Transport of Iron and Phosphorus By Authigenic Nanoparticles in Baseflow of the Southern Piedmont.

Naturally-occurring amorphous nanoparticles containing iron (Fe) and phosphorus (P) have been identified at the anoxic/oxic interface of various aquatic ecosystems, forming upon the oxidation of reduced Fe. Little is known about the prevalence of these authigenic nanoparticles in streams, their impact on biogeochemical fluxes, or the bioavailability of P associated with them. In this paper we used transmission electron microscopy to document the presence of crystalline and amorphous nanoparticles in baseflow of urban and rural streams in the southern Piedmont region of the U.S. We used a simple centrifugation and ultrafiltration technique to separate amorphous nanoparticles from truly dissolved (<1 kDa) and crystalline mineral/coarse organic fractions in baseflow, employing three different quality control methods to verify a successful separation. This allowed us to quantify the amount of Fe and P in three different fractions of baseflow: truly dissolved, amorphous nanoparticles, and crystalline mineral/coarse organic particles. Amorphous nanoparticles often transport the majority of Fe and P at baseflow, depending upon seasonality and the time elapsed since the last storm event.