Impacts of biochar on phosphorus distributions in salt marsh surface soils in Delaware

Date
2024
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
Salt marshes store nutrients, including phosphorus (P) in their soils thereby providing the ecosystem service of reduced nutrient export to estuaries. Contrasting other ecosystem services, nutrient storage may be enhanced in stands of the invasive common reed, Phragmites australis (hereafter Phragmites), compared to native marsh grasses. Restoration efforts to remove Phragmites may thus reduce marsh P storage and allow more P into coastal waters where it can contribute to eutrophication. Prescribed burning to control Phragmites introduces biochar which, due to its surface chemistry and high surface area, may increase the sorption and storage of P in salt marsh soils and recoup this service. To study this P storage potential, cores were collected from 3 Delaware marshes with different burn histories for analysis of organic and inorganic P contents (OP, IP). These P components were also measured in field incubation plots with and without biochar addition in both native and invasive grass stands to further investigate the impact of biochar and plant species on soil P distributions. Because P form influences its aqueous mobility and storage potential, samples were further differentiated for P speciation on a continuum of mobility/lability (immediately plant available/labile, easily exchangeable, intermediately exchangeable, recalcitrant). P composition and distribution were examined for relationships with depth, tidal cycles, elevation, nutrients, pH, and organic and black carbon concentrations. Total and recalcitrant forms of P were expected to be highest in previously burned marsh environments and the biochar amended plots demonstrating a P storage ecosystem service provided by the biochar inputs. Further, P concentrations were expected to be higher in the soil of Phragmites stands compared to Spartina. Neither burn frequency nor biochar application demonstrated a relationship with total organic or inorganic P concentrations suggesting no influence of burned materials on P sorption. Further, the presence of biochar was associated with a reduction in recalcitrant P concentrations. The lack of biochar-induced enhancement in P sorption may be due to the specific characteristics of the biochars produced from the burns and used in the experimental plots. Biomass, grass species, and pH were found to most strongly influence P distribution in the sampled marshes. The data show greater P content in Phragmites soils compared to native grass soils, suggesting that burning Phragmites and replacing it with native grasses may reduce P retention in marshes. The results of this study will add to the understanding of how prescribed burns and biochar impact P composition and cycling in salt marsh environments. Future work should explore the ubiquity of this finding and whether biochars of differing characteristics (feedstock, production conditions, mixing ratios) may provide a P storage ecosystem service.
Description
Keywords
Biochar, Invasive management, Phosphorus, Phragmites, Prescribed burning, Salt marsh
Citation