Turbidity and suspended solids levels and loads in a sediment enriched stream: implications for impacted lotic and lentic ecosystems

Abstract

The implementation of an automated stream monitoring unit that features four probe-based turbidity (Tn) measurements per hour and the capability to collect frequent (e.g., hourly) samples for total suspended solids (TSS) analyses during runoff events to assess the dynamics of Tn, TSS and corresponding loads in sediment-rich Onondaga Creek, NY, was documented. Major increases in both Tn (maximum of 3,500 NTU) and TSS (maximum of 1630 mg/L) were reported for the stream during runoff events. Relationships between Tn, TSS and stream flow (Q) were developed and applied to support estimates of TSS loading (TSSL). Tn was demonstrated to be a better predictor of TSS than Q, supporting the use of the frequent field Tn measurements to estimate TSSL. During the year of intensive monitoring, 65% of the TSSL was delivered during the six largest runoff events that represented 18% of the annual flow. The high Tn levels and extensive in-stream deposition have negatively impacted the stream's biota and the esthetics of a downstream harbor. Onondaga Creek is reported to be the dominant allochthonous source of inorganic particulate material to downstream Onondaga Lake. These sediment inputs have important implications for the lake, within the context of two on-going rehabilitation programs aimed at contaminated lake sediments and the effects of extreme cultural eutrophication, by contributing substantially to sedimentation and turbidity. A satellite image documented the occurrence of a conspicuous turbidity plume that emanated from Onondaga Creek following a minor runoff event, suggesting such an effect is common and that related impacts are not spatially uniform.