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.     

First records of primary producers of epiglacial and supraglacial lakes in western Dronning Maud Land, Antarctica

Epiglacial and supraglacial lakes are characteristic lake types in Antarctica, and regardless of their mostly seasonal existence and ultraoligotrophy, some lakes have a relatively diverse microbial community. The results of water chemistry and phytoplankton, based on basic limnological methods, from five epiglacial and two supraglacial seasonal lakes are presented from western Dronning Maud Land, an area where only physical studies have been previously carried out. Electric conductivity varied mostly between 0.1 and 10 mS m^?1 (25 °C), phosphorus concentration was <5 mg m^?3, and nitrogen concentration was <300 mg m^?3 except in some shore areas, and water pH ranged from 6 to 11. Low phytoplankton biomasses (in most cases <10 mg m^?3) supported the ultraoligotrophic status of the lakes. Phytoplankton was found from both types of lakes, but less was found from supraglacial lakes. The charophyte Mesotaenium cf. berggrenii dominated the supraglacial lakes, while cyanoprokaryotes such as Gloeocapsopsis cf. magma, Planktothrix prolifica/rubescens, Nostoc cf. sphaericum, Cyanothece sp. and Phormidium sp. dominated the biomass in some epiglacial lakes. Chrysophytes (e.g. Pseudopedinella-type flagellates) were observed in both types of lakes, and they were occasionally dominant. The green alga Botryococcus braunii, some diatoms (Cyclotella sp., Diatoma tenuis, Luticola muticopsis), and non-planktonic microalgal colonies visible to the eye (incl. the cyanoprokaryote Nostoc commune) were also found. Signs of a living ecosystem with a food web were observed in one epiglacial lake, but not elsewhere, which indicates extreme circumstances in the Antarctic seasonal lakes. Altogether, only some 25 taxa were discovered.     

Geographical distribution,morphology and water quality of caldera lakes: a review

The geographical distribution, morphometry and water quality of lakes within large calderas (> 2 km in diameter) were evaluated through a review of the literature and maps. Eighty-eight lakes in 75 calderas were located in 31 volcanic subregions. As a group, the lakes varied greatly in elevation, surface area, maximum depth, and shoreline development. The average surface area was 16.9 km², surface elevation 873 m, depth 151.1 m, and shoreline development 1.35. Water quality ranged from ultraoligotrophic to highly eutrophic. None of the lakes had an inlet that originated outside the calderas. Most lakes did not have a surface outlet, were circular or subcircular in shape, and covered only parts of the caldera basins. Water clarity in some lakes was among the highest recorded for freshwater systems, but there are indications of possible declining clarity in some cases. Secondary volcanic activity, such as primary (hydrothermal) water and eruptions, has been associated with deteriorated water quality conditions in some lakes.     

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.     

Copepod communities in karstic mediterranean lakes along the eastern Adriatic coast

The copepod communities of karstic lakes along the eastern Adriatic coast were studied. Lakes were divided in several groups according to their morphology (deep, shallow, barrage and reservoirs), production (oligotrophic, mesotophic and eutrophic), and salinity of water: freshwater and brackish. Copidodiaptomus steueri, Eucyclops serrulatusand Macrocyclops albidus belong to the group that inhabited most of the lakes under the study, regardless of lake type. The shallow karstic lakes are usually inhabited by Thermocyclops dybowskii, T. oithonoides, Cyclops vicinus and Eudiaptomus padanus etruscus in freshwater biotopes, and Calanipedia aquaedulcis and Copidodiaptomus steueri in brackish biotopes. The last two species can also be found in deep karstic lakes with brackish water (Bacina lakes in the Neretva River delta). Species like Cyclops abyssorumcan be found in most deep freshwater lakes. Some Calanoida were recorded in only one lake, like Eudiaptomus transsylvanicusin the deep Lake Vrana on the island of Cres, or Eudiaptomus hadzici in the barrage Lake Visovac. Production of the lakes, expressed as copepod biomass, depends on lake trophy, and in some lakes also on hydrology and salinity. Most of the meso-eutrophic lakes in the study area had Calanoida dominating, while Cyclopoida dominated in some oligotrophic and eutrophic lakes as well.     

