Deep mixing events in Lake Garda

Abstract

The main drivers of the mixing events (air temperature, surface temperature, bottom temperature and heat budget) are analyzed and discussed with the purpose of understanding and quantifying these processes. The main goal is to better understand the influence of the seasonal and annual variations in vertical mixing on the distribution and concentration of phytoplankton through analysis on Chl a and TSM signal upon the lake. Studying the effect of these mixing on the physics and biology of the lake will lead to a deeper knowledge of the dynamics and a better understanding of the nutrients supply cycle of Lake Garda in a "synoptic" view. Deep mixing processes of Lake Garda are analyzed using: in-situ observations of surface and deep water temperature, simulated surface water temperature and remote sensing data of surface chlorphyll-a (Chl a) and total suspended matter (TSM) over the whole lake surface. During the years 2004, 2005 and 2006 full overturn events occurred characterized by anomalous temperature differences between the surface and the bottom of the lake with a corresponding increase of Chl a and TSM at the surface. The year 2005, represented a crucial year for this analysis as the mean concentration of Chl a and TSM signal result to be the strongest record among the others due to strong mixing at the beginning of the year and Saharan dust deposition in July 2005.