2002-2018年滇池外海蓝藻水华暴发时空变化特征及其驱动因子

为弄清滇池外海蓝藻水华暴发时空变化规律及其影响因素,将滇池外海分为北、中、南3个区域,基于2002—2018年期间中分辨率成像光谱仪(MODIS)反演的水华面积,分析了上述3个区域蓝藻水华的时空变化特征。基于2007—2018年水文、气象和出入流数据,构建了外海三维水动力生态模型(AEM3D),并计算了各区域的水力滞留时间。通过冗余分析(RDA)、随机森林(RF)和斯皮尔曼相关分析方法,分析了影响以上区域蓝藻水华暴发的主要驱动因子。结果表明：2002—2018年期间,整个滇池外海区域年平均水华面积比(水华面积占该区域总面积比例)呈缓慢下降趋势,空间上由北向南依次递减,整个外海水华暴发面积最大主要发生在秋季。在外海北部区域,其东部水华较西部更为严重,而在中部和南部区域,呈现西部水华较东部更为严重的空间分布模式。通过对各影响因子的统计分析发现,风速、水温和日照时长是上述各区域中蓝藻水华暴发的主要决定性因素。水华暴发期间以西南风为主导风向,且上述区域的水华面积比随风速增加呈下降趋势。在外海各区域,水力滞留时间与水华暴发面积均呈显著正相关,空间上水力滞留时间由北向南逐渐增大,风速和风向是影响蓝...     

东昌湖浮游生物群落多样性季节变动与水质关系

报道了浮游生物物群落多样性指数与水质关系及初步分析了东昌湖的水质情况。2004年4月至2005年3月,采用PFU法及化学检测法对国内第二大人工湖——山东东昌湖的三个湖区9个采样点的浮游生物及水化学指标进行了初步调耷。共观察到浮游藻类76种,其中污染指示种为17种;原生动物92种,其中污染指示种为21种。浮游生物物种组成的多样性指数及化学水质分析显示,各湖区水质优劣程度依次为南湖区〉东南湖区〉西北湖区,调查结果表明东昌湖属于富营养化水体。     

The annual cycle of heat content and mechanical stability of hypersaline Deep Lake,Vestfold Hills,Antarctica

Deep Lake, a hypersaline lake of about ten times seawater concentration, rarely freezes and is characterized by a monomictic thermal cycle, Winter circulation, at c. –17 °C, lasts for two to three months. In summer, epilimnetic temperatures from 7–11 °C result in large vertical thermal gradients (21–26 °C) which combine with the enhanced rate of density change per degree Celsius, accompanying such high salt concentration, to produce a particularly stable density configuration in Deep Lake (Schmidt stability c. 8000 g-cm cm^–2; 0.785 J cm^–2). The Birgean annual heat budget (c. 24500 cal cm^–2; 102.7 10³ J cm^–2) is comparable to that of a temperate lake with a similar mean depth, despite the comparatively high ratio of Birgean wind work to annual heat budget (0.37 g-cm cal^–1). Deep lake retains c. 50% of the incident solar radiation during the short summer heating period; within the range estimated for first class lakes in North America. Extended daylight hours certainly contribute to the high maximum rate of heating in the lake (444 cal cm^–2 day^–1; 1.86 10³ J cm^–2 day^–1). Deep Lake cools at a rate less than half its average heating rate. Partitioning the total stability into thermal and saline components shows that salinity can contribute up to c. 20% of the maximum summer Schmidt stability. In early summer, the effect of small melt-streams is to increase stability by diluting the epilimnion. In autumn, evaporative water loss can overtake this effect, creating small de-stabilizing salinity gradients. The usually short-term stabilizing influence of snowfall and drift is less predictable, but is probably more common in winter when strong winds are most frequent.Hypersalinity has a profound effect on the physical cycle of Deep Lake, through freezing point depression and the increased rate of density change with temperature. These changes affect the lake's biota, both in relation to osmotic stress, and by effectively exposing them to a more thermally extreme environment. A comparison between Deep Lake and a smaller lake of similar salinity (Lake Hunazoko, Skarvs Nes), demonstrates that it is inappropriate to consider the biological effects of salinity in isolation. The smaller lake offers warmer epilimnetic conditions for at least part of the summer, which may explain the much greater limnetic algal production in Lake Hunazoko.     

