Biotic Ligand Model estimation of copper bioavailability and toxicity in the Yacyretá Reservoir on the Paraná River

The Biotic Ligand Model (BLM) was used to assess copper bioavailability, toxicity and water-effect ratios (WER) for the Yacyretá Reservoir on the Paraná River. Copper in the Yacyretá Reservoir watershed is ubiquitous (median dissolved concentration = 4.4 µg L⁻¹), being contributed mainly by non-point surface run-off from citrus fields and urban sewage point sources. BLM simulations indicated that copper bioavailability is negligible, as almost 100% of the dissolved copper is complexed by dissolved organic carbon (DOC). Copper bioavailability in the Paraná River, which has a mean hardness concentration of 16.5 mg CaCO₃ L⁻¹, is controlled by the presence of humic substances (≈60% of humic acids) in DOC. BLM estimates of acute toxicity for a cyprinid fish species were of the same order of magnitude as those corresponding to daphnids (EC₅₀ = 63.54 µg L⁻¹). However, zooplankton species were chosen to represent the aquatic biota for water quality regulatory purposes because of their slightly higher sensitivity to copper toxicity. Based on the corresponding minimum WER (14.6) for copper in Yacyretá Reservoir on the Paraná River, a site-specific copper criterion for the protection of the aquatic biota of 24 µg L⁻¹ was derived. All measured dissolved copper concentrations for Yacyretá Reservoir during the 2001–2002 period were in compliance with this criterion. Development and application of the BLM provides a useful tool for managing metal loads in reservoir environments.     

基于四种水体指数的艾比湖水面提取及时空变化分析

以Landsat5/7/8系列遥感影像为数据源,利用归一化差异水体指数(Normalized difference water index,NDWI)、改进的归一化差异水体指数(Modified normalized difference water index,MNDWI)、自动水体指数(Automated water extraction index,AWEI)、改进的自动水体指数(Modified automated water extraction index,MAWEI )提取艾比湖水体,建立混淆矩阵对4种水体指数提取结果进行对比分析,利用精度最高指数提取艾比湖面积并通过动态度分析湖泊面积变化趋势,同时对艾比湖面积变化的驱动因素进行分析。结果表明:MAWEI指数精度最高,精度达到95%以上,Kappa系数＞0.94。2000—2003年期间,艾比湖面积从768.93 km²增加至982.27 km²,湖泊面积增加27.74％、动态度为9.24％;2003—2014年期间,湖泊面积减至447.08 km²,湖泊面积缩减54.48％、动态度为-4.95％;2014—2018年期间,湖泊面积再次增加至852.77 km²,湖泊面积增加90.74%、动态度为22.68％;2018-2020年湖泊面积减至593.79 km²,湖泊面积缩减30.36％、动态度为-15.18％,总的来说近20 a艾比湖面积变化呈现先扩张再退缩的趋势。湖泊面积变化与年均降水量呈正相关,与蒸发量呈负相关,与博尔塔拉河和精河径流量呈正相关。水资源的减少及其周围人口、灌溉面积及生产值持续增长引起经济社会总用水量的激增,对湖泊面积变化产生一定的影响。研究成果对艾比湖生态环境保护有一定参考意义。     

Phytoplankton primary production, chlorophyll-a and nutrient concentrations in the water column of mountainous Lake Phewa, Nepal

The seasonal patterns of phytoplankton primary production, chlorophyll‐a concentration, cell number and several other limnological variables in Lake Phewa, located in the active monsoon zone in Central Himalaya, Nepal, were studied for a year beginning in April 2001. During the study period, the gross primary production and chlorophyll‐a concentrations were relatively low during the monsoon season. The phytoplankton cell number, represented by 24 genera, also fluctuated seasonally, but tended to increase in the pre‐ and post‐monsoon period. These results suggest that the monsoon plays a crucial role in the primary production and phytoplankton dynamics for Lake Phewa. Among the phytoplankton species, Microcystis aeruginosa, a representative species for eutrophic lakes, was the dominant phytoplankton. At the same time, however, it is clear that the lake is not yet heavily eutrophic. The present study suggests that the exchange of lake water during the monsoon season contributes to maintaining the health of the lake against further degradation. Nevertheless, the silt carried in the monsoon rain run‐off from the lake's catchment area suggests increasingly serious degradation problems for this small mountainous lake.     

