Study of the saltwater pond at Capoterra,southern Sardinia: General characteristics

Capoterra Pond in southern Sardinia is described and analyzed with respect to its morphological, meteorological, physical and chemical characteristics, and its zoobenthic, zooplankton, and phytoplankton biocenoses. The birdlife, flora, and riparian associations of vegetation are studied in order to draw international attention to the importance of this lagoon, the precariousness of its ecosystem, the seriousness of current attempts to destabilize it, and the need to encourage the Sardinian authorities to initiate conservation measures, especially as rare birds have found their niches there.     

The change of gaseous carbon fluxes following the switch of dominant producers from macrophytes to algae in a shallow subtropical lake of China

Successions of lake ecosystems from clear-water, macrophyte-rich conditions into turbid states with abundant phytoplankton have taken place in many shallow lakes in China. However, little is know about the change of carbon fluxes in lakes during such processes. We conducted a case study in Lake Biandantang to investigate the change of carbon fluxes during such a regime shift. Dissolved aquatic carbon and gaseous carbon (methane (CH₄) and carbon dioxide (CO₂)) across air–water interface in three sites with different vegetation covers and compositions were studied and compared. CH₄ emissions from three sites were 0.62±0.36, 0.70±0.36, and 1.31±0.57 mg m⁻² h⁻¹, respectively. Correlation analysis showed that macrophytes, rather than phytoplankton, directly positively affected CH₄ emission. CO₂ fluxes of three sites in Lake Biandantang were significantly different, and the average values were 77.8±20.4, 52.2±14.1 and 3.6±26.8 mg m⁻² h⁻¹, respectively. There were an evident trend that the larger macrophyte biomass, the lower CO₂ emissions. Correlation analysis showed that in different sites, dominant plant controlled CO₂ flux across air–water interface. In a year cycle, the percents of gaseous carbon release from lake accounting for net primary production were significantly different (from 39.3% to 2.8%), indicating that with the decline of macrophytes and regime shift, the lake will be a larger carbon source to the atmosphere.     

长江口邻近水域浮游植物群落动态变化及其环境因子的研究

根据1998-2003年长江口邻近水域(30°-32°N,121°27′-122°30′E),丰水期和枯水期10个航次、20个点位的海洋监测结果,对浮游植物动态变化及其环境影响因子进行了研究。6年内共检出浮游植物238种,其中大部分为硅藻。研究结果表明,深水航道附近水域中,浮游植物种类、丰度和生物多样性均呈下降趋势。相反,航道内浮游植物总丰度呈直线上升(R=0.81,P<0.05)。对航道内12个环境因子做主成分分析,盐度、溶解氧、硅酸盐和浊度为主要环境主要因子。其中浊度和硅酸盐与浮游植物群落变化关系密切,是影响浮游植物群落动态变化的关键因子,并受深水航道工程影响。     

An individual-based analysis of the dynamics of two coexisting phytoplankton species in the mixed layer

In marine ecosystems ecological and environmental conditions continuously change, possibly supporting the wide range of phytoplankton species coexisting in aquatic environments. Phytoplankton communities are not homogeneously distributed in the water column due to the spatial and temporal variability of turbulent mixing and the concurrent biological response. In this paper an individual-based model (Lagrangian method) simulating the basic physiology of two coexisting phytoplankton species has been developed. The species, sharing the same availability of light and nutrient resource, are characterized by different photo-physiological parameters. The spatial and temporal evolution of turbulent mixing is simulated introducing vertical profiles of measured eddy diffusivity. Three case studies have been examined to analyze the role of environment–individual interactions in determining bloom conditions for both the selected species. The organisms experience recurrent fluctuations of light, temperature, and nutrient concentration gradients, due to the turbulent mixing in the water column, which have significant effects on the growth of the phytoplankton species. In all the numerical experiments, the temporal and spatial variability of different forcings do not support the prevalence of one species over the other over the time scale typical of a phytoplankton bloom.A well mixed water column favours the growth of both the populations while a variable mixing regime limits their growth reducing the photophysiological differences between the species.     

