Spatial-Scale Effects on Relative Importance of Physical Habitat Predictors of Stream Health

A common theme in recent landscape studies is the comparison of riparian and watershed land use as predictors of stream health. The objective of this study was to compare the performance of reach-scale habitat and remotely assessed watershed-scale habitat as predictors of stream health over varying spatial extents. Stream health was measured with scores on a fish index of biotic integrity (IBI) using data from 95 stream reaches in the Eastern Corn Belt Plain (ECBP) ecoregion of Indiana. Watersheds hierarchically nested within the ecoregion were used to regroup sampling locations to represent varying spatial extents. Reach habitat was represented by metrics of a qualitative habitat evaluation index, whereas watershed variables were represented by riparian forest, geomorphology, and hydrologic indices. The importance of reach- versus watershed-scale variables was measured by multiple regression model adjusted-R² and best subset comparisons in the general linear statistical framework. Watershed models had adjusted-R² ranging from 0.25 to 0.93 and reach models had adjusted-R² ranging from 0.09 to 0.86. Better-fitting models were associated with smaller spatial extents. Watershed models explained about 15% more variation in IBI scores than reach models on average. Variety of surficial geology contributed to decline in model predictive power. Results should be interpreted bearing in mind that reach habitat was qualitatively measured and only fish assemblages were used to measure stream health. Riparian forest and length-slope (LS) factor were the most important watershed-scale variables and mostly positively correlated with IBI scores, whereas substrate and riffle-pool quality were the important reach-scale variables in the ECBP.     

Chemical and microbial hypotheses explaining the effect of wastewater treatment plant discharges on the nitrifying communities in freshwater sediment

Nitrification is a microbial key step of the nitrogen cycle, which performs the oxidation of ammonium to nitrate, via nitrite. In aquatic environments, it mainly takes place in the sediment or is associated with suspended particles. Wastewater treatment plant (WTP) discharges in rivers may disrupt sediment nitrification: this impact is related to nitrogen inputs (mainly NH(4)(+) and organic nitrogen) but could also depend on the nitrifying bacteria inputs which have been proved to survive downstream WTP discharge points. The aim of the present study was to assess the effect of NH(4)(+) and nitrifying bacteria inputs on the two steps of nitrification in freshwater sediments.To avoid natural sites constraints and to control the main environmental parameters, we used microcosms to simulate a river receiving different types of WTP discharges. These microcosms were composed of five glass dual-walls reactors (6 l) containing sediment and continuously filled (controlled flow) with river water and WTP effluent. Two types of effluents were tested: a non-nitrified one (high NH(4)(+) input, very few nitrifying bacteria) and a nitrified one (low NH(4)(+) input, more nitrifying bacteria), at different effluent/freshwater ratios (0/100, 20/80, 40/60 and 80/20). Changes in the ammonium- and nitrite-oxidizing communities were assessed by the Most Probable Number method, and changes in potential ammonium-oxidizing activity and potential nitrite-oxidizing activity were determined by incubations with specific inhibitors (sodium chlorate and allylthiourea).In most of the cases the presence of effluent induced significant changes of the nitrifying bacteria densities and potential activities in the sediment. This effect indicates generally a loss of specific potential activity and in most of the time is significant for a high effluent/river water ratio (40% to 80%). In our experimental conditions and in the case of a large WTP discharge, the nitrifying potential in freshwater sediments could thus be significantly modified.     

Testicular histopathology in deer mice (Peromyscus maniculatus) following exposure to polychlorinated biphenyl

Adult deer mice testes were subjected to routine histopathology following exposure to Aroclor 1254 supplemented diet (5 ppm), for 30 days. Body and testicular weight revealed no statistical significance between the control and treated animals. From a histological standpoint the testes of the controls were similar to normal murids and other animals. In contrast, the testes from treated animals displayed seminiferous tubules with significant degenerative alterations. These alterations included fewer layers of seminiferous epithelium exaggerated intercellular spaces and appearance of pyknotic nuclei. Most tubules displayed subluminal nuclei that morphologically could be identified as part of spermatozoa heads and these usually lacked tails, indicating that the treatment interfered with spermiogenesis. Therefore, we concluded that Aroclor 1254 as an environmental contaminant is highly destructive to seminiferous tubules, and that these histological alterations undoubtedly are responsible for the depressed fertility in Peromyscus following chronic exposure to PCBs, that has been reported in the literature.     

