A song of ice and vessels: Seasonal trends in the soundscape of the western arm of Lake Superior

The soundscapes of marine systems have been studied for decades to determine spatial and temporal patterns of biological, geological, and anthropogenic activity. However, comparatively little is known about freshwater soundscapes. Lake Superior is the world’s largest freshwater lake by surface area and home to a variety of aquatic animals. The Twin Ports of Duluth and Superior, located in the western arm of Lake Superior, are annually closed because of ice cover, providing a unique opportunity to explore sound levels in the absence of vessel traffic. Passive acoustic monitoring was conducted over 15 months between November 2018 and March 2020 to investigate seasonal patterns. Sound pressure levels were significantly lower (8 dB) at low frequencies (<100 Hz) during the winter and spring months (when ice cover increased). Quieter ambient sound pressure levels may provide an acoustic refuge to soniferous animals, especially those that vocalise during winter spawning. During the ice-free months, commercial shipping introduces a near continuous source of sound, increasing sound levels by up to 25 dB (at frequencies < 1,000 Hz). Climate change is expected to further reduce ice cover and thickness allowing the shipping season into the Twin Ports to be extended, thus warranting concern about the effect of noise from vessel activity on aquatic life. This study provides a baseline of the soundscape in the western arm of Lake Superior, against which scientists and environmental managers can assess future changes to this important habitat.     

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.     

How light conditions influence theoretical pelagic to benthic primary production ratios in small lakes

Theoretical pelagic primary production of phytoplankton and benthic primary production of periphyton were modelled for two small lakes in Estonia (Northeast Europe). Although located only 500 m apart, the water colour and light attenuation of these two lakes differed markedly. The Secchi depth (SD) in the clear‐water lake was 4.5 m and only 0.47 m in the dark‐water lake. The total phosphorus (TP) concentrations were, respectively, 15 μg/l and 28 μg/l. An empirical model whose inputs were morphometric, light conditions and dissolved organic carbon parameters obtained from in situ measurements was employed for the present study. The model calculated primary production with a time‐step of 10 min, and a spatial resolution of 10 cm, from sunrise to sunset and from lake surface to lake bottom. The primary production of periphyton and phytoplankton was almost equal in the clear lake, whereas only phytoplankton contributed to whole‐lake primary production in the dark lake because of the stronger light attenuation in the water column. The results of the present study indicated the depth‐distribution profiles differed dramatically between the two lakes. The clear lake had a deep, U‐shaped curve, with the productive layer reaching considerable depth soon after sunrise and maintaining a similar profile throughout the light hours. In contrast, the dark lake production declined rapidly with increasing depth, whereas the profile changed over the day reaching the greatest depth at noon.     

Water use (and abuse) and its effects on the crater‐lakes of Valle de Santiago,Mexico

Most Mexicans live in the arid and semiarid regions that represent two‐thirds of the Mexican territory, where water is scarce. Natural, as well as human, causes are favouring the degradation of Mexican lakes. There is a clear need to develop and implement sustainable water‐use programmes at a catchment scale. However, the accelerated degradation rate of the Mexican lakes means that there will not be enough time to perform whole‐basin evaluations to establish sustainable water‐use programmes before the lakes dry up. The case of the Valle de Santiago crater‐lakes clearly illustrates the declining trend that Mexican inland aquatic resources follow. Vegetation clearance, overgrazing, abatement of phreatic waters and salinization have induced severe erosion and overall desertification (land degradation) in the basin for what, it seems, a long time (i.e. prehispanic times). In this way, human activities could be provoking at least the following negative consequences: a hotter and drier local climate, water scarcity, dust storms and soil salinization. The aquatic (surface and groundwater) resources of the Valle de Santiago basin have been seriously threatened. Two of the four crater‐lakes have already dried up and phreatic mantle abatement reaches up to 2.5 m per year. In spite of these facts, no sustainable water‐use programme has been established yet. The future scenery of this Mexican basin looks alarmingly like many other basins in the central and northern Mexican territories.     

Evidence of successful river spawning by lake trout (Salvelinus namaycush) in the Lower Niagara River,Lake Ontario

