Development of a spatially resolved linked hydrodynamic and exposure model (LOTOX2) for PCBs in Lake Ontario

A linked hydrodynamic–hydrophobic organic chemical mass balance and food chain bioaccumulation model, LOTOX2, was developed to support the Lake Ontario Lakewide Management Plan (LaMP) for establishing contaminant load reduction strategies. This paper describes the development of LOTOX2, including the linkage with a relatively finer-scale hydrodynamic model (the Princeton Ocean Model, POM). An important component of this development was the reconstruction of PCB loading history (1930–2005), which was used to understand historic trends and to conduct model calibration/confirmation for total PCBs (tPCBs) in the lake water, sediments, and adult lake trout using data for the last 25 years. A separate mass balance was conducted for the radioisotope cesium-137 (¹³⁷Cs) in order to develop a sorbent mass balance model for the system. Following calibration and confirmation, a diagnostic application of the model showed that the lake is not yet at steady-state with current loads. It will take more than 50 years for tPCB concentration in lake trout to decrease to a steady-state value of about 0.4 ppm if year 2005 loads remain constant. If all external loads were instantaneously eliminated in 2005, it would take approximately 40 years for the adult lake trout tPCB concentration to reach 0.05 ppm (the uniform Great Lakes protocol value for unrestricted consumption) from its current level of 0.74 ppm.     

长荡湖、滆湖、竺山湾藻类功能群结构组成与环境因子的关系

为研究太湖流域上游长荡湖、滆湖、竺山湾三大典型浅水湖泊藻类功能群结构组成与环境因子的关系,基于2019年2月至2020年10月水文、水质及浮游植物数据,采用Q指数、香农-维纳多样性指数、TLI综合富营养化指数分析了3个湖泊的水质状况,采用非度量多维尺度变换(NMDS)分析了浮游植物群落结构组成特征,采用冗余分析探讨了浮游植物功能群与环境因子的关系。结果表明：长荡湖和滆湖水质整体属于轻度富营养化,竺山湾除冬季外,均属于中度富营养化;长荡湖、滆湖、竺山湾分别有浮游植物7门61属96种、8门75属129种和6门53属124种,分别划分为9、10和11个优势功能群;3个湖泊藻类功能群变化的共同环境因子是水温、高锰酸盐指数和总磷,而总氮和氮磷比对3个湖泊功能群结构变化的作用并不明显。     

Pesticide residues in Volta Lake, Ghana

The Volta River basin comprises ≈ 70% of mainland Ghana, being inhabited by a majority of the country's population. The purpose of this study was to analyse water and sediment samples at six locations in Volta Lake for residues of persistent organochlorine pesticides. Residues were extracted by use of two types of extractions, including a standardized solid phase extraction procedure for water samples and a Soxhlet extraction procedure for sediment samples. All samples were analysed by gas chromatography. Lindane and endosulfan were identified in concentrations ≤ 0.008 p.p.b. and 0.036 p.p.b., respectively, in water, and ≤ 2.3 p.p.b. and 0.36 p.p.b., respectively, in sediments. Dichlorodiphenyltrichloroethane and dichlorodiphenyldichloroethylene were also found in sediment samples (in concentrations ≤ 9.0 p.p.b. and 52.3 p.p.b., respectively). No significant contamination was noted in the lake. The distribution of pesticide residues in water and neighbouring sediment are briefly discussed. Different bioconcentration factors obtained in this study allowed the confirmation of the complex processes already reported in the literature regarding the partitioning of chemicals between sediment and water.     

