Search

Linkages between the micro‐scale of soil water and landscape scale of hydrological data could be improved with the analysis of soil factors in preferential flow rates. This rearrangement of the terminology on soil pore size from published literature focused on the relationship between aggregate and pore size. In the range of pore size relevant to water flow (>0.005 mm), a 2:1 ratio of aggregate to pore diameter approximated the mean of proposed pore size categories. Major functional change points in soil pore size were identified where water becomes mobile in soil (0.005 mm), where preferential flow among aggregate surfaces begins (0.3 mm), and where water flows without soil interaction (bypass flow ∼1.0 mm). A number of published equations supported the application of soil pore size in permeability estimation for modeling hydraulic conductivity. Common understanding of soil pore terminology would support water flow estimation from soil to landscape scales. Core Ideas: Preferential flow refers to water flowing faster through soil void space than through the soil matrix.Soil pore diameter of ∼0.3 mm is associated with the initiation of preferential flow in modeling.Soil cracks and biopores >1 mm could be classified as bypass flow following pipe flow theory.Soil pore size can be estimated from aggregate diameter ratio or from mean pore size ranges.Soil pore size, specific surface area, or void ratio can be used to estimate permeability in K equations. [ABSTRACT FROM AUTHOR]

Willow (Salix viminalis spp.) shrubs are being planted along riverbanks, on erodible and marginal farmland. Wood chips made from the woody biomass could improve the properties of light-textured soils with low organic matter content in potato-based systems. Willow chips were applied at 0, 20, 40, and 60mgha?1 (fresh weight) as a soil amendment. Soil health parameters were evaluated after 12months, followed by C and N contents in whole soil, particulate, and mineral-associated organic matter fractions after 18months. Willow chip application increased soil aggregation, respiration, C and N contents in whole soil, and plant-available K. On plante l'osier blanc (Salix viminalis spp.) le long des berges ainsi que sur les terres agricoles sujettes à l'érosion ou peu rentables. Des copeaux de bois tirés de la biomasse ligneuse pourraient améliorer les propriétés des sols à texture légère pauvres en matière organique, comme ceux servant à la culture de la pomme de terre. Les auteurs ont appliqué un amendement correspondant à 0, 20, 40 ou 60 Mg (poids frais) de copeaux d'osier par hectare. Douze mois plus tard, ils ont évalué la vitalité du sol puis, au bout de dix-huit mois, la teneur en C et en N du sol complet ainsi que les fractions de matière organique associées aux particules et aux minéraux. Les copeaux d'osier améliorent l'agrégation et la respiration du sol, la concentration de C et de N dans le sol complet, de même que le K assimilable par les plantes. [Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

The Bayesian inverse approach proposed by Woodbury and Ulrych (2000) is extended to estimate the transmissivity fields of highly heterogeneous aquifers for steady state ground water flow. Boundary conditions are Dirichlet and Neumann type, and sink and source terms are included. A first-order approximation of Taylor's series for the exponential terms introduced by sinks and sources or the Neumann condition in the governing equation is adopted. Such a treatment leads to a linear finite element formulation between hydraulic head and the logarithm of the transmissivity--denoted as ln(T)--perturbations. An updating procedure similar to that of Woodbury and Ulrych (2000) can be performed. This new algorithm is examined against a generic example. It is found that the linearized solution approximates the true solution with an [R.sup.2] coefficient = 0.96 for an ln(T) variance of 9 for the test case. The addition of hydraulic head data is shown to improve the ln(T) estimates, in comparison to simply interpolating the sparse ln(T) data alone. The new Bayesian code is also employed to calibrate a high-resolution finite difference MODFLOW model of the Edwards Aquifer in southwest Texas. The posterior ln(T) field from this application yields better head fit when compared to the prior ln(T) field determined from upscaling and cokriging. We believe that traditional MODFLOW grids could be imported into the new Bayes code fairly seamlessly and thereby enhance existing calibration of many aquifers., Introduction One well-recognized difficulty for ground water model applications is to obtain sufficient and reliable hydrogeological parameters for model input. Aquifers are often highly heterogeneous and the large spatial variability [...]

