Transition of carbon-nitrogen coupling under different anthropogenic disturbances in subtropical small mountainous rivers

Li-Chin Lee; Gabriele Weigelhofer; Thomas Hein; Shin-Chien Chan; Ying-San Liou; Chien-Sen Liao; Fuh-Kwo Shiah; Yu-Lin Yu; Tsung-Yu Lee; Jr-Chuan Huang

doi:10.1016/j.scitotenv.2023.162017

Transition of carbon-nitrogen coupling under different anthropogenic disturbances in subtropical small mountainous rivers

Sci Total Environ. 2023 Apr 20:870:162017. doi: 10.1016/j.scitotenv.2023.162017. Epub 2023 Feb 3.

Authors

Li-Chin Lee¹, Gabriele Weigelhofer², Thomas Hein³, Shin-Chien Chan⁴, Ying-San Liou⁵, Chien-Sen Liao⁶, Fuh-Kwo Shiah⁷, Yu-Lin Yu⁸, Tsung-Yu Lee⁹, Jr-Chuan Huang¹⁰

Affiliations

¹ Department of Geography, National Taiwan University, Taipei, Taiwan; Department of Water, Atmosphere and Environment, Institute of Hydrobiology and Aquatic Ecosystem Management, University of Natural Resources and Life Sciences, Vienna, Austria.
² Department of Water, Atmosphere and Environment, Institute of Hydrobiology and Aquatic Ecosystem Management, University of Natural Resources and Life Sciences, Vienna, Austria; WasserCluster Lunz, Lunz am See, Austria.
³ Department of Water, Atmosphere and Environment, Institute of Hydrobiology and Aquatic Ecosystem Management, University of Natural Resources and Life Sciences, Vienna, Austria; WasserCluster Lunz, Lunz am See, Austria; Christian Doppler Laboratory for Meta Ecosystem Dynamics in Riverine Landscapes, University of Natural Resources and Life Sciences, Vienna, Austria.
⁴ Department of Geography, National Changhua University of Education, Changhua, Taiwan.
⁵ Department of Natural Resources and Environmental Studies, National Dong Hwa University, Hualien, Taiwan.
⁶ Department of Biological Science and Technology, I-Shou University, Kaohsiung, Taiwan.
⁷ Research Center for Environmental Changes, Academia Sinica, Taipei, Taiwan.
⁸ Department of Geography, National Taiwan University, Taipei, Taiwan.
⁹ Department of Geography, National Taiwan Normal University, Taipei, Taiwan.
¹⁰ Department of Geography, National Taiwan University, Taipei, Taiwan. Electronic address: riverhuang@ntu.edu.tw.

PMID: 36739020
DOI: 10.1016/j.scitotenv.2023.162017

Abstract

The commonly observed inverse relationship between dissolved organic carbon (DOC) and nitrate (NO₃^-) concentrations in aquatic systems can be explained by stoichiometric and thermodynamic principles regulating microbial assimilation and dissimilation processes. However, the interactive effects of human activities and dissolved oxygen (DO) on the DOC and DIN (dissolved inorganic nitrogen, mainly composed of NO₃^--N and NH₄⁺-N) relations are not well identified, particularly in subtropical small mountainous rivers (SMRs). Here, we investigated the exports and relations of DOC-DIN in 42 Taiwan SMRs under different anthropogenic disturbances. Results showed that the island-wide mean concentrations of the three solutes in streams are generally low, yet the abundant rainfall and persistent supply contrarily lead to disproportional high DOC and DIN yields. The inverse DOC-NO₃^--N relation does not appear under well‑oxygenated conditions, regardless of low or high human disturbance. However, a significant inverse relationship between DOC-NO₃^--N would emerge in highly-disturbed watersheds under low-oxygenated conditions (mean annual DO <6.5 mg L^-1), where excess N accumulates as NH₄⁺-N rather than NO₃^--N. The controlling mechanism of DOC-DIN relations would shift from energetic constraints to redox constraints in low-oxygenated conditions. Although riverine concentrations of DOC, NO₃^--N, and NH₄⁺-N could be elevated by human activities, the transition of DOC-DIN relation pattern is directly linked to DO availability. Understanding the mechanism that drives CN coupling is critical for assessing the ecosystem function in the delivery and retention of DOC and DIN in aquatic ecosystems.

Keywords: Dissolved inorganic nitrogen (DIN); Dissolved organic carbon (DOC); Ecological stoichiometry; Small mountainous rivers (SMRs); Taiwan; Thermodynamic constraint.