The concentration, apparent molecular weight and chemical reactivity of silica from groundwater in southern Nevada

Sorption of radionuclides, metals and organic compounds to colloidal particles has been suggested to increase the mobility of these pollutants in groundwater. Because silicates and alumino-silicates can be important components of groundwater colloids, we have conducted a study to characterize the nature of silica in various springs and wells in Southern Nevada and to determine the extent that silica may be associated with colloidal particles that can participate in pollutant transport. The total silica content was measured using inductively coupled plasma emission spectroscopy (ICP). In addition, reactive silica was measured using the silica molybdate colorimetric technique. The apparent molecular weight of the silica was investigated using split-flow-lateral-transport-thin-cell-fractionation (SPLITT) which can readily distinguish between colloidal and low molecular weight associations. This study indicates that silica does not tend to form stable inorganic colloids in Southern Nevada groundwaters but exists as low molecular weight species. However, water from one of the test facilities on the Nevada Test Site (NTS) did contain stable siliceous colloids that could have important implications for the modeling the transport of radionuclides at this site.     

Remediation of MTBE from drinking water: air stripping followed by off-gas adsorption

The widespread use of methyl tertiary butyl ether (MTBE) as an oxygenate in gasoline has resulted in the contamination of a large number of ground and surface water sources. Even though air stripping has been proven to be an effective treatment technology for MTBE removal, off-gas treatment often is required in conjunction with it. This study evaluated the combined treatment technologies of air stripping followed by off-gas adsorption on a pilot scale for the treatment of MTBE-contaminated water. The effect of air/water ratios on the treatment efficiency was studied, and the mass transfer coefficient was determined. Air/water ratios of 105:1, 151:1, 177:1, 190:1, 202:1, and 206:1 were used, and a treatment efficiency of >99% was achieved for all the runs conducted. The depth of packing required to achieve maximum treatment efficiency decreased with increasing air/water ratio. Relative humidity (RH) impacts on the MTBE adsorption capacity of a granular activated carbon (GAC) and carbonaceous resin were determined from pilot plant studies. Breakthrough profiles obtained from the pilot plant studies conducted at 20, 30, and 50% RH indicated that GAC has a higher adsorptive capacity than resin. The adsorptive capacity of GAC decreased with increasing RH, whereas RH did not impact the resin adsorptive capacity.     

Development of emission factors for polycarbonate processing

Emission factors for selected volatile organic compounds (VOCs) and particulate emissions were developed while processing eight commercial grades of polycarbonate (PC) and one grade of a PC/acrylonitrile-butadiene-styrene (ABS) blend. A small commercial-type extruder was used, and the extrusion temperature was held constant at 304 degrees C. An emission factor was calculated for each substance measured and is reported as pounds released to the atmosphere/million pounds of polymer resin processed [ppm (wt/wt)]. Scaled to production volumes, these emission factors can be used by processors to estimate emission quantities from similar PC processing operations.     

THE UNITED NATIONS GROUND WATER EXPLORATION AND DEVELOPMENT PROGRAMME - A FIFTEEN YEAR PERSPECTIVE

The United Nations ground water exploration and development programme during 15 years of active life, has resulted in substantial socio-economic benefits to 57 developing countries through some 100 ground water projects. Systematic study, development and use of this important resource have contributed to intensification of agricultural production through supplemental irrigation from ground water; alleviation of water shortages in urban and industrial areas through construction of supply wells; improvement and stabilization of pastoral and rural economies, thereby counteracting in some measure adverse demographic trends of migration to the cities; and other related benefits in training, institutional development, and development of national water policies and plans.     

Assessment of relative accuracy in the determination of organic matter concentrations in aquatic systems

Accurate determinations of total (TOC), dissolved (DOC) and particulate (POC) organic carbon concentrations are critical for understanding the geochemical, environmental, and ecological roles of aquatic organic matter. Of particular significance for the drinking water industry, TOC measurements are the basis for compliance with US EPA regulations. The results of an interlaboratory comparison designed to identify problems associated with the determination of organic matter concentrations in drinking water supplies are presented. The study involved 31 laboratories and a variety of commercially available analytical instruments. All participating laboratories performed well on samples of potassium hydrogen phthalate (KHP), a compound commonly used as a standard in carbon analysis. However, problems associated with the oxidation of difficult to oxidize compounds, such as dodecylbenzene sulfonic acid and caffeine, were noted. Humic substances posed fewer problems for analysts. Particulate organic matter (POM) in the form of polystyrene beads, freeze-dried bacteria and pulverized leaf material were the most difficult for all analysts, with a wide range of performances reported. The POM results indicate that the methods surveyed in this study are inappropriate for the accurate determination of POC and TOC concentration. Finally, several analysts had difficulty in efficiently separating inorganic carbon from KHP solutions, thereby biasing DOC results.     

