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Research article2023Peer reviewedOpen access

The fate of nitrogen in the Zarin-Gol River receiving trout farm effluent

Ghojoghi, Altin; Ghorbani, Rasoul; Patimar, Rahman; Salmanmahiny, Abdolrassoul; Naddafi, Rahmat; Fazel, Abdolazim; Jardine, Timothy D.


This study investigated the Zarrin-Gol River ecosystem in Iran to trace organic matter in the food web and evaluate the impact of aquaculture farm effluent using stable isotopes of nitrogen (delta 15N) and carbon (delta 13C). Using a previously-developed model (Islam 2005), we estimated that a trout farm in the vicinity released 1.4 tons of nitrogen into the river. This was comparable to an estimated total nutrient load of 2.1 tons of nitrogen for the six-month fish-rearing period based on a web-based constituent load estimator (LOADEST). A model estimate of river nitrogen concentration at the time of minimum river discharge (100 L/s) was 2.74 mg/L. Despite relatively high nitrogen loading from the farm, isotope data showed typical food web structure. Several biological groups had elevated delta 13C or delta 15N values, but there was limited evidence for the entry of organic matter from the trout farm into the food web, with sites above and below trout farms having inconsistent patterns in 15N enrichment. By coupling nitrogen load modeling with stable isotope analysis we showed that stable isotopes might not be effective tracers of organic matter into food webs, depending on surrounding land use and other point sources of nutrients. The Zarrin-Gol River ecosystem, like other basins with high human population density, remains vulnerable to eutrophication in part due to trout farm effluent.

Published in

Scientific Reports
2023, Volume: 13, number: 1, article number: 21762

    UKÄ Subject classification

    Environmental Sciences

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