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Nutrient Effects on Belowground Organic Matter in a Minerogenic Salt Marsh, North Inlet, SC
Citation:
Wigand, C., E. Davey, R. Johnson, K. Sundberg, J. Morris, P. Kenny, E. Smith, AND M. Holt. Nutrient Effects on Belowground Organic Matter in a Minerogenic Salt Marsh, North Inlet, SC. Estuaries and Coasts. Estuarine Research Federation, Port Republic, MD, 38(6):1838-1853, (2015).
Impact/Purpose:
Our study supports the SHC:RAP, 3.3.11 Wetlands and Nitrogen in Narragansett Bay Watershed, and the completion of FY14 product, Technical report on cultural eutrophication effects on belowground structure of salt marshes. In our study we examine nutrient effects on roots, rhizomes, soil organic matter, and carbon dioxide emission rates among different coastal marsh systems, including a 12-year fertilized marsh, in the North Inlet (SC). These coastal marsh systems are minerogenic, dominated by depositional processes, which is typical of coastal marsh systems in the southeastern USA. We use traditional and innovative methods such as computer-aided tomography (CT) imaging to examine and quantify belowground structural and functional responses to nutrient additions. It is unclear whether nutrients have a positive or negative effect on peat build up and the sustainability of coastal marsh systems, and our study helps address how soil matrix and marsh type (minerogenic or biogenic) influence belowground marsh responses to nutrient additions. For the first time, we provide CT three dimensional images of the belowground structure of the SC marshes. Two important findings of our study are first that nutrient additions clearly increased coarse root and rhizome volume and organic content, and second that the input of sediments to minerogenic marsh systems may have a mitigating effect on nutrient inputs. The present study also reports on soil characteristics (organic content, bulk density) and carbon dioxide emission rates among the marsh systems in the North Inlet to broaden our understanding of the links between soil structure and belowground marsh soil processes. We believe our study better elucidates belowground structure and the process of peat build up in southeastern US coastal marsh systems and will assist in the better management of minerogenic marsh systems.
Description:
Belowground structure and carbon dioxide emission rates were examined in minerogenic marshes of the North Inlet estuary, a system dominated by depositional processes and typical of the southeastern USA. Three areas were sampled: a long-term nutrient enrichment experiment (Goat Island); a fringing marsh that only receives drainage from an entirely forested watershed (upper Crab Haul Creek); and three locations along a creek basin that receives drainage from a residential and golf course development situated at its headwaters (Debidue Creek). Responses to fertilization at Goat Island were an increase in soil organic matter, an increase in number of rhizomes, enlarged rhizome diameters, decreased fine root mass, and increased carbon dioxide emission rates. At the Crab Haul Creek, the greatest abundances of coarse roots and rhizomes were observed in the high marsh compared to the low marsh and creekbank. The upper and mid Debidue Creek, which may be influenced by nutrient inputs associated with land development, had significantly fewer rhizomes compared to the mouth, which was dominated by exchange with bay waters. Carbon dioxide emission rates at the fertilized Goat Island plots were similar in magnitude to the upper Debidue Creek and significantly greater than the Goat Island control plots and the Crab Haul Creek. Inputs of sediment and particulates in marshes dominated by depositional processes such as the North Inlet may buffer the system from adverse effects of nutrient exposure, and increases in organic matter and rhizome abundances in response to nutrients may have a positive effect on peat build up.
