Versauerung der Birgter Quelle - nordwestlicher Teutoburger Wald im Messintervall der hydrologischen Jahre 1988 – 2000 – 2008

Abstract

Lethmate, J.: Acidification of the Birgter Spring - North-Western Teutoburger Forest in the measuringinterval of the hydrological years 1988 – 2000 – 2008. - Hercynia N. F. 44 (2011): 27 – 38.The acidification of the Birgter Spring (BS), a silicate spring in a small watershed of the north-westernTeutoburger Forest (sandstone ridge), is analysed comparing the spring waters of the hydrological years1987/1988, 1999/2000 and 2007/2008. The characteristic physico-chemical data of the spring waterare contrasted in mean values and variation range for each year. The water types of the measuring periodsare examined and compared one among the other and with the geogene water type on the basisof mean values. Five acidification indices are calculated, which show a statistically significant correlationto the pH-value: the acidification index Ca*+Mg*/SO*+NO3-, the ΔAlk model, the equivalent sumSO4*+NO3-, the alkalinity model for acid waters (HCO3--H+-Al3+) and the acid neutralising capacityANC as Σ(base cations)-Σ(acid anions). To examine the relative influence of the acid anions sulfate andnitrate, the N/S-ratio NO3-/SO4*+NO3- is calculated additionally (*= seasalt correction).The results lead to two conclusions: (1) the BS is acidified chronically. (2) A delayed acidification reversalis recognisable, but not an ecological recovery. Sulfate remains the dominant acidifying anion overthe whole measuring period, the influence of nitrate increases. The development of the BS water is illustratedin a graphic time phase model of freshwater acidification and discussed against the backgroundof geo-ecological characteristics of the research area and other comparable areas in NW-Germany.Key words: spring water, Teutoburger Forest, chronic acidification, delayed acidification reversal