Lake Tanganyika endemic gastropods also occur in the Lukuga River

Ancient lakes with their endemic species assemblages, like Lake Tanganyika in East Africa, are regarded as hotspots of aquatic biodiversity and as natural laboratories providing insights into evolutionary processes, such as intra-lacustrine speciation. The origin of the gastropod species super flock in Lake Tanganyika has been debated intensively and remains unclear to date. For the fish community, it is generally assumed that it was derived from ancestors occurring in the Congo River Basin. Recently, a central biogeographical role of the Lukuga River system and the connected Lualaba River has been indicated. In an attempt to trace the origin of the enigmatic thalassoid gastropods of Lake Tanganyika, the fauna of the Lukuga-Lualaba systems is currently being studied. A recent expedition allowed collecting mollusc material from the eastern shores of Lake Tanganyika around Kalemie and down the Lukuga River until Niemba. We found gastropods known to be endemic to Lake Tanganyika living in the Lukuga River as far down as 95 km, in populations with reasonable abundances. Based on mitochondrial DNA sequences, these populations are partially genetically distinct from Lake Tanganyika’s populations. However, sister taxa to the species flock have not yet been found in the Lukuga River. Our results are discussed in the context of intra-riverine evolutionary dynamics over shorter time periods. They will also help to understand the biogeographical and evolutionary dynamics within a large spatial and temporal framework, covering Lake Tanganyika and the Congo River system.     

Interannual variability of water quality conditions in the Nyanza Gulf of Lake Victoria,Kenya

The Nyanza Gulf of Lake Victoria is considered eutrophic with degrading water quality, as shown by harmful algal blooms formed by cyanobacteria of the genus Microcystis. The dilution of gulf water occurs mainly through the wide Rusinga Channel, whereas the much narrower and shallower Mbita Channel was reopened in May 2017. Specific conductivity and phytoplankton biovolume composition were monitored monthly from July 2017 to July 2018 at three stations and compared with records during 2008 – 2009, when higher eutrophication was observed, in the west gulf (WG, closely located to the Mbita Channel), the mid gulf (central part of the gulf), and the east gulf (EG, close to Kisumu City). As previously observed, conductivity showed a distinct increase from the WG to the EG but compared with records 2008–2009 it had decreased. Water level fluctuations, resulting from wind possibly causing water exchange with the main basin, were related to the decrease in conductivity at the EG. When all three stations were compared, the environmental variable transparency was positively related to most phytoplankton genera, whereas the genera Dolichospermum, Microcystis, and Aulacoseira were related to eutrophication. Compared with the period 2008–2009, the proportion of Microcystis decreased, while the proportion of Aulacoseira increased. Compared with the period 2008–2009, the observed dilution at the EG was primarily related to the overall increased water level in the main basin. The observed dilutional influence might have led to a decline in nuisance phytoplankton and overall improved water quality conditions.     

First report of tubenose goby (Proterorhinus semilunaris) in the eastern basin of Lake Erie

The tubenose goby (Proterorhinus semilunaris), native to the Ponto-Caspian region, was first discovered in the Laurentian Great Lakes in 1990 after it was introduced through ballast water discharge. Compared with Neogobius melanostomus, another exotic gobiid from the Ponto-Caspian, colonization of the Great Lakes by P. semilunaris has been slow, with reports of the species being largely confined to the Huron-Erie Corridor (HEC) and western portions of Lake Erie and Lake Superior. This is the first report of P. semilunaris in the Great Lakes east of the western basin of Lake Erie. Between 28 June and 27 July, 2012, 176 P. semilunaris were collected from shallow (< 1.2 m) water of Marina Lake, a 40 ha embayment in Presque Isle State Park (Erie, PA). The large number of P. semilunaris collected at the site and the presence of individuals as small as 17 mm total length suggest an established population. However, the mechanism by which P. semilunaris was introduced to Presque Isle Bay is not clear.     

