Partitioning the contributions of minerogenic particles and bioseston to particulate phosphorus and turbidity

Abstract

Protocols to partition the contributions of bioseston and minerogenic particles to turbidity (Tn) and particulate phosphorus (PP), as described by summations of the 2 components, are developed, tested, and applied. The analysis is based on coincident observations of Tn, PP, chlorophyll a (Chl), and the summation of the projected areas of individual minerogenic particles per unit volume (PAVm) for the wide variations encountered in time and between near-shore and pelagic sites over an 8-year study of Cayuga Lake, New York. PAVm was determined from an individual particle analysis technique, scanning electron microscopy interfaced with automated image, and X-ray analyses (SAX). The partitionings are based on a stoichiometric approach that adopts Chl and PAVm as the metrics of bioseston and minerogenic particles, respectively, and estimates developed here for stoichiometric ratios that relate Tn and PP to these 2 components. The systematically higher Tn and PP levels at the near-shore site, particularly following runoff events, are demonstrated to be a result of elevated PAVm associated with allochthonous inputs. A reasonably good match of the partitioned 2-component summations with bulk observations is reported. Application of the 2-component PP model establishes minerogenic particles made, on average, noteworthy (~10%) to substantial (≥20%) contributions to PP. The minerogenic particle component of PP was largely responsible for the greater summer average total phosphorus (TP) concentrations at the near-shore versus the pelagic site, the interannual variations in the differences between these sites, and exceedance of the TP water quality limit at the near-shore site. Minerogenic particles were the dominant component of Tn, a finding that is demonstrated to be consistent with optical theory, based on the much greater efficiency of side-scattering for minerogenic versus organic particles.