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.     

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 conservation status of athalassic lakes in New South Wales,Australia

To provide an overview for the State Pollution Control Commission of NSW, 102 lakes were visited throughout the state during the 1988–9 summer to ascertain their ecological condition. The sites chosen covered a spectrum of geomorphic types in approximate proportion to their perceived relative abundance. Field work concentrated on some physicochemical parameters and on zooplankton and littoral invertebrates. A summary of these features of the lakes of NSW is given.The most widespread problem is eutrophication, though for many lakes changes in trophic status could be part of wider changes in lakes since European settlement. A significant number of lakes suffer eroded shorelines and sedimentation. The introduced mosquito fish, Gambusia affinis, is associated with decreased diversity mainly in coastal lakes where also alien plants may be pestiferous. A few lakes in western areas have their flooding regime altered, while a number in the east are drained. With few exceptions there are no management programs to improve the conservation status of degraded lakes in NSW.     

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.

     

Acid rain — perspectives on lake recovery

During the 1970‘s and 1980‘s, the acidification of surface waters by atmospherically deposited sulphur became a major international concern. Large sulphur emission control programs were implemented in Europe and North America with the expectation that many affected aquatic ecosystems would recover. Because of a variety of factors, these positive expectations have been slow to be realized. Only limited evidence of the chemical recovery of acid lakes has emerged from areas other than the Sudbury, Canada region, where sulphur emission reductions were particularly large. Lake response models indicate that when current sulphur emission control strategies in Europe and North America are fully implemented, many lakes will still be acid-damaged even though substantial overall improvements in lake chemistry are expected. An increasing body of evidence indicates that substantial biological recovery, among many groups of organisms,can be expected when chemical conditions improve in lakes. Not all species, however, are capable of unassisted recovery and some lakes can pose biological or physical barriers to colonizers. Thus, stocking may be an important element in management strategies for the restoration of some recovering lakes. Communities in recovered lakes may not achieve pre disturbance conditions, but establishment of typical communities appears to be a reasonable recovery target. This revised version was published online in July 2006 with corrections to the Cover Date.     

Tracking Recovery Patterns in Acidified Lakes: A Paleolimnological Perspective

Long-term data are often lacking to effectively assess patterns of lake acidification and recovery. Fortunately, paleolimnological techniques can be used to infer past changes in lakewater acidity and related variables by means of biological indicators, such as diatom valves and chrysophyte scales, preserved in ²¹⁰Pb-dated sediment cores. We summarize paleolimnological data that we have gathered from 36 Sudbury (Ontario) and 20 Adirondack Park (New York) lakes to estimate the magnitude of lake acidification and any subsequent recovery in these lake systems. In both regions, many lakes were shown to have acidified considerably, some over two pH units, since the 1850s. Although some recovery was noted in both lake regions, Sudbury lakes generally showed larger increases in inferred lakewater pH with recent declines in sulfur emissions. Possible explanations of these differences include the greater decrease in sulfate deposition in the Sudbury area, as well as generally longer residence times of lakes in Sudbury, perhaps allowing for more in-lake alkalinity generation. In addition, Sudbury lakes generally had higher pre-industrial pH levels, suggesting that lakes with higher natural buffering capacities are more likely to recover more quickly with declines in deposition, even if they had been acidified to a great extent.     

