Use of Robotic Monitoring to Assess Turbidity Patterns in Onondaga Lake, NY

Abstract

Selected temporal and vertical patterns of turbidity (Tn) are documented for an eutrophic urban lake, Onondaga Lake, NY, and their diagnostic value in identifying hydrodynamic and metabolic processes and in estimating clarity is established. The analysis is supported by five years (spring to fall) of daily robotic profiling of Tn, temperature (T), and dissolved oxygen, and an array of more temporally limited measurements that included Tn and T levels in the major tributary input of terrigenous solids; lake particle characterizations with a profiling particle counter and a scanning electron microscope coupled with automated image analysis and X-ray microanalysis; and Secchi disc transparency (SD). Major runoff events are demonstrated to cause conspicuous short-term increases in Tn that are manifested as metalimnetic peaks in summer and early fall, associated with the entry of the negatively buoyant primary tributary source as an interflow. The annual occurrence of Tn maxima within the oxycline of the metalimnion in October is documented. Evidence supports the position that this layer is a bacterial plate of oxidizing bacteria that develops seasonally in response to increasing vertical transport of reduced species from the hypolimnion with the approach to fall turnover. A strong relationship between SD and Tn in the upper waters is reported, that is demonstrated to have utility in resolving the dynamics of substantial changes in SD that occur in the lake during clear water phases.