Land use, vegetation composition, water quality and benthic macroinvertebrates assemblages in the Njoro and Kamweti Rivers, Kenya

Abstract

Land use transformation patterns in watershed impacts riparian vegetation, stream water quality and macroinvertebrate assemblages. The understanding of this relationship is important for the management of water resources. This research established the link between land use, vegetation, water quality and benthic macroinvertebrate in the Njoro and Kamweti Rivers. Five sampling sites which represented the major land use categories were selected in each river to for data collection. Sampling was carried out from August 2018 to August 2019. For vegetation data collection, three 70-m quadrants were established and three plots established. Trees were sampled in 10×10 m plots, 5×2 m plots for shrubs and 2×0.5 m for the grasses and herbs. In situ, readings of temperature, pH, Electrical Conductivity (EC) and Dissolved Oxygen (DO) were determined using a Hanna HI 9829 Multi-parameter meter. Nutrient analysis were determined in the laboratory following APHA procedures. Samples of benthic macroinvertebrates were collected using a kick net and identified to the family level. Remote sensing datasets, utilized from 1988 to 2019, 10 years epoch. The results indicated that in 2019, the LULC in the Njoro River Catchment were Forest, 29.31 %, Farm Land 50.34%, Built Up Areas 5.24%, and in Kamweti River Catchment the Forest, 62.34%, Farm Land 3.29%, Built Up Areas 3.06%. In Njoro River recording 124 plant species from 40 families and Kamweti River recording 128 species from 44 families. In the forest areas, water sample recorded high levels of DO, lower temperatures, EC and nutrient concentrations as compared to the sites downstream. Benthic macroinvertebrates data displayed a similar pattern along the land use gradient. Ephemeroptera and Diptera orders dominated the Njoro River with Ephemeroptera mostly present in forest areas with high abundance. Kamweti River, forest site was dominated by order EPT with decreased densities downstream. One way Analysis of Similarity (ANOSIM), revealed that the sites were similar in Njoro River (R= -0.27, p=0.92) whereas Kamweti River, the sites were not similar (R= 0.65, p= 0.01) in benthic macroinvertebrates assemblages. This results indicates that vegetation abundance and diversities, water quality and benthic macroinvertebrates structure is influenced by the adjacent land uses. From the findings of the study the enforcement of water pollution prevention techniques such as increasing forest and land conservation, improving and protecting the riverine areas and reducing sediment and nutrient runoff to the stream are encouraged.