My general research interests are within the field of Global Change Biology, particularly global carbon cycling and carbon sequestration in soils as a climate-change-mitigating strategy. More specifically, I would like to focus my research on the role of soil aggregates in soil C stabilization and storage and the use of stable and radioisotopes to reveal the different mechanisms of soil carbon retention.

Terrestrial ecosystems have the potential to sequester significant amounts of atmospheric CO2 by increasing photosynthetic C gain over plant or soil respiratory C losses. At a global scale, the accumulation of dead plant biomass and litter represent C input into the soil. Soil organic matter stored in soils (SOM) is one of the largest C reservoirs that is in rapid exchange with atmospheric CO₂, and thus it is important as a potential source and sink of this greenhouse gas over time scales of human concern (Schimel, 1995). The positive balance for net C retention in ecosystems can be further enhanced in ecosystems with lower soil respiration rates as a result of the decrease of plant decomposition rates through constrained microbial activity in soils. Furthermore, certain biogeochemical conditions in soils such as anoxia promote long-term storage of C by reducing soil respiration and hence, slowing the C turnover. In Nature, wetland ecosystems fit the required conditions and can have substantial feedbacks on atmospheric GHGs (Misth and Gosselink, 2000). Wetlands are ecosystems where saturation with water is the dominant factor determining the nature of their soils. Their high water tables prevent oxygen diffusion in depth generating anoxia in soils and reducing soil CO₂ efflux. These particular hydrological, geological, and biogeochemical features allow wetlands to maintain a sustained C sequestration rate. According to Gorham (1991), the global total C presently stored in wetlands is 535 Gt C and mean C densities in wetland soils are in the range of 210-700 t C ha-1 (Mistch, 1994; Matthews and Fung, 1987; Ramsar Convention, 1971; Gorham, 1991). At a global scale, wetlands have been shown to be currently accumulating C at rates that range from 0.2 to 1.4 t C ha-2 yr-1 (Roulet, 2000; Mitra et al., 2005). In terms of GHGs mitigation strategies, wetland’s C retention potential and their large soil C stocks resof these ecosystems as perfect targets for increasing GHGs sinks. However, the efficiency of wetlands to remove C from the atmosphere is reduced by trace gas emissions of methane (CH4) from soils, which is a more potent greenhouse gas than CO₂. Whether wetlands will act as natural modulators or amplifiers of global change will depend on the balance between net CO₂ uptake and CH4 emission.

Natural wetlands are unique environments with high C sequestration potential, nowadays largely damaged and globally under their C storage capacity. Drainage of wetland ecosystem during conversion to agriculture have resulted in the loss of large amounts of C, as soil organic matter previously stored under anaerobic conditions is exposed to atmospheric oxygen and therefore oxidized to CO₂. The organic C that had been accumulated over centuries to millennia in wetland’s soil horizons have been lost in years or decades. The rate of total C emissions from the conversion of wetlands to agricultural lands is currently estimated to range between 2.5-10 t C ha-1 yr-1 (Maltby and Immirzi, 1993). Emissions from terrestrial ecosystems due to such land use changes can be reduced, and previous losses of C can be recaptured into biomass and soils with the proper management. Therefore the restoration of soil C to pre-cultivation levels in abandoned crop fields represents an excellent target for C sequestration. This will be in addition to other significant benefits such as improved soil and water quality, maintenance of better wildlife habitats, reduced soil erosion and decreased nutrient loss.

The Wetlands Initiative (TWI) is a nonprofit corporation dedicated to restoring the wetland resources of the Midwest to improve water quality, increase wildlife habitat and biodiversity, and reduce flood damages. In 2001, The Corporation began restoration at the Hennepin & Hopper Lakes Project, 2,600 acres of former backwater lakes and wetlands pumped dry for 80 years to make way for corn and soybean fields. TWI focus restoration efforts on reversing the environmental damage created by the drainage providing an unprecedented opportunity for study the potential of these ecosystems as natural modulators of global change through an increased C retention as they reach the pre-drained C budget that largely exceeds the capacity of the current land-use. Estimates are that about 50% of the global wetland area has been lost as a result of human activities (Dahi, 1990). This initiative opens new avenues to explore the role of wetlands management and reclamation in international policies controlling GHGs’ emissions in the coming century.

The purpose of this project is to initiate C turnover studies on restored wetlands that will provide a mechanistic understanding of this ecosystem as a natural modulator of climatic warming.  We propose to study the mechanisms of C-uptake and retention along the Hennepin site. We will address three core questions: (1) what is the current rate of C accrual in the Hennepin restored wetland, (2) the evolution of C dynamics along the ecosystem recovery process, and (3) what is the interactive role of CO2 and CH4 fluxes as ultimate drivers of C storage and GHGs balance in restored wetland ecosystems.