Anthropogenic Impacts on Water Quality in a Small, Forested Mountain Catchment: A Case Study of the Seebächle, Black Forest, Southern Germany

The aims of this case study are to assess water quality in a small, forested mountain catchment in the Black Forest, forming part of a National Park and Natura 2000 zone. Field work was carried out in the catchment of the Seebächle torrent, a small headwater basin of the River Acher, a confluent of the Rhine, in Southern Germany between late winter and early summer of 2018. The catchment has a diverse natural setting of water bodies, including springs, torrents, and a lake, and is impacted by anthropogenic activities such as summer tourism, winter sports, two quarries, road traffic, and an isolated construction site. Physio-chemical and bacterial water samples were obtained at 10 measurement sites, including a spring, a lake (Mummelsee), a fountain, artificial and natural snow on and next to a ski run (Seibelseckle), artificial ditches and parking lots draining the ski run, and the Seebächle torrent above two granite mines. Samples were either taken directly on site or analyzed in corresponding hydrology and hospital microbiology laboratories. Water of the Seebächle is oxygen-rich, peaty, and mostly acidic, but the pH varies between 4.1 and 9.5 throughout the catchment, inclining towards acid in the fountain and below the ski run and towards alkaline in the lake. Conductivity is spatially highly variable, reaching the most elevated values below the ski run and its parking lot (149 µS/cm). A high density of bacteria including enterobacteria was detected at nearly all sites. Human pathogenic bacteria were found below and surrounding the ski run, at parking lots draining the ski run, as well as at the lowest site during the mid-spring campaign. They were also detected in the touristically highly frequented lake and in the spring feeding the lake during the end-of-spring campaign. Whilst most physico-chemical parameters followed a similar pattern and fell within good to very good EU drinking water quality status, the lake turbidity levels (19.2 NTU) by far exceeded norms after ice thawing. The most contaminated site in terms of bacteria and turbidity (5.2 NTU), ammonium nitrogen (0.18 mg/L), and total nitrogen (5.06 mg/L) was the spring feeding the Mummelsee draining the construction site of a new restaurant. These field analyses show that the water quality of a virtually uninhabited, natural headwater catchment is strongly interconnected and can degrade both by direct and indirect impacts of overtourism.