Effects of Catchment Land Use on Water Quality in Maragua and Mathioya Riverine Wetlands, Murang’a County, Kenya

Wetland ecosystems in Murang’a County are diminishing due to increased catchment land use practices. Part of wetlands have been converted into farmlands where various agricultural activities are carried out while some parts have been converted into settlement points. Agricultural practices carried out along wetland ecosystems involve the use of excessive agrochemicals during crop production which later contribute to wetland pollution through nutrients and heavy metals inflows. This study aimed at assessing the effects of catchment land use on water quality parameters in Maragua and Mathioya river basins in Murang’a County. Water samples were collected using the Grab technique, packed in plastic containers, kept in cool boxes, and transported to the research laboratory for analysis. Salinity, turbidity, total dissolved solids (TDS), electrical conductivity (EC) and PH were analyzed across the sampling levels using hand-held portable pH 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. TDS values differed across sampling levels: Down-Stream (mean = 135.43 ± 1.46 mg/L, range: 132.60 to 139.30 mg/L), Mid-Stream (mean = 138.63 ± 6.60 mg/L, range: 122.70 to 150.60 mg/L), and Up-Stream (mean = 47.18 ± 10.43 mg/L, range: 26.70 to 65.40 mg/L). EC showed significant variation across sampling levels: Down-Stream (mean = 0.20 ± 0.00 mS/cm, range: 0.19 to 0.20 mS/cm), Mid-Stream (mean = 0.21 ± 0.01 mS/cm, range: 0.19 to 0.23 mS/cm), and Up-Stream (mean = 0.07 ± 0.02 mS/cm, range: 0.04 to 0.10 mS/cm). The pH levels varied across the different sampling levels: Down-Stream (mean = 6.47 ± 0.03, range: 6.40 to 6.51), Mid-stream (mean = 6.31 ± 0.10, range: 6.01 to 6.45), and Up-Stream (mean = 6.00 ± 0.22, range: 5.50 to 6.48). Salinity levels varied significantly: Down-Stream (mean = 146.05 ± 1.81 mg/L, range: 141.40 to 150.20 mg/L), Mid-Stream (mean = 150.93 ± 6.15 mg/L, range: 135.00 to 161.60 mg/L), and Up-Stream (mean = 51.88 ± 11.52 mg/L, range: 28.90 to 71.70 mg/L) and Turbidity levels also varied: Down-Stream (mean = 170.50 ± 15.40 NTU, range: 128.30 to 194.60 NTU), Mid-Stream (mean = 173.53 ± 8.13 NTU, range: 158.40 to 190.90 NTU), and Up-Stream (mean = 137.10 ± 15.00 NTU, range: 108.20 to 177.50 NTU). Post-hoc analysis showed a significant difference in pH between Down-Stream and Up-Stream (mean difference = 0.465, p = .043). Significant differences noted in EC between Down-Stream and Up-Stream (mean difference = 0.130, p < .001), and Mid-Stream and Up-Stream (mean difference = 0.139, p < .001). However, no significant difference was observed between Down-Stream and Mid-Stream. For TDS, significant differences were observed between Down-Stream and Up-Stream (mean difference = 88.250, p < .001), and Mid-Stream and Up-Stream (mean difference = 91.450, p < .001). No significant difference was observed between Down-Stream and Mid-stream. Significant differences in salinity were found between Down-Stream and Up-Stream (mean difference = 94.175, p < .001), and Mid-Stream and Up-Stream (mean difference = 99.050, p < .001). No significant difference was found between Down-Stream and Mid-stream. Variation in the analyzed 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.