An ecosystem report on the Panama Canal: monitoring the status of the forest communities and the watershed

In 1996, the Smithsonian Tropical Research Institute and the Republic of Panama's Environmental Authority, with support fromthe United States Agency for International Development, undertook a comprehensive program to monitor the ecosystem of the Panama Canal watershed. The goals were to establish baselineindicators for the integrity of forest communities and rivers. Based on satellite image classification and ground surveys, the2790 km² watershed had 1570 km² of forest in 1997, 1080 km² of which was in national parks and nature monuments. Most of the 490 km² of forest not currently in protected areas lies along the west bank of the Canal, and its managementstatus after the year 2000 turnover of the Canal from the U.S. to Panama remains uncertain. In forest plots designed to monitorforest diversity and change, a total of 963 woody plant specieswere identified and mapped. We estimate there are a total of 850–1000 woody species in forests of the Canal corridor. Forestsof the wetter upper reaches of the watershed are distinct in species composition from the Canal corridor, and have considerably higher diversity and many unknown species. Theseremote areas are extensively forested, poorly explored, and harbor an estimated 1400–2200 woody species. Vertebrate monitoring programs were also initiated, focusing on species threatened by hunting and forest fragmentation. Large mammals are heavily hunted in most forests of Canal corridor, and therewas clear evidence that mammal density is greatly reduced in hunted areas and that this affects seed predation and dispersal. The human population of the watershed was 113 000 in 1990, and grew by nearly 4% per year from 1980 to 1990. Much of this growth was in a small region of the watershed on the outskirts of Panama City, but even rural areas, including villages near and within national parks, grew by 2% per year. There is no sewage treatment in the watershed, and many towns have no trashcollection, thus streams near large towns are heavily polluted. Analyses of sediment loads in rivers throughout the watershed did not indicate that erosion has been increasing as a result ofdeforestation, rather, erosion seems to be driven largely by total rainfall and heavy rainfall events that cause landslides.Still, models suggest that large-scale deforestation would increase landslide frequency, and failure to detect increases inerosion could be due to the gradual deforestation rate and the short time period over which data are available. A study of runoff showed deforestation increased the amount of water fromrainfall that passed directly into streams. As a result, dry season flow was reduced in a deforested catchment relative to aforested one. Currently, the Panama Canal watershed has extensive forest areasand streams relatively unaffected by humans. But impacts of hunting and pollution near towns are clear, and the burgeoningpopulation will exacerbate these impacts in the next few decades.Changes in policies regarding forest protection and pollution control are necessary.     

Response of Mercury Contamination in Fish to Decreased Aqueous Concentrations and Loading of Inorganic Mercury in a Small Stream

Approximately 250 000 kg of mercury was lost towater and soils at the U.S. Dept. of Energy Y-12 Plantin Oak Ridge, Tennessee in the 1950s and early 1960s. A creek originating within the plant receivedcontinuous inputs of waterborne mercury, predominantlyas dissolved inorganic mercury, from groundwater,streambed contamination, and sump and process waterdischarges to the contaminated storm sewer network.These produce aqueous total mercury concentrations of1–2 g L^-1 in the upper reaches of the stream,decreasing to about 0.1–0.2 g L^-1 in its lowerreaches. A program to reduce mercury concentrationsin the creek identified specific sources (buildingsumps, contaminated springwater seeps, foundationdrains, and contaminated piping) and rerouted wateraround contaminated portions of the drain system orcollected and treated mercury-contaminated waterbefore discharging it. As a result, waterbornemercury concentrations in the creek and total mercuryloading were reduced from 1.8 g L^-1 to0.6 g L^-1 and 100 to 20 g d^-1, respectively, in the last 5 yr.Mean mercury concentrations in fish nearest sourceareas in the creek headwaters decreased at roughly thesame rate as waterborne total mercury concentrationsover the past five years, but at the facility boundarydownstream the decline in mercury bioaccumulation wasmuch less. At sites 5–15 km farther downstream, nodecrease was evident. Dissolved methylmercury tendedto increase with distance downstream in a patterninverse to that noted for its dissolved inorganicmercury precursor.Improvements in water quality and modification ofweirs to allow the passage of fish have resulted inthe establishment of large populations of fish inmercury-contaminated headwater areas previously devoidof fish. It may be that the accumulation, retention,and eventual downstream transport of this reservoir ofbiologically incorporated methylmercury has acted tobuffer against expected reductions in mercury in fishat downstream sites.     

