Riverine dissolved organic carbon in Rukarara River Watershed, Rwanda

Fabien Rizinjirabake; Abdulhakim M Abdi; David E Tenenbaum; Petter Pilesjö

doi:10.1016/j.scitotenv.2018.06.194

Riverine dissolved organic carbon in Rukarara River Watershed, Rwanda

Sci Total Environ. 2018 Dec 1:643:793-806. doi: 10.1016/j.scitotenv.2018.06.194. Epub 2018 Jun 27.

Authors

Fabien Rizinjirabake¹, Abdulhakim M Abdi², David E Tenenbaum², Petter Pilesjö²

Affiliations

¹ Department of Physical Geography and Ecosystem Science, Lund University, Sweden; Department of Biology, College of Science and Technology, University of Rwanda, Rwanda. Electronic address: fabien.rizinjirabake@nateko.lu.se.
² Department of Physical Geography and Ecosystem Science, Lund University, Sweden.

PMID: 29958168
DOI: 10.1016/j.scitotenv.2018.06.194

Abstract

Dissolved organic carbon (DOC) loading is rarely estimated in tropical watersheds. This study quantifies DOC loading in the Rukarara River Watershed (RRW), a Rwandan tropical forest and agricultural watershed, and evaluates its relationship with hydrological factors, land use and land cover (LULC), and topography to better understand the impact of stream DOC export on watershed carbon budgets. The annual average load for the study period was 977.80 kg C, which represents approximately 8.44% of the net primary productivity of the watershed. The mean daily exports were 0.37, 0.14, 0.075 and 0.32 kg C/m² in streams located in natural forest, tea plantation, small farming areas, and at the outlet of the river, respectively. LULC is a factor that influences DOC loading. The quick flow was the main source of stream DOC at all study sites. Stream DOC increases with increasing water flow, indicating a positive relationship. Thus, the expectation is that a change in land cover and/or rainfall will result in a change of stream DOC dynamics within the watershed. Topography was also found to influence the dynamics of stream DOC through its effect on overland flow in terms of drainage area and total length of flow paths. Tea plantations were located in areas of high drainage density and projected increase of rainfall in the region, as a consequence of climate change, could increase stream DOC content and affect stream water quality, biodiversity, balance between autotrophy and heterotrophy, and bioavailability of toxic compounds within the RRW.

Keywords: Dissolved organic carbon; Land use and land cover; Rwanda; Stream water; Watershed.