Stream Phosphorus Transport in the Lake Tahoe Basin, 1989–1996

Lake Tahoe is undergoing the initial stages of culturaleutrophication due to human alteration of the airshed andwatershed. The lake's switch from nitrogen (N) to phosphorus (P)limitation has been attributed primarily to atmospheric Nloading. This places an increased importance on controllingwatershed movement of P to the lake. A stream water qualitymonitoring data set consisting of nine streams in the Lake Tahoebasin has been analyzed to characterize the spatiotemporalvariation of P delivery to the lake. This data is from the LakeTahoe Interagency Monitoring Program (LTIMP), which providesscientific data for planning and regulatory agencies to addressenvironmental problems in the Lake Tahoe basin. Results indicatethat P delivery (concentrations, loads) varies greatly atinterannual, seasonal, and spatial scales. Annual and seasonaltotal P (TP) concentrations can vary up to three orders ofmagnitude in a given stream and are strongly associated withsuspended sediment. Particulate P is the major form of Ptransported by Tahoe streams and was strongly correlated withpercent surficial geologic deposits, which are primarily locatednear streams. Tahoe streams with the highest annualP concentrations often had the lowest annual P loads, and visaversa. P loading is greatest during the spring snowmelt (75% ofannual average). Potential watershed parameters influencing Pdelivery to Lake Tahoe have been identified as precipitation,basin area, basin steepness, and road and human developmentcoverage. Results also suggest that human development impacts onstream P loads are most prevalent during high precipitationyears. Identification and quantification of stream sediment andP sources such as streambanks and impervious surface isnecessary to aid in watershed restoration efforts.     

Aggregation of Adenovirus 2 in Source Water and Impacts on Disinfection by Chlorine

It is generally accepted that viral particles in source water are likely to be found as aggregates attached to other particles. For this reason, it is important to investigate the disinfection efficacy of chlorine on aggregated viruses. A method to produce adenovirus particle aggregation was developed for this study. Negative stain electron microscopy was used to measure aggregation before and after addition of virus particles to surface water at different pH and specific conductance levels. The impact of aggregation on the efficacy of chlorine disinfection was also examined. Disinfection experiments with human adenovirus 2 (HAdV2) in source water were conducted using 0.2 mg/L free chlorine at 5 °C. Aggregation of HAdV2 in source water (≥3 aggregated particles) remained higher at higher specific conductance and pH levels. However, aggregation was highly variable, with the percentage of particles present in aggregates ranging from 43 to 71 %. Upon addition into source water, the aggregation percentage dropped dramatically. On average, chlorination CT values (chlorine concentration in mg/L × time in min) for 3-log₁₀ inactivation of aggregated HAdV2 were up to three times higher than those for dispersed HAdV2, indicating that aggregation reduced the disinfection rate. This information can be used by water utilities and regulators to guide decision making regarding disinfection of viruses in water.     

Laboratory validation study of new vapor‐phase‐based approach for groundwater monitoring

Recent improvements in field‐portable analytical equipment allow accurate on‐site measurement of VOCs present in air at concentrations of less than 0.1 parts per million volume (ppmv). The objective of this project is to determine if the use of these instruments for vapor‐phase measurements of headspace in a monitoring well can serve as a reliable and accurate method for monitoring volatile organic compound (VOC) concentrations in groundwater under equilibrium conditions. As part of a comprehensive research project investigating the utility of this proposed monitoring method, the authors have completed a laboratory validation study to identify instruments and sample‐collection methods that will provide accurate measurement of VOC concentrations in groundwater. This laboratory validation study identified two field‐portable instruments (a gas chromatograph and a photoionization detector) with sufficient sensitivity to measure VOCs in groundwater at concentrations below typical monitoring standards (i.e., 1 to 5 μg/L). The accuracy and precision of these field instruments was sufficient to satisfy typical data‐quality objectives for laboratory‐based analysis. In addition, two sample‐collection methods were identified that yield vapor‐phase samples in equilibrium with water: direct headspace sampling and passive diffusion samplers. These sample‐collection methods allow the field instruments (which measure VOC concentrations in vapor‐phase samples) to be used to measure VOC concentrations in water. After further validation of these sample‐collection methods in the field, this monitoring method will provide a simple way to obtain accurate real‐time measurements of VOC concentrations in groundwater using inexpensive field‐portable analytical instruments. © 2009 Wiley Periodicals, Inc.     

