Fluvial transport of carbon along the river-to-ocean continuum and its potential impacts on a brackish water food web in the Iwaki River watershed, northern Japan

Tomoya Iwata, Takao Suzuki, Hiroyuki Togashi, Naoto Koiwa, Hideaki Shibata, Jotaro Urabe

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)

Abstract

Riverine transport of dissolved inorganic carbon (DIC) from land to the ocean is an important carbon flux that influences the carbon budget at the watershed scale. However, the dynamics of DIC in an entire river network has remained unknown, especially in mountainous Japanese watersheds. We examined the effects of watershed land use and geology on the transports of inorganic carbon as well as weathered silica (Si) and calcium (Ca) in the Iwaki River system where agricultural and residential areas have developed in the middle and lower parts of the watershed. The concentration and stable carbon isotope ratios (δ13C) of DIC showed the longitudinal increase of 13C-depleted inorganic carbon along the river. As a result, most streams and rivers were supersaturated in dissolved CO2 that will eventually be emitted to the atmosphere. The possible origin of 13C-depleted carbon is CO2 derived from the decomposition of organic matter in agricultural and urban landscapes, as well as from in-stream respiration. In addition, agricultural and urban areas, respectively, exported the large amount of dissolved Si and Ca to the rivers, suggesting that CO2 increased by respiration accelerates the chemical weathering of silicate and carbonate materials in soils, river sediments, and/or urban infrastructure. Furthermore, riverine bicarbonate flux is likely to enter shell carbonates of Corbicula japonica, an aragonitic bivalve, in the downstream brackish lake (Lake Jusan). These results revealed that the flux of DIC from the human-dominated watersheds is a key to understanding the carbon dynamics and food-web structure along the land-to-river-to-ocean continuum.

Original languageEnglish
Pages (from-to)703-716
Number of pages14
JournalEcological Research
Volume28
Issue number5
DOIs
Publication statusPublished - 2013 Sept

Keywords

  • Brackish water food web
  • Chemical weathering
  • Dissolved inorganic carbon
  • Land use
  • Stable and radioactive carbon isotopes

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