Modeling the impacts of climate change on the thermal and oxygen dynamics of Lake Volta

Climatic changes influence the thermal and oxygen dynamics of a lake and thus its ecological functioning. The impacts of climatic changes on tropical lakes are so far poorly studied and the extent of the effects is therefore uncertain, most investigations describing only potential effects. In this study, we applied the one-dimensional lake ecosystem model GOTM-ERGOM to quantify the effects of climate change on thermal stratification, oxygen dynamics, and primary production in meso-oligotrophic Lake Volta. GOTM-ERGOM was calibrated and validated using two years of observed data. The validated model was used to evaluate a series of future climate change scenarios. The model simulations showed good agreement with observed water temperature, dissolved oxygen and chlorophyll-a and indicated intensified stratification and reduced oxygen levels in the productive water layers of the lake. However, the longer-lasting stratification (prolonged stability) did not translate into permanent stratification. A relatively small (1?m) upward shift of thermocline depth resulted in an 8%–12% volume loss of the oxygen-rich upper mixed layer, which may be significant for the fisheries of the lake as it diminishes the size of suitable fish habitats. Light limitation of primary production renders the lake somewhat resilient to intensive algae blooms, as traceable in both the present and in the future climate scenarios. In the long term, the ongoing climate change may affect riparian communities that depend on the lake's fisheries for their livelihood. In consequence, future lake management strategies for implementation need to account for the impacts of future climate change.     

Quantification of internal phosphorus load in large,partially polymictic and mesotrophic Lake Simcoe,Ontario

Hypoxia and cyanobacteria still occur occasionally in large, mesotrophic Lake Simcoe, and total phosphorus (TP) concentration has remained relatively constant despite external nutrient load reduction. This may indicate a potential internal P source. Internal load as redox-dependent P release from bottom sediments is hard to determine in such a relatively shallow and mostly mixed lake. This study represents the first attempt to quantify internal P loading over many years for the three main sections of Lake Simcoe. Internal load was determined (a) as in situ estimate based on TP increases between July and October and (b) as gross estimate from the product of experimentally determined P release rates and hypoxic extent of sediment surfaces in space and time. Hypoxic extent was quantified (1) as the hypoxic factor determined from dissolved oxygen profiles below the level of 3.5 mg/L, and (2) as active sediment area release factor (AA) modeled from summer euphotic TP concentration, which is especially useful in the mixed sections. Annual internal load for the whole lake was determined as a near constant 62.2 metric tonnes/yr (86 mg/m²/yr) for 1980–2011 using the gross estimates of the AA approach and 88 t/yr before and 53 t/yr after external load abatement and zebra mussel invasion using in situ estimates. Means of in situ and AA-based estimates for 2000–2011 are in close agreement except for polymictic Cook's Bay. These estimates are 45 to 89% of external load, which suggests that internal loading is an important source of P in Lake Simcoe.     

松花湖富营养化评价及防治措施

采用修正的卡森状态指数法进行松花湖水体富营养化评价,评价结果表明红石水库水质最好,白山水库次之,松花湖水质综合评价最差。由于辉发河带入的污染物较多,造成松花湖水质上游次于下游,越到下游水质越好,丰满水库的水质最优。全流域的富营养化指数为45.64,根据本研究选择的湖泊富营养状态分级标准,松花湖流域的富营养化总体处于中营养阶段,辉发河河口富营养程度最高,已达到轻度富营养化程度。     

淀山湖富营养化现状及生态修复措施分析

根据2008—2010年淀山湖水质监测数据,评价该湖富营养化趋势。结果显示,2008年后,淀山湖的富营养化程度呈改善趋势,但水体富营养化存在区域差异。主要表现在:①2008—2010年的整个湖区水体中主要的富营养化指标TN、TP、SS、Ch-la质量浓度均呈下降趋势;②淀山湖上游来水区水体中TN、TP质量浓度比下游出水区高,综合营养状态指数同样也高;③淀山湖每年夏季暴发蓝藻水华的水域面积在不断减小。结果表明,淀山湖东南区域富营养化程度最轻,水生植物对水体净化、生态系统恢复具有重要价值;淀山湖的生态系统在逐步恢复。为使生态系统能巩固并形成良性循环,一些影响因素亟待解决。     

