In this study the radionuclide databases for two versions of the Clean Air Act Assessment Package-1988 (CAP88) computer model were assessed in detail. CAP88 estimates radiation dose and the risk of health effects to human populations from radionuclide emissions to air. This program is used by several U.S. Department of Energy (DOE) facilities to comply with National Emission Standards for Hazardous Air Pollutants regulations. CAP88 Mainframe, referred to as version 1.0 on the U.S. Environmental Protection Agency Web site (http://www.epa.gov/radiation/assessment/CAP88/), was the very first CAP88 version released in 1988. Some DOE facilities including the Savannah River Site still employ this version (1.0) while others use the more user-friendly personal computer Windows-based version 3.0 released in December 2007. Version 1.0 uses the program RADRISK based on International Commission on Radiological Protection Publication 30 as its radionuclide database. Version 3.0 uses half-life, dose, and risk factor values based on Federal Guidance Report 13. Differences in these values could cause different results for the same input exposure data (same scenario), depending on which version of CAP88 is used. Consequently, the differences between the two versions are being assessed in detail at Savannah River National Laboratory. The version 1.0 and 3.0 database files contain 496 and 838 radionuclides, respectively, and though one would expect the newer version to include all the 496 radionuclides, 35 radionuclides are listed in version 1.0 that are not included in version 3.0. The majority of these has either extremely short or long half-lives or is no longer in production; however, some of the short-lived radionuclides might produce progeny of great interest at DOE sites. In addition, 122 radionuclides were found to have different half-lives in the two versions, with 21 over 3 percent different and 12 over 10 percent different.
The Louisiana-Texas coast is one of the largest areas of seasonal, coastal hypoxia. The hypoxic zone has increased in size since the 1900s and has significantly increased in thickness since 1985. Hypoxia can negatively affect fish through direct mortality, reduced fecundity, and reduced preyavailability. Movement algorithms were used to model fish movement and avoidance of hypoxia in 2-D and 3-D with static and dynamic environmental fields. Output from a 3-D, coupled, hydrodynamic-water quality model was used for the environmental conditions of the model. A particle tracking module for the hydrodynamic model was used to track fish movement. Movement algorithms were added to the tracking module to allow for active movement. Three movement algorithms for use outside of hypoxic conditions were compared in static 2-D scenarios. There was not a large difference in hypoxia exposure for the three algorithms, but there was a difference in sinuosity (amount of wiggle in the fish track). Comparing static and dynamic environmental fields in 2-D resulted in higher exposures for dynamic conditions. There was also an unexpected effect from a narrow region of normoxic water surrounded by hypoxic water. The presence of this thin area resulted in more outliers in hypoxia exposure. Three algorithms for hypoxia avoidance were compared in dynamic conditions. Two of the algorithms were found to be similar, but a third that used both dissolved oxygen and temperature as inputs had much higher exposures. Balancing the two environmental cues resulted in poor hypoxia avoidance. Comparing 2-D and 3-D scenarios resulted in lower exposure for fish in 3-D scenarios. Two different methods of perception ranges were used and found to result in similar hypoxia exposures. The research highlighted the need to include 3-D movement in fish models for the Gulf of Mexico hypoxia region. Also, high-resolution field data need to be collected to calibrate and validate such models and facilitate selection of appropriate movement algorithms.
The reviewer suggests that using controlled and manipulated spatial maps would enable a clearer analysis of the effects spatial variability.While this always true, the downside is that any artificial manipulation of the spatial maps of dissolved oxygen
Abstract. The hypoxic zone in the northern Gulf of Mexico varies spatially (area, location) and temporally (onset, duration) on multiple scales. Exposure to hypoxic dissolved oxygen (DO) concentrations (
Matrix assisted ionization is an effective tool for producing rapid and accurate uranium isotope ratios with minimal laboratory infrastructure needs compared to traditional mass spectrometry methods.
Abstract. The hypoxic zone in the northern Gulf of Mexico varies spatially (area, location) and temporally (onset, duration) on multiple scales. Exposure of fish to hypoxic dissolved oxygen (DO) concentrations (< 2 mg L−1) is often lethal and avoided, while exposure to 2 to 4 mg L−1 occurs readily and often causes the sublethal effects of decreased growth and fecundity for individuals of many species. We simulated the movement of individual fish within a high-resolution 3-D coupled hydrodynamic water quality model (FVCOM-WASP) configured for the northern Gulf of Mexico to examine how spatial variability in DO concentrations would affect fish exposure to hypoxic and sublethal DO concentrations. Eight static snapshots (spatial maps) of DO were selected from a 10 d FVCOM-WASP simulation that showed a range of spatial variation (degree of clumpiness) in sublethal DO for when total sublethal area was moderate (four maps) and for when total sublethal area was high (four maps). An additional case of allowing DO to vary in time (dynamic DO) was also included. All simulations were for 10 d and were performed for 2-D (bottom layer only) and 3-D (allows for vertical movement of fish) sets of maps. Fish movement was simulated every 15 min with each individual switching among three algorithms: tactical avoidance when exposure to hypoxic DO was imminent, strategic avoidance when exposure had occurred in the recent past, and default (independent of DO) when avoidance was not invoked. Cumulative exposure of individuals to hypoxia was higher under the high sublethal area snapshots compared to the moderate sublethal area snapshots but spatial variability in sublethal concentrations had little effect on hypoxia exposure. In contrast, relatively high exposures to sublethal DO concentrations occurred in all simulations. Spatial variability in sublethal DO had opposite effects on sublethal exposure between moderate and high sublethal area maps: the percentage of fish exposed to 2–3 mg L−1 decreased with increasing variability for high sublethal area but increased for moderate sublethal area. There was also a wide range of exposures among individuals within each simulation. These results suggest that averaging DO concentrations over spatial cells and time steps can result in underestimation of sublethal effects. Our methods and results can inform how movement is simulated in larger models that are critical for assessing how management actions to reduce nutrient loadings will affect fish populations.
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