The Vertical Distribution of Runoff and its Suspended Load in Lake Malawi

Lake Malawi, in south-eastern Africa, is subject to increasing loading of suspended solids caused by land use pressure in its watershed. Whether this load is transported into the lake as overflow, interflow or deep underflow determines to a large extent its effect on the lake ecosystem. In this paper, vertical distributions of suspended solids in the Linthipe River delta region of the lake are described from multiple surveys during two rainy seasons. These data are supplemented by data from a single survey near four northern rivers also tributary to the lake. Profiles of temperature, conductance, and suspended solids concentrations (SSC, estimated from optical backscatter and beam transmission) are used to identify fluvial intrusions into the water column. Most inflow plunged to the seasonal metalimnion where it spread along high density gradients as interflow. While SSC in surface plumes rarely exceeded 10 g m⁻³, and in intrusions in the lower metalimnion was rarely greater than 1 g m⁻³, concentrations up to 420 g m⁻³ were recorded in interflow near the thermocline. Although storm runoff density often exceeded 100 m depth-equivalence in the lake, underflow density was reduced to metalimnion-equivalence (30–50 m depth) within a few 100s of meters of the river mouth. We attribute bottom-attached turbid layers, and the few unattached turbid layers in the lower metalimnion, all with positive conductance anomalies, to sediment resuspension and not to runoff. We conclude that the upper metalimnion is the prevailing pathway carrying watershed runoff horizontally throughout Lake Malawi.     

Determination of the status of stakeholder participation in the management of the Lake Malawi basin through application of Integrated Lake Basin Management

Lake Malawi is the southernmost of the Great Rift Valley Lakes of Africa and boasts the world's greatest freshwater fish biodiversity. Along with its basin, the lake provides many benefits to the country of Malawi. Settlements, agriculture and fishing are some of the major uses of the lake basin, making community involvement a necessary component of its management. With the use of key informant interviews, questionnaire survey, document review and site observations, this study demonstrates the applicability of the Integrated Lake Basin Management framework in the Lake Malawi Basin in regard to stakeholder participation. The main objective was to assess the participation of stakeholders, especially local communities, in the management of the lake basin. The framework applied in this study is discussed. The study findings indicate strong to very strong stakeholder participation, with notably high levels of awareness and women's involvement. Enhancing the understanding of the complex nature of lake basin issues, especially those related to the linkages between the water body and the basin, is a topic requiring further attention.     

The Effect of Suspended Solids Loading from the Linthipe River on Light in Lake Malawi

Increasing land use pressure has resulted in increasing suspended solids loading to many African lakes in recent decades, causing concern that littoral habitat may be degraded by sedimentation and light limitation. In a companion paper in this issue, we showed that much runoff into Lake Malawi plunges below the euphotic zone and spreads through the lake via the upper metalimnion, thus mitigating nearshore and upper water column impacts. In this study we use data from multiple surveys through two rainy seasons to describe spatio-temporal distributions of suspended solids concentration (SSC) and transparency caused by the flow of runoff through the Linthipe River delta region of Lake Malawi. SSC in interflow at 30–50 m depth was typically an order of magnitude greater than in surface plumes. Seasonal median transparency near the river mouth was inversely proportional to the suspended load in surface-buoyant inflow, but independent of total loading. This is because storm runoff was more dense (cooler and with higher SSC) than runoff during low-flow periods, so that it was more likely to plunge. The effect was to moderate inter-annual variability in light attenuation near the river mouth because transparency was lower (due to more surface-buoyant inflow of turbid water) in the year when solar irradiance was higher (less cloud cover). The effect was, however, local. Beyond a few kilometers of the river mouth upward mixing of suspended particles carried in interflow reasserted the more intuitive inverse dependence of transparency on total loading.     

