Grantee Research Project Results
Tracer Release Experiments in the Hudson RiverEPA Grant Number: U915241
Title: Tracer Release Experiments in the Hudson River
Investigators: Ho, David T-Y.
Institution: Columbia University
EPA Project Officer: Just, Theodore J.
Project Period: January 1, 1997 through January 1, 2000
Project Amount: $102,000
RFA: STAR Graduate Fellowships (1997)
Research Category: Ecological Indicators/Assessment/Restoration , Academic Fellowships , Fellowship - Geology
The objectives of this research project are to: (1) investigate mixing and gas exchange in the upper, nontidal part of the Hudson River; (2) provide information on mixing, gas exchange, and biological changes within a "tagged" watermass; and (3) provide insights into the relative importance of the different processes governing the dissolved oxygen (DO) budget.Approach:
I will conduct two tracer experiments in the Hudson River. In the first experiment, the 3He-SF6 method will be used to investigate mixing and gas exchange in the upper, nontidal reach of the Hudson River. This area of the river is interesting because there are many navigational dams and large waterfall (Baker's Fall; > 15 meters relief), which are likely to influence transport and fate of volatile pollutants. Because this is an area of the river where two capacitor plants discharged large quantities of polychlorinated biphenyls (PCBs) directly into the Hudson River in the past and where fresh PCB inputs via fissures in the surrounding bedrock have occurred as recently as 1994, it is important to improve our understanding of the spreading of pollutants and the effects of hydraulic structures on mixing and gas exchange.
The second planned experiment will occur in the intermediate salinity reaches of the Hudson River. The approach of this experiment is similar to the one in the upper Hudson. The focal point of the experiment will be a Lagrangian study following a water mass tagged with SF6 and 3He. The tracers will be injected into the deep water (below the salinity gradient) in the intermediate salinity reaches of the Hudson River where a strong density gradient exists between the top and bottom layer because of saline water intrusion. The procedure for injection of the tracers will be similar to that previously used in coastal and open-ocean experiments (Upstill-Goddard, et al., 1991; Watson, et al., 1991; Coale, et al., 1996). Hudson River water will be drawn from the deep layers into a large container on the deck of a boat. After the water has been saturated with SF6 and 3He, it will be pumped back into the deep water. This procedure differs from the first experiment in the upper Hudson, and allows injected tracers to be confined to the bottom waters. The procedures for sampling and mapping the tracer patch will be the same as those described for the first experiment. The temporal evolution of the tracer distributions will be monitored by daily collection of water samples from small boats. Simultaneously, the DO, partial pressure of CO2 (pCO2), total CO2 (TCO2), alkalinity, salinity, temperature, and nutrient concentrations (NO2, NO3, NH4, PO4, H4SiO4) in the tagged water mass also will be measured. The experiment will provide insights into physical, chemical, and biological changes in a tagged water mass over time. The physical component of the study will yield information about vertical mixing and horizontal dispersion in the Hudson River. Physicochemical studies will revolve around determining the rate of air-water gas exchange. Biological measurements will concentrate on DO, pCO2, TCO2, alkalinity, and nutrient concentrations.
The two tracer experiments will help to establish the contributions of several different processes that contribute to the water quality of the Hudson River. The first experiment will enable us to understand the behavior of volatile substances discharged into the upper Hudson River and the effects of the hydraulic structures (e.g., waterfalls, dams) on gas exchange. Simultaneously, we will derive important information on dispersion coefficients from the temporal evolution of the tracer patch. The second experiment will enable us to better understand the relative importance of advection/dispersion, gas exchange, and in situ production/consumption for the DO dynamics of the estuary portion of the Hudson River. Furthermore, the mixing coefficients and gas exchange rates derived from the two experiments will be valuable constraints for the calibration of models used for the simulation of pollutant transport and/or the balance of DO in the Hudson River.Supplemental Keywords:
fellowship, Hudson River, gas exchange, dissolved oxygen, DO, polychlorinated biphenyls, PCBs, nutrients, pollutants, pollutant transport, air-water gas exchange.