ESTIMATION OF STREAMFLOW,BASE FLOW,AND NITRATE‐NITROGEN LOADS IN IOWA USING MULTIPLE LINEAR REGRESSION MODELS1

Nineteen variables, including precipitation, soils and geology, land use, and basin morphologic characteristics, were evaluated to develop Iowa regression models to predict total streamflow (Q), base flow (Qb), storm flow (Qs) and base flow percentage (%Qb) in gauged and ungauged watersheds in the state. Discharge records from a set of 33 watersheds across the state for the 1980 to 2000 period were separated into Qb and Qs. Multiple linear regression found that 75.5 percent of long term average Q was explained by rainfall, sand content, and row crop percentage variables, whereas 88.5 percent of Qb was explained by these three variables plus permeability and floodplain area variables. Qs was explained by average rainfall and %Qb was a function of row crop percentage, permeability, and basin slope variables. Regional regression models developed for long term average Q and Qb were adapted to annual rainfall and showed good correlation between measured and predicted values. Combining the regression model for Q with an estimate of mean annual nitrate concentration, a map of potential nitrate loads in the state was produced. Results from this study have important implications for understanding geomorphic and land use controls on streamflow and base flow in Iowa watersheds and similar agriculture dominated watersheds in the glaciated Midwest.     

A regional environmental quality management model: An assessment

The principal purpose of this paper is to discuss the research and policy lessons learned from a large environmental quality management model constructed for the Lower Delaware River Valley Region, The policy lessons involve estimates of the costs of meeting varying standards on air and water quality and the impact on those costs of certain region-wide management alternatives. The research lessons concern: (a) the desirability of considering air and water quality, and solid waste disposal, simultaneously in a single model; (b) the costs of and returns to including nonlinear models of natural systems in a regional optimization framework; and (c) the feasibility of working with constraints on the geographic distribution of the costs of environmental quality improvement within the regional, nonlinear model.     

Substituting pollution taxation for general taxation: Some implications for efficiency in pollutions taxation

Earlier papers have recognized that nonenvironmental benefits will be realized if pollution taxes are substituted for other taxes which impose efficiency losses on society. The purpose of this paper is to investigate the importance of these nonenvironmental benefits for the design of an efficient pollution tax. It is found that the efficient tax may be higher or lower than that conventionally defined as optimal, and that the net benefit from unrestrained pollution can have important implications for the size of the tax.     

Stable carbon isotope composition (δ13C values) of the halogenated monoterpene MHC-1 as found in fish and seaweed from different marine regions

Six samples of the red seaweed Plocamium cartilagineum (two both from Helgoland/Germany, Ireland, and the Antarctic) were analyzed by stable isotope analysis. The bulk δ(13)C values (-31 to -38‰) confirmed that this seaweed was exceptionally highly depleted in (13)C. The δ(15)N values were in the reported range for algae, and a moderate correlation between (13)C and (15)N content was observed. These measurements indicated that the season had a higher impact on the δ(13)C values than the location. Compound specific carbon isotope analysis by gas chromatography coupled with isotope ratio mass spectrometry (GC-IRMS) was used to verify an even stronger depletion in (13)C in the halogenated natural product (HNP) MHC-1 isolated from the seaweed samples. The δ(13)C values of MHC-1 in the range -42 to -45‰ are the lightest determined to date for polyhalogenated compounds in the molecular mass range between 250 and 800 Da. MHC-1 was also isolated from two fish samples. The much higher (13)C content in MHC-1 from the fish samples (-35.6 to -39.2‰) indicated carbon isotope enrichment due to partial transformation. In processes such as the reductive debromination, the partial transformation is associated with an increase in the (13)C content in the remaining non-metabolized share of a compound. Stable isotope analysis may thus provide insights into the degree of transformation of HNPs in environmental samples.     

Evaluation of optimal conditions for determination of low selenium content in shellfish samples collected at Todos os Santos Bay,Bahia, Brazil using HG-AFS

This work proposes a procedure for the determination of total selenium content in shellfish after digestion of samples in block using cold finger system and detection using atomic fluorescent spectrometry coupled hydride generation (HG AFS). The optimal conditions for HG such as effect and volume of prereduction KBr 10 % (m/v) (1.0 and 2.0 ml) and concentration of hydrochloric acid (3.0 and 6.0 mol L^?1) were evaluated. The best results were obtained using 3 mL of HCl (6 mol L^?1) and 1 mL of KBr 10 % (m/v), followed by 30 min of prereduction for the volume of 1 mL of the digested sample. The precision and accuracy were assessed by the analysis of the Certified Reference Material NIST 1566b. Under the optimized conditions, the detection and quantification limits were 6.06 and 21.21 μg kg^?1, respectively. The developed method was applied to samples of shellfish (oysters, clams, and mussels) collected at Todos os Santos Bay, Bahia, Brazil. Selenium concentrations ranged from 0.23?±?0.02 to 3.70?±?0.27 mg kg^?1 for Mytella guyanensis and Anomalocardia brasiliana, respectively. The developed method proved to be accurate, precise, cheap, fast, and could be used for monitoring Se in shellfish samples.