Correlations between in situ denitrification activity and nir-gene abundances in pristine and impacted prairie streams

Denitrification is a process that reduces nitrogen levels in headwaters and other streams. We compared nirS and nirK abundances with the absolute rate of denitrification, the longitudinal coefficient of denitrification (i.e., K_den, which represents optimal denitrification rates at given environmental conditions), and water quality in seven prairie streams to determine if nir-gene abundances explain denitrification activity. Previous work showed that absolute rates of denitrification correlate with nitrate levels; however, no correlation has been found for denitrification efficiency, which we hypothesise might be related to gene abundances. Water-column nitrate and soluble-reactive phosphorus levels significantly correlated with absolute rates of denitrification, but nir-gene abundances did not. However, nirS and nirK abundances significantly correlated with K_den, as well as phosphorus, although no correlation was found between K_den and nitrate. These data confirm that absolute denitrification rates are controlled by nitrate load, but intrinsic denitrification efficiency is linked to nirS and nirK gene abundances.     

Noncatalytic Auto Exhaust Combustor

Present methods for the determination of carbon monoxide are discussed including indicator tubes, the iodine pentoxide reaction and measurement by gas chromatography. In the gas chromatographic method an air sample is separated on a gas-solid chromatogra-phic column and the separated CO is converted to methane by hydrogenation at elevated temperature. The separated CO, in the form of methane, is passed into a hydrogen flame detector and measured. The conversion from CO to methane allows the use of a sensitive ionization detector in place of the thermal conductivity cell which is insufficiently sensitive for the measurement of trace amounts of CO. The optimum operating conditions are discussed. It is possible to determine one ppm CO in air. The iodine pentoxide reaction with CO has been combined with electrometric measurement. The iodine liberated is passed into a Ditte cell and the current generated is measured by an electrometerrecorder combination. This method is continuously direct reading with a permanent record. It is suitable for the continuous routine analysis of one ppm CO.     

Concentration and Recovery of Viruses from Water: A Comprehensive Review

Enteric viruses are a cause of waterborne disease worldwide, and low numbers in drinking water can present a significant risk of infection. Because the numbers are often quite low, large volumes (100–1,000 L) of water are usually processed. The VIRADEL method using microporous filters is most commonly used today for this purpose. Negatively charged filters require the addition of multivalent salts and acidification of the water sample to effect virus adsorption, which can make large-volume sampling difficult. Positively charged filters require no preconditioning of samples, and are able to concentrate viruses from water over a greater pH range than electronegative filters. The most widely used electropositive filter is the Virosorb 1MDS; however, the Environmental Protection Agency has added the positively charged NanoCeram filters to their proposed Method 1615. Ultrafilters concentrate viruses based on size exclusion rather than electrokinetics, but are impractical for field sampling or processing of turbid water. Elution (recovery) of viruses from filters following concentration is performed with organic (e.g., beef extract) or inorganic solutions (e.g., sodium polyphosphates). Eluates are then reconcentrated to decrease the sample volume to enhance detection methods (e.g., cell culture infectivity assays and molecular detection techniques). While the majority of available filters have demonstrated high virus retention efficiencies, the methods to elute and reconcentrate viruses have met with varying degrees of success due to the biological variability of viruses present in water.     

State-Space Modeling of the Relationship between Air Quality and Mortality

ABSTRACT

A portion of a population is assumed to be at risk, with the mortality hazard varying with atmospheric conditions including total suspended particulates (TSP). This at-risk population is not observed and the hazard function is unknown; we wish to estimate these from mortality count and atmospheric variables. Consideration of population dynamics leads to a state-space representation, allowing the Kalman Filter (KF) to be used for estimation. A harvesting effect is thus implied; high mortality is followed by lower mortality until the population is replenished by new arrivals.

The model is applied to daily data for Philadelphia, PA, 1973-1990. The estimated hazard function rises with the level of TSP and at extremes of temperature and also reflects a positive interaction between TSP and temperature. The estimated at-risk population averages about 480 and varies seasonally. We find that lags of TSP are statistically significant, but the presence of negative coefficients suggests their role may be partially statistical rather than biological. In the population dynamics framework, the natural metric for health damage from air pollution is its impact on life expectancy. The range of hazard rates over the sample period is 0.07 to 0.085, corresponding to life expectancies of 14.3 and 11.8 days, respectively.