Long Term Impact of Wastewater Irrigation on Soil and Crop Quality Parameters in Gaza Strip

Abstract

The use of recycled wastewater (RWW) for irrigation is increasingly considered as an effective solution of water resources scarcity. The present study was undertaken to assess the long term impacts of wastewater irrigation on soil and crop parameters. Analysis for soil was done from the BeitLahya Pilot Project (BLPP) area where wastewater effluent from BLWWTP was used for alfalfa irrigation since 2003. Starting from the surface to a 60 cm depth, 12 boreholes were driven over the BLPP area. Each bore hole was divided into two layers each of 30 cm thickness and 12 soil samples were collected from each layer. Three alfalfa samples were being analyzed in addition to two irrigated wastewater samples. Analysis was done for soil and wastewater key chemical and physical parameters (Ec, pH, Na, Ca, Mg, OM, P and K). Biological (Fecal and Tot. Coliform) and heavy metal (Cu, Pb, Zn) parameters for soil, alfalfa and wastewater samples were also analyzed. Results revealed that BLWWTP effluent is suitable to be used for irrigation as its quality match the local and international standards for wastewater irrigation except Na, Cl and Pb. Long term wastewater irrigation increased salt, organic matter and plant nutrients in both soil layers. Soil pH was not consistently affected. Even pH values were slightly decreasing with time for both soil layers it still within permissible range (6-8.5). By the time, soil exhibited permeability and infiltration problems when RWW used. Comparison of soil properties before and six years after RWW shows soil salinity EC, SAR, and Na increased by 570, 200 and 84% in both layers respectively. Average alfalfa FC level was 3000 CFU/100ml in the first year then it decreased while TC was higher than the usual range all the time (6000no/100ml). Lead was the dominant heavy metal in wastewater and alfalfa crop. Although Pb level was in the acceptable range for soil, it was noticed that Pb has higher levels in alfalfa compared with other metals all the time with irregular Pb increase noticed after Israeli aggression on Gaza as its level was 240% (7.2ppm) higher than before. Alfalfa yield increased as long as the period of wastewater irrigation increases. Alfalfa yield with wastewater irrigation was 240% higher than alfalfa yield by well water in the first year. Estimation of WW quantities that can be used for irrigation showed that nearly about 45Mm3/year is needed by the restricted cops over GS. Regular monitoring of site-specific water and soil and appropriate management are needed to mitigate the negative impacts of sodium and salts accumulations.