Noise susceptibility: A comparison of two naval aviator populations

The identification of characteristics of noise-susceptible (S) or noise-resistant (R) individuals is necessary for the development of noise-susceptibility risk profiles. Fifty-six naval aviators, categorized as having either incurred a hearing loss, i.e., hearing threshold levels (HTLs) > 40 dB at 4–8 kHz or retained normal hearing, i.e., HTLs ≤ 25 dB at 125 Hz-8 kHz, after thousands of flight hours were compared along several auditory and non-auditory dimensions. A number of variables occurred differentially in the two groups: Minimal Auditory Intensity Differential (MAID) scores at 2 kHz (p < 0.01) and 4 kHz (p < 0.001); iris pigmentation (blue eyes were over-represented in the S group; p < 0.05); systolic blood pressure (sitting; S group was higher; p < 0.05); calcium, albumin, and LDH levels (higher in the R group; p < 0.05); and present tobacco usage (more S aviators were currently smokers; p < 0.05). The S population also tended (p < 0.10) to exhibit elevated cholesterol and triglyceride levels as well as higher contralateral acoustic reflexes, and to have fewer individuals who had never smoked. Although no classic profile of the S or R individual definitely emerged, results suggested that at least one measurement device (MAID test) may serve as an “early warning” of imminent noise-induced damage. Further research, however, is required to test this possibility.     

Southwestern corn borer damage to maize: Influence of plant age at time of larval infestation

A maize (Zea mays L.) hybrid was infested with 30 southwestern corn borer [Diatraea grandiosella (Dyar)] larvae per plant at 4, 5, 6, 7 or 8 weeks after planting in a three-year study conducted at Mississippi State, Mississippi. Visual ratings of leaf feeding damage were highest when plants were infested 5 weeks after planting. Plant height increased linearly with the age of plants at infestation. Height of infested plants was significantly less than uninfested plants only when infestations were made 4 weeks after planting. The relationship between age of plants at infestation and yield was curvilinear. Yields were significantly reduced at all infestation times; however, the least yield reduction occurred when plants were infested 6 weeks after planting. To evaluate resistance to southwestern corn borer damage, infestation at 4 or 5 weeks after planting appeared to be most satisfactory. Yield reductions following infestation at 7 and 8 weeks after planting indicated that, when infestations are late, leaf feeding damage ratings alone may not be satisfactory indicators of plant damage.     

An Automated Technique for Delineating and Characterizing Valley-Bottom Settings

Accurate delineation and characterization of valley-bottom settings is crucial to the assessment of the biological and geomorphological components of riverine systems; yet, to date, most valley-bottom mapping endeavors have been done manually. To improve this situation, we developed automated techniques in a Geographic Information System (GIS) for delineating and characterizing valley-bottom settings in river basins ranging in size from approximately 1,000–10,000 km². All procedures were developed with ARC/INFO GIS software and fully automated in Arc Macro Language (AML). The GRID module is required for valley-bottom delineation and slope calculations; whereas characterization (i.e., measuring the width of the valley-bottom zone) requires Coordinate Geometry (COGO) in the ARCEDIT module. The process requires three inputs: a polygon coverage of the analysis area; an arc coverage of its hydrography, and a grid representing its digital elevation. The AML is designed to operate within a wide range of computer memory/disk space options, and it allows users to customize several procedures to match the scale and complexity of a given analysis area with available computer hardware.     

Kinetics of uranium uptake by the crab Pachygrapsus laevimanus and the zebra winkle Austrocochlea constricta

The crab Pachygrapsus laevimanus and the zebra winkle Austrocochlea constricta were exposed for 40 d to uranium (1.5 to 10 mg l^-1) in continuous-flow sea water in separate starved and fed treatments, and the kinetics of uranium bioaccumulation were estimated from an exponential model. Starved and fed crabs took up U at a similar rate, which suggests that sea water was the major source of U to the crab; the fed crabs excreted U more rapidly than the starved crabs and this led to a lower net uptake of U by fed crabs. Fed and starved winkles took up U at similar rates and excreted it at similar rates, so the sea water was also the major source of U to winkles. Crabs took up more U than winkles; the concentration factors were 7 to 18 and 4, respectively. Uranium turnover was quite slow for both species (11 to 36 d) as it was also for winkle shells (6 d); this suggests that the rate-limiting processes which control turnover are biological (e.g. growth or tissue replacement) or physical (e.g. diffusion into the shell) rather than chemical (e.g. precipitation, adsorption or exchange). There was no effect of increasing U concentration in water on the U kinetic parameters.     

