Modelling the temperature and the phytoplankton distributions at the Aveiro near coastal zone,Portugal

The main objective of this paper is to implement a coupled three-dimensional physical and ecological model for the Aveiro coast, and to apply it to study the temperature and the phytoplankton biomass spatial distributions along the coastal ecosystem. The Aveiro coast is located at Portugal within the upwelling system of the Atlantic Iberian coast, characterized by nutrients availability and phytoplankton biomass accumulation, from April to October. In order to implement the ecological model, its validation was assessed by comparing simulations to data relative to the horizontal and vertical distributions of the temperature, nutrients and phytoplankton biomass, obtained during the CICLOS I survey off the Portuguese coast [Moita, M.T., 2001. Estrutura, Variabilidade e Dinâmica do Fitoplâncton na Costa de Portugal Continental. PhD Thesis. Faculdade de Ciências da Universidade de Lisboa, 272 pp.]. A sensitivity analysis of the model has been performed in order to assess the influence of the main ecological model variables. The simulation results show that the model is capable of predicting realistic the temperature, the nutrients and the chlorophyll-a distributions for the study area. The scenarios evidence the setup of a thermal stratification pattern resulting from the upwelling of deep and rich in nutrients water to the surface layer and a chlorophyll-a maxima extending offshore, along the picnocline and the nutricline. The results confirm the crucial role played by the physical processes in the phytoplankton bloom along the Aveiro coast. They also evidence the close link between the surface phytoplankton distribution and the surface temperature distribution.     

应用浮游植物群落结构指数评价海域富营养化

探讨了浮游植物对海水富营养化程度的指示作用,并用浮游植物群落结构指数对天津近岸海域的富营养化水平进行了现状评价,结果表明,天津近岸海域水质基本属中营养水平,但某些站位在有些季节呈严重的富营养水平,并呈现枯水期和丰水期高,平水期低的特征,与化学指标的评价结果相比,结果基本一致,说明该方法是可行的,特别是当浮游植物大量繁殖,消耗了大量的营养盐,生物学指标更能正确合理地进行水质评价     

Submerged vegetation removal promotes shift of dominant phytoplankton functional groups in a eutrophic lake

Historical data indicate that the dominance of submerged plants in Dianchi Lake in the 1960 s was characterized by low algal density with dominance of non-toxic group J（Scenedesmus,Pediastrum,etc.）. The removal of submerged plants,which began in the 1970 s,resulted in the expansion of bloom-forming Microcystis（group M）. Laboratory experiments suggested that Microcystis aeruginosa was inclined to grow and develop at elevated temperatures. The growth of Scenedesmus obliquus was slower than that of co-cultivated M. aeruginosa in the absence of Ceratophyllum demersum,especially at higher temperatures. The existence of submerged plant C. demersum could inhibit the growth of the harmful algae M. aeruginosa and this inhibitory effect by C. demersum was enhanced with an increase in temperature. Instead,with C. demersum,the growth of S. obliquus was not inhibited,but the co-cultivated M. aeruginosa was eliminated in a short time. Combined with the historical data and laboratory experiments,it was indicated that the submerged plants might play important roles in the dominance of the non-toxic group J in the historical succession. Consequently,the introduction of the submerged plant such as C. demersum might alter the dominant phytoplankton functional groups from M to J and benefit the restoration of the eutrophic lake.     

Development of categorical mapping for quantitative assessment of eutrophication

Spatial distribution of nutrient and phytoplankton variables is often illustrated using categorical mapping for each variable. However, the assessment of eutrophication cannot be derived from a single parameter since a synthesis of the environmental variables related to eutrophication is required. These shortcomings are further complicated since it is difficult to discriminate between distinct trophic states along natural environmental gradients. In the present work, a methodological procedure for quantitative assessment of eutrophication at a spatial scale was examined in the Gulf of Saronicos, Greece, based on a thematic map generated from the synthesis of four variables characterising eutrophication. The categorical map of each variable was developed using the Kriging interpolation method and four trophic levels were indicated (eutrophic, upper-mesotrophic, lower-mesotrophic and oligotrophic) based on nutrient and phytoplankton concentration scaling. Multi-criteria choice methods were applied to generate a final categorical map showing the four trophic levels in the area. This synthesis of categorical maps for assessing eutrophication at a spatial scale is proposed as a methodological procedure appropriate for coastal management studies.     

Developing an empirical model of phytoplankton primary production: a neural network case study

We describe the development of a neural network model for estimating primary production of phytoplankton. Data from an enriched estuary in the eastern United States, Chesapeake Bay, were used to train, validate and test the model. Two error backpropagation multilayer perceptrons were trained: a simpler one (3-5-1) and a more complex one (12-5-1). Both neural networks outperformed conventional empirical models, even though only the latter, which exploits a larger suite of predictive variables, provided truly accurate outputs. The application of this neural network model is thoroughly discussed and the results of a sensitivity analysis are also presented.     

