11 Blue Carbon and Global Change: Mechanisms, Modeling

AAAS Pacific Division
2015 San Francisco Meeting
Symposium Abstracts
11 Blue Carbon and Global Change: Mechanisms, Modeling, Management
Connecting Conservation of Coastal Systems with Climate Change Mitigation Through Blue Carbon, STEPHEN
CROOKS (Environmental Science Associates, 550 Kearny Street Ste 800, San Francisco, CA 94108; SCrooks@
esassoc.com).
Coastal and marine ecosystems play a substantial role in carbon sequestration and storage (referred to as “blue
carbon”), representing ~50% of carbon burial across only 2% of ocean area. Yet, despite the importance of these
ecosystems to local livelihoods, in maintaining commercial fisheries, and environmental conditions, they are being
destroyed at a high rate. At the current pace almost all of the world mangroves will be lost this century, with
marshes and seagrasses heavily depleted. There is a critical need for science-based policy, management and
financial mechanisms to protect and restore these ecosystems.
Last year saw progress towards recognizing the value of coastal wetlands in climate regulation. The IPCC
provided technical guidance to countries on accounting for GHG emissions and removals associated with human
activities in wetlands. Restore America’s Estuaries submitted for review to the Verified Carbon Standard outlines
the first global carbon procedures for connecting restoration of coastal wetlands to voluntary carbon markets. Blue
Carbon demonstration activities and programs are building in a number of key countries.
While these activities are a start much has yet to be done. Refined science is needed on human impacts to
carbon storage. Intriguingly, there appears also to be a link to buffering coastal waters from global ocean
acidification which requires further investigation. And there are opportunities to connect blue carbon with greengrey infrastructure approaches in coastal systems. Example policies need to be developed that link the goals and
aspirations of local people with the need of all for a balanced climate.
Tracking Carbon in Coastal Ecosystems: Sources and Sink in the Muck and the Mire, LISA SCHILE* and
PATRICK MEGONIGAL (Smithsonian Environmental Research Center, Edgewater, MD 21035; [email protected]).
Coastal and marine ecosystems, including tidal wetlands, mangroves, and seagrass beds, store significant
amounts of carbon, termed ‘blue carbon’, at rates that exceed tropical and temperate forests. These blue carbon
ecosystems also can release carbon naturally and through anthropogenic influences such as diking, deforestation,
and shrimp farming. Recent recognition of the value of these ecosystems as significant carbon sinks has
strengthened worldwide interest in their management, conservation, and restoration for the purpose of climate
change mitigation. However, many gaps in understanding carbon sequestration in coastal ecosystems remain,
creating challenges for the application of coastal ecosystem carbon research at local, regional and global scales. A
major limitation is the fact that most research on this topic has been conducted in relatively few temperate and
tropical ecosystems, despite a tremendous amount of spatial variability in carbon stocks across gradients of climate,
hydrology, geomorphology, and tide range. Climate change, especially accelerated sea-level rise, threatens their
survival. This talk will explore the global distribution and significance of coastal wetlands, and international
research to understand carbon dynamics under a changing climate.
The Carbon Sink in Low Salinity/Freshwater Reaches of the San Francisco Estuary: Historic Impacts and Future
Resiliency, JUDITH DREXLER (U.S. Geological Survey, California Water Science Center, Sacramento, CA
95819; [email protected]).
Tidal marsh soils that form in low salinity and freshwater environments often contain high amounts of organic
carbon. Such “peat” soils accumulate over hundreds to thousands of years and are a major carbon sink. In the San
Francisco Estuary, peat soils exist in Suisun Marsh and the Sacramento-San Joaquin Delta. Various practices,
including drainage and conversion to agriculture and/or impoundment and hydrologic management, have impacted
the carbon sink in these areas. In the last 150+ years, large amounts of organic carbon held in peat soils have been
lost, leading to land-surface subsidence of up to 8 meters on farmed lands. Due to the plight of sensitive species,
there is great interest in restoring wetland habitats in the Delta as well as Suisun Marsh. The success of restoration in
these areas relies heavily on re-establishing the conditions that result in peat formation. This is challenging in an era
of rapid sea-level rise and decreasing sediment availability, which along with organic matter is an essential
component of peat. The Wetland Accretion Model of Ecosystem Resilience was recently used to explore the future
sustainability of marshes in the Delta under a broad range of future scenarios. Overall, the modeling results showed
that upstream reaches of the Delta, where sea-level rise may be attenuated, and stretches along major river channels,
which have high inorganic sedimentation rates, are the best bet for wetland restoration projects because of the longterm sustainability of marshes in these settings.
