Effects of Land Use and Seasonality on the Distribution of Mayflies and Water Quality along Thika River, Kenya.

Abstract

Mayfly order (Ephemeroptera) is a widely distributed taxon that is used commonly in the biological assessment of water quality due to its sensitivity to changes in water quality. Despite its values in water quality assessment, studies on the taxa are still very scanty in most tropical countries, including Kenya. Water quality deterioration remains a vital threat in most rivers. The primary objective of this study, was therefore to investigate the spatial and temporal changes in community structure of mayflies in relation to water quality changes influenced by land use along Thika River. Sampling sites were selected based on the main land use along the river and marked with a global positioning system (G.P.S). Triplicate samples of dissolved oxygen, conductivity, total dissolved solids, temperature, transparency which are water quality parameters and Ephemeroptera, were collected for six months (3 dry and 3 wet months) and later taken for laboratory analysis. Mean overall spatial for dissolved oxygen concentration was 9.8±0.24 𝑚𝑔/𝑙 and conductivity level was 63.3±4.98 μ𝑆/𝑐𝑚. The overall average temperature was 19.4±0.540𝐶 and total dissolved solids were 32.8±2.49𝑚𝑔/𝑙 in sites. Student Newman’s Keul’s multiple range tests revealed significant variability of the means of these water parameters in the three sampling sites at 𝑝=0.05. For temporal variation, only temperature and transparency were significant, with means of 19.37±0.730𝐶 and 0.54±0.05𝑚 respectively.Thirteen morphologically distinct taxa belonging to 6 families were identified. The dominant genera were Acanthiops (70.4%) and Afronurus (13.3%). The mean abundance of mayfly larvae was 1238 𝑖𝑛𝑑𝑖𝑣./𝑚2, and temporal mean of 83.9±25.7. Kruskal-Wallis test revealed that species abundance between sites was significantly different (𝑝<0.05) but not between seasons. Correlation coefficient showed that there was a weak but not significant relationship between water quality and abundance of mayfly larvae. However, most of the water parameters were significantly correlated with each other. Results of this study can be used in the bioassessment of water quality in the same river in future or rivers in the same region for comparison purposes. It can also be used by environmental health sector in enlightening people on the importance of environmental conservation of water bodies.