Trace metal concentration in water and sediments of satellite lakes within Lake Victoria (Kenya) basin

Lakes Kanyaboli, Sare and Namboyo are three important freshwater satellite lakes in the northern region of the Lake Victoria (Kenya) basin. Lake Simbi, a small alkaline -saline crater-lake is located near the southern shoreline of the Nyanza Gulf of Lake Victoria. The three freshwater lakes provide unique aquatic habitats for the important indigenous fish species and other aquatic biodiversity, as well as serving as water resources for the surrounding communities. Surface and sediment samples were collected and examined to characterize these lake systems. Metal partitioning among the various defined geochemical phases also was determined. Based on the measured concentrations, the satellite lake waters are relatively uncontaminated with regard to Al (aluminium), manganese (Mn), zinc (Zn), copper (Cu) and chromium (Cr). Levels of most elements were below detection limits, as well as being well below the desirable drinking water guideline values proposed by the World Health Organization. The exception was the elevated iron (Fe) contents (>300 μg L⁻¹). The sediments exhibited a relatively low level of contamination with regard to heavy metals. The mean values of the measured metals in the sediments were compared to levels in adjacent Lake Victoria. The study results from these poorly-studied, and relatively unperturbed ecosystems, compared to the main body of lake Victoria, highlight their importance as conservation areas, despite the small-scale fishery activity, potential threats from human activities and their sensitivity to fluctuating environmental conditions.     

Assessment of element distribution and heavy metal contamination in Chilika Lake sediments (India)

Chilika Lake is situated on the Indian east coast. It is one of the largest lagoons in the world, with a unique assemblage of marine, brackish water and freshwater species. Due to the opening of new connections to the sea in the years 2000 and 2008, an environmental change is expected in the lagoon. The study gives an assessment of sediment contamination by heavy metals on the verge of this change (sampling campaign in 2000). Sediment samples from two surface levels (0–5 and 30–35 cm), and from depth profiles, were analysed for mineralogical composition, main and trace element concentrations, and element bonding forms. Background concentrations from a depth profile were also examined. The profile spans a time of ≈13 500 years. Age determinations by radiocarbon dating and the ¹³⁷Cs- and ²¹⁰Pb-method were carried out. The composition of the surface sediments is generally uniform. The heavy metals exhibit slightly decreasing concentrations from NE to SW, thus indicating the supply of contaminants from the Mahanadi River. The anthropogenic portion of the heavy metal supply is mainly bound to Fe-oxide-hydroxides. Phosphorus is enriched in the sediments of the southern lake sector. Changes in element concentrations in the last 13 500 years have occurred mainly in two steps. The long-term variations exceed the anthropogenic changes caused by the Mahanadi River inputs. The very sensitive response of coastal area fabrics on climate changes also causes fast geogenic changes in element concentrations in sediments (similar grain sizes). This prevents the use of element concentrations from deep sediment horizons to define contaminations in those areas.     

Bacterial abundance on the skin,gills and intestines of Cyprinus carpio in Lake Naivasha,Kenya: Implications for public health and fish quality

Cyprinus carpio is the most important fish species in the Lake Naivasha fishery, comprising 51% of the total catch in the lake. Microflora, especially enteric bacteria of human or animal origin, are the causative agent for fish contamination and spoilage. Poor sanitation standards and poor sewage treatment and disposal methods within Lake Naivasha and its catchment pose a great threat for degrading the quality of C. carpio. The potential impact is rejection of the fish in the local, regional and international markets, risking the collapse of the Lake Naivasha fishery. This study determined the bacterial quality of water and C. carpio from three different sites within Lake Naivasha, namely Malewa River mouth, sewage discharge point and a mid‐lake site, based on plate count techniques. Physicochemical parameters characterizing the lake water also were also measured in situ. This study results indicated that both the fish and water in Lake Naivasha exhibited poor bacterial quality. All the physicochemical parameters were within the recommended range for fish culture, although they also were conducive to the proliferation of bacteria. Most of the sampling sites exhibited significant spatial variation in their bacterial abundance (P < 0.05). The sewage discharge sampling site exhibited the highest mean density values for bacterial densities and clearly degrade the quality of the fish in the lake. Proper sewage treatment, and the installation of modern sanitation facilities, is recommended to improve the bacterial quality of the fish.     

