Foraging mechanisms of age-0 lake trout (Salvelinus namaycush)

Reaction distances under various light intensities (0-19 uE/m2/s), angles of attack, swimming speeds, and percentage of overall foraging success were measured. Extensive efforts have been invested in restoring lean lake trout (Salvelinus namaycush) populations in the Laurentian Great Lakes, but successful natural recruitment of lake trout continues to be rare outside of Lake Superior and parts of Lake Huron. There is evidence of high mortality during the first several months after eggs hatch in the spring, but little is known about the foraging mechanisms of this age-0 life stage. We developed a foraging model for age-0 lake trout (S. namaycush) in response to amphipods (Hyalella azteca) and mysids (Mysis diluviana) by simulating underwater environmental conditions in the Great Lakes using a temperature-controlled chamber and spectrally matched lighting. Reaction distances under various light intensities (0–19 uE/m²/s), angles of attack, swimming speeds, and percentage of overall foraging success were measured. Intake rates under different light intensities and prey densities were also measured. Age-0 lake trout were non-responsive in the dark, but were equally responsive under all light levels tested. Age-0 lake trout also demonstrated a longer reaction distance in response to moving prey, particularly mysids, which had an escape response that reduced overall foraging success. We determined that prey intake rate (numeric or biomass) could be modeled most accurately as a function of prey density using a Michaelis–Menton equation and that even under low mysid densities (3 individuals/m²), age-0 lake trout could quickly satisfy their energetic demands in a benthic setting.     

Using satellite data to extract volume–area–elevation relationships for Urmia Lake,Iran

Urmia Lake in the northwest of Iran is the second largest hyper-saline lake worldwide. During the past two decades, a significant water level decline has occurred in the lake. The existing estimations for the lake water balance are widely variable because the lake bathymetry is unknown. The main focus of this study is to extract the volume–area–elevation (V–A–L) characteristics of Urmia Lake utilizing remote sensing data and analytical models. V–A–L equations of the lake were determined using radar altimetry data and their concurrent satellite-derived surface data. Next, two approximate models, a power model (PM) and a truncated pyramid model (TPM), were parameterized for Urmia Lake and checked for accuracy. Results revealed that in comparison with the satellite-derived reference volume–elevation equation, the PM slightly over-predicts the volume of Urmia Lake while the TPM under-estimates the lake storage. Variations of the lake area and volume between 1965 and 2011 were examined using the developed V–A–L equations. Results indicated that the lake area and volume have declined from the historical maximum values by 2200 km² and 33 km³, respectively. To restore Urmia Lake to a level to maintain ecological benefits, 13.2 km³ of water is required. This study demonstrates the use of remote sensing data of different types to derive V–A–L equations of lakes. Substituting satellite-derived V–A–L equations for common empirical formulas leads to more accurate estimations of a lake water balance, which in turn, provides insight to water managers for properly assessing and allocating water resources to downstream ecosystems.     

Firms’ willingness to invest in a water fund to improve water-related ecosystem services in the Lake Naivasha basin,Kenya

A valuation scenario was designed using a contingent-valuation approach and presented to decision makers in business firms in Kenya’s Lake Naivasha basin to test how applicable a water fund might be as a potential financing mechanism for a payment for water-related ecosystem services scheme. The findings indicate that measuring a firm’s willingness to invest in ecosystem services could help determine whether a firm would invest and engage with other stakeholders to pool their investments in ecosystem services. Linking the institutional decision-making behaviour of a firm and its willingness to invest in a water fund is the novelty of this article.     

Determinants of temperature in small coastal embayments of Lake Ontario

Along 25 km of the Lake Ontario shoreline near Toronto, Ontario, small coastal embayments (0.4–32 ha) have been constructed or modified by lake-infilling to restore warmwater fish habitat. The variation in thermal habitat quality for warmwater fishes among these embayments is very high; temperatures range from those found within a small pond to those of much cooler Lake Ontario. Since meteorological conditions and surface heat fluxes are almost identical, the temperature variation among embayments must be caused by differences in bathymetry or exchange with Lake Ontario. However, a previous study on these embayments found paradoxically that temperatures were not strongly associated with channel size or embayment bathymetry. This paper resolves the paradox by showing that flushing times for almost all of the constructed embayments were less than 1 day, and often less than 12 h. With so little time to warm within the embayments, water temperatures of almost all embayments remained very close to the temperatures of the adjacent lake waters. The coldest embayments connected directly to open Lake Ontario and warmer embayments connected to Lake Ontario through other embayments or protected harbors, where the inflowing water from Lake Ontario had already substantially warmed. To allow embayments along the exposed shoreline of Toronto to reach acceptable temperatures for warmwater fish, we use heat budgets to calculate that average summer flushing times must be increased from their current length of 1.5 to 5.5 h to approximately 30 h. Such changes could be achieved through large reductions in the channel cross section.     

By-catch in the Saginaw Bay,Lake Huron commercial trap net fishery

This study provides species-specific catch and baseline mortality estimates of non-target species (by-catch) for the Saginaw Bay, Lake Huron commercial trap net fishery. By-catch can represent a significant mortality source that is often unknown. By-catch and by-catch mortality rates in the Saginaw Bay commercial trap net fishery, which primarily targets lake whitefish (Coregonus clupeaformis), yellow perch (Perca flavescens), and channel catfish (Ictalurus punctatus), are currently unknown. From May through August 2010, we observed onboard commercial trap net vessels and took species-specific counts of by-catch and estimated initial by-catch mortality (i.e., morbid or floating fish). The high levels of walleye (Sander vitreus) catch and mortality observed within inner Saginaw Bay have not been previously documented in the Laurentian Great Lakes. Walleye by-catch averaged 127.3 individuals per trap net lift and 42% of those caught were morbid. The levels of lake trout (Salvelinus namaycush) catch observed were within the range observed in previous studies, but mortality (percent) was higher than has been previously observed. Lake trout by-catch averaged 39.4 individuals per lift and 39.2% of those were morbid. Through the use of generalized linear models, this analysis also indicated factors that most influenced catch of non-target species including time of year and soak time (i.e., time interval between trap net lifts). Surface water temperature and trap net depth most influenced mortality. These results may inform fishers and fisheries managers and highlight the need for comprehensive by-catch monitoring throughout the Great Lakes.     

