Nitrate transport in shallow groundwater at the stream–riparian interface in an urbanizing catchment

Drive point peizometers were installed at the stream–riparian interface in a small urbanizing southern Ontario catchment to measure the effect of buffers (presence/ absence) and land use (urban/agricultural) on the movement of NO^? ₃-N in shallow groundwater from the riparian area to the stream. Mean NO^? ₃-N concentrations ranged from 1.0 to 1.3 mg L^?1 with maximum values of 9.4 mg L^?1. Holding land use constant, there was no significant difference (p>0.05) in NO^? ₃3-N concentration between buffered and unbuffered sites. Nitrate-N levels were not significantly different (p>0.05) as a function of land use. The lack of difference between sites as a function of buffer absence/presence and land use is probably due to the placement of some peizometers in low conductivity materials that limited groundwater flow from the riparian zone to the stream. Subsurface factors controlling the hydraulic gradient are important in defining buffer effectiveness and buffer zones should not be used indiscrim inately as a management tool in urban and agricultural landscapes to control nitrate-N loading in shallow groundwater to streams without detailed knowledge of the hydrogeo logic environment.     

Insights into the nature of secondary organic aerosol in Mexico City during the MILAGRO experiment 2006

This study targets understanding the secondary sources of organic aerosol in Mexico City during the Megacities Impact on Regional and Global Environment (MIRAGE) 2006 field campaign. Ambient PM_2.5 was collected daily at urban and peripheral locations. Particle-phase secondary organic aerosol (SOA) products of anthropogenic and biogenic precursor gases were measured by gas chromatography mass spectrometry. Ambient concentrations of SOA tracers were used to estimate organic carbon (OC) from secondary origins (SOC). Anthropogenic SOC was estimated as 20–25% of ambient OC at both sites, while biogenic SOC was less abundant, but was relatively twice as important at the peripheral site. The OC that was not attributed secondary sources or to primary sources in a previous study showed temporal consistency with biomass-burning events, suggesting the importance of secondary processing of biomass-burning emissions in the region. The best estimate of biomass-burning-related SOC was in the range of 20–30% of ambient OC during peak biomass burning events. Low-molecular weight (MW) alkanoic and alkenoic dicarboxylic acids (C₂–C₅) were also measured, of which oxalic acid was the most abundant. The spatial and temporal trends of oxalic acid differed from tracers for primary and secondary sources, suggesting that it had different and/or multiple sources in the atmosphere.     

Land application of tylosin and chlortetracycline swine manure: Impacts to soil nutrients and soil microbial community structure

The land application of aged chortetracycle (CTC) and tylosin-containing swine manure was investigated to determine associated impacts to soil microbial respiration, nutrient (phosphorus, ammonium, nitrate) cycling, and soil microbial community structure under laboratory conditions. Two silty clay loam soils common to southeastern South Dakota were used. Aerobic soil respiration results using batch reactors containing a soil-manure mixture showed that interactions between soil, native soil microbial populations, and antimicrobials influenced CO₂ generation. The aged tylosin treatment resulted in the greatest degree of CO₂ inhibition, while the aged CTC treatment was similar to the no-antimicrobial treatment. For soil columns in which manure was applied at a one-time agronomic loading rate, there was no significant difference in soil-P behavior between either aged CTC or tylosin and the no-antimicrobial treatment. For soil-nitrogen (ammonium and nitrate), the aged CTC treatment resulted in rapid ammonium accumulation at the deeper 40cm soil column depth, while nitrate production was minimal. The aged CTC treatment microbial community structure was different than the no-antimicrobial treatment, where amines/amide and carbohydrate chemical guilds utilization profile were low. The aged tylosin treatment also resulted in ammonium accumulation at 40 cm column depth, however nitrate accumulation also occurred concurrently at 10 cm. The microbial community structure for the aged tylosin was also significantly different than the no-antimicrobial treatment, with a higher degree of amines/amides and carbohydrate chemical guild utilization compared to the no-antimicrobial treatment. Study results suggest that land application of CTC and tylosin-containing manure appears to fundamentally change microbial-mediated nitrogen behavior within soil A horizons.     

