Mining lakes in a disturbed landscape: Application of the EC Water Framework Directive and future management strategies

Some of the several hundred Lusatian mining lakes originating from lignite mining will be among the largest and deepest lakes in Germany. A special problem of many of these lakes is severe acidification. According to the EC Water Framework Directive (WFD), artificial lakes larger than 0.5 km² have to be monitored and managed in order to establish or maintain a state of so-called good ecological water quality. Therefore the WFD demands the definition of type-specific reference conditions as those of the closest comparable surface water body type in nature, such as natural acidic volcanic crater lakes or oligo- to mesotrophic neutral hard water lakes. We propose a classification scheme for mining lakes applying acidity and planktonic colonization as criteria. Five types of lakes are distinguished ranging from extremely acidic to neutral hard water lakes. Phytoplankton and especially metazoan zooplankton are introduced as intriguing and simple indicators for different states of ecological quality in highly acidic mining lakes. We recommend that extremely and very acidic lakes should remain in the acidic state to protect these as valuable ecosystems, whereas moderately and weakly acidic lakes can be managed by external flooding, chemical or ecotechnological measures to achieve neutral water quality conditions necessary for recreation or fishery use.     

Some aspects of the seasonal distribution of flagellates in mountain lakes

In a larger regional survey in Tyrol, phytoplankton species composition and biovolume of mid-altitude and high-mountain lakes was studied. Results from eight lakes showed that flagellates (mainly Chrysophyceae, Dinophyceae, and Cryptophyceae) are important components of the phytoplankton.In the mid-altitude lakes a spring and an autumn maximum of Chrysophyceae as well as a summer maximum of large dinoflagellates are observed, whereas Cryptophyceae and Dinophyceae show irregular distributions. In the high-mountain lakes the seasonal variations of phytoplankton, including flagellates, are limited by the long duration of the winter situation. However similar sequences of phytoplankton assemblages as in the midaltitude lakes can be observed. Flagellates in high-mountain lakes are important to sustain phytoplankton standing crop under the winter snow and ice cover.In order to show similarities and differences of high-mountain and mid-altitude lakes, vertical profiles of phytoplankton from three lakes and seasonal patterns of Gymnodinium uberrimum from two lakes are compared. In addition the patterns of cryptomonads differing in their ecological requirements (Cryptomonas spp. and Rhodomonas minuta) are shown for a meromictic mid-altitude lake.     

On the occurrence, causes and potential consequences of low zooplankton to phytoplankton ratios in New Zealand lakes

SUMMARY. 1. New Zealand lakes are shown to have lower average zooplankton biomasses than north-temperate lakes of similar average phytoplankton biomass, expressed as cell volume or chlorophyll a , or similar average total phosphorus concentration, typically by a factor of 5 or more.
2. Evidence suggests that the relatively low zooplankton biomasses of New Zealand lakes may be related to a tendency for them to be dominated by large algae that are not directly available as food for zooplankton, with oligotrophy lakes in particular differing from north-temperate lakes in this respect.
3. This difference in turn may be related largely to their mixing regimes. All of the New Zealand lakes are polymietic or monomietic, whereas the northern lakes used for comparison are mostly dimietic. Also, hetero-cystous cyanobacteria are favoured by the low inorganic nitrogen concentrations that are typical of New Zealand lakes.
4. Poor nutritional quality of the phytoplankton, relating to nitrogen limitation in many New Zealand lakes, might supplement the effects of cell size.
5. Low exploitation of phytoplankton by zooplankton can be expected to produce a shift in the metabolism of New Zealand lakes towards the sediments. Among the potential consequences of this effect are increased hypolimnetic oxygen demand with increased susceptibility to development of large internal loads of nutrients, and consequently, increased sensitivity to accelerated eutrophication from any increase in external nutrient loads.     

