Assessment of the effects of a port expansion on algae appearance in a costal bay through mathematical modelling. Application to San Lorenzo Bay (North Spain)

In the last years several episodes of algae appearance affecting bathing areas have been observed in San Lorenzo Bay (north of Spain). The analysis of the collected algae revealed that they might come from near intertidal or shallow subtidal zones due to eutrophication processes or through drift algae movement by the action of marine currents. In the vicinity of this area, the expansion of the Port of Gijón (now under construction) supposes a significant modification of the coastal geometry. The magnitude of such an expansion could cause changes in the patterns of currents in the bay, with the consequent alteration of the observed algal appearance phenomena. A mathematical modelling study to evaluate the risk of generation of eutrophication processes in the San Lorenzo Bay area and the transport of drift algae from near sea bed areas was developed. This study required the use of different hydrodynamic models in order to characterize the currents caused by tides, winds and waves. The eutrophication processes in the bay were analyzed with a depth-averaged two-dimensional eutrophication model which deals with eight water quality variables. Calibration of model parameters with the observed data from a field survey was performed. A reasonable agreement with the field measurements was achieved. Model results showed that the maximum phytoplankton concentrations were below eutrophic conditions. Although, the port expansion has led to an increment of phytoplankton concentrations, chlorophyll a levels were not representative of eutrophic conditions. To analyse the transport of drift algae, a methodology based on the utilization of a two-dimensional model which solves the depth-averaged advection-diffusion equation considering seaweed as a conservative tracer was developed and applied. Numerical modelling allowed the identification of the coastal areas that seems to be the source of the seaweed found on the beach. It was also proven that port expansion does not significantly affect drift algae transport in the area.     

Predicting future effects from nutrient abatement and climate change on phosphorus concentrations in Lake Bourget, France

Like many temperate European lakes, Lake Bourget (France) has suffered from eutrophication during the second half of the last century. Due to a remarkable restoration program, the lake has been recovering for the past 25 years after a massive decrease in total phosphorus (TP) loading. TP concentrations have decreased from about 100-120 to 20-25 μg/L. Additional efforts are, however, still required to obtain a perennially sustainable good ecological status and model parameterisation of fluxes can assist in predicting future outcomes, especially in the context of global warming. In this paper, a dynamic model (MeroLakeMab) was developed and tested with the purpose to reconstruct the loading history of Lake Bourget and to predict TP concentrations during scenarios of increased temperature, decreased water runoff and decreased P loading. Simulations suggested that the historical TP loading decrease may have been as extensive as 88%. Decreases in water discharge to Lake Bourget at magnitudes forecasted by the Intergovernmental Panel on Climate Change (IPCC) would not affect TP concentrations notably, but marked concentration changes could, however, occur if decreases in runoff would have a strong impact on the TP loading. Increasing temperature effects on yearly mean TP concentrations in the water column would be very small compared to effects from changes in the TP loading. Predictions such as these could be instrumental for future successful lake management.     

The Role of Macrophytes in the Retention of Phosphorus in the River Thame,England

The effects of the growth of the dominant species of macrophytes on phosphorus transport in the River Thame, a nutrient enriched lowland clay catchment in southern England, were assessed using a mass-balance approach. Macrophyte abundance was estimated between late March and early June at three sites along the river. the plant biomass of phosphorus and the total phosphorus content of sediments in the main part of the river channel and sediments associated with the plant roots were measured on each occasion. Total phosphorus concentrations in the river water were measured at weekly intervals at a gauging station at the lower end of the study reach.

The results showed that the phosphorus content of plants at the site most impacted by sewage derived phosphorus was < 1% of the flux of total phosphorus estimated for the water column in April and May. Phosphorus contained in the total standing crop of macrophytes at the least impacted site was estimated as approximately 3% of the mean daily flux of total phosphorus in the water. Although no trends were found in the total phosphorus contents of the roots, shoots or sediments through the season, differences in the phosphorus content of the sediments were found between sites with different phosphorus loading. Higher porewater and Equilibrium Phosphate Concentrations (EPC_oS) were recorded at the site most impacted by sewage effluent when compared to an upstream sampling site.     

