Land use affects total dissolved nitrogen and nitrate concentrations in tropical montane streams in Kenya

Suzanne R Jacobs; Lutz Breuer; Klaus Butterbach-Bahl; David E Pelster; Mariana C Rufino

doi:10.1016/j.scitotenv.2017.06.100

Land use affects total dissolved nitrogen and nitrate concentrations in tropical montane streams in Kenya

Sci Total Environ. 2017 Dec 15:603-604:519-532. doi: 10.1016/j.scitotenv.2017.06.100. Epub 2017 Jun 20.

Authors

Suzanne R Jacobs¹, Lutz Breuer², Klaus Butterbach-Bahl³, David E Pelster⁴, Mariana C Rufino⁵

Affiliations

¹ Karlsruhe Institute of Technology, Institute of Meteorology and Climate Research, Atmospheric Environmental Research (KIT/IMK-IFU), Kreuzeckbahnstr. 19, 82467 Garmisch-Partenkirchen, Germany; Centre for International Forestry Research (CIFOR), c/o World Agroforestry Centre, United Nations Avenue, Gigiri, P.O. Box 30677, 00100 Nairobi, Kenya; Institute for Landscape Ecology and Resources Management (ILR), Justus Liebig University, Heinrich-Buff-Ring 26, 35392 Giessen, Germany; Mazingira Centre, International Livestock Research Institute (ILRI), P.O. Box 30709, 00100 Nairobi, Kenya. Electronic address: suzanne.jacobs@kit.edu.
² Institute for Landscape Ecology and Resources Management (ILR), Justus Liebig University, Heinrich-Buff-Ring 26, 35392 Giessen, Germany; Centre for International Development and Environmental Research (ZEU), Justus Liebig University, Senckenbergstr. 3, 35390 Giessen, Germany. Electronic address: lutz.breuer@umwelt.uni-giessen.de.
³ Karlsruhe Institute of Technology, Institute of Meteorology and Climate Research, Atmospheric Environmental Research (KIT/IMK-IFU), Kreuzeckbahnstr. 19, 82467 Garmisch-Partenkirchen, Germany; Mazingira Centre, International Livestock Research Institute (ILRI), P.O. Box 30709, 00100 Nairobi, Kenya. Electronic address: klaus.butterbach-bahl@kit.edu.
⁴ Mazingira Centre, International Livestock Research Institute (ILRI), P.O. Box 30709, 00100 Nairobi, Kenya. Electronic address: d.pelster@cgiar.org.
⁵ Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, United Kingdom. Electronic address: m.rufino1@lancaster.ac.uk.

PMID: 28645050
DOI: 10.1016/j.scitotenv.2017.06.100

Abstract

African tropical montane forests are facing fast and dynamic changes in land use. However, the impacts of these changes on stream water quality are understudied. This paper aims at assessing the effect of land use and physical catchment characteristics on stream water concentrations of dissolved organic carbon (DOC), total dissolved nitrogen (TDN), nitrate (NO₃-N) and dissolved organic nitrogen (DON) in the Mau Forest, the largest tropical montane forest in Kenya. We conducted five synoptic stream water sampling campaigns at the outlets of 13-16 catchments dominated by either natural forest, smallholder agriculture or commercial tea and tree plantations. Our data show a strong effect of land use on TDN and NO₃-N, with highest concentrations in stream water of catchments dominated by tea plantations (1.80±0.50 and 1.62±0.60mgNl^-1, respectively), and lowest values in forested catchments (0.55±0.15 and 0.30±0.08mgNl^-1, respectively). NO₃-N concentration increased with stream temperature and specific discharge, but decreased with increasing catchment area. DOC concentrations increased with catchment area and precipitation and decreased with specific discharge, drainage density and topographic wetness index. Precipitation and specific discharge were also strong predictors for DON concentrations, with an additional small positive effect of tree cover. In summary, land use affects TDN and NO₃-N concentrations in stream water in the Mau Forest region in Kenya, while DOC and DON were more related to hydrologic regimes and catchment properties. The importance of land use for NO₃-N and TDN concentrations emphasizes the risk of increased nitrogen export along hydrological pathways caused by intensified land use and conversion of land to agricultural uses, which might result in deterioration of drinking water quality and eutrophication in surface water in tropical Africa.

Keywords: Dissolved organic carbon; Dissolved organic nitrogen; Forest; Land use; Streams; Topography.

MeSH terms

Agriculture
Carbon
Environmental Monitoring*
Forests
Kenya
Nitrates / analysis*
Nitrogen / analysis*
Rivers / chemistry*

Substances

Nitrates
Carbon
Nitrogen