Inland waters play an important role in global carbon and greenhouse gas cycling. Understanding controls on the rate of carbon burial in lentic systems is necessary for accurate quantification of the global carbon sink and predicting how it will respond to change. Recent work demonstrates that (1) ponds and small agricultural catchments may have an outsized role in lentic carbon burial at the global scale, (2) not all carbon burial pathways have been considered in quantifying the lentic carbon sink, and (3) anthropogenic and climate change pressures can lead to both positive and negative feedbacks in regard to rates of lentic carbon burial. These studies highlight recent advances – and remaining uncertainties – in the inland aquatic carbon sink. The goal of this session is to bring together scientists studying carbon burial across inland waters to present their latest findings. We welcome scientists who work across different systems and use various techniques to measure rates of carbon burial, identify sources of organic matter that is buried, quantify controls on C burial, and predict how the carbon sink of inland waters might change in response to anthropogenic pressures and global change.
Lead Organizer: Nicholas Ray, Cornell University (ner35@cornell.edu)
Co-organizers:
Meredith Holgerson, Cornell University (meredith.holgerson@cornell.edu)
Adam Heathcote, Science Museum of Minnesota (aheathcote@smm.org)
Presentations
05:00 PM
An updated estimate of the global lentic carbon sink (5560)
Primary Presenter: Nicholas Ray, Cornell University (ner35@cornell.edu)
Inland waters play an important role in global carbon cycling. They emit large amounts of greenhouse gases into the atmosphere and sequester and store significant quantities of carbon over centuries and millennia. Here, we present an updated estimate of the global lentic carbon sink. To do this, we compiled previously published rates of sediment carbon burial for lakes, reservoirs, ponds, and inland wetlands, including published global datasets and more recent studies. We then used a random forest regression approach to identify factors regulating carbon burial rates, considering properties unique to each waterbody or wetland such as area, maximum and mean depth, and age, as well as conditions in the region surrounding the waterbody, such as ecoregion, climate, and land use. Using identified relationships, we present an updated global estimate of carbon burial in lakes, reservoirs, and wetlands and report updated estimates of global lentic carbon burial on an annual basis. This approach simultaneously identifies regions that contribute substantially to the global lentic carbon sink and reduces uncertainty in global carbon burial estimates.
05:15 PM
Old burial, new emissions: carbon remobilization from exposed sediments in drying lakes (6188)
Primary Presenter: Rafael Marcé, Catalan Institute for Water Research (ICRA) (rmarce@icra.cat)
Many lakes in the World, particularly from endorheic basins in arid and semi-arid areas, are shrinking. This implies that the sedimentary carbon sink, sometimes the result of thousands of years of burial, may be prone to remobilization once the accumulated organic matter is exposed to atmospheric oxygen. To test this hypothesis, we have visited the endorheic lake Laguna de Gallocanta in Spain, and the largest vanishing lake on Earth, the Aral Sea in Kazakhstan. Applying a time for space substitution approach, we investigate if the organic carbon content of the sediments follows a chronosequence of drying, whether carbon emissions are actually happening in those sediments, and which organic carbon fractions are being remobilized. We put our results in the greater context of the potential implications of emissions from those emerged sediments for the global carbon cycle, and also discuss the potential role of recovering those lakes as a mitigation action against climate change compared to other customary mitigation alternatives.
05:30 PM
Acidic polysaccharides drive carbon export to sediments in a eutrophic Mediterranean reservoir (6466)
Primary Presenter: Andres Martinez-Garcia, University of Granada (andresmartinezgarcia2@gmail.com)
Reservoirs are crucial carbon sinks that rely on carbon sedimentation and sequestration exceeding CO2 and CH4 emissions. Acid polysaccharides (APs) released by phytoplankton and bacteria promote carbon sedimentation by coagulating into particulates that are exported towards sediments when ballasted by minerals or detritus. The Mediterranean region experiences seasonal fluctuations that influence biological productivity in reservoirs, such as Saharan dust deposition. Despite the importance of carbon sedimentation, there is limited research on the factors driving this process. This study identifies the main drivers behind the sedimentation of APs and particulate organic carbon (POC) in a eutrophic Mediterranean reservoir and infers the degree of synchrony between these drivers and carbon sedimentation. Results indicate a marked seasonality in APs and POC sedimentation, with the highest levels occurring in summer and fall associated with biological productivity. APs sedimentation ranged from 7.23 to 849.30 mg C m-2 d-1, and POC sedimentation ranged from 30.28 to 1327.70 mg C m-2 d-1. The POC and APs sedimentation are synchronized, while Saharan dust deposition and chlorophyll-a promote POC sedimentation with a four-week time lag. APs sedimentation is synchronized with cyanobacteria abundance, divalent cations with a two-week lag, and prokaryotic abundance with a four-week time lag. These findings highlight the importance of acidic polysaccharides in promoting carbon export to sediments and the complex interplay of biotic and chemical factors.