Field demonstration of visible opacity photographic systems

The Digital Opacity Compliance System (DOCS) is an innovative method that uses digital imaging technology to quantify visible opacity of stationary sources. DOCS, which has been demonstrated at pilot and full scale as a technically defensible and economically attractive alternative to U.S. Environmental Protection Agency (EPA) Reference Method 9 (Method 9), uses commercial-off-the-shelf (COTS) digital cameras in combination with a user-friendly computer software package to determine opacity. To date, all DOCS field testing has been conducted using two models of digital cameras, notably, Kodak Models DC265 and DC290, both of which are no longer commercially available. To ensure that field-validated digital cameras will be available to future DOCS users, a suite of new digital cameras was evaluated with the opacity determination software including the following: (1) Sony Model Cybershot Model DSC-WI, (2) Nikon Model Coolpix 5200, (3) Fuji Finepix Model E500, and (4) Kodak Model DX6490. Within the opacity range of regulatory interest, that is, 0-40%, the Sony Cybershot Model DSC-WI and Nikon Coolpix Model 5200 digital cameras were found to generate plume photographs of which the DOCS opacity analysis yielded results that were statistically equivalent to the previously field-validated Kodak Model DC290. In contrast, the Fuji Finepix Model E500 generated plume photographs of which the DOCS opacity analysis were, on average, 2.2% less than those generated by the Kodak Model DC290 photographs, a difference that was determined to be statistically significant. Over the same opacity range, photographs taken by the Kodak Model DX6490 yielded DOCS opacity readings that were found to be statistically equivalent to a Method 9-certified transmissometer. Based on the results from the current digital camera validation testing approach, EPA has developed a new camera-based visible opacity measurement method titled "Determination of Visible Emission Opacity from Stationary Sources Using Computer-Based Photographic Analysis Systems." The proposed method is expected to be promulgated after closure of the public comment period.     

Storm flow export of metolachlor from a coastal plain watershed

During an 18-month (1994-1995) survey of the surface water in an Atlantic Coastal Plain watershed, metolachlor was most frequently detected during storm flow events. Therefore, a sampling procedure, focused on storm flow, was implemented in June of 1996. During 1996, three tropical cyclones made landfall within 150 km of the watershed. These storms, as well as several summer thunderstorms, produced six distinct storm flow events within the watershed. Metolachlor was detected leaving the watershed during each event. In early September, Hurricane Fran produced the largest storm flow event and accounted for the majority of the metolachlor exports. During the storm event triggered by Hurricane Fran, the highest daily average flow (7.5 m2 s-1) and highest concentration (5.1 micrograms L-1) ever measured at the watershed outlet were recorded. Storm flow exports leaving the watershed represented 0.1 g ha-1 or about 0.04% of active ingredient applied.     

Climate change vulnerability assessments as catalysts for social learning: four case studies in south-eastern Australia

Technical assessments of vulnerability and/or risk are increasingly being undertaken to assess the impacts of climate change. Underlying this is the belief that they will bring clarity to questions regarding the scale of institutional investments required, plausible adaptation policies and measures, and the timing of their implementation. Despite the perceived importance of technical assessments in 'evidence-based' decision environments, assessments cannot be undertaken independent of values and politics, nor are they capable of eliminating the uncertainty that clouds decision-making on climate adaptation As such, assessments can trigger as many questions as they answer, leaving practitioners and stakeholders to question their value. This paper explores the value of vulnerability/risk assessments in climate change adaptation planning processes as a catalyst for learning in four case studies in Southeastern Australia. Data were collected using qualitative interviews with stakeholders involved in the assessments and analysed using a social learning framework. This analysis revealed that detailed and tangible strategies or actions often do not emerge directly from technical assessments. However, it also revealed that the assessments became important platforms for social learning. In providing these platforms, assessments present opportunities to question initial assumptions, explore multiple framings of an issue, generate new information, and galvanise support for collective actions. This study highlights the need for more explicit recognition and understanding of the important role social learning plays in climate change vulnerability assessments and adaptation planning more broadly.     

Why do females have so few extra-pair offspring?

It is generally accepted that if a female can improve her offspring’s genetics via extra-pair copulations (EPC), it is by copulating with extra-pair males whose phenotypes are more superior or whose genes are more compatible to hers than those of her bonded male. Here, we present a model that puts together uncertainties about the male genetic quality, a postcopulatory sperm bias in favor of the better or the more compatible genes, and costs that females pay by being choosy about extra-pair male quality. The model’s conclusions challenge traditional views of good genes explanations of EPC. When phenotypes give incomplete information about genotypes, a female choosing a phenotypically superior extra-pair male, may nevertheless find herself trading good genes of a bonded male for poor genes of an extra-pair male. Such “unfortunate sperm replacements” can limit the female involvement in EPC even when EPC are otherwise cost-free. The model also shows that even a female bonded to a phenotypically superior male may benefit by EPC, provided that sperm competition is biased toward sperm with more fit or more compatible genes. Furthermore, if choosiness is sufficiently costly, a female may even do best by copulating with a random extra-pair male.