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Carbon dioxide and methane in the North American Great Lakes

OHSU-B-1546
ABSTRACT:

Recently, there has been considerable interest on the potential impacts of lakes, rivers and other inland waters on the global carbon \(C) budget. In the past, these inland waters were commonly unaccounted for, but it is now known that lakes are a substantial part of the global C cycle. The North American Great Lakes are the largest freshwater system on Earth, but C dynamics in these large lakes are currently understudied. For example, it is not known whether the Great Lakes are a source for atmospheric C like smaller lakes, or a sink for C like in ocean systems. This is particularly important to study as atmospheric greenhouse gas concentrations increase and temperatures on Earth warm, because aquatic ecosystems may experience undocumented feedbacks, which have the potential to alter the Great Lakes C cycle.

Here, I present the results of two modern-day studies of the C cycle of the North American Great Lakes. In chapter one, I present the results of a 13-month study of methane (CH4) emissions from Lake Erie. I measured CH4 surface fluxes throughout the lake once every season and calculated a weighted area flux to estimate annual emissions. I found that the largest CH4 emissions were in the western basin. The highest rates co-occur with the highest rates of nutrient loading and algae blooms in Lake Erie. The annual lake-wide estimate indicated that CH4 emissions are driven by late spring and summer fluxes. Winter emissions were similar between the lake basins, indicating minimal emissions from natural gas wells and pipelines, in contrast to previous work. This work indicates Lake Erie is a CH4 emissions source almost all year round
and is a possible positive feedback to increasing precipitation.

In chapter two, I present the results of a study of carbon dioxide (CO2) emissions from Lake Superior, Lake Michigan, and Lake Erie. During the summer of 2016, pH, alkalinity, and stable isotopic ratios of 13C dissolved inorganic carbon (δ13C-DIC) (in Lake Erie only) were measured in surface and bottom water. I found that surface water CO2 emissions of the lakes were relatively small negative fluxes or near equilibrium with the atmosphere. Our data indicated that higher DIC concentrations have more depleted δ13C-DIC signatures in bottom waters in Lake Erie indicating that CH4 is a substrate for respiration. These results indicate that as CO2 concentrations increase in the atmosphere, the Great Lakes may be vulnerable to acidification, which may affect native and invasive species health in the Great Lakes in unpredictable ways.

Overall, these studies indicate that the North American Great Lakes have a C cycle that is vulnerable to anthropogenic perturbations such as climate warming, increasing precipitation, and increasing atmospheric CO2 concentrations. Since the Great Lakes are the most intensively utilized freshwater systems on Earth for both water and food resources, it is important to understand the C cycle in this system in the face of forthcoming changes that could affect these resources.

LENGTH: 69 pages
Brochure

Anticipated Impacts of Climate Change on 21st Century Maumee River Discharge and Nutrient Loads

OHSU-RS-1562
ABSTRACT:

Climate change holds great potential to affect the Lake Erie ecosystem by altering the timing and magnitude of precipitation driven river discharge and nutrient runoff in its highly agricultural watershed. Using the SWAT hydrologic model and an ensemble of global climate models, we predicted Maumee River (Ohio) discharge during the 21st century under two Intergovernmental Panel on Climate Change (IPCC) greenhouse gas emissions scenarios: RCP4.5 (mid-range, moderate reductions) and RCP8.5 (high, “business as usual”). Annual discharge was projected to increase under both scenarios, both in the near-century (RCP4.5 = 6.5%; RCP8.5 = 2.0%) and late-century (RCP4.5 = 9.2%; RCP8.5 = 15.9%), owing to increased precipitation and reduced plant stomatal conductance. Holding fertilizer application rates at baseline levels, we found that reduced winter surface runoff and increased plant phosphorus (P) uptake led to a respective decrease in annual total P (TP) runoff in the near-century (RCP4.5 = − 4.3%; RCP8.5 = − 6.6%) and by the late-century (RCP4.5 = − 14.6%; RCP8.5 = − 7.8%). Likewise, soluble reactive P (SRP) runoff was predicted to decrease under both scenarios in the near-century (RCP4.5 = − 0.5%; RCP8.5 = − 3.5%) and by the late-century (RCP4.5 = − 11.8%; RCP8.5 = − 8.6%). By contrast, when fertilizer application was modeled to increase at the same rate as plant P uptake, TP loading increased 4.0% (0.9%) in the near-century and 9.9% (24.6%) by the late-century and SRP loading increased 10.5% (6.1%) in the near-century and 26.7% (42.0%) by the late-century under RCP4.5 (RCP8.5). Our findings suggest that changes in agricultural practices (e.g., fertilization rates) will be key determinants of Maumee River discharge during the 21st century.