1999年太湖流域特大洪水防御工作的回顾与思考

1999年太湖流域发生了20世纪有记录以来的最大一次洪水,在国家防汛抗旱总指挥部的正确领导下,通过流域各省（直辖市）的团结抗洪,将洪涝灾害损失降到最低程度,取得了抗洪救灾的全面胜利。通过回顾1999年太湖流域特大洪水防御工作及主要经验,结合10年来流域防汛抗旱工作取得的成效,分析了当前面临的新形势。提出了进一步加强流域防汛抗旱工作的设想。     

复杂围岩的应力与位移计算方法研究

岩体具有流变性能 ,围岩开挖后 ,视之为粘弹性体与粘塑性体的组合体比较恰当 ;在围岩的粘弹性区采用中村模型 ,用数学的方法 ,求出粘弹性区、粘塑性区的应力和位移表达式     

浅议鄱阳湖的生态问题

本文介绍了水利与生态、鄱阳湖与长江及流域内五河的关系,分析了鄱阳湖水情变化对鄱阳湖湿地、候鸟栖息、鱼类及江豚保育等生态问题的影响,认为科学调配鄱阳湖水资源是解决鄱阳湖生态问题最重要的基础条件.     

碟形湖在鄱阳湖湿地生态系统的作用和意义

"碟形湖"是指鄱阳湖湖盆区内枯水季节显露于洲滩之中的季节性子湖泊,具有特殊的地貌特征和水文特性、复杂多变的湿地景观和丰富的生物多样性等特征.在碟形湖及其周边,湿生与水生植物群落有序分布、季节性演替;静水水域有利于底栖动物和鱼类生长育肥;缓慢下降的水位、逐渐伸展的泥滩为越冬候鸟持续提供丰富的食物和歇息环境,全湖80%以上的水鸟在碟形湖区域越冬.高低不一、分布广泛的碟形湖群有效地缓解了干旱、洪水灾害对鄱阳湖湿地生态系统的冲击,对于维护全球生态系统的完整性和生物多样性具有重要作用.最后提出了加强碟形湖保护和管理的对策.     

Relationship of sediment influx to ostracode populations on the variably deforested Luiche and Mahale platform coasts of Lake Tanganyika,Tanzania

We investigated the hypothesis that ostracode populations are sensitive to variations in sediment discharge related to watershed differences at Lake Tanganyika. Many ostracode species are documented to be sensitive to high turbidity which increases during runoff from strong rainfall events and changes in ostracode populations can impact organisms higher in the food web. We compared surficial death assemblages of ostracodes around two sites with extensive shell beds, the highly deforested Luiche Platform area, heavily populated since the 20th Century, and the less deforested Mahale Platform area, with recent population increases, to understand the impacts of increasing sedimentation within and between sites. The study found that whereas the Mahale Platform area is less disturbed, the faunal differences between sites is not large. The data showed high species richness and abundance of ostracodes at 10–20 m depth at both sites, within shell bed zones, with no statistical difference in raw species richness between the sites. The Mahale Mountain area ostracode populations were however statistically more diverse (Shannon H) than at Luiche. We conducted a multi-response permutation procedure and found that the sites are statistically different, but with very small differences in species richness and ostracode abundance. Non-metric multidimensional scaling ordination of species assemblages shows that most samples overlap on both major axes. This study synthesized with ongoing research about shell bed communities in less disturbed regions of the lake will give insights into how conservation projects can be optimized to preserve the lake’s benthic ecosystem from the effects of deforestation.     

High Variability of Phytoplankton Photosynthesis in Response to Environmental Forcing in Oligotrophic Lake Malawi/Nyasa

