeneration failure or the shifts in forest distribution.     

Heat and mass transfer in the vadose zone with plant roots

The vadose zone is the intermediate medium between the atmosphere and groundwater. The modeling of the processes taking place in the vadose zone needs different approaches to those needed for groundwater transport problems because of the marked changes in environmental conditions affecting the vadose zone. A mathematical model to simulate the water flow, and the fate and transport of recalcitrant contaminants was developed, which could be applied to various bioremediation methods such as phytoremediation and natural attenuation in the vadose zone. Two-phase flow equations and heat flux models were used to develop the model. Surface energy, balance equations were used to estimate soil surface temperature, and root growth and root distribution models were incorporated to represent the special contribution of plant mots in the vegetated soils. Interactions between the roots and environmental conditions such as temperature and water content were treated by incorporating a feedback mechanism that made allowance for the effects of water and temperature stresses on root distribution and water uptake by roots. In conducting the modeling study, Johnson grass and unplanted soil were simulated to compare the effect of root water uptake on soil water content. After the numerical experiments were conducted to investigate model behavior, the proposed model was applied to estimate actual water flow and heat flow in field lysimeter experiments over a 1-year period. Root growth and distribution for Johnson grass and rye grass were simulated to compare the warm season grass to the cold season grass. A significant agreement was observed between the simulations and measured data.     

Changes in primary productivity associated with liming and reacidification of an Adirondack lake

The addition of calcium carbonate to a clearwater acidic lake had a significant effect on phytoplankton abundance and on the biomass-specific rate of production. Chlorophyll concentrations and productivity: biomass ratios were strongly correlated with changes in lake acidity associated with liming and reacidification (r2=0.89 and 0.73, respectively). Summer mean chlorophyll increased by 0.9 mg m(-3) for each unit increase in lake pH, whereas productivity:biomass ratios decreased from > 2 to < 1 with an increase in pH from 5.5 to 7.0. Higher phytoplankton standing crops after liming were attributed to lower grazing rates following the decline of the dominant zooplankton taxa. A model relating biomass-specific productivity to incident light levels was found to be useful in interpreting treatment effects on productivity. Incident light and biomass (based on chlorophyll) accounted for 81% of the variability in productivity at the treated site. Comparisons of photosynthesis-irradiance curves indicated that the maximum photosynthetic capacity was higher following the watershed liming, compared to data collected after lake liming and during reacidification.     

Complex interactions between autotrophs in shallow marine and freshwater ecosystems: implications for community responses to nutrient stress

The relative biomass of autotrophs (vascular plants, macroalgae, microphytobenthos, phytoplankton) in shallow aquatic ecosystems is thought to be controlled by nutrient inputs and underwater irradiance. Widely accepted conceptual models indicate that this is the case both in marine and freshwater systems. In this paper we examine four case studies and test whether these models generally apply. We also identify other complex interactions among the autotrophs that may influence ecosystem response to cultural eutrophication. The marine case studies focus on macroalgae and its interactions with sediments and vascular plants. The freshwater case studies focus on interactions between phytoplankton, epiphyton, and benthic microalgae. In Waquoit Bay, MA (estuary), controlled experiments documented that blooms of macroalgae were responsible for the loss of eelgrass beds at nutrient-enriched locations. Macroalgae covered eelgrass and reduced irradiance to the extent that the plants could not maintain net growth. In Hog Island Bay, VA (estuary), a dense lawn of macroalgae covered the bottom sediments. There was reduced sediment-water nitrogen exchange when the algae were actively growing and high nitrogen release during algal senescence. In Lakes Brobo (West Africa) and Okeechobee (FL), there were dramatic seasonal changes in the biomass and phosphorus content of planktonic versus attached algae, and these changes were coupled with changes in water level and abiotic turbidity. Deeper water and/or greater turbidity favored dominance by phytoplankton. In Lake Brobo there also was evidence that phytoplankton growth was stimulated following a die-off of vascular plants. The case studies from Waquoit Bay and Lake Okeechobee support conceptual models of succession from vascular plants to benthic algae to phytoplankton along gradients of increasing nutrients and decreasing under-water irradiance. The case studies from Hog Island Bay and Lake Brobo illustrate additional effects (modified sediment-water nutrient fluxes, allelopathy or nutrient release during plant senescence) that could play a role in ecosystem response to nutrient stress.     

