Acidification by nitric acid — Future considerations

HNO₃ is more efficient in acidifying lakes than has been generally believed. This is because as nitrate loading to lakes increases, the efficiency of in-lake nitrate removal decreases markedly. Efficiencies decrease because algal N requirements are exceeded and because denitrification, which becomes an important removal process, is not as efficient as algal removal. Thus, nitrate and the accompanying H⁺ accumulate and HNO₃ becomes an important factor in acidification. Data from an experimentally acidified system suggest that midsummer surface-water nitrate concentrations in excess of only 1 µmol L^?1 indicate that algal requirements have been exceeded. While 1 µmol L^?1 NO₃ ^? is not a significant quantity in terms of affecting the acidity of the water, it is useful as an indicator to identify lakes where algal requirements have been exceeded and where further increases in HNO₃ loading could lead to lake acidification.