Periphyton structure and stoichiometry along a gradient of urban land use in Sub-Antarctic streams from Tierra del Fuego, Argentina

Abstract

We analyzed periphyton structure, elemental composition: carbon (C), nitrogen (N) and phosphorus (P), and algal composition along an urban gradient in three water courses of Ushuaia City. We hypothesize that periphyton stoichiometric ratios (C:N, C:P and N:P) decrease with the increase of urban land use. Also, community structure is affected by urban land use; sites with major surrounding urban and higher nutrient load host larger biomass and different algae composition compared to more pristine sites. P content and mass fractions of periphyton increased along the urban gradient as well as dissolved P in the water. Periphyton molar ratios N:P and C:P showed a negative lineal relationship with the gradient of urban land use. In general, periphyton was dominated by diatoms although Chlorophyta biovolume, mainly composed of filamentous algae, increased significantly in sites with 70% of urban land use. Our data suggest that there is no homeostatic balance in the periphyton community in Sub-Antarctic streams; we detected more P in periphyton in urban sites and the community became thus less heterotrophic. This study helps to better understand the dynamics of nutrients and its influence over a sessile community in sub-Antarctic lotic ecosystems impacted by urbanization.