Short-term changes in phosphorus storage in an oligotrophic Everglades wetland ecosystem receiving experimental nutrient enrichment

Abstract

Natural, unenriched Evergladeswetlands are known to be limited by phosphorus(P) and responsive to P enrichment. However,whole-ecosystem evaluations of experimental Padditions are rare in Everglades or otherwetlands. We tested the response of theEverglades wetland ecosystem to continuous,low-level additions of P (0, 5, 15, and30 μg L⁻¹ above ambient) in replicate,100 m flow-through flumes located in unenrichedEverglades National Park. After the first sixmonths of dosing, the concentration andstanding stock of phosphorus increased in thesurface water, periphyton, and flocculentdetrital layer, but not in the soil or macrophytes. Of the ecosystem components measured, total P concentration increased the most in the floating periphyton mat (30 μg L⁻¹: mean = 1916 μg P g⁻¹, control: mean =149 μg P g⁻¹), while the flocculentdetrital layer stored most of the accumulated P(30 μg L⁻¹: mean = 1.732 g P m⁻²,control: mean = 0.769 g P m⁻²). Significant short-term responsesof P concentration and standing stock wereobserved primarily in the high dose (30 μgL⁻¹ above ambient) treatment. Inaddition, the biomass and estimated P standingstock of aquatic consumers increased in the 30and 5 μg L⁻¹ treatments. Alterationsin P concentration and standing stock occurredonly at the upstream ends of the flumes nearestto the point source of added nutrient. Thetotal amount of P stored by the ecosystemwithin the flume increased with P dosing,although the ecosystem in the flumes retainedonly a small proportion of the P added over thefirst six months. These results indicate thatoligotrophic Everglades wetlands respondrapidly to short-term, low-level P enrichment,and the initial response is most noticeable inthe periphyton and flocculent detrital layer.