Small farm ponds: overlooked features with important impacts on watershed sediment transport

Despite their size, small farm ponds are important features in many landscapes. Yet hydrographical databases often fail to capture these ponds, and their impacts on watershed processes remain unclear. For a 230‐km² portion of central Texas, United States (U.S.), we created a historical inventory of ponds and quantified the accuracy of automated detection methods under varying drought conditions. In addition, we documented pond dredging/enlargement events and identified sites that had been abandoned. We also analyzed sediment cores from downstream reservoirs to track changes in watershed sediment transport. Over 75 years, pond densities increased more than 350% — to among the highest documented in the U.S. — and the ability of automated methods to detect these ponds was highly dependent on drought severity (R² = 0.96). Approximately 5% of ponds present in the 1950s were no longer present in 2012, while 33% were dredged between 1937 and 2012. Downstream reservoir sedimentation has decreased by an average of 55% as ponds have increased in number. These findings suggest that small ponds and the maintenance of trapping efficiency have large‐scale impacts on sediment dynamics. Accurately accounting for these storage effects is vital to water resource planning efforts.     

The EU effect: does trade with the EU reduce CO2 emissions in the developing world?

The European Union (EU) is an important destination for developing country exports. Has the EU’s commitment to the Kyoto Protocol induced developing countries to reduce their carbon dioxide (CO₂) emissions? Our analyses of 136 developing countries from 1981 through 2007 suggests that: developing countries’ export dependence on the EU is associated with CO₂ emission reductions post-Kyoto in relation to the pre-Kyoto time period; this also holds for SO_2, which, while not covered under Kyoto, is linked with CO₂ emission levels; this does not hold for PM₁₀, a pollutant which is not covered under Kyoto and is not directly associated with CO₂ emissions related to industrial activities; developing countries’ export dependence on non-EU developed countries and on the rest of the world is not associated with significant reductions in emissions between pre- and post-Kyoto for these pollutants . In sum, even in the absence of binding regulatory mandates, the EU appears to exert market leverage to project its regulatory preferences abroad.     

Effectiveness of emergent and submergent aquatic plants in mitigating a nitrogen–permethrin mixture

Hydraulically connected wetland microcosms (～50?L) in series were used to test the effectiveness of varying combinations of two common aquatic vascular plants, parrot feather (Myriophyllum aquaticum) and cattail (Typha latifolia), for mitigating contamination from a mixture of nitrogen (ammonium nitrate) and permethrin. The upstream series included Myriophyllum only (M) and Typha only (T) while the combination upstream effluent into downstream series included Myriophyllum into Myriophyllum (M?+?M) and Typha into Myriophyllum (T?+?M). During flow, M into M?+?M more efficiently mitigated nitrogen than T into T?+?M. Post-flow, nitrogen removal efficiency was greater for T versus M and M?+?M versus T?+?M. Mean aqueous dissipation half-lives (t_1/2) of NH₄-N and NO₃-N were more rapid in T than M treatments. Ammonium and nitrate t_1/2 was highly correlated with aquatic plant above-ground shoot biomass. Permethrin mitigation efficiencies and t_1/2 were not significantly affected by plant species either singly or in combination. Trans-permethrin t_1/2 was moderately correlated with plant biomass, but not cis-permethrin t_1/2. Results of this study indicate differences in aquatic plant species and flow path influence nitrogen removal but not permethrin. However, plant species appears less important than overall plant biomass in ascertaining aquatic plant effectiveness in mitigating a nitrogen–permethrin mixture.     

Effects of Spatial Distribution of Prairie Vegetation in an Agricultural Landscape on Curve Number Values

The curve number (CN) method is used to calculate runoff in many hydrologic models, including the Soil and Water Assessment Tool (SWAT). The CN method does not account for the spatial distribution of land cover types, an important factor controlling runoff patterns. The objective of this study was to empirically derive CN values that reflect the strategic placement of native prairie vegetation (NPV) within row crop agricultural landscapes. CNs were derived using precipitation and runoff data from a seven‐year period for 14 small watersheds in Iowa. The watersheds were planted with varying amounts of NPV located in different watershed positions. The least squares and asymptotic least squares methods (LSM) were used to derive CNs using an initial abstraction coefficient (λ) of 0.2 and 0.05. The CNs were verified using leave‐one‐out cross‐validation and adjustment for antecedent moisture conditions (AMC) was tested. The asymptotic method produced CN values for watersheds with NPV treatment that were 8.9 and 14.7% lower than watersheds with 100% row crop at λ = 0.2 and λ = 0.05, respectively. The derived CNs produced Nash‐Sutcliffe efficiency values ranging from 0.4 to 0.7 during validation. Our analyses show the CNs verified best for the asymptotic LSM, when using λ of 0.05 and adjusting for AMC. Further, comparison of derived CNs against an area weighted CN indicated that the placement of vegetation does impact the CN value. Editor's note : This paper is part of the featured series on SWAT Applications for Emerging Hydrologic and Water Quality Challenges. See the February 2017 issue for the introduction and background to the series.     

