The thermal behaviour of French water bodies: From ponds to Lake Geneva

The management of French freshwater bodies (lakes, reservoirs, ponds, etc.) needs to face the challenges imposed by the effects of climate change and by legal requirements to develop standards for water temperature and other physicochemical indicators. While 1D hydrodynamical models could be helpful in improving the knowledge of the thermal and hydrodynamic behaviour of French water bodies, the scarcity of data for calibration and validation, in addition to the unavailability of some forcing data, makes their application difficult for most French water bodies. In this article we explore an alternative statistical approach that takes advantage of the available data in order to inform future modelling applications. We used official monitoring data and satellite measurements to study the thermal characteristics of more than 400 French water bodies (depth: 1–310 m, surface area: 0.1–577 km², volume: 0.1–89,000 hm³). The objective was to identify the importance of size on their thermal behaviour. For this we analysed the annual temperature cycle, the summer temperature profiles and within-lake spatial variability. Together with size, geography and transparency determine the thermal behaviour of water bodies through complex interactions. As a result of the analysis we propose a classification of French water bodies as a function of depth and surface area that reflects the summer vertical temperature gradient and the processes influencing the deepening of the thermocline.     

Effects of lake-basin morphological and hydrological characteristics on the eutrophication of shallow lakes in eastern China

The Yangtze River floodplain contains numerous oxbow or riverine lakes, all of which were openly connected with the Yangtze River or its major tributaries prior to 1950s. However, stresses resulting from human settlement and utilization of catchment resources have exerted great pressures on these lake ecosystems changing their morphology, connectivity and trophic state lakes. This study examined the interaction of these changes and their impact on eutrophication for 90 shallow lakes in eastern China in 2008 to 2011. TN and TP in the study lakes had negative relationships with mean water depth (Z_mean), but no single lake-basin characteristic was found to dominate chlorophyll-a (Chl-a) growth. Instead, water depth and surface area were found to interactively affect Chl-a concentrations in smaller lakes. That is, Chl-a concentration in the lakes with Z_mean > 2 m and surface area (SA) ≤ 25 km² was significantly higher than that in relatively larger lakes with Z_mean > 2 m and SA > 25 km² (p-value ≤ 0.038). Chl-a concentration was higher in the lakes located within the lower Yangtze River basin which had longer retention times, than in the lakes located within the middle Yangtze River basin, where flow velocity is relatively larger. As expected, the water quality was found to be better in the lakes hydraulically connected with rivers than in those isolated from the river. This study revealed that lake-basin morphology and hydrology dominated algal blooms in the highly eutrophic shallow lakes in eastern China.     

The effects of water retention time and watershed features on the limnology of two tropical reservoirs in Brazil

Although reservoirs are similar to natural lakes in many respects, such driving forces as water retention time and watershed features can play important roles in the limnology of manmade lakes. With the goal of investigating how these factors influence the limnology of tropical reservoirs, physical and chemical variables were measured at four sampling sites in two reservoirs in southern Brazil, from June 2002 to June 2003. Funil Reservoir is located in one of the most-populated areas in the country, in the Paraíba do Sul river basin, which drains and drastically influences the water quality of the reservoir. In contrast, Lajes Reservoir is located in a well-preserved area, with its water retention time varying from six to 30 times longer than for Funil Reservoir. Funil Reservoir is a turbid (median euphotic zone = 4.3 m), eutrophic reservoir (median total phosphorus (TP) = 3.1 µm ), with a high phytoplankton biomass (median chlorophyll-a concentration = 10.0 µg L⁻¹). In contrast, Lajes Reservoir is a transparent (median euphotic zone = 9.2 m), mesotrophic water system (median TP = 1.0 µm ), with a low phytoplankton biomass (median chlorophyll-a = 1.9 µg L⁻¹). Both reservoirs were stratified during the summer months, but isothermy was only observed in Funil Reservoir. Because of its short water retention time, Funil Reservoir is a much more dynamic system than Lajes Reservoir, with a pronounced temporal pattern related to changes in its water column and its phytoplankton biomass. Spatial heterogeneity is more evident in Lajes Reservoir, mainly as a consequence of its location in a preserved area, long water retention time and the presence of net cages for fish culture in the waterbody. The typical spatial zonation found in reservoirs, related to nutrient sedimentation and light availability, however, is more evident in Funil Reservoir than in Lajes Reservoir. Despite the similarities between these two water systems, which are in the same geographical region with similar climate, and are comparable in size, the distinct watershed features and water retention time are responsible for marked differences between these reservoirs.     

