Terrestrial loads of dissolved organic matter drive inter-annual carbon flux in subtropical lakes during times of drought

Chih-Yu Chiu; John R Jones; James A Rusak; Hao-Chi Lin; Keisuke Nakayama; Timothy K Kratz; Wen-Cheng Liu; Sen-Lin Tang; Jeng-Wei Tsai

doi:10.1016/j.scitotenv.2020.137052

Terrestrial loads of dissolved organic matter drive inter-annual carbon flux in subtropical lakes during times of drought

Sci Total Environ. 2020 May 15:717:137052. doi: 10.1016/j.scitotenv.2020.137052. Epub 2020 Feb 4.

Authors

Chih-Yu Chiu¹, John R Jones², James A Rusak³, Hao-Chi Lin⁴, Keisuke Nakayama⁵, Timothy K Kratz⁶, Wen-Cheng Liu⁷, Sen-Lin Tang⁸, Jeng-Wei Tsai⁹

Affiliations

¹ Research Center for Biodiversity, Academia Sinica, 128 Academia Road, Section 2, Nankang, Taipei 11529, Taiwan. Electronic address: bochiu@sinica.edu.tw.
² School of Natural Resources, University of Missouri, 103 Anheuser-Busch Natural Resources Building, Columbia, MO 65211, USA. Electronic address: JonesJ@missouri.edu.
³ Dorset Environmental Science Centre, Ontario Ministry of the Environment, Conservation and Parks, 1026 Bellwood Acres Road, P.O. Box 39, Dorset, ON P0A 1E0, Canada; Department of Biology, Kingston, Queen's University, 116 Barrie Street, Kingston, ON K7L 3N6, Canada. Electronic address: jim.rusak@ontario.ca.
⁴ Research Center for Biodiversity, Academia Sinica, 128 Academia Road, Section 2, Nankang, Taipei 11529, Taiwan.
⁵ Department of Civil Engineering, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe, Hyogo 657-8501, Japan. Electronic address: nakayama@phoenix.kobe-u.ac.jp.
⁶ University of Wisconsin-Madison, Trout Lake Station | 3110 Trout Lake Station Dr. Boulder Junction, WI 54512, USA.
⁷ Department of Civil and Disaster Prevention Engineering, National United University, NO.2, Lien Da, Nan Shih Li, Miao-Li 36003, Taiwan. Electronic address: wcliu@nuu.edu.tw.
⁸ Research Center for Biodiversity, Academia Sinica, 128 Academia Road, Section 2, Nankang, Taipei 11529, Taiwan. Electronic address: sltang@gate.sinica.edu.tw.
⁹ Department of Biological Science and Technology, China Medical University, No.91, Hsueh-Shih Road, Taichung 40402, Taiwan. Electronic address: tsaijw@mail.cmu.edu.tw.

PMID: 32084680
DOI: 10.1016/j.scitotenv.2020.137052

Abstract

Lentic ecosystems are important agents of local and global carbon cycling, but their contribution varies along gradients of dissolved organic matter (DOM) and productivity. We investigated how contrasting summer and autumn precipitation can shape annual and inter-annual variation in ecosystem carbon (C) flux (gross primary production (GPP), ecosystem respiration (ER), and CO₂ efflux) in two subtropical lakes differing substantially in trophic state and water color. Instrumented buoys recorded time series of free-water DO, terrestrial DOM (tDOM), chlorophyll a, water temperature profiles, and meteorological measurements over five years (2009-2011 and 2014-2015). Reduced precipitation caused immediate and prolonged effects on C flux in both lakes. During the drought year (2014) GPP and ER declined by 60 to 80% and both lakes were either CO₂ sinks or neutral. In the subsequent wet year (2015), GPP and ER increased by 40 to 110%, and both lakes shifted to strong net CO₂ emitters. Higher ecosystem R resulted from larger GPP while higher tDOM contributed to a dramatic increase in dissolved inorganic carbon, which intensified CO₂ emission in both lakes. C flux was more responsive in the clear mesotrophic lake, declining by approximately 40% in the cumulative GPP and ER, and increasing by >400% in CO₂ efflux whereas changes in the oligotrophic colored lake were more modest (approximately 30% and 300% for metabolic declines and efflux increases, respectively). Temporal variation and magnitude of C flux were governed by tDOM-mediated changes in epilimnetic nutrient levels and hypolimnetic light availability. This study demonstrated terrestrial loads of DOM strongly influence the inter-annual response and sensitivity of ecosystem C flux to variation in inter-annual precipitation. Our findings have important implications for predicting the trend, magnitude, duration, and sensitivity of the response of C flux in subtropical lakes/reservoirs to future changes in precipitation patterns under altered climatic conditions.

Keywords: Carbon flux; Rainy season; Subtropical lake; Terrestrial DOM; Trophic status.