Dutch lakes suffer from eutrophication

Shallow soft-water lakes in the Netherlands are recovering from acidification but remain under threat from eutrophication.

Due to national and international policy measures the atmospheric deposition of nitrogen and sulphur compounds in shallow Dutch soft-water lakes over the last three decades has decreased by about 50 and 90 per cent, respectively. At the same time, concentrations of sulphate and ammonium in the lakes decreased substantially, much faster than in deep lakes in other European countries. However, increased decomposition of the sediment, also enhanced by climate change, has caused internal eutrophication, particularly in the lakes with steep shores.

Current total nitrogen deposition on these Dutch lakes is estimated at about 0.75 kilomoles per hectare per year (kmol/ha/y), while the critical load for poorly buffered lakes in the Netherlands is 0.36–0.71 kmol/ha/y. The current sulphur deposition is about 0.13 kmol/ha/y, which is well below the critical load of 0.40 kmol/ha/y.

Nutrients are stored in the sediments as a legacy of excessive atmospheric deposition in the past. While careful removal of accumulated organic matter might prevent further eutrophication, this is not a sustainable measure as long as the atmospheric deposition remains above the critical load. Under current policy, a reduction in atmospheric nitrogen deposition of only 10–15 per cent by 2030 is expected.

Source: “Partial recovery of shallow acid-sensitive lakes from acidification.” By H. van Dam and A. Mertens, Environmental Scientist, April 2013.

In this issue