Mapping the spatial changes in Lake Volta using multitemporal remote sensing approach

Lake Volta is the world's largest man‐made lake by surface area, and the fourth largest by water volume. Located completely within Ghana, it has a surface area of about 8502 km² (3283 square miles). Like many other lakes on the African continent, Lake Volta is a major natural resource for Ghana, storing water for the operation of the hydroelectric dam, water supply for domestic, agricultural and industrial purposes, habitat for diverse aquatic species, an avenue for recreational activities, means of navigation between the north and south parts of the country, and a climate modulator for the tropical region. The lake has experienced variable water level and surface area changes attributable to climate change and excessive water abstractions. Using histogram thresholding techniques, this study produced binary images and vector maps of the lake. Spatial extent mapping of the lake using Landsat TM 1990, ETM + 2000 and ETM + 2007 images indicated the lake experienced both increased and decreased surface area changes during the study period. The lake's surface area varied by about 197 km² between 1990 and 2007, with the water level fluctuating between ±7 m. Factors thought to be contributing to these changes include human factors (regulated flows, deforestation, increased water abstractions and pollution) as well as natural phenomenon (climate change, water run‐off and subsequent sediment transport).     

Investigation of Aksehir and Eber Lakes (SW Turkey) Coastline Change with Multitemporal Satellite Images

Detection and analyses of coastline changes are an important task in environmental monitoring. Several factors such as geology, hydrology, climate impact, environmental problems etc. play an important role in this change. The main objective of this study is to determine coastline change in the Aksehir and Eber lakes (SW, Turkey) by using different remote sensing methods on the multitemporal satellite images. In present study, Landsat MSS (1975), Landsat TM (1987), Landsat ETM+ (2000) and ASTER (2006–2008) satellite images were used. In order to explain reasons of coastline change, geological, hydrogeological and hydrological investigations were carried out. Also, surface area and volume calculations were performed with the aid of bathymetric map which was digitized by using the Arc GIS 9 version software program. The obtained data show that precipitation, evaporation and surface flow are effective in the Aksehir and Eber coastline change. The Eber Lake was evaluated with level measurements due to aquatic plants covered surface of the lake. The coastline change of the Eber Lake is related to hydraulic factors. The Aksehir Lake volume and surface area have decreased 1.11 km³ and 257.95 km², respectively from 1975 to 2006 years. Furthermore, the Lake Akşehir was dried up completely in 2008.     

基于遥感的1973-2015年武汉市湖泊水域面积动态监测与分析研究

近年来,武汉市城市内涝频发,湖泊的减少被认为是导致其发生的重要原因。然而目前尚未有一个统一、科学的数据来表示整个武汉市湖泊的历史变迁。为了掌握近几十年武汉市湖泊的时空变化规律,基于多源遥感数据,采用归一化差异水体指数（NDWI）和面向对象分割结合的水体提取算法,对1973-2015年武汉市的湖泊分布进行了提取,并结合武汉市气象资料和统计年鉴对引起其变化的影响因素进行了分析。结果如下：（1）1973年,武汉市辖区内的湖泊水域面积为1170.84 km²,2015年为856.27 km²,42年间减少了314.57 km²,剧烈减少时期发生在1973-2005年,2005年以后,基本趋于稳定。（2）1973年武汉市中心城区湖泊水域面积为148.90 km²,1973年到1996年,湖泊水域面积基本趋于稳定,而在1996年之后,武汉市中心城区湖泊水域面积开始剧烈减少,2010年之后,武汉市中心城区的湖泊水域面积基本趋于稳定;2015年,武汉市中心城区湖泊水域面积为99.94km²,相对于1973年,减少了48.96 km²。（3）1973年到2015年,武汉市年降水量呈现略增加的趋势,年平均气温则有一定的增加趋势;而在1990年之后,武汉市人口的增加、城镇的快速发展及房地产开发导致了大量的湖泊被侵占;气候变化和人类活动共同导致了武汉市的湖泊水域面积减少,其中人类活动是其变化的主要因素。     

