Andrew E. Laursen

Scaling the gas transfer velocity and hydraulic geometry in streams and small rivers

Scaling is an integral component of ecology and earth science. To date, the ability to determine the importance of air – water gas exchange across large spatial scales is hampered partly by our ability to scale the gas transfer velocity and stream hydraulics. Here we report on a metadata analysis of 563 direct gas tracer release experiments that examines scaling laws for the gas transfer velocity. We found that the gas transfer velocity scales with the product of stream slope and velocity, which is in alignment with theory on stream energy dissipation. In addition to providing equations that predict the gas transfer velocity based on stream hydraulics, we used our hydraulic data set to report a new set of hydraulic exponents and coefficients that allow the prediction of stream width, depth, and velocity based on discharge. Finally, we report a new table of gas Schmidt number dependencies to allow researchers to estimate a gas transfer velocity using our equation for many gasses of interest.

Forensic Fingerprinting of Oil-Spill Hydrocarbons in a Methanogenic Environment–Mandan, ND and Bemidji, MN

In recent decades forensic fingerprinting of oil-spill hydrocarbons has emerged as an important tool for correlating oils and for evaluating their source and character. Two long-term hydrocarbon spills, an off-road diesel spill (Mandan, ND) and a crude oil spill (Bemidji, MN) experiencing methanogenic biodegradation were previously shown to be undergoing an unexpected progression of homologous n-alkane and n-alkylated cyclohexane loss. Both exhibited degradative losses proceeding from the high-molecular-weight end of the distributions, along with transitory concentration increases of lower-molecular-weight homologs. Particularly in the case of the diesel fuel spill, these methanogenic degradative patterns can result in series distributions that mimic lower cut refinery fuels or admixture with lower cut fuels. Forensic fingerprinting in this long-term spill must therefore rely on more recalcitrant series, such as polycyclic aromatic hydrocarbon or drimane sesquiterpane profiles, to prove if the spilled oil is single-sourced or whether there is verifiable admixture with other extraneous refinery fuels. Degradation processes impacting n-alkanes and n-alkylated ring compounds, which make these compounds unsuitable for fingerprinting, nevertheless are of interest in understanding methanogenic biodegradation.

Evaluation of low-copy genetic targets for waterborne bacterial pathogen detection via qPCR.

Recent developments in water quality research have highlighted difficulties in accurately predicting the incidence of pathogens within freshwater based on the viability, culturability and metabolic activity of indicator organisms. QPCR-driven assays are candidates to replace standard culture-based methods, however, protocols suitable for routine use have yet to be sufficiently validated. The objective of this study was to evaluate five oligonucleotide primers sets (ETIR, SINV, exoT, VS1 and ipaH2) for their potential applicability in qPCR assays to detect contamination from five waterborne bacterial pathogens (Escherichia coli O157:H7, Salmonella Typhimurium, Campylobacter jejuni, Pseudomonas aeruginosa, and Shigella flexneri). An enrichment-free qPCR protocol was also tested using S. Typhimurium-seeded source water, combining membrane filtration and mechanical, chemical and enzymatic lysis techniques to recover the bacterial cells. All five primer sets were found to have high specificity and sensitivity for the tested organisms. Four of the primers were able to detect pathogen loads as low as 10 cells/mL while 200 cells/mL of C. jejuni were detectable in pure culture. Although sensitivity decreased in an artificially contaminated environmental matrix, it was still possible to detect as few as 10 S. Typhimurium cells without enrichment. The primers and protocols evaluated in this study have demonstrated potential for further validation for possible application alongside traditional indicator techniques.

Utilization of multiple organisms in a proposed early-warning biomonitoring system for real-time detection of contaminants: preliminary results and modeling

During past decades, biomonitors were deployed in lakes and rivers to rapidly detect hazardous chemicals by measuring the endpoints of a single aquatic species at defined short intervals. Most biomonitors, however, are only capable of indicating a departure from baseline water conditions without identifying the cause. In order to provide a more comprehensive assessment, a biomonitoring system which features a library of stereotyped responses of multiple aquatic species in various water conditions is proposed. A preliminary library was constructed by characterizing the behavioural and physiological responses of Daphnia magna, Hyalella azteca, Lumbriculus variegatus, and Pseudokirchneriella subcapitata to various concentrations of atrazine and tributyltin. By employing multivariate statistical tools such as principal component analysis (PCA) and discriminant analysis, this library (which contained responses after 6h of exposure to contaminants) was used as a template to classify and to model other sets of earlier measurements at 2 and 4h, resulting in an accuracy of 73 and 97%, respectively. These findings demonstrated the potential capability of the proposed early-warning biomonitoring system to provide real-time water quality assessment and early-warning contaminant detection.