High levels of nitrate leaching losses from potato rotation systems have caused concerns for both drinking water quality and aquatic ecosystem protection in Prince Edward Island ( PEI). Paired-field experiments were carried out in commercial fields to evaluate the potential of delayed plowing forages within potato rotation from fall to spring on reducing nitrate leaching at two separate sites in PEI during 2010 and 2013. Monitoring showed that fall plowing resulted in elevated tile-drain nitrate concentrations compared to spring plowing, probably mainly due to crop residue mineralization during fall which was hastened by earlier herbicidal termination of forage (i.e., herbicidal killing) at Site 1. A similar trend was also observed regarding nitrate concentrations of shallow groundwater at Site 2 during the forage phase. The practice of delaying the plowing of forages and/or associated earlier herbicidal termination of forage until spring reduces forage-phase nitrate leaching loss by 20 to 61%, and should therefore be encouraged for nitrate mitigation. The study also demonstrated that only a small fraction (9.6 to 22%) of the fall plow-down forages decayed during the forage phase and a large portion was retained in the soil into the next season. Growers should consider accounting for some of the carried-over N for the subsequent crops regardless implementing fall or spring plowing. [ABSTRACT FROM AUTHOR]

Understanding agricultural contamination in bedrock aquifers is challenging due to complexity of fracture networks and limitations in data acquisition imposed by instrumentation and drilling costs. Engineered assemblages known as multilevel monitoring systems ( MLSs) maximize data from each borehole by providing numerous, depth-discrete monitoring intervals for profiles of hydraulic head and hydrochemistry. This article describes a hybrid MLS that uses key components of the Waterloo MLS, with extra piezometers of sufficient diameter to accommodate removable transducers for continuous pressure monitoring, attached to the outside using custom clamps. Monitoring intervals are created with sand packs separated by bentonite seals, either via backfilling from surface or tremie placement. The hybrid MLS is best suited for use in rotary drilled boreholes 12 to 15 cm diameter, smaller holes have insufficient space for the MLS and added piezometer(s) while larger holes have excessive backfill material and purge requirements. Variations were installed to 60 m depth in sandstone in Prince Edward Island, and to 150 m in dolostone in southwestern Ontario. Transducers in the external piezometers provided temporal head data under ambient and stressed conditions in key intervals, and manual measurements in all ports provided detailed vertical hydraulic snapshots. Combined with hydrochemistry profiles from groundwater sampling, the hybrid MLS provided detailed composite datasets for interpreting flow and transport in these bedrock aquifers. The hybrid MLS offers promise as a versatile low-cost option for groundwater studies in agricultural areas providing improved insights on groundwater flow systems and vertical distribution of nitrate and other contaminants, allowing more informed management decisions. [ABSTRACT FROM AUTHOR]

Potato production is critical to economy of Prince Edward Island ( PEI), but has been linked to increasing groundwater nitrate contamination and anoxic events in estuaries. Given that PEI is entirely groundwater-dependent for potable water, this has resulted in considerable pressure to find solutions to protect water quality. However, our understanding of the controls on nitrate loading to groundwater, and the consequent potential to mitigate nitrate loading through beneficial management practices ( BMPs), is limited. In PEI, flow and nitrate transport in the vadose zone are controlled by the matrix porosity of the till and sandstone, while flow and transport in the saturated zone are controlled by a conductive fracture network with limited storage capacity. Diffusion of nitrate stored in the matrix may introduce a significant time lag between reduced nitrate loading from implementation of BMPs and measureable improvement in groundwater quality. BMPs with potential to mitigate nitrate loading to groundwater through improved nitrogen fertilizer practices in producing potato crops have been identified, but implementation of these practices alone is not sufficient to control nitrate loading due to the economic context of potato production. Additional BMPs for improved potato cropping systems have also been identified; however, reducing the intensity of agricultural production, including the proportion of land in potato production, at the watershed level may be required to meet the drinking water guideline for nitrate in PEI. Given the important role of market forces in determining profitability of crop production, it becomes challenging to modify crop production practices to meet an environmental goal without some additional external incentive or public pressure. [ABSTRACT FROM AUTHOR]