Extreme water level rise across the upper Laurentian Great Lakes region: Citizen science documentation 2010–2020

As the global water balance accelerates in a warming climate, extreme fluctuations in the water levels of lakes and aquifers are anticipated, with biogeochemical, ecological and water supply consequences. However, it is unclear how site-specific factors, such as location, morphometry and hydrology, will modulate these impacts on regional spatial scales. Here, we report water level time series collected by citizen scientists for 15 diverse inland lakes in the upper Laurentian Great Lakes region from 2010 to 2020, and we compare these time series with those for the two largest Great Lakes, Lake Superior and Lake Michigan-Huron. Combined with historical data (1942–2010), the findings indicate that lakes spanning seven orders of magnitude in size (10^?2 to 10⁵ km²) all rebounded from record low to record high water levels during the recent decade. They suggest coherent water level oscillations among regional lakes (large and small) implying a common, near-decadal, climatic driver that may be changing.     

Large Lakes of the World

An inventory of the distribution, origin, and morphometry of the world's large lakes has been undertaken. Natural lakes, fresh and salt, with a surface area greater than 500 km² are included; 253 such lakes have been identified. Large lakes occur on all continents, except Antarctica, but nearly half of them (48 percent) are found in North America and most of these lie above the 40th parallel, attesting to the scouring action of continental glaciers. Tectonic belts, such as the Riff Valley of east Africa and the Lake Baikal region of Siberia, are the second most common loci of large lakes. Tabular morphometric data include: surface area, drainage basin, elevation, mean and maximum depth, volume, length and breadth, and orientation of longest axis. These data show that the large lakes of the world occupy a surface area of 1,456,000 km² and they have an estimated volume of 202,000 km³. Large lakes account for approximately 90 percent of the total surface area and volume of water held in all lakes of the world. Revisions and supplements to the data presented are welcomed.     

Characterization of water quality in a small hydropower plant reservoir in southern Brazil

The construction of large reservoirs can cause profound environmental changes. Reduced water flow, increased water residence time, thermal stratification, increased sedimentation rates and decreased dissolved oxygen concentrations are examples of such changes. These changes can affect water quality and the biota in the environments adapted to the natural conditions of a river. Small reservoirs developed in conjunction with hydropower plants, however, could reduce the degraded water quality. This study focuses on characterizing water quality in a small hydroelectric reservoir. The study reservoir has an area of 1.4 km² and a short water retention time. The Monte Claro Hydroelectric Power Plant is part of a complex consisting of three plants on the Antas River in the north‐west of Rio Grande do Sul state, Brazil. The reservoirs associated with these plants are operated as run‐of‐the‐river facilities. Monitoring results obtained by CERAN, the Energetic Company of Antas River (Companhia Energética Rio das Antas), were used to evaluate the reservoir water quality. Three samples were collected seasonally (spring, summer, autumn and winter) in the area of influence of this plant following the filling of the reservoir (2005–2008). The examined water quality parameters were electrical conductivity, colour, turbidity, alkalinity, pH, biological oxygen demand (BOD), chemical oxygen demand (COD), total phosphorus, dissolved oxygen, sulphate, nitrate, nitrite, ammonia, suspended and dissolved solids, chlorophyll‐a, total and faecal coliforms, water temperature and Secchi depth transparency. The results were interpreted using an index of water quality, Trophic State Index, reservoir water quality and CONAMA Regulation 357/05 (Brazilian legislation). Based on these analyses, no significant changes were exhibited in the water quality of the reservoir from the hydroelectric plant operation.     

