Thermal response of Sanabria Lake to global change (NW Spain)

Abstract

Thermal response of Sanabria Lake to global change (NW Spain)Are large water bodies able to act as sensors of global change? As accumulators of water and heat, some of their thermal characteristics might be altered by long term (decadal) hydrometeorological changes and thus may be used as indicators of the effects of global change on fluvial ecosystems. This work focuses on the effect of global change (climate change plus water quantity and land use changes) in the internal organization of Sanabria Lake, specifically in its thermal annual cycle. The existence of temporal trends in the thermal behaviour of the lake was investigated based on the water temperature profiles that are available since 1986. Data analyses include the non-parametric Mann-Kendall trend test and the Sen slope estimate to evaluate long term and seasonal patterns of hydrometeorological and in-lake thermal variables. The main results surprisingly point to a net lake cooling that could be explained by a stronger thermocline and a weaker vertical transfer of heat to the hypolimnion during the stratification period. These results contribute to understand and quantify the effects of global change on Iberian freshwater bodies.

Reduced precipitation can induce ecosystem regime shifts in lakes by increasing internal nutrient recycling

“…The lake thermal regime is typically holomictic, with stratification from April to December. The lake has been experiencing epilimnetic autumn warming and hypolimnetic annual cooling during the last decades 33 . The temperature range in the upper layers is wide (Table 1 ), with epilimnetic waters > 20 °C during the summer months.…”

“…However, the eventual drivers of the ecosystem regime shift were not evident. Therefore, we contrasted two main hypotheses: (1) increased diffuse external nutrient loading, perhaps related to the increasing afforestation of the catchment or the recreational use, or (2) increased internal nutrient loading and recycling within the lake basin, eventually related to changing climate conditions in the region 33 . The external nutrient loading trends were evaluated using (1) 30-year monthly nutrient data from the main inflow and (2) modeling external nutrient sources informed by a 2-year intensive sampling of the primary sources in the catchment (i.e., atmospheric deposition, livestock, recreation, runoff, erosion, subsurface flow, wastewater).…”