Anthony R. Prestigiacomo

Whole-lake nitrate addition for control of methylmercury in mercury-contaminated Onondaga Lake, NY

Methylmercury (MeHg) strongly bioaccumulates in aquatic food webs resulting in exposure to humans and wildlife through consumption of fish. Production of MeHg is promoted by anaerobic conditions and the supply of inorganic Hg (Hg(2+)), sulfate (SO4(2-)), and labile organic carbon. The anaerobic sediments of stratified lakes are particularly active zones for methylation of Hg(2+) and can be an important source of MeHg to the water column during summer anoxia and fall turnover. Nitrate (NO3(-)) addition has recently been proposed as a novel approach for the control of MeHg accumulation in the hypolimnia of Hg-contaminated lakes. In 2011, a whole-lake NO3(-) addition pilot test was conducted in Hg-contaminated Onondaga Lake, NY with the objective of limiting release of MeHg from the pelagic sediments to the hypolimnion through maintenance of NO3(-)-N concentrations >1mgN/L. A liquid calcium-nitrate solution was added to the hypolimnion as a neutrally buoyant plume approximately three times per week during the summer stratification interval. Maximum hypolimnetic concentrations of MeHg and soluble reactive phosphorus (SRP) decreased 94% and 95% from 2009 levels, suggesting increased sorption to Fe and Mn oxyhydroxides in surficial sediments as the regulating mechanism. Increased MeHg concentrations in the upper waters during fall turnover, which had been a generally recurring pattern, did not occur in 2011, resulting in decreased exposure of aquatic organisms to MeHg. Over the 1992-2011 interval, the hypolimnetic NO3(-) supply explained 85% and 95% of the interannual variations in hypolimnetic accumulations of SRP and MeHg, respectively.

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 streams 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.

Resolution of Turbidity Patterns from Runoff Events in a Water Supply Reservoir, and the Advantages of In Situ Beam Attenuation Measurements

Abstract The impact of runoff events on light scattering, or turbidity, levels in a water supply reservoir, and the comparative performance of three surrogate metrics of light scattering, are documented for the spring through fall interval of a high runoff year. The analysis is supported by: (1) frequent (42 d) field measurements of the beam attenuation coefficient at 660 nm (c660) and “optical” backscattering (OBS) collected with rapid profiling instrumentation at multiple sites; (2) laboratory measurements of c660 and turbidity (Tn); and (3) characterizations of inorganic particles with scanning electron microscopy interfaced with automated image and X-ray analyses. Conspicuous increases in light scattering levels are reported following runoff events, as reflected in increases in c660, OBS and Tn, associated with terrigenous inputs of clay minerals. The extent of this impact is demonstrated to be driven by the magnitude of the runoff event. Terrigenous inputs of turbidity are shown to enter as density currents, which travel the entire length of the reservoir for major runoff events, manifested as peak scattering levels in subsurface layers. Strong longitudinal and lateral differences are documented soon after runoff peaks. Scattering levels and spatial gradients are shown to diminish rapidly, with pre-event conditions approached within a week. Systematically lower c660 values are reported for laboratory measurements compared to in situ observations, particularly at high scattering levels, consistent with the operation of particle coagulation. In situ measurement of c660is identified as the preferred surrogate metric of light scattering.

Tripton, trophic state metrics, and near-shore versus pelagic zone responses to external loads in Cayuga Lake, New York, U.S.A.

An analysis of limnological and input monitoring data for Cayuga Lake, New York, U.S.A., is presented that addresses differences in trophic state metrics and turbidity between pelagic waters and a shallow (< 6 m) near-shore area (shelf) that receives multiple inputs. The effects of tripton (inanimate particles) on the observed patterns, and the contrasting responses of the shelf to local inputs of tripton versus phosphorus (P), are demonstrated. The analysis is based on a combination of long-term monitoring and shorter-term studies, including: (1) 10 to 20 years of concentrations of chlorophyll-a (Chl), total P (TP), and other forms of P; (2) 10 years of Secchi disc (SD) and surrogates of the light scattering coefficient, including turbidity (T n ) and the beam attenuation coefficient at 660 nm [c(660)]; (3) loading estimates of T n and forms of P in point sources and tributaries to the shelf (4 to 10 y) and; (4) longitudinal patterns of thermal stratification, fluorometric Chl, and c(660) from a lake-wide 40 site transect; and (5) 10 years of hourly measurements of near-surface temperature on the shelf. The generally higher TP, particulate P, c(660), and T n , and lower SD on the shelf compared to pelagic waters, particularly after runoff events, is shown to reflect higher tripton levels in the near-shore area. Tripton was also an important regulator of these attributes in pelagic waters. The effects of tripton compromise TP and SD as trophic state metrics in this lake. The light scattering and clarity impacts of tripton are demonstrated to be primarily attributable to clay mineral particles in the 1-10 μm size range. Despite the P loads received from local sources, summer average Chl levels on the shelf were not significantly higher than in bounding pelagic waters because the flushing rate associated with mixing processes, particularly from seiche activity, was high compared to phytoplankton growth rates.