Diel variations of selected physico-chemical parameters in Lake Kissimmee,Florida

Every two months, diel depth profiles were made of dissolved oxygen, pH, temperature and conductivity at two stations in Lake Kissimmee, Florida, from July 1974 through June 1975. Results suggest that stratification does not occur in the large (137 km²), shallow (mean depth 2.5 m) lake, though steep vertical gradients in these parameters may develop. The data also suggest that when these gradients do occur, they rapidly degenerate at night or under slight wind stress. Since many Florida lakes are relatively shallow (mean depth < 5 m) and topography offers little obstruction to wind action, it is believed that the holomictic condition observed in Lake Kissimmee may be typical of the state's lakes, particularly those in the central portion of the peninsula.     

Invasion biology of Ponto-Caspian onychopod cladocerans (Crustacea: Cladocera: Onychopoda)

Lake Taihu is characterized by its shallowness (mean depth = 1.9 m) and large surface area (2,338 km²). Runoff sources are mostly from the mountainous west and southwest, and outflows are located throughout East Taihu. This causes shorter retention times in the south. In contrast, urban pollutants discharge into northern Taihu and result in poor water quality. Non-point pollution from rural areas and sewage wastewater is the primary pollution source. Water current velocity ranges from 10–30 cm s⁻¹, and surface currents normally follow wind direction. Bottom currents appear to be a compensation flow. Most wave heights are less than 40 cm, and underwater irradiance correlates to seston in the water column. Lacustrine sediment is distributed in littoral zones, mostly along the western shoreline, with almost no accumulation in the lake center. Intensive aquaculture in East Taihu caused eutrophication and hampered water supply in surrounding areas. In addition, development of marshiness in the eastern littoral zones and East Taihu has occurred. The function of flood discharging of East Taihu has been limited by flourishing macrophytes. The problems facing in Lake Taihu will be alleviated by improving the management of nutrient sources into the lake. Guest editors: B. Qin, Z. Liu & K. Havens Eutrophication of shallow lakes with special reference to Lake Taihu, China     

Exchange between littoral and pelagic waters in a stratified lake due to wind-induced motions: Lake Kinneret, Israel

We used field data and three-dimensional numerical simulations to investigate the exchange processes between the lake boundaries (littoral) and lake interior (pelagic) due to wind-induced motions in Lake Kinneret, Israel. The field data showed large-scale metalimnion oscillations with amplitudes up to 10 m in response to westerly diurnal winds, the existence of a well-defined turbidity intrusion into the metalimnion of the lake and a benthic boundary layer (BBL). The observed vertical and horizontal movements of the turbidity were explained by the vertical and horizontal advection associated with basin-scale wave motions and a residual circulation set up by the basin-scale motions and the wind field. The horizontal advective transport in the metalimnion, associated with the velocities induced by the basin-scale mode-two Poincaré wave, provided the primary control for the exchange between the lake boundaries and lake interior on daily time scales. Detailed comparison of simulation results with both temperature and velocity profiles revealed excellent agreement for time scales from hours to days. The validated numerical model was used to extract the residual motions that provided the secondary exchange flows, in the various regions of the lake on time scales from days to weeks. The residual motion in the surface layer consisted of a combination of an anticlockwise gyre in the western half of the lake and a weak clockwise gyre along the eastern boundary that were forced by the curl of the wind field. In the metalimnion, residual motions were predominantly forced by the basin-scale internal wave motions and an anticlockwise gyre established itself throughout the whole basin. Lastly in the BBL, residual motions consisted of an anticlockwise gyre, but the geographic distribution was patchy. Together these results provide new insight into a proper characterization of the processes underlying the flux paths of water and particles between the lake boundaries and lake interior. Handling editor: L. Naselli-Flores     

Methane production in meromictic Ace Lake,Antarctica

Methane occurred in the monimolimnion, at depths greater than 11 m, of an antarctic meromictic lake, Ace Lake (depth 24.7 m). Although the water of the lake was of approximate marine salinity, bottom waters were depleted in sulfate (less than 1 mmol 1^–1). The temperature of the bottom waters of the lake were constantly between 1 °C and 2 °C. Rates of methanogenesis from ¹⁴C-labelled precursors (bicarbonate, formate and acetate) were determined in time course experiments with the detection of ¹⁴CH₄ produced by a gas chromatography-gas proportional counting system. Rates of ¹⁴CH₄ production were difficult to determine as the reactions were always near our limit of detection.Reliable determinations of rates of methanogenesis at some depths using some precursors were obtained, the fastest rate being 2.5 µmol kg^–1 day^–1 at depth 20 m. Assuming constant rates of methanogenesis with time, this would equate to a turnover of methane in the lake every two years.The slow rate of methanogenesis suggests that the methanogens in Ace Lake may be working at well below their optimum temperature although definitive statements regarding the presence of psychrophilic methanogens in this antarctic lake must await isolation attempts or longer field studies using alternative methodologies.     

