SUPERVISOR: Thomas HEIN

PROJECT ASSIGNED TO: Flavia BYEKWASO 

Abstract

Tropical riverine wetlands are important ecosystems providing a wide range of goods and services to support people’s livelihoods. Globally over the last few decades, these carbon rich wetland ecosystems have been invaded by mankind through widespread degradation and drainage for various land uses ranging from agriculture, flood management, water production and wastewater treatment systems among others. In Sub-Sahara Africa, studies investigating the impact of wastewater discharge in wetlands with their associated greenhouse gas fluxes and changing carbon tocks remains limited. In Uganda, the coverage of wetlands has been reduced from 15.6% (1994), 10.9% in 2008 and 8.9% in 2019 (Uganda Water and Environment Report., 2019). Uganda’s GHG emissions have slowly increased from 53 442 GgCO2e in 2005 to 90 230 GgCO2e in 2015. The Land Use and Land Use Change and Forestry category was dominant, accounting for 59.5% (53 670 GgCO2e) of the total emissions. The Land sector was estimated to be a source of emissions instead of a sink with Agriculture in the second largest, contributing 26.9%, followed by energy (10.7%) and waste (2.3%). The Industrial processes and product use (IPPU) sector was insignificant in terms of emissions (Ministry of Water and Environment., 2019). Specifically, Lubigi wetland is under immerse multiple pressures and it has been degraded by area of over 40% which has driven by land use changes due to its proximity in urban centres such as Kampala, capital City of Uganda (Kayima et al., 2018). Lubigi wetlands has been channelized into Nsooba-Lubigi storm water drainage system and construction of Lubigi sewage treatment plant receiving effluent of about 4000m3 per day (National Water and Sewage Corporation., 2014). However, practitioners practicing water development are receiving constructive criticism on their potential environmental and climate change impacts on wetland ecosystems. The water sector is feeling the pressure to make their flood protection, water production and wastewater treatment systems more climate smart and environmentally friendly. The potential impacts usually highlighted include emissions of (GHG) greenhouse gases (carbon dioxide, methane, nitrous oxide) and eutrophication related to management regimes of wetland systems, thereby leading to loss of their regulatory and provisioning of ecosystem services. Anthropogenic disturbances in the wetland landscapes interfere with their biogeochemical, functional and structural links of terrestrial and aquatic ecosystems, thereby affecting their functions of providing water and climate resources. Against this background, a major research undertaking of which  this study will be part, firstly to evaluate the spatial and seasonal variations of water quality  of  Lubigi wetland receiving wastewater discharge, secondly assessing the effects of drying and wetting cycles on GHG (CO2, CH4, N2O) fluxes in the floodplain, and thirdly investigate the effects of soil greenhouse gas (CO2, CH4, N2O) production potentials in vegetated and non-vegetated (open water) zones of  Lubigi  wetlands. The broad PhD project outcome is to provide insightful information on the environmental controls, and expound further on the role of stable soil organic matter reservoirs in tropical wetlands located in industrialized riverine landscapes, with their response to changes in land use to receiving wastewater discharge which simultaneously has global implications on the ecosystem, regional and global climate change agenda.

This PhD research study will contribute to the two research clusters in the HR21 Doctoral School:

i) Metabolism of natural and social systems

Tropical wetlands are vital green nature-based solutions (NBS) in polishing received wastewater discharge from grey infrastructure (sewage treatment plant and storm water drainage channel systems driven by societal activities). The wastewater contains carbon and nitrogen compounds which are transformed through physical, chemical and biological mechanisms to other reactive and benign forms. The high concentrations of reactive forms have negative consequences to the environment such as the heat trapping gases commonly known as greenhouse gases released from soil organic carbon (SOC) which has undergone biogeochemical processes that control the gradual accumulation of additional layers in soil and microbial respiration by producing carbon dioxide, whereas anaerobic mineralization of organic carbon by methanogens produces methane and nitrous oxide which requires both aerobic and anaerobic conditions.

ii) Vulnerability of systems to impacts and risks

The continuous loading of wastewater discharge into wetlands leads to increasing concentrations of dissolved organic carbon, ammonium and nitrates which are essential substrates for processing and exchange of nutrients in the microbial communities. This leads to shifting their equilibrium as carbon sinks to carbon sources with regard to greenhouse gas fluxes.