Seasonal and Long‐Term Variations in Hydraulic Head in a Karstic Aquifer: Roswell Artesian Basin,New Mexico1

Abstract: Water levels in the karstic San Andres limestone aquifer of the Roswell Artesian Basin, New Mexico, display significant variations on a variety of time scales. Large seasonal fluctuations in hydraulic head are directly related to the irrigation cycle in the Artesian Basin, lower in summer months and higher in winter when less irrigation occurs. Longer‐term variations are the result of both human and climatic factors. Since the inception of irrigated farming more than a century ago, over‐appropriation of water resources has caused water levels in the artesian aquifer to fall by as much as 70 m. The general decline in hydraulic head began to reverse in the mid‐1980s due to a variety of conservation measures, combined with a period of elevated rainfall toward the end of the 20th Century.     

To what extent are hepatic concentrations of heavy metals in Anguilla anguilla at a site in a contaminated estuary related to body size and age and reflected in the metallothionein concentrations?

We explored how hepatic [metal]s in Anguilla anguilla at a contaminated estuarine site are influenced by body size, age and season, and the extent that [Cu], [Cd] and [Zn]s are reflected in [metallothionein (MT)]s. Although each [metal] and [MT] increased significantly with length, weight and age, those biotic variables explained <10% of the variation in each [metal] and only 11-16% for [MT]. Seasonal changes in [Cu] and [Cd] were paralleled by [MT]. The variation in [MT] explained by Cu (42%) was greater than by Zn (16%) and Cd (13%), and seasonally lay between 43 and 69% for those metals collectively. Thus, hepatic [MT] in eels is closely correlated with hepatic [heavy metal]s. However, the great variability among [MT]s for eels of similar sizes and ages, which reflects marked variability in hepatic [heavy metal]s, means that this variable reflects imprecisely the contamination level at a particular site.     

Oxygen depletion in relation to water residence times

The relationship between residence time and oxygen saturation was investigated in a mesotidal lagoon in southern Portugal. The system receives no significant freshwater input during the summer months and has a high evaporation rate. These features enable an estimate of residence time from the salinity differences between ocean water entering the system and lagoon water. More than 10,000 GPS referenced measurements of oxygen saturation, temperature and salinity were made during large spring tides in September, 2006. The lowest oxygen saturation ( approximately 44%) was measured in the waters with the highest calculated residence times (7 days). There was a significant linear decrease in the oxygen saturation with increasing residence time of approximately 16% per day. This was similar to the rate measured on a neap tide in August, 2005. The high salinity, low oxygen saturated water was spatially confined to one inner channel, except at high water when this water was pushed into other channels. Although the tides investigated were the largest for several years, the oxygen saturation did not exceed 70% in this inner region. It is proposed that the direct discharge of oxygen consuming effluent, including domestic sewage, into this inner channel is responsible for this persistent oxygen deficit.     

Soil carbon stock estimations: methods and a case study of the Maranhão State,Brazil

Environment, Development and Sustainability - Soils feature significant variations in soil carbon stocks through land-use changes, management practices, and intrinsic characteristics. The aim of...     

Impact of alternative metrics on estimates of extent of occurrence for extinction risk assessment

In International Union for Conservation of Nature (IUCN) Red List assessments, extent of occurrence (EOO) is a key measure of extinction risk. However, the way assessors estimate EOO from maps of species’ distributions is inconsistent among assessments of different species and among major taxonomic groups. Assessors often estimate EOO from the area of mapped distribution, but these maps often exclude areas that are not habitat in idiosyncratic ways and are not created at the same spatial resolutions. We assessed the impact on extinction risk categories of applying different methods (minimum convex polygon, alpha hull) for estimating EOO for 21,763 species of mammals, birds, and amphibians. Overall, the percentage of threatened species requiring down listing to a lower category of threat (taking into account other Red List criteria under which they qualified) spanned 11–13% for all species combined (14–15% for mammals, 7–8% for birds, and 12–15% for amphibians). These down listings resulted from larger estimates of EOO and depended on the EOO calculation method. Using birds as an example, we found that 14% of threatened and near threatened species could require down listing based on the minimum convex polygon (MCP) approach, an approach that is now recommended by IUCN. Other metrics (such as alpha hull) had marginally smaller impacts. Our results suggest that uniformly applying the MCP approach may lead to a one‐time down listing of hundreds of species but ultimately ensure consistency across assessments and realign the calculation of EOO with the theoretical basis on which the metric was founded.     

Direct and short-term culture preparation of chorionic villi. Is any one method best?

Chorionic villi from 20 diagnostic cases were prepared for cytogenetic analysis by a direct and two short-term culture methods. No significant differences were found between the methods in the quality and quantity of metaphases obtained. A further study using villi from 20 pre-termination patients indicated an inherent variation in the quality of villi resulting in inconsistent processing and variation in the response of a sample to the methods. This suggests that it would be advantageous to process the villi by more than one method.     

Lake sediments record sensitivity of two hydrologically closed upland lakes in Mexico to human impact

We provide evidence of rapid, recent environmental change in two lakes in the highlands of central Mexico. Multiple sediment cores were obtained from Lago de Zirahuén (Michoacán) and Laguna de Juanacatlán (Jalisco). Analysis of diatom assemblages, magnetic susceptibility, and metal concentrations was carried out, with the chronology provided by 210Pb dating, 14C dating, and tephrochronology. There is evidence of catchment disturbance during the colonial period in both basins, but the most striking feature at both sites is the rapid change in diatom assemblages during the last 20 y, indicating the onset of eutrophication. Limnological data from Lago de Zirahuén support this interpretation, although none are available from Laguna de Juanacatlán. Paleolimnology is a powerful tool in tracking recent change, particularly in the absence of regular limnological monitoring programs. These lakes appear to be highly sensitive to changes in catchment exploitation, which must be considered in future drainage basin management.     