In southern Lake Malawi, seasonal pelagic chlorophyll means were 1.0 ± 0.3 μg L⁻¹ in the deep mixing season (DMS) (May–August), 0.8 ± 0.3 μg L⁻¹ in the dry stratified season (DSS) (September to November) and 0.7 ± 0.3 μg L⁻¹ in the wet stratified season (WSS) (December to April). Despite the low variability in chlorophyll, there was a wide range in chlorophyll specific photosynthetic activity. The photosynthetic parameters, P^b_m (the light saturated rate) and α^b (the light limited slope), varied significantly among seasons and were highly positively correlated, with lowest values in the DSS and highest values in WSS. During deep mixing, P^b_m did not covary with α^b; and the light saturation index, E_k (=P^b_m/α^b), varied in response to changes in α^b rather than in P^b_m. Phytoplankton appeared to be nutrient deficient at all times but less deficient during deep vertical mixing in the DMS. Average daily rates of integrated phytoplankton primary productivity were lowest in the DSS (337 mg C m⁻² d⁻¹) and highest in the WSS (629 mg C m⁻² d⁻¹) despite nearly identical mean chlorophyll concentrations. Along a near shore transect off the Linthipe River, chlorophyll concentrations were higher and more variable (1.4 ± 1.3 μg L⁻¹), phytoplankton were not strongly nutrient deficient and chlorophyll specific photosynthetic activity was as high or higher than at the offshore station. Estimates of phytoplankton productivity in this tropical great lake must account for spatial and temporal variability in photosynthetic parameters imposed by seasonal changes in mixing dynamics.     

Fish Assemblages and Environmental Conditions in the Lower Reaches of Northeastern Lake Erie Tributaries

Lake Erie and its tributaries have experienced extensive changes in environmental conditions and community structure during recent decades. To assess the relative importance of environmental conditions in determining fish community composition, fish communities and their associated environmental conditions were sampled from the lower reaches and mouths of the tributaries flowing into the northeastern basin of Lake Erie. These data were used to assess relationships between habitat and fish community composition on spatial and temporal scales using correspondence analysis and canonical correspondence analysis. Multivariate analyses revealed that the fish assemblage was size structured and related to water chemistry but also showed influences due to temperature, sampling date and aquatic macrophytes. The community composition showed the effects of biotic interactions, predominantly negative predator-prey associations, but there were also assemblage differences specific to particular tributaries and sampling methodologies.     

洱海水体富营养化的演变及其研究进展

本文分析了1992-2001年洱海水质监测数据，得出洱海富营养化的变化趋势；综述了洱海水体富营养化的演变进程以及近年来对洱海富营养化的研究成果；提出了引水济洱，建设湖滨带湿地生态恢复系统，走可持续发展和生态恢复之路来解决洱海富营养化问题的思路，为保护和治理洱海提供科学依据。     

Escherichia coli (E. coli) distribution in the Lake Malawi nearshore zone

Residents along the shoreline of Lake Malawi depend on nearshore water for drinking, cooking, and bathing. Despite the importance of clean nearshore waters to public health, we are aware of no published studies of shoreline water quality in the lake. To address this gap, we explore seasonal and temporal trends of the fecal indicator bacteria Escherichia coli (E. coli) in nearshore water and sand. E. coli concentrations in sand ranged from 0 to 17,600 colony forming units (CFU)/100?ml, and in water concentrations ranged from 0 to 21,200?CFU/100?ml. Fifty-three percent of water samples exceeded the U.S. Environmental Protection Agency Recreational Water Quality Criteria of 126?CFU/100?ml, and 90% exceeded the World Health Organization drinking water standard of 0?CFU/100?ml. Distance from shore was the variable most predictive of E. coli concentration, with the level of beach use also playing a significant role. At 15?m from the shore, E. coli concentrations dropped to between 0.3% and 17% of shoreline values. Results suggest that the collection of water at distances >15?m from the beach could substantially decrease exposure to fecal bacteria. Further studies are needed to identify sources of fecal pollution and to determine the utility of E. coli as a predictor of the potential for waterborne disease.     

Evidence supporting the importance of nutrient regeneration by nano- and micrograzers for phytoplankton photosynthesis in Lake Malawi/Nyasa