The limnology of Cabora Bassa, Moçambique, during its first year

SUMMARY. Cabora Bassa, a new impoundment in the Middle Zambezi River, was closed in December 1974, filling rapidly to 12m below full supply by May 1975.
The lake, with five basins, lies along a west–east axis almost parallel to prevailing south-easterly winds. Limnological records, from several stations along the lake axis, indicated homoiothermal conditions until September, the hot dry season. From then until records ceased in December, thermoclines and oxyclines were present in the deeper eastern basins. Hydrogen sulphide was recorded in hypolimnial waters towards the end of the year. Open water of the shallow, wind- and wave-swept eastern basins remained oxygenated throughout the year.
Water transparency increased fivefold from April to December, increasing too from east to west. pH was alkaline becoming more acid in cool winter months and in bottom waters of stratified basins. Conductivity ranged from 95 to 119 °S cm⁻¹ with higher values in shallow lake margins. Chemical content of surface waters showed little seasonal or spatial variation and was, in general, comparable with pre-impoundment levels.
Duration of the initial 'productive phase' will probably be shorter than Kariba due to more rapid lake water exchange but indications are that productivity will be higher in the maturation phase.     

Modeling impacts of Yangtze River water transfer on water ages in Lake Taihu, China

To improve water quality and alleviate eutrophication in Lake Taihu, the third largest freshwater lake in China, a Yangtze River water transfer project was initiated in 2002 to bring water from the Yangtze River to Lake Taihu to dilute and divert pollutants out of the lake. We used a three-dimensional numerical model, Environmental Fluid Dynamics Code, to study the impacts of water transfer on the transport of dissolved substances in the lake by using the concept of water age. In particular, the influences of inflow tributaries and wind forcing on water age were investigated. Model results showed that the effect of water transfer on transport processes in the lake is strongly influenced by hydrodynamic conditions induced by wind and inflow/outflow tributaries. During the simulation year (2005), the water ages in Lake Taihu were highly variable both spatially and temporally, with a mean of approximately 130 days in summer and 230 days in the other seasons. Southeasterly winds—dominant in the summer—could improve the quality of water by reducing the water age in the eastern areas of the lake, which are used as a drinking water source, and in Meiliang Bay, the most polluted bay. In terms of dilution, the most efficient flow rate for transferred water was predicted to be approximately 100 m³/s. The spatial distribution of water ages showed that water transfer may preferentially enhance exchanges in some areas of the lake unless nutrient concentrations in the transferred water are reduced to a reasonable level. This study provides useful information for a better understanding of the complex hydrodynamic and mass transport processes in the lake, which is important for developing and implementing effective ecological restoration strategies in the region.     

The Role of Fish Communities in Water Quality Management of a Large Shallow Lake

Management measures of Lake Balaton such as wetland reconstruction at the main inflow to the lake along with the “unplanned” commercial fishery led to great changes in the density and biomass of fish populations. There was no significant difference in CPUE data between the two, eastern and western, basins. Biomass of total fish stock in Lake Balaton has decreased substantially, 2–3 times between 1991–1999, and ranges between 120–194 kg ha⁻¹. Bottom‐up effects are more important than the top‐down effects due to the impact of internal nutrient load. Changes in the biomass and thus the activity of omnivorous fish in the lake lowered the intensity of various indirect effects and feedback mechanisms causing changes in the nutrient metabolism of the lake. Intensified fishery effort in Lake Balaton did not result in an increased stock of piscivores. The ratio of piscivores and omnivores remained at 5% during the whole study period. Despite this low piscivores to omnivores ratio, the water quality has improved in all basins.     

