Current Research
Biological feedbacks of wetland ecosystems on climate change
Wetlands may significantly mediate global climate change by sequestering CO2 in recalcitrant plant biomass or anoxic soils. Alternatively, these ecosystems may be sites of greenhouse gas (CH4, CO2, N2O) production. My current research tests the extent to which fluxes of greenhouse gases, especially N2O, are stimulated by increasing loads of anthropogenic nutrients to marine and freshwater wetlands. I am also interested in the extent to which nitrogen loading interacts with other drivers of global change (sea level rise and biological invasions) to alter gas fluxes from coastal marshes. My lab uses existing bay-wide anthropogenic nitrogen gradients in Narragansett Bay, RI and Waquoit Bay, MA as “natural laboratories” to test human impacts on marsh biogeochemistry. Our results thus far suggest that marsh ecosystems, which are thought to major sinks of C may, through anthropogenic disturbance, become sources of greenhouse gases.
Looking beneath the soil surface:
Wetland landscapes are dominated and often characterized by their visible plant communities. Plant rhizospheres (roots and surrounding soils) in coastal sediments are active sites of microbially-mediated nutrient transformations, including nitrification (the oxidation of ammonium) and denitrification (the reduction of nitrate to N2 gas), both of which can produce the greenhouse gas N2O. However, wetland soils beyond the rhizosphere are often anoxic, and thus microbial communities in these soils may also be sources of methane (CH4). Plant species vary in their interactions with rhizosphere microbes and the rate and extent to which they modify sediments through oxygenation, assimilate nutrients, and act as conduits of gases from wetland sediments to the atmosphere. Thus, I am interested in exploring how community shifts among plants, in response to short-term anthropogenic effects (i.e. nitrogen loading, introduced species, restoration) or long-term climate change (sea level rise, increased temperatures and CO2), affect greenhouse gas production and the roles of wetland ecosystems in global biogeochemical cycles.
Expanding our scope beyond temperate marshes:
Many coastal ecosystems are impacted by human nutrient loads. Thus, my laboratory's past research has included subtidal ecosystems, wastewater treatment plants, and mangrove ecosystems. With funding from NSF Ocean Sciences, we tested how invertebrates (shellfish) may affect greenhouse gas emissions from subtidal ecosystems either directly or indirectly through their feeding and respiration. A manuscript is in preparation regarding our findings of oyster-associated denitrification responses to N loading in Point Judith pond estuary (the thesis work of Ashley Hamilton (formerly Hogan) with funding from RI Sea Grant. Through these projects, we are building cross-system perspectives on how a range of coastal organisms respond to nitrogen loading, and we hope to learn how human impacts on multiple valuable coastal systems may become more sustainable.
New Frontiers for the MV laboratory: NASA project
With collaborators Drs. Dawn Cardace and Soni Pradanang, our lab is developing methods for measuring methane emissions from serpentinite outcrops. These are places where rocks from the earth's mantle has been thrust upwards by tectonic activity and dynamic seepage of (mostly abiotic) methane can occur. This is relevant to NASA because methane has been detected on Mars where similar types of rocks have been observed. By constraining the size and duration of methane production from serpentinites on Earth, NASA scientists can better discern potential sources for methane observed on Mars. Our lab will be acquiring a portable methane and carbon dioxide analyzer and piloting methods in a variety of New England landscapes to customize flux chambers for these measurements. Then in 2023, we will begin measurements in the primary field site- McLaughlin Nature Preserve in Lower Lake CA.
Wetlands may significantly mediate global climate change by sequestering CO2 in recalcitrant plant biomass or anoxic soils. Alternatively, these ecosystems may be sites of greenhouse gas (CH4, CO2, N2O) production. My current research tests the extent to which fluxes of greenhouse gases, especially N2O, are stimulated by increasing loads of anthropogenic nutrients to marine and freshwater wetlands. I am also interested in the extent to which nitrogen loading interacts with other drivers of global change (sea level rise and biological invasions) to alter gas fluxes from coastal marshes. My lab uses existing bay-wide anthropogenic nitrogen gradients in Narragansett Bay, RI and Waquoit Bay, MA as “natural laboratories” to test human impacts on marsh biogeochemistry. Our results thus far suggest that marsh ecosystems, which are thought to major sinks of C may, through anthropogenic disturbance, become sources of greenhouse gases.
