Increasing chloride concentrations in Lake Constance: characterization of sources and estimation of loads
Müller, Beat ; Gächter, René
In: Aquatic Sciences, 2012, vol. 74, no. 1, p. 101-112
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- The chloride concentration in Lake Constance, by volume the second largest lake in Europe, has increased by a factor of 2.4 during the past 40years. Based on a chloride budget for the year 2006, we estimated total chloride imports to the catchment at 101ktyear−1. Road deicing salts contributed 52%, waste water 23%, farming 11%, soil weathering 9%, precipitation and solid waste incineration 3% to this import. River monitoring programs in Switzerland, Germany, and Austria in 2006 traced an average total chloride export from the catchment into Lake Constance of almost 70kt and an export from the lake of 56kt. About one-third of this load to the lake originated from the Alpine Rhine catchment (Switzerland), and about 60% from various smaller tributaries in Austria and Germany. The average annual import of chloride to Lake Constance for the years 1995-2007 was 60kt, the export almost 57kt. This budget is in good agreement with the observed increase in the chloride content of the lake and thus confirms the appropriateness and quality of the long-term monitoring program conducted by Swiss, German and Austrian laboratories. For the year 2006, we estimated that about 65% of the chloride spread onto roads for deicing and manure on cultivated land reached the lake within the year of their application. The missing 35% remained transiently in the soil and groundwater of the catchment