Detecting land use/land cover changes in the Lake Hayq (Ethiopia) drainage basin, 1957–2007

Land use/land cover changes in a lake drainage basin reflect changes in the magnitude of the water balance components and rate of sediment deposition in a lake as a reflection of the fundamental linkage between what happens in a lake considered against what is happening in the drainage basin of the lake. The objective of this study was to quantify the spatio‐temporal land cover/land use changes across the Lake Hayq 1 1 Lake Hayq is also locally called Lego.
closed drainage basin in north‐east Ethiopia over a 50‐years period, using multitemporal remote sensing and geospatial data. Two historical occasions of aerial photographs (1957 and 1986) and one satellite image (2007) were examined with image analysis tools: Leica Photogrammetric Suite (LPS 9.2) Project Manager, ArcGIS10.0, and ERDAS EMAGINE 9.2. Seven aerial coverage of land use/land cover categories were identified and mapped for the past three historical times. The results indicated that farmlands/settlements and shrublands/degraded lands increased by 43.1% and 136.9%, at an annual rate of 27.4 and 13.5 ha year^?1, respectively, between 1957 and 2007. In contrast, bushlands, grasslands, forestlands and lake surface area were diminished by 68.8%, 62.7%, 90.5% and 7.6%, at a rate of 24.0, 7.6, 6.1 and 3.7 ha year^?1, respectively, over the past five decades. The basin had undergone significant transformation in land use/land cover over the past half century, affecting the lake's biophysical stability by accelerating soil erosion in the basin, sediment accumulation, and a reduced quantity and quality of cumulative stream flow into the lake.     

Investigation of physical and bathymetric characteristics of Lakes Abaya and Chamo, Ethiopia, and their management implications

The purpose of this study was to investigate the physical parameters of Lakes Abaya and Chamo in the Ethiopian rift lakes system, including such physical characteristics as depth, water resources capacity, hydrology, water balances, and impacts of water use and degradation of their watersheds. These parameters have not previously been studied for these two lakes to any significant extent. This study describes the bathymetry survey undertaken for these two lakes, and the morphometric characteristics derived from it. This study is part of a research project developed to provide further details on such parameters as hydrology, water quality, sediment inflows and deposition, lake hydrodynamics and consumptive water uses. The bathymetric survey was conducted, utilizing a combination of global positioning system (GPS) and echo sounder. To calculate the morphometric characteristics, the background lake map was digitized, and the surveyed primary data were developed as digital values. The digital values were interpolated, generating grids of the elevation surface. The elevation area and elevation volume curves (capacity curves) of the two lakes were developed from the digital values, describing the water resources capacity of the lake water basins. The results of this study increase our understanding of the water resources of these two lakes, as well as provide better understanding of their vulnerability to human activities because of their shallow depths. Immediate application of the results, as a basis for continuation of this study, also is highlighted.     

Degradation of Lake Ziway,Ethiopia: A study of the environmental perceptions of school students

Lake Ziway in Ethiopia is a freshwater lake supporting multitude uses, including irrigation, fishing, water supply and recreation. However, the lake is being degraded primarily because of various land‐ and water‐use activities in its watershed. Recognizing these human impacts on the lake's water quality and quantity, the perceptions of school students were surveyed under the belief that the future of the lake is largely dependent on this younger generation. The goal of this study was to better understand how students actually recognize the extent to which various human activities impact the water quantity and quality of Lake Ziway. As major stakeholders in their communities, the perceptions of school students from four high schools regarding the changes to the lake over time were investigated. Students were contacted by purposive sampling, based on criteria of student academic performances, and their proximity to the lake. Their perceptions were studied on the basis of an interview survey. The majority of students indicated that high levels of human activities, especially water abstractions and water pollution, were the main lake impacts. Students believe there is a lack of sustainable utilization and protection of the lake. They suggested coordinated activities among all lake stakeholders in the participation and decision‐making process to properly manage the lake. Provision of awareness to both local administrations and local communities, concern for establishing an appropriate regulatory body and allocating a sufficient budget, and strict controls on flower farm practices in the lakeshore, also was considered to be of high priority as a means of conserving the sustainability of the lake. The result derived from this survey has important implications for facilitating improved school curricula, and for federal, regional and district level water resource management authorities, in setting priorities and developing policies for the sustainability of Lake Ziway.     