A Hydrologic/Water Quality Model Applicati11

Abstract: This paper presents a procedure for standard application of hydrologic/water quality models. To date, most hydrologic/water quality modeling projects and studies have not utilized formal protocols, but rather have employed ad hoc approaches. The procedure proposed is an adaptation and extension of steps identified from relevant literature including guidance provided by the U.S. Environmental Protection Agency. This protocol provides guidance for establishing written plans prior to conducting modeling efforts. Eleven issues that should be addressed in model application plans were identified and discussed in the context of hydrologic/water quality studies. A graded approach for selection of the level of documentation for each item was suggested. The creation and use of environmental modeling plans is increasingly important as the results of modeling projects are used in decision‐making processes that have significant implications. Standard modeling application protocols similar to the proposed procedure herein provide modelers with a roadmap to be followed, reduces modelers’ bias, enhances the reproducibility of model application studies, and eventually improves acceptance of modeling outcomes.     

ROLE OF WATERSHED SUBDIVISION ON MODELING THE EFFECTIVENESS OF BEST MANAGEMENT PRACTICES WITH SWAT1

Distributed parameter watershed models are often used for evaluating the effectiveness of various best management practices (BMPs). Streamflow, sediment, and nutrient yield predictions of a watershed model can be affected by spatial resolution as dictated by watershed subdivision. The objectives of this paper are to show that evaluation of BMPs using a model is strongly linked to the level of watershed subdivision; to suggest a methodology for identifying an appropriate subdivision level; and to examine the efficacy of different BMPs at field and watershed scales. In this study, the Soil and Water Assessment Tool (SWAT) model was calibrated and validated for streamflow, sediment, and nutrient yields at the outlet of the Dreisbach (623 ha) and Smith Fry (730 ha) watersheds in Maumee River Basin, Indiana. Grassed waterways, grade stabilization structures, field borders, and parallel terraces are the BMPs that were installed in the study area in the 1970s. Sediment and nutrient outputs from the calibrated model were compared at various watershed subdivision levels, both with and without implementation of these BMPs. Results for the study watersheds indicated that evaluation of the impacts of these BMPs on sediment and nutrient yields was very sensitive to the level of subdivision that was implemented in SWAT. An optimal watershed subdivision level for representation of the BMPs was identified through numerical simulations. For the study watersheds, it would appear that the average subwatershed area corresponding to approximately 4 percent of total watershed area is needed to represent the influence of these BMPs when using the SWAT model.     

The infinite-lived rat—An equal-age replacement process

Equal-age replacement is used to formulate the competing-risk problem in terms of a set of nonhomogenous Poisson processes whose mean value functions are the set of cumulative hazards (the integrals of the age-and cause-specific incidence rates). Cumulative hazard is estimated by a weighted count that is the sum of the reciprocals of numbers at risk at the times of occurrence of the specific risk. Occurrence data are generally insufficient to distinguish between plausible forms of the distribution function or types of nonparametric shifts with dose. More emphasis has to be given to understanding the biological mechanisms that dictate the parametric form to be fitted to the data.     

