Eutrophic reservoir water suitability for irrigation in semi-arid region

Eutrophication is a common problem for the dams situated within an urban or agricultural catchment with a high source of untreated plant nutrients. This can negatively affect the hydro ecosystem, recreational and other uses of water. On the other hand, such eutrophic dams could also be a rich source of nutrients for agricultural use. Thinking irrigation as an alternative means of eutrophic reservoir water management, water suitability for irrigation was investigated for Roodeplaat Dam, South Africa using physicochemical parameters recorded (1981–2017) at five sampling stations. Irrigation suitability was evaluated in terms of nutrient content, salinity, soil infiltration, and toxicity problems to irrigated plants. Plant nutrients: NH4_N, NO3_NO2_N, PO4_P, are within the normal range. But K is above the normal range for irrigation use and can cause nitrogen deficiency. The salinity of 0.44 dS/m was found within the normal range with none restriction for irrigation use. Na toxicity in terms of SAR and Cl toxicity was none for both surface and sprinkler irrigated plants. The pH value of 8.4 was within the normal range (6.5–8.4). Generally, the quality of the reservoir water was categorized under C2S1 (medium salinity and low sodium hazard). Irrigation water can cause slight to moderate soil infiltration problem. Therefore, eutrophic reservoirs can be a potential source of readily available nutrients for irrigation and, hence irrigation use can be considered as one of the remedial measures to decrease nutrient accumulation in the reservoir. The existing water conveyance system can be used to transport water to agricultural fields.