INCREASED BASEFLOW IN IOWA OVER THE SECOND HALF OF THE 20TH CENTURY1

ABSTRACT: Historical trends in annual discharge characteristics were evaluated for 11 gauging stations located throughout Iowa. Discharge records from nine eight‐digit hydrologic unit code (HUC‐8) watersheds were examined for the period 1940 to 2000, whereas data for two larger river systems (Cedar and Des Moines Rivers) were examined for a longer period of record (1903 to 2000). In nearly all watersheds evaluated, annual base flow, annual minimum flow, and the annual base flow percentage significantly increased over time. Some rivers also exhibited increasing trends in total annual discharge, whereas only the Maquoketa River had significantly decreased annual maximum flows. Regression of stream discharge versus precipitation indicated that more precipitation is being routed into streams as base flow than as storm flow in the second half of the 20th Century. Reasons for the observed stream flow trends are hypothesized to include improved conservation practices, greater artificial drainage, increasing row crop production, and channel incision. Each of these reasons is consistent with the observed trends, and all are likely responsible to some degree in most watersheds.     

不同碳源条件下草菇内切型纤维素酶基因（eg1）转录表达的分析

利用Northernblot方法分析了不同碳源条件下草菇切型纤维素酶基因(eg1)的表达.结果发现,在含有纤维素的液体培养基中生长10d,eg1在草菇菌丝中有高效表达;纤维二糖、α-乳糖、β-乳糖,也能诱导eg1的表达,但和纤维素相比,eg1的表达量相对较低,并且它们的诱导效应在加入这类糖12h后迅速减弱;槐糖和龙胆二糖的诱导作用非常弱.在天然稻草为基质的固体栽培料生长时,草菇eg1的表达和草菇菌丝生长与出菇相对应,在菌丝生长期(d8)可见eg1的表达,d12时菌丝已长满,表达减弱,在出菇及菇体的分化及增大期,eg1的表达量逐渐增强,在成熟期达到最高水平;表明在草菇菇体发育中需要更多碳源及能源的补充,eg1在这方面起着非常重要的作用.图4参14     

DETECTING CILANGES IN THE SPATIAL DISTRIBUTION OF NITRATE CONTAMINATION IN GROUND WATER1

ABSTRACT: Many studies of ground water pollution in general and nitrate contamination in particular have often relied on a one-time investigation, tracking of individual wells, or aggregate summaries. Studies of changes in spatial distribution of contaminants over time are lacking. This paper presents a method to compare spatial distributions for possible changes over time. The large-scale spatial distribution at a given time can be considered as a surface over the area (a trend surface). The changes in spatial distribution from period to period can be revealed by the differences in the shape and/or height of surfaces. If such a surface is described by a polynomial function, changes in surfaces can be detected by testing statistically for differences in their corresponding polynomial functions. This method was applied to nitrate concentration in a population of wells in an agricultural drainage basin in Iowa, sampled in three different years. For the period of 1981–1992, the large-scale spatial distribution of nitrate concentration did not show significant change in the shape of spatial surfaces; while the magnitude of nitrate concentration in the basin, or height of the computed surfaces showed significant fluctuations. The change in magnitude of nitrate concentration is closely related to climatic variations, especially in precipitation. The lack of change in the shape of spatial surfaces means that either the influence of land use/nitrogen management was overshadowed by climatic influence, or the changes in land use/management occurred in a random fashion.     

Mechanism and kinetic model for the decolorization of the azo dye Reactive Black 5 by hydrogen peroxide and UV radiation

A kinetic model for the decolorization of C.I. Reactive Black 5 by the combination of hydrogen peroxide and UV radiation was developed based on experimental results and known chemical and photochemical reactions. The observed kinetic reaction coefficient was determined and correlated as a function of hydrogen peroxide concentration and UV intensity. The validity of the rate expression was tested experimentally in a parameterization study. The decolorization rate follows pseudo-first order kinetics with respect to dye concentration. The rate increases linearly with UV intensity and nonlinearly with increasing hydrogen peroxide concentration, going from a linear relationship at low H(2)O(2) concentrations to a maximum as hydrogen peroxide concentration continues to increase. The decolorization rate expression derived from the proposed reaction mechanism was reconciled with that used for correlating the experimental data.     

