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Nitrogen and phosphorus dynamics in a large river estimated by an in situ Lagrangian tracking approach
Author(s) -
Kobayashi Yuta,
Iwata Tomoya
Publication year - 2017
Publication title -
freshwater biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.297
H-Index - 156
eISSN - 1365-2427
pISSN - 0046-5070
DOI - 10.1111/fwb.13044
Subject(s) - nutrient , environmental science , ecosystem , river ecosystem , hydrology (agriculture) , phosphorus , lake ecosystem , streams , benthic zone , abiotic component , ecology , biology , chemistry , geology , computer network , geotechnical engineering , organic chemistry , computer science
Abstract Streams and rivers transport and process land‐derived nutrients to coastal ecosystems, but few empirical studies quantify in‐stream processing of nutrients in large rivers due to methodological constraints. Here we suggest a novel Lagrangian method to estimate the net nutrient dynamics of a large river (sixth‐order Fuji River, discharge 20–48 m 3 /s) by concurrently tracking a specific water parcel along the river course and measuring the longitudinal profiles of inorganic nutrient (nitrogen and phosphorus) concentrations. Our method revealed exceedingly high net nutrient removal rates ( U net ) for both NH 4 and PO 4 . Moreover, net release of both NO 2 and NO 3 were observed, likely from benthic nitrification, indicating the considerable contribution of biotic and abiotic in‐stream processing to fluvial nutrient dynamics in a large river. In the Fuji River, net uptake velocity ( v f‐net ) and net uptake length ( S net ) were lower and longer, respectively, for NH 4 and PO 4 than would be expected from high net nutrient removal ( U net ), because of the high nutrient concentration and fast water velocity. The results suggest that in high‐relief mountainous areas, anthropogenic nutrients loaded in large rivers are influential on distant downstream ecosystems despite high nutrient processing rates in river ecosystems.