Dissolved organic carbon leaching flux in a mixed agriculture and forest watershed in Rwanda

Abstract

Study region: Rukarara River Watershed (RRW), Rwanda. Study focus: DOC leaching has important environmental consequences for both terrestrial and aquatic ecosystems. This paper measures leached dissolved organic carbon (LDOC) and the factors controlling its variation in the RRW, a mixed agriculture and forest watershed in Rwanda. The study describes the relationship of LDOC with land use/land cover (LULC), soil properties, rainfall characteristics, and stream DOC using linear regression and linear mixed effects models. New hydrological insights: The annual LDOC flux from topsoil to deeper soil horizons was 13.62 tonnes of carbon for the study area. This annual LDOC flux represents approximately 2% of the net primary productivity and 0.02% of the soil carbon stock. The plantation forest and natural forest sites showed higher LDOC fluxes than other LULC classes. Soil TOC, TN, rainfall intensity and amount positively affected LDOC flux (7 ≤ R2 ≤ 30%) in the RRW. Cation exchange capacity, runoff, and rainfall storage negatively affected the RRW (7 ≤ R2 ≤ 23%). LDOC flux explained 14% of the variation of stream DOC in the RRW. Our results imply that, under ongoing climate and LULC changes, an increase of the proportion of plantation forest and rainfall intensity throughout the watershed will increase LDOC flux, and will have a weak positive effect on stream DOC. Keywords: Dissolved organic carbon, Leaching, Land cover, Watershed, Rainfall characteristics, Soil properties, Linear models