Perceptions of using low-quality irrigation water in vegetable production in Morogoro,Tanzania

This study was conducted to examine perceptions of the farmers and key informants on the use of low-quality irrigation water for vegetable production in urban and peri-urban areas in Morogoro, Tanzania. The methods used to collect data were farmer surveys (n = 60), focus group discussions (n = 4) and key informants interviews (n = 15). The results showed that the respondents had a positive perception on using low-quality irrigation water for vegetable production. The reported benefits include availability of water throughout the year, highest soil and crop nutrients in irrigation water, less costs of buying commercial fertilizers, vegetable production all year round, sustainable income generation from selling vegetables and also jobs creation in the community among farmers and vegetable sellers. Findings from Mann–Whitney U test and Kruskal–Wallis test score on farmers perception scales indicate an association between the source of low-quality water used and the respondents’ sex. Accordingly, female farmers had higher positive perception on the benefits of low-quality water compared to male farmers. Higher perception score was also observed among farmers who used polluted river water in irrigation vegetable production compared to farmers who used wastewater. Since low-quality irrigation water is a good strategy of coping with scarcity of freshwater for communities which have no alternative source of irrigation water, the study recommends multi-sectorial agencies across the country to be involved in formulating policies and creating health promotion awareness for safe use of low-quality water for benefit maximization and health risk reduction.     

Comparison of PoraPak Rxn RP and XAD-2 adsorbents for monitoring dissolved hydrophobic organic contaminants

Accurate determination of the levels of dissolved hydrophobic organic contaminants (HOCs) is an important step in estimating the dynamics of their inputs and losses in aqueous systems. This study explores an alternative method for efficiently sampling dissolved HOCs while mitigating a number of sampling artifacts associated with traditional methods. The adsorption characteristics of a new polymeric resin, PoraPak Rxn RP (PPR), were assessed using sorption isotherm experiments and fixed bed adsorption studies. The adsorption capacities and breakthrough times for four model contaminants (phenol, p-nitrophenol, naphthalene, and 2,4,6-tribromophenol) were proportional to the contaminant’s hydrophobicity. The ability of PPR to isolate dissolved polychlorinated biphenyls (PCBs) in real samples was compared with that of XAD-2, a well-known macroporous polymer that suffers from high background contamination. The results indicated that the PPR resin can be effectively used for monitoring HOCs, with low ∑PCB levels in blanks, decreasing solvent use, and reducing extraction times.     

Soil climate and decomposer activity in Sub-Saharan Africa estimated from standard weather station data: a simple climate index for soil carbon balance calculations

Soil biological activity was calculated on a daily basis, using standard meteorological data from African weather stations, a simple soil water model, and commonly used assumptions regarding the relations between temperature, soil water content, and biological activity. The activity factor r(e_clim) is calculated from daily soil moisture and temperature, thereby taking the daily interaction between temperature and moisture into account. Annual mean r(e_clim) was normalized to 1 in Central Sweden (clay loam soil, no crop), where the original calibration took place. Since soils vary in water storage capacity and plant cover will affect transpiration, we used this soil under no crop for all sites, thereby only including climate differences. The Swedish r(e_clim) value, 1, corresponds to ca. 50% annual mass loss of, e.g., cereal straw incorporated into the topsoil. African mean annual r(e_clim) values varied between 1.1 at a hot and dry site (Faya, Chad) and 4.7 at a warm and moist site (Brazzaville, Congo). Sites in Kenya ranged between r(e_clim) = 2.1 at high altitude (Matanya) and 4.1 in western Kenya (Ahero). This means that 4.1 times the Swedish C input to soil is necessary to maintain Swedish soil carbon levels in Ahero, if soil type and management are equal. Diagrams showing daily r(e_clim) dynamics are presented for all sites, and differences in within-year dynamics are discussed. A model experiment indicated that a Swedish soil in balance with respect to soil carbon would lose 41% of its soil carbon during 30 y, if moved to Ahero, Kenya. If the soil was in balance in Ahero with respect to soil carbon, and then moved to Sweden, soil carbon mass would increase by 64% in 30 y. The validity of the methodology and results is discussed, and r(e_clim) is compared with other climate indices. A simple method to produce a rough estimate of r(e_clim) is suggested.