Modelling natural conditions and impacts of consumptive water use and sedimentation of Lake Abaya and Lake Chamo, Ethiopia

There is few available information regarding the water resource systems of Abaya Lake and Chamo Lake, which are found in the Southern Rift Valley Region of Ethiopia. This paper describes modelling of the water balance components of these lakes, as well as the impacts of water uses, and sediment transport and deposition in the lakes. The various parameters and data needed for the water balance model are derived on the basis of various surveys, analysis of data and modelling efforts. The watershed characteristics are derived using geographical information system, whereas the morphometry of the lakes is investigated by undertaking bathymetry surveys. The hydrometeorological components of this lake system also were investigated through the development of relevant database and information systems, by identifying regional relationships, and by a rainfall‐run‐off model. These information systems have subsequently been integrated to model the water balance of the two lakes, and simulating the in‐lake water levels. Several scenarios reflecting the natural conditions, water consumptive development possibilities, and sedimentation impacts have been investigated in this study. Based on the model simulation results, and on the computation of the life expectancies of the two lakes, it was found that sediment inflow and deposition significantly threaten their existence.     

Bed morphology, flow structure, and sediment transport at the outlet of Lake Huron and in the upper St. Clair River

An integrated multibeam echo sounder and acoustic Doppler current profiler field survey was conducted in July 2008 to investigate the morphodynamics of the St. Clair River at the outlet of Lake Huron. The principal morphological features of the upper St. Clair River included flow-transverse bedforms that appear weakly mobile, erosive bedforms in cohesive muds, thin non-cohesive veneers of weakly mobile sediment that cover an underlying cohesive (till or glacio-lacustrine) surface, and vegetation that covers the bed. The flow was characterized by acceleration as the banks constrict from Lake Huron into the St. Clair River, an approximately 1500-m long region of flow separation downstream from the Blue Water Bridge, and secondary flow connected to: i) channel curvature; ii) forcing of the flow by local bed topography, and iii) flow wakes in the lee side of ship wrecks. Nearshore, sand-sized, sediment from Lake Huron was capable of being transported into, and principally along, the banks of the upper St. Clair River by the measured flow. A comparison of bathymetric surveys conducted in 2007 and 2008 identifies that the gravel bed does undergo slow downstream movement, but that this movement does not appear to be generated by the mean flow, and could possibly be caused by ship-propeller-induced turbulence. The study results suggest that the measured mean flow and dredging within the channel have not produced major scour of the upper St. Clair River and that the recent fall in the level of Lake Huron is unlikely to have been caused by these mechanisms.     

Bathymetric distribution of chironomid larvae (Diptera: Chironomidae) in Lake Saiko,Japan

The distribution of benthic macroinvertebrate on 8 March 2009 was studied in Lake Saiko (73.2 m maximum depth). The average density of the benthic community for the entire lake was 19 583 individuals m^?2, being comprised of oligochaetes and chironomid larvae, with densities of 18 163 (92.8%) and 1274 (6.5%), respectively. The average wet weights of oligochaetes and chironomid larvae were 15.96 and 1.67 g m^?2, respectively. The oligochaetes inhabited the entire lake bottom, with their densities being higher in the transitional region (20–40 m) and deeper region (>40 m) than in the shallower region. However, the densities of chironomid larvae were low in the deeper region (>40 m), with only a few chironomid larvae being found in the centre of the lake (>60 m). The most abundant species (Micropsectra chuzeprima) exhibited the widest distribution (from 10.1 to 65.5 m depth), followed by Polypedilum nubeculosum. The results of this study also were compared to previous data on oligochaetes and chironomid larvae reported by Kitagawa (1973) . The density of these animals increased throughout the whole lake in 2009. However, the chironomid species compositions did not changed. The larval distribution pattern of chironomid changed since Kitagawa’s study, being distributed from 11 to 68 m in 1973. In contrast, almost all chironomid larvae were found in the transitional (e.g. M. chuzeprima) and shallower (e.g. Procladius choreus and P. nubeculosum) regions in 2009, with only a few individuals being observed in the deeper regions (>60 m). In contrast, the oligochaete density increased in the deeper regions. Large environmental changes must have affected the oligochaetes and chironomids densities, especially in the deeper regions with low dissolved oxygen concentrations. Consequently, the distribution pattern of oligochaetes and chironomids in the lake has changed. These study findings suggest the lake is experiencing increasing eutrophication.     

