Abstract
The present study reported the effect of natural and anthropic environmental variables on the fish assemblages in the pampean streams, in the coastal strip along the Río de la Plata, Buenos Aires province, Argentina. Five streams were sampled at 12 sites surrounded by land devoted to different uses. A correspondence analysis sorted the streams into two groups: a less impacted group formed by sites surrounded by livestock- raising pastures and a more impacted one passing through urban sites and including a stream adjacent to a modest rural urbanization with a dairy in the stream's basin. The nutrient concentrations were significantly higher in the more impacted group; with species richness, diversity, abundance, and biomass being significantly lower. A canonical-correspondence analysis linked the more impacted sites to high concentrations of soluble reactive phosphorus and impoverished fish assemblages, composed of species tolerant to environmental pollution. On the other hand, sites with higher oxygen concentrations and pH were related to richer assemblages pointing to good environmental conditions at the sites surrounded by livestock-raising pastures. The downstream sites on the less impacted streams contained fish assemblages in which the juvenile stages of species corresponding to the Río de la Plata were dominant.
Highlights
Water quality in streams is strongly dependent on the surrounding terrestrial environment (Wallace et al 1999, Pinto et al 2006)
The sites were sorted into two groups: the reaches surrounded by urban land use on the Rodriguez Stream (R1-R3), along with the Zapata Stream, bordered by a small rural urbanization and a dairy in the basin (Z2 & Z3), were grouped together, and will hereafter be termed the more impacted (MI); whereas the rest of the sites, located on streams surrounded by pasturing livestock (P1-P3, B1-B3, and JB), constituted the second group, which will hereafter be called the less impacted (LI)
Nutrient concentrations were an order of magnitude higher in the reaches associated with the MI group than those of the LI group, pointing to the effect on adjacent streams of contaminant loads from urban and land used by industry
Summary
Water quality in streams is strongly dependent on the surrounding terrestrial environment (Wallace et al 1999, Pinto et al 2006). The principal modifications include increased agriculture, horticulture, urban and industrial development. The effects of urbanization involve increased concentrations of nutrients, metals, and pesticides plus erratic hydrology, channelization, and bank destabilization (Paul & Meyer 2001, Allan 2004). Streams draining urban basins have often exhibited low richness and diversity of the fish species (Klein 1979, Helms et al 2009), low biomass, and the absence of pollution-sensitive species (Lenat & Crawford 1994, Oronato et al 2000). The number of invasive species was observed to increase (Boet et al 1999), whereas the biotic integrity was found to decrease in urban basins (Steedman 1988, Wang et al 1997, Yoder et al 1999)
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