Spatial and temporal variations of dissolved CO2, CH4 and N2O in Lakes Edward and George (East Africa)

We report dissolved CO₂, CH₄ and N₂O concentrations in two large East African lakes, Edward (surface area 2,325 km², average depth of 37 m) and George (surface area 273 km², average depth of 2 m). Lake George showed modest seasonal and spatial variations, and lower partial pressure of CO₂ (pCO₂) (26 ± 16 ppm, mean ± standard deviation), CH₄ (234 ± 208 nmol/L) and N₂O saturation levels (%N₂O) (80 ± 9 %) than Lake Edward (404 ± 145 ppm, 357 ± 483 nmol/L, 139 ± 222 %). Surface waters in both lakes were over-saturated in CH₄, and Lake George was under-saturated in CO₂ while Lake Edward was slightly over-saturated in CO₂. This difference was related to higher phytoplankton biomass in Lake George than Lake Edward, with average chlorophyll-a concentrations of 177 ± 125 and 18 ± 25 µg/L, respectively. Permanent high cyanobacterial biomass in Lake George led to uniform dissolved CO₂, CH₄ and N₂O concentrations. In surface waters of Lake Edward, spatial variations of pCO₂, CH₄ and N₂O were related to bottom depth, and locally (in particular in Katwe Bay) also related to the inputs of water from Lake George via the Kazinga Channel, a 40-km natural channel connecting the lakes. Short-term mixing events related to storms increased CO₂, CH₄ and N₂O content in surface waters, in particular for CH₄ and N₂O. This indicates that mixing events in response to storms can create ‘hot moments’ for CH₄ and N₂O emissions to the atmosphere in tropical lakes, given the weaker vertical density gradients compared to higher latitude systems.     

Satellite based lake bed elevation model of Lake Urmia using time series of Landsat imagery

This study presents a lake bed elevation model of Lake Urmia. In the course of model generation, a time series of the extent of the lake surface was derived from 129 satellite images with different acquisition dates based on the Landsat sensors Thematic Mapper (TM), Enhanced Thematic Mapper Plus (ETM+), and Operational Land Imager (OLI). Due to the rapid shrinking of the lake during the last two decades, lake surface areas ranging from 890 km² to 6125 km² could be covered. The water edge of the various lake extents was then linked to the observed water level on the day of the satellite image acquisition. The resulting contour lines, covering water levels between 1270.04 m and 1278.42 m a.s.l. and thus representing the lakebed morphology in its shallow parts, were merged with existing data (deeper parts) and interpolated to generate a lake bed elevation model. Finally, Lake Urmia’s Level-Area-Volume relationships were derived from the lake bed elevation model and compared to bathymetric data previously published.     

Monitoring water level and volume changes of lakes and reservoirs in the Yellow River Basin using ICESat-2 laser altimetry and Google Earth Engine

Monitoring the water level and volume changes of lakes and reservoirs is essential for deepening our understanding of the temporal and spatial dynamics of water resources in the Yellow River Basin, with a view to better utilizing and managing water resources. In recent years, there have been many studies on monitoring water level and volume changes in inland waters, but they were mainly focused on radar altimetry and the full waveform LiDAR ICESat, which was retired in 2010. Few studies based on the latest photon-counting LiDAR ICESat-2 have been reported. Compared with previous sensors, ICESat-2 has great advantages in footprint size, transmitting frequency, pulse number, etc, but its performance in monitoring water level and volume changes in inland waters has not been fully explored. Here we investigated the spatial distribution of water level and volume changes of 11 lakes and 8 reservoirs in the Yellow River Basin based on ICESat-2 and Google Earth Engine, and analyzed the factors affecting the measurement uncertainties. In-situ validation of lake level in Lake Qinghai indicates that the Root Mean Square Error (RMSE) of our result is only 7 cm after the reference coordinate system conversion. We found that the water level trend of the natural lake shows significant seasonal variations, while the water level trend of the reservoir shows a sharp rise and fall. In addition, precipitation plays a decisive role in the changes in natural lake levels and indirectly affects the artificial control of reservoirs’ water discharges. The uncertainty of water volume change monitoring is mainly affected by water level measurement uncertainty for lakes, while for reservoirs, that is affected by the combination of water level and area measurement uncertainties. The stability of lake level measurement increases with the increase in photon counts. The introduction of ICESat-2 ATL13 Significant Wave Height might lead larger standard deviation in water level measurement. According to the law of propagation of uncertainty, the uncertainty of the water volume change estimation by the combination of ICESat-2 and GEE is less than 9 %.     

