OBSERVATIONS ON PHYTOPLANKTON PRODUCTIVITY IN RELATION TO HYDROGRAPHY IN THE NORTHERN ADRIATIC

This work, carried out within the framework of the PRISMA II project, aims at evaluating the effects of the Po River flow on primary productivity, measured by C with in situ sample incubations. A total of four cruises was carried out in late winter and early summer (1996-1998) along transects from the coast offshore. In both seasons, the highest primary productivity was found in the most oligohaline stations. The effects of the Po River inputs were therefore clearly evident in the westernmost area, both in high productivity values and in the shape of productivity profiles. In late winter, extensive blooms of Skeletonema costatum and Pseudo-nitzschia delicatissima resulted in productivity values that were sometimes higher than in early summer. In early summer 1996, greatly reduced river flow clearly influenced productivity which was much lower than in 1997.     

Changes in the Biochemical Composition of Tetraselmis Suecia and Isochrysis Galbana During Growth and Decay

The variations of the biochemical composition of Tetraselmis suecica and Isochrysis galbana during growth and decay were determined. the content of chlorophyll a (Chl-a) of the cultures, as expected, slowly degraded into phaeopigments during decay, confirming that chlorophyll measurements do not always provide an accurate estimate of phytoplanktonic biomass and, consequently, may fail if used to measure the food availability of particulate matter for consumers. Measurements of total amounts of proteins, carbohydrates and lipids, related to the nutritional value of particles in terms of caloric content, are shown to provide information on the readily available food for consumers, particularly during the blooms. the protein/carbohydrate, C/N and POC/Chl-a ratios were used to evaluate the differences between these two species during the growth and the decomposition processes. A comparison between experimental and field conditions was undertaken to implement our understanding of the growth and degradation processes of particulate organic matter of phytoplanktonic origin in the sea and its role on natural systems, during and after phytoplankton blooms.     

鄱阳湖浮游藻类群落特征及与环境因子典范对应分析

通过2018—2019年夏冬季在鄱阳湖布设17个采样点,采样检测浮游藻类和水质参数,并采用典范对应分析法研究该湖浮游藻类群落结构特征及其与环境因子的相互关系。结果表明,两次调查共检测出浮游藻类7门31科58属,浮游藻类丰度范围为3.5×105 L-1～1.15×107 L-1,主要由绿藻门、硅藻门和蓝藻门组成,绿藻门为夏、冬季主要优势种群。典范对应分析结果显示,鄱阳湖冬季湖区水环境空间差异较大,而夏季差异较小;夏季氮磷营养盐和DO是影响浮游藻类群落时空分布的主要环境因子,冬季氮磷营养盐、BOD5和IMn是影响浮游藻类群落时空分布的主要环境因子。     

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.     

The representation of cyanobacteria life cycle processes in aquatic ecosystem models

Two simplified versions of a numerical life cycle model for diazotrophic cyanobacteria (of the order Nostocales) are developed and evaluated. Both consider two-life cycle stages, one growing, nitrogen-fixing stage and one stage that combines the resting, germinating and vegetative stages. The versions differ in the vertical resolution of the non-diazotrophic stage: version 1 collects the biomass in one layer at the bottom, version 2 considers sinking and rising of biomass explicitly. The results of the two versions are compared with a complex cyanobacteria life cycle model which describes four different life cycle stages each with two internal quotas for energy and nitrogen. The two simplified approaches show a good agreement with respect to the main characteristics of cyanobacteria dynamics (timing and duration of blooms, magnitude of nitrogen fixation, interannual variability). Our model study shows that both simplified approaches are suitable to be implemented into three-dimensional coastal or lake models.     

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.