Phosphorus cycling in a periphyton-dominated freshwater wetland

Periphyton, the community of microorganisms growing on submerged substrates, is a conspicuous feature of shallow, interior Everglades slough habitats. This research was conducted to identify major pathways and storages involved in P cycling. Specifically, this work centered on mechanisms functioning in unimpacted, periphyton dominated areas of the northern Everglades (Water Conservation Area 2A). The field site was dominated by calcareous blue-green algae (cyanobacteria).; Total P content was in the order of benthic (BP) {dollar}>{dollar} epiphytic (EP) = floating (FP) periphyton, and was in the range of 130-390 mg kg{dollar}sp{lcub}-1{rcub}{dollar}. Calcium carbonate content accounted for 20-50% of periphyton dry weight. Total P in BP was approximately equal to that in the surficial soil. Inorganic P (P{dollar}sb{lcub}rm i{rcub}{dollar}), associated with Ca, was highest in the surface 0-2 cm of soil and was directly related to of increased CaCO{dollar}sb3{dollar} deposition due to calcification by BP. The presence of BP on the soil surface was shown to maintain higher soil porewater concentrations of dissolved reactive P (DRP) and Ca{dollar}sp{lcub}2+{rcub}{dollar} than when the BP was removed.; Phosphorus uptake rates, measured in the laboratory, were 0.04-0.62 {dollar}mu{dollar}mol P g{dollar}sp{lcub}-1{rcub}{dollar} min{dollar}sp{lcub}-1{rcub}{dollar} (dry weight periphyton) for EP and 0.02-0.2 {dollar}mu{dollar}mol P g{dollar}sp{lcub}-1{rcub}{dollar} min{dollar}sp{lcub}-1{rcub}{dollar} for BP. Uptake parameters for EP were; V{dollar}sb{lcub}rm max{rcub}{dollar} = 0.85 {dollar}mu{dollar}mol P g{dollar}sp{lcub}-1{rcub}{dollar} min{dollar}sp{lcub}-1{rcub}{dollar}, K{dollar}sb{lcub}rm m{rcub}{dollar}= 9.9 {dollar}mu M{dollar}, and for BP were; V{dollar}sb{lcub}rm max{rcub}{dollar} = 0.10 {dollar}mu{dollar}mol P g{dollar}sp{lcub}-1{rcub}{dollar} min{dollar}sp{lcub}-1{rcub}{dollar}, K{dollar}sb{lcub}rm m{rcub} = 2.5 mu M{dollar}. Inorganic (P{dollar}sb{lcub}rm i{rcub}{dollar}) and organic P (P{dollar}sb{lcub}rm o{rcub}{dollar}) uptake rates by periphyton was higher under field conditions than under laboratory cultures. Both biotic and abiotic processes were shown to regulate P uptake by periphyton, with CaCO{dollar}sb3{dollar} as a barrier between living periphyton and adjacent water column. Abiotic uptake accounted for 10-30% of {dollar}sp{lcub}32{rcub}{dollar}P activity in one hour and 3-8% after 12 hours, suggesting that P initially associated with CaCO{dollar}sb3{dollar} surfaces is biotically incorporated with time.; In situ P uptake was greater in cores with intact BP layers (+BP) than in cores without BP ({dollar}-{dollar}BP). Under greenhouse conditions {dollar}-{dollar}BP uptake of P was initially as rapid as +BP cores. With continued P loading {dollar}-{dollar}BP cores lost the ability to effectively remove water column P. This suggests adsorption to soil mineral surfaces, or uptake by soil microbes can rapidly assimilate P but have limited capacity for P removal. Partitioning {dollar}sp{lcub}32{rcub}{dollar}P in intact cores (+BP) resulted in 14% abiotic uptake vs. 86% biotically incorporated.; Laboratory studies were conducted to determine conditions necessary for CaCO{dollar}sb3{dollar} precipitation and subsequent P coprecipitation. Phosphorus was removed from solution when pH {dollar}>{dollar} 8.6 for prolonged periods. Phosphorus reduction was not observed when solution pH varied between 7.0-8.8 on 12 h cycles. Mineral equilibria modeling, using SOILCHEM, generally predicted hydroxyapatite as the stable mineral P form in field and reactor solutions. X-ray diffraction analysis of dried BP, and peat soil from 0-2 cm and 2-5 cm depths showed the presence of calcite but not of mineral Ca-P.; Periphyton activity controls short-term P retention via biotic uptake and creates conditions, by influencing Ca{dollar}sp{lcub}2+{rcub}{dollar} activity, that increases long-term, stable, ab...