Towards better water security in North China

Water shortages and related environmental degradation in North China are major issues facing the country. As runoff from the mountainous parts of the region steadily decrease and water resources become overcommitted, serious water and environmental problems have resulted. These include drying-up of rivers, decline in groundwater levels, degradation of lakes and wetlands, and water pollution. Thus, 4000,km of the lower reaches of the Hai River – some 40% of its length – has experienced zero flows and, as result, parts of this river have become an ephemeral stream. The area of wetland within the Basin has decreased from 10,000,km² at the beginning of 1950s to 1,000km² at present. Over-extraction of groundwater occurs beneath 70% of the North China Plain, with the total groundwater over-extraction estimated at 90,billion m³. Thus, problems of water shortage and related environmental issues in North China have become the most significant limiting factors affecting sustainable development in this important region of China. This paper addresses the water security issues facing North China in the 21st Century using the Hai River basin as an example. We describe hydrologic cycles under changing environments, water-saving agriculture, assessment of water resource security, and efforts towards achieving integrated catchment management.     

Estimation of Small Reservoir Storage Capacities with Remote Sensing in the Brazilian Savannah Region

Small reservoirs play an important role in supporting the local economy in the savannah areas of Brazil and are primarily used for the provision of water for irrigation and watering livestock. Hundreds of small reservoirs have been built in the last few decades in the Preto River Basin, but efficient water management and sound planning are hindered by inadequate knowledge of the number, storage capacity and spatial distribution of reservoirs in the basin. The main reason for the lack of this information is that current methodologies for quantifying the physical parameters of reservoirs are laborious, time consuming and costly. To address this lack of data, a simple method to estimate reservoir storage volumes based on remotely sensed reservoir surface area measured with LANDSAT was developed. The method was validated with a subset of reservoirs in the Preto River Basin for which surface areas, shapes and depths were determined with ground-based survey measurements. The agreement between measured and the remotely sensed reservoir volumes was satisfactory, indicating that remotely-sensed images can be used for improved management of water in the Brazilian Savannah region. With the newly developed methods we found that the Preto River Basin’s 147 small reservoirs can store 19 × 10⁶ m³ of water at full capacity.     

Diffusive emissions of methane and nitrous oxide from a cascade of tropical hydropower reservoirs in Kenya

The present study investigated diffusive emissions of methane (CH₄) and nitrous oxide (N₂O) to the atmosphere from three relatively small (3–120 km²) reservoirs (Masinga, Kamburu and Gitaru) on the Tana River (Kenya). Sampling was conducted biweekly in 2011, 2012 and 2013, at sampling sites upstream and downstream of these reservoirs while five sampling campaigns were carried out in 2011, 2012 and 2013 for different sites within each of the reservoirs. The dissolved CH₄ (range: 19–2101 nmol/L) and N₂O (range: 6.2–11.5 nmol/L) concentrations in the surface waters were generally very low in the three reservoirs, compared with other reservoirs globally. The lower diffusive emissions of CH₄ (20–216 µmol/m² day^?1) and N₂O (1.0–1.6 µmol/m² day^?1) from these reservoirs, compared with other tropical reservoirs, are probably related to their age (30–40 years), and lower vegetation biomass (savannah) originally present and submerged during their commissioning. The reservoirs with longer water residence times were characterized by higher diffusive CH₄ fluxes (216 ± 666 µmol/m² day^?1) and slightly lower N₂O fluxes (1.0 ± 1.5 µmol/m² day^?1). The relative contribution of turbine fluxes of CH₄ and N₂O, compared to diffusive fluxes, was also highly variable among the three dams, being lower in Masinga Reservoir and higher in Gitaru Reservoir.     