Apportionment of bioavailable phosphorus loads entering Cayuga Lake, New York

The integration of the phosphorus (P) bioavailability concept into a P loading analysis for Cayuga Lake, New York, is documented. Components of the analyses included the: (1) monitoring of particulate P (PP), soluble unreactive P (SUP), and soluble reactive P (SRP), supported by biweekly and runoff event-based sampling of the lakes four largest tributaries; (2) development of relationships between tributary P concentrations and flow; (3) algal bioavailability assays of PP, SUP, and SRP from primary tributaries and the three largest point sources; and (4) development of P loading estimates to apportion contributions according to individual nonpoint and point sources, and to represent the effects of interannual variations in tributary flows on P loads. Tributary SRP, SUP, and PP are demonstrated to be completely, mostly, and less bioavailable, respectively. The highest mean bioavailability for PP was observed for the stream with the highest agriculture land use. Point source contributions to the total bioavailable P load (BAPL) are minor (5%), reflecting the benefit of reductions from recent treatment upgrades. The BAPL represented only about 26% of the total P load, because of the large contribution of the low bioavailable PP component. Most of BAPL (>70%) is received during high flow intervals. Large interannual variations in tributary flow and coupled BAPL will tend to mask future responses to changes in individual inputs.

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.

The effect of municipal wastewater effluent on nitrogen levels in Onondaga Lake, a 36-year record.

This work presents a retrospective analysis of long-term trends in loading of forms of nitrogen (N) from the Metropolitan Syracuse Wastewater Treatment Plant (Metro), N concentrations in the receiving urban lake (Onondaga Lake, New York), and related water quality status for the period from 1972 to 2007. The history of the evolution of treatment and discharge at Metro, as it affected N loading, is reviewed and forms the basis for identification of five regimes during which unifying conditions of loading and in-lake conditions prevailed. Changes in industrial waste inputs have complicated the effects of upgrades in treatment at Metro from primary (until 1978) to advanced (starting in 2004). Current N loading from Metro is approximately 35% lower than the peak levels observed in the late 1980s to late 1990s, but the areal rate to the lake remains extremely high (approximately 97 g/m(2).y), representing approximately 75% of the overall N load. Implementation of year-round nitrification treatment has resulted in transformation of the composition of the N load from Metro from ammonia (T-NH3) to nitrate (NO3(-)) dominance. High N concentrations have prevailed in the upper waters of the lake throughout the study period with averages of total N ranging from 2.6 to 4.3 mg/L for the five regimes. Total N levels and partitioning among the forms in the lake generally have tracked Metro loading conditions for the five regimes. The effects of Metro loading on seasonal in-lake patterns are demonstrated to be modified by both hydrologic inputs from tributaries and in-lake operation of biochemical processes. Resolution of these effects is supported by application of both empirical and dynamic mass balance models. Water quality problems related to high concentrations of forms of N are documented, including (1) augmentation of dissolved oxygen depletion during fall mixing from in-lake nitrification events, enabled by high T-NH3 levels; (2) violations of ammonia toxicity limits; and (3) violations of nitrite toxicity standards. These problems were either greatly ameliorated or eliminated by Metros most recent treatment upgrades. Prevailing conditions are considered in a management context, including (1) likelihood of exceedances of toxicity limits in the future and (2) potential role of elevated nitrate levels in preventing mobilization of methyl mercury from the lakes sediments.

