Temporal changes in the remote sensing reflectance at Lake V?nern

The Aerosol Robotic Network -Ocean Color (AERONET-OC) instrument located at the Palgrunden site in Lake Vanern provides values of remote sensing spectral reflectance RRS(2,,,) since 2008. These in situ RRS(2,,,) indicated a temporal increase from 2015 at center-wavelengths in the green and red spectral regions. To investigate the environmental and climate processes responsible for this increase, water color trends in Lake Vanern were analyzed considering in situ limnological measurements, meteo-climatic quantities and additionally satellite-derived data products from the Moderate Resolution Imaging Spectroradiometer on board the Aqua platform (MODIS-A). Satellite ocean color RRS(2,,,) data assessed against in situ RRS(2,,,) from the Palgrunden site showed satisfactory agreement at a number of spectral bands. Relying on these validation results, comprehensive statistical analysis were performed using MODIS-A RRS(2,,,). These indicated periodical changes between 2002 and 2021 with clear minima occurring between 2010 and 2013. The complementary analyses of temporal changes characterizing limological and meteo-climatic quantities, and also relationships between these quantities and RRS(2,,,), indicated the existence of complex and concurrent bio-geochemical processes influencing water color in Lake Vanern. In particular, significant correlations were observed between RRS(2,,,) and turbidity, and also between RRS(2,,,) and total biovolume. Additionally, an early warming of Lake Vanern surface waters was identified since spring 2014. This occurrence could potentially affect the vertical mixing and water exchange between turbid coastal and pelagic waters with implications for phytoplankton phenology. (c) 2023 The Authors. Published by Elsevier B.V. on behalf of International Association for Great Lakes Research. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/ 4.0/).