Tributary Plunging in an Urban Lake (Onondaga Lake): Drivers, Signatures, and Implications¹

Abstract

A combination of long‐term fixed‐frequency and robotic monitoring information for a polluted urban lake, Onondaga Lake, New York, and two of its tributaries is used to resolve the propensity for, and occurrences of, tributary plunging. Cooler temperatures (T) and higher salinity (S) are primarily responsible for the elevated density and plunging of one of these polluted streams for the summer through early fall interval. In‐lake transport of this plunging tributary, which receives inputs from combined sewer overflows (CSOs), is tracked by its high S during dry weather, its high turbidity (Tn) with associated lower S (dilution with rainwater) following runoff events, and by its characteristic ionic composition. These signatures are documented extending from the creek mouth, through a connecting navigation channel, through the inflow zone of the lake, and into metalimnetic depths of pelagic portions of the lake. The entry of this polluted tributary below the depth interval(s) of primary production and contact recreation has important implications for the ongoing major rehabilitation program for this lake. The plunging phenomenon diminishes the benefits previously expected for related features of the lake’s water quality from ongoing management efforts to abate CSO inputs and reduce nonpoint nutrient loading from the tributary. Previously this tributary tended to instead enter the upper layers of the lake during the operation of an adjoining soda ash manufacturing facility (closure in 1986), as a result of high lake S caused by the industry’s ionic waste discharge.

Modeling the Fate and Transport of Plunging Inflows to Onondaga Lake

“…The predicted inflow centroid depths in spring (Figure a) were deeper, when lake stratification was relatively weak. Moreover, the predicted centroid depth was somewhat deeper on these three days for Onondaga Creek compared to Ninemile Creek, consistent with the usually greater negative buoyancy of Onondaga (Effler et al ., ). Differences in fraction of inflow to the UML (Path B) were also predicted for these days and the two tributaries.…”

“…Onondaga and Ninemile Creeks (Figure ) are the largest tributaries to the lake, with nearly equal size watersheds (~300 km 2 ), annual contributions to total inflow (~30%) (Effler, ), and similar loading rates for bioavailable forms of P (Effler et al ., ). Both streams are unusually saline, making noteworthy contributions to their negative buoyancies (Effler et al ., ). Natural groundwater seepage of sodium chloride brine occurs in Onondaga Creek (Owens et al ., ), while the salinity ( S , ‰) of Ninemile Creek is mostly residual waste from soda ash manufacturing (Effler and Matthews, ).…”

“…Ninemile Creek has a nonurban watershed. Monitoring of the buoyancy of Onondaga Creek relative to the lake, resolution of in‐lake interflow signatures, and the results of a single dye study (Effler et al ., ; Owens et al ., ), established that a portion of this inflow plunges during summer. Subsequently, the plunging of both Onondaga and Ninemile Creeks in the lake during a summer runoff event was established through detailed monitoring and simulations with ELCOM (Owens et al ., ).…”

“…Owens et al . () used ELCOM to simulate two plunging tributaries in Onondaga Lake, an urban lake where this phenomenon is potentially critical to major rehabilitation initiatives (Effler et al ., ; Matthews et al ., ). In preliminary testing, this model performed well in simulating features of transport for these two tributaries, including observed vertical distribution of inflow for deliberate (dye) and natural tracers, and realistic partitioning of flow inputs to the metalimnion (Path A) and the upper mixed layer (UML) (Path B).…”

Characterization of the dissolved phosphorus uptake kinetics for the effluents from advanced nutrient removal processes

“…The results from this study suggest one should characterize dissolved P according to its uptake kinetics instead of operationally classifying P fractions merely based on wet chemistry analyses (Hudson et al, 2000;Rigler, 1968). Also, recent research has shown that particulate P (PP) in municipal effluents may have a lesser contribution to effective P loading due to sediment deposition (Effler et al, 2009(Effler et al, , 2012. The assumption that the mineralization of particulate P is similar to dissolved P is also problematic.…”