DOI: 10.1016/j.jglr.2016.08.008 VOLUME: 42 ISSUE: 6 LENGTH: 10 pages
Reprint

Quantifying Emissions of Methane Derived From Anaerobic Organic Matter Respiration and Natural Gas Extraction in Lake Erie

OHSU-RS-1550
ABSTRACT:

Despite a growing awareness of the importance of inland waters in regional and global carbon © cycles, particularly as sources of the greenhouse gases carbon dioxide (CO2) and methane (CH4), very little is known about C sources and fluxes in the Laurentian Great Lakes, Earth’s largest surface freshwater system. Here, we present a study of CH4 dynamics in Lake Erie, which has large spring algae blooms linked to fertilizer runoff and followed by hypoxia, as well as an extensive network of natural gas wells and pipelines in Canadian waters. Lake Erie is a positive source of CH4 to the atmosphere in late summer, even in shallow regions without water column hypoxia. Stable isotopic measurements indicate that both biogenic and thermogenic CH4 contribute to emissions from Lake Erie. We estimate that Lake Erie emits 1.360.6 3 105 kg CH4-C d21 in late summer, with approximately 30% of CH4 derived from natural gas infrastructure. Additional work is needed to determine the spatial and temporal dynamics of CH4 emissions from Lake Erie and to confirm estimates of source contribution. Studies of the C cycle in large lakes are not as straightforward as those in smaller lakes, as, in addition to O2 availability, subsurface currents and high winds may exert significant control over dissolved CH4 patterns. If climate warming and increasing precipitation intensity lead to increased algal biomass and/or greater extent and duration of hypoxia, this may increase emissions of CH4 from Lake Erie in a positive feedback to climate change.

DOI: 10.1002/lno.10273 VOLUME: 61 ISSUE: 1 LENGTH: 10 pages
Reprint

Ice Cover Extent Drives Phytoplankton and Bacterial Community Structure in a Large North-temperate Lake: Implications For a Warming Climate

OHSU-RS-1567
ABSTRACT:

Mid-winter limnological surveys of Lake Erie captured extremes in ice extent ranging from expansive ice cover in 2010 and 2011 to nearly ice-free waters in 2012. Consistent with a warming climate, ice cover on the Great Lakes is in decline, thus the ice-free condition encountered may foreshadow the lakes future winter state. Here, we show that pronounced changes in annual ice cover are accompanied by equally important shifts in phytoplankton and bacterial community structure. Expansive ice cover supported phytoplankton blooms of filamentous diatoms. By comparison, ice free conditions promoted the growth of smaller sized cells that attained lower total biomass. We propose that isothermal mixing and elevated turbidity in the absence of ice cover resulted in light limitation of the phytoplankton during winter. Additional insights into microbial community dynamics were gleaned from short 16S rRNA tag (Itag) Illumina sequencing. UniFrac analysis of Itag sequences showed clear separation of microbial communities related to presence or absence of ice cover. Whereas the ecological implications of the changing bacterial community are unclear at this time, it is likely that the observed shift from a phytoplankton community dominated by filamentous diatoms to smaller cells will have far reaching ecosystem effects including food web disruptions.

DOI: 10.1111/1462-2920.12819 VOLUME: 18 ISSUE: 6 LENGTH: 15 pages
Reprint

Why We Don’t Believe Science: A Perspective From Decision Psychology

OHSU-CAST-1568

In a perfect world, people are objective when they perceive risks and make decisions in climate and other domains. But psychological research suggests that this is not always how the human mind works.

DURATION: ~ 1 hr, 3 mins
Broadcast, Podcast, Webinar

OSU F.T. Stone Laboratory's Climate Expedition

OHSU-EP-1510

Activity sheet for learning how climate is measured and how climate changes affect our environment.

LENGTH: 1 page
Education / Curriculum Publication

Climate Change and Harmful Algal Blooms in Maumee Bay Webinar

OHSU-CAST-1527

This webinar covers the potential for future algal blooms in Lake Erie’s western basin.

ABSTRACT:

Harmful algal blooms (HABs) are a global problem and have reemerged as a concern in Lake Erie during the last decade. While some have hypothesized HABs in Lake Erie will become more frequent and larger, there are few studies linking predicted climate and watershed models to examine this issue. This talk will describe the methods and results of an ongoing project that links climate models, watershed models and HABs models to predict the frequency and magnitude of HABs through 2099.
This webinar will describe:

Predicted climate for the Maumee Basin through 2099
How climate change is likely to affect river discharge and harmful algal blooms in western Lake Erie
Modeling tools that can help people understand and manage the impacts of extreme weather events and climate change

DURATION: ~ 1 hr, 4 mins
Broadcast, Podcast, Webinar

Climate Change and Harmful Algal Blooms in Lake Erie Webinar

OHSU-CAST-1509

This 2013 climate webinar provides information about historical climate and potential future impacts of climate change in the Lake Erie basin.

ABSTRACT:

Harmful algal blooms continue to be a problem for the Lake Erie ecosystem and lakeshore communities, and predicted climate change impacts like increased heavy precipitation and higher temperatures have the potential to worsen these problems in the future. Focusing on Lake Erie, this webinar will provide information about historical climate and potential future impacts of climate change in the Lake Erie basin; how climate change could impact Lake Erie nutrient levels that drive harmful algal blooms; the potential effects of reduced lake ice and higher temperatures on algal blooms’ length and size. Speakers: Dr. Rick Stumpf of NOAA and Molly Woloszyn of Midwestern Regional Climate Center

Broadcast, Podcast, Webinar
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