Weaver L.,Institute of Environmental Science and Research Ltd. |
Karki N.,Institute of Environmental Science and Research Ltd. |
Mackenzie M.,Institute of Environmental Science and Research Ltd. |
Sinton L.,Institute of Environmental Science and Research Ltd. |
And 6 more authors.
Science of the Total Environment | Year: 2016
Rising demand on food is leading to an increase in irrigation worldwide to improve productivity. Irrigation, for pastoral agriculture (beef, dairy and sheep), is the largest consumptive use of water in New Zealand. There is a potential risk of leaching of microbial contaminants from faecal matter through the vadose zone into groundwater. Management of irrigation is vital for protection of groundwater from these microbial contaminants and maintain efficient irrigation practices. Our research investigated flood and spray irrigation, two practices common in New Zealand. The aim was to identify the risk of microbial transport and mitigation practices to reduce or eliminate the risk of microbial transport into groundwater. Cowpats were placed on lysimeters over a typical New Zealand soil (Lismore silt loam) and vadose zone and the leachate collected after irrigation events. Samples of both cowpats and leachate were analysed for the microbial indicator Escherichia coli and pathogen Campylobacter species.A key driver to the microbial transport derived from the model applied was the volume of leachate collected: doubling the leachate volume more than doubled the total recovery of E. coli. The persistence of E. coli in the cowpats during the experiment is an important factor as well as the initial environmental conditions, which were more favourable for survival and growth of E. coli during the spray irrigation compared with the flood irrigation. The results also suggest a reservoir of E. coli surviving in the soil. Although the same was potentially true for Campylobacter, little difference in the transport rates between irrigation practices could be seen due to the poor survival of Campylobacter during the experiment. Effective irrigation practices include monitoring the irrigation rates to minimise leachate production, delaying irrigation until 14. days post-cowpat deposition and only irrigating when risk of transport to the groundwater is minimal. Aim: To compare the risk of microbial contamination of groundwater from cowpats using two irrigation practices onto pasture. © 2015 Elsevier B.V.
Snelder T.H.,IRSTEA |
Snelder T.H.,Aqualinc Research |
Datry T.,IRSTEA |
Lamouroux N.,IRSTEA |
And 4 more authors.
Hydrology and Earth System Sciences | Year: 2013
Understanding large-scale patterns in flow intermittence is important for effective river management. The duration and frequency of zero-flow periods are associated with the ecological characteristics of rivers and have important implications for water resources management. We used daily flow records from 628 gauging stations on rivers with minimally modified flows distributed throughout France to predict regional patterns of flow intermittence. For each station we calculated two annual times series describing flow intermittence; the frequency of zero-flow periods (consecutive days of zero flow) in each year of record (FREQ; yr−1), and the total number of zero-flow days in each year of record (DUR; days). These time series were used to calculate two indices for each station, the mean annual frequency of zero-flow periods (mFREQ; yr−1), and the mean duration of zero-flow periods (mDUR; days). Approximately 20% of stations had recorded at least one zero-flow period in their record. Dissimilarities between pairs of gauges calculated from the annual times series (FREQ and DUR) and geographic distances were weakly correlated, indicating that there was little spatial synchronization of zero flow. A flow-regime classification for the gauging stations discriminated intermittent and perennial stations, and an intermittence classification grouped intermittent stations into three classes based on the values of mFREQ and mDUR. We used random forest (RF) models to relate the flow-regime and intermittence classifications to several environmental characteristics of the gauging station catchments. The RF model of the flow-regime classification had a cross-validated Cohen's kappa of 0.47, indicating fair performance and the intermittence classification had poor performance (cross-validated Cohen's kappa of 0.35). Both classification models identified significant environment-intermittence associations, in particular with regional-scale climate patterns and also catchment area, shape and slope. However, we suggest that the fair-to-poor performance of the classification models is because intermittence is also controlled by processes operating at scales smaller catchments, such as groundwater-table fluctuations and seepage through permeable channels. We suggest that high spatial heterogeneity in these small-scale processes partly explains the low spatial synchronization of zero flows. While 20% of gauges were classified as intermittent, the flow-regime model predicted 39% of all river segments to be intermittent, indicating that the gauging station network under-represents intermittent river segments in France. Predictions of regional patterns in flow intermittence provide useful information for applications including environmental flow setting, estimating assimilative capacity for contaminants, designing bio-monitoring programs and making preliminary predictions of the effects of climate change on flow intermittence. © 2013 Author(s).
Lamouroux N.,IRSTEA |
Pella H.,IRSTEA |
Snelder T.H.,Aqualinc Research |
Sauquet E.,IRSTEA |
And 2 more authors.
Journal of the American Water Resources Association | Year: 2014
Spatially comprehensive estimates of the physical characteristics of river segments over large areas are required in many large-scale analyses of river systems and for the management of multiple basins. Remote sensing and modeling are often used to estimate river characteristics over large areas, but the uncertainties associated with these estimates and their dependence on the physical characteristics of the segments and their catchments are seldom quantified. Using test data with varying degrees of independence, we derived analytical models of the uncertainty associated with estimates of upstream catchment area (CA), segment slope, and mean annual discharge for all river segments of a digital representation of the hydrographic network of France. Although there were strong relationships between our test data and estimates at the scale of France, there were also large relative local uncertainties, which varied with the physical characteristics of the segments and their catchments. Discharge and CA were relatively uncertain where discharge was low and catchments were small. Discharge uncertainty also increased in catchments with large rainfall events and low minimum temperature. The uncertainty of segment slope was strongly related to segment length. Our uncertainty models were consistent across large regions of France, suggesting some degree of generality. Their analytical formulation should facilitate their use in large-scale ecological studies and simulation models. © 2013 American Water Resources Association.