Characteristics of the delta formation resulting from sediment deposition in Lake Nasser, Egypt: Approach to tracing lake delta formation

A major problem encountered by managers of large reservoirs, such as Lake Nasser (located in the south of Egypt), is the continuous deposition of sediments, resulting in a bed-level increase, a decrease in lake capacity, and the creation of a new delta that might eventually hinder navigation. To investigate the sedimentation problem in Lake Nasser, a series of surveyed cross-sections were reviewed and samples of suspended sediment and bed material collected. These sets of data were analysed to investigate the progress of the delta formation, the change in its properties in all directions and the corresponding patterns of suspended and deposited sediment particles. Results showed that deposited sediments, characterized by a variable pattern of particle composition, are building up at the lake entrance. Although the expansion of the delta is multidirectional, its accelerated advance towards the High Aswan Dam would depend on the frequent occurrence of high floods following extended drought periods. Based on the calculated deposited sediment volume in Lake Nasser during the period 1964–1998, the lifetime of the dead storage zone allocated for sediment deposition (31 × 10⁹ m³) is estimated at a minimum of 310 years.     

Restoration of hypolimnetic dissolved oxygen through light irradiation-induced periphyton production

Large quantities of detritus can accumulate on the bottom sediments of eutrophic lakes, leading to depletion of dissolved oxygen (DO) in the hypolimnion. Decreased redox potential associated with low hypolimnetic DO concentrations can accelerate the remobilization of ammonia and phosphorus from the sediments back into the water column. As maintenance of aerobic conditions in the hypolimnion is an important consideration for successful lake management, this research focused on the use of periphyton production of DO to control hypolimnetic DO levels. To augment periphyton photosynthesis, light was irradiated to the bottom sediments via glass fibres, in order to examine the effects of light irradiation on DO restoration on bottom sediments in test chambers. Dissolved oxygen restoration by periphytic photosynthesis was confirmed in these experiments, with both temperature and light intensity having positive effects on the areal net oxygen production rate. The Q ₁₀ temperature coefficient for net oxygen production was estimated to be 2.24. In typical temperate-zone lakes, the hypolimnetic water temperature is <15 °C, resulting in an expected areal net oxygen production rate ranging from 100 to 200 mg O₂ m⁻² day⁻¹ at a light irradiation of 50 μE m⁻² s⁻¹. Based on these experimental results, the condenser area required to achieve DO restoration under hypolimnetic light irradiation alone was estimated to be 3.2–4.1% of the hypolimnetic area. Thus, hypolimnetic light irradiation combined with hypolimnetic aeration can reduce energy consumption required for hypolimnetic aeration in DO restoration efforts.     

Lake whitefish (Coregonus clupeaformis) energy and nutrient partitioning in lakes Michigan,Erie and Superior

A concurrent decrease in lake whitefish (Coregonus clupeaformis) condition and Diporeia spp. abundance in Lake Michigan has spurred investigations into possible links between the two phenomena. We examined female lake whitefish δ¹³C and δ¹⁵N stable isotopes, growth, reproductive investment, dorsal muscle total lipid and docosahexaenoic acid (DHA) contents from lakes Erie, Michigan and Superior to determine whether differences in food source were correlated with measures of stock success. Stocks with higher somatic growth rates and mean reproductive potential had higher energy stores in terms of percent total lipid. Stocks with low muscle lipid concentration also had smaller egg sizes as egg number increased. Diet varied among stocks as evidenced by δ¹³C and δ¹⁵N stable isotope analyses; however, muscle total lipid and DHA were not correlated to apparent Diporeia spp. prey use. When compared to stocks from lakes Erie and Superior, Lake Michigan stocks had lower growth, reproduction, and lipid stores. While stocks in Lake Michigan with access to declining Diporeia spp. populations may still feed on the amphipod, it appears that they are unable to consume the quantities necessary to maintain historical growth and reproduction. Stable isotope analyses of lakes Erie and Superior stocks, with higher growth rates and lipid values, indicated different feeding strategies with no indication of reliance on Diporeia spp. While differences in prey resources may have an effect on lake whitefish stocks, differences in Diporeia spp. abundance alone cannot explain differences in lake whitefish condition observed among the Great Lakes included in this study.     