Photosynthesis and nutrient status measurements were compared in size fractioned water samples collected in southern Lake Malawi in three different seasons. The size fractions analyzed were 0–2.0 μm, 0–20 μm, and 0–200 μm. Total chlorophyll concentrations were relatively invariant at about 1 μg L^?1 in all seasons (wet stratified, deep mixing, dry stratified). Over 90% of total chlorophyll was < 20 μm and 40–50% < 2 μm. Stoichiometric ratios of carbon (C):nitrogen (N) and C:phosphorus (P) for the < 2-μm seston were similar to < 20-μm and < 200-μm seston samples and indicated that all size fractions were moderately N and P deficient in all seasons. N and P uptake experiments demonstrated that when the < 2-μm picoplankton were isolated from the larger sizes, they showed high N and P nutrient debts, apparently in response to the removal of nano- and micrograzers. This effect was strongest for N debt in the dry stratified season, but was apparent for P debt in all seasons. The chlorophyll-normalized light saturated rate of photosynthesis, P^b_m, was always higher in whole water samples compared to the rates of the isolated picophytoplankton which were lowest in the dry season. We infer that nano- and micrograzers were an especially important source of regenerated nutrients when the lake was stratified although their removal as a source of nutrient to the picophytoplankton may affect P^b_m in all seasons. Nitrogen regeneration was especially critical to the picophytoplankton in the dry stratified season but less important in the windy deep mixing season.     

Changes in the biomass of chambo in the southeast arm of Lake Malawi: A stock assessment of Oreochromis spp.

Lake Malawi has one of the most diverse fish faunas in the world (500–650 species) and is a major source of protein for the people of Malawi. Chambo (Oreochromis spp.) is one of the most important food fishes; its abundance has declined sharply over the last twenty-years. Surveys by the Malawi Department of Fisheries have shown a decrease in chambo density in the southeast arm of the lake and the annual harvest has dropped substantially since 1985. We conducted a dynamic stock assessment of Oreochromis spp. which included all vessel and gear types and covered the entire southeast arm of Lake Malawi. Chambo biomass peaked in 1982 and then declined continuously through the early 2000s. The biomass is highly correlated with the mean lake height two years prior suggesting that recruitment may be linked to increased nutrient input, and spawning and nursery habitat associated with the flooding of low lying areas. The main driver of chambo biomass, however, was fishing pressure which was above the level that would achieve maximum sustainable yield during the entire time series. This study provides a baseline from which to measure changes due to future management actions or climate variations.     

长江九江段、鄱阳湖枯水期水位偏低原因分析与思考

本文通过3个不同时段描述了长江九江段、鄱阳湖枯水期水位下降趋势,并分析了其水位偏低的主要原因,提出避免和解决长江九江段、鄱阳湖枯水水位偏低的相应措施.     

太湖流域典型区域水生态环境系统模拟平台研究

针对流域水环境管理数字化和业务化的需求,基于地理信息系统、数字可视化和计算机仿真技术,在.Net框架下采用C#语言,开发出太湖流域典型区域数字水环境系统平台.该平台以水生态环境模拟模型为核心,面向数据和用户、界面友好、方便操作,解决了模型输人复杂易错、数据管理困难、模拟结果可视性低的问题,将水生态环境模型和GIS功能无缝连接.实现了对流域环境过程的长期连续模拟预测和仿真演示.可为流域水环境管理和水污染防治提供技术支撑.     

Vitaliyi Cheslavovich Dorogostaisky: A Pioneer Investigator of the Flora and Fauna of Lake Baikal

V. Ch. Dorogostaisky was born in Irkutsk Province, and devoted much of his professional work to the study of Lake Baikal, Siberia, and its surrounding region. His studies spanned the first third of the 20th Century, beginning at the time when only isolated investigations of the lake were made. He organized and contributed to the shift toward systematic, sustained studies conducted by groups of specialists. His own contributions included both basic and applied efforts. Although he collected algae and vascular plants and described new species, Dorogostaisky devoted his principal attention in limnology to invertebrates and fish. He appears to have grasped the fundamentals of fish management and fur farming well ahead of the development of the technology. His most noteworthy contribution to basic science was his realization that the ecological speciation among the gammarids and fish of Baikal was a recent phenomenon. At a time when the very origin and antiquity of the lake itself was not known, he essentially documented adaptive radiation. Dorogostaisky's evidence impressed Cockrell (1927) to parallel Baikal's faunistic evolution with that of the Hawaiian Islands.