Lacustrine wetland in an agricultural catchment: nitrogen removal and related biogeochemical processes

摘要

The role of specific catchment areas, such as the soil-river or lakeinterfaces, in removing or buffering the flux of N from terrestrial toaquatic ecosystems is globally recognized but the extreme variability ofmicrobiological and hydrological processes make it difficult to predict theextent to which different wetlands function as buffer systems. In this paperwe evaluate the degree to which biogeochemical processes in a lacustrinewetland are responsible for the nitrate removal from ground waters feedingCandia Lake (Northern Italy). A transect of 18 piezometers was installedperpendicular to the shoreline, in a sub-unit formed by 80 m of poplarplantation, close to a crop field and 30 m of reed swamp. The chemicalanalysis revealed a drastic NO₃–-N ground water depletion from thecrop field to the lake, with concentrations decreasing from 15–18 mg N/l tothe detection limit within the reeds. Patterns of Cl–, SO₄2–,O₂, NO₂–-N, HCO₃– and DOC suggest that themetabolic activity of bacterial communities, based on the differential useof electron donors and acceptors in redox reactions is the key function ofthis system. The significant inverse relationship found betweenNO₃–-N and HCO₃– is a valuable indicator of thedenitrification activity. The pluviometric regime, the temperature, theorganic carbon availability and the hydrogeomorphic properties are the mainenvironmental factors affecting the N transformations in the studiedlacustrine ecosystem.