Effects of stage of colony cycle,context, and intercolony distance on conspecific tolerance by paper wasps (Polistes fuscatus)

Summary We observed in the field how resident females of the social wasp, Polistes fuscatus, treated female nestmates, non-nestmate first cousins, and unrelated non-nestmates. Behavioral observations were made 1, 3, 4, 6, 7, 8, and 11 weeks after the emergence of a colony's first workers. Resident females were highly tolerant of female nestmates but highly intolerant of unrelated non-nestmates throughout the post-worker-emergence phase of the colony cycle. First cousins were treated either highly tolerantly or highly intolerantly, although most cousins ( 63%) were treated highly intolerantly. The treatment of cousins suggests that they are treated either tolerantly (like nestmates) or intolerantly (like unrelated non-nestmates) depending on whether they fall above or below an acceptance threshold, respectively. Resident females did not significantly change their tolerance nestmates, first cousins, and unrelated females between different observation periods. However, all conspecifics were generally treated the most intolerantly 11 weeks post-worker-emergence, a time in the colony cycle when combs no longer contain brood. This decreased tolerance and its associated variance patterns late in the colony cycle are consistent with a more restrictive acceptance threshold. The optimal level of the acceptance threshold appears to be a compromise between the fitness consequences of accepting unrelated non-nestmates and rejecting one's nestmates. In a laboratory study, resident females were equally tolerant of female nestmates on and off the comb but significantly less tolerant of unrelated females on the comb than off the comb. Thus, females can modify their tolerance rapidly in different recognition contexts. In a second laboratory study, resident females were equally intolerant of unrelated females, regardless of whether they were from colonies 50 m or 50 km distant.Offprint requests to: G.J. Gamboa     

Napropamide residues in runoff and infiltration water from pepper production

A field study was conducted on a Lowell silty loam soil of 2.7% organic matter at the Kentucky State University Research Farm, Franklin County, Kentucky. Eighteen universal soil loss equation (USLE) standard plots (22 x 3.7 m each) were established on a 10% slope. Three soil management practices were used: (i) class-A biosolids (sewage sludge), (ii) yard waste compost, each mixed with native soil at a rate of 50 ton acre(-1) on a dry-weight basis, and (iii) a no-mulch (NM) treatment (rototilled bare soil), used for comparison purposes. Devrinol 50-DF "napropamide" [N,N-diethyl-2-(1-naphthyloxy) propionamide] was applied as a preemergent herbicide, incorporated into the soil surface, and the plots were planted with 60-day-old sweet bell pepper seedlings. Napropamide residues one hour following spraying averaged 0.8, 0.4, and 0.3 microg g(-1) dry soil in sewage sludge, yard waste compost, and no-mulch treatments, respectively. Surface runoff water, runoff sediment, and napropamide residues in runoff were significantly reduced by the compost and biosolid treatments. Yard waste compost treatments increased water infiltration and napropamide residues in the vadose zone compared to sewage sludge and NM treatments. Total pepper yields from yard waste compost amended soils (9187 lbs acre(-1)) was significantly higher (P < 0.05) than yield from either the soil amended with class-A biosolids (6984 lbs acre(-1)) or the no-mulch soil (7162 lbs acre(-1)).     

RIPARIAN LAND USES AND PRECIPITATION INFLUENCES ON STREAM BANK EROSION IN CENTRAL IOWA1

Human alterations to the Iowa landscape, such as elimination of native vegetation for row crop agriculture and grazing, channelization of streams, and tile and ditch drainage, have led to deeply incised channels with accelerated streambank erosion. The magnitude of streambank erosion and soil loss were compared along Bear Creek in central Iowa. The subreaches are bordered by differing land uses, including reestablished riparian forest buffers, row crop fields, and continuously grazed riparian pastures. Erosion pins were measured from June 1998 to July 2002 to estimate the magnitude of streambank erosion. Total streambank soil loss was estimated by using magnitude of bank erosion, soil bulk density, and severely eroded bank area. Significant seasonal and yearly differences in magnitude of bank erosion and total soil loss were partially attributed to differences in precipitation and associated discharges. Riparian forest buffers had significantly lower magnitude of streambank erosion and total soil loss than the other two riparian land uses. Establishment of riparian forest buffers along all of the nonbuffered subreaches would have reduced stream‐bank soil loss by an estimated 77 to 97 percent, significantly decreasing sediment in the stream, a major water quality problem in Iowa.