OPINION Endless summer: internal loading processes dominate nutrient cycling in tropical lakes

SUMMARY. 1. Fossil diatom assemblages deposited in more than a dozen African lakes roughly 9500 years BP were dominated by a single planktonic species, Stephanodiscus astraea (Ehrcnb.) Grun. (although realistically this is likely to be a species complex). These diatoms flourished when lake-levels were maximal. Data are included from many of (he large African lakes, and others extending from Lake Abhé0, Ethiopia, to Lake Cheshi, Zambia.
2. Because the ecological physiology of Stephanodiscus species is well known one can predict the nutrient regime that must have existed when Stephanodiscus bloomed. Owing to competition for resources Stephano-discus species dominate when the supply ratio of silicon to phosphorus (in moles) in the epilimnion is relatively low (Si:P∼1). Consequently, lakes dominated by S. astraea are often hypereutrophic.
3. We propose a series of hypotheses to explain why tropical lakes have decreasing Si:P ratios as lake-levels increase, primarily owing to internal P-loading processes in the epilimnia. These observations appear to contradict present conceptions of the fundamental relationships governing nutrient loadings to and within lakes. Tropical lakes appear to have had increasing epilimnetic phosphorus loading as lake-levels increased. In contrast, large, deep lakes in the temperate zone are usually oligotrophic, with high Si:P ratios.
4. Our major conclusion is that regeneration rates are greater than removal rates for phosphorus in tropical lakes as compared to temperate lakes, especially where epilimnelic mixing exceeds 50 m. Biological control of the elemental cycles dominate in tropical lakes, whereas nutrient cycles in temperate lakes are dominated by physical processes for a large part of the year. This results in major differences in the fundamental mechanisms of nutrient regeneration and their relationships to morphometric features of lakes in the two regions.     

城市河湖生态系统健康评价——以北京市“六海”为例

健康的城市河湖才能发挥生态环境功能,体现景观和人文价值。城市河湖健康评价是城市河湖科学管理和生态恢复的前提和基础。对城市河湖生态系统健康概念和内涵进行了探讨,建立了评价指标体系和评价模型。以北京“六海”为例,对各子湖的健康状况进行比较评价。结果表明,中海和南海处于不健康向临界转化的状态,其余4个湖均处于不健康状态;水环境质量、水生态系统结构和功能以及水滨空间结构是影响“六海”健康水平的制约因素;除南海外,各湖的健康程度都处于很差的级别。中海和南海的整体生态环境好于其余4湖,对健康和临界状态的隶属度之和接近0.6,可恢复程度处于中等水平;其余4湖对健康和临界状态的隶属度之和均小于0.3,恢复困难。对“六海”的生态恢复和科学管理提出建议:①控制点源、面源污染,改善入湖和湖水水质;②改善“六海”的水文条件;③恢复水生态系统结构和水滨空间。     

Relationships between morphometry,geographic location and water quality parameters of European lakes

I addressed the question how lake and catchment morphometry influences water chemistry and water quality over a large scale of European lakes, and developed the regression equations between most closely related morphometric and water quality indices. I analysed the data of 1,337 lakes included in the European Environment Agency (EEA) database, carrying out separate analyses for three basic lake types: large lakes (area ≥100 km², 138 lakes), shallow lakes (mean depth ≤3 m, 153 lakes) and large and shallow lakes (area ≥100 km² and mean depth ≤8 m, 35 lakes). The study revealed that in Europe, the lakes towards North are larger but shallower and have smaller catchment areas than the southern lakes; lakes at higher altitudes are deeper and smaller and have smaller catchment areas than the lowland lakes. Larger lakes have generally larger catchment areas and bigger volumes, and they are deeper than smaller lakes, but the relative depth decreases with increasing surface area. The lakes at higher latitudes have lower alkalinity, pH and conductivity, and also lower concentrations of nitrogen and phosphorus while the concentration of organic matter is higher. In the lakes at higher altitudes, the concentration of organic matter and nutrient contents are lower and water is more transparent than in lowland lakes. In larger lakes with larger catchment area, the alkalinity, pH, conductivity and the concentrations of nutrients and organic matter are generally higher than in smaller lakes with smaller catchments. If the lake is deep and/or its residence time is long, the water is more transparent and the concentrations of chlorophyll a, organic matter and nutrients are lower than in shallower lakes with shorter residence times. The larger the catchment area is with respect to lake depth, area and volume, the lower is the water transparency and the higher are the concentrations of the nutrients, organic matter and chlorophyll as well as pH, alkalinity and conductivity. The links between lake water quality and morphometry become stronger towards large and shallow lakes. Along the decreasing gradients of latitude, altitude and relative depth, the present phosphorus concentration and its deviation from the reference concentration increases.     