05:45 PM
Spatial and temporal changes in organic carbon sources to Great Lakes sediments measured by bulk elements, isotopes, and lignin-phenol biomarkers (5244)
Primary Presenter: Kathryn Schreiner, University of Minnesota Duluth (kschrein@d.umn.edu)
Lacustrine systems contain a small fraction of the world’s water but collectively account for nearly half of the world’s annual total organic carbon (OC) burial. The Laurentian Great Lakes (LGLs) together hold nearly 20% of the Earth’s fresh water and contain ecosystems which are vital to surrounding communities. Despite this, the fate, chemistry, and sources of OC to LGL sediments is poorly understood. In order to address this, we have embarked on a 5-year study to characterize the chemical composition and sources of OC spatially and temporally in all five of the LGLs. Here we will present the results from two LGLs: Lakes Superior (sampled in summer 2021) and Huron (sampled in summer 2022). Surface sediments were collected at 31 sites in each lake and analyzed for bulk elemental composition, stable carbon and nitrogen isotopes, and lignin-phenol biomarkers. Three cores were also taken in Lake Superior to analyze temporal trends in OC source and burial. Interestingly, sediments at some offshore sites in Lake Superior were found to contain higher concentrations of both total OC and total lignin-phenols than nearshore sites, indicating terrestrial carbon delivered by coastal or riverine sources may not be a significant source of OC to the lake. Lignin-phenol ratios of OC in offshore sediments indicate that airborne pollen is likely a major source of terrestrially-sourced OC at these sites, indicating that aeolian inputs of OC into lakes may be influential. Temporal trends show pollen has been a major source of terrestrial OC to Lake Superior sediments for hundreds of years.
06:00 PM
From clear to turbid and back again: linking eutrophication resilience to carbon cycling through lake ecosystem modelling (6295)
Primary Presenter: Mandy Velthuis, Radboud University (mandy.velthuis@ru.nl)
Freshwater lakes play a vital role in the global carbon cycle, acting as both a source of greenhouse gases (GHG) such as CO2 and CH4 as well as a carbon sink through burial processes in their sediments. While the role of lakes in the carbon cycle has received quite some scientific attention, little is known about the drivers behind the balance of carbon storage and GHG emissions in these ecosystems. Lakes exhibit resilience to pressures like eutrophication, and exceeding their resilience capacity will lead to a shift in ecosystem state. This is displayed, especially in shallow lakes, as a shift from a clear, plant-dominated state to a turbid phytoplankton-dominated state. In this work, we evaluate how lake resilience to eutrophication is linked to lake carbon cycling. To this end, we expanded the existing ecosystem model PCLake+ with carbon-related processes: GHG emissions and carbon burial. PCLake+ is an open source lake model that explicitly models ecological processes (biotic and abiotic interactions) within the general framework of resilience assessment. It has been used extensively in both research and water management. We hypothesized that GHG emissions are minimized, and carbon storage potential is maximized in a clear ecosystem state, whereas GHG emissions (in particular CH4) would be enhanced in a turbid ecosystem state. Through our model expansion we study net carbon storage and emission along a gradient of eutrophication, expanding the focus of water management from improvements on water quality towards inclusion of carbon storage potential.
06:15 PM
Changes in the carbon cycle of an urban lake after an anthropogenically-driven transition to meromixis (6703)
Primary Presenter: Elizabeth Swanner, Iowa State University (eswanner@iastate.edu)
Warming, eutrophication, and land use changes are all major drivers in increasing lake hypoxia, an important control on carbon cycling in lakes. Culturally meromictic lakes with permanently anoxic monimolimnia are an extreme response to such perturbations. Here we present results from water column and sediment core measurements at Brownie Lake (Minnesota, U.S.A.), which transitioned to meromixis due to basin disturbances in the 1910s, and enhanced stratification due to runoff of road deicing salts since the 1950s. Brownie Lake has some of the highest methane emissions reported for freshwaters with low C:N and depleted δ <sup>13</sup>C indicating an autochthonous source of particulate organic carbon. Iron is the dominant terminal electron acceptor in the monimolimnion due to the dearth of oxygen, sulfate, and nitrate resulting in ‘ferruginous’ conditions (i.e., abundant dissolved ferrous iron). A reaction-transport model based on data from the water and sediments shows a high efficiency of methanogenesis compared to other modes of organic carbon remineralization, indicating the importance of terminal electron acceptor availability in carbon dynamics of anoxic lakes. The average sediment organic carbon decreased after the onset of meromixis (from 26 wt% to 9 wt%). The average sediment iron increased (from 0.4 wt% to 2.60 wt%) after the onset of ferruginous conditions. Future results will include DNA sequencing and biomarker analysis to determine if there was a coeval shift in microbial community and carbon cycling in the lake during these transitions.
SS031B Old Carbon, New Ideas – Recent Advances in Understanding Lentic Carbon Burial
Description
Time: 5:00 PM
Date: 9/6/2023
Room: Sala Menorca B