Evaluation of the Microbiological Quality of Water in the Rice-Growing System of the Lis Valley, Portugal

Abstract

Society’s demand for the preservation of water resources has stimulated technological advances and improved agricultural management, to limit its negative impacts, favor socio-economic development and promote the conservation of natural resources. This study assessed the impact of a rice farming system in the Mediterranean area on the microbiological quality of water, representing the irrigation and cultivation conditions of the Lis Valley Irrigation District (LVID). Indicators used include the counting of total coliforms (TC), fecal coliforms (FC), fecal enterococci (FE) and ampicillin-resistant Enterobacteriaceae (Ampr), and a phenotypic characterization of antibiotic (AB) resistances. The results show that the water at the LVID inlets contained high microbiological contamination due to sources outside the perimeter. The rice paddy agroecosystem had a beneficial impact on the load of TC, FC and FE of the respective drainage water, with a decrease of two orders of magnitude between the values of these counts at the inlets and at the outlets of the rice fields. However, the relative frequency of Enterobacteriaceae Ampr increased in the rice paddy soil, possibly as a result of the favorable conditions provided by this wetland ecosystem for the transfer of AB resistance genes. The analysis of AB resistance patterns revealed high relative resistance percentages for both β-lactams and non-β-lactams in all samples. This study made it possible to assess the risks of microbiological contamination of irrigation water and the beneficial effect of the rice-growing system in controlling the applied indicators.