Horticultural land use effect on fish assemblages in Neotropical lowland streams, Buenos Aires, Argentina

Agriculture is one of the main factors associated with global biodiversity loss. The present study assesses the impact of horticultural land use on water quality and fish assemblage composition in lowland Pampean streams. Four samplings were conducted with seasonal frequency during 2018 and 2019 in three horticultural stream reaches (HSR) and three grassland reaches (GSR) with low anthropic intervention, two also located in a biosphere reserve area. Environmental parameters were determined, and water and sediment samples were taken for nutrient and pesticide analysis, respectively. Fish assemblages were sampled in two habitat types: open water (OW) and vegetated patches (VP). The concentration of soluble reactive phosphorus and the detection frequency and concentration of pesticides were significatively higher in HSR mainly attributed to the runoff events following application of fertilizers and pesticides to the surrounding crops. Specific richness was significantly higher in GSR for both OW and VP environments. Diversity and evenness in the VP were significantly higher in GSR, while abundance was significantly higher in HSR due to the dominance of the environmental pollution-tolerant taxa of the order Cyprinodontiformes. The multivariate analysis recorded a major contribution of the order Cyprinodontiformes in the HSR, while the GSR species of the order Characiformes, common in environments of low environmental impact, were better represented. Our study demonstrated water quality deterioration associated with horticultural land use resulting in a ruderal fish community. On-going horticulture expansion is expected to cause further deterioration within the region, unless managerial practices are implemented.