Workshop on Factors Controlling Soil Organic Matter Accumulation

Network All Scientist’s Meeting

Seattle, WA Friday, September 19, 2003

Linda Blum and Chris Craft

Approximately 30 people attended the Soil Organic Matter Workshop. A list of active participants is included at the end of this document.

This workshop was a continuation of discussions about the factor(s) that are control organic matter accumulation in wetland sediments. A core group of individuals (Anderson, Blum, Christian, Craft, Hopkinson, and Morris) have shared data sets and completed analyses of the data sets to generate hypotheses that address the question about why some wetlands accumulate organic matter while others do not. The results of these discussions and statistical analysis have been summarized primarily through the efforts of Chris Craft and were presented at the September 19 workshop. Additionally, Sherry Mitchell presented data from the FCE, Rudolf Jaffe presented the results of work conducted on samples collected after a previous workshop, and Cassondra Thomas presented the results of recent experiments at the VCR. After the presentations, potential cross-site experiments and additional site characterization efforts were discussed.

Chris Craft’s presentation summarized the results of several LTER Network-supported workshops where data sets were brought together and analyzed for patterns in wetland sediment organic matter content. Data sets for a variety of fresh and salt water, tidal and non-tidal wetlands were included in the analysis. Sites contributing data included five Long Term Ecological Research LTER) sites (Plum Island (MA), Virginia Coast Reserve (VA), North Inlet (SC), Georgia Coastal Ecosystems (GA) and Everglades/Florida Bay (FL)). Data from New Jersey (Sturdevant et al. 2003), Virginia (C.B. Craft unpublished data) and North Carolina marshes (Craft et al. 1993, 1999, 2003) also were included in the dataset. The goal of this analysis was to identify drivers of SOC patterns at global scales.  The analysis concluded that at continent scales sediment organic matter concentration (SOM) in wetland soils is controlled by a combination of mean annual average temperature (MAAT), regional (tide range), and landscape-level salinity.  A multiple regression equation based on these three variables explained 55% of the variation in the dataset with tide range explaining the most variation (R=0.33). Thus,

SOM concentration = 49.6 – 1.08 (MAAT) – 7.07 (Tide Range) – 0.31 (Salinity)            R²=0.55

            At regional scales like those representing the Everglades ecosystem (Sherry Mitchell’s presentation) or the Virginia portion of the Delmarva Peninsula (Cassondra Thomas’ presentation). This relationship doesn’t hold and other factors become more critical in determining organic matter accumulation. For example, in the FCE, the type of available electron acceptors plays a dominant role in organic matter accumulation while at the VCR, preliminary experiments indicate that top-down control by burrowing invertebrates maybe a key to understanding organic matter accumulation.

            Rudolf Jaffe’s presentation highlighted the way in which mass spectrometry of organic carbon in wetlands could be useful in further characterization of the sites examined in Chris’ analysis or in a cross-site comparison experiment. Rudolf showed how some of the analyses his group did on samples from the FCE, GCE, and VCR LTERs indicated that there are differences in the susceptibility of the organic materials to decay among these three sites. Rudolf proposed that additional comparisons of this type would provide information about important differences in the digenesis of sediment organic matter among the sites that might useful.

            Discussions for future directions included ideas for additional evaluation of the data sets in hand supplemented with other data sets from a wider range of wetland types (e.g., fresh water wetlands) with broader geographic coverage (e.g., Gulf and Pacific coasts, and cooler climates) and a two experimental manipulations (nutrient addition, reciprocal transplants of sediment cores). The consensus of the workshop participants was that the most progress could be made by soliciting additional data sets to include in an analysis like that done by Chris and to supplement the current data set with additional information on variables/processes that have been shown to be important in more local areas where similar questions have been or are being addressed.

Future plans for the wetland sediment working-group will focus on this workshop’s recommendations to develop a proposal that would provide funds for additional sediment characterization and process information from sites that have already submitted data sets.

List of Workshop Participants

Linda Blum, chair

Chris Craft

Bob Christian

Chuck Hopkinson

Sherry Mitchell

Steve Macko

Iris Anderson

Steve Newell

Cassondra Thomas

Rudolf Jaffe

Karen McGlathery

Approximately, 15-20 others in the audience