The potential of epilimnetic withdrawal to counteract global warming: Insights from the Lichtenberg drinking water reservoir, Germany

Globally, lake surface water temperatures have warmed rapidly relative to air temperatures, but changes in deepwater temperatures and vertical thermal structure are still largely unknown. We have compiled the most comprehensive data set to date of long-term (1970–2009) summertime vertical temperature profiles in lakes across the world to examine trends and drivers of whole-lake vertical thermal structure. We found significant increases in surface water temperatures across lakes at an average rate of + 0.37 °C decade−1, comparable to changes reported previously for other lakes, and similarly consistent trends of increasing water column stability (+ 0.08 kg m−3 decade−1). In contrast, however, deepwater temperature trends showed little change on average (+ 0.06 °C decade−1), but had high variability across lakes, with trends in individual lakes ranging from − 0.68 °C decade−1 to + 0.65 °C decade−1. The variability in deepwater temperature trends was not explained by trends in either surface water temperatures or thermal stability within lakes, and only 8.4% was explained by lake thermal region or local lake characteristics in a random forest analysis. These findings suggest that external drivers beyond our tested lake characteristics are important in explaining long-term trends in thermal structure, such as local to regional climate patterns or additional external anthropogenic influences.

Sex steroid profile and plasma vitellogenin during the annual reproductive cycle of the crested newt ( Triturus carnifex laur.)

The surface air and water temperatures increased at all seasonal and annual time scales during the last 40 yr in Lake Ontario. The annual mean air and surface water temperatures have increased by 1.43° ±0.39° and 1.26° ±0.32°C, respectively, over 1970–2009. The air temperature increased at a faster rate than the surface water temperature in winter and autumn, whereas in spring and summer the surface water temperature warmed faster than the air temperature. The length of summer stratified season has increased by 12 ± 2 days since the early 1970s due to the increase in water temperature. The decline of surface wind speed over Lake Ontario resulted in a shallower surface mixed layer and enhanced the summer thermal stratification, which increased the summer surface water temperature more rapidly than the air temperature.

Water temperature plays a primary role in controlling a wide range of physical, geochemical, and ecological processes in lakes, with considerable influences on lake water quality and ecosystem functioning. In this paper, we report on the ability of two one-dimensional (1-D) lake models, i.e. the Hostetler and FLake models, to simulate the surface water temperature in eight selected Moroccan lakes: Sidi Ali, Tislit, Ifni, Daït Erroumi, Ouiouane, Aguelmam Azegza, Sidi Boughaba, and Iffer, which present a wide range of morphometry and hydrological characteristics, over a five-year period from 2008 to 2012. The FLake and Hostetler lake models perform adequately for small subgrid-scale lakes and for large resolved lakes with shallow depth. The two lake models exhibit specific strengths and weaknesses. Hostetler calculates too rapid spring warming and too warm surface water temperature, especially in large and deep lakes; FLake tends to damp the diurnal cycle of surface water temperature. These differences could be partially attributed to the biases in the driving data and most importantly to the lack of representation of complex processes in the models, such as horizontal transfer of water and heat, etc. Statistical performance evaluation is conducted on the models’ results. On the other hand, Schmidt stability showed a significant increase for deep lakes and near ~0 for shallow depth lakes. The predictive models can be used to obtain a first-order estimation of surface water temperature in Moroccan lakes.

Increasing water temperature of the largest freshwater lake on the Mediterranean islands as an indicator of global warming

The study has aimed to evaluate the changes in air temperature, surface water temperature, rainfall, discharge (flow) and dissolved oxygen during the last 30 years in Periyar River, the longest river in Kerala, from a climate change perspective. Trend analysis is carried out on the 30 year annual average data of hydro-climatic variables (air temperature, surface water temperature, discharge, rainfall, and dissolved oxygen) of the river to forecast scenarios for 2020, 2040, 2060, 2080, 2100. Statistical analysis, correlation and simple linear regression are performed on the secondary data to derive equations relating to hydroclimatic variables. Emission scenarios, hypothesized for South Asian countries in the Global Circulation model output given in the Intergovernmental Panel on Climate Change (IPCC) report 2007, are then applied in the equations so derived, to predict surface water temperature and discharge of the river. The projections for dissolved oxygen, surface water temperature, and discharge are carried out using a time series model through SPSS 6.1 software. From the trend analysis we could infer that for each scenario considered there is an increasing trend for all variables except for dissolved oxygen. Time series model indicates that there is reduction in dissolved oxygen and an increase in discharge and surface water temperature of the river by the year 2100. It is apparent from the results that the dissolved oxygen is found to decrease with an increase in surface water temperature. Such inferences will be helpful in modifying the current management plans in practice and for deciding future management plans which are to be implemented, in mitigating the effects on the already polluted river. River Basin Management VII 387 www.witpress.com, ISSN 1743-3541 (on-line) WIT Transactions on Ecology and The Environment, Vol 172, 2013 WIT Press © doi:10.2495/RBM130321

