56. Gnadensee

Bodensee-Untersee, the smaller part of Lake Constance, covers an area of 62 km between Konstanz and Stein am Rhein and is divided into several basins by peninsulas and the Island Reichenau. The northeastern basin is Gnadensee, with an area of about 10 km, a maximum depth of 20 m, and a water table at 394 m above sea level (a.s.l.). Only minor tributaries flow into Gnadensee coming from the Bodanrück peninsula to the north (elevation up to 600 m a.s.l.). The climate is sub-oceanic, with annual average temperatures of 9 °C and annual precipitation of 750 mm. The potential natural vegetation in the lake catchment would be deciduous forest dominated by Fagus sylvatica L. with Abies alba Mill., Quercus petraea Liebl., Quercus robur L., Acer pseudoplatanus L., Fraxinus excelsior L., Ulmus glabra Huds., Carpinus betulus L., locally Tilia cordata Mill., Tilia platyphyllos Scop. and a rich and diverse shrub and herb layer. Today, Gnadensee is surrounded by densely settled cultural landscape and therefore the vegetation is strongly influenced by agriculture and urbanisation, except for the extended wetlands to the east belonging to the nature reserve ‘Wollmatinger Ried–Untersee–Gnadensee’. Recently, several pollen profiles have been studied in this area (Rösch et al. 2021); the closest pollen profiles come from: Mainau, 9.5 km to the east, Mindelsee, 6.5 km to the northwest, and Hornstaad, 4.5 km to the west.