McDowell R.W.,Agresearch Ltd. |
Snelder T.H.,Aqualinc Research |
Cox N.,Agresearch Ltd. |
Booker D.J.,NIWA - National Institute of Water and Atmospheric Research |
Wilcock R.J.,NIWA - National Institute of Water and Atmospheric Research
Marine and Freshwater Research | Year: 2013
The management of streams and rivers can be aided by knowledge of reference conditions. Data from >1000 sites across New Zealand was used to develop a technique to estimate median ammoniacal-N, clarity, Escherichia coli, filterable reactive phosphorus, nitrate-N, suspended solids, and total nitrogen and phosphorus values under reference conditions for streams and rivers as classified by the River Environment Classification (REC). The REC enabled us to account for natural variation in climate, topography and geology when estimating reference conditions. Values for minimally disturbed sites (i.e. <5% in intensive agriculture) were generally within the confidence limits for estimated reference values. Metrics that described: (1) the percentage of anthropogenic contribution to analyte values; and (2) the degree of enrichment beyond the reference conditions, showed that lowland sites classified as warm-wet, warm-dry or cool-dry exhibited the greatest anthropogenic input and enrichment. The consideration of natural variation by REC class informs the setting of water quality objectives through avoiding water quality limits or targets that are either too restrictive, and impossible to meet (e.g. below reference conditions), or too high, such that they have little ecological benefit. We recommend reference conditions be considered by regulatory authorities when assessing water quality impacts, objectives and limits. © 2013 CSIRO.
Close M.,Institute of Environmental Science and Research |
Dann R.,Institute of Environmental Science and Research |
Flintoft M.,AquaLinc Research |
Havelaar P.,Environment Canterbury |
Peterson M.,Plant and Food Research
Vadose Zone Journal | Year: 2012
This technical note describes a novel large diameter vadose zone sampler (VZS) that has been developed to permit easy and safe access to deep unconsolidated vadose zone profiles and the gathering of information that has not been possible previously. The purpose is to allow investigations to be performed cost effectively at locations of interest rather than being restricted to areas with suitable exposures. The VZS is designed to be used with 1.2-m-diameter auger holes and consists of a light-weight crane and several 1.15-m-diameter, 1.5-m-high, cylindrical steel sections, which bolt together to provide a temporary casing for the auger hole. The sections have removable openings to permit examination and sampling of the vadose zone profile. The VZS is relatively inexpensive to construct and has been designed to be mobile and provide access to the vadose zone at a wide range of locations, rather than the usual restriction to available outcrops in cuttings or gravel pits. We describe the use of the VZS to characterize the profile of an alluvial gravel system at four locations in Canterbury, New Zealand and to carry out a field calibration for a neutron probe that had been installed to a depth of 3 m into an alluvial gravel profile. The VZS enabled collection of samples for physical, chemical, and gravimetric moisture determination at precise depth locations. This information will ultimately lead to better characterization and understanding of water and contaminant transport and transformation through vadose zones. © Soil Science Society of America.
Dann R.,Institute of Environmental Science and Research ESR |
Dann R.,Snowy Mountain Engineering Corporation SMEC |
Thomas S.,The New Zealand Institute for Plant and Food Research Ltd |
Waterland H.,The New Zealand Institute for Plant and Food Research Ltd |
And 3 more authors.
Vadose Zone Journal | Year: 2013
Understanding nitrogen (N) processes within the vadose zone is important to estimate N losses to groundwater systems. A field trial was undertaken to examine the dynamics of nitrate (NO3) and nitrous oxide (N2O) in an alluvial gravel vadose zone underlain by shallow groundwater. Synthetic urine (980 kg N ha-1) with a bromide (400 kg Br ha-1) tracer was applied to the surface of a 10- by 20-m plot, and changes in subsurface NO3, Br, and N2O concentrations were compared with those from an adjacent plot, with just the Br tracer applied. Soil solution and air were monitored at multiple depths (from 0.2 to 5 m) over an 18-mo period. Transport of solution was rapid in the gravel material with some Br transported to 3-m depth immediately after the urine application. N2O was produced within the soil after urine application. NO3 to Br ratios indicated denitrification in the soil above the gravels, but none within the alluvial gravel vadose zone. In the "-urine" plot N2O concentrations increased with depth, with upward fluxes above the water table to the soil, suggesting N2O production near the water table. A different pattern was observed in the "+urine" plot where N2O was produced both at the soil zone above the gravels and near the water table leading to both upward and downward N2O fluxes. Overall N2O fluxes in the soil zone were greater than at the water table. © Soil Science Society of America 5585 Guilford Rd., Madison, WI 53711 USA. All rights reserved.