Looking beneath the soil surface:
Wetland landscapes are dominated and often characterized by their visible plant communities. Plant rhizospheres (roots and surrounding soils) in coastal sediments are active sites of microbially-mediated nutrient transformations, including nitrification (the oxidation of ammonium) and denitrification (the reduction of nitrate to N2 gas), both of which can produce the greenhouse gas N2O. However, wetland soils beyond the rhizosphere are often anoxic, and thus microbial communities in these soils may also be sources of methane (CH4). Plant species vary in their interactions with rhizosphere microbes and the rate and extent to which they modify sediments through oxygenation, assimilate nutrients, and act as conduits of gases from wetland sediments to the atmosphere. Thus, I am interested in exploring how community shifts among plants, in response to short-term anthropogenic effects (i.e. nitrogen loading, introduced species, restoration) or long-term climate change (sea level rise, increased temperatures and CO2), affect greenhouse gas production and the roles of wetland ecosystems in global biogeochemical cycles.
Expanding our scope beyond temperate marshes:
Many coastal ecosystems are impacted by human nutrient loads. Thus, my laboratory's past research has included subtidal ecosystems, wastewater treatment plants, and mangrove ecosystems. With funding from NSF Ocean Sciences, we tested how invertebrates (shellfish) may affect greenhouse gas emissions from subtidal ecosystems either directly or indirectly through their feeding and respiration. A manuscript is in preparation regarding our findings of oyster-associated denitrification responses to N loading in Point Judith pond estuary (the thesis work of Ashley Hamilton (formerly Hogan) with funding from RI Sea Grant. Through these projects, we are building cross-system perspectives on how a range of coastal organisms respond to nitrogen loading, and we hope to learn how human impacts on multiple valuable coastal systems may become more sustainable.
New Frontiers for the MV laboratory: NASA project
With collaborators Drs. Dawn Cardace and Soni Pradanang, our lab is developing methods for measuring methane emissions from serpentinite outcrops. These are places where rocks from the earth's mantle has been thrust upwards by tectonic activity and dynamic seepage of (mostly abiotic) methane can occur. This is relevant to NASA because methane has been detected on Mars where similar types of rocks have been observed. By constraining the size and duration of methane production from serpentinites on Earth, NASA scientists can better discern potential sources for methane observed on Mars. Our lab will be acquiring a portable methane and carbon dioxide analyzer and piloting methods in a variety of New England landscapes to customize flux chambers for these measurements. Then in 2023, we will begin measurements in the primary field site- McLaughlin Nature Preserve in Lower Lake CA.
Past research
Nitrogen Fixation in wetland ecology and conservation
The productivity of coastal wetlands has historically been nitrogen limited and supported in large part by bacteria that fix nitrogen in plant rhizospheres (roots and surround sediments). Tight mutualistic relationships have evolved between diazotrophs and dominant wetland plants including seagrasses and cordgrasses. My research has explored changes in the activity and diversity of diazotrophs in response to several anthropogenic impacts described below:
Biological invasions: The fundamental role of microbes in facilitating growth of wetland primary producers is exemplified through their interactions not only with native plants also invasive species. My research examined effects of two invasive trees, the mangrove Avicennia marina and salt cedar Tamarix spp., and one invasive mussel, Musculista senhousia, on nitrogen fixation rates and diazotroph diversity in wetlands of southern California. I found species and site-specific effects on nitrogen fixation that highlighted potential for invasions to fundamentally alter wetland nutrient dynamics.
Wetland succession and restoration: Nitrogen-fixing (diazotrophic) microbes influence wetland succession through their relationships with plant and macrofaunal communities. Nitrogen fixing microbes, particularly cyanobacteria are an important food item for macrofauna in the restored marsh of Tijuana Estuary (Moseman et al. 2004). In a 2 year, biannual study of nitrogen fixation rates, I also found significantly higher activity in a restored than a natural Spartina foliosa salt marsh at Tijuana Estuary (Moseman et al. 2009). Seasonal patterns of nitrogen fixation reflected changes in plant growth, and diazotroph communities in the natural marsh showed greater differentiation between surface sediments and plant rhizospheres than in the restored marsh (Moseman et al. 2009). These results support key roles of nitrogen fixers in facilitating restoration of wetland plant and macrofaunal communities.
