The Mixing Regime and Turbidity of Lake Banyoles (NE Spain): Response to Climate Change

Teresa Serra,Jordi Colomer,Josep Pascual,Ramon Brunet

doi:10.3390/w12061621

Abstract

This study analyses the water temperature changes in Lake Banyoles over the past four decades. Lake Banyoles, Spain’s second highest lake, situated in the western Mediterranean (NE Iberian Peninsula). Over the past 44 years, the warming trend of the lake’s surface waters (0.52 °C decade−1) and the cooling trend of its deep waters (−0.66 °C decade−1) during summer (July–September) have resulted in an increased degree of stratification. Furthermore, the stratification period is currently double that of the 1970s. Meanwhile, over the past two decades, lake surface turbidity has remained constant in summer. Although turbidity did decrease during winter, it still remained higher than in the summer months. This reduction in turbidity is likely associated with the decrease in groundwater input into the lake, which has been caused by a significant decrease in rainfall in the aquifer recharge area that feeds the lake through groundwater sources. As a unique freshwater sentinel lake under the influence of the climate change, Lake Banyoles provides evidence that global warming in the western Mediterranean boosts the strength and duration of the lake’s stratification and, in response, the associated decrease in the turbidity of its epilimnion.

Highlights

Lakes can be considered sentinels of current climate condition and, are critical to understanding the effects global climate change on aquatic ecosystems [1]
Over the past 46 years, the air temperature in Banyoles has risen during the summer months of the JAS period at a warming rate of 0.52 ◦ C decade−1, R2 = 0.3643 and p < 0.01 (Figure 2a)
The surface water temperature of the karstic Mediterranean Lake Banyoles during summer has increased over the past 44 years at a rate of 0.52 ◦ C decade−1 and the temperature of the bottom layer has decreased at a rate of −0.66 ◦ C decade−1 resulting, in a strengthening of the lake’s summer stratification

Summary

Introduction

Lakes can be considered sentinels of current climate condition and, are critical to understanding the effects global climate change on aquatic ecosystems [1]. Studies of lake responses to climate change have assessed the warming of the surface layers in lakes around the globe [2]. From 1985 to 2009, the summer surface water temperature of 211 lakes studied warmed at a rate in the range of 0–1 ◦ C decade−1 (depending on the region) [2]. O’Reilly et al [2] attributed this trend in the temperature of the water surface to the rapid annual increase in air temperature Zhang et al [3] attributed the increase in the temperature of the water surface to the increment in the air temperature and the wind velocity reduction. The warming trend of surface water layers of lakes results in an increase in the lake stratification strength [7]

Methods

Results

Conclusion