Tropical lakes — functional ecology and future development:. The need for a process-orientated approach

The major classes of tropical lakes include shallow, lowland lakes; deep, tertiary lakes; high altitudinal lakes; rainforests lakes; and man-made lakes at all latitudes and altitudes. Basic ecological processes are similar in temperate and tropical lakes, including grazing, competition, predation and abiotic adaptation. Small tropical lakes of intermediate age are probably not biotically more complicated than similar-sized temperate lakes. The structure of the areas of adaptative radiation and the dispersal ability of the species are important for the present distribution of taxa. Fish play a key role in the tropics since many species both consume zooplankton and compete with them for algal and pelagic sestonic food. This important co-evolution between fish and algae, leaving a fraction of the algal community with a predation refuge, may have decreased the ability of zooplankton to exploit algae. In addition, heavy predation from juvenile and adult fish may greatly simplify the zooplankton community, and have resulted in the scarcity of Cladocera, notably the efficient filter-feeder Daphnia. Little is known of possible physiological constraints to cladoceran distribution, however. Thus similar co-evolution as hypothesized between fish and algae seems not to have occurred to such a great extent between fish and zooplankton. Diurnal patterns in habitat selection of fish may also influence nutrient re-distribution in the tropics as in many temperate lakes. Serious environmental problems threaten tropical lakes, including eutrophication, clear-cutting of the rain forest, unwise introduction of new species not adapted to prevailing conditions, overfishing, extensive use of biocids, and probably acidic rain in areas with poorly buffered waters. Important processes in tropical lakes could be elucidated by concentrating research upon the fate of phytoplankton successional production, involving competition, grazing, sinking, fungi and bacterial attack. Co-evolution of fish and algae should be further investigated as it could in part explain the general scarcity and simplicity of the zooplankton community. Limnocorral experiments should also be used for further assessing processes in tropical lakes.     

The alkaline,saline lakes of Uganda: a review

Most saline lakes in Uganda are alkaline and occur in closed basins associated with the Western Rift Valley. They are small shallow lakes exhibiting considerable temporal variation in volume and surface area. They have been categorized as maar lakes. Salinity in these lakes results from evaporative concentration of ions leached from their drainage basins. These lakes can be grouped into three broad categories: carbonate-chloride, sulphate-chloride, and chloride lakes according to the dominant anion(s). The relative amounts of ions in solution determines, in part, the limnochemical characteristics of the lakes. There is some evidence of thermal and chemical stratification in the deeper lakes. Records of the limnobiology in these lakes are scarce and not exhaustive.     

Current status and future tendency of lake eutrophication in China

Current trophic status and trend of Chinese freshwater lakes were investigated in this study. The results showed that all lakes studied were commonly undergoing the eutrophication process, water quality decreased and lake's ecosystem is being declined. Most of the urban lakes are facing serious eutrophication. Many medium-sized lakes are in metrophic or eutrophic status, some local water are even approaching the hypertrophic level. The famous five freshwater lakes in China have entered into eutrophication in the condition of higher nutrient load. Lake Taihu, Hongze and Caohu are already in eutrophic state. Eutrophic lakes are mainly distributed in the middle and lower reaches of Yangtze River and Yungui plateau. Lake eutrophication developed rapidly. Among the 34 lakes studied in 1970's, most of lakes were in the mesotrophic status,mesotrophic water area accounted for 91.8%. With the nine year of 1978-1987 the area percentage of oligotrophic lakes decreased from 3.2% to 0.53%, and that of eutrophic lakes increased from 5.0% to 55.01%. Recent data showed 57.5% lakes were in eutrophic and hypertrophic status of the 40 surveyed lakes.Eutrophic trend of Lake Taihu, Chaohu and Xuanwu in the region of the middle and lower reaches of Yangtze River was predicated using the ecological stress model. The results showed that in 2008 Lake Taihu, Chaohu and Xuanwu might be of eutrophication, eutrophication and hypertrophication, respectively if no control measurement is taken. Provided the pollution water treatment rate is 60% in 2030, approximately 30 billion ton pollution water would still be discharged directly in the lakes. Therefore, in 2030 the urban lakes in China might be eutrophication or hypertrophication, and most of the medium-sized lakes at the urban-rural fringe might be in eutrophication or hypertrophication. The famous five biggest freshwater lakes in China might be eutrophication if control countermeasures are taken as now.Lake eutrophication has become a serious environmental problem in China. Based on the domestic and foreign experiences of the eutrophic control technologies, both nutrient pollution control and lake ecological restoration should be carried out and this may be the guidance for the eutrophic control of lakes in China.     