阳宗海叶绿素a、磷、氮动态特征及富营养化趋势

分析2002-2012年阳宗海TN、TP、Chl-a、氮磷比的动态变化特征及相互关系,并用综合营养状态指数法评价阳宗海的富营养化状态。结果表明：阳宗海富营养化呈上升趋势,2007年从之前的贫营养级上升为中营养级;Chl-a、TN、TP浓度在2007年后均呈快速上升趋势。 Chl-a浓度与TN、TP浓度呈正相关,且氮磷比越接近阈值16∶1,Chl-a浓度上升就越快。指出若营养盐输入得不到有效控制,预测阳宗海将在2017年前后达到富营养级水平,水质将进一步下降。     

梦湖水资源平衡分析

采用参证站连续水文资料,对无资料地区梦湖水资源进行平衡分析。为开发梦湖风景区,充分发挥梦湖在抚州市美化环境的作用,提高梦湖水资源的保证率提出了建议:湖区应进行防渗处理,雨、污分流,避免污水进入湖区等。     

兴凯湖生态水位分析

基于兴凯湖1914~1957年水位过程线和水位-面积-库容曲线,通过计算兴凯湖多年平均和80%保证率水平年的来水量,并结合近期和远期需水量,进行水量平衡分析。结果表明,兴凯湖具有较大的调节功能,即使连续6年出现历史上水位从多年平均水位下降至历史最低水位,兴凯湖也能满足近期和远期水量需求。经分析、计算和推理,认为以1925年兴凯湖水位67.88 m为最低生态水位是合适的。     

石亭江底栖动物群落结构季节变化与生态评价

汶川地震后石亭江山前河段冲刷严重;对河流生态产生重要影响;然而目前尚缺乏对山前冲刷河段的定量生态评价。选取石亭江、绵远河和游江为研究对象;根据 2021 年秋季（10 月）和 2022 年夏季（7 月）采集的大型无脊椎底栖动物样本与环境观测数据;分析了石亭江底栖动物群落结构、多样性、功能摄食类群和功能习性类群的季节变化特点。结果表明:石亭江秋季共采集底栖动物 54 种;隶属 4 门 6 纲 35 科;夏季共采集到底栖动物 33 种;隶属 1 门 1 纲 18 科;其中牧食收集者为优势程度最大的功能摄食类群;捕食者的优势程度最小;秋季固着型生物的优势程度最大;夏季蔓生型生物的优势程度最大;攀爬型生物的优势程度在秋季和夏季均为最小。基于底栖动物完整性评价的多参数（MMI）指数;将 3 条河流栖息地斑块的生态质量划分为极差、差、中等、良好和极好 5 个等级。结果显示:3 条河流栖息地斑块生态质量整体为良好;局部为中等;绵远河与湔江的栖息地斑块生态质量整体高于石亭江;秋季石亭江栖息地斑块的生态质量好于夏季。     

Structure and Ordination of Epiphytic Invertebrate Communities of Four Coastal Wetlands in Green Bay,Lake Michigan

Epiphytic macroinvertebrate communities of four coastal wetlands of Green Bay, Lake Michigan were compared by taxonomic composition, feeding group composition, and environmental influences using Bray-Curtis ordination. Ordination scores from the most sheltered oligotrophic site, Portage Marsh, were distinct from the eutrophic, exposed sites located in middle and lower Green Bay— Seagull Bar, Little Tail Point, and Dead Horse Bay. Epiphyton chlorophyll a, phytoplankton chlorophyll a, and specific conductance strongly correlated to the ordination axes, indicating the trophic gradient within Green Bay was a primary environmental influence. The feeding group compositions at the sites were consistent with the type and abundance of food available. Portage Marsh is a scraper-shredder system, with macroinvertebrates feeding mainly on epiphyton and coarse particulate detritus. Dead Horse Bay and Little Tail Point are collector systems, sustained by phytoplankton and fine particulate organic matter. Seagull Bar is intermediate in trophic position along the ordination axes, but more closely resemble the latter two sites. The type and abundance of food resources available to these invertebrate communities are influenced by wave exposure, light attenuation, nutrient levels, and algae levels of the littoral and pelagial waters. Macroinvertebrate communities were sensitive to shifts in food resources, which generated shifts in trophic structure.