Nutrient loading and sedimentation: Sewage pollution and human-induced sedimentation affect coasts worldwide. At Tijuana Estuary (CA), construction of the congressionally-mandated Triple Border Fence in 2008 threatened to smother many acres of wetland habitat by destabilizing sediments. Through field manipulations of sediment and nitrogen inputs to a Spartina foliosa marsh in the estuary, I tested impacts on the diversity and activity of nitrogen-fixing microbes. Results showed a rapid and significant decline in nitrogen fixation rates in parallel with increased diversity of diazotroph communities in response to nitrogen additions (Moseman et al. 2010). Further, nitrogen concentrations in the pore water of the marsh were higher and persisted longer in the presence of sediment inputs, illustrating a non-linear interaction between the two forms of disturbance. By tracing recently fixed nitrogen in isotopic enrichment studies, this study also suggested that sedimentation and nutrient loading could alter fundamental dynamics of wetland food webs (Moseman et al. 2010). My findings that heavy anthropogenic inputs of reactive nitrogen quickly shut down biological nitrogen fixation led me to explore- through postdoctoral research- ways that excess nitrogen leaves wetlands through the process of denitrification.
The productivity of coastal wetlands has historically been nitrogen limited and supported in large part by bacteria that fix nitrogen in plant rhizospheres (roots and surround sediments). Tight mutualistic relationships have evolved between diazotrophs and dominant wetland plants including seagrasses and cordgrasses. My research has explored changes in the activity and diversity of diazotrophs in response to several anthropogenic impacts described below:
Biological invasions: The fundamental role of microbes in facilitating growth of wetland primary producers is exemplified through their interactions not only with native plants also invasive species. My research examined effects of two invasive trees, the mangrove Avicennia marina and salt cedar Tamarix spp., and one invasive mussel, Musculista senhousia, on nitrogen fixation rates and diazotroph diversity in wetlands of southern California. I found species and site-specific effects on nitrogen fixation that highlighted potential for invasions to fundamentally alter wetland nutrient dynamics.
Wetland succession and restoration: Nitrogen-fixing (diazotrophic) microbes influence wetland succession through their relationships with plant and macrofaunal communities. Nitrogen fixing microbes, particularly cyanobacteria are an important food item for macrofauna in the restored marsh of Tijuana Estuary (Moseman et al. 2004). In a 2 year, biannual study of nitrogen fixation rates, I also found significantly higher activity in a restored than a natural Spartina foliosa salt marsh at Tijuana Estuary (Moseman et al. 2009). Seasonal patterns of nitrogen fixation reflected changes in plant growth, and diazotroph communities in the natural marsh showed greater differentiation between surface sediments and plant rhizospheres than in the restored marsh (Moseman et al. 2009). These results support key roles of nitrogen fixers in facilitating restoration of wetland plant and macrofaunal communities.
Nutrient loading and sedimentation: Sewage pollution and human-induced sedimentation affect coasts worldwide. At Tijuana Estuary (CA), construction of the congressionally-mandated Triple Border Fence in 2008 threatened to smother many acres of wetland habitat by destabilizing sediments. Through field manipulations of sediment and nitrogen inputs to a Spartina foliosa marsh in the estuary, I tested impacts on the diversity and activity of nitrogen-fixing microbes. Results showed a rapid and significant decline in nitrogen fixation rates in parallel with increased diversity of diazotroph communities in response to nitrogen additions (Moseman et al. 2010). Further, nitrogen concentrations in the pore water of the marsh were higher and persisted longer in the presence of sediment inputs, illustrating a non-linear interaction between the two forms of disturbance. By tracing recently fixed nitrogen in isotopic enrichment studies, this study also suggested that sedimentation and nutrient loading could alter fundamental dynamics of wetland food webs (Moseman et al. 2010). My findings that heavy anthropogenic inputs of reactive nitrogen quickly shut down biological nitrogen fixation led me to explore- through postdoctoral research- ways that excess nitrogen leaves wetlands through the process of denitrification.