Lakes are sentinels and integrators of environmental and climatic changes occurring within their watershed. The influence of climate change on lakes is becoming increasingly concerning worldwide. Understanding the complex behavior of lakes in a changing environment is essential to effective water resource management and mitigation of climate change effects. The increase in summer temperatures has been estimated at 0.34 °C per decade with lake specific parameters like morphology contributing to the diversity of response at the regional level. The frequency of heatwave events in Europe is increasing and the recent IPPC report on climate change estimated an over 90% likelihood that there will continue to be an increase in the frequency of heat extremes over the 21st century in Europe, especially in southern regions. In July 2019, a heatwave occurred in Europe with record daily maximum temperatures over 40 °C observed in several places. Temperatures were locally 6 to 8 °C higher than the average warmest day of the year for the period 1981-2010. Heatwaves can have implications for the water quality and ecological functioning of aquatic systems, and for example in Europe several of these events have been associated with increased phytoplankton blooms. Of particular concern is the predicted increase in potentially harmful summer blooms of cyanobacteria with combined pressures of climate change and eutrophication. The ESA Climate Change Initiative (CCI) Lakes ECV Project (https://climate.esa.int/en/projects/lakes/) combines multi-disciplinary expertise to exploit satellite Earth Observation data to create the largest and longest possible consistent, global record of five lake climate variables: lake water level, extent, temperature, surface-leaving reflectance (e.g., chlorophyll-a and suspended solid concentrations), and ice cover. The first version of the database covers 250 globally distributed lakes with temporal coverage, depending on parameter, ranging from 1992 up to 2019. This is expanded to 2000 lakes in version 2. The ESA Lakes_cci dataset was found to be a key resource for examining the implications of heatwave events on lakes. We examined heatwave events for European lakes, focusing on the 2019 event. The response of lake chlorophyll-a concentration, a proxy of phytoplankton abundance, was dependent on the lake type, especially lake depth, stratification and trophic state. However, the timing of the heatwave event itself was also important in the type of response observed. In many cases, the effects of resulting storms that ended the heatwave were more discernable than the heatwave itself. For example, in some shallow lakes, following the storm, chlorophyll-a concentrations increased markedly and remained high for the duration of the summer. Comparing the high frequency WISPstation data (2018-2020) with the CCI dataset allows for detailed cross validation. Some of the rapid fluctuations visible from the satellite record are supported by the in situ data. In addition, utilizing the phycocyanin pigment estimates from the WISPstation and microscopic counts, showed how cyanophytes played a key role in the sudden increases and declines in chlorophyll-a in mid to late summer. Heatwaves and subsequent storms appeared to play an important role in structuring the phenology of the primary producers, with wider implications for lake functioning.
Using Lakes CCI satellite products to detect the influence of heatwave events on chlorophyll-a in Europe
Mariano Bresciani;Monica Pinardi;Giulio Tellina;
2022
Abstract
Lakes are sentinels and integrators of environmental and climatic changes occurring within their watershed. The influence of climate change on lakes is becoming increasingly concerning worldwide. Understanding the complex behavior of lakes in a changing environment is essential to effective water resource management and mitigation of climate change effects. The increase in summer temperatures has been estimated at 0.34 °C per decade with lake specific parameters like morphology contributing to the diversity of response at the regional level. The frequency of heatwave events in Europe is increasing and the recent IPPC report on climate change estimated an over 90% likelihood that there will continue to be an increase in the frequency of heat extremes over the 21st century in Europe, especially in southern regions. In July 2019, a heatwave occurred in Europe with record daily maximum temperatures over 40 °C observed in several places. Temperatures were locally 6 to 8 °C higher than the average warmest day of the year for the period 1981-2010. Heatwaves can have implications for the water quality and ecological functioning of aquatic systems, and for example in Europe several of these events have been associated with increased phytoplankton blooms. Of particular concern is the predicted increase in potentially harmful summer blooms of cyanobacteria with combined pressures of climate change and eutrophication. The ESA Climate Change Initiative (CCI) Lakes ECV Project (https://climate.esa.int/en/projects/lakes/) combines multi-disciplinary expertise to exploit satellite Earth Observation data to create the largest and longest possible consistent, global record of five lake climate variables: lake water level, extent, temperature, surface-leaving reflectance (e.g., chlorophyll-a and suspended solid concentrations), and ice cover. The first version of the database covers 250 globally distributed lakes with temporal coverage, depending on parameter, ranging from 1992 up to 2019. This is expanded to 2000 lakes in version 2. The ESA Lakes_cci dataset was found to be a key resource for examining the implications of heatwave events on lakes. We examined heatwave events for European lakes, focusing on the 2019 event. The response of lake chlorophyll-a concentration, a proxy of phytoplankton abundance, was dependent on the lake type, especially lake depth, stratification and trophic state. However, the timing of the heatwave event itself was also important in the type of response observed. In many cases, the effects of resulting storms that ended the heatwave were more discernable than the heatwave itself. For example, in some shallow lakes, following the storm, chlorophyll-a concentrations increased markedly and remained high for the duration of the summer. Comparing the high frequency WISPstation data (2018-2020) with the CCI dataset allows for detailed cross validation. Some of the rapid fluctuations visible from the satellite record are supported by the in situ data. In addition, utilizing the phycocyanin pigment estimates from the WISPstation and microscopic counts, showed how cyanophytes played a key role in the sudden increases and declines in chlorophyll-a in mid to late summer. Heatwaves and subsequent storms appeared to play an important role in structuring the phenology of the primary producers, with wider implications for lake functioning.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