Phytoplankton patchiness and their role in the modelled productivity of a large, seasonally stratified lake

Phytoplankton concentration in Lake Kinneret (Israel) has varied up to 10-fold in space and time, with horizontal patches ranging from a couple of kilometres to a basin scale. Previous studies have used a 1D model to reproduce the temporal evolution of physical and biogeochemical variables in this lake. The question that arises then is how appropriate is a 1D approach to represent the dynamic of a spatially heterogeneous system, where there are non-linear dependencies between variables. Field data, a N-P-Z model coupled to both a 1D and a 3D hydrodynamic model, a 1D diffusion-reaction equation and scaling analysis are used to understand the role of spatial variability, expressed as phytoplankton patchiness, in the modelling of primary production. The analysis and results are used to investigate the effect of horizontal variability in the forcing and in the free mechanisms that affect the growth of patterns. The study shows that the use of averaged properties in a 1D approach may produce misleading results in the presence of localised patches, in terms of both concentration and composition of phytoplankton. The reason lies in the fact that the calibration process of ecological parameters in the 1D model appears to be site and process specific. That is, it depends on the pattern's characteristics and the underlying physical processes causing them. And this is a critical point for the success of numerical simulations under spatial variability. In this study, it is also shown that a length scale based on diffusion and growth rate of phytoplankton could be used as a criterion to assess the appropriateness of the 1D assumption.     

Role of specific microbial communities in the bioavailability of iron in Doñana National Park

The Doñana National Park contains highly complex microbial communities that play critical roles in the bioavailability and biogeochemical cycling of elements. In this study, we analyzed the formation of Fe-rich films on the surface of shallow waters at Doñana National Park as a model for future applications in bioremediation. Phytoplankton composition and abundance, physicochemical measurements, culture enrichments, and molecular detection of microorganisms were determined during this study. Natural samples were incubated in the laboratory and enrichments producing similar phenomena were obtained. Bacteria belonging to the genera Enterobacter were the major participants in surface Fe-film formation in laboratory enrichments. Film formation was dependent on wind exposure and only those sites protected from the direct influence of wind developed these films. A higher concentration of euglenophytes was found in the proximity of film-covered waters. Available iron (Fe²⁺) and total Fe concentrations were high (18.8 and 46.6 mg/L, respectively) underneath the surface film, and higher than in film-free waters and pore-sediment water. The concentration of phosphate and its availability were higher in the iron-rich film sediment, as 61% of total P was bound to iron oxy-hydroxides. Our results provide evidence of the link between P and Fe biogeochemical cycling in aquatic systems on sandy soils at the Doñana National Park. In addition, they provide significant insights into the bioavailability of these elements with potential interest in the role of microorganisms for metal sequestration in natural environments and utilization in bioremediation processes.     

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.     

连云港港区海洋环境质量状况

为分析连云港海洋环境质量,对连云港港区水质、沉积物及生物因子进行监测。结果表明,港区内某些点位水质中无机氮含量较高,达到污染程度,其余点位监测指标均正常,沉积物中的重金属尚未对该海域造成污染。浮游植物31种,其中甲藻门8种,硅藻门23种,浮游植物数量变动为1.84×104m-3~1.16×105m-3;底栖生物17种,多样性指数平均值为1.89。港区内水域环境时空变化表明,海水中锌含量连续大幅增加,其余指标均下降50%,沉积物重金属含量变化不大。     

地表水浮游植物叶绿素a测定方法比较研究

比较了浮游植物叶绿素a测定方法中的丙酮萃取法和热乙醇萃取法.结果表明,应用反复冻融植物细胞的丙酮萃取法对地表水中浮游植物叶绿素a的萃取率显著高于其他方法,且重复测定的精密度较高.     

蟒蛇河水域浮游植物调查与水生态评价

2012—2013年春(3月)、秋(9月)两季,从蟒蛇河上游大纵湖至下游新洋港大桥,共设置6个监测点位,调查浮游植物种类组成及群落结构,并利用群落结构指数等方法评价其水生态状况,结果表明:蟒蛇河水域共监测到浮游植物64种,以硅藻门、绿藻门和蓝藻门为主要门类;各监测点位浮游植物密度呈现秋季显著高于春季的季节性变化趋势;春、秋季节浮游植物优势种存在交叉演替的现象;蟒蛇河浮游植物多样性较好,指征水体污染程度为尚清洁;Shannon-wiener多样性指数、Margalef物种丰富度指数和Pielou均匀度指数数值均表现为春季高于秋季,且上、下游点位间差异不明显。