Aquatic plant composition and environmental relationships in grazed Northwest Patagonian wetlands, Argentina

Abstract

Aquatic macrophyte assemblages and environmental features were assessed in 30 wetlands from North- west Patagonia subjected to different intensity of grazing pressure. Species richness was surveyed in wetlands from three biozones of the Patagonia Ecoregion: Andean-Humid, Sub-Andean Sub-Humid and Extra-Andean Occidental. A total of 50 species of macrophytes were recorded, with the Cyperaceae, Jun- caceae, Poaceae and Ranunculaceae the best represented groups. Canonical Correspondence Analysis (CCA) reflected the distribution of species along a gradient of disturbance (CCA1: salinity and ammo- nia). There was also a correspondence among community composition and intensity of grazing pressure at isolated wetlands, with total species richness, richness of natives and aquatic plant coverage significantly decreasing towards most disturbed sites. Only the species Distichlis spicata, Xanthium spicatum and Eleocharis melomphala appeared as indicators of wetland deterioration associated with degraded sites, subjected to strong erosion processes which increase the natural soil salinity. The submersed Lilaeopsis macloviana was the most tolerant species being recorded over a wide range of environments and inten- sity of land uses. Variables related to wetland size and connectivity (CCA2: depth, length, elevation and dissolved oxygen) displayed higher explanatory power on community assemblages, and subsequently macrophyte life-forms were clearly distinguished across this gradient. Most of species recorded in this work were native, however the proportion of exotics reached 25% in areas with intermediate and high grazing intensity. Although we were not able to clearly separate natural from grazing effects this study provides a first look at natural and anthropogenic controls of macrophytes in Patagonian wetlands.