Environmental fate and bioavailability of agent orange and its associated dioxin during the vietnam war

BACKGROUND: In 1996, the Committee on the Assessment of Wartime Exposure to Herbicides in Vietnam of the National Academy of Sciences' Institute of Medicine (IOM) issued a report on an exposure model for use in epidemiological studies of Vietnam veterans. This exposure model would consider troop locations based on military records; aerial spray mission data; estimated ground spraying activity; estimated exposure opportunity factors; military indications for herbicide use; and considerations of the composition and environmental fate of herbicides, including changes in the TCDD content of the herbicides over time, the persistence of TCDD and herbicides in the environment, and the degree of likely penetration of the herbicides into the ground. When the final report of the IOM Committee was released in October 2003, several components of the exposure model envisioned by the Committee were not addressed. These components included the environmental fate of the herbicides, including changes in the TCDD content over time, the persistence of TCDD and herbicides in the environment, and the degree of likely penetration of herbicides into the ground. This paper is intended to help investigators understand better the fate and transport of herbicides and TCDD from spray missions, particularly in performing epidemiological studies. METHODS: This paper reviews the published scientific literature related to the environmental fate of Agent Orange and the contaminant, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and discusses how this affected the potential exposure to TCDD of ground troops in Vietnam. Specifically, the mechanisms of dissipation and degradation as they relate to environmental distribution and bioavailability are addressed. RESULTS: The evaluation of the spray systems used to disseminate herbicides in Vietnam showed that they were capable of highly precise applications both in terms of concentrations sprayed and area treated. Research on tropical forest canopies with leaf area indices (a measure of foliage density) from 2 to 5 indicated that the amount of herbicide and associated TCDD reaching the forest floor would have been between 1 and 6% of the total aerial spray. Studies of the properties of plant surface waxes of the cuticle layer suggested that Agent Orange, including the TCDD, would have dried (i.e., be absorbed into the wax layer of the plant cuticle) upon spraying within minutes and could not be physically dislodged. Studies of Agent Orange and the associated TCDD on both leaf and soil surface have demonstrated that photolysis by sunlight would have rapidly decreased the concentration of TCDD, and this process continued in shade. Studies of 'dislodgeable foliar residues' (DFR, the fraction of a substance that is available for cutaneous uptake from the plant leaves) showed that only 8% of the DFR was present 1 hr after application. This dropped to 1% of the total 24 hrs after application. Studies with human volunteers confirmed that after 2 hrs of saturated contact with bare skin, only 0.15-0.46% of 2,4,5-T, one of the phenoxy acetic acid compounds that was an active ingredient of Agent Orange, entered the body and was eliminated in the urine. CONCLUSIONS: The prospect of exposure to TCDD from Agent Orange in ground troops in Vietnam seems unlikely in light of the environmental dissipation of TCDD, little bioavailability, and the properties of the herbicides and circumstances of application that occurred. Photochemical degradation of TCDD and limited bioavailability of any residual TCDD present in soil or on vegetation suggest that dioxin concentrations in ground troops who served in Vietnam would have been small and indistinguishable from background levels even if they had been in recently treated areas. Laboratory and field data reported in the literature provide compelling evidence on the fate and dislodgeability of herbicide and TCDD in the environment. This evidence of the environmental fate and poor bioavailability of TCDD from Agent Orange is consistent with the observation of little or no exposure in the veterans who served in Vietnam. Appreciable accumulation of TCDD in veterans would have required repeated long-term direct skin contact of the type experienced by United States (US) Air Force RANCH HAND and US Army Chemical Corps personnel who handled or otherwise had direct contact with liquid herbicide, not from incidental exposure under field conditions where Agent Orange had been sprayed.     

Trends in organochlorine and mercury levels in Gannet eggs

Levels of DDE, HEOD, PCBs and mercury were measured in Gannet eggs from several colonies around Britain during 1971-1987. At two colonies (Ailsa Craig and Bass Rock) sampled throughout this period, organochlorine levels declined between the early 1970s and 1983, and then increased again. The trends at other colonies, sampled over shorter periods, were generally consistent with those at Ailsa Craig and Bass Rock. Trends in mercury levels were more variable, and increases were observed at four colonies and declines at two. Some shell-thinning occurred in association with DDE contamination. However, levels of this chemical were too low to affect breeding success in the years concerned. The same was probably true of the other chemicals.     

Legal implications in development and use of Expert Systems in agriculture

Applications of Artificial Intelligence, particularly Expert Systems, are rapidly increasing. This science promises to give computer-based systems the capability of reasoning and decision making in near human-like fashion. Whether used for farm management or intelligent machine control, Expert Systems will find many agricultural applications. Much of the development and distribution of such systems will probably take place in the public sector, particularly the Cooperative Extension Service. A major nontechnical factor affecting the development and extensive use of Expert Systems is the legal issue of products, liability, and negligence. The legal issues surrounding Expert Systems have not yet been fully tested and defined by the courts. Developers and users of Expert Systems must consider these factors for each particular application.