H33C-01
Field-testing of a Passive Surface Water Flux Meter for the Direct Measurement of Water and Solute Mass Fluxes
The measurement of water and solute mass discharges in surface water flow systems is a fundamental hydrologic task for ecological and economic decision making. However, due to the extensive monetary, labor, and time costs of traditional monitoring devices and methods, many water quality monitoring programs lack the resources necessary to provide comprehensive descriptions of surface water impairments. The Passive Surface Water Flux Meter (PSFM) is a recently developed passive sampling device that measures water and solute fluxes within flowing surface water bodies. Devoid of mechanical components and power supply requirements, the relatively low-maintenance, low-cost design of the PSFM gives it considerable potential as a tool for extensive, large-scale surface water quality characterization and monitoring. The novelty of the PSFM extends to its direct mass-based approach to solute flux measurement, as compared to conventional, indirect concentration-based approaches. During this field-testing campaign, the PSFM was deployed in flowing surface water bodies of north- central Florida. The device contained a dual-packed porous media cartridge that performed simultaneous ion exchange to determine phosphate mass flux and equilibrium tracer desorption to determine water flux within the stream. The PSFM demonstrated accurate measurement of steady-state water and phosphate mass fluxes to within 15% over a range of stream velocities, solute concentrations, and deployment durations. The PSFM design described here was found to perform well in steady-flow conditions. The device was also shown to be effective under transient conditions of limited variability, but full transient testing remains for future work.
H33C-02
An Investigation of the Effects of Body Design on Measurement Accuracy and Optimal Deployment Duration of a Passive Surface Water Flux Meter
Water quality monitoring is essential for evaluating and complying with Total Maximum Daily Loads (TMDL). Conventional methods for gathering water and solute flux data from surface waters involves collecting, compiling and analyzing discrete point measurements to obtain cumulative flux data. The Passive Surface Water Flux Meter (PSFM) is designed to measure water and solute fluxes by automatically integrating instantaneous data in situ; therefore replacing the need for individual sample collections and data processing. A small cartridge within the device contains two types of porous media which simultaneously sorb solutes and release a resident tracer so that solute and water flux may be quantified. The PSFM utilizes the natural pressure gradient created by water flowing around the device. This gradient is used to induce flow through a small cartridge containing sorptive porous media pre-equilibrated with a resident tracer. In general, higher velocities correlate to larger pressure gradients across the cartridge and therefore reduce the amount of time a device can be deployed. However, the magnitude of the pressure gradient depends not only on the velocity of the water but the body design of the device. Body design can be modified to adjust the range of pressure gradients produced. Devices that are more blunt (cylindrical) in nature create higher gradients than more streamlined devices. Therefore, optimal shape and water velocity play an important role in the length of time a PSFM can be deployed and the accuracy of the measurements. Two designs, a blunt (cylindrical) and a streamlined (Joukowsky profile) device, were tested in this study. Laboratory experiments were performed in a large tilting flume to determine maximum deployment times for both devices across velocities ranging from 25-65 cm/s. Optimal deployment time was determined from the amount of resident tracers remaining within the cartridge and accuracy was determined by comparing measurement performance between both devices. Results from these experiments showed that the blunt device provided more accurate water and solute flux measurements at lower velocities, whereas the streamlined shape provided more accurate measurements at higher velocities. Results also indicated that optimal deployment time is dependent on the type of resident tracer as well as device shape. These findings indicate that the shape profile of the PSFM may be adjusted to provide the most accurate cumulative water and solute flux measurements when deployed in flow regimes of known hydrological conditions.
