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Research article - Peer-reviewed, 2020

Land-use dominates climate controls on nitrogen and phosphorus export from managed and natural Nordic headwater catchments

de Wit, Heleen A.; Lepisto, Ahti; Marttila, Hannu; Wenng, Hannah; Bechmann, Marianne; Blicher-Mathiesen, Gitte; Eklof, Karin; N. Futter, Martyn; Kortelainen, Pirkko; Kronvang, Brian; Kyllmar, Katarina; Rakovic, Jelena

Abstract

Agricultural, forestry-impacted and natural catchments are all vectors of nutrient loading in the Nordic countries. Here, we present concentrations and fluxes of total nitrogen (totN) and phosphorus (totP) from 69 Nordic headwater catchments (Denmark: 12, Finland:18, Norway:17, Sweden:22) between 2000 and 2018. Catchments span the range of Nordic climatic and environmental conditions and include natural sites and sites impacted by agricultural and forest management. Concentrations and fluxes of totN and totP were highest in agricultural catchments, intermediate in forestry-impacted and lowest in natural catchments, and were positively related %agricultural land cover and summer temperature. Summer temperature may be a proxy for terrestrial productivity, while %agricultural land cover might be a proxy for catchment nutrient inputs. A regional trend analysis showed significant declines in N concentrations and export across agricultural (-15 mu g totN L-1 year(-1)) and natural (-0.4 mu g NO3-N L-1 year(-1)) catchments, but individual sites displayed few long-term trends in concentrations (totN: 22%, totP: 25%) or export (totN: 6%, totP: 9%). Forestry-impacted sites had a significant decline in totP (-0.1 mu g P L-1 year(-1)). A small but significant increase in totP fluxes (+0.4 kg P km(-2) year(-1)) from agricultural catchments was found, and countries showed contrasting patterns. Trends in annual concentrations and fluxes of totP and totN could not be explained in a straightforward way by changes in runoff or climate. Explanations for the totN decline include national mitigation measures in agriculture international policy to reduced air pollution and, possibly, large-scale increases in forest growth. Mitigation to reduce phosphorus appears to be more challenging than for nitrogen. If the green shift entails intensification of agricultural and forest production, new challenges for protection of water quality will emerge possible exacerbated by climate change. Further analysis of headwater totN and totP export should include seasonal trends, aquatic nutrient species and a focus on catchment nutrient inputs.

Keywords

agriculture; bioeconomy; forest; forestry; long-term trend; mitigation; monitoring; stream

Published in

Hydrological Processes
2020, volume: 34, number: 25, pages: 4831-4850
Publisher: WILEY

Authors' information

de Wit, Heleen A.
Norwegian Institute for Water Research (NIVA)
Lepisto, Ahti
Finnish Environment Institute
Marttila, Hannu
University of Oulu
Wenng, Hannah
Norwegian University of Life Sciences
Bechmann, Marianne
Norwegian Inst Bioecon Res NIBIO
Blicher-Mathiesen, Gitte
Aarhus University
Swedish University of Agricultural Sciences, Department of Aquatic Sciences and Assessment
Swedish University of Agricultural Sciences, Department of Aquatic Sciences and Assessment
Kortelainen, Pirkko
Finnish Environment Institute
Kronvang, Brian
Aarhus University
Swedish University of Agricultural Sciences, Department of Soil and Environment
Swedish University of Agricultural Sciences, Department of Soil and Environment

Sustainable Development Goals

SDG6 Clean water
SDG13 Climate action

UKÄ Subject classification

Oceanography, Hydrology, Water Resources

Publication Identifiers

DOI: https://doi.org/10.1002/hyp.13939

URI (permanent link to this page)

https://res.slu.se/id/publ/108726