Current status and future tendency of lake eutrophication in China

Current trophic status and trend of Chinese freshwater lakes were investigated in this study. The results showed that all lakes studied were commonly undergoing the eutrophica-tion process, water quality decreased and lake's ecosystem is being declined. Most of the urban lakes are facing serious eutrophication. Many medium-sized lakes are in metrophic or eutrophic status, some local water are even approaching the hypertrophic level. The famous five freshwater lakes in China have entered into eutrophication in the condition of higher nutrient load. Lake Taihu, Hongze and Caohu are already in eutrophic state. Eutrophic lakes are mainly distributed in the middle and lower reaches of Yangtze River and Yungui plateau. Lake eutrophication developed rapidly. Among the 34 lakes studied in 1970's, most of lakes were in the mesotrophic status, mesotrophic water area accounted for 91.8%. With the nine year of 1978-1987 the area percentage of oligotrophic lakes decreased from 3.2% to 0.53%, and that of eutrophic lakes increased from 5.0% to 55.01%. Recent data showed 57.5% lakes were in eutrophic and hyper trophic status of the 40 surveyed lakes. Eutrophic trend of Lake Taihu, Chaohu and Xuanwu in the region of the middle and lower reaches of Yangtze River was predicated using the ecological stress model. The results showed that in 2008 Lake Taihu, Chaohu and Xuanwu might be of eutrophication, eutrophication and hypertrophication, respectively if no control measurement is taken. Provided the pollution water treatment rate is 60% in 2030, approximately 30 billion ton pollution water would still be discharged directly in the lakes. Therefore, in 2030 the urban lakes in China might be eutrophication or hypertrophication, and most of the medium-sized lakes at the urban-rural fringe might be in eutrophication or hypertrophication. The famous five biggest freshwater lakes in China might be eutrophication if control countermeasures are taken as now. Lake eutrophication has become a serious environmental problem in China. Based on the domestic and foreign experiences of the eutrophic control technologies, both nutrient pollution control and lake ecological restoration should be carried out and this may be the guidance for the eutrophic control of lakes in China.     

Thermal regimes of Florida lakes

Water column temperatures were determined monthly for 24 lakes and bimonthly for 5 lakes in peninsular Florida during 1979. Three geographical groups (north, central, south) were delineated from mean monthly water column temperatures for individual lakes. On a monthly basis, northern lakes were least similar to southern lakes, while central Florida lakes displayed greater affinity to the southern than to the northern lake group. Temperature differences between lake groups broke down during late summer. Subtropical lakes have been defined tentatively as those Florida lakes south of 28° latitude which possess warm monomictic circulation and a mean annual temperature of 24.2 ± 4.8 °C with minimum water column temperature rarely less than 14 °C and summer maxima rarely exceeding 31 °C. While all lakes in Florida are clearly warm monomictic annual nutrient cycling and productivity patterns may be influenced by inter-group differences in the timing and duration of water column circulation.     

城市湖泊富营养化成因和特征*

城市湖泊的功能主要体现在旅游、如愿、洪涝调蓄排水、调节气候以及改善城市生态环境等方面。根据湖泊所处地理位置和湖泊水质退化现象,阐述了城市湖泊水体从贫营养到富营养转变的主要原因;从水质的理化指标、底质污染物含量和水生态系统等方面初步时论了城市型浅水湖泊富营养化的特征。同非城市湖泊相比:大部分城市湖泊的水体透明度下降,污染严重的湖泊还会出现水体发黑或出现水华;水质和底质的氮磷及其它污染物含量较高,水生态系统急剧退化,水生植物以浮游植物为主,藻类大量繁殖,高等水生植物不断消亡。根据综合营养度指数对我国主要城市湖泊进行分级评价的结果表明,我国城市湖泊均达到了富营养化或严重富营养化程度。     

