Assessment of ecosystem services in natural wetlands and rice fields in Nyando floodplain, Kenya

Abstract

Natural wetlands are crucial ecosystems capable of providing provisioning, regulatory and cultural ecosystem services (ES). However, globally, wetlands are constantly under threats of degradation of their functions and loss or reduction of wetland coverage area, as a result of agricultural intensification due to demands for food production. Natural wetlands in Nyando floodplain are no exception as a result of conversion into rice fields. Such conversions may compromise some of the ecosystem services (ES) (benefits people obtain from ecosystems) in natural wetlands even though rice fields also deliver ES which are important in supporting livelihoods in the area. Therefore, this study aimed to assess ES in Ombeyi natural wetland and rice fields in Nyando floodplain to quantify ES in both systems despite the continuous conversion influence on ES delivery to the community. This study was done for a period of four months running between December 2014 and March 2015. Questionnaire survey and Focus Group Discussion were used to assess provisioning and cultural ecosystem services in Ombeyi natural wetland and rice fields using indicators of measurements for ES such as rice yield, fish quantity, price and aesthetic value among others. The effect of water purification as an ecosystem service was evaluated by analysis of water quality changes through in-situ measurements of physico-chemical parameters, nutrients and sediments content in water from River Ombeyi, Ombeyi natural wetland, rice fields and drainage canals. Water samples were collected twice a month in the inlets and outlets of rice fields and the natural wetland, rice fields’ drainage canals and River Ombeyi for nutrients and total suspended solids (TSS) analysis using standard methods. The results showed that the natural wetland had retention of 19.6% for nitrate-nitrogen, 28.8% for Soluble Reactive Phosphorus, 50% for total phosphorus, 19.1% for total nitrogen and 45.6% for (TSS). In the rice fields the retention of 58.21% for TSS, 36.89% for nitrate, TN 35.72%, SRP 79.16% and TP 60.52% were obtained. The chi-square test showed that rice fields retained more nutrients and sediments compared to the natural wetland (p<0.05) except for ammonium in both systems which were not significantly different (p>0.05). Rice fields were observed to be source of ammonium while natural wetlands acted as transformers. Cultural and provisioning services were graded as low both in the natural wetland and rice fields mainly due to continuous conversion of the natural wetland into rice fields.