Global data set of long-term summertime vertical temperature profiles in 153 lakes

Measurement(s) : temperature of water, temperature profile Technology Type(s) : digital curation Factor Type(s) : lake location, temporal interval Sample Characteristic - Environment : lake, reservoir Sample Characteristic - Location : global Machine-accessible metadata file describing the reported data: https://doi.org/10.6084/m9.figshare.14619009Climate change and other anthropogenic stressors have led to long-term changes in the thermal structure, including surface temperatures, deepwater temperatures, and vertical thermal gradients, in many lakes around the world. Though many studies highlight warming of surface water temperatures in lakes worldwide, less is known about long-term trends in full vertical thermal structure and deepwater temperatures, which have been changing less consistently in both direction and magnitude. Here, we present a globally-expansive data set of summertime in-situ vertical temperature profiles from 153 lakes, with one time series beginning as early as 1894. We also compiled lake geographic, morphometric, and water quality variables that can influence vertical thermal structure through a variety of potential mechanisms in these lakes. These long-term time series of vertical temperature profiles and corresponding lake characteristics serve as valuable data to help understand changes and drivers of lake thermal structure in a time of rapid global and ecological change

Global data set of long-term summertime vertical temperature profiles in 153 lakes

Climate change and other anthropogenic stressors have led to long-term changes in the thermal structure, including surface temperatures, deepwater temperatures, and vertical thermal gradients, in many lakes around the world. Though many studies highlight warming of surface water temperatures in lakes worldwide, less is known about long-term trends in full vertical thermal structure and deepwater temperatures, which have been changing less consistently in both direction and magnitude. Here, we present a globally-expansive data set of summertime in-situ vertical temperature profiles from 153 lakes, with one time series beginning as early as 1894. We also compiled lake geographic, morphometric, and water quality variables that can influence vertical thermal structure through a variety of potential mechanisms in these lakes. These long-term time series of vertical temperature profiles and corresponding lake characteristics serve as valuable data to help understand changes and drivers of lake thermal structure in a time of rapid global and ecological change

Phytoplankton assemblages respond differently to climate warming and eutrophication: A case study from Pyhäjärvi and Taihu

Long-term monitoring data from two lakes located at different latitudes were used to test the hypothesis that phytoplankton communities respond differently to environmental changes (e.g., global warming and anthropogenic activities, mainly eutrophication). Lake Pyhäjärvi (temperate area) and Lake Taihu (subtropical area) are both shallow and productive lakes. Presence/absence data indicated that phytoplankton taxa present did not change significantly in the two lakes over the last two decades. However, biomass data showed that dominance relationships of species changed in both lakes. Results of assemblage ordination indicated that climate change played a vital role in mediating phytoplankton assemblage dynamics in Lake Pyhäjärvi, while eutrophication was the primary factor driving the phytoplankton assemblage dynamics in Lake Taihu. In Lake Pyhäjärvi, the variability of the climatic variables was greater than in Lake Taihu. In Lake Pyhäjärvi, increasing wind speed decreased Secchi depth, promoting shade-tolerant taxa such as Planktothrix. At the same time, increased mixing reduced the loss rate of the heavy taxa such as Tabellaria. Increased nutrient concentrations and water temperature would also promote both Planktothrix and Tabellaria. In the warmer Lake Taihu, the biomass of the dominant Microcystis, which has high optimum temperature for growth, was strongly related to conductivity and less to temperature. Our results showed that climate change potentially enhanced cyanobacteria dominance in lakes Pyhäjärvi and Taihu but by different mechanisms. In Lake Pyhäjärvi, the former dominant species were replaced by cyanobacteria; in Lake Taihu, cyanobacterial dominance was accentuated by climate warming

Zooplankton of Lake Kivu

peer reviewedThe dominant species of the crustacean plankton in Lake Kivu are the cyclopoid copepods Thermocyclops consimilis and Mesocyclops aequatorialis and the cladoceran Diaphanosoma excisum. Mean crustacean biomass over the period 2003–2004 was 0.99 g C m−2. The seasonal dynamics closely followed variations of chlorophyll a concentration and responded well to the dry season phytoplankton peak. The mean annual crustacean production rate was 23 g C m−2 year−1. The mean trophic transfer efficiency between phytoplankton and herbivorous zooplankton was equal to 6.8 %, indicating a coupling between both trophic levels similar to that in other East African Great lakes. These observations suggest a predominant bottom-up control of plankton dynamics and biomass in Lake Kivu. Whereas the present biomass of crustacean plankton in Lake Kivu is comparable to that of other African Rift lakes, the zooplankton biomass before Limnothrissa introduction was 2.6 g C m−2, based on estimation from available historical data. So, if the sardine introduction in the middle of the last century led to a threefold decrease of zooplankton biomass, it did not affect zooplankton production to a level which would lead to the collapse of the food web and of the fishery

Impacts of climate warming on the long-term dynamics of key fish species in 24 European lakes

Fish play a key role in the trophic dynamics of lakes. With climate warming, complex changes in fish assemblage structure may be expected owing to direct effects of temperature and indirect effects operating through eutrophication, water level changes, stratification and salinisation. We reviewed published and new long-term (10–100 years) fish data series from 24 European lakes (area: 0.04–5,648 km2; mean depth: 1–177 m; a north–south gradient from Sweden to Spain). Along with an annual temperature increase of about 0.15–0.3°C per decade profound changes have occurred in either fish assemblage composition, body size and/or age structure during recent decades and a shift towards higher dominance of eurythermal species. These shifts have occurred despite a reduction in nutrient loading in many of the lakes that should have benefited the larger-sized individuals and the fish species typically inhabiting cold-water, low-nutrient lakes. The cold-stenothermic Arctic charr has been particularly affected and its abundance has decreased in the majority of the lakes where its presence was recorded. The harvest of cool-stenothermal brown trout has decreased substantially in two southern lakes. Vendace, whitefish and smelt show a different response depending on lake depth and latitude. Perch has apparently been stimulated in the north, with stronger year classes in warm years, but its abundance has declined in the southern Lake Maggiore, Italy. Where introduced, roach seems to take advantage of the higher temperature after years of low population densities. Eurythermal species such as common bream, pike–perch and/or shad are apparently on the increase in several of the lakes. The response of fish to the warming has been surprisingly strong and fast in recent decades, making them ideal sentinels for detecting and documenting climate-induced modifications of freshwater ecosystems