Observations of Toxic Blue-Green Algae (Cyanobacteria) in Some Scandinavian Lakes

Blooms of blue-green algae from 51 eutrophic Scandinavian lakes were investigated during the period 1978–1984, to ascertain the occurrence of toxinogenic species. Toxicity assays were performed by intraperitoneal injection of suspensions of freeze-dried algal material in mice. Toxin-producing blue-green algae were found in 30 lakes. They belonged to 11 different species of the six genera Anabaena, Aphanizomenon, Gomphosphaeria, Microcystis, Nodularia and Oscillatoria. The presence of toxinogenic strains of blue-green algae seemed quite constant in several of the localities studied. In some lakes, more than one toxic species were found to develop simultaneously. The level of toxicity showed large variation (MLD100, 6 to > 2500 mg/kg), but clinical and pathological changes were quite uniform. The results indicate that water-blooms of toxin-producing blue-green algae, in the geographical area in question, are regionally widespread. In some localities, blooms of blue-green algae are apparently always toxic. Several aspects of the toxic blue-green algae problem are discussed.     

Impact of Mount St. Helens Eruption on Bacteriology of Lakes in the Blast Zone

Lakes lying within the blast zone of Mount St. Helens showed dramatic increases in heterotrophic bacterial numbers after the eruption of 18 May 1980. The total microscopic counts of bacteria in some of the most severely affected lakes were more than 10⁷ cells per ml, an order of magnitude above the counts in outlying control lakes. Likewise, the numbers of viable bacteria reached levels of more than 10⁶ cells per ml, compated with fewer than 10⁴ cells per ml in control lakes. The CPS medium used for enumeration provided growth of up to 81.5% of the bacteria during sampling of one of the blast zone lakes. The high numbers of bacteria and the efficacy of the viable enumeration procedure are evidence that the lakes have been transformed rapidly from oligotrophy to eutrophy due to the eruption and its aftermath. Organic material leached from the devastated forest vegetation is thought to be responsible for the enrichment of heterotrophs. Total coliform bacteria were found in all of the blast zone lakes, and some lakes contained fecal coliform bacteria. Klebsiella pneumoniae was the predominant total coliform and was also identified as one of the fecal coliform bacteria, although Escherichia coli was the predominant species in that category. Our data indicate that bacterial populations peaked in the outer blast zone lakes in the summer of 1980 and in most of the inner lakes during the summer of 1981.     

Geographical, geological and hydrochemical distribution of saline lakes in Khakasia, Southern Siberia

There are over one hundred mineralized lakes in Khakasia with areas in excess of 0.01 km² including periodically dry lakes. These saline lakes are situated within the Chebakovo-Balakhtinskaya and Yuzhno-Minusinsk depressions of the Minusinsk intermontane trough, bounded by Kuznetsk Alatau, Western and Eastern Sayan mountains. The depressions are characterised by steppe landscape, low topographic relief and an arid climate (annual rainfall ca. 300 mm y^–1). The mineralisation of the various lakes ranges from some 2 to 150 g l^–1. Mg⁺⁺, Na⁺ and Ca⁺⁺ cations, SO₄ ⁼ and Cl^– anions dominate the composition of soluble salts. The degree of variation of the lakes' mineralisation increases in dry periods. The majority of lakes are associated with synclinal structures and terrigenous red-bed Upper Devonian clastic deposits which bear indicators of accumulation in an evaporite environment (the presence of gypsum layers). Some mineral lakes are situated in Carboniferous carbonate-terrigenous deposits, containing scattered pyroclastics and features of evaporite sedimentation. The high salinity of the lakes is explained (i) by the availability of readily soluble minerals in Palaeozoic strata (gypsum, anhydrite, halite and others), which may be dissolved in groundwater and transported to lake catchments, and (ii) by the high degree of surface water evaporation due to the arid climate. The mineralized waters of some lakes can be recommended for balneological purposes. A deterioration is noted in the ecological status of some saline lakes due to anthropogenic contamination.     

