Abstract

The production of macrophyte biomass holds a crucial role in supporting diverse life forms within wetland ecosystems. However, this biomass production is intricately tied to hydrology of the inland wetland system, which in turn is driven by the local climate's seasonal patterns. The response of macrophyte biomass production to seasonal changes in water depth, influenced by rainfall patterns and air temperatures in the freshwater King’wal riverine wetland of Kenya, remains unclear. This study investigated seasonal productivity of emergent macrophytes in relation to water depth and human-induced disturbances in the King’wal riverine wetland of Kenya. Water depths were measured across four study sites using a graduated meter-ruler. Monthly harvesting of above-ground emergent macrophyte biomass took place just above the soil surface in three 1 m² quadrats at each of the four sites, spanning from September 2021 to August 2022. The harvested macrophyte samples were cut, air dried, and oven dried at 65°C to constant weight. The weight was expressed in grams per square meter. Historical rainfall data spanning from 2011 to 2021 was acquired for two stations near the wetland. Daily data for both rainfall and temperature were collected for the study period from three stations: Baraton, Tebeson farm, and Moi University. The Mann-Kendall test was employed, revealing a significant reduction in rainfall (tau = -0.102, P < 0.05) in the area. A negative and significant relationship was established between water depth in the wetland and biomass productivity (rho = - 0.59; P < 0.001). Biomass accumulation and productivity can indicate climate change impacts over a longer period of time.

Key words: Rainfall Anomaly Index, Temperature, above ground biomass, Inland wetland, Kenya.