多波束测深技术在高坝洲坝前淤积测量中的应用

介绍在高坝洲坝前淤积测量中引进的水下多波束测深系统测量方法,该方法具有范围大、速度快、精度高、记录数字化以及成图自动化等优点,能精确、快速测定沿航线一定宽度内水下目标的大小、形状、最高点和最低点,较可靠地描绘出水下地形的精细特征,高坝洲坝前水下三维地形扫测结果表明,该方法能直观、准确地反映坝前淤积情况。     

Distribution of Diatoms in Lake Superior Sediments

Four maps showing semiquantitative abundance patterns of diatoms throughout Lake Superior were made by examination of 170 cores at sediment depths of 0–1, 10, 20, and 50 cm. These maps show a decrease in diatom abundance with sediment depth and an absence of diatoms in most open-lake sediments. Diatoms in surficial sediments are most abundant in Jive regions in Lake Superior: Thunder Bay, Keweenaw Bay, the Thunder Bay and northshore troughs, and a region to the southwest of Isle Royale. Only three of these five regions still show relatively abundant diatoms at the 50-cm sediment depth. Diatom abundance in the sediments is positively correlated with sedimentation rates, water depth, and proximity to shore. Nearshore deep-water troughs act as depositional traps for diatoms in western Lake Superior and Keweenaw Bay. Later transport of diatoms by waves and currents generally erases any relationship between diatom abundance in the sediments and diatom biomass in the overlying water. Diatom abundances at 10- and 20-cm depths correlate positively with sedimentation rates, suggesting that biogenous and terrigenous components are eroded, transported, and redeposited as a mixture, rather than being hydraulically separated. Diatoms are abundant at 0–1 cm in regions of both low and high sedimentation rates.     

Local governance of Gunao Lake,Tikub Lake and Dagatan Lake: Small lakes of the Mount Banahaw–San Cristobal–Malepunyo Corridor,Philippines

Although many lakes in the Philippines are threatened, the effectiveness of their governance has not received sufficient attention to date. This predicament is most severe in regard to small lakes as their localized governance has least been given consideration over the years. Predicated on this observation, this study explores the local governance of three small lakes (Gunao Lake; Tikub Lake; Dagatan Lake) situated between the Mount Banahaw–San Cristobal and Mount Malepunyo area. Specifically, it analyses the role of local governments in managing and developing the small lakes. Using data from interviews, observations and the few existing documents on these lakes, this study contends that the main feature of governance regarding the three lakes is the Municipal Governments’ commitment and determination, which is consequential in their development over time. For Gunao Lake, the failure of the Municipal Government of Dolores to link the development of the lake with the tourism agenda in the Mount Banahaw area has resulted in its lack of tourism development. For Tikub Lake, the consistent push of the Municipal Government of Tiaong for its tourism agenda is key in the incremental improvement and preservation of the lake. For Dagatan Lake, the persistence of the Municipal Government of San Antonio in pursuing the restoration project and searching for a patron to finance the endeavour is crucial in the revival of the lake. Overall, this study highlights the distinct praxis of local governance regarding each of these small lakes, extends scholarship in regard to lake governance and offers a broad template for managing the many existing small lakes in the country.     

Accumulation of heavy metals in the physical and biological systems of Lake Koka,Ethiopia: Implications for potential health risks

Lake Koka has several important socioeconomic uses, hydroelectric power generation, domestic water supply, irrigation, recreation and fishery. It is currently under serious threat, however, because of point and nonpoint pollution inputs. The objective of the present study was to examine the concentration of heavy metals (Mn, Cr, Pb, Zn, Cu, Ni and Cd) and their bioaccumulation, and biomagnification factors along the lake's food chain in order to assess the potential human and ecological health risks. Water, sediment and plankton samples were collected from seven sampling sites and fishes were purchased on site from fishers. The analyses were performed using a graphite furnance atomic absorption spectrophotometer. Heavy metals levels in the sediment samples were ranked in the order of Mn > Cr > Pb > Zn > Cu > Ni > Cd. Similarly, the metal concentration in the fish muscles was Cr > Cu > Pb > Cd. The sediment bioaccumulation factor (<1) and water bioaccumulation factor (>1) for Cd, Pb and Cr indicated the lake water exhibited higher concentrations than the sediment. In parallel, the Cr biomagnification factor for zooplankton, catfish, Nile tilapia and common carp was 1.63, 1.18, 1.36 and 2.28, respectively. The Cr concentrations at the Modjo (or Mojo) Upstream, Modjo Downstream and Kentare sites, and the Pb concentrations at riverine sites were above the permissible limits established by the World Health Organization. Cr ranked as fish species > zooplankton > phytoplankton, being above the permissible limits in catfish, Nile tilapia and common carp. Generally, the weekly intake estimates were considerably lower than the tolerable human intake values provided by WHO and others. However, Cr biomagnified along the trophic levels ultimately reaching the top consumers, with Cr (VI) being carcinogenic. The lake is a major fishery source, indicating care must be taken in regard to the weekly intake of the fishes, particularly common carp.     

