No abstract

Free chlorine is a potent oxidizing agent and has been used extensively as a disinfectant in processes including water treatment. The presence of free chlorine residual is essential for the prevention of microbial regrowth in water distribution systems. However, excessive levels of free chlorine can cause adverse health effects. It is a major challenge to maintain appropriate levels of free chlorine residual in premise plumbing. As the first effort to assessing the fate of chlorine in premise plumbing using actual premise plumbing pipe sections, three piping materials frequently used in premise plumbing, i.e. copper, galvanized iron, and polyvinyl chloride (PVC), were investigated for their performance in maintaining free chlorine residual. Free chlorine decay was shown to follow first-order kinetics for all three pipe materials tested. The most rapid chlorine decay was observed in copper pipes, suggesting the need for higher chlorine dosage to maintain appropriate levels of free chlorine residual if copper piping is used. PVC pipes exhibited the least reactivity with free chlorine, indicative of the advantage of PVC as a premise plumbing material for maintaining free chlorine residual. The reactivity of copper piping with free chlorine was significantly hindered by the accumulation of pipe deposits. In contrast, the impact on chlorine decay by pipe deposits was not significant in galvanized iron and PVC pipes. Findings in this study are of great importance for the development of effective strategies for the control of free chlorine residual and prevention of microbiological contamination in premise plumbing.

No abstract

West Tennessee’s supplemental irrigation management at a field level is profoundly affected by the spatial heterogeneity of soil moisture and the temporal variability of weather. The introduction of precision farming techniques has enabled farmers to collect site-specific data that provide valuable quantitative information for effective irrigation management. Consequently, a two-year on-farm irrigation experiment in a 73 ha cotton field in west Tennessee was conducted and a variety of farming data were collected to understand the relationship between crop yields, the spatial heterogeneity of soil water content, and supplemental irrigation management. The soil water content showed higher correlations with soil textural information including sand (r = −0.9), silt (r = 0.85), and clay (r = 0.83) than with soil bulk density (r = −0.27). Spatial statistical analysis of the collected soil samples (i.e., 400 samples: 100 locations at four depths from 0–1 m) showed that soil texture and soil water content had clustered patterns within different depths, but BD mostly had random patterns. ECa maps tended to follow the same general spatial patterns as those for soil texture and water content. Overall, supplemental irrigation improved the cotton lint yield in comparison to rainfed throughout the two-year irrigation study, while the yield response to supplemental irrigation differed across the soil types. The yield increase due to irrigation was more pronounced for coarse-textured soils, while a yield reduction was observed when higher irrigation water was applied to fine-textured soils. In addition, in-season rainfall patterns had a profound impact on yield and crop response to supplemental irrigation regimes. The spatial analysis of the multiyear yield data revealed a substantial similarity between yield and plant-available water patterns. Consequently, variable rate irrigation guided with farming data seems to be the ideal management strategy to address field level spatial variability in plant-available water, as well as temporal variability in in-season rainfall patterns.

Basalt aquifers are common in many parts of Canada and the United States; however, little is known about their microbial ecology. Microbial populations were characterized at a basalt aquifer with 7 m of clay and silt in the vadose zone and a saturated zone extending from 7 to 500 m. Planktonic total counts and viable counts were 1.7 × 105 and 2.3 × 104 cells/mL, while sessile total counts and viable counts were 1.9 × 107 and 1.7 × 105 cells/g, respectively. Some of the physical and chemical habitat conditions measured were pH (7.1), Eh (135 mV), dissolved O2 (4.1 mg/L), temperature (10 °C), NH4+ (4 μM), NO3− (253 μM), Fe (0.17 μM), and Mn (36 nM). Variation in physical and chemical variables correlated with depth and the region of the aquifer sampled. One hundred forty-nine random isolates of the dominant culturable bacteria from groundwater and subsurface cores were submitted to phenotypic analysis on the basis of antibiotic responses. The resultant dominant bacteria were Gram-negative, mesophilic heterotrophs. Cluster analysis revealed at least 14 discernible clusters containing representatives from the genera Pseudomonas, Bacillus, Acinetobacter, Arthrobacter, Micrococcus, and Clavibacter. Centrotype representatives were selected from each cluster and tentatively identified.Key words: basalt aquifer bacterial ecology.