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Science of The Total Environment
Volume 817, 2022, 152784

Forest cover controls the nitrogen and carbon stable isotopes of rivers

Fausto Machado-Silvaa,b, Vinicius Neres-Limaa,c, Andrea Franco Oliveirad, Timothy Peter Moultona,c

Programa de Pós-Graduação em Ecologia e Evolução, IBRAG, Universidade do Estado do Rio de Janeiro, 20550-900 Rio de Janeiro, Brazil.

Abstract

Deforestation affects the ecological integrity of rivers and streams, threatening biodiversity and ecosystem services worldwide. However, few studies have strictly analyzed the effect of the functional responses of tropical streams to changes in forest cover since deforested basins are usually also influenced by confounding anthropogenic inputs. Here we address tropical streams and test whether the stable isotopic ratios of nitrogen (N, δ15N) and carbon (C, δ13C) and the ratio of C:N of ecosystem components vary along a forest cover gradient. We also assess the ecological integrity of streams by in situ measurements using physical features commonly used in stream quality assessments. The results showed that the δ15N of most aquatic components, δ13C of particulate matter and omnivorous fish, and C:N of particulate matter and algae vary significantly with forest cover, indicating the role of terrestrial vegetation in regulating stream biogeochemistry. The dual stable isotope analysis satisfactorily indicated the changes in terrestrial-aquatic connections regarding both N and C cycles, thus showing the role of algae and particulate matter in influencing stream fauna through food web transfers. Our results support the use of stable isotopes to monitor watershed deforestation and highlight the need for reassessment of the effects of anthropogenic inputs on δ15N increase in globally distributed inland waters since the loss of forest is a significant cause in itself.

Keywords: Riparian vegetation, Deforestation, Aquatic food webs, N cycle, Land coverLand use.

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