Dynamic modeling of organic carbon fates in lake ecosystems

• Published in: Ecological Modelling
• Main Authors: McCullough, Ian M., Dugan, Hilary A., Farrell, Kaitlin J., Morales-Williams, Ana M., Ouyang, Zutao, Roberts, Derek C., Scordo, Facundo, Bartlett, Sarah L., Burke, Samantha M., Doubek, Jonathan P., Krivak-Tetley, Flora E., Skaff, Nicholas K., Summers, Jamie C., Weathers, Kathleen C., Hanson, Paul C.
• Other Authors: Biological Sciences
• Format: Text
• Language: English
• Published: 2018
• Subjects: Carbon cycle; Mass balance; Dissolved organic carbon; Particulate organic carbon; LTER; GLEON; Arctic
• Online Access: http://hdl.handle.net/10919/93392; https://doi.org/10.1016/j.ecolmodel.2018.08.009

Lakes are active processors of organic carbon (OC) and play important roles in landscape and global carbon cycling. Allochthonous OC loads from the landscape, along with autochthonous OC loads from primary production, are mineralized in lakes, buried in lake sediments, and exported via surface or groundwater outflows. Although these processes provide a basis for a conceptual understanding of lake OC budgets, few studies have integrated these fluxes under a dynamic modeling framework to examine their interactions and relative magnitudes. We developed a simple, dynamic mass balance model for OC, and applied the model to a set of five lakes. We examined the relative magnitudes of OC fluxes and found that long-term (> 10 year) lake OC dynamics were predominantly driven by allochthonous loads in four of the five lakes, underscoring the importance of terrestrially-derived OC in northern lake ecosystems. Our model highlighted seasonal patterns in lake OC budgets, with increasing water temperatures and lake productivity throughout the growing season corresponding to a transition from burial- to respiration-dominated OC fates. Ratios of respiration to burial, however, were also mediated by the source (autochthonous vs. allochthonous) of total OC loads. Autochthonous OC is more readily respired and may therefore proportionally reduce burial under a warming climate, but allochthonous OC may increase burial due to changes in precipitation. The ratios of autochthonous to allochthonous inputs and respiration to burial demonstrate the importance of dynamic models for examining both the seasonal and inter-annual roles of lakes in landscape and global carbon cycling, particularly in a global change context. Finally, we highlighted critical data needs, which include surface water DOC observations in paired tributary and lake systems, measurements of OC burial rates, groundwater input volume and DOC, and budgets of particulate OC. US National Science Foundation's MacroSystems Biology Program [EF1137353, EF1137327]; NSF Long-Term Ecological Research program (North Temperate Lakes) [DEB-1440297] This project was a product of the Global Lake Ecological Observatory Network (GLEON) Fellowship program supported by the US National Science Foundation's MacroSystems Biology Program (Awards #EF1137353 and EF1137327). Logistical support was provided by the University of Wisconsin-Madison Center for Limnology, the Cary Institute of Ecosystem Studies, the University of Wisconsin Trout Lake Station, the Lake Sunapee Protective Association, and Grace Hong. Limnological data providers included the NSF Long-Term Ecological Research program (North Temperate Lakes DEB-1440297 and Arctic LTER), the Swedish Meteorological and Hydrological Institute, the Swedish University of Agricultural Sciences and the Canadian Dorset Environmental Science Centre. Additional details on data sources were included online in the appendix (Supplementary material). IMM, HAD, KJF, AMM, ZO, DR, FS and PCH acquired data, developed the model, and performed data analyses. All authors participated in conceiving and developing the project and writing the paper. We thank two reviewers for constructive comments on a draft of this manuscript. Analysis scripts and public data (LTER lakes and Lake Vanern) can be freely downloaded here: https://github.com/GLEON/SOS.