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Environmental Science Faculty

Christopher B. Craft
Professor
President, Society of Wetland Scientists
Professional Wetland Scientist
Associate Editor, Wetlands

Ph.D., North Carolina State University, 1987

Research Profile

Using wetlands as a model, Professor Craft’s research focuses on biogeochemical linkages between vegetation, soils and soil fauna and the effects of human activities on these linkages. Our research concentrates on the impacts of natural (grazing, sea level rise) and anthropogenic (nutrients, hydrologic alteration, cultivation and soil disturbance, shading) disturbance on ecosystem structure and function and on restoration of ecosystem integrity following disturbance. Funding to support the research program comes from federal (National Science Foundation (NSF), US Environmental Protection Agency (EPA), US Department of Transportation (DOT), US Fish & Wildlife Service, US Department of Interior-Everglades National Park, National Oceanic and Atmospheric Administration (NOAA), state (New Jersey Department of Environmental Protection, North Carolina DOT) and not-for-profit (The Nature Conservancy) organizations. The main areas of research are summarized below. For more information about our lab, please go here.

Climate Change

Tidal marshes provide important ecosystem services to society. They serve as a buffer against storm tides, improve water quality by trapping sediment, nutrient and other pollutants, serve as nurseries for many commercially and recreationally important finfish and provide habitat for wading birds and other animals. Marshes also sequester carbon, a greenhouse gas, and convert nitrate, a pollutant in water, to di-nitrogen gas returning it to the atmosphere.

One consequence of global warming is an accelerated rise in sea level and, in some coastal regions, sea level is predicted to rise a meter or more during the next 100 to 150 years. There is concern that, if sea level rise accelerates, tidal marshes, and their ecosystem services, will shrink or disappear as marshes convert to open water or transgress landward and shrink as they migrate onto steeper landforms. In addition to global warming, climate change also will result in greater variability or extremes in climatic events such as drought and flooding that will lead to greater inter-annual variability in delivery of ecosystem services.

With funding from the US EPA Science to Achieve Results (STAR) program, we are investigating the effects of rising sea level and climate variability on the delivery of ecosystem services provided by tidal marshes. Set along the southeastern Atlantic (Georgia) coast, we use a combination of field measurements, geographic information systems (GIS) and modeling approaches to predict how climate change-induced sea level rise and climate variability will affect the area and distribution of tidal marshes and their delivery of ecosystem services. For more information about the project, please go here.

Or visit our project Web site at www.spea.indiana.edu/wetlandsandclimatechange.

As part of the Georgia Coastal Ecosystems Long Term Ecological Research (GCE LTER) study funded by the National Science Foundation, we are investigating the role of freshwater pulsing on long-term stability of tidal marshes in the region. We measure marsh accretion-subsidence (using benchmarks), sediment deposition and carbon dynamics (productivity, decomposition, accumulation) at ten marshes to determine which processes govern marsh accretion and stability in the face of rising sea level. For more information about our work with the GCE LTER, please go here.

Or visit the GCE LTER Web site at http://gce-lter.marsci.uga.edu/lter/.

Carbon Sequestration

It has been suggested that global warming can be combated by storing excess atmospheric CO2 in biomass of vegetation and soils. Wetlands, because of their high plant productivity and anaerobic soils, are an important sink for atmospheric CO2 through peat accretion and burial by sediment. Although they occupy less than 2% of the world’s land surface, wetland soils store 12% of the world’s soil organic C. We are investigating environmental controls of organic C accumulation in a variety of freshwater and estuarine wetland soils. In freshwater peatlands, climate as measured by mean annual air temperature (MAAT) and pH are important drivers of C accumulation as an increase in either factor leads to a reduction in soil organic C accumulation (Figure 1). In estuarine wetlands, C accumulation is driven by tide range and salinity and MAAT. An increase in any of the three factors leads to a decrease in C accumulation. The inverse relationship between MAAT and C accumulation indicates that global warming has the potential to reduce C sequestration in both freshwater and estuarine wetland soils. This data suggests that climate change will reduce wetland C sequestration and possibly create a positive feedback that increases atmospheric CO2 and exacerbates global warming.

