Trophic status and sedimentation rate as effective indicators of condition in alpine lake restoration

Abstract

Introduction: Oligotrophic alpine lakes are highly vulnerable to eutrophication and shoreline erosion under intense recreational and livestock pressure. Lake Peñalara serves as a case study to evaluate ecotourism impacts on mountain lakes and their recovery following the implementation of management and restoration measures. Objectives: This study aims to evaluate long-term changes in eutrophication and soil erosion in response to targeted management actions, offering guidance for similarly impacted high mountain lakes. Methods: We applied change-point analysis to identify distinct recovery phases in trophic indicators (total phosphorus [TP], chlorophyll a [Chl], and Secchi transparency) and sedimentation rate (as a proxy for catchment erosion); and trend analysis to detect longer-term tendencies. Results: Two distinct recovery phases were identified for both eutrophication and shoreline erosion. Eutrophication recovery began with a 5-year period marked by a sharp decline in TP and Chl, along with increased water transparency. This was followed by a 20-year phase with moderate-to-low nutrient levels; although a slight long-term increasing trend was observed. Shoreline erosion recovery also occurred in two phases: an initial 8-year period of decline, followed by a sustained phase of low erosion rates. Conclusions: Recovery was achieved by reducing external nutrient inputs and trampling through visitor management (bans on swimming and camping, park rangers, limits on prolonged stays, and defined trails), by revegetating eroded areas, and by restricting livestock access with perimeter fencing. These results underscore the effectiveness of targeted activity management over merely reducing visitor numbers and highlight the need for decades-long monitoring to capture ecosystem recovery dynamics.