H33C-03
Evaluating Water Supply and Water Quality Management Options for Las Vegas Valley
The ever increasing population in Las Vegas is generating huge demand for water supply on one hand and need for infrastructure to collect and treat the wastewater on the other hand. Current plans to address water demand include importing water from Muddy and Virgin Rivers and northern counties, desalination of seawater with trade- payoff in California, water banking in Arizona and California, and more intense water conservation efforts in the Las Vegas Valley (LVV). Water and wastewater in the LVV are intrinsically related because treated wastewater effluent is returned back to Lake Mead, the drinking water source for the Valley, to get a return credit thereby augmenting Nevada's water allocation from the Colorado River. The return of treated wastewater however, is a major contributor of nutrients and other yet unregulated pollutants to Lake Mead. Parameters that influence the quantity of water include growth of permanent and transient population (i.e., tourists), indoor and outdoor water use, wastewater generation, wastewater reuse, water conservation, and return flow credits. The water quality of Lake Mead and the Colorado River is affected by the level of treatment of wastewater, urban runoff, groundwater seepage, and a few industrial inputs. We developed an integrated simulation model, using system dynamics modeling approach, to account for both water quantity and quality in the LVV. The model captures the interrelationships among many variables that influence both, water quantity and water quality. The model provides a valuable tool for understanding past, present and future pathways of water and its constituents in the LVV. The model is calibrated and validated using the available data on water quantity (flows at water and wastewater treatment facilities and return water credit flow rates) and water quality parameters (TDS and phosphorus concentrations). We used the model to explore important questions: a)What would be the effect of the water transported from the northern counties on the water supply and water quality of Lake Mead? b)What would be the impact of increased reuse of wastewater on return credits? c)What would be the effect of treating runoff water on the load of nutrients to Lake Mead?
H33C-04
Dioxin Chronology and Fluxes in Sediments of the Houston Ship Channel, Texas: Influences of Non-steady State Sediment Transport and Total Organic Carbon
Polychlorinated dibenzo-p-dioxins and dibenzofurans (dioxins) are persistent contaminants that bio-accumulate and pose serious risks to biota and humans. The primary objective of this study was to determine the history and mechanisms of dioxin accumulation in sediments of the Houston Ship Channel (HSC) using analytical data on natural and anthropogenic radionuclides (7Be, 137Cs and 210Pb) and dioxins. Results showed that present-day sedimentary dioxin accumulation rates are orders of magnitude higher than atmospheric inputs to the HSC, as determined from a wetland sediment core (FW1) and direct measurements. Most stations showed dioxin peaks in the near surface, indicating continuing inputs despite federal regulations. Stations with high dioxin inventories (11270 > 11193 > 16499 > 15979 > 11261) reflect accentuated accumulation in the HSC as one moves west towards Buffalo Bayou (11270, 15979), at the confluence of the HSC and the San Jacinto River (11261) and upstream in the San Jacinto River (11193). While station 11270 had the highest dioxin inventory, and nearby station 11261 had the highest sediment accumulation rates and dioxin fluxes, present-day dioxin fluxes at 11270 are less than average fluxes and inventories for station 11261 are less than average inventories, for all sites. These results support the interpretation that the HSC is influenced by episodic sediment resuspension, erosion and lateral transport processes driven by tides, wind, shipping and dredging, which can cause intermittently high accumulations of dioxins.
H33C-05
How frequently do rivers have to be sampled to accurately estimate carbon fluxes?: LOADEST (Load Estimator) estimates on the Mississippi River alkalinity flux for 1990- 1998.
Riverine flux is one of the most important terms balancing many global elemental cycles. Since flux is estimated by multiplying concentrations and discharge, it would be ideal to collect the both data frequently. However, compared to estimating daily discharge, analyzing concentrations of riverine constituents on daily basis is expensive. Using a new data base from near the mouth of the Mississippi River, where alkalinity has been monitored on daily basis, we explored the importance of sample size to accurate flux estimates. Combining daily discharge values from the nearby USGS gauging stations at Vicksburg (station id: 07289000), daily alkalinity flux was calculated for the Mississippi over 1990 - 1998. The daily alkalinity fluxes were also estimated using USGS Loadest software with a variety number of observations from 2 to 52 observations per year, which corresponds to bi-seasonal and weekly observations, respectively. Results demonstrate that even with a small number of observations, the Loadest software successfully estimates yearly fluxes.