River and landscape engineering along the east coast rivers have negatively impacted tidal freshwater wetland ecosystem and their functions. These fringe habitats are vital in climate modification because their soils store a disproportionately higher amount of organic carbon compared to other ecotypes. On-going efforts to reestablished tidal freshwater wetland habitats have been successful along the Patuxent and Anacostia Rivers in Maryland and DC. While restored wetland plant productivity reestablishes in a few short years, oftentimes their soils fail to provide similar ecosystem services as their natural counterparts. There are many reasons why soil functions in restored wetlands differ from their natural counterparts. For one, soil organic matter (SOM) pools, a critical source of nutrients and energy for soil microbial activity, are diminished. Additionally, engineering practices tend to change wetland structure and shift site soil texture. There is little understanding of how shifts in site soil texture affect long-term SOM accumulation, soil microbial ecology, and soil biogeochemical processes. In this study, we selected two marshes along the Patuxent River in Anne Arundel County, Maryland to identify and compare major mechanisms controlling organic matter bioavailability and quantify the effects of soil texture on carbon (C) decomposition, nutrient availability, and soil microbial community diversity over time.
Results/Conclusions
Wooton's Landing Wetland Park (WLWP) is a restored marsh (est. 1992) and Patuxent Wetland Park (PWP) is a “natural” undisturbed ecosystem. The soils at WLWP are composed of glauconite, and these soils have a greater sand content (62 ± 6.2%) compared to PWP (5.6 ± 0.6%). As expected, SOM levels at WLWP (4.5 ± 0.6) are significantly reduced compared to PWP (18 ± 2.1%). Following a wet sieving fractionation procedure, we discovered the distribution of four aggregate size fractions differed between marshes. In PWP, macroaggregates (>2000 μm) made up the largest aggregate size fraction and 250-2000 μm were the largest fractions in WLWP. We also documented C concentrations were greater in macroaggregate compared to micoaggregates (53 – 250 and 250 – 2000) and silt+clay (<53 μm) mineral fractions. Macroaggregate pools are a vital source of nutrients for the surrounding plant and microbial community because they provide more bioavailable carbon and nitrogen. Given these results, we expect to find a lower concentration of nitrogen and a higher production of carbon dioxide and methanogenesis in WLWP compared to PWP. We continue to investigate how these differences between WLWP and PWP organic matter bioavailability, microbially mediated decomposition, and microbial diversity.