Restoration of a wild-produced lake trout Salvelinus namaycush population in Lake Ontario has not been successful despite the adult population often meeting or exceeding restoration targets. Lack of high-quality spawning habitat in Lake Ontario is suggested as one impediment to recruitment of wild lake trout, although the quantity and location of spawning habitat is poorly understood. If high-quality spawning habitat is limited in Lake Ontario, lake trout may be using uncommon spawning locations such as rivers. Anecdotal angler accounts point to the Niagara River as a lake trout spawning location. To better understand the potential of the Niagara River as a spawning location, egg and juvenile fish collections were conducted 12–14 river kilometers from the mouth of the Niagara River from 2010 to 2012; and mature female lake trout with surgically implanted acoustic tags were monitored from 2015 to 2019. Genetic analyses confirmed 60% of collected eggs and 93% of collected post-hatch juvenile fish in the Niagara River were lake trout. Tagged female lake trout returned to the Niagara River over consecutive years during the spawning season. The short duration of lake trout presence in the river (mean = 56 days/year) suggests female lake trout use the Niagara River primarily for spawning. Diversity in spawning locations may provide lake trout population’s resilience against environmental variability through a portfolio effect. Improved identification of riverine spawning locations, including their overall contribution to wild recruitment, may be a useful tool for managers to restore a wild-produced population of lake trout in Lake Ontario.     

云南九大高原湖泊保护与治理资金保障机制研究

资金保障是开展湖泊保护治理工作的重要后盾。目前湖泊治理资金的来源仍较为单一,缺乏有效的融资手段,难以满足湖泊治理的需要,因此,有必要开展湖泊保护与治理资金保障机制的研究。近年来,云南省对省内九大高原湖泊持续开展了大规模的保护和治理工作,取得了一些成功经验。在归纳总结云南九大高原湖泊保护治理资金保障机制现状的基础上,分析了目前资金投入保障机制存在的问题,并结合流域实际情况对如何建立和完善湖泊经济支撑体系进行了探索,提出了持续健康的高原湖泊保护和治理资金保障长效机制。     

Implications for the design of artificial lakes of a study of the Craigavon lakes

Two linked artificial lakes in the new town of Craigavon in Northern Ireland are used for both stormwater management and recreation. The lakes have not only fulfilled their engineering function of preventing flooding but the water quality has been high enough to allow recreation on and beside them. A study of water quality has shown that phosphorus loading-trophic state models apply to these artificial lakes. These models may be able to be used in the design of artificial lakes elsewhere to achieve optimum design and acceptable water quality.     

Simulation of water-bloom in a eutrophic lake—IV Modeling the vertical migration in a population of Microcystis aeruginosa

Simulation of the water-bloom dominated by Microcystis (blue-green algae) was carried out by modifying the mathematical model presented previously on the rising and sinking of the algal colonies through a still water-column. In contrast to the earlier work on the simulation of single colonies, an overall behavior of many algal colonies, having not only the size distribution but also having distribution initially throughout the water-column was simulated. The points of the model modified are: (i) the specific growth rate was shown by a quadratic function of light intensity that takes the inhibitory effect into account and (ii) the extinction coefficient incorporated the light-shielding effect by the algal cells existent depthwise in the water-column rather than a linear function of the concentration of suspended materials in the water.The numerical solutions of the model (280 dimensions) were in agreement qualitatively with the observations ever reported on Microcystis behavior in eutrophic lakes. Factors relevant to the extinction coefficient underwater, i.e. the concentrations of either Microcystis colonies or other suspended materials were significant from the viewpoint to control the algal growth as a whole, assuming that no nutrients were limiting. The vertical mixing of lake waters was effective for decreasing the average value of the specific growth rate expecially when the concentrations of colonies or other materials were large. Consequently, an artificial aeration was suggested to be a commendable means to ward off the water-bloom.     

长江中游底泥质量现状调查研究

为研究长江中游底泥的质量现状,选取干流和湖泊点采集底泥样品,对主要指标(重金属、总P、总N及有机质)进行测试分析,采用NOAA泥沙质量标准和背景值质量标准对底泥质量进行模糊综合评价。从总体上看,中游干流底泥质量较好,而湖泊点底泥质量不容乐观。中游干流八处采样点中七处底泥质量良好,城陵矶莲花塘底泥质量最差,对水体环境存在一定有害风险;中游五处湖泊采样点中监利天鹅洲白暨豚保护区和洪湖深水区两处底泥质量良好,洞庭湖和武汉东湖质量一般,而梁子湖底泥质量较差。为维护长江的水生生态环境,应有效控制进入长江(尤其是邻近湖泊)的点源及面源污染。     

小型湖泊应用于地表水源热泵时的热承载能力分析

介绍了小型湖泊应用于地表水源热泵时的两种热承载能力计算方法——水面温度法和均匀混合法，并采用这两种方法计算了杭州小型湖泊应用于地表水源热泵时的热承载能力。计算结果表明：水面温度法较客观地反映了实际的排水混合及水温恢复过程，可信度更高。用水面温度法对7个代表性城市小型湖泊热承载能力进行分析的结果表明：夏季热承载能力在23.4～29.5 W/m2之间，冬季热承载能力在31.6～45.7W/m2之间；在设计这类系统时关键在于满足夏季热承载能力的约束。