Eutrophication Phenomenon with Special Reference to the Kasštela Bay

Abstract

The paper discusses the eutrophication phenomenon as a result of pollution from land-based sources with special reference to the experience gained in the Kas?tela Bay Project.

The Bay of Kas?tela is a semi-enclosed bay of a total volume of 1.4 km³. It receives a great amount of untreated waste water, both domestic and industrial.

Results of the analyses of long-term data series of dissolved oxygen, nutrients, transparency and phytoplankton have shown a continuous increase of eutrophication in the Bay. While the concentration of oxygen in the euphotic layer increases due to a higher phytoplankton productivity, in the bottom layer it decreases as a result of the activity of heterotrophic bacteria. the nitrogen/phosphorus ratio in sea water has decreased, and today is much lower than in the open sea. From the Secchi-disc data it is clear that transparency has also decreased for the last three decades. Primary production as well as phytoplankton biomass has also increased. the structure of phytoplankton community has been changed and dinoflagellate species have become dominant rather than diatoms.     

安徽淮北矿区地表水氮的富营养化特征及来源解析

为探索淮北临涣矿区地表水体中氮的分布和来源,采集研究区河流和沉陷积水区样品,测试分析其水化学指标和氮、氧同位素特征值,并采用IsoSource模型计算不同端源氮的污染贡献率。结果表明:研究区地表水处于中度富营养化状态,矿区地表水中氮的输入源受含氮肥料、土壤有机氮和粪肥污水共同影响,所发生的硝化及反硝化作用微弱;矿区河水中氮的主要输入源为粪肥污水,贡献率达66.6%,沉陷积水区氮主要受含氮肥料输入的影响,贡献率达52.0%。     

Using Ecological Risk Assessment to Identify the Major Anthropogenic Stressor in the Waquoit Bay Watershed,Cape Cod,Massachusetts

The Waquoit Bay Watershed ecological risk assessment was performed by an interdisciplinary and interagency workgroup. This paper focuses on the steps taken to formulate the analysis plan for this watershed assessment. The workgroup initially conducted a series of meetings with the general public and local and state managers to determine environmental management objectives for the watershed. The workgroup then decided that more information was needed on the impacts of six stressors: nutrient enrichment, physical alteration of habitat, altered freshwater flow, toxic chemicals, pathogens, and fisheries harvesting. Assessment endpoints were selected to establish the link between environmental management objectives, impacts of stressors, and scientifically measurable endpoints. The following assessment endpoints were selected: estuarine eelgrass cover, scallop abundance, finfish diversity and abundance, wetland bird distribution and abundance, piping plover distribution and abundance, tissue contaminant levels, and brook trout distribution and abundance in streams. A conceptual model was developed to show the pathways between human activities, stressors, and ecological effects. The workgroup analyzed comparative risks, by first ranking stressors in terms of their potential risk to biotic resources in the watershed. Then stressors were evaluated by considering the components of stressors (e.g., the stressor chemical pollution included both heavy metals and chlorinated solvents components) in terms of intensity and extensiveness. The workgroup identified nutrient enrichment as the major stressor. Nutrient enrichment comprised both phosphorus enrichment in freshwater ponds and nitrogen enrichment within estuaries. Because phosphorus impacts were being analyzed and mitigated by the Air Force Center for Environmental Excellence, this assessment focused on nitrogen. The process followed to identify the predominant stressor and focus the analyses on nitrogen impacts on eelgrass and scallops will serve as an example of how to increase the use of the findings of a watershed assessment in decision making.     