Sediment phosphorus characteristics in the clearwater state of Lake Mogan, Turkey

This study examined the vertical distributions of total phosphorus (TP) and phosphorus fractions, and the iron and organic matter, in the littoral sediment in a macrophyte‐dominated, clearwater state in Lake Mogan between September 2005 and August 2006. Benthic macroinvertebrates and total bacteria in the sediment also were determined. No clear seasonal or depth‐related (0–20 cm) patterns were found in sediment concentrations for the measured parameters. The phosphorus release was quantitatively very low, and a negative phosphorus release (–0.132 µg m^?2 day^?1) was measured during the summer months. The TP concentrations of the sediment samples ranged between 675.00 and 1463.80 µg g^?1 dry weight (DW), and the trophic level of the lake was eutrophic. On average, inorganic phosphorus fractions comprised the largest fraction (63%), while organic‐bound phosphorus (Org ≈ P) constituted 37% of the TP in Lake Mogan. The most important phosphorus‐immobilizing factors are high iron content (14 200–47 750 µg g^?1 DW), the sediment's clay content (47.80–51.80%), and an abundance of macrophytes at the sampling station. The low abundance of benthic macroinvertebrates (510–850 individuals m^?2), which depend on sediments with high iron and low organic matter (5.42–13.30%), played a role in the sediment phosphorus retention. Although bacterial abundance in the surficial sediment appeared to be positively correlated to temperature, the overlying water did not experience anoxic conditions, supporting a state in which bacteria were able to retain phosphorus in their cell structures. Long‐term changes in the sediments of Lake Mogan must be monitored lake. In order to optimize the management of the lake, and to determine the longevity of a clearwater state following management measures and continued external phosphorus loading, long‐term changes in the sediments of Lake Morgan must be monitored.     

Resting cladoceran eggs and their contribution to zooplankton diversity in a lagoon of the Upper Paraná River floodplain

Zooplankton produce resting eggs and diapause stages as strategies to promote their survival during periods of adverse environmental conditions, thereby ensuring the community diversity. The goal of this study is to investigate the contribution of these eggs, which were present in the sediment of an isolated lagoon in the Upper Paraná River floodplain, to cladoceran diversity. The species hatching from the resting eggs in the sediment do not occur in the plankton. Sediment samples were collected at six sampling sites in the Osmar Lagoon banks, in September 2004 and June, July, August and September 2005. Zooplankton were sampled in the pelagic region, using a motorized pump (1000 L) and plankton net (68 µm). The pH, water temperature (°C), electrical conductivity (µS cm⁻¹) and dissolved oxygen concentration (mg L⁻¹) also were measured. The resting eggs were counted in the laboratory, being maintained under constant temperature and photoperiod until their analyses. The resting eggs were examined daily until hatching. A higher abundance of these eggs was observed in July, during a period of lower temperature and electrical conductivity, and higher pH and dissolved oxygen concentrations. ANOVA results indicated significant differences in resting egg abundance among the sampling months. Ceriodaphnia reticulata, Macrothrix spinosa, Ilyocryptus spinifer, Ephemeroporus tridentatus and Diaphanosoma sp. hatched from the resting eggs, although they were not observed in the plankton samples. C. reticulata was observed for the first time in this floodplain, with these study results corroborating the hypothesis that resting cladoceran eggs do contribute to zooplankton diversity in the lagoon.     

