The effects of triclopyr on 2,4‐D mineralization in two soils

Abstract

The effects of the herbicide triclopyr (3,5,6‐trichloro‐2‐pyridinyloxyacetic acid) on the mineralization of 2,4‐D (2,4‐dichlorophenoyxacetic acid) in two soils which differed in their histories of prior exposure to the two herbicides were investigated. The relative effects of triclopyr on 2,4‐D mineralization and most probable numbers of 2,4‐D degraders were dependent upon the soil. Triclopyr was shown to increase 2,4‐D mineralization rates in a soil which had been exposed to both 2,4‐D and triclopyr, but decreased the mineralization rate of 2,4‐D and inhibited the increase of most probable numbers of 2,4‐D degraders in a soil that had not been directly exposed to either herbicide.     

ESTIMATING TRANSMISSIVITY AND HYDRAULIC CONDUCTIVITY OF CHICOT AQUIFER FROM SPECIFIC CAPACITY DATA1

ABSTRACT: Specific capacity data obtained from Well Construction reports which are available from USGS offices, can provide useful estimates of tranamissivity (T), and hydraulic conductivity (K), of an aquifer. The Chicot Aquifer in Louisiana is one of the largest sources of fresh ground water in North America. Hydrologic data collected for the Chicot Aquifer indicate that specific capacity tests can be used in estimating local and regional values for T and K, if the Cooper-Jacob equation for transient flow is used with proper corrections for well loss and partial penetration. Where full scale pumping test data are scarce, specific capacity test data that are adequately distributed spatially can be used to map changes in T and K values and can be summarized statistically to indicate applicable regional values. A computer program called “TGUESS” which is available from International Ground Water Modeling Center, Holcomb Research Institute, was used in this study. The contour maps for T and K values are prepared for different well depth intervals to avoid wide variation of values.     

FUNDAMENTAL INVESTIGATION OF GRAVITY CURRENTS WITH VARYING DENSITY1

ABSTRACT: A one-dimensional, gradually varying, non-uniform, flow equation is developed to describe the movement of a variable density gravity current through a reservoir. A linearly decreasing underflow density function is used to investigate the effect of in-reservoir density reduction on typical gravity current flow profiles. Only two types of flow profiles are found to exist for varying density underflows: Type I profiles where the underflow asymptotically approaches a horizontal surface, and Type III profiles where the underflow vertically approaches critical depth. Type I profiles pass through a transitional depth as the underflow density approaches that of the upper layer. Results indicate that a reservoir can be segmented into four distinct spatial regions with well defined flow profile characteristics. The location of these regions allows the sketching of interfacial flow profiles along with identifying the location of transitional depth conditions. Transitional depth conditions are utilized as the logical starting point for Type I flow profile numerical computation. (KEY WORDS: density; fluid flow; reservoirs; hydraulics.)     

Assessment of medical care costs of injuries due to alcohol-related motor vehicle crashes

The purpose of this study was to estimate the total medical care costs of individuals injured in motor vehicle crashes and in crashes where alcohol was involved. Crashes were studied that involved 2,728 vehicle occupants and 191 pedestrians with injuries as reported in 1979 by the National Accident Sampling System, a probability sample of all motor vehicle crashes occurring in the united States. Medical care costs were assigned by using Abbreviated Injury Scale codes in accordance with other published research. Determination of alcohol involvement was based on crash characteristics. Results indicate that 20.2 % of medical care costs for motor vehicle crash injuries may be due to crashes where alcohol was involved. It was estimated that alcohol-related motor vehicle crashes cost between $434 million and $483 million in medical care alone in the United States in 1979.     

MANGANESE CYCLE IN IMPOUNDMENT WATER

Manganese entering impounded water will undergo a cyclic transformation. Oxidation precipitates manganese from top waters. At the bottom of the lake, biological activity will render manganese soluble by both intracellular as well as extracellular activity. The study was made to demonstrate that biological reduction and transformation, organometallic complexation, together with the presence of carbon dioxide and the lowering of pH all have some effect on the solubility of manganese. Dissolved manganese may be brought back to top waters during the lake overturn and therefore deteriorates the water quality.     

Quantifying the global fractionation of polychlorinated biphenyls

Due to the wide range of their physical-chemical properties, polychlorinated biphenyls (PCBs) have played an important role in the derivation of the global fractionation hypothesis, which predicts changes in the composition of persistent organic pollutant mixtures with latitude. Recent historical emission estimates, the derivation of an internally consistent property data set, in combination with a zonally averaged global fate and transport model, allow a quantitative investigation of the compositional shifts PCBs experience as a function of environmental compartment, latitude and time. Model simulations reproduce the higher relative abundance of lighter PCB congeners with increasing latitude, observed in air and soil, and quantify the relative importance of partitioning, persistence and emissions in establishing PCB patterns. Compositional variations consistent with global fractionation, as well as inverted concentration profiles with higher levels in the Arctic than at lower latitudes, are consistent with only minor fractions of the global PCB inventory being transferred northward.     