Usefulness of natural regions for lake management: Analysis of variation among lakes in northwestern Wisconsin,USA

A map of summer total phosphorus in lakes was compiled recently for a three-state area of the upper Midwest for purposes of identifying regional patterns of total phosphorus in lakes and attainable lake trophic state. Spatial patterns in total phosphorus from approximately 3000 lakes were studied in conjunction with maps of geographic characteristics that tend to affect phosphorus balance in lakes to identify regions of similarity in phosphorus concentrations in lakes or similarity in the mosaic of values as compared to adjacent areas. While degrees of relative homogeneity are apparent at many scales, the map was designed at a scale that would yield regions with sufficient homogeneity to be useful for lake management throughout the area. In this study, data from 210 lakes in a 1560-mi² area in northwestern Wisconsin, sampled by the Wisconsin Department of Natural Resources in the spring of 1988 (subsequent to the compilation of the phosphorus map), were examined to: (1) substantiate the existence of the regions depicted on the map in northwest Wisconsin, (2) determine the nature and relative precision of the regional boundaries, (3) determine the relative importance of natural and anthropogenic watershed characteristics, lake types, lake area, and lake depth in explaining within-region differences in lake phosphorus, and (4) demonstrate how the regions might be used by local lake managers.     

Geochemical stability of phosphorus solids below septic system infiltration beds

Review of 10 mature septic system plumes in Ontario, revealed that phosphorus (P) attenuation commonly occurred close to the infiltration pipes, resulting in discrete narrow intervals enriched in P by a factor of 2-4 (. MSc thesis, Dept. Earth Sci., University of Waterloo, Waterloo, Ont.; Ground Water 36 (1995) 1000; J. Contam. Hydrol. 33 (1998) 405). Although these attenuation reactions appeared to be sustainable under present conditions, the potential for remobilization of this P mass, should geochemical conditions change, is unknown. To test the stability of these P solids, dynamic flow column tests were carried out using sediments from three of the previously studied sites (Cambridge, Langton and Muskoka) focusing on sediments from the 'High-P' and underlying (Below) zones. Tests were continued for 166-266 pore volumes (PVs), during which time varying degrees of water saturation were maintained. During saturated flow conditions, relatively high concentrations of PO4 were eluted from the Cambridge and Langton High-P zones (up to 4 and 9 mg/l P, respectively), accompanied by elevated concentrations of Fe (up to 1.4 mg/l) and Mn (up to 4 mg/l) and lower values of Eh (<150 mV). The Below zones from Cambridge and Langton, however, maintained lower concentrations of P (generally<2 mg/l), Fe (<0.2 mg/l) and Mn (<1 mg/l) and maintained higher Eh (>250 mV) during saturated flow conditions. During unsaturated flow, P and Fe declined dramatically in the High-P zones (P<1 mg/l, Fe<0.2 mg/l), whereas concentrations remained about the same during saturated and unsaturated flow in the Below zones. This behavior is at least partly attributed to the development of reducing conditions during saturated flow in the High-P zones, leading to reductive dissolution of Fe (III)-P solids present in the sediments. Reducing conditions did not develop in the Below zones apparently because of lower sediment organic carbon (OC) contents (0.03-0.04 wt.%) compared to the High-P zones (0.2-0.65 wt.%). At the Muskoka site, where the sediments were noncalcareous, low values of P (<0.2 mg/l) were maintained in both the High-P and Below columns and reducing conditions did not develop. Results indicate the possibility of remobilizing P accumulated below septic system infiltration beds should conditions become more reducing. This could occur if sewage loading patterns change, for example when a seasonal use, lakeshore cottage is converted to a permanent dwelling.     

盐城市区饮用水源富营养化趋势研究

运用综合营养指数法对盐城市区饮用水源地水质的富营养化趋势进行了评价,针对饮用水污染状况提出了防治意见和建议。     

湖泊水体中营养盐控制技术研究进展

营养盐物质是造成湖泊水体富营养化的关键因素,在对湖泊水体营养盐控制技术探讨过程中,分析了营养盐的来源形式,从物理、化学、生物生态学角度分别对营养盐的控制技术进行了论述和思考,并指出了今后湖泊水体中营养盐控制技术发展方向。