白洋淀流域分布式水文模型开发与验证

针对白洋淀流域水资源保护工作开发了分布式水文模型WEP-L模型。WEP-L模型是对流域水循环过程与能量循环过程的综合模拟,具有较高的模拟精度。对白洋淀流域1956 } 2000年的径流模拟计算表明:主要水文站的相对误差在5%以内,Nash-Sutcliffe效率系数在0. 8以上,可以用于白洋淀流域的水文循环分析。     

CAS理论在滇池流域水资源配置中的应用

基于复杂适应系统（CAS—Complex Adaptive System）理论,研究滇池流域水资源配置系统的演化机制,描述滇池复杂适应水资源配置系统“学习”的特点和本质、各用水及供水主体的影响因素和反应规则。随后,建立了滇池流域水资源配置的CAS模型。基于此模型,利用Matlab优化平台,预测了不同规划年滇池流域各部门的需水量,给出了流域仅在滇池水域与掌鸠河云龙水库供水条件下的水资源配置结果。最后,分析了利用CAS理论研究流域水资源配置的优越性,并给出了相应的结论。     

太湖流域水灾害应急对策研究

太湖流域是我国经济社会高度发达的地区之一,发生水灾害时往往会造成重大经济损失。对发生各类水灾害时的应急对策展开研究总结,以减轻水灾害,避免人员伤亡,保障经济社会可持续健康稳定发展,并通过分析典型案例的实际应对过程,为今后开展类似工作提供参考。     

Analysing decadal land use/cover dynamics of the Lake Basaka catchment (Main Ethiopian Rift) using LANDSAT imagery and GIS

Development of accurate classification methods for rapidly changing catchments like that of Lake Basaka is fundamental to better understanding the catchment dynamics, which were not addressed in previous studies. Thus, the aim of this study was to map the decadal land use/cover (LUC) regimes of the Lake Basaka catchment, utilizing time series of LANDSAT images and to analyse the changes that occurred at different time periods. Both unsupervised and supervised image classification systems were utilized in Earth Resources Data Analysis System (ERDAS) Imagine (9.1). Appropriate pre‐ and postprocessing also was utilized. Seven major LUC classes were identified in the final land cover maps produced after the supervised (maximum likelihood) classification exercise. The analysis results indicated the Lake Basaka catchment had experienced a drastic change in its LUC conditions over the last 4–5 decades because of rapid increases in human settlement, deforestation, establishment of irrigation schemes and Awash National Park (ANP). Approximately 18 924 ha of forest and 4730 ha of grazing lands were devastated between 1973 and 2008. At the same time, there was a shift in land cover from forests/woodlands to open woodlands, shrub and grazing lands. The land cover classifications generally were achieved at a very high overall accuracy (84.34%) and overall kappa statistics (0.802), substantiating the value of using the classified LUC in this study as an input to hydrological models. This study results provide an opportunity to better understand and quantify the hydrological response regimes of the lake catchment from the perspective of changing LUC conditions during different hydrological periods and the resulting dynamics of the lake water balance.     

Phytoplankton biomass and primary production dynamics in Lake Kariba

The present study examined spatial, seasonal and depth variations in phytoplankton biomass and primary production (PP), compared with those reported for other tropical African lakes, to determine whether or not measured phytoplankton changes might be linked to climate warming. The biomass of three major phytoplankton classes (Cyanophyceae; Chlorophyceae; Bacillariophyceae) and net PP were measured during the midwinter and midsummer at six different depths at 35 sampling sites distributed across the lake’s five basins. A more rigorous sampling regime was used in the fifth basin, with phytoplankton biomass and PP rates measured every second month over a 24 month period at six different depths at ten sampling sites located in riverine and lacustrine waters. Cyanophyceae, which displayed a gradient of decreasing biomass from Basins 2 to 5, contributed 69% of the total phytoplankton biomass in the lake’s five basins during summer. This percentage was approximately four times greater than that contributed by the Bacillariophyceae and about ten times greater than that contributed by the Chlorophyceae. During winter, Bacillariophyceae biomass was equivalent to that of the Cyanophyceae, but displayed an opposing gradient of increasing biomass from Basins 1 to 3, with a subsequent biomass decline from Basins 3 to 5. Chlorophyceae exhibited no distinct biomass gradient across the five lake basins, being undetectable during winter. The biomass of all three phytoplankton classes and the net PP varied in magnitude and direction monthly between the lacustrine and riverine waters, with increasing water depth and with no distinct seasonal patterns being evident. The monthly variations in biomass were related to the thermal stratification cycle, hydrological gradients and the extent of water mixing, being similar to those reported for other tropical African lakes. It is noteworthy that total phytoplankton biomass and PP in Lake Kariba have declined by about 95% and 50%, respectively, since the 1980s. These declines correspond to an upward shift in the depth of the thermocline, associated with an average temperature increase of 1.9 °C and a 50% reduction in the depth of the euphotic zone, since the 1960s.