Two stage biological treatment of a diazo reactive textile dye and the fate of the dye metabolites

A two stage anaerobic/aerobic bacterial process was used to decolorize and partially mineralize a reactive vinyl sulfone diazo dye C.I. Reactive Black 5 (RB5) in a synthetic wastewater. Since the anchor group of reactive dyes reacts during the dyeing process, the effect the degree of hydrolysis of the vinyl sulfone dye had on decolorization, mineralization and toxicity in each stage was investigated. An overall color removal of approximately 65% was found for both the fully and partially hydrolyzed dye. Partial mineralization of the fully hydrolyzed RB5 was achieved in the two stage rotating disc reactors. While the anchor group metabolite p-aminobenzene-2-hydroxyethylsulfonic acid (p-ABHES) was mineralized, an oxidized form of the center metabolite (1,2-ketimino-7-amino-8-hydroxynaphthalene-3,6-disulfonic acid) remained in the aerobic stage effluent, causing the effluent to be colored although no RB5 was present. Partially hydrolyzed dye in the influent with vinyl forms of the anchor group caused cessation of biogas production and a reduction in decolorization efficiency in the anaerobic stage. No evidence for mineralization of the partially hydrolyzed dye or its metabolites was found. A method for evaluating dye mineralization using lumped parameters is presented.     

Evaluation of ceramic and membrane diffusers under operating conditions with the dynamic offgas method.

The aeration systems of two full-scale, activated-sludge basins were compared during a period of three years, under the same operating conditions, using dynamic offgas testing. Only the material of the diffuser was different (membrane versus ceramic-tube diffusers). The investigation has shown that, although the membrane diffusers have higher initial standard-oxygen-transfer efficiency (alphaSOTE) and standard-aeration efficiency (alphaSAE), these decreased over time, while the alphaSAE of the ceramic diffusers started lower, but increased slightly over the whole period. A cost comparison makes clear how important it is to evaluate the aeration system under process conditions. The operating costs were the dominant factor (approximately 10x higher than capital costs), and operating costs were approximately 20% higher for membrane versus ceramic diffusers. The poor performance of the membrane-tube diffusers under process conditions could be explained on the basis of the actual alphaAE values in the basin, not the standardized values.     

Revisiting nitrate concentrations in the Des Moines River: 1945 and 1976-2001

Recent compilations of historical and contemporary riverine nitrate (NO3) concentrations indicate that concentrations in many rivers in the north-central USA increased during the second half of the 20th century. The Des Moines River near Des Moines, Iowa, however, was reported to have had similar NO3 concentrations in 1945 and the 1980s, in spite of substantially greater N input to the watershed during the latter period. The objective of this study was to reconsider the comparison of historical and contemporary NO3 concentrations in the Des Moines River near Des Moines in light of the following: (i) possible errors in the historical data used, (ii) variations in methods of sample collection, (iii) variations in location of sampling, and (iv) additional data collected since 1990. We discovered that an earlier study had compared the flow-weighted average concentration in 1945 to arithmetic annual average concentrations in the 1980s. The intertemporal comparison also appeared to be influenced by differences in sample collection methods and locations used at different times. Depending on the model used and the estimated effects of composite sample collection, the 1945 arithmetic average NO3 concentration was between 44 and 57% of the expected mean value at a similar water yield during 1976-2001. The flow-weighted average NO3 concentration for 1945 was between 54 and 73% of the expected mean value at a similar water yield during 1976-2001. The difference between NO3 concentrations in 1945 and the contemporary period are larger than previously reported for the Des Moines River.     

不同碳源条件下草菇内切型纤维素酶基因(egl)转录表达的分析

利用Northern blot方法分析了不同碳源条件下草菇內切型纤维素酶基因(eg1)的表达.结果发现,在含有纤维素的液体培养基中生长10 d,eg1在草菇菌丝中有高效表达;纤维二糖、α-乳糖、β-乳糖,也能诱导eg1的表达,但和纤维素相比,eg1的表达量相对较低,并且它们的诱导效应在加入这类糖12 h后迅速减弱;槐糖和龙胆二糖的诱导作用非常弱.在天然稻草为基质的固体栽培料生长时,草菇eg1的表达和草菇菌丝生长与出菇相对应,在菌丝生长期(d 8)可见eg1的表达,d 12时菌丝已长满,表达减弱,在出菇及菇体的分化及增大期,eg1的表达量逐渐增强,在成熟期达到最高水平;表明在草菇菇体发育中需要更多碳源及能源的补充,eg1在这方面起着非常重要的作用. 图4 参14