Carbon Sequestration in Natural and Restored Tidal Wetlands in San Francisco Bay, JOHN C. CALLAWAY1*,
EVYAN L. BORGNIS1, R. EUGENE TURNER2, and CHARLIE S. MILAN2 (1Department of Environmental
Science, University of San Francisco, San Francisco, CA 94117; 2Department of Oceanography and Coastal
Sciences, Louisiana State University, Baton Rouge, LA 70803; [email protected]).
There is growing interest in carbon sequestration within tidal wetlands as California and other states consider
incorporating tidal wetland restoration activities into carbon trading programs. Our research was designed to
establish a baseline for carbon credits for tidal wetland restoration in the San Francisco Bay Estuary. We measured
sediment accretion and carbon sequestration rates at six natural tidal wetlands, which serve as potential analogs for
long-term carbon sequestration in restored wetlands. Cores from natural wetlands were dated using Cs-137 and Pb210. Although long-term accretion rates could not be measured at restored wetlands, cores were collected from two
restored wetlands for comparison of soil organic matter and bulk density. Carbon sequestration rates averaged
approximately 80 g/sq. m/yr over the 100-year time span of Pb-210, and rates were slightly higher based on Cs-137.
Variation in sequestration rates across sites and stations was smaller than the variation in mineral inputs, and there
was little difference in sequestration rates among sites, or across stations within sites, indicating that a single
sequestration rate could be used for crediting tidal wetland restoration projects within the Estuary. Surface soil
organic matter and bulk density values were similar across natural and restored wetlands, supporting the use of
sequestration data from natural wetlands as a surrogate for future sequestration in restored tidal wetlands. Given the
need for long-term carbon burial to receive credits within the carbon trading program, we recommend that carbon
credit accounting be based on sequestration rates obtained from Pb-210 or other long-term dating methods.
Measuring, Monitoring and Modeling Blue Carbon Sinks for Policy Needs: Optimal Integration of Field Data and
Remote Sensing of U. S. Coastal Wetlands, LISAMARIE WINDHAM-MYERS (U.S. Geological Survey, 345
Middlefield Road, MS 480, Menlo Park, CA 94025; [email protected]).
Managing soil carbon (C) storage in coastal “blue carbon” wetlands (such as mangroves, marshes and seagrass
habitats) can be a small but significant long-term sink for mitigating carbon pollution, while providing co-benefits
such as storm surge attenuation and wildlife support. Although tidal wetlands can store even more C than forests and
for longer, they require a unique form of carbon accounting to meet requirements for national and market-based
interventions. Whereas forest soil C pools become saturated despite continued tree growth, in tidal wetlands, the soil
C pool continues to grow due to organic accumulation commensurate with sea level rise, even as the vegetation C
pool becomes saturated. Incorporating “blue carbon” into broadscale C accounting portfolios requires better
validation and integration of national-scale datasets on soil C pools, relative sea level rise, and land-cover and landuse changes. A multi-disciplinary team will be evaluating use of Tier 1, 2, and 3 protocols from the IPCC Wetlands
Supplement (2013) for documenting the C flux implications of wetland transitions as well as determining constraints
for coastal C flux budgets. Our approach leverages recent process-based research and widespread field data on rates
of soil C accumulation and loss to model and validate landscape-scale estimates informed by remotely sensed data
and GIS modeling. The greatest uncertainty in current “blue carbon” inventory-approaches arises from scaling-up
point data across the estuarine landscape. One goal will be to determine the extent to which finer habitat
classifications (hydrology, salinity, sea-level rise) continue to inform C accounting with greater accuracy.