Insights for the structure of a reservoir turbidity model from monitoring and process studies

Abstract An array of in situ and laboratory measurements were made and in situ settling velocity experiments were conducted to support identification of model structure features necessary to simulate transient turbidity impacts in Schoharie Reservoir, NY, from runoff events. The program included: (1) extended deployments of recording instruments measuring temperature (T) and specific conductivity (SC) in the primary tributary and the reservoir surface waters; (2) automatic sampling of the tributary during runoff events for laboratory turbidity (Tn) measurements; (3) collection of vertically detailed profiles of T, SC, and the beam attenuation coefficient at 660 nm (c660; a surrogate of Tn) at multiple sites along the longitudinal and lateral axes of the reservoir with rapid profiling instrumentation; (4) chemical and morphometric characterizations of individual particles from the tributary and reservoir during dry weather conditions and for a runoff event with scanning electron microscopy coupled with automated image analysis and X-ray microanalysis (SAX); and (5) in situ measurements of settling velocity (SV) as a function of particle size with a LISST-ST®. A strong positive relationship between Tn, associated primarily with clay minerals, and tributary flow (Q), and a negative relationship between SC and Q, were reported. The entry of the primary tributary as a plunging turbid density current because of its lower T, and associated spatial and temporal patterns in c660 and SC imparted in the reservoir, were documented for two runoff events. SC was identified as a viable tracer of the movement of density currents in the reservoir, and the internal contribution of resuspension to c660 levels was depicted. The results of SAX analyses demonstrated a substantial fraction (i.e., 30–40%) of the Tn that enters the reservoir from the primary tributary was associated with particles >9.1 μm in diameter that do not contribute to Tn levels in the lacustrine portions of the reservoir. Higher SV values were observed for larger particles, but were much lower than Stokes Law conditions, suggesting that they existed as aggregates. The monitoring and SV experiment results were considered within the context of the structural needs of turbidity models, for two levels of complexity, to simulate the transient impacts of runoff events on the reservoir. A two- or three-dimensional transport submodel will be necessary to represent spatial patterns, and a kinetics submodel will need to represent (either implicitly or explicitly) size dependent settling, particle coagulation, and sediment resus-pension.

Partitioning phosphorus concentrations and loads in tributaries of a recovering urban lake

Abstract The partitioning of phosphorus (P) loading to culturally eutrophic lakes according to sources is fundamental information to guide rehabilitation programs and support mathematical models. Patterns of concentrations and loading rates of forms of P are documented for the major tributaries of Onondaga Lake, New York, United States, an urban lake that has recently demonstrated marked recovery from extreme cultural eutrophy as a result of decreased P loading from a domestic wastewater treatment plant (WWTP). This analysis is based on long-term (19 yr) biweekly monitoring of total, dissolved, and soluble reactive forms of P at the mouths of the three largest tributaries, and shorter-term higher frequency monitoring of one of the streams at two sites to resolve rural versus urban contributions. Signatures of anthropogenic sources were identified, including: (1) combined sewer overflows, (2) leaky sewers or other dry weather discharges, and (3) hydrogeologic sediment sources. On an annual average basis, the prevailing tributary and WWTP contributions to the total P load are approximately 70 and 30%, respectively. However, in terms of effective P loading, that which can be used to support primary production during the critical summer months, the tributaries contributed substantially less (∼35%) of the P load. Under the prevailing WWTP loading rate, reductions in tributary loading from aggressive tributary loading management efforts (e.g., 20–30% decrease) would not be expected to yield conspicuous improvements in related features of lake water quality. However, noteworthy improvements are a reasonable expectation from such tributary management efforts following the mandated further reductions in WWTP loading.

Characterizations and modeling of turbidity in a water supply reservoir following an extreme runoff event

Abstract The findings from an integrated program of short- and long-term monitoring, individual particle analyses (IPA), and mechanistic modeling to characterize and simulate the turbidity (Tn) effects of an extreme runoff event (2011) on a water supply reservoir were documented. A robotic profiling platform and rapid profiling instrumentation resolved turbidity and temperature (T) patterns in time and space in the reservoir. Metalimnetic enrichment in Tn following the event was reported and attributed to the entry of turbid stream water as density currents, or plunging inflows. The diminishment of high Tn levels following the event was well represented by a first-order loss rate of about 0.023 d−1. The highest Tn levels were avoided in water withdrawn for the water supply following the event by selection of vertical intake alternatives, although Tn values in the withdrawal remained distinctly above typical baseline conditions for nearly 2 months. Based on IPA, the Tn-causing particles were mostly clay minerals in the 1–20 μm size range. The operation of sorting processes determining settling losses from the minerogenic particle population, according to their size and shape, following the runoff event was resolved. The set-up and testing of a mechanistic Tn model, composed of 2 submodels, a 2-dimensional hydrothermal/transport submodel, and a Tn kinetics submodel, is described. The hydrothermal/transport submodel was tested separately and performed well in simulating the dynamics of the reservoir’s stratification regime and the entry of the dense streams as plunging inflows during the extreme runoff event. The overall Tn model needed to represent the loss processes of both settling and coagulation to perform well in simulating the in-reservoir and withdrawal Tn patterns following the runoff event.