Synchronization between terrestrial and aquatic primary productionLakes are closely coupled to their surrounding watersheds through shared climatic fluctuations and fluxes of water, nutrients, and organic carbon. This aquatic-terrestrial coupling may give rise to synchronization, i.e., the persistent relatedness of fluctuations in state variables between lakes and the terrestrial landscapes in which they are embedded. However, synchrony between ecosystems is not well understood and resolving when and why ecosystems fluctuate synchronously is necessary for understanding long-term dynamics under future environmental conditions (Wilkinson et al. 2020). We investigated the degree to which primary production in lakes is synchronized with primary production in the adjacent terrestrial landscape. Our findings suggest that hydrologic connectivity mediates the synchrony between terrestrial and aquatic primary production at inter-annual timescales (Walter et al. 2021). This work was funded by the National Science Foundation.
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Control Points on Coupled Nutrient Cycling in Hypereutrophic LakesLakes and reservoirs are carbon (C) and nutrient processing factories in the landscape, altered by both climate change and anthropogenic eutrophication. As such, there is an immediate need to identify the control points (i.e., the critical drivers that affect ecosystem dynamics over time and space) on C-cycling in lakes now, as it is vital for estimating regional and global C budgets and developing accurate models to forecast the biogeochemical response of lakes to eutrophication and climate change in the future. While there has been substantial progress in understanding the rate of C-cycling in oligotrophic, mesotrophic, and dystrophic lakes, we still lack a fundamental understanding of the control points on C-cycling across timescales in lakes, particularly in those lakes already under extreme nutrient enrichment. In partnership with the CFL Community Water Monitoring Network, we are investigating C-cycling rates in a suite of hypereutrophic shallow lakes in Dane County, Wisconsin to better understand the mechanisms driving the magnitude of pools and fluxes in these waterbodies. This work is being led by Jess Briggs and is funded by the National Science Foundation DEB as a CAREER award.
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Sources and Fates of Organic Matter in WaterbodiesA long-standing focus of our research has been quantifying the pools of terrestrial C in surface waters and understanding the dynamic flux of terrestrial material into lakes. Using stable isotopes in a comparative survey of north temperate lakes, we demonstrated that particulate and dissolved organic matter pools are dominated by terrestrial material, particularly in smaller ecosystems (Wilkinson et al. 2013). This terrestrial material is also assimilated into the food web, more so when aquatic resources such as phytoplankton are scarce (Wilkinson et al. 2013, 2014). Terrestrial C can also enter lakes as carbon dioxide where it is subsequently emitted to the atmosphere. Using high frequency measurements combined with whole-lake nutrient addition experiments, we demonstrated that even under eutrophic conditions lakes can act as vents of CO2 to the atmosphere due to influx from shallow groundwater (Wilkinson et al. 2016). Finally, accumulated organic C in the sediments of inland and coastal waters is another major pool of C in aquatic ecosystems. In a literature synthesis of organic C burial rates across aquatic ecosystems (freshwater to marine), we found that burial rates spanned four orders of magnitude and were poorly constrained for most ecosystems (Wilkinson et al. 2018). Given this paucity of information, we have investigated the contribution of terrestrial (salt marsh) carbon to sediment stocks in seagrass beds (Greiner et al. 2016, Oreska et al. 2018).
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