DELTA LEAD SCIENTIST: Greenhouse Gas Emissions and Carbon Budgets

At the February meeting of the Delta Stewardship Council, Delta Lead Scientist Dr. Laurel Larsen continued profiling the work of the 2018 class of Delta Science Fellows and updated the Council on the activities of the Delta Science Program.

Dr. Larsen began by reminding the Council members of the presentation several months ago about the potential use of the Delta for deep carbon sequestration; that presentation referred to the transport of carbon dioxide via pipelines to the Delta, where it would then be injected deep into the bedrock.

But there is another way the Delta could potentially become a sink for carbon as wetlands, such as those in the Delta, can also remove carbon at the surface.  Dr. Larsen explained that plants take up carbon through photosynthesis and convert it into biomass; when those plants die and decay, some of the carbon is re-emitted to the atmosphere by microbes, but much of it can become incorporated into the soil, particularly if the soil is kept wetted and oxygen is scarce.  Organic carbon-rich soil created in this way is called peat.

Dr. Larsen noted that there is now a lot of interest in funding wetland restoration through a statewide or national carbon market in which a certain number of carbon credits would be assigned for a certain acreage and type of wetland that is restored.  However, figuring out how many carbon credits should be given requires a better understanding and more precise quantification of the rate Delta wetlands remove carbon from the atmosphere for long-term storage.

Matthew Bogard from the University of Washington made these types of measurements for a wetland in the Suisun Marsh using sensors that measure gaseous carbon dioxide transport and sensors that measure the transport of dissolved carbon away from their wetlands by flowing water.

In particular, Matthew’s team was interested in quantifying how much of the net carbon taken up by plants is lost from the wetland via this lateral transport by flowing water, a term that’s not typically quantified in wetland carbon balance studies and is poorly understood in general.  They ended up finding that 41% of the net carbon uptake by plants is lost laterally in this way, with the remaining 59% incorporated into the peat.

Now this 41% lateral loss might sound like inefficiency in using wetlands as engines for carbon sequestration, but Matthew’s results suggested that this actually isn’t the case.  

They found that 91% of this lateral loss is in the form of dissolved inorganic carbon, most of which is known to be transported directly to the ocean, where it remains stored for millennia without being released back to the atmosphere,” said Dr. Larsen.  “Right now, the ocean is taking up massive amounts of the excess carbon dioxide that we’re putting into the atmosphere.  So, thus this carbon may effectively be considered sequestered as well over the timescales that we’re interested in, which is a good thing for the climate.”

Hydrologic Export Is a Major Component of Coastal Wetland Carbon Budgets, authored by Matthew J. Bogard, Brian A. Bergamaschi, David E. Butman, Frank Anderson, Sara H. Knox, Lisamarie Windham-Myers

Tyler Anthony of UC Berkeley is working to understand the role of former wetlands that have been drained and used for agriculture in greenhouse gas cycles.  Dr. Larsen reminded that peat needs wet oxygen scarce conditions to form.  So when peat is drained and oxygen enters the soil, the organic matter contained within the soil becomes easy fuel for microbes, which convert the solid carbon to gaseous CO2 through their respiration, much like what happens in our own bodies.  In this way, the loss of organic material is the same process that causes soil subsidence and results in these lands in the Delta a large source of greenhouse gases.

One way to slow subsidence and carbon dioxide emissions is to return water to the fields during the winter when the land is not actively being used to grow crops.  However, she noted that this winter flooding could result in other microbial byproducts of respiration that do not require oxygen; those byproducts may include methane or nitrous oxide, which are even more potent greenhouse gases than carbon dioxide with a longer lifetime in the atmosphere.

A relevant question here is whether these practices can be managed differently to reduce these greenhouse gas emissions.  For example, if the application of fertilizers rich in nitrogen is contributing to nitrous oxide emissions during winter flooding, then perhaps the timing or the amount of fertilization could be changed to minimize those emissions.

Tyler and his team used sensors to directly measure emissions of methane and nitrous oxide during winter flooding have drained Delta peatlands,” she said.  “They found that nitrous oxide was not substantially impacted by fertilizer application, but rather by the flooding itself.  So they found that several weeks of flooding combined with warmer soil temperatures greater than about 50 degrees Fahrenheit contributed to the highest emissions, which does suggest that the timing and duration of this managed flooding could be strategically altered in order to reduce emissions.”

Dr. Larsen noted that both studies are important because as California moves towards a carbon-neutral future, it is important to properly account for the effects of agriculture or environmental management actions on the region’s greenhouse gas footprint.  By quantifying these effects, we can also modify practices such as agricultural flooding practices to make the agricultural parts of the landscape less of a carbon source.