The Lake Erie Agricultural Systems for Environmental Quality project: an introduction

In the last part of the twentieth century, recognition became widespread of the important effect of agricultural runoff on the health of aquatic ecosystems in the Lake Erie basin and elsewhere. Because of the efforts to remediate Lake Erie, the "dead lake" among the Laurentian Great Lakes, a number of research and demonstration projects were undertaken in the Lake Erie basin to evaluate and foster adoption of conservation tillage and other farming techniques that would reduce runoff while maintaining productivity. In addition, intensive water quality studies of long duration were begun on major tributaries to Lake Erie during this time. The Lake Erie Agricultural Systems for Environmental Quality (LEASEQ) project examined governmental programs, changes in agriculture, and changes in water and soil quality during the period 1975-1995, and sought to evaluate the linkages among these factors. The study area is characterized by extensive agricultural land use of soils developed from glacial materials deposited on Paleozoic sedimentary bedrock, mostly limestone. Tile drainage is extensive, particularly in slow-draining clay-rich lacustrine soils in the lower reaches of the watersheds. This paper introduces the study area, its geology, geography, soils, and agricultural history. In addition, we provide an overview of the LEASEQ concept and introduce the 11 other papers in this series, which provide a detailed exposition of the results of our studies.     

Die Umsetzung des EU Weißbuches zur Chemikalienpolitik

Background

Aim and Scope. Implementation of the European Union White Paper on chemicals policy shall provide more safety and more transparency in chemicals use. In the past, when assessing existing commercial substances there was often a lack of information in the fields of application of the chemicals and the exposures arising in those contexts. The White Paper therefore calls for ‘shared responsibility’. Processors and commercial users of substances are to be involved much more closely in the risk evaluation process than has hitherto been the case. They are to provide data on substance applications and exposures, and, to some extent, they are also to carry out exposure assessments and risk assessments themselves. By analysing case studies, the paper highlights the consequences of this approach.

Results and Discussion

Fear has often been voiced that these new tasks will completely overburden small and medium-sized enterprises. It is assumed that many chemicals are no longer available for smallvolume applications, as — for cost reasons — producers do not include these applications in their registration. The wording of the White Paper is not precise enough to be able to appraise the costs that will be associated with the required intensified communication. In this situation, it is essential to analyse prototypical substances and their applications in order to gain an improved understanding of the principle of shared responsibility.

Conclusions

The concrete study of several product chains has shown that the flow of information required between producers and users is very likely feasible within the context of the REACH system. For the producers of chemicals, the intensified communication will presumably make it simpler to procure information in the fields of application and exposures. However, in order to avoid users being overburdened, it will be important that registration requirements and focuses are shaped in a manner doing justice to practical realities. Users will need to undertake community-wide efforts on an industry federation and branch level. In this context, the protection of company know-how also needs to be ensured.

Recommendation and Outlook

In practice, implementation of the principle of shared responsibility can lead to intensified communication among the producers and users of chemicals. This can greatly facilitate exposure assessments and risk assessments. There is a need to develop manageable procedures that can also be implemented by small and medium-sized enterprises. Numerous proposals have been made in this context, and extensive reference material is now available.     

Flooding patterns of the Okavango Wetland in Botswana between 1972 and 2000

The inundated area of the Okavango Delta changes annually and interannually. The variability relates to regional precipitation over the catchment area in the Angolan highlands, and to local rainfall. The patterns of the wetland were captured using more than 3000 satellite images for the period 1972 to 2000, near daily NOAA AVHRR data for 1985-2000, and less frequent images of the Landsat sensors from 1972 onwards. One AVHRR image for every 10-day period was classified into land and water using an unsupervised classification method. Evaluation against Landsat TM and ERS2-ATSR data indicate an agreement of 89% for the size of estimated inundation area. Results show that the wetland area has varied between approximately 2450 km2 and 11400 km2 during the last 30 years.     

DIN Retention‐Transport Through Four Hydrologically Connected Zones in a Headwater Catchment of the Upper Mississippi River1

Abstract: Dissolved inorganic nitrogen (DIN) retention‐transport through a headwater catchment was synthesized from studies encompassing four distinct hydrologic zones of the Shingobee River Headwaters near the origin of the Mississippi River. The hydrologic zones included: (1) hillslope ground water (ridge to bankside riparian); (2) alluvial riparian ground water; (3) ground water discharged through subchannel sediments (hyporheic zone); and (4) channel surface water. During subsurface hillslope transport through Zone 1, DIN, primarily nitrate, decreased from ～3 mg‐N/l to <0.1 mg‐N/l. Ambient seasonal nitrate:chloride ratios in hillslope flow paths indicated both dilution and biotic processing caused nitrate loss. Biologically available organic carbon controlled biotic nitrate retention during hillslope transport. In the alluvial riparian zone (Zone 2) biologically available organic carbon controlled nitrate depletion although processing of both ambient and amended nitrate was faster during the summer than winter. In the hyporheic zone (Zone 3) and stream surface water (Zone 4) DIN retention was primarily controlled by temperature. Perfusion core studies using hyporheic sediment indicated sufficient organic carbon in bed sediments to retain ground water DIN via coupled nitrification‐denitrification. Numerical simulations of seasonal hyporheic sediment nitrification‐denitrification rates from perfusion cores adequately predicted surface water ammonium but not nitrate when compared to 5 years of monthly field data (1989‐93). Mass balance studies in stream surface water indicated proportionally higher summer than winter N retention. Watershed DIN retention was effective during summer under the current land use of intermittently grazed pasture. However, more intensive land use such as row crop agriculture would decrease nitrate retention efficiency and increase loads to surface water. Understanding DIN retention capacity throughout the system, including special channel features such as sloughs, wetlands and floodplains that provide surface water‐ground water connectivity, will be required to develop effective nitrate management strategies.