The importance of groundwater flow to the formation of modern thrombolitic microbialites

Modern microbialites are often located within groundwater discharge zones, yet the role of groundwater in microbialite accretion has yet to be resolved. To understand relationships between groundwater, microbialites, and associated microbial communities, we quantified and characterized groundwater flow and chemistry in active thrombolitic microbialites in Lake Clifton, Western Australia, and compared these observations to inactive thrombolites and lakebed sediments. Groundwater flows upward through an interconnected network of pores within the microstructure of active thrombolites, discharging directly from thrombolite heads into the lake. This upwelling groundwater is fresher than lake water and is hypothesized to support microbial mat growth by reducing salinity and providing limiting nutrients in an osmotically stressful and oligotrophic habitat. This is in contrast to inactive thrombolites that show no evidence of microbial mat colonization and are infiltrated by hypersaline lake water. Groundwater discharge through active thrombolites contrasts with the surrounding lakebed, where hypersaline lake water flows downward through sandy sediments at very low rates. Based on an appreciation for the role of microorganisms in thrombolite accretion, our findings suggest conditions favorable to thrombolite formation still exist in certain locations of Lake Clifton despite increasing lake water salinity. This study is the first to characterize groundwater flow rates, paths, and chemistry within a microbialite‐forming environment and provides new insight into how groundwater can support microbial mats believed to contribute to microbialite formation in modern and ancient environments.     

A spatio‐temporal framework for efficient inventories of natural resources: A case study with submersed macrophytes

Questions: Does a reduced nutrient load in open water increase species richness and the importance of regional and local site characteristics for species abundance and spatial distribution? Can we build lake‐specific models of macrophyte abundance and distribution based on site characteristics in order to prepare a cost‐efficient framework for future surveys? Location: Lake Constance, 47°39′N, 9°18′E. Methods: Generalized additive models (GAMs) were used to predict the potential distributions of eight species and overall species richness. Submersed macrophyte distribution in 1993 was compared with corresponding data from 1978, when eutrophication was at its maximum. Results: Spatial predictions for eight species and overall species richness were relatively accurate and independent of water chemistry. Depth was confirmed as a main predictor of species distribution, while effective fetch distance was retained in many models. Mineralogical variables of sediment composition represent allogenic and autogenic sediment sources and their east‐west gradient in Lake Constance corresponded to east‐west gradients of species distribution and richness. GAMs appeared more efficient than generalized linear models (GLMs) for modelling species responses to environmental gradients. Conclusions: Reduced trophic status increases species richness and the importance of regional and local site characteristics for species abundance and distribution. Our models represent a spatio‐temporal framework for future lake monitoring purposes and allow the development of effective monitoring; this could be generalized for many ecosystem types and would be particularly efficient for large lakes such as Lake Constance.     

Protist diversity in a permanently ice-covered Antarctic Lake during the polar night transition

The McMurdo Dry Valleys of Antarctica harbor numerous permanently ice-covered lakes, which provide a year-round oasis for microbial life. Microbial eukaryotes in these lakes occupy a variety of trophic levels within the simple aquatic food web ranging from primary producers to tertiary predators. Here, we report the first molecular study to describe the vertical distribution of the eukaryotic community residing in the photic zone of the east lobe (ELB) and west lobe (WLB) of the chemically stratified Lake Bonney. The 18S ribosomal RNA (rRNA) libraries revealed vertically stratified populations dominated by photosynthetic protists, with a cryptophyte dominating shallow populations (ELB–6 m; WLB–10 m), a haptophyte occupying mid-depths (both lobes 13 m) and chlorophytes residing in the deepest layers (ELB–18 and 20 m; WLB–15 and 20 m) of the photic zone. A previously undetected stramenopile occurred throughout the water column of both lobes. Temporal variation in the eukaryotic populations was examined during the transition from Antarctic summer (24-h sunlight) to polar night (complete dark). Protist diversity was similar between the two lobes of Lake Bonney due to exchange between the photic zones of the two basins via a narrow bedrock sill. However, vertical and temporal variation in protist distribution occurred, indicating the influence of the unique water chemistry on the biology of the two dry valley watersheds.     

