Recent climate warming has caused distinct changes in the biology and chemistry of high alpine lakes. This relatively small water bodies are particularly sensitive to changes in air temperature, and snow and ice cover duration. The glacier retreat in their catchment areas additionally affects the amount of particulate and solute matter transported to these lakes. In this project we want to focus on the lakes located in the mountains surrounding the Matschertal which is an LTER site since 2013. So far brooks and rivers, and terrestrial ecosystem processes have been studied within this LTER. We aim at including lakes, which are abundant in this area, especially the ponds and lakes in the Saldur area, but also Lake Matscherjoch, Lake Upia, and Lakes Hochaltl. We hypothesize that - despite their relative vicinity -these water bodies are affected quite differently by recent climate warming, depending on the interaction of the following drivers:

• duration of the ice free seasons, water temperature, and input of organic matter from the catchment as driver for changes in productivity, species composition, and chemistry in the lakes;
• glacier retreat and diminished particulate input as driver for a transition from turbid to clear water bodies;
• rock glacier melt water as source for solutes that increase the lakes´ conductivity and acidity,
• development status of new lakes freshly formed on the slopes previously covered by glaciers.

In order to capture the interplay of these drivers, we want to study the lakes across an altitudinal gradient (2700-3200 m a.s.l.), including lakes with and without direct glacier influence. We propose to

(i) bi-annually monitor the twelve lakes and ponds in the Saldur area, and the four lakes Upia, Hochaltl (upper and lower), and Matscherjoch, and any of their effluents. We want to detect the main drivers for seasonal and annual changes in water chemistry and link them to the data available from the weather station in the Saldur area. This data will be provided for comparison with the monitoring data of the brooks and rivers in this LTER area.

(ii) perennially monitor water temperature and conductivity in four of the lakes, two located very high (3218 and 2922 m a.s.l.), and two located next to each other, but one with, and one without glacier influence.

(iii) reconstruct changes in the relative importance of glacier versus direct temperature impact over the last 10000 years by investigating two neighboring lakes, one with and one without direct glacier impact (Unterer Saldursee 2747 m a.s.l., Fischersee 2754 m, located in 85m distance on the same mountain slope), and compare them with the 10000 year record form Oberer Saldursee 2922 m. The chironomid remains in Fischersee will allow for a temperature reconstruction over the last 10000 years. The difference in particulate input in these three lakes will provide information about glacier variability over the same period.

Background

The Matschertal and its surrounding slopes are in the focus of the Long Term Ecological Research (LTER) complex site Matsch/Mazia. The aim is to gain high quality, continuous records of the abiotic and biotic processes that characterize the ecosystems in Matschertal. Short and long term climate impacts are in the centre of the research interest of  LTER. We propose to complement the ongoing studies by (i) continuously monitoring high alpine lakes along an altitudinal gradient (2700 – 3200 m a.s.l.), and (ii) by palaeoecological multi-proxy study of lake sediments. The monitoring will provide insight into what is driving the bio-geochemical changes in a variety of high alpine lakes, i.e. with and without glacier impact, of different age, and at different altitudes. The palaeoecological investigation will provide a temperature reconstruction over the last 10000 years, and aims at reconstructing glacier fluctuations, i.e. of Saldur Ferner. These data will be available for comparison with the ongoing LTER studies, e.g. the fluctuation of turbidity and water temperature in brooks. The study itself will also profit form the ongoing LTER Matsch/Mazia reserach, especially the freshwater, climate, and ecological data.

The major aims of the projects are:

1. disentangling climate change and glacier impacts on high alpine lakes by continuously monitoring parameters strongly affected by recent warming, i.e. temperature and conductivity in four lakes with and without glacier impact, along an altitudinal gradient (2700-3200)
2. trace changes in productivity, weathering and glacier impact in 16 water bodies along an altitudinal gradient (2700-3200)by bi-annually sampling all major limnochemical parameters and metal contents
3. reconstructing temperature and glacier fluctuations over the last 10000 years for the Saldur area by studying lake sediments

Expected results

So far there is no Holocene temperature record available for a lake in Southern Tyrol. The two lakes we have sampled were either not suitable or turned out not to work with the existing data set. We hope to close this gap with the core from Fischersee and would thus provide the first Holocene temperature reconstruction for the Vintschgau. We aim to reconstruct the glacier fluctuations from the neighbouring lake Untere Saldursee. This provides an unique opportunity as these two lakes are so close and affected by the same climate processes, including precipitation, but differ in the glacier impact. From the recent limnological investigation we will gain a more detailed understanding of the climate impact on lake ecosystems and its long term effects.