Author(s)

A. Groß-Wittke, F. Selge & G. Gunkel

Abstract

In the context of climate change artificial recharge of groundwater becomes increasingly important. The two main climate change factors affecting ground water recharge performance are water warming and extreme precipitation events with drought and floods. This will strongly influence self-purification processes, indirectly due to changes in the stratification and circulation characteristics of the lake and directly due to the intensification of metabolic processes and biodegradation efficiency, which are responsible for water self-purification. At the study site Lake Tegel, Berlin (Germany), epilimnion water warming of 0.9°C per decade from 1980 to 2007 was detected. Moreover, continuous measurements of temperature for a yearly period from 2010 to 2011 in the openwater epilimnion and littoral zone showed a maximum difference of 5.2°C on a sunny summer day (TLake,max= 25.3°C, TAir,max= 26.2°C). The present work describes the development and operation of enclosure field experiments conducted to simulate water warming (up to 30°C) and to provide a detailed picture of the processes which occur in the uppermost sediment layers (0–20 cm depth) at a littoral bank site. To illustrate the performance of the enclosure setup with a mean temperature increase of 4.6°C (May–August 2012), microbial activity as well as pore water analysis was examined monthly. Microbial activity was measured by enzymatic TTC- and FDA-methods. Both showed a highly microbial active upper layer down to 5 and 10 cm depth, respectively. However, no clear water warming effects on redox-chemical and microbial activity could be detected. This paper is intended to contribute to an ongoing discussion, if in-situ enclosures enable realistic experimental studies to allow investigations of the

Keywords

bank filtration, climate change, enclosure, groundwater recharge, microbial activity, water temperature