Groundwater Recharge Assessment for the Kalahari Catchment of North-eastern Namibia and North-western Botswana with a Regional-scale Water Balance Model

Groundwater is the only source of drinking water for the inhabitants of the Kalahari. Thus understanding spatial and temporal variations in groundwater recharge is very important and a regional-scale water balance model has therefore been set up for a 209,149 km² catchment in north-eastern Namibia and north-western Botswana. The model has a spatial resolution of 1.5 × 1.5 km, daily model time-steps, and climatic input parameters for 19 years are used. The distributed, GIS-based, process-oriented, physical water balance model (MODBIL) used in this study considers the major water balance components: precipitation, evapotranspiration, groundwater recharge, and surface runoff/interflow. Mean precipitation for the study area is 409 mm a⁻¹, while mean actual evapotranspiration is 402 mm a⁻¹ and mean groundwater recharge is 8 mm a⁻¹ (2% of mean annual precipitation). The recharge pattern is mainly influenced by the distribution of soil and vegetation units. Groundwater recharge shows a high inter- and intra-annual variability, but not only the sum of annual precipitation is important for the development of groundwater recharge; a large amount of precipitation in a relatively short period is more important. Published independent data from the Kalahari in Namibia, Botswana and the Southern African region under similar climatic conditions are used to verify the modelling results.     

First assessment of the ecological status of Karaoun reservoir,Lebanon

Many reservoirs have been constructed throughout the world during the 20th century, with many also suffering from eutrophication. The resulting increased phytoplankton biomass in reservoirs impairs their use. Except for Lake Kinneret, the environmental status of lakes and reservoirs in the Middle East is poorly documented. Karaoun reservoir, also known as Qaroun, Qaraoun or Qarun, is the largest water body in Lebanon, having been constructed for irrigation and hydropower production. This present study reviews Karaoun reservoir, including its characteristics, uses, water quality and phytoplankton succession, to assess the environmental status of the reservoir on the basis of the few existing previous publications about the reservoir. Since 2004, which is 39 years after its construction, the reservoir is considered to be hypereutrophic, with low phytoplankton biodiversity and regular blooms of toxic cyanobacteria. The nutrient and trace metal concentrations would not prevent use of the reservoir for a drinking water supply for Beirut, as is currently being planned, although not all the micropollutants in the lake were documented. Karaoun reservoir is compared to other monitored lakes and reservoirs around the Mediterranean Sea. They share annual toxic cyanobacteria blooms of Aphanizomenon ovalisporum and of Microcystis aeruginosa. The phytoplankton composition and succession of Karaoun reservoir is more similar to El Gergal reservoir (Spain) than nearby natural lakes such as Lake Kinneret (Israel) and Lake Trichonis (Greece). Phytoplankton diversity in Karaoun reservoir was the lowest, due to higher nutrient concentrations and a larger decrease in water level in the dry season. Karaoun reservoir represents an interesting example of the potential response of the phytoplankton community in other lakes and reservoirs during the drought periods expected to occur as a result of global climate change.     