We also are investigating in estuarine marshes of the continental U.S. In this study, salinity, rather than temperature, is the driving force that controls C sequestration in these marshes. For example, tidal freshwater and brackish marshes exhibit greater C sequestration as compared to salt marshes (Figure 2) that is attributed to greater vertical accretion and soil organic C content.

Nutrient Enrichment & Eutrophication

Eutrophication or nutrient over-enrichment is the result of excess nitrogen (N) and phosphorus (P) from fertilizer runoff, domestic wastewater and other anthropogenic sources. In wetlands, eutrophication increases plant growth, accelerates cycling of N and P and alters plant diversity as aggressive “weedy” species replace native vegetation. With funding from US EPA, we are working to identify vegetation- and soils-based indicators of nutrient enrichment in freshwater wetlands of the Midwestern US. We focus our efforts on three ecoregions (VI - Eastern Corn Belt, VII - Mostly Glaciated Dairy, IX - Southeastern Temperate Forested Plains and Hills) that vary in intensity of agricultural land use and nutrient inputs. Preliminary findings suggest that, in the Midwest US, wetland vegetation is limited by N. Furthermore, vegetation response to N varies among ecoregions. Ecoregions with extensive forest cover and low nutrient loadings (e.g., ecoregions VI and IX) respond positively to N enrichment whereas ecoregions with extensive agricultural land use and nutrient loadings (e.g., ecoregion VI) exhibit little to no response to N (Figure 3).

Our results contrast with other studies of wetland eutrophication (e.g., Florida Everglades) where P is observed to be the primary limiting nutrient. In both the Everglades and Midwest wetlands, cattail (Typha) invades and dominates the plant community with progressive nutrient enrichment (Figure 4). These findings suggest that abundance of cattail and other aggressive species may serve as an indicator of the degree of wetland enrichment and eutrophication. For more information about this research, please see our technical report, here, and our article in Ecological Indicators, here.

With funding from the GCE LTER, we also are investigating the effects of N versus P enrichment of tidal freshwater marshes of the southeast coast. In this study, we are adding N, P and N+P to 2m by 2m plots in a tidal freshwater marsh along the Altamaha River Georgia. Preliminary results after one year of fertilization suggest that N limits productivity of emergent vegetation in these marshes also. For more information about the experiment, click here,

Ecosystem Restoration

There is much interest in restoring and rehabilitating ecosystems damaged by human activities. Restoration of wetlands is considered a priority because of the important ecosystem services (flood control, water purification, high biological productivity, biodiversity) they provide to society. We are evaluating how quickly (or slowly) ecosystem development proceeds following creation and restoration of estuarine (salt) marshes. With one of the longest records of data (nearly 30 years) for wetland restoration projects worldwide, we are constructing trajectories of development over time for a suite of ecological attributes related to biological productivity, biodiversity, C cycling and water quality functions on created and on natural marshes. Whereas some attributes develop within a few years following restoration, other attributes require even longer than the 30 year period-of-record to achieve equivalence to natural marshes (Figure 5). These findings demonstrate that (1) many (but not all) ecological attributes develop in a predictable manner over time, (2) different ecological attributes develop at different rates and (3) full or complete restoration of ecological structure and function does not occur quickly and, in some cases, may take decades or longer to occur.

For more information about our restoration research in natural, agricultural and urban landscapes, please go here.

Recent Publications

Craft, C., J. Clough, J. Ehman, S. Joye, D. Park, S. Pennings, H. Guo and M. Machmuller. 2008. Effects of Accelerated Sea level Rise on Delivery of Ecosystem Services Provided by Tidal Marshes: A Simulation of the Georgia (USA) Coast. Frontiers in Ecology and the Environment. In press.