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.     

Progress Toward the Rehabilitation of Lake Trout (Salvelinus namaycush) in South Bay,Lake Huron

Our objective was to evaluate the status of lake trout Salvelinus namaycush rehabilitation in South Bay, Lake Huron. Standardized surveys were conducted to quantify natural recruitment, annual mortality, and the contribution of wild-versus hatchery-origin lake trout. Some indicators suggest a high level of natural recruitment. The spawning population was comprised of multiple ages, and the mean age of spawners (8.4 years for females, 7.9 years for males) was at least 1 year older than the age at 50% maturity (5.8 years). Estimated annual total mortality rates (0.20–0.25) and sea-lamprey induced mortality rates (0.02) were less than maximum allowable values. The proportion of wild-origin fish captured was high among spawners but varied among sampling programs (42% in fall trap nets, 70% in fall gill nets, and 88% in summer gill nets). A strong year class (1997) could be tracked from 2001 to 2005. Few fish were captured from early (< 1996) or later (1999–2002) year classes. Possible explanations for low natural recruitment during these later years include declining spawning habitat quality caused by low water levels and/or invasion of non-native mussels (Dreissena spp.) and/or direct or indirect effects of alewife (Alosa pseudoharengus).     

埃塞俄比亚ADAMA风电工程风机吊装进度的主要影响因素及对策综述

总结了埃塞俄比亚ADAMA风电项目风机吊装施工进度的主要影响因素,如:风速、机位间道路、物流、货损的修复进度等,并提出了相应解决措施。在国外工程实践中,合理控制了工期,有效降低了工程成本,取得了良好效果。     

Diet and Prey Selection by Lake Superior Lake Trout during Spring, 1986–2001

We describe the diet and prey selectivity of lean (Salvelinus namaycush namaycush) and siscowet lake trout (S. n. siscowet) collected during spring (April–June) from Lake Superior during 1986–2001. We estimated prey selectivity by comparing prey numerical abundance estimates from spring bottom trawl surveys and lake trout diet information in similar areas from spring gill net surveys conducted annually in Lake Superior. Rainbow smelt (Osmerus mordax) was the most common prey and was positively selected by both lean and siscowet lake trout throughout the study. Selection by lean lake trout for coregonine (Coregonus spp.) prey increased after 1991 and corresponded with a slight decrease in selection for rainbow smelt. Siscowet positively selected for rainbow smelt after 1998, a change that was coincident with the decrease in selection for this prey item by lean lake trout. However, diet overlap between lean and siscowet lake trout was not strong and did not change significantly over the study period. Rainbow smelt remains an important prey species for lake trout in Lake Superior despite declines in abundance.     

Development issues regarding Bunot Lake: the Lesser Lake among the seven lakes of San Pablo City,Philippines

Bunot Lake exhibits the worst conditions among the seven crater lakes of San Pablo City in the Philippines. It is the most polluted lake, being oversaturated with fish pens/cages. It also hosts the largest concentration of illegal settlements. These attributes strongly suggest that Bunot Lake merits much greater attention in the agenda of its two administrative agencies, the Laguna Lake Development Authority (LLDA) and the City Government. The reality, however, is that Bunot Lake is lacking key development initiatives and programmes and seems to occupy a low priority to the LLDA and the City Government. This reality is particularly perplexing as the lake is located very near the urban centre, is closest to the premier lake (Sampaloc Lake), and is the site of the first commercial production of tilapia in floating cages in the city. Against this background, the present study identifies and analyses the immediate development issues for Bunot Lake. It contends that Bunot Lake should be given preference by the LLDA and the City Government, specifically by: (i) modifying their model‐template approach; and (ii) taking steps to tackle a basic need of Bunot Lake, namely the formulation of a zoning‐development plan. The present study also was designed to directly address the lacuna in Philippine lake studies, namely the paucity of research under the social science perspective (which is currently dominated by the natural science perspective) and on small lakes (which is currently concentrated on the largest lakes in the country).     