Phytoplankton in 63 limed lakes in comparison with the distribution in 500 untreated lakes with varying pH

As a result of the different weathering of lime in soils and varying acid deposition, the pH of Swedish oligotrophic lake waters has a broad range from ca. 4 to 8.5. Phytoplankton species occur in all lakes, but the composition and species richness varies in relation to pH. The maximum number of taxa was recorded within the pH-range 7.0–7.6, while the number decreased at higher pH and especially at pH below 5.6. During 1975–1985, thousands of lakes in Sweden were limed with the intention to restore biotic diversity and production. In order to find out whether there are differences in quality between limed and unacidified waters, the distribution of 57 selected phytoplankton taxa in 63 limed lakes was compared with that in 500 unlimed lakes with varying pH. The study shows that most common species in unacidified lakes also occur in the limed ones. However, several species of Cyanophyceae and Conjugatophyceae were missing especially in lakes that were strongly acidified before liming. On the other hand, some taxa were more frequent in the limed lakes.     

新疆天山北坡不同盐湖微生物菌群结构及其影响因子

新疆分布的众多湖泊由于干旱气候成盐作用强烈,近半数已演化到盐湖发展阶段,不同盐湖中也因此蕴含着丰富的耐盐及嗜盐微生物资源。为更好的掌握新疆盐湖微生物资源分布规律及对环境因子变化的响应规律,利用高通量测序技术对新疆天山北坡5个不同演化阶段盐湖湖底沉积物中细菌、古菌多样性和菌群结构及其主要驱动因子进行研究,探讨盐湖演化过程中原核微生物群落结构变化规律。分别采集5个盐湖湖底沉积物样本,进行理化因子测试与细菌和古菌16S rRNA扩增子测序分析,比较不同盐湖理化性质和原核微生物菌群差异,并对原核微生物丰度与环境因子进行关联分析。实验结果表明：5个盐湖湖底沉积物总盐和Na⁺含量顺序为：巴里坤湖 > 伊吾湖 > 艾比湖 > 盐湖 > 柴窝堡湖,除艾比湖外其他四个盐湖沉积物均呈碱性。Alpha多样性结果显示5个盐湖细菌richness、chao1、ACE和shannon丰富度指数均大于古菌相应丰富度指数,不同盐湖细菌丰富度指数差异较大,古菌丰富度指数差异相对较小。从5个盐湖湖底沉积物中共检测获得细菌58门、68纲、138目、253科和560属,古菌4门、8纲、12目、21科和60属,细菌以变形菌门为主,古菌以广古菌门为主。不同盐湖细菌和古菌优势属种类均不相同,巴里坤湖主要是一些嗜盐和耐盐细菌属,而伊吾湖主要是嗜盐和耐盐古菌属,PCoA分析结果也表明不同盐湖微生物在OTUs水平有其独特菌群结构类型。RDA和Bioenv分析结果表明,盐湖湖底沉积物中微生物菌群群落结构主要受Na⁺和总盐（TS）浓度的影响,对细菌菌群结构影响较大,而古菌菌群结构可能受多种理化因子共同调节。此外,盐湖特殊卤水成分会对微生物群落结构产生重大影响。     

Lake acidity,fish predation,and the distribution and abundance of some littoral insects

Densities of Corixidae (Hemiptera), larval Odonata, and large larval Trichoptera were estimated in the littoral zone of small lakes in an acid-stressed area near Sudbury, Ontario. Fish were present in some lakes and absent in others, and fishless lakes occurred across a wide range of pH. Corixidae were significantly more abundant in lakes without fish than in lakes with fish, and their numbers were not related to the pH of fishless lakes. Anisoptera (Odonata) larvae tended to be more numerous in benthic samples from fishless lakes than from lakes with fish, and their exuviae were significantly more abundant around fishless lakes. In most lakes, the assemblage was dominated by three species; Leucorrhinia glacialis, Libellula julia, and Cordulia shurtleffi. In lakes containing white sucker, Catostomus commersoni, Gomphus spp. were most numerous. In the most acid fishless lakes, L. julia was uncommon, and L. glacialis was extremely abundant. In fishless lakes, numbers of Anisoptera larvae and exuviae were negatively correlated with pH, though species richness was positively correlated with pH. Exuviae of Zygoptera (Odonata) were more abundant around fishless lakes, irrespective of pH. Larvae of Limnephilus (Trichoptera) were most abundant in non-acid fishless lakes, and absent at pH<5.2. Abundances of Banksiola (Trichoptera) were negatively correlated with the pH of fishless lakes.     

