Nutrient Effects on Belowground Organic Matter in a Minerogenic Salt Marsh, North Inlet, SC

Abstract

Soil organic matter, roots, rhizomes, and carbon dioxide (CO2) emission rates were examined in minerogenic marshes of the North Inlet Estuary, a system dominated by sediment depositional processes and typical of the Southeast USA. Three marsh sites were sampled: a long-term nutrient enrichment experiment at Goat Island; the high marsh, low marsh, and creekbank of Crab Haul Creek, a fringing marsh that only receives drainage from a forested watershed; and three creekbank locations in Debidue Creek, which receives drainage from a residential and golf course development situated at its headwaters. Goat Island responses to 12 years of nutrient fertilization were an increase in soil organic matter (OM), an increase in number of rhizomes, enlarged rhizome diameters, and increased CO2 emission rates. At soil depths of 10–20 cm, all Debidue creekbank locations had significantly more rhizomes than the reference Crab Haul creekbank. The rhizome diameters at the mid and upper Debidue creekbank locations were significantly larger than the Debidue mouth and reference Crab Haul creekbank. The upper Debidue and the Crab Haul creekbanks had similar soil percent OM, which was significantly greater than the mid Debidue, which was greater than the Debidue mouth. CO2 emission rates at the fertilized Goat Island plots were similar in magnitude to the upper Debidue and significantly greater than the Goat Island control plots and the reference Crab Haul Creek. Inputs of sediment in marshes dominated by depositional processes may buffer the system from adverse effects of nutrient exposure, while increases in soil OM and rhizomes in response to nutrients may contribute to peat formation.