Dr. Larsen noted that more studies such as Matthew Bogard’s are needed to synthesize knowledge of how different types of Delta wetlands contribute to carbon sequestration.  She also noted that one such synthesis is coming in the 2022 State of Bay-Delta Science Report, tentatively expected to be released in December.

Activities of the Delta Science Program

The 2022-2026 Delta Science Action Agenda

The public review period for the Science Action Agenda closed in late January; over a dozen comment letters were submitted, including one from the Delta Independent Science Board.  Many comments highlighted the need to better connect the prioritized science actions to relevant legislation, regulations, and existing efforts and suggested some minor revisions to the science actions themselves.  Other comments focused on the need to allude more specifically to water supply reliability-related science needs and better package the science actions into an overall science vision.

We’ve implemented many changes in response to these comments,” said Dr. Larsen.  “One example is a rewritten forward that highlights how all of the science actions fall into a theme of integration: integration across agencies and interest groups for the production of science, integration of our existing understanding of individual species or variables like water quality to understand how the estuary functions as a whole, and integration across different datasets, models and experiments.”

The revisions are nearly complete and with the final document being prepared.  The final Science Action Agenda is expected to be presented to the Council for endorsement at the April 2022 meeting.

Delta Science Fellows

As a reminder, the request for applications for Delta Science Fellows is still active.  The Delta Science Fellows includes master students through postdoctoral scholars for the 2022-24 academic years.  All interested applicants must file a Notice of Intent to Apply by February 28.

They are also recruiting community mentors to match with the applicants.  Community mentors are practitioners in using science for management or policy in the Delta.  Those interested in serving as a community mentor can contact either Dr. Larsen or Lauren Hastings.   They will be working to match up these community mentors with interested applicants.

Final applications will be due on April 20, 2022.

Adapting Restoration for a Changing Climate Symposium

The symposium, Adapting Restoration for a Changing Climate, was a two-day event held in early February.  There were 423 participants, one of the highest for workshop participants, demonstrating a high degree of interest in the topic.

The workshop consisted of presentations and very stimulating panel discussions.  It showcased creative strategies for restoring flooded islands through the use of floating wetlands, such as highlighting lessons learned from horizontal levees, emphasizing the importance of cross watershed and cross estuary coordination, and helping resident communities cultivate a connection to nature.

Featured speakers included government, academic, tribal, and private sector scientists, policymakers, and even an artist.  Dr. Larsen said there was a lot of positive visioning of the future, which left participants feeling inspired and hopeful.  Products of the workshop are pending, and next month’s packet will contain a more detailed report out.

Interagency Ecological Program Workshop

The Interagency Ecological Program (IEP) workshop will be held virtually from March 22 through 24th.  Registration will be free.  The IEP workshop is an informal event held each spring to share new research results that advance science important to IEP in the larger adult Delta science community.

This year’s Planning Committee has chosen to emphasize early career scientists and managers within our community.  The planning committee is looking forward to discussions led by and for those with newer roles in the ranks,  The workshop will include poster sessions, lightning talks, and even a poetry slam.

Delta Governance Brown Bag Series

The Delta Governance Brown Bag Series is a three-part series.  The March 1 webinar will focus on environmental governance; the April 13 webinar will focus on collaborative governance; and the May 5 webinar will focus on adaptive governance.

Each webinar will feature a panel of speakers and a set of questions posed to the panelists.  The panelists are selected to represent a wide range of perspectives from federal, state, local and tribal government, collaborative partnerships between government and non-government entities, and academic social scientists.

The upcoming March 1 webinar will feature Delta Councilmember Don Nottoli, Carl Wilcox from California Department of Fish and Wildlife, Mark Lubell from UC Davis, and Kaylee Allen from the US Fish and Wildlife Service.

I have seen a preview of the questions, and I’m personally really excited about what is shaping up to be a riveting discussion,” said Dr. Larsen.

Delta Lead Scientist Ask Me Anything

The latest installment of the Delta Lead Scientist will occur Monday, February 28, at noon and will focus on the upcoming launch of the Delta Science Tracker.  The Delta Science Tracker is a searchable database of all funded research that concerns the Delta.  It provides visualization tools and readily available information about which projects are addressing which science actions or priorities, which investigators are tackling common or complementary topics, and what products result from the investment of research dollars.  The co-hosts will be Maggie Chrisman from the Delta Science Program and Clint Alexander from ESA technologies.

Dr. Larsen noted that recordings of previous Ask Me Anything sessions, including January’s, which focused on the Delta Science Program’s ongoing synthesis efforts, are available on the Council’s Instagram TV.


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