淀山湖浮游植物营养限制因子的研究

通过藻类增长的生物学评价(Nutrient Enrichment Bioassay)研究淀山湖浮游植物生长限制性因子,并采用析因方差分析和事后比较方法分析营养盐（PO^3-₄P、NH₃N、NO^-₃N）对浮游植物生长速度、平均最大现存量和平均最大特定增长率的影响。研究表明：磷对浮游植物生长有明显的促进作用,能提高浮游植物的生长速度和现存量,且促进作用随磷浓度（0.13～0.53 mg/L）的增加而加强,磷是淀山湖浮游植物增长的第一限制性因子;低浓度硝氮（2.91～5.91 mg/L）对浮游植物生长有微小的促进作用,但高浓度（5.91～8.91 mg/L）的硝氮表现出抑制作用;氨氮对浮游植物生长有抑制作用,并随浓度（1.25～7.25 mg/L）的增加而增大;添加磷+硝氮能明显促进浮游植物生长,磷与硝氮之间存在一定的交互作用.     

Embedded reservoir and constructed wetland for drinking water source protection: Effects on nutrient removal and phytoplankton succession

An embedded reservoir that provides an efficient nutrient removal system protects drinking water.However,embedded reservoirs are rarely used in eutrophic shallow lakes because of their undetermined nutrient retention efficiency and unknown effects by the phytoplankton community.In this study,we aim to investigate the nutrient retention and algae succession in an embedded reservoir and adjacent wetland from April 2017 to September 2018 in the eastern part of Lake Taihu,China.More than 40% of total phosphorus(TP) and 45% of particulate phosphorous entering the reservoir were retained semiannually,and the highest TP removal efficiency was achieved in the reservoir during autumn with an average value of 53.3% ± 9.9%.The overall nitrogen retention efficiency(21.7% ± 37.8%) was lower than that of TP(41.8% ± 27.8%).Similar trends were obtained in the wetland area.An important pathway for phosphorus removal is through particulate matter retention.Our study revealed that nutrient retention mechanisms in the reservoir were primarily via macrophyte absorption,particulate substance sedimentation,and prolonged water residence time.Consequently,the phytoplankton biomass(Chl-a) in the reservoir decreased(from 48.0 to 25.2 μg/L) and water transparency improved,due to the decreased P level and transformation of the phytoplankton group into simple structures with good ecological status.Therefore,the combination of embedded reservoir and constructed wetland ecosystem can be used successfully to protect surface water.The results will be advantageous to groups seeking to preserve drinking water sources.     

Natural and Anthropogenic Effects On Phytoplankton Primary Productivity in Mangroves

Spatial and temporal variations and the factors influencing primary production have been studied in three different mangrove waters (Pichavaram, Ennore Creek and Adyar Estuary) of South India characterised by different anthropogenic impacts. the gross primary productivity in the unpolluted Pichavaram mangrove was 113 g Cm^-2yr^-1 exhibiting natural variability with the environmental forcing factors. Human activities have elevated primary productivity in the Ennore Creek mangrove (157g Cm^-2yr^-1) primarily through the direct discharge of fertilizer effluents. By contrast, a combination of domestic and industrial effluent discharges into the Adyar Estuary mangrove has considerably reduced phytoplankton primary productivity 83g Cm^-2yr^-1 the Redfield N: P ratio varies from 0.96 N: 1P at Ennore Creek, 1.75N: 1P at Adyar Estuary to 15.2 N: 1P at Pichavaram mangroves. This suggests that the Pichavaram mangroves represent a well equilibrated ecosystem with N: P ratio close to steady-state values in contrast to the anthropogenically altered mangrove ecosystems studied. Results show a significant temporal variability in nutrient concentration in the three mangrove areas. Distinct differences in nutrient concentrations between the dry and the wet seasons have been observed.     

Mixture Toxicity of the Antifouling Compound Irgarol to the Marine Phytoplankton Species Dunaliella tertiolecta

This study examined the toxicity of irgarol, individually and in binary mixtures with three other pesticides (the fungicide chlorothalonil, and the herbicides atrazine and 2,4-D), to the marine phytoplankton species Dunaliella tertiolecta. Standard 96-h static algal bioassays were used to determine pesticide effects on population growth rate. Irgarol significantly inhibited D. tertiolecta growth rate at concentrations ≥ 0.27 μ g/L. Irgarol was significantly more toxic to D. tertiolecta than the other pesticides tested (irgarol 96 h EC₅₀ = 0.7 μ g/L; chlorothalonil 96 h EC₅₀ = 64 μ g/L; atrazine 96 h EC₅₀ = 69 μ g/L; 2,4-D 96 h EC₅₀ = 45,000 μ g/L). Irgarol in mixture with chlorothalonil exhibited synergistic toxicity to D. tertiolecta, with the mixture being approximately 1.5 times more toxic than the individual compounds. Irgarol and atrazine, both triazine herbicides, were additive in mixture. The toxicity threshold of 2,4-D was much greater than typical environmental levels and would not be expected to influence irgarol toxicity. Based on these interactions, overlap of certain pesticide applications in the coastal zone may increase the toxicological risk to resident phytoplankton populations.