Macrophyte regional patterns, metrics assessment and ecological integrity of isolated ponds at Austral Patagonia (Argentina)

Abstract

Anthropogenic and natural changes are threatening pond ecological integrity in Patagonia and tools for bioassessment are required. Macrophytes are good candidates to determine the conservation status of ponds; nevertheless metric selection procedures should be founded on an adequate knowledge of plant ecological responses. We assessed the main environmental constraints driving variation in macrophyte assemblages, and trophic status at 29 ponds located at the continental and insular region Patagonia. We screened 20 potential macrophyte metrics as indicators of pond condition that included origin (exotic, endemic, native), lifeforms (perennial, annual/biannual), functional groups (submersed, emergent, floating-leaved, landforms), and community attributes. A set of 106 taxa were recorded, and richness per site (10.2 species) was unexpectedly high for a cold temperate area, reinforcing the value of isolated ponds as habitat for macrophytes in the Patagonian landscape. Most assemblages were dominated by natives, nevertheless exotics were present at 24 ponds and contributed with high cover (>45%) at 15% of them. Macrophyte assemblages were mainly determined by natural factors over anthropogenic drivers, with temperature, rainfall, conductivity and nutrients explaining most variation in patterns. However, pond eutrophication symptoms (high phosphorous contents and chlorophyll a) were associated with extensive cattle grazing and urbanization. Generalized linear models captured natural variables (temperature, alkalinity) as most powerful explaining richness measures. Nevertheless models also indicated that both richness of emergent and endemics were negatively affected by total phosphorous increases. Land cover factors: grasses/herbaceous, mallín and trees (%) in 100 m buffer around ponds appeared as additional ecological drivers of macrophyte patterns, particularly of submersed (>50%) and native richness (36%). Natural and anthropogenic gradients were overlapped, making it difficult to generalize our conclusions. Further studies are needed to test the performance of the macrophyte metrics selected here, which are a vital tool for the conservation of the most austral ponds in South America.