Nitrogen budget of Lago Maggiore: the relative importance of atmospheric deposition and catchment sources
Publication Type:Journal Article
Source:J. Limnol., Volume 60, p.27-40 (2001)
Keywords:atmospheric deposition, catchment, Lago Maggiore, nitrogen budget, river water
Hydrological and chemical data of 1996 and 1997 are used to evaluate the relative contributions of atmospheric deposition and
urban/industrial wastewaters to the nitrogen budget of Lago Maggiore. The atmospheric load of nitrogen was about 80% of the total
input to the lake, with negligible variations in dry (1997) and wet (1996) years. A comparison of the two study years with the yearly
N budgets evaluated from 1978 to 1998, showed that the N load was higher with increasing amounts of precipitation/water inflow.
Soils and vegetation act as N sinks; the % retention varies between 40-60% for the forested catchments with low population density
in the central-northern part of the basin, to values close to zero or even negative in the south, indicating a net leaching from the
soils. The Traaen & Stoddard (1995) approach revealed that all the catchments of the major inflowing rivers were oversaturated
with nitrogen. The long-term trend of nitrogen concentrations in Lago Maggiore (1955-99) is analogous to the trend for atmospheric
deposition (1975-99), which is related to emissions of nitrogen oxides and ammonia in the atmosphere. The relationships between
the present N load and in-lake concentrations are discussed using a budget model, which is also used to infer the pristine load of N.
The close relationships between N trends in lakes Maggiore, Como and Iseo, and the geographical and anthropogenic features common
to their catchments, suggest that the results obtained for Lago Maggiore can be extended to a wider area.