Nutrient export and population density relationships in a stream-lake basin from the Patagonian Andean Region

Abstract

Eutrophication is a key human-induced stressor in streams and often a consequence of intensified land use. We characterised how population density influences dissolved nutrients and its ratio in Patagonian Andean streams during the baseflow hydrological period. Research was conducted at stream Gutiérrez drainage basin (41°09′36.18″S 71°24′37.19″W) located in Nahuel Huapi National Park, Argentina. A fraction of this basin corresponds to the city of San Carlos de Bariloche, where households use on-site wastewater treatment systems (OWTS) not connected to the city’s main sewer system. Our results reflect a positive relationship between population density and export of nitrate–nitrogen and soluble reactive phosphorus. Nitrates leaching from OWTS into groundwater were incorporated into the stream ecosystem, but phosphorus seemed to be retained by the soils. The increase in N:P ratio along with population density suggests the presence of additional N sources beyond OWTS. Our results are relevant in N-limited ecosystems such as those from the Northwest-Patagonian region. As a consequence, these aquatic systems are liable to eutrophication by increased demographic pressure. Thus, it would be necessary to consider and evaluate the use of alternative OWTS, with higher denitrification capacity, to reduce release of nitrates into groundwater.