Lake bathymetry from Indian Remote Sensing (P6‐LISS III) satellite imagery using artificial neural network model

The remote sensing technique provides a rapid and relatively inexpensive means of identifying silted areas in large water bodies, in order that desilting activities can be effectively conducted. This study developed lake bathymetry for a selected lake system (Akkulam–Veli Lake, Kerala, India) from the Indian Remote Sensing (IRS P6‐LISS III) satellite imagery, using an artificial neural network (ANN) model. The water depth was measured for 17 months at different points in the lake on the same date of overpass of the IRS satellite. The satellite imageries obtained for 12 December 2007 and 16 February 2009 were identified as cloud‐free images. ANN models were developed with the four input series of radiance values from green, red, NIR and MIR bands observed for the satellite imagery obtained on 12 December 2007 at the sampling sites, with actual water depth measurements also being taken on the same date. A three‐layered feed forward neural network with back propagation training algorithm was developed for this study. To train the model, it was run several times by changing the number of neurons, learning rate and the momentum constants until the mean square error was minimum. When the number of neurons is increased to 35, and the logsig function is used as ANN transfer function, the error becomes minimum. To test the model, the developed ANN was run for a new set of input from the satellite imagery taken on 16 February 2009. Comparing the predicted and measured values for the same sites for the same day, it was found that the model is best suited for predicting water depth using ANN and the radiance values for four bands of IRS satellite imagery. The results of this study indicated that, for the shallow lake with lower depth, the difference between the actual and predicted value was considerable. In contrast, this was not the case where the lake water depth was greater, indicating an increased prediction accuracy with ANN with increasing depths for shallow lakes. A bathymetry map prepared with ANN indicated only the lake shoreline, as well as the shallow littoral zones. The approach used in this study requires further refinement, including further of the model based on using more field measurements to obtain a better bathymetry map.     

Utility of remotely operated underwater vehicle in flood inundation mapping for dam failure: A case study of Lake Tuscaloosa Dam

A remotely operated underwater vehicle (ROV) is a tethered underwater mobile device that can conduct a bathymetric survey cost-efficiently. Assessment of the utility of ROV-based bathymetric surveys in flood inundation mapping remains limited. This study aims to examine the utility of ROV-based bathymetric surveys in high-resolution flood inundation mapping for a hypothetical case study of the Lake Tuscaloosa Dam breach in the state of Alabama, USA. This study conducted the sensitivity test of flood inundation mapping to the river channel depth (ROV-based vs. digital elevation model [DEM]-based) and initial flow condition (e.g., wet vs. dry), via six different simulations of the parallelized diffusion hydrodynamic model (pDHM). This study found that the ROV-based pDHM runs had higher maximum water depths over the flood-inundated areas, ranging from +73% to +166% of the simulated depths of the DEM-based pDHM runs. However, the impact of initial streamflow condition on the maximum depths was limited. This study also found that the pDHM runs with a dry initial flow condition delayed the time to reach the maximum depth after the dam breach by 2 h relative to the pDHM runs with a wet initial streamflow condition. This study suggests that ROV-based bathymetry surveys improve flood inundation mapping by emphasizing the influence of river channel depth, initial streamflow conditions, and bathymetry, thereby bolstering community resilience to a potential human-made hazard such as dam failure.     

Pollution of Winam Gulf, Lake Victoria, Kenya: A case study for preliminary risk assessment

A preliminary risk assessment was undertaken on the Kenyan part of Lake Victoria to identify the major causes of degradation of water quality. Urban, industrial and agricultural loads were quantified and related to geographical and climatic conditions. A few analyses of persistent contaminants were carried out on fish. Monthly limnological investigations were conducted together with river water quality analyses. Phosphorus loads and consequent eutrophication were identified as the major causes of water quality degradation.     

太湖底泥生态疏浚技术的初步研究

太湖底泥生态疏浚是湖体生态修复工程之一．工程注重生物多样性保护，并为后续生物技术介入提供基质条件、综合分析底泥污染物垂直分布、沉积相特征、主要污染物分布受人为干扰影响程度、沉水植物生物特性、淤泥土壤水动力学、沉积地球化学特征和疏浚后基面高程控制等参数，太湖底泥疏浚深度控制40～50cm为宜、施工总体设计强须注重建立物种保护区和排泥场淤泥的安全处置及尾水达标排放．依据底泥的不同密度选择不同的疏浚机械，疏浚挖掘头部设备的密封和抽吸是关键．竣工时应做好基底修复．