Lake surface water temperature is a fundamental metabolic indicator of lake ecosystems that affects the exchange of material and energy in lake ecosystems. Estimating and predicting changes in lake surface water temperature is crucial to lake ecosystem research. This study selected Dianchi Lake, a typical urban lake in China, as the research area and used the Air2water model combined with the Mann-Kendall mutation statistical method to analyze the temporal and spatial variation in the surface water temperature of Dianchi Lake under three climate models. The research results show that, under the RCP 5-8.5 scenario model, the surface water temperature change rate for Dianchi Lake from 2015 to 2100 would be 0.28 ℃/10a, which was the largest change rate among the three selected scenarios. The rate of change during 2015–2100 would be 9.33 times higher than that during the historical period (1900–2014) (0.03 °C/10a). Against the background of Niulan River water diversion and rapid urbanization, the surface water temperature of Dianchi Lake experienced abrupt changes in 1992, 2016, 2017, and 2022. Against the background of urbanization, the impact of human activities on the surface water temperature of urban lakes will become greater.

We monitored lake surface water temperatures from 1992 to 2019 in Lake Kasumigaura, a shallow lake in Japan. We hypothesized that increases of shortwave radiation had increased surface water temperatures and heat fluxes more than had the increases of air temperature. We used the heat flux analyses and the sensitivity analyses to test the hypothesis. The fluxes of solar radiation gradually increased during the study period in a manner consistent with the phenomenon of global brightening. The increase was especially apparent in the spring. The rate of increase of surface water temperature was especially significant in May. Air temperature did not significantly increase in May, but it increased significantly in June (0.40 °C decade−1). A sensitivity analysis of the heat fluxes at the lake surface (shortwave radiation, longwave radiation, latent heat flux, and sensible heat flux) revealed that surface water temperature was more sensitive to changes of shortwave radiation than to air temperature during the spring. Although other factors such as inflows of groundwater and river water may also have impacted surface water temperatures, the increase of solar radiation appeared to be the major factor responsible for the increase of surface water temperature during the spring in Lake Kasumigaura.

Lake restoration is commonly assessed by changes in water transparency, nutrients and biomass of phytoplankton, while information about changes in zooplankton that is triggered by lake management is often missing. In our 19-year study we used rotifers and crustaceans to document the effect of restoration measures on zooplankton in the oxbow lake Alte Donau, a former side-arm of the Danube River which is most popular for recreation and angler (cyprinid-dominated shallow water). The record covers four management periods: the period before restoration, the restoration (including years of chemical phosphate precipitation by Riplox treatment), the re-establishment of macrophytes and the sustained ‘stable conditions’. We found the highest abundance of all zooplankton in the first Riplox-year, with decreasing zooplankton abundance in following periods associated with the decline of phytoplankton. In the long term, the main compositional change related to a shift from a cladoceran-rotifer-rich to a copepod-rotifer-rich zooplankton assemblage. Thus, the large-bodied zooplankton shifted from a community composed of mainly filter-feeding herbivorous cladocerans under eutrophic algal-turbid conditions to mainly selective-feeding omnivorous and herbivorous copepods under mesotrophic transparent-water conditions. While the carbon ratio between zoo- and phytoplankton increased significantly during the first three periods and remained high under ‘stable conditions’, the mean body size of zooplankton did not exhibit a long-term trend. Short-term increases of large-bodied zooplankton coincided with an intermittent increase of calanoid copepod abundance (Eudiaptomus gracilis) during the chemical treatment concomitant with a drastic phytoplankton biomass reduction and the occurrence of large-bodied cladocerans (Simocephalus vetulus and Sida crystallina) in some years with re-established underwater vegetation. Besides the main response of zooplankton to the ‘bottom up’ control that was triggered by the reduction of phytoplankton food supply by one order of magnitude, we studied the zooplankton response to climate change. The impact of climate warming was evident from intra-annual coincidence of the climate signal (NAODJFM) and water temperature (WT) in winter and early spring, the increase of surface water temperature (SWT) by 1.52 °C per decade in April and the prolongation of the warm period (SWT > 22 °C) by 10.5 days per decade in summer. This prolongation of the warm season seemed to support the summer development of the medusa stage of freshwater jellyfish (Craspedacusta sowerbii). During the transition from spring to summer, the progressively earlier clear-water phase followed two trends. The first period with a 33-day earlier clear-water phase per decade coincided with pronounced ecosystem changes from a high to a low eutrophic state created by chemical restoration measures. The second period with a moderate earlier progression of 7 days per decade was accompanied by a further, slight TP decrease associated with the re-establishment of macrophytes. When comparing rotifers, cladocerans, calanoid and cyclopoid copepods, the latter group benefits most from seasonal temperature increases and climate warming.