Environmentally Virtuous Agriculture: How and When External Goods and Humility Ethically Constrain (or Favour) Technology Use

This paper concerns virtue-based ethical principles that bear upon agricultural uses of technologies, such as GM crops and CRISPR crops. It does three things. First, it argues for a new type of virtue ethics approach to such cases. Typical virtue ethics principles are vague and unspecific. These are sometimes useful, but we show how to supplement them with more specific virtue ethics principles that are useful to people working in specific applied domains, where morally relevant domain-specific conditions recur. We do this while still fulfilling the need for principles and associated practical reasoning to flexibly respect variation between cases. Second, with our more detailed approach we criticize and improve upon a commonly discussed principle about ecosystemic external goods that are crucial for human flourishing. We show this principle is far more conservative than appreciated, as it would prohibit many technology uses that are uncontroversially acceptable. We then replace this principle with two more specific ones. One identifies specific conditions in which ecosystem considerations are against a technology use, the other identifies favorable conditions. Third, we uncover a humility-based principle that operates within an influential “hubris argument” against uses of several biotechnologies in agriculture. These arguments lack a substantive theory of the nature of humility. We clarify such a theory, and then use it to replace the uncovered humility-based principle with our own more specific one that shifts focus from past moral failings, to current epistemic limits when deciding whether to support new technologies.     

Are Irrigators Different from Dryland Operators? Insights from a Comparative Study in Australia

Social researchers tasked with advising practitioners on effective stakeholder engagement often develop typologies that distinguish operators on key attributes. We build on emerging research exploring the efficacy of occupational identity by investigating a potentially important difference among rural landholders that, to our knowledge, remains untested: irrigated operations and dryland operations. Using primary data collected from a large sample of operators in the North Central region of Victoria, Australia, we compared irrigators with dryland operators across a range of characteristics, controlling for the influence of occupational identity. We find evidence that irrigators tend to hold a stronger business orientation toward their properties and that dryland operators tend to hold stronger environmental concerns. But, it is important not to overdraw contrasts on business‐environment tradeoffs. Both place value on financial aspects of their properties and both hold environmental concerns. But, the especially close coupling of life and work among irrigators encourage a stronger orientation toward farming, and the natural resource base, as a means of sustaining livelihoods. We discuss the implications of the findings for future research and for stakeholder engagement efforts.     

Response of Nitrogen Loading to the Chesapeake Bay to Source Reduction and Land Use Change Scenarios: A SPARROW‐Informed Analysis

In response to concerns regarding the health of streams and receiving waters, the United States Environmental Protection Agency established a total maximum daily load for nitrogen in the Chesapeake Bay watershed for which practices must be in place by 2025 resulting in an expected 25% reduction in load from 2009 levels. The response of total nitrogen (TN) loads delivered to the Bay to nine source reduction and land use change scenarios was estimated using a Spatially Referenced Regression on Watershed Attributes model. The largest predicted reduction in TN load delivered to the Bay was associated with a scenario in which the mass of TN as fertilizer applied to agricultural lands was decreased. A 25% decrease in the mass of TN applied as fertilizer resulted in a predicted reduction in TN loading to the Bay of 11.3%, which was 2.5–5 times greater than the reductions predicted by other scenarios. Eliminating fertilizer application to all agricultural land in the watershed resulted in a predicted reduction in TN load to the Bay of 45%. It was estimated that an approximate 25% reduction in TN loading to the Bay could be achieved by eliminating fertilizer applied to the 7% of subwatersheds contributing the greatest fertilizer‐sourced TN loads to the Bay. These results indicate that management strategies aimed at decreasing loading from a small number of subwatersheds may be effective for reducing TN loads to the Bay, and similar analyses are possible in other watersheds.     

In situ treatment of a dilute chlorinated solvent plume in an acidic aerobic aquifer

In situ bioremediation was selected in the Record of Decision (ROD) as the remedial technology for a 29‐acre dilute, acidic and aerobic, chlorinated solvent plume (principally trichloroethylene [TCE] and 1,1‐dichloroethylene) for a Superfund site located in central New Jersey. Implementation of the remedy at full‐scale began in late 2010, using reductive dechlorination and bioaugmentation, and treatment has continued steadily over the last 9 years. The amendments injected include electron donor and alkaline (bicarbonate) buffer solution and, once anaerobic aquifer conditions became established, a bioaugmentation culture. Amendment injections occurred in multilevel injection wells (IWs), to maintain control over the vertical interval of amendment delivery. The areal coverage of the plume has been reduced by 59% based on the 10 µg/L TCE isocontour and the contaminant mass has been reduced by 79% through the 9 years of treatment. Lessons learned from this project include the need for bioaugmentation in the acidic aquifer and an efficient and effective manner of well construction and amendment injection using multiscreen single casing IWs and packer systems. Additional lessons learned include differences in longevity of the electron donor amendment versus the bicarbonate neutralization additive, and the need for varied amendment delivery techniques (IWs, direct injection, horizontal well installation) in selected lower permeable zones to attain treatment.     

Policy and Practice Certainty for Effective Uptake of Diffuse Pollution Practices in A Light-Touch Regulated Country

Environmental Management - Although the link between agriculture and diffuse water pollution has been understood for decades, there is still a need to implement effective measures to address this...