Phosphorus,Nitrogen, and Silica as Controls on Phytoplankton Biomass and Species Composition in Lake Champlain (USA-Canada)

The long-standing assumption that the phytoplankton in Lake Champlain are phosphorus limited was tested through measurement of physiological indicators of phosphorus status (alkaline phosphatase activity and orthophosphate turnover time) and enrichment experiments conducted four times during the growth season. Phosphorus addition to experimental carboys incubated 4–5 days in situ substantially increased phytoplankton biomass relative to controls in June, but had only a mild impact in July and September, and no effect in May. Nitrogen addition augmented biomass in one of four experiments (in June), while silica had no impact at any time. In summer and fall, addition of N and P in combination always yielded more phytoplankton biomass than singular P addition. In spring, even combined addition of N, P, and Si failed to stimulate phytoplankton growth. The phytoplankton groups responding to fertilization were largely the same as those that flourished in controls (diatoms and green algae), suggesting that enclosure was a more powerful determinant of species composition than nutrient inputs. Orthophosphate turnover times and levels of alkaline phosphatase activity in the lake indicated spatial and temporal variability in phytoplantkon P status, with P sufficiency as common as P deficiency. We conclude that multiple interacting factors influence the abundance and species composition of phytoplankton in Lake Champlain. In spring, phytoplankton growth is not limited by N, Si, or P, but by some factor yet to be determined (perhaps light or temperature). In summer, P is the principal limiting nutrient, but N exerts an influence that deserves further investigation.     

湄公河与洞里萨湖水量交换特征

洞里萨湖是湄公河最大的连通湖泊,湄公河与洞里萨湖水量交换特征一直是国际社会关注的热点问题,但相关研究成果较少。利用4个河湖控制站的长系列水文资料,分析了湄公河与洞里萨湖水量交换特征,结果表明:湄公河与洞里萨湖的水量交换强度大,洞里萨湖对湄公河径流调峰补枯作用明显,每年汛期5—9月份均会发生倒灌,1995—2011年年均倒灌历时122 d,倒灌水量377亿m³,占湄公河干流同期来水的14.4%,倒灌洪峰流量8 402 m³/s,占干流同期来水的20%,其中7—9月份倒灌水量占全年的88.6%;汛后10月份—次年4月份洞里萨湖向湄公河补水,年均补水历时244 d,补水水量711亿m³,是湄公河倒灌入湖水量的1.96倍,占湄公河下游同期来水的29.9%,其中10月份—次年1月份补水量占全年的83.1%。年倒灌历时、水量与洪峰流量,年补水历时、水量与峰值的年际变化较小,变幅分别为76 d、283亿m³、6 095 m³/s和76 d、474 亿m³、4 677 m³/s,变差系数为0.07～0.24。倒灌、补水水量不仅与湄公河和洞里萨湖的来水大小有关,还受到河湖水位差及洞里萨河水位等因素影响。研究成果可为湄公河三角洲和洞里萨湖区治理提供科学依据。     

洞里萨湖的水位和面积变化特征

洞里萨湖是湄公河最大的连通湖泊,其水位、面积变化对洞里萨湖的结构和功能产生重要影响,辨识水位、面积演变规律对洞里萨湖区与湄公河三角洲防汛抗旱和生态环境保护具有重要指导意义。基于金边港、波雷格丹和甘邦隆站长系列的日均水位数据及湖区地形资料,定量分析了洞里萨湖水位、面积的年际与年内变化特征。结果表明:洞里萨湖水位涨落缓慢,涨水天数少于退水天数,涨水率高于落水率。洞里萨湖年际水位波动频繁,年平均水位、年最高水位、年水位极差值、年洪水历时、年平均洪水位、日涨水率年际变化总体呈小幅下降趋势,年最低水位、退水天数、日落水率年际变化呈上升趋势。洞里萨湖水位、面积年内呈单峰型变化,5月份最低,平均水位1.51 m,相应面积2 487 km²,实测最低水位1.11 m,相应面积2 053 km²;10月份最高,平均水位8.70 m,相应面积12 768 km²,实测最高水位为10.54 m,相应面积15 261 km²,多年平均年内水位变幅7.63 m,面积变幅10 628 km²。研究成果为下一步洞里萨湖区的综合治理规划奠定了基础。     