基于星载雷达测高资料估计博斯腾湖水位-水量变化研究

为了理解气候变化背景下的内陆湖泊水位、面积、水量波动变化规律,科学合理地指导湖泊水资源利用与开发。利用1990-2015年Landsat TM/ETM/OLI影像和2002-2015年多源星载雷达测高资料,借助归一化水体指数(Normalized Difference Water Index,NDWI)提取博斯腾湖湖泊水域面积,结合湖泊水位观测数据,对星载雷达测高数据提取的湖面瞬时水位估计值进行对比与分析;根据湖泊面积与水位、水量与水位的关系式,构建湖泊面积-水位-水量波动时变序列,并探讨湖泊水位和水量变化的年际特征。结果表明:ICESat-GLAS、ENVISatERS、Jason-12的当日水位估计值与附近扬水站的水位观测值绝对误差分别小于0. 21、0. 18、0. 15 m,而且具有较强的相关性和一致性。1990-2002年湖泊水位持续增长阶段; 2002-2015年期间,湖泊水位持续下降。2015年湖泊水域面积比1990年减少了(32. 20±3. 5) km2,年均水位下降了(0. 81±0. 19) m,湖泊水量减少了(9. 49±0. 022)×108m3。因此,湖泊水量变化为气候系统和人类活动的影响机制的理解提供了参考依据。     

Spatio‐temporal variation of gross CO2 and CH4 diffusive emissions from Australian reservoirs and natural aquatic ecosystems,and estimation of net reservoir emissions

Carbon dioxide (CO₂) and methane (CH₄) diffusive emissions were measured during two field surveys in Queensland and Tasmania, Australia, using the floating chamber method. Bubbling and degassing emissions in 2010 were estimated in Koombooloomba Dam reservoir using only inverted funnels and gas concentrations, respectively. A total of 14 reservoirs and 16 rivers and lakes were sampled from 2006 to 2010. Spatial variation was substantial within each water body, as well as between them. The main drivers of diffusive emission variation were physiographic region and climate, with a clear demarcation being observed between diffusive emissions from tropical Queensland and temperate Tasmania, and between the humid West Coast Range (Tasmania) and dry Central Plateau (Tasmania). Higher CO₂ and CH₄ diffusive emissions were observed during the dry season, when long water residence times would promote organic matter degradation. Estimated total gross emissions, including diffusive, bubbling and degassing emissions, for Koombooloomba Dam reservoir were about 1.5 × 10⁶ t CO₂eq km² per year, or 24 × 10⁶ t CO₂eq per year. This corresponds to a plant emission factor of 3.18 kg CO₂eq MWh^?1. Using an estimate of terrestrial emissions derived from literature data for the Tully River catchment area, rough estimated net emissions from the catchment area are about 44 kt CO₂eq per year, or 5.83 kg CO₂eq MWh^?1, which is in the lower range of the studied reservoirs.     

Sensitivity of Ancient Lake Ohrid to Local Anthropogenic Impacts and Global Warming

Human impacts on the few ancient lakes of the world must be assessed, as any change can lead to an irreversible loss of endemic communities. In such an assessment, the sensitivity of Lake Ohrid (Macedonia/Albania; surface area A = 358 km², volume V = 55 km³, > 200 endemic species) to three major human impacts—water abstraction, eutrophication, and global warming—is evaluated.It is shown that ongoing eutrophication presents the major threat to this unique lake system, even under the conservative assumption of an increase in phosphorus (P) concentration from the current 4.5 to a potential future 9 mg P m⁻³. Eutrophication would lead to a significant reduction in light penetration, which is a prerequisite for endemic, deep living plankton communities. Moreover, a P increase to 9 mg P m⁻³ would create deep water anoxia through elevated oxygen consumption and increase in the water column stability due to more mineralization of organic material. Such anoxic conditions would severely threaten the endemic bottom fauna. The trend toward anoxia is further amplified by the predicted global warming of 0.04°C yr^–1, which significantly reduces the frequency of complete seasonal deep convective mixing compared to the current warming of 0.006°C yr⁻¹. This reduction in deep water exchange is triggered by the warming process rather than by overall higher temperatures in the lake. In contrast, deep convective mixing would be even more frequent than today under a higher temperature equilibrium, as a result of the temperature dependence of the thermal expansivity of water. Although water abstraction may change local habitats, e.g., karst spring areas, its effects on overall lake properties was shown to be of minor importance.