Title: Drivers of carbon dioxide and methane fluxes from headwater streams in the Mara River, Kenya
Author: David Wanjala Namwaya
Supervising Institution: IHE Delft - Institute for Water Education
Headwater streams are important sources of carbon dioxide (CO2) and methane (CH4) in inland aquatic ecosystems playing role in global emissions. Land use and stream geophysical characteristics were hypothesized to influence emissions and concentrations due to changing organic matter sources and stream characteristics. Sampling for three months at an interval of two weeks was done in the headwaters of the Mara River, Kenya. Water quality parameters including nutrients, dissolved organic carbon and dissolved oxygen were measured in different land use types and used to determine relationships with CO2 and CH4 concentration and fluxes. There were 48 sampling sites, 14 in forested land use, 19 in Agricultural land use; 6 in mixed; and 9 classified as livestock that included watering holes and streams. The carbon in CO2 molecule (CO2 - C) flux ranged from 31.2 ± 9.13 to 66.7 ± 16.7 (mg m-2 h-1) across all sites, corresponding to a CO2 concentration of 1.06 ± 0.08 (mgL-1). CH4-C flux had a mean range of 0.20 ± 0.07 mgm-2h-1 from mixed sites to 0.55 ± 0.17 mgm-2h-1 from agricultural sites, with a mean concentration of 0.007 ± 0.0009 (mgL-1) of C - CH4. DO concentration was significantly lower in the livestock sites (4.50 ± 0.4mg/l) compared to agricultural site (6.14 ± 0.1 mg/l) and forest sites (6.61 ± 0.1mg/l). High DOC mean concentration (6.89 ± 0.17 mg/l) and NH4+ (0.38 ± 0.08 mg/l) was measured from livestock sites. Relationships between land use and water quality variables and CO2 and CH4 gas fluxes were determined using multiple linear regression with mixed modelling techniques. DOC, DO, NO3 and stream discharge are the biogeochemical variables and physical variables that drive CO2 and CH4 concentration and fluxes from the Mara head water streams.