Changes in pollution indicators in Lake Victoria,Kenya and their implications for lake and catchment management

Monitoring of aquatic pollution is important for ascertaining the relationship between fisheries and the general ecosystem health of a lake. This study evaluated the use of changes in pollution indicators in Lake Victoria, Kenya, as a decision support tool for fisheries management and productivity. Principal component analysis (PCA; R² ≥ 0.5, P < 0.05) of physical and chemical parameters delineated sampling sites into ecological cluster zones consisting of the inner gulf (C1), mid‐gulf (C2) and open lake (C3). Test results for lead (Pb) and mercury (Hg) levels in the Nile perch tissues were found to be compliant with EU standards. The inner and mid‐gulfs of the Winam Gulf had high levels of total (1818.8 ± 102–1937.78 ± 94 cfu 100 mL^?1) and faecal (390 ± 21 cfu 100 mL^?1) coliforms attributable to urban sewage and industrial effluents exceeded WHO standards. Similarly, Winam Gulf was more polluted than the open lake, with higher total phosphorus and nitrogen concentrations, turbidity levels and electrical conductivity. Low phytoplankton biovolume and a low number of macroinvertebrates genera, and high zooplankton densities and pollution‐tolerant catfishes (e.g., Schilbe victoriae; Clarias gariepinus) were observed in Winam Gulf. Faecal coliforms and dissolved oxygen influenced the abundance of tolerant fish species (e.g., S. victoriae) in the lake. This study indicated a declining trend of ecological integrity in the Winam Gulf, compared with the open waters of Lake Victoria. An integrated management approach directed to minimizing pollution levels, especially in the Winam Gulf, is recommended to enhance fishery production.     

陈桥东湖浮游生物群落结构特征及水质评价

陈桥东湖是新乡黄河湿地鸟类国家级自然保护区中部实验区的常年集水区之一,是许多珍稀鸟类的繁殖及栖息地,具有重要的生物多样性保护和潜在的科学研究、生态旅游价值。为了解陈桥东湖浮游生物群落结构特征及水质状况,于2017年1月、4月、7月和10月对陈桥东湖进行浮游生物采样调查,并利用浮游生物多样性指数评价水质状况。结果共发现浮游植物有8门67属118种,其中绿藻47种,种类最多,占39.83%;其次是硅藻,有35种;甲藻最少,只有2种。各采样点浮游植物丰度变化范围为(2.52~39.7)×10⁶ cells/L,全年主要优势门类为硅藻、绿藻和蓝藻。共发现浮游动物34种,轮虫种类最多,共21种,占61.76%;丰度变化为68~1 342 cells/L。全年轮虫为主要优势种类,轮虫滤食者RF为主要浮游动物功能群。浮游生物多样性指数结果显示陈桥东湖水体整体呈中度污染状况,且夏季最差,冬季相对较好,与水体理化指标调查结果一致。研究成果可为新乡黄河湿地水环境保护及生态修护提供参考依据。     

博斯腾湖流域环境风险源指标体系研究

由于流域环境风险源识别和等级划分缺乏一套完整成熟的方法,在分析流域环境风险源风险度的基础上,从"驱动力—压力—状态"的框架模型出发,构建了博斯腾湖流域环境风险源识别指标体系,主要包括指标体系构建、评价指标选取和等级划分等内容,并采用多级灰色关联分析方法对博斯腾湖流域环境风险源进行风险源识别。研究结果表明:环境风险源识别区分度较高,识别指标体系合理,评估方法具有科学性和实用性,构建的环境风险源识别指标体系和采用的识别方法符合开展环境风险管理工作的要求,为环境风险源管理提供技术支持和决策信息。     