Nitrite and Freshwater Fish

Nitrite occurs naturally in fresh waters as a result of nitrification of ammonia and denitrification of nitrate, and its concentration can be enhanced by partial oxidation of ammoniacal discharges. Nitrite is toxic to vertebrates including fish and a principal effect is the conversion of haemoglobin to methaemoglobin which is incapable of oxygen transport although there are circulatory and tissue effects as well. The toxic species is the nitrite ion (NO₂) which is believed to enter the blood via the branchial chloride/bicarbonate exchange and fish such as salmonids with high chloride uptake rates are more susceptible than those with low chloride uptake rates, for example carp. Nitrite toxicity is strongly aleviated by chloride and the concentration ratio of these ions is of great importance in assessing toxicity. Short term and long term toxicity data for a variety of fish species are presented. There are no field data on fish populations in waters where nitrite was the only pollutant. However extensive field surveys indicated that, waters with a mean chloride concentration of 25 mg l^-1 in good salmon fisheries were associated with concentrations of nitrite below 50 μg l^-1 N · NO₂, good coarse fisheries below 100 μg l^-1 N · NO₂.     

Influence of Riparian Seepage Zones on Nitrate Variability in Two Agricultural Headwater Streams

Riparian seeps have been recognized for their contributions to stream flow in headwater catchments, but there is limited data on how seeps affect stream water quality. The objective of this study was to examine the effect of seeps on the variability of stream NO₃‐N concentrations in FD36 and RS, two agricultural catchments in Pennsylvania. Stream samples were collected at 10‐m intervals over reaches of 550 (FD36) and 490 m (RS) on 21 occasions between April 2009 and January 2012. Semi‐variogram analysis was used to quantify longitudinal patterns in stream NO₃‐N concentration. Seep water was collected at 14 sites in FD36 and 7 in RS, but the number of flowing seeps depended on antecedent conditions. Seep NO₃‐N concentrations were variable (0.1‐29.5 mg/l) and were often greater downslope of cropped fields compared to other land uses. During base flow, longitudinal variability in stream NO₃‐N concentrations increased as the number of flowing seeps increased. The influence of seeps on the variability of stream NO₃‐N concentrations was less during storm flow compared to the variability of base flow NO₃‐N concentrations. However, 24 h after a storm in FD36, an increase in the number of flowing seeps and decreasing streamflow resulted in the greatest longitudinal variability in stream NO₃‐N concentrations recorded. Results indicate seeps are important areas of NO₃‐N delivery to streams where targeted adoption of mitigation measures may substantially improve stream water quality.     

Development of the Spatial Rainfall Generator (SRGEN) for the Agricultural Policy/Environmental Extender Model

Accurate spatial representation of climatic patterns is often a challenge in modeling biophysical processes at the watershed scale, especially where the representation of a spatial gradient in rainfall is not sufficiently captured by the number of weather stations. The spatial rainfall generator (SRGEN) is developed as an extension of the “weather generator” (WXGEN), a component of the Agricultural Policy/Environmental eXtender (APEX) model. SRGEN generates spatially distributed daily rainfall using monthly weather statistics available at multiple locations in a watershed. The spatial rainfall generator as incorporated in APEX is tested on the Cowhouse watershed (1,178 km²) in central Texas. The watershed presented a significant spatial rainfall gradient of 2.9 mm/km in the lateral (north‐south) directions based on four rainfall gages. A comparative analysis between SRGEN and WXGEN indicates that SRGEN performs well (PBIAS = 2.40%). Good results were obtained from APEX for streamflow (NSE = 0.99, PBIAS = 8.34%) and NO₃‐N and soluble P loads (PBIAS ≈ 6.00% for each, respectively). However, APEX underpredicted sediment yield and organic N and P loads (PBIAS: 24.75‐27.90%) with SRGEN, although its uncertainty in output was lower than WXGEN results (PBIAS: ?13.02 to ?46.13%). The overall improvement achieved in rainfall generation by SRGEN is demonstrated to be effective in the improving model performance on flow and water quality output.     

Incentives for Biological Conservation: Costa Rica's Private Wildlife Refuge Program

Abstract: The alarming pace of tropical biodiversity loss requires development of innovative approaches for in situ biodiversity conservation. Incentive-based approaches have emerged as one possible option. We interviewed 68 private nature reserve owners to learn more about one of Costa Rica's incentive programs. The interview group included all reserve owners participating in the government's Private Wildlife Refuge Program (n = 22) and a control group of nonparticipating owners (n = 46). Quantitative and qualitative data led to seven main conclusions on the use of incentive programs: (1) a developing country can expand and enhance its formal park system through conservation incentives; (2) insufficient promotion, and resulting information gaps, can prevent an incentive program from realizing its full potential; (3) landowners enter a program not only in response to the intended incentive package, but also for several powerful and hidden incentives such as publicity and marketing purposes; (4) underutilization of official incentives by participants, in part due to sporadic delivery of incentives by the government, can undermine program effectiveness; (5) biodiversity protection goals can be accomplished by means of a wide range of incentives; (6) programs that require only a short-term commitment by landowners can still lead to long-term biodiversity protection; and (  7) a program can produce unanticipated negative consequences at the national level, including putting conservation at odds with social justice. These and other lessons on the use of incentives should be of interest wherever biodiversity is threatened, wherever new conservation partners are being sought, and wherever incentive-based approaches are being considered.