First results on bathymetry and limnology of high-altitude lakes in the Gokyo Valley, Sagarmatha (Everest) National Park, Nepal

The aim of this study was to investigate for the first time the morphology, physical and chemical characteristics of three high-altitude lakes in the Gokyo Valley, Everest National Park, Nepal. The moraine-dammed glacial lakes were studied for three seasons to create baseline data. The second, third, and fourth lakes in the Gokyo Valley are deeper than previously assumed. The vertical profiles of temperature and dissolved oxygen indicated that the thermocline zone varied between 10 and 20 m below the surface during the post-monsoon season. Although most of the analyzed metal concentrations were below the level recommended by the WHO for safe drinking water, lead (Pb) and cadmium (Cd) levels exceeded the limits in some of the samples. This has created great concern for human health. The probable route of these two pollutants is monsoon precipitation that carries industrial pollutants along its route. The sedimentation rates of Gokyo Lakes range from 0.069 to 0.089 cm per annum, which is within the limits of other high-altitude lakes. The present findings created a baseline database for some of the remote high-altitude lakes in Nepal that can be used for lake management and for assessing future changes in lake characteristics in the Himalayan region.     

Effects of Introduced Groundwater on Water Chemistry and Fish Assemblages in Central Florida Lakes

We assessed effects of groundwater pumping to elevate lake levels on lake water chemistry and fish population metrics at seven Florida lakes. Following groundwater pumping, lake level fluctuation was reduced and lake water samples increased in mean pH, total alkalinity, total phosphorus, chloride and Secchi depth compared to historical means, indicating a close resemblance to the chemistry of aquifer water in the region. Fish community metrics from the augmented lakes were compared to 36 non-augmented lakes in Florida. The mean values for catch per unit effort, species richness and biomass of harvestable fishes, determined by electrofishing, were lower in augmented lakes compared to non-augmented lakes. Canonical correspondence analysis (CCA) indicated a high probability of a low abundance of individual species in augmented lakes compared to a majority of non-augmented lakes. The augmented lake with the lowest pumping rate exhibited less of a shift in limnological variables from historical values, and had fish population characteristics more closely resembling those of non-augmented lakes. Thus, reduced volumes of groundwater introduction could lower impacts to limnological and fish population characteristics. Augmentation allows for lakes to be utilized for recreational activities, and without augmentation some lakes in central Florida would likely go dry due to groundwater withdrawals for water supply. Therefore, allowing more natural water level fluctuations and possible reductions in total pumpage are recommended to reduce impacts to limnological and fish population characteristics, while still allowing sufficient groundwater pumping to preserve lake habitats.     

Acidification and weathering processes in high mountain lakes in Southern Alps

About 200 lakes in Southern Alps (Italy and Switzerland) were studied in order to quantify their acidification. Although samplings were carried out in summer, long after the acid shock caused by snowmelt, some lakes were found to be acidic and 47% of them show alkalinity values of below 50 μeq 1^-1. Losses in alkalinity (acidification levels) were evaluated using a titration model with variable F-factor. Factor analysis shows that the main factors influencing water chemistry are related to rock weathering and nitrate uptake by vegetation. In watersheds containing carbonatic rocks the weathering of calcite is responsible for the most of the alkalinity production. We therefore focused on a set of 19 low-alkalinity lakes in the Maggia Valley lying in watersheds containing mainly acidic rocks. Results show that the weathering of silicate and calcite (present in small quantities, but highly soluble) and nitrate uptake account for most of the alkalinity production. Other watershed and in-lake processes may be important in some cases, but they never account for more than 27 % of the alkalinity production in these lakes.