Dissolved reactive phosphorus loads to western Lake Erie: the hidden influence of nanoparticles

Session: Nutrient Sources, Transport, and Internal Cycling (3)

Mark River, University of Pittsburgh, [email protected]

Abstract

Increased dissolved reactive phosphorus (DRP) fluxes in the Maumee River have been cited as a cause of recent hypoxia and toxic algal blooms in Western Lake Erie.  DRP is operationally defined as the molybdate-reactive P that passes through a 0.45?m filter, based on tradition dating back to the 1940s.  This dissolved versus particulate operationally-defined threshold may be limiting scientific understanding of the transport of reactive P in the Lake Erie watershed (and beyond).  Naturally-occurring nanoparticles smaller than 0.45?m can pass through filters, inflating DRP values.  Transmission electron microscopy of filtered samples from the Maumee River reveals nanoparticles of various mineralogy, which are rich in P.  By analyzing public data, we estimate that approximately half of the DRP flux in the Maumee River is not truly dissolved orthophosphate; rather it is instead particulate P which has passed through 0.45?m filters.  We also conducted a centrifugation experiment on previously-filtered samples which likewise removed 40% of DRP and 75% of Fe.  The influence of nanoparticles on DRP loads to Lake Erie has implications including: 1) helping to elucidate where reactive P originates on the landscape; 2) designing best management practices; and 3) improving our models of ecological response of nonpoint P loading.