Isotopic biomonitoring of N pollution in rivers embedded in complex human landscapes

Variation in the delta N-15 of epilithon within and between rivers reflected localised and diffuse N inputs from inorganic and organic sources. Negative epilithon delta N-15 values (<0 parts per thousand) indicated inorganic pollution from agriculture. Values between 4 parts per thousand and 8 parts per thousand and those above 8 parts per thousand respectively indicated moderate organic pollution from urban areas, and high organic pollution, mostly from waste waters. The diversity and abundance of snails decreased with increasing water pollution. While their isotopic variations reflected between-river differences, they failed to indicate within-river variations in anthropogenic N inputs, since the proportion of epilithon in their diet varied along the rivers. Concluding, epilithon was a reliable indicator of anthropogenic N sources across a wide range of nutrient concentrations and anthropogenic inputs, and the proposed approach allowed us to determine the nature of nitrogen pollutants, their sources, location and dispersion along rivers embedded in complex human landscapes. (C) 2019 Elsevier B.V. All rights reserved.