Effect of upper catchment management and water cover plants on quantity and quality of water in reservoirs and their implications on Livestock Water Productivity (LWP)

Abstract

Seasonal water fluctuations both in quality and quantity negatively affect livestock production and subsequently reduce livestock-water productivity (LWP) in rainfed pastoral production systems. The major contributing factors to this phenomenon are poor upper catchment and water resource management which result in contamination, sedimentation/silting, eutrophication due to nutrient enrichment, and excessive discharge of runoff into water reserviors. This study investigated the effect of upper catchment management (un-vegetated and vegetated catchment, un-vegetated and vegetated gullies); and water cover plants on water quality and quantity in surface water reservoirs, and their impacts on livestock water productivity (LWP) in rainfed pastoral production systems of Uganda. Water quality and quantity in sixteen reserviors were monitored on a monthly basis in Nakasongola and Kiruhura districts for a period of one year covering two dry and two rain seasons. Sedimentation studies showed that about 250 m3 of silt from un-vegetated catchment entered a reservoir, reducing the storage capacity by 18% in a period of one year. The silt that entered the reservoir was responsible for degradedation of about 47 m3 of water. Un-vegetated upper catchments therefore had detrimental impacts on water reservoirs. Total coliform (TC), feacal coliform (FC), ammonium-nitrogen (NH4–N) and total phosphorus (TP) levels were significantly higher (p < 0.001) in reservoirs receiving water from open gullies while reservoirs with un-vegetated catchments had significantly higher concentrations (p < 0.001) of nitrite-nitrogen (NO2–N), nitrate-nitrogen (NO3–N), total nitrogen (TN), total dissolved solids (TDS), total suspended solids (TSS) and turbidity. TC and FC concentrations were significantly high (p < 0.001 and p < 0.05, respectively) in the dry season, with highest concentrations recorded in reservoirs receiving water from open gullies. NO2–N and NO3–N were significantly high (p < 0.001) in the rain season. There were significant interactions between season and treatment effects on the concentration of NO2–N, NO3–N, TSS and turbidity (p < 0.001). Reservoirs receiving water from un-vegetated catchments had high NO2–N, TSS and turbidity in the rain season while those with vegetated gullies had high NO3–N in the rain season. Four plant species (Pistia, Azolla, Lemna and Nymphaea spp.) were identified as the common plant species covering water reserviors in the study area. The results showed that reservoirs covered by Lemna sp had significantly lower (p < 0.001) TC, FC, NO2–N, NO3–N, TN, TSS, and turbidity than reservoirs covered by other cover plants in the study, indicating its potential application in water quality improvement for livestock production systems. Nymphaea spp had significantly higher (p < 0.001) concentrations of nitrite, total nitrogen, TDS, TSS and turbidity while Azolla spp had significantly high (p < 0.001) TC concentrations compared to other water cover plants. This indicated that Nymphaea spp is an undesirable water cover plants species and hence should be eliminated. Improvement of upper catchment and water resource management greatly increased livestock water productivity (LWP) by 353%, 518% and 280% in the settled, semi-settled and non-settled pastoral communities. In addition, un-vegetated catchments and gullies were shown to have detrimental impacts on the reservoir water quality. Therefore, a great potential exists for improving livestock water productivity in the pastoral communities of Uganda through use of vegetated catchments and gullies. Although the amount of rainfall in the pastoral communities of Uganda greatly contributes to the quantity of water available in reservoirs to sustain livestock and human needs through dry seasons, other factors such as evaporation, sedimentation and degradation of water quality may critically reduce the availability of water in pastoral communities. Therefore, increasing water supply through creation of more surface water resources without proper upper catchment and water management practices would only provide a temporal solution to problems of livestock water scarcity in dry seasons within the rangeland pastoral communities of Uganda due to high evaporation and reservoir sedimentation rates experienced in these communities.