Salt Lakes in Australia: Present Problems and Prognosis for the Future

Australia is a land of salt lakes and despite low human population density, many lakes are adversely impacted by a range of factors. Secondary salinisation is the most pernicious force degrading lakes, especially in south-west Western Australia where up to 30% of the landscape is predicted to be affected. Mining also impinges on many salt lakes in this state, mainly through the dewatering of saline groundwater. Exploitation of groundwater for irrigation caused some lakes in Victoria, Australia, to dry, especially the significant Red Rock Complex. Global climate change will result in new water balances in endorheic lakes, with most having less water, particularly the seasonal lakes of southern Australia. This has already happened in Lake Corangamite, Victoria, but the prime reason is diversion of inflowing floodwater. Consequently, the lake has retreated and become salinised compromising its status as a Ramsar site. Various other lakes suffer from enhanced sedimentation, have introduced biota or their catchments are being disturbed to their detriment. Enlightened management should be able to maintain some important lakes in an acceptable condition, but, for most others, the future is bleak.     

The Saline Lakes of Saskatchewan II. Locale,Hydrography and other Physical Aspects

The geology and physiography, climate, soils and vegetation of the saline lakes region of southern Saskatchewan are briefly reviewed. The location and morphometry of 60 saline lakes was determined. Some of them are large (307 km²) but mean depths do not exceed 10 m and many are very shallow. Light penetration varied considerably from very turbid shallow lakes to Redberry Lake where the 1% light level was below 16.5 m. Light extinction coefficients for the entire water column of deeper lakes (7) varied from 0.256 to 2.558. Shallow lakes failed to stratify thermally but a dozen deeper lakes stratified for at least several months. Higher salinity tends to prolong stratification. Thermal stratification augmented chemical stratification in two meromictic lakes. Maximum temperature up to 30 °C in very saline shallow waters was recorded while temperatures as low as-3 °C occurred under the ice. Freezing was delayed and thawing accelerated in more saline lakes. Annual heat budgets varied from 3350 to 13,900 g cal cm-² in seven lakes. Oxygen concentration was reduced below thermoclines and was virtually absent below the ice in very shallow lakes and, at times, in a very productive lake.     

Goals,methods and possibilities for directing development of limnic ecosystems

Case studies illustrating lake and wetland ecosystem problems as well as restoration methods are given. Among these methods, aeration of deep lakes, sediment removal from shallow, polluted lakes, sediment manipulation in polluted and acidified lakes, biomanipulation and wetland management methods are considered. A treatment program for directing ecosystem development is designed in each individual case according to lake type, degradation problems and goals of restoration. The most common goal in treatment of lakes is to meiotrophicate (oligotrophicate) hypertrophicated ecosystems. In the case of wetlands, conservation and restoration aspects are combined with a growing interest focused on biomass production by emergent macrophytes. Within practical frames of applied limnology, basic limnological research and training of doctorands have been organized as team-work for ecosystem-oriented investigations.     

Prediction of biological acid neutralization in acid-sensitive lakes

Sulfate and nitrate removal, and the resulting sulfuric and nitric acid neutralization within acid-sensitive lakes, were predicted from a simple model requiring knowledge only of water residence time, mean depth, and average mass transfer coefficients for nitrate and sulfate removal. The model applies to lakes with oxic hypolimnia which are typical of acid-sensitive lakes. Average mass transfer coefficients for sulfate and nitrate were obtained by two independent methods which agreed well with each other. A model such as this is necessary for predicting the rates at which different lakes acidify and recover from acidification, and explains why lakes with short water residence times are especially susceptible to acidification.     

云南抚仙湖、洱海、滇池水生植被的生态特征

抚仙湖、洱海和滇池是云南高原上较大的三个断层构造湖泊。作者于1981—1983年对这三个湖泊的水生植物种类、分布、产量、植被类型以及演替作了调查。其结果是:(1)抚仙湖、洱海和滇池的湖盐形态、湖水的理、化性质以及生物生态条件是很不相同的:抚仙湖是我国第二深水湖泊,洱海是半深水湖,而滇池却是一个浅水湖泊。因此,水生植物的生态特征也是各不相同的;(2)随着湖泊的逐渐发育和演化水生植物的种类由少到多,而植被类型及其演替则由简单到复杂(即抚仙湖→洱海→滇池);(3)制约水生植物生长、分布的主要环境因素是水深、风浪、透明度以及沉积物的组成等;(4)水生植物的生态特征指示了滇池和洱海已经进入老年化阶段,其沼泽化程度是:滇池>洱海>抚仙湖;(5)滇池自受到工业废水污染以后,水生植被遭受到破坏,湖泊生态系统失去自然平衡,许多水生植物受到危害或者濒于绝灭(如海菜花、微齿眼子菜等),但是,漂浮植物却得到了发展(如凤眼莲)。     

