Nutrient Levels and Organic Matter Decomposition Following Prescribed Burns in Mid-Atlantic Coastal Marshes.

Prescribed winter burning is a commonly used management practice in coastal marshes along the Atlantic Coast to promote the growth of wetland vegetation species favorable for waterfowl habitat, and to facilitate hunting and trapping activities. However, the effects of burning on plant nutrient availability and soil organic matter decomposition rates have not been studied. Two manipulative experiments were conducted at Blackwater National Wildlife Refuge in Cambridge, MD within long-term annual burn and no-burn management areas. The study aimed to elucidate the impacts of the two primary postulated burn mechanisms (ash deposition and canopy removal) on nutrient dynamics and plant-soil responses. Data were collected on plant nutrient contents for two dominant species, growing season nutrient availability (resin capsules and porewater), plant ash elements, and soil organic matter decomposition rates (cotton tensile strength loss; CTSL). No-burn areas with canopy removal treatments showed significantly lower decomposition rates (66.5 ± 5.46% CTSL) than treatments with a canopy (74.1 ± 4.89% CTSL; P=0.04) in July. Porewater nutrient measurements at no-burn plots in July showed significantly lower amounts of NH4+ (P=0.04) and PO43+ (P=0.02) in sites with canopy removal (0.15 ± 0.06 mg NH4+/L and 0.04 ± 0.01 mg PO43+/L) compared to sites with a canopy (0.73 ± 0.28 mg NH4+/L and 0.08 ± 0.02 mg PO43+/L). Annually burned areas also had significantly lower porewater NH4+ readings in sites with the canopy removed by burning (0.13 ± 0.04 mg/L) in July compared with the canopy replacement treatment (0.79 ± 0.20 mg/L; P=0.005). Through the mechanism of canopy removal, organic matter decomposition rates in marsh areas tended to decrease later in the growing season, corresponding with a decrease in porewater ammonium and phosphate, which were taken up in much higher quantities in the biomass. Plant ash provided a fertilizer pulse of 0.22 ± 0.02 g N/m2 and 0.16 ± 0.02 g P/m2, which are amounts of nitrogen and phosphorus too small to increase plant productivity, and this likely holds true across all coastal marsh habitats.