A dynamic compartment model to predict sedimentation and suspended particulate matter in coastal areas

Late glacial-Holocene paleoclimatic and paleoceanographic evolution of the Aegean Sea: micropaleontological and stable isotopic evidence

The purpose of this study was to determine status and long-term trends of dissolved oxygen concentrations (DO) in Corpus Christi Bay, Texas, U.S.A. A 20-year record of randomized stations was used to determine the trend of surface water DO, salinity, and temperature over space and time. A 13-year record of two fixed stations was used to determine the temporal nutrient trends. A 10-year record of fixed stations in the southeastern region of Corpus Christi Bay was used to determine the status of disturbance caused by low DO in bottom waters. From 1982 to 2002, there was a significant decrease in surface water DO at a rate of 0.06 mg L(-1) yr(-1) and a significant increase in surface water temperature at a rate of 0.07 degrees C yr(-1). The southeastern region of Corpus Christi Bay had the lowest average DO, and during July and August, DO are steadily declining at a rate of 0.09 mg L(-1) yr(-1). It is not likely that eutrophication is causing hypoxia, because freshwater inflow rates have significantly decreased since 1941 and nutrient levels have not changed from 1987 to 2000. Even though long-term trends indicate that average surface DO is decreasing, disturbance by hypoxia appears to be stable, but this may be due to just eight years of data. In fact, if the current trend continues, surface water DO will not meet exceptional aquatic life standards (< or = 5 mg L(-1)) in 2032.

A series of empirically-derived equations were developed from data spanning the 32 year history (1969-2000) that predict or reconstruct water temperatures of the inflowing river, the near surface or epilimnion, and the deep and outflowing waters of subtropical Canyon Reservoir on the Guadalupe River in southcentral Texas, USA. Inflowing and near surface water temperatures both can be predicted from local air temperatures. We used a 5 day or 1 day (in the case of high inflows associated with storm fronts) averaging period of air temperature for the river and a 30 day period for the reservoir surface water. Predictions of deep water and outflow temperatures were more complex in this bottom-draining reservoir. During the winter months, when the reservoir was nearest to being isothermal, air temperature was the primary factor used to predict deep temperatures. For the remainder of the year, the rate at which water was released from the reservoir tended to be the most important factor in predicting deep temperatures, although the air temperature of the previous winter could also be important. During drier years, the cold hypolimnetic waters are retained throughout the stratified period, and outflows were as cool as 12-13 °C in August and September. During very wet years the cold hypolimnetic waters are lost downstream early, and August and September outflows may be as warm as 23 - 24 °C. Therefore, interannual variation in the temperature of the hypolimnion and tailwaters is quite high. This represents a thermal stress to the local biota that is very different from the idea of thermal constancy commonly associated with other reservoir tailwater habitats. Because of this reservoir's particular sensitivity to variation in flow, projections of future change in runoff (as the climate changes) may have a greater effect on the thermal environment of this reservoir than will change in atmospheric temperature.

Forecasting impacts of climate change on Great Lakes surface water temperatures

Solar-driven enhanced chemical adsorption and interfacial evaporation using porous graphene-based spherical composites