Isotopic evidence for the source and fate of phosphorus in Everglades wetland ecosystems

► Oxygen isotopic analysis of phosphate is a useful tool for studying source and degree of microbial cycling of phosphorus (P) in freshwater ecosystems. ► P was quickly cycled in the water column and the dissolved inorganic phosphate (DIP) pool consisted entirely of biologically cycled P in relatively pristine areas of the Everglades wetland ecosystem. ►In wetland areas highly impacted by agricultural runoff, biological cycling of P was not rapid enough to completely remove the fertilizer δ18O signature. ►DIP pool in these areas consisted of biologically cycled P as well as fertilizer P, with fertilizer P accounting for about 15-100% of the total DIP.