Understanding the patterns and mechanisms of urban water ecosystem degradation: phytoplankton community structure and water quality in the Qinhuai River, Nanjing City, China

The temporal and spatial distribution characteristics of environmental parameters and the phytoplankton community were investigated in October 2010 and January 2011 in the Qinhuai River, Nanjing, China. Results showed that the water quality in the study area was generally poor, and the main parameters exceeding standards (level V) were nitrogen and phosphorus. The observed average concentrations of the total nitrogen (TN) were 4.90 mg?L^?1 in autumn and 9.29 mg?L^?1 in winter, and those of the total phosphorus (TP) were 0.24 mg?L^?1 in autumn and 0.88 mg?L^?1 in winter, respectively. Thirty-seven species, 30 genera, and four phyla of phytoplankton were detected in the river. Cyanophyta and Bacillariophyta were the dominant phyla in autumn, with average abundance and biomass of 221.5?×?10⁴?cells?L^?1 and 4.41 mg?L^?1, respectively. The dominant population in winter was Bacillariophyta, and the average abundance and biomass were 153.4?×?10⁴?cells?L^?1 and 6.58 mg?L^?1, respectively. The results of canonical correspondence analysis (CCA) between environmental parameters and phytoplankton communities showed that Chlorophyta could tolerate the higher concentrations of the permanganate index, nitrogen, and phosphorus in eutrophic water; Bacillariophyta could adapt well to changing water environments; and the TN/TP ratio had obvious impacts on the distributions of Cyanophyta, Euglenophyta, and some species of Chlorophyta. CCA analyses for autumn and winter data revealed that the main environmental parameters influencing phytoplankton distribution were water temperature, conductivity, and total nitrogen, and the secondary factors were dissolved oxygen, NH₄ ⁺–N, NO₃–N, TN, COD_Mn, TN/TP ratio, and oxidation-reduction potential.     

Influence of lead acetate on soil microbial biomass and community structure in two different soils with the growth of Chinese cabbage (Brassica chinensis)

A greenhouse pot experiment was conducted to evaluate the impact of different concentrations of lead acetate on soil microbial biomass and community structure during growth of Chinese cabbage (Brassica chinensis) in two different soils. The field soils were used for a small pot, short-term 60-day growth chamber study. The soils were amended with different Pb concentrations, ranging from 0 to 900mgkg(-1) soil. The experimental design was a 2 soilx2 vegetation/non-vegetationx6 treatments (Pb)x3 replicate factorial experiment. At 60 days the study was terminated and soils were analyzed for microbial parameters, namely, microbial biomass, basal respiration and PLFAs. The results indicated that the application of Pb at lower concentrations (100 and 300mgkg(-1)) as lead acetate resulted in a slight increase in soil microbial biomass, whereas Pb concentrations >500mgkg(-1) caused an immediate gradual significant decline in biomass. However, the degree of impact on soil microbial biomass and basal respiration by Pb was related to management (plant vegetation) or the contents of clay and organic matter in soils. The profiles of 21 phospholipid fatty acids (PLFAs) were used to assess whether observed changes in functional microbial parameters were accompanied by changes in the composition of the microbial communities after Pb application at 0, 300 and 900mg Pbkg(-1) soil. The results of principal component analyses (PCA) indicated that there were significant increases in fungi biomarkers of 18:3omega6c, 18:1omega9c and a decrease in cy17:0, which is an indicator of gram-negative bacteria for the high levels of Pb treatments In a word, soil microbial biomass and community structure, therefore, may be sensitive indicators reflecting environmental stress in soil-Pb-plant system. However, further studies will be needed to better understand how these changes in microbial community structure might actually impact soil microbial community function.     

Responses of phytoplankton functional groups to environmental factors in the Pearl River,South China

The variations of phytoplankton functional groups and their correlation with environmental factors, as well as the applicability of phytoplankton functional groups to serve as biological water quality indicator in the Pearl River, South China, were studied in the present study. A total of 96 samples were collected and divided into 21 functional groups from September 2016 to July 2017. The phytoplankton functional groups P and G were dominant during the investigation, and their biomass contributing was ranged 0.06 to 89.07%, the average 30.73%, and ranged 1.47 to 62.40%, the average 9.33% of the total biomass, respectively. The results showed environmental estrogens—BPA (bisphenol A), E2 (17β-estradiol), E1 (estrone), 4-t-OP (4-tert-octylphenol), 4-NP (nonylphenol), TCS (triclosan), and TCC (triclocarban)—in the Pearl River were significantly different, and with average values of 269.30 ng L^?1, 2.76 ng L^?1, 4.24 ng L^?1, 53.68 ng L^?1, 952.72 ng L^?1, 16.79 ng L^?1, and 8.61 ng L^?1, respectively. This was likely responsible for the differences in the phytoplankton functional groups. We observed positive correlations between P and A, and G and J. Functional groups P biomass decreased significantly with functional groups L_M increased, and functional groups M and J with X2. We found positive correlations between functional group G and concentrations of E1 and TCC; functional group A and total nitrogen (TN), 4-NP, 4-t-OP, and E2; functional groups L_M and L1 and total suspended particles, BPA, and TCS; and functional group G and negative total phosphorus (TP), pH, and TCS. The study showed that TN, TP, and the environmental estrogens in the aquatic ecosystems were correlation with phytoplankton functional groups type, and affected the ecological balance in aquatic environments.

