Biotic and abiotic uptake of phosphorus by periphyton in a subtropical freshwater wetland

Phosphorus (P) demand in extremely oligotrophic shallow water wetlands often exceeds supply and maintains water chemistry in a P-limiting condition. Phosphorus uptake by the calcareous periphyton community in the oligotrophic Florida Everglades was examined. Phosphorus removal from solution was used to obtain uptake parameters for epipelon, epiphyton, and metaphyton. Nutrient ratios (C:N:P) were higher in epiphyton compared to metaphyton or epipelon but all periphyton types were P-limited. Michaelis-Menten kinetic experiments resulted in K-m values ranging from 8.5 to 16.4 muM and V-max values ranging from 0.24 to 0.74 mumol g(-1) dry weight min(-1), in the order epiphyton, metaphyton, epipelon. Removal of inorganic P (P-i) as KH2PO4 and dissolved organic P (P-o) as ATP from solution was best described by a first-order equation with rate constants ranging between 0.02 and 0.17 min(-1). The values of K,, were greater than ambient dissolved reactive P (DRP) concentrations (<0.2 muM); therefore V-max not reached under normal field conditions. The hydrolysis of P-o as ATP was rapid, being >0.67 mumol g(-1) DW min(-1). After hydrolysis P-o uptake was similar to P-i uptake. It was hypothesized that P adsorption with CaCO3 in the periphytic matrix would add to the removal of P from solution. Using (H3PO4)-P-32 and [P-32]ATP and a 0.01 M HCl extraction technique, P incorporated by epipelon was partitioned into biotic and abiotic compartments. The biotic compartment contained >83% of the incorporated P after 12h incubations. Biological demand exceeds abiotic adsorption in this P-limited system but adsorption mechanisms are responsible for a portion (< 15%) of water column P removal. (C) 2003 Elsevier B.V. All rights reserved.