Soil phosphorus in a nutrient-enriched Everglades wetland: The effect of prescribed burns on P storage

Phosphorus (P) is the limiting nutrient in the Everglades, and its availability influences productivity and plant species dominance.  P availability can be affected by nutrient loading, soil mineral content, and redox.  Fire may lead to P availability changes by removing biomass, changing surface water chemistry with ash addition, and changing the physical environment.  As part of a large ecosystem study to determine the effectiveness of fire as a tool for accelerating ecosystem recovery, a Before-After-Control-Impact Paired Study design was established in a highly and moderately P-enriched Everglades wetland.  This study focused on the short-term effects of fire on soil P forms and availability.  We hypothesized that the addition of ash to the near-surface soils will increase Ca/Mg-bound P due to precipitation with calcium (Ca), but decrease Fe/Al-bound P due to the increase in pH which decreases iron (Fe III) sorption capacity.  Different P forms in the floc, 0-2 cm, and 2-5 cm depths were measured pre-burn and twice post-burn.  The Ca/Mg-bound fraction of inorganic P increased two weeks post-burn significantly at the highly impacted site and insignificantly at the moderately impacted site and returned to pre-burn levels by the 5^th week.  Fe/Al-bound P decreased two weeks post-burn at both sites and then increased by the 5^th week post-burn.  Exchangeable P was not significantly affected by fire.  It is unknown what immediate affect fire had on pore water P.  The magnitude of site response to fire may be related to different species composition and leaf P concentrations between the two sites.