IMPACT OF CATCHMENT LAND USE ON THE WATER QUALITY OF WETLANDS IN MURANG’A COUNTY, KENYA

Abstract

Wetland ecosystems in Murang’a County are diminishing due to increased catchment land use practices. Agricultural practices carried out along wetland ecosystems involve excessive use of agrochemicals during crop production, contributing to wetland pollution via surface run-offs. This study was conducted to assess the impact of catchment land use on the water quality of Maragua and Mathioya riverine wetlands in Murang’a County, Kenya. The insights derived from this research are anticipated to contribute to policy formulation and sustainable management of wetlands. Both descriptive survey and experimental research designs were incorporated in this study. Questionnaires, containing items testing knowledge and attitude on the impacts of land use on the wetlands’ water quality, were used to collect data from thirty sample of farmers. Several significant inter-question correlations were observed within the knowledge questions. Particularly, there is a negative correlation between Q5 and Q7 (-0.382, p = 0.037), suggesting that farmers who know that wetlands drain into the River Mathioya are less likely to believe that the amounts of agrochemicals used can harm wetlands. Several significant inter-correlations among the attitude questions further illustrate the complexity of farmers' attitudes. Water and sediment samples were collected concurrently from upstream, midstream and downstream levels of the Maragua and Mathioya riverine ecosystems during both the dry and wet seasons. Elemental analysis was performed using Microwave Plasma-Atomic Emission Spectroscopy (MP-AES) instrument. Mean concentrations of lead during dry seasons were 0.147 ± 0.002 mg/L and 0.378 ± 0.004 mg/L for the wet season. Zinc were 0.01 ± 0.003 mg/L during dry season and 0.015 ± 0.004 mg/L during the wet season. Lead (Pb) concentrations surpassed the recommended WHO maximum residue level of 0.01 mg/L for drinking water. The mean of phosphate concentration was 0.0259 ± 0.0051 mg/L with a standard deviation of 0.0124 mg/L. Nitrate mean concentration during dry season was 9223.37 ± 2672.33 µg/L with a standard deviation of 6545.84 µg/L, and during wet season, it remained the same at 9223.37 ± 2008.17 µg/L with a standard deviation of 4919.00 µg/L. Pesticide residues were analyzed using HPLC-UV. Malathion residue mean concentration was 0.00575524 mg/L; 0.000580078 mg/L for thiamethoxam; 0.001241848 mg/L for diazinon while carbendazim was ˂LOQ across all the samples.All pesticide residues were below the recommended WHO maximum limits for drinking water. Thiametoxam showed a significant difference between sediment and water sample types with a p-value of 0.000. Malathion concentration was asymmetrically distributed with a right tail; implying that a few samples contain significantly higher concentration than the average. Salinity, turbidity, total dissolved solids (TDS), electrical conductivity (EC) and pH were analyzed across the sampling levels using hand-held portable water quality monitor meter. Salinity mean concentration across the three sampling levels was 116.28 ± 14.31 mg/L; 107.08±13.32 mg/L for TDS; 0.16±0.02 mS/cm for electrical conductivity (EC), turbidity:160.38 ± 8.53 NTU and a pH mean of 6.26±0.09. Variation in water parameters across the sampling levels showed that the wetlands have been polluted and the potential sources of pollution are agricultural run-offs and anthropogenic activities. The results highlight the need for integrated catchment management strategies that address land use practices to safeguard wetland health and ecosystem services in Murang’a County.