Current status and future tendency of lake eutrophication in China

Current trophic status and trend of Chinese freshwater lakes were investigated in this study. The results showed that all lakes studied were commonly undergoing the eutrophication process, water quality decreased and lake’s ecosystem is being declined. Most of the urban lakes are facing serious eutrophication. Many medium-sized lakes are in metrophic or eutrophic status, some local water are even approaching the hypertrophic level. The famous five freshwater lakes in China have entered into eutrophication in the condition of higher nutrient load. Lake Taihu, Hongze and Caohu are already in eutrophic state. Eutrophic lakes are mainly distributed in the middle and lower reaches of Yangtze River and Yungui plateau. Lake eutrophication developed rapidly. Among the 34 lakes studied in 1970’s, most of lakes were in the mesotrophic status, mesotrophic water area accounted for 91.8%. With the nine year of 1978–1987 the area percentage of oligotrophic lakes decreased from 3.2% to 0.53%, and that of eutrophic lakes increased from 5.0% to 55.01%. Recent data showed 57.5% lakes were in eutrophic and hypertrophic status of the 40 surveyed lakes.

Eutrophic trend of Lake Taihu, Chaohu and Xuanwu in the region of the middle and lower reaches of Yangtze River was predicated using the ecological stress model. The results showed that in 2008 Lake Taihu, Chaohu and Xuanwu might be of eutrophication, eutrophication and hypertrophication, respectively if no control measurement is taken. Provided the pollution water treatment rate is 60% in 2030, approximately 30 billion ton pollution water would still be discharged directly in the lakes. Therefore, in 2030 the urban lakes in China might be eutrophication or hypertrophication, and most of the medium-sized lakes at the urban-rural fringe might be in eutrophication or hypertrophication. The famous five biggest freshwater lakes in China might be eutrophication if control countermeasures are taken as now.

Lake eutrophication has become a serious environmental problem in China. Based on the domestic and foreign experiences of the eutrophic control technologies, both nutrient pollution control and lake ecological restoration should be carried out and this may be the guidance for the eutrophic control of lakes in China.

     

Chlorophyll-phosphorus relationship in acidified lakes of the High Tatra Mountains (Slovakia)

Concentrations of total phosphorus (TP) and chlorophyll a (CHLA) were measured in 28 lakes in the High Tatra Mountains (Slovakia) from 1983 to 1990. The relationship between log CHLA and log TP in the Tatra lakes is similar to relationships developed for lakes in other regions, but variation is higher. A part of this variation is caused by acidification of the lakes. In the lakes with pH between 4.9 and 6.3 the CHLA concentrations are often extremely low while TP concentrations decreased, but not as drastically.     

Productivity of clear and humic lakes: nutrients,phytoplankton, bacteria

The relationships between long-term surface average concentrations of humic acids measured as water colour, dissolved organic carbon (DOC) or Secchi disk transparency and trophic state variables were studied with literature data from more than 600 freshwater lakes. The geometric means of summer surface average nutrient (phosphorus and nitrogen) concentration, phytoplankton biomass (chlorophyll concentration), and hypolimnetic anoxia (anoxic factor) were significantly higher in coloured than in clear lakes. The regressions of colour or DOC on these trophic state variables were positive and significant throughout a range of three orders of magnitude. Phytoplankton or primary productivity was higher in coloured lakes, when expressed per volume of epilimnion. Annual integral primary productivity expressed on an areal basis was smaller in coloured lakes, probably a reflection of shallower phototrophic depths in these lakes. There is evidence that annual integral bacteria productivity is much higher in coloured lakes for two reasons: first, epilimnetic bacteria production was ca. four times higher in coloured lakes, second, other studies have shown that hypolimnetic bacteria production is commonly higher than epilimnetic production, especially in anoxic hypolimnia that are frequent in coloured lakes. All volumetrically expressed variables indicated higher productivity in coloured lakes. In addition, high bacteria productivity reflects a different food chain involving mixotrophs, possibly compensating for low light conditions. Our analyses indicate that primary and secondary productivity is as high as or higher than in clear lakes. This revised version was published online in July 2006 with corrections to the Cover Date.