草海丰水期chl-a空间分布与环境因子相关关系

水体富营养化是我国湖泊面临的主要问题,分析叶绿素a含量的变化特征及其影响因素,能为湖泊水质评价提供可靠基础。以2017年7月草海丰水期水质数据为参考,对各监测点叶绿素a与环境因子(TN,TP,NH_3-N,COD_(Mn),DO,WT)进行相关性分析并预测叶绿素a的变化趋势。结果表明:草海丰水期叶绿素a的均值为8.07μg/L,处于中营养化状态;叶绿素a与TN,TP,NH_3-N,COD_(Mn)呈显著正相关,而与其他环境因子相关性不显著,表明营养盐对浮游植物影响程度最大;将spearman秩相关系数及多元线性回归方程计算的叶绿素a预测值与实测值进行相关性拟合,得到较好的相关性(R~2=0.85,P0.01),表明该方法的预测结果能为预测草海叶绿素a变化趋势提供参考。草海上游及人类活动较大区域污染程度高,TP是草海藻类生长的限制因子,因此控制TP含量的输入是改善水质的关键。     

Widespread infection of lake whitefish Coregonus clupeaformis with the swimbladder nematode Cystidicola farionis in northern lakes Michigan and Huron

We estimated the prevalence, intensity, and abundance of swimbladder nematode infection in 1281 lake whitefish (Coregonus clupeaformis) collected from four sites in northern lakes Huron (Cheboygan and DeTour Village) and Michigan (Big Bay de Noc and Naubinway) from fall 2003 through summer 2006. Morphological examination of nematode egg, larval, and mature stages through light and scanning electron microscopy revealed characteristics consistent with that of Cystidicola farionis Fischer 1798. Total C. farionis prevalence was 26.94%, while the mean intensity and abundance of infection was 26.72 and 7.21 nematodes/fish, respectively. Although we detected C. farionis in all four stocks that were examined, Lake Huron stocks generally had higher prevalence, intensity, and abundance of infection than Lake Michigan stocks. A distinct seasonal fluctuation in prevalence, abundance, and intensity of C. farionis was observed, which does not coincide with reported C. farionis development in other fish species. Lake whitefish that were heavily infected with C. farionis were found to have thickened swimbladder walls with deteriorated mucosa lining, which could affect swimbladder function. Whether C. farionis infection may be negatively impacting lake whitefish stocks in the Great Lakes is unclear; continued monitoring of C. farionis infection should be conducted to measure responses of lake whitefish stocks to infection levels.     

Quantification of soil erosion and sediment yield for ungauged catchment using the RUSLE model: Case study for Lake Basaka catchment in Ethiopia

Soil erosion is a monumental land degradation problem in many parts of the world, threatening the well‐being of humans and ecosystems. The Lake Basaka catchment is heavily affected by serious land degradation problems related to land use–land cover changes (LULC), population dynamics and settlement, introduction of large‐scale irrigation schemes, etc. Accordingly, the objective of the present study was to quantify the magnitude of soil lost from the Lake Basaka catchment and the sediment subsequently delivered to the lake on the basis of the limited available dataset in a distributed manner using the RUSLE model in a GIS environment. The results indicated about 36 million m³ of soil were lost from the catchment between 1973 and 2007. Soil erosion and sedimentation in the lake catchment continue to increase from time to time, being attributed to the significant LULC occurring in the catchment. About 23 cm of the economically productive top soil in the catchment was lost during the study period (1960–2015), which translates into a significant degradation of the catchment (e.g. further reduction of infiltration capacity, thereby accelerating run‐off and erosion rates). Similarly, about a 1.3 m deep sediment layer was deposited in the lake during the same period. The computed sediment yield indicates about 14% of the lake incremental volume and depth in recent periods (post‐2000s) is attributable to sedimentation. Certain coincidental changes are also occurring in the catchment, including organic matter declines, soil nutrient depletion and soil depth decrement, which may lead to decreased production and productivity and associated ecosystem imbalances. The present study identified the potential areas that contribute significantly to erosion and sedimentation, thereby providing guidance regarding where land use/cover practices must be implemented to limit/reduce, if not avoid, the impacts of erosion and subsequent sedimentation in Lake Basaka.