Impact of irrigation with fish-processing effluents on nitrification and ammonia-oxidizer abundances in Patagonian arid soils

This study aimed to evaluate the short-term effects of irrigation with diluted fish-processing effluents on soil pH, electrical conductivity, nitrification rate and abundance of ammonia oxidizers. To accomplish that, we constructed microcosms of soil from an undisturbed arid ecosystem of Patagonia, and irrigated them for 2 months with diluted effluents from a fish-processing factory or with water as control. In the initial soil sample, and along the experiment, we determined soil pH, electrical conductivity, and the concentration of inorganic nitrogen forms, which we used to calculate the net nitrification rate. We further estimated the abundances of ammonia-oxidizing archaea and bacteria in the initial soil sample and at the end of the experiment, by qPCR of amoA genes. Soil pH decreased and electrical conductivity increased in both irrigation treatments, although the effect was higher in effluent-irrigated microcosms. Soil nitrate + nitrite concentration, and thus the nitrification rate, was higher in effluent than in water-irrigated microcosms. The abundance of archaeal amoA genes was higher under effluent than water-irrigation, but that of bacterial amoA genes did not vary significantly between treatments. Neither ammonia-oxidizing archaea nor bacteria were influenced by the changes in soil pH and electrical conductivity induced by effluent irrigation.