Effects of a suspended shade cloth cover on water quality of an agricultural reservoir for irrigation

Water availability and quality are two fundamental factors for agriculture in arid and semi-arid regions. This study evaluates the effects of a water-permeable, Suspended Shade Cloth Cover (SSCC), on the quality of water stored in an on-farm Agricultural Water Reservoir (AWR). Water quality (water temperature, electrical conductivity, chlorophyll-a concentration, dissolved oxygen concentration and water turbidity) and environmental (evaporation, rainfall, wind speed and solar radiation) parameters were measured over a 2-year period in a typical AWR located in south-eastern Spain. In the first year, the AWR remained uncovered and the behaviour was quasi-isothermal. In the second year, installing a SSCC induced a thermal gradient in the water that reached a maximum temperature difference of 12 °C during summer. The lack of turbulence under the cover and the reduction in photosynthesis (95% reduction of chlorophyll-a) reduced the concentration of dissolved oxygen to 1.5 mg L⁻¹, and turbidity from 40 NTU at installation to less than 1 NTU. The positive balance between rainfall and evaporation during the second year reduced the electrical conductivity of the water by 8.2%. The improvement in water quality associated with the installation of a SSCC increases the efficiency of drip irrigation systems by reducing the water filtering requirements, the likelihood of emitter clogging, and the risk of irrigation-induced salinity.