鄱阳湖渔业资源现状及其环境监测

1997－1999年对鄱阳湖区渔业资源与环境进行了动态监测,统计渔获物2778kg,生物学测定1627尾,采集到鱼类122种,隶属于12目21科77属,其中鲤科鱼类种类最多,计65种,占53．3％,湖区渔获物个体偏小,以1－2龄鱼为主,鲤、鲫基本上是当年鱼,鄱阳湖现有鲤,鲫产卵场33处,主要分布在湖区东,南,西部,年均有效产卵面积616．66km^2,年均产卵量56．85亿,鄱阳湖区湖口,蛤蟆石,星子,康山水域湖水的pH,COD,Cr^ 6,Cd,Zn,Cu,Pb,总磷,氨氮,总汞均未超过渔业水质标准,鄱阳湖区水质良好。     

Effects of Imposed Salinity Gradients on Dissimilatory Arsenate Reduction, Sulfate Reduction, and Other Microbial Processes in Sediments from Two California Soda Lakes

Salinity effects on microbial community structure and on potential rates of arsenate reduction, arsenite oxidation, sulfate reduction, denitrification, and methanogenesis were examined in sediment slurries from two California soda lakes. We conducted experiments with Mono Lake and Searles Lake sediments over a wide range of salt concentrations (25 to 346 g liter⁻¹). With the exception of sulfate reduction, rates of all processes demonstrated an inverse relationship to total salinity. However, each of these processes persisted at low but detectable rates at salt saturation. Denaturing gradient gel electrophoresis analysis of partial 16S rRNA genes amplified from As(V) reduction slurries revealed that distinct microbial populations grew at low (25 to 50 g liter⁻¹), intermediate (100 to 200 g liter⁻¹), and high (>300 g liter⁻¹) salinity. At intermediate and high salinities, a close relative of a cultivated As-respiring halophile was present. These results suggest that organisms adapted to more dilute conditions can remain viable at high salinity and rapidly repopulate the lake during periods of rising lake level. In contrast to As reduction, sulfate reduction in Mono Lake slurries was undetectable at salt saturation. Furthermore, sulfate reduction was excluded from Searles Lake sediments at any salinity despite the presence of abundant sulfate. Sulfate reduction occurred in Searles Lake sediment slurries only following inoculation with Mono Lake sediment, indicating the absence of sulfate-reducing flora. Experiments with borate-amended Mono Lake slurries suggest that the notably high (0.46 molal) concentration of borate in the Searles Lake brine was responsible for the exclusion of sulfate reducers from that ecosystem.     

Microbial sulfate reduction in a brackish meromictic steppe lake

Patterns of sulfate reduction were studied in water and sediments of Lake Shira, South Siberia, Russia. The lake was characterized by a high level of sulfate (91-116 mM). The concentration of hydrogen sulfide in the anoxic waters of the lake reached 0.6 mM. In summer the sulfate reduction rate in the water column, measured by radiometric technique, varied from 0.25 to 9.81 mol sulfate l^-1 d^-1. There were two peaks of sulfate reduction activity: just below the chemocline and near the sediment surface. Sulfate reduction rate in the profundal silts ranged from 4.1 to 90.6 mol l^-1 d^-1. The zone of the most active sulfate reduction was restricted to the surface sediment layers. The acceleration of sulfate reduction rate (up to 236 mol l^-1 d^-1) and the increase of density of viable sulfate reducers (up to 2 x 10⁵ cells ml^-1) were recorded in the littoral sediments adjacent to the mouth of the Son River and sewage discharge. It was apparently caused by the input of allochthonous organic substrates and also by a high environmental temperature. On an areal basis, sulfate reduction rate in the water was approximately 8 times higher than that in the profundal sediments. Sulfate reduction was the most important process of anaerobic oxidation of organic carbon in Lake Shira. In summer in the profundal zone of the lake, sulfate reducers were able to mineralize about 67% of the daily integrated primary production of phototrophic and chemotrophic organisms.     

太湖湖滨带生态系统健康评价

根据湖滨带生态系统的特点,运用综合健康指数法建立了湖滨带生态系统健康评价体系,由目标层、准则层、指标层构成,其中准则层由湖滨带水质状况、底泥状况、植被状况、其它生物状况(浮游动物、浮游植物、底栖动物)、岸带物理状况5项组成,指标层由总氮、总磷、溶解氧、挺水植物覆盖率等15项指标构成。采用专家打分法、熵值法分别确定了准则层、指标层的权重系数。对太湖湖滨带33个点位进行了采样分析,并进行无量纲化处理后应用到所建立的评价体系中。评价结果显示33个点位中为"很健康"、"健康"、"亚健康"、"疾病"、"严重疾病"的分别占0%、24.2%、21.2%、51.5%及3.0%,也即超过一半的点位处于"疾病"状态。只有东太湖刚刚超过"健康"分数的下限,东部沿岸、贡湖、南部沿岸均处于"亚健康"状态,而梅梁湾、竺山湾、西部沿岸属于"疾病"状态,且竺山湾的生态健康状态最差。该评价结果与太湖湖滨带各分区的实际调查情况相符合,评价方法可靠性、可行性较强,可为其它湖泊湖滨带的生态系统健康评价提供一定的参照。     