Aldous, A.R., C.B. Craft, C.J. Stevens, M.J. Barry, and L.B. Bach. 2007. Soil phosphorus release from a restoration wetland, Upper Klamath Lake, Oregon. Wetlands 27(4):1025-1035.

Cornell, J.A., C. Craft, P. Megonigal. 2007. Ecosystem gas exchange across a created salt marsh chronosequence. Wetlands 27:240-250.

Craft, C., K, Krull and S. Graham. Ecological indicators of nutrient condition, freshwater wetlands, Midwestern United States (U.S.). Ecological Indicators. 7:733-750.

Craft, C.B. Freshwater input structures soil properties, vertical accretion and nutrient accumulation of Georgia and United States (U.S.) tidal marshes. Limnology and Oceanography 52:1220-1230.

Struck, S.D., C.B. Craft, E.R. Elswick and L.M. Pratt. Stable isotopes as indicators of soil reduction and organic matter sequestration following brackish marsh creation. Estuaries. In review.

Craft, C.B. 2008. Soils of the Everglades Peatlands. In, C.J. Richardson (ed.), The Everglades Experiments. New York: Springer-Verlag. Pp.59-72.

Craft, C., J. Schubauer-Berigan. 2006. The role of freshwater wetlands in a water quality trading program. Conference Proceedings: Innovations in Reducing Nonpoint Source Pollution Methods, Policies, Programs, and Measurement. Pp. 143-158.

Craft, C.B. 2005. Natural and constructed wetlands. In M.G. Anderson (ed.), Encyclopedia of Hydrologic Sciences, pp. 1639-1656. New York: John Wiley and Sons.

Aldous, A., P. McCormick, C. Ferguson, S. Graham and C. Craft 2005. Hydrologic regime controls soil phosphorus fluxes in restoration and undisturbed wetlands. Restoration Ecology 13:341-347.

Graham, S.G., C.B. Craft, P.V. McCormick and A. Aldous. 2005. Peat accretion and phosphorus accumulation: Water Quality Management at Upper Klamath Lake, Oregon, through wetland restoration. Wetlands 25:594-606.

Struck, S.D., C.B. Craft, S.W. Broome, M. SanClements and J.N. Sacco. 2004. Effects of bridge shading on estuarine marsh benthic invertebrate community structure and function. Environmental Management 34:99-111.

Zheng, L., R.J. Stevenson and C. Craft. 2004. Changes in benthic algal attributes during salt marsh restoration. Wetlands 24:309-323.

Craft. C.B. and J.N. Sacco. 2003. Long-term succession of benthic infauna communities on constructed Spartina alterniflora marshes. Marine Ecology — Progress Series 257:45-58 .

Craft, C.B., J.P. Megonigal, S.W. Broome, J. Cornell, R. Freese, R.J Stevenson, L. Zheng and J. Sacco. 2003. The pace of ecosystem development of constructed Spartina alterniflora marshes. Ecological Applications 13:1317-1432.

Sturdevant, A., C.B. Craft and J.N. Sacco. 2003. Effects of impoundment on ecological functions of estuarine marshes along Woodbridge River, NY/NJ harbor. Urban Ecosystems 6:163-181.

Craft, C.B. and C. Chiang. 2002. Forms and amounts of soil nitrogen and phosphorus across a longleaf pine – depressional wetland landscape. Soil Science Society of America Journal 66:1713-1721.

Markewitz, D., F. Sartori and C. Craft. 2002. Soil change and carbon storage in longleaf pine planted on marginal agricultural land. Ecological Applications 12:1276-1285.

Craft, C.B., S.W. Broome and C.L. Campbell. 2002. Fifteen years of vegetation and soil development following brackish-water marsh creation. Restoration Ecology 10:248-258.

Craft, C.B. 2001. Soil organic carbon, nitrogen and phosphorus as indicators of recovery in restored Spartina marshes. Ecological Restoration 19:87-91.