Nitrogen and Phosphorus Loss Potential from Biosolids-Amended Soils and Biotic Response in the Receiving Water

Application of municipal biosolids to agricultural soil can improve soil quality and improve crop yields. However, runoff or tile leachate from biosolids-applied fields may contribute to localized eutrophication of surface water. A laboratory experiment was conducted to determine loss potential of nutrients from soils amended with two different biosolids (anaerobically digested and chemically stabilized) relative to loss from a reference soil and to determine response in freshwater microcosms to nutrients lost from soils. Total phosphorus (TP) and total nitrogen (TN) were measured in runoff, and equivalent amounts were added to reference microcosms to determine if aquatic systems would respond similarly to TN and TP loading in bioavailable forms (PO, NH, NO) simulating loading related to inorganic fertilizer application. Nutrient concentrations (TP, TN, PO, NH, NO, and organic P and N) were similar in the runoff from the two biosolids-amended soils and higher than those in the runoff from the reference soil. Runoff from biosolids-amended soils stimulated algal growth and production (chlorophyll a and dissolved oxygen) relative to runoff from reference soil, but the response was weaker than in microcosms receiving equivalent amounts of inorganic N and P. Nutrient runoff from land-applied biosolids does have potential to increase algal production in receiving waters; however, this experiment suggests receiving waters may absorb a single large nutrient loading event associated with runoff from biosolids-amended soil without substantial impact. Moreover, the response to N and P in biosolids versus inorganic nutrient additions suggests biosolids may contribute relatively less to eutrophication than inorganic fertilizers, assuming equivalent TN and TP loading to aquatic systems.

Bacterial cultures capable of facultative growth on methane under thermophilic or thermotolerant conditions

Bacteria cultured from thermal features (cultures OS and 44) and from sedimentary rock of the continental margin (SA) are capable of growth on methane as a sole carbon source under thermotolerant (...

Vertical Phosphorus Migration in a Biosolids-Amended Sandy Loam Soil in Laboratory Settings: Concentrations in Soils and Leachates

The impacts of biosolids land application on soil phosphorus and subsequent vertical migration to tile drainage were assessed in a laboratory setup. Soil, representing typical “nonresponse” Ontario soil as specified by Ontario Ministry of Agriculture, Food, and Rural Affairs (OMAFRA), was amended with anaerobically digested biosolids at a rate of 8 Mg ha−1 (dry weight). Over five months, these amended soil samples from two different depths were sequentially fractionated to determine various inorganic and organic phosphorus pools in order to evaluate phosphorus vertical migration within a soil profile. Soil leachate was analyzed for soluble reactive phosphorus. The results indicated that biosolids application did not significantly affect phosphorus concentrations in soil and did not cause phosphorus vertical migration. The concentrations of soluble reactive phosphorus also were not significantly affected by biosolids.

Erratum to: Vegetation Placement for Summer Built Surface Temperature Moderation in an Urban Microclimate

The first sentence in the ‘‘Acknowledgments’’ section is incorrect. It should be read as ‘‘Comments provided by three anonymous reviewers helped to improve an earlier version of this manuscript’’ instead of ‘‘We would like to acknowledge three anonymous reviewers for their comments helped to improve an earlier version of this manuscript.’’ Hence, the correct version of acknowledgements section is presented below.

Automated image analysis of Euglena gracilis Klebs (Euglenophyta) for measuring sublethal effects of three model contaminants.

The short-term impacts of atrazine (herbicide), tributyltin (organometal) and copper on the behaviour of Euglena gracilis Klebs (Euglenophyta) were assessed. First, the ECOTOX automated image analysis system was used, which measured swimming velocity, cell shape, percentage of cells swimming upwards, and randomness of swimming. Next, visual observation by microscopy was used to measure percentage of cell motility and cell shape. Behavioural changes can be used as an indicator of stress in less than 24 h, potentially making them suitable for inclusion in early-warning systems for water quality. Findings indicate that E. gracilis is a very sensitive organism to copper, showing inhibition of motility with visual observation at 0.8 μmol/L within 1 h. The image analysis system was in general less sensitive than visual observation for detecting behavioural changes after incubation in copper. In contrast, after exposure to organic contaminants atrazine and tributyltin, the ECOTOX system detected small changes in the number of cells swimming upwards (antigravitactic behaviour) at higher concentrations.