Numerical modeling of vertical stratification of Lake Shira in summer

A one-dimensional numerical model and a two-dimensional numerical model of the hydrodynamic and thermal structure of Lake Shira during summer have been developed, with several original physical and numerical features. These models are well suited to simulate the formation and dynamics of vertical stratification and provide a basis for an ecological water-quality model of the lake. They allow for the quantification of the vertical mixing processes that govern not only the thermal structure but also the nutrient exchange, and more generally, the exchange of dissolved and particulate matter between different parts of the lake. The outcome of the calculations has been compared with the field data on vertical temperature and salinity distributions in Lake Shira. Lake Shira is meromictic and exhibits very stable annual stratification. The stratification is so stable because of the high salinity of the water. If the water in Lake Shira were fresh and other parameters (depth, volume, and meteorology) were the same, as now, the lake would be mixed in autumn. Using the newly developed models and using common meteorological parameters, we conclude that Lake Shira will remain stratified in autumn as long as the average salinity is higher than 3‰.     

近十年太湖生态系统服务功能价值变化评估

理解和把握近年来湖泊生态系统服务功能退化规律的最佳手段是评估其生态系统服务功能价值的变化。以太湖为例,基于近十年来太湖生态系统的科学调查数据,综合运用生态学及经济学方法,对太湖生态系统的四大类功能和11个亚类的服务价值进行了综合评估。研究结果表明,2000年、2003年、2007年和2009年太湖生态系统服务总价值分别为1627.98亿元、1908.68亿元、1503.99亿元和3528.73亿元,保持逐渐升高的趋势,但是在2007年却意外降低。从2000年到2009年太湖生态系统服务功能价值构成发生了一些变化,2000年以供水功能为主体,约占总价值的43%,2003年和2007年变为以航运功能为主体,分别占总价值的41.31%和38.73%,而2009年又变为以旅游功能为主体,约占总价值的52.52%,总体上由供给功能向文化功能转变。航运功能和旅游功能急剧上升而供水功能急剧下降不利于长远发挥的太湖生态服务功能。蓝藻水华的发生可能降低太湖供给功能、支持服务功能和文化服务功能,进而对太湖生态服务的总价值产生负面影响。研究认为太湖生态系统对支持和保护人类社会具有重要的作用,为管理者和决策者有效的保护和管理湖泊生态系统提供了重要的信息。     

Thermal, mixing, and oxygen regimes of the Salton Sea, California, 1997–1999

The Salton Sea is a shallow (mean depth = 8 m; maximum depth = 15 m), saline (41–45 g l^–1), intermittently mixing, 57 km long, 980 km² lake located in the arid southwestern United States. The Sea is a wind driven system, with predominant winds paralleling the long axis of the lake, being strongest in spring and weakest in summer and fall. The Sea mixed daily or nearly daily between September and January. During this cooling period, moderate to high levels of dissolved oxygen (3–11 mg l^–1) were found throughout the water column. Mean water column temperature ranged from a minimum of 13–14 °C in early January to a maximum of 30–34 °C in July–September. During most of this warming period, the Sea was thermally stratified but subject to periodic wind driven mixing events. Winds were stronger in spring 1998 than in 1997 or 1999, causing more rapid heating of the lake that year and also delaying onset of anoxic conditions in bottom waters. During summer months, mid-lake surface waters were sometimes supersatured with oxygen, and bottom waters were hypoxic or anoxic with sulfide concentrations > 5 mg l^–1. Oxic conditions (> 1 mg O₂ l^–1) often extended a few meters deeper nearshore than they did well offshore as a consequence of greater mixing nearshore. Mixing events in late summer deoxygenated the entire water column for a period of days. Consumption of oxygen by sulfide oxidation likely was the principal mechanism for these deoxygenation events. Sulfide concentrations in surface waters were 0.5–1 mg l^–1 approximately 3 days after one mixing event in mid-August 1999. These mixing events were associated with population crashes of phytoplankters and zooplankters and with large fish kills. In the southern basin, freshwater inflows tended to move out over the surface of the Sea mixing with saline lake water as a function of wind conditions. Salinity gradients often contributed more to water column stability than did thermal gradients in the southeasternmost portion of the lake.