Marine and Freshwater Research Marine and Freshwater Research Society
Advances in the aquatic sciences

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Nitrogen nutrients in a subtropical river: Temporal variation and analysis at different spatial scales

Rodrigo Moncayo-Estrada , Carlos Escalera-Gallardo , Miriam Arroyo-Damián , Oswaldo Campos-Campos , José Silva-García

Abstract

We provide a framework for evaluating the spatiotemporal variation of nitrate and ammonium and their relationships with environmental and anthropogenic variables at different scales. Bimonthly samples were collected from 28 sites in Duero River, Mexico, from May to December of 2013. The river flow changed and lost connectivity during the dry season because more water was diverted for irrigation. Four sites had the highest nitrate and ammonium values (7.6 and 22.1 mg L-1, respectively), which were related to direct wastewater discharge. The remaining 24 sites were analyzed with a multivariate approach. Using hierarchical cluster analysis, seasonal trends were identified with two groupings during July and five in December. Sites were grouped into those with constant discharge and nitrates influenced by springs and those with poor water quality (high concentrations of ammonium). Non-metric multidimensional scaling simultaneously revealed the variation in time and space, organized sites into an environmental ammonium gradient and differentiated between seasons according to the nitrate level. Regression tree analysis established a relationship between nutrients and independent variables. At the landscape level, the agricultural area influenced nitrate (75%) and urban area ammonium (45%), and at the basin level, the road density influenced both (10.68 km 25 km-2)

MF16344  Accepted 17 January 2017

© CSIRO 2017