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Research article - Peer-reviewed, 2007

Nitrate-depleted conditions on the increase in shallow northern European lakes

Weyhenmeyer GA, Jeppesen E, Adrian R, Arvola L, Blenckner T, Jankowski T, Jennings E, Noges P, Noges T, Straile D

Abstract

We determined relative nitrate-nitrogen (NO3- N) loss rates in 100 north-mid-European lakes from late spring to summer by using the exponential function N-2 5 N-1e(-k)( (t)(2) - (t)(2)), where N-1 and N-2 are NO3- N concentrations at the beginning (t(1)) and the end (t(2)) of the time interval, respectively, and k is the specific NO3- N loss rate. We found that k decreased with increasing lake depth. Adjusting k to the lake depth (k(adj)), we observed that k(adj) was positively related to spring NO3-N concentrations, but this relationship became insignificant at mean lake depths exceeding 12.5 m. A relationship between k(adj) and spring NO3- N concentrations in lakes shallower than 12.5 m implies that changes in spring NO3-N concentrations influence the NO3- N loss rate and thereby summer NO3- N concentrations. Time series from one Estonian, one German, and 14 Swedish lakes shallower than 12.5 m since 1988 revealed that May to August NO3-N concentrations have decreased over time everywhere, and the number of time periods exhibiting a NO3-N depleted condition, i.e., NO3-N levels below 10 mu g L-1, in these lakes has tripled since 1988. We explained the decreasing NO3-N concentrations by a reduction in external nitrogen loading including atmospheric deposition, and by changes in climate. The observed prolongation of NO3- N depleted conditions might be one possible explanation for the increasing occurrence of nitrogen- fixing cyanobacteria in a variety of lake ecosystems

Published in

Limnology and Oceanography
2007, volume: 52, number: 4, pages: 1346-1353
Publisher: AMER SOC LIMNOLOGY OCEANOGRAPHY

Authors' information

Weyhenmeyer, Gesa
Swedish University of Agricultural Sciences, Department of Environmental Assessment
Straile, Dietmar
University of Konstanz

UKÄ Subject classification

Environmental Sciences related to Agriculture and Land-use
Fish and Aquacultural Science

Publication Identifiers

DOI: https://doi.org/10.4319/lo.2007.52.4.1346

URI (permanent link to this page)

https://res.slu.se/id/publ/16681