     

Biomarkers of a native fish species (Cnesterodon decemmaculatus) application to the water toxicity assessment of a peri-urban polluted river of Argentina

Environmental monitoring by means of biomarker parameters assessed in different species is a useful tool. It has the advantage of providing a quantitative response as well as valuable information of ecological relevance on the chronic adverse effects caused by water pollution. The aim of this study was to assess the response of biochemical and physiological parameters of Cnesterodon decemmaculatus, a native teleost, simultaneously caught in two sites of Reconquista river, a highly polluted peri-urban river. This study compared the measured parameters with that of specimens of the same species captured in an unpolluted body water, and correlated the detected changes with the physicochemical profile of the water at each site. A comparison was made of selected parameters of gill, brain and liver and of somatic indices of fish collected from polluted and reference sites. The main parameters whose changes allowed to discriminate between sampling sites were gill (Na(+),K(+))-ATPase, brain acetylcholinesterase (AChE) and liver aminotransaminases activities; tissues' protein content and liver somatic index (LSI) were also sensitive biomarkers in brain and liver, respectively. The results showed that the response of the measured biomarkers allowed for the differentiation of sampling sites according to their water quality and confirmed that Cnesterodon decemmaculatus may be a useful test organism for the biomonitoring of freshwater environments. In addition, the simultaneous measurement of the physicochemical parameters of the water samples showed a good correspondence between the biomarkers responses and the environmental chemical stress conditions.     

Cometabolic degradation kinetics of TCE and phenol by Pseudomonas putida

Modeling of cometabolic kinetics is important for better understanding of degradation reaction and in situ application of bio-remediation. In this study, a model incorporated cell growth and decay, loss of transformation activity, competitive inhibition between growth substrate and non-growth substrate and self-inhibition of non-growth substrate was proposed to simulate the degradation kinetics of phenol and trichloroethylene (TCE) by Pseudomonas putida. All the intrinsic parameters employed in this study were measured independently, and were then used for predicting the batch experimental data. The model predictions conformed well to the observed data at different phenol and TCE concentrations. At low TCE concentrations (<2 mg l(-1)), the models with or without self-inhibition of non-growth substrate both simulated the experimental data well. However, at higher TCE concentrations (>6 mg l(-1)), only the model considering self-inhibition can describe the experimental data, suggesting that a self-inhibition of TCE was present in the system. The proposed model was also employed in predicting the experimental data conducted in a repeated batch reactor, and good agreements were observed between model predictions and experimental data. The results also indicated that the biomass loss in the degradation of TCE below 2 mg l(-1) can be totally recovered in the absence of TCE for the next cycle, and it could be used for the next batch experiment for the degradation of phenol and TCE. However, for higher concentration of TCE (>6 mg l(-1)), the recovery of biomass may not be as good as that at lower TCE concentrations.     

Phytoplankton Community and Chlorophyll a as Trophic State Indices of Lake Skadar (Montenegro,Balkan) (7 pp)

Background, Aims and Scope Phytoplankton, as a first step in trophic cascades of lakes, can be a good indicator of trophic states, considering that every environmental change affects this community and many species of this community are sensitive to changes, and that they response very quickly. In this study, we tried to assess and predict the trophic state of Lake Skadar according to phytoplankton data.Methods Water samples were collected using Ruttner sampling bottle. Temperature, dissolved oxygen, ph, conductivity and transparence were measured in situ using portable equipment. Nutrients and chlorophyll a were measured using standard spectrophotometric methods. A determination of phytoplankton species was performed using relevant keys and the counting of cells was performed using sedimentation methods.Results and Discussion The species composition of Lake Skadar revealed 95 taxa, with Chlorophyceae and Bacillariophyceae being represented best. According to an average chlorophyll a concentration of 5.9 &#181;g/l, Lake Skadar belongs to the mesotrophic level of the trophic scale. Developed prediction equation for chlorophyll a revealed a good prediction (R2=0.71) and the parameter Secchi depth was primarily correlated with chlorophyll a concentration. Trophic state indices derived from chlorophyll a and transparency, were close together, but both were below the phosphorous index. Values of trophic state indices rank the Lake Skadar as being mesotrophic. This study also showed that indices of diversity based on phytoplankton are weak indicators of trophic status and that they can well characterize only differences between assemblages and associations. According to calculated saprobic indices (ranging from 1.5 to 2.15), Lake Skadar is on betamesosaprobic level of saprobity, which means that it is moderately polluted with organic compounds. Conclusions Total phosphorus is not the main limiting factor for the phytoplankton community in Lake Skadar. Disagreements between chlorophyll and the transparency index, on the one hand, and the total phosphorus index, on the other, suggest that the phytoplankton in Lake Skadar is probably limited by other factors than phosphorus, such as nitrogen, toxic substances or intense zooplankton grazing. According to the majority of investigated parameters and indices derived from phytoplankton data, Lake Skadar is mesotrophic, with tendencies toward eutrophic levels during the summer period. Recommendations and Outlook Long-term monitoring is required for a better estimation of state and the conditions of Lake Skadar. Further studies on factors influencing the phytoplankton community, especially zooplankton grazing and toxic substances, which were not included in this study, should be continued in the future to improve the efficiency of phytoplankton usage in estimating the ecological and trophic conditions of Lake Skadar.