Presentations 2016

Direct monitoring of agriculture impact on groundwater quality

Ben Gurion University of the Negev

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Minimization subsurface pollution is much dependent on the capability to provide real-time information on the chemical and hydrological properties of the percolating water. Today, most monitoring programs are based on observation wells that enable data acquisitions from the saturated part of the subsurface. Unfortunately, identification of pollutants in well water is clear evidence that the contaminants already crossed the entire vadose-zone and accumulated in the aquifer water to detectable concentration. Therefore, effective monitoring programs that aim at protecting groundwater from pollution hazard should include vadose zone monitoring technologies that are capable to provide real-time information on the chemical composition of the percolating water. Obviously, identification of pollution process in the vadose zone may provide an early warning on potential risk to groundwater quality, long before contaminates reach the water-table and accumulate in the aquifers. Since productive agriculture must inherently include down leaching of excess lower quality water, understanding the mechanisms controlling transport and degradation of pollutants in the unsaturated is crucial for water resources management.A vadose-zone monitoring system (VMS), which was specially developed to enable continuous measurements of the hydrological and chemical properties of percolating water, was used to assess the impact of various agricultural setups on groundwater quality, including: (a) intensive organic and conventional greenhouses, (b) citrus orchard and open field crops , and (c) dairy farms. In these applications frequent sampling of vadose zone water for chemical and isotopic analysis along with continuous measurement of water content was used to assess the link between agricultural setups and groundwater pollution potential. Transient data on variation in water content along with solute breakthrough at multiple depths were used to calibrate flow and transport models. These models where then used to assess the long term impact of various agricultural setups on the quantity and quality of groundwater recharge. Relevant publications: Turkeltaub et al., WRR. 2016; Turkeltaub et al., J. Hydrol. 2015: Dahan et al., HESS 2014. Baram et al., J. Hydrol. 2012.

Tools for monitoring and evaluating potential sources of nitrates to ground water, Eastern Idaho

Idaho Department of Environmental Quality

https://www.youtube.com/watch?v=yGs8gaW020g&index=2&list=PLZC-5vj9_JAYC2i99zybgBpF-Iq1U3Tb4

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Ground water is the primary source of drinking water for more that 95 percent of Idaho residents, including public water systems and private wells. Agricultural and domestic fertilizer applications, animal feeding operations and dairies, septic and onsite waste water treatment systems, and industrial wastewater sources are potential sources of nitrate in ground water. Idaho Department of Environmental Quality (IDEQ) has a leading role in monitoring to identify areas of degraded ground water, understand potential nitrate sources, and evaluating best management practices to address those sources. Understandings gained by IDEQ studies at the regional and local level is aimed at protecting public and private drinking water sources, aiding groups such as local soil and water conservation districts to protect ground water quality through improving agricultural land use practices, and helping to restore degraded ground water. The following suggested tools are based on IDEQ-led investigations of ground water in Eastern Idaho and are meant to be used as a resource for other IDEQ regional offices or other decision makers to understand potential regional sources of nitrates to ground water.In this study, monitoring wells are identified within randomly selected square-mile sections for regional-scale (100’s of square miles) characterization. Smaller scale monitoring networks are also identified for subareas sharing similar hydrogeology and land use. Well selection criteria favors newer wells producing from the shallow-most aquifer. The number of sites selected for the subareas is based on the mean and variance of existing nitrate data, which estimates the bounds of confidence and prediction intervals for future sampling. Data collected from each site include: field parameters (pH, temperature, conductivity, dissolved oxygen); bacteria (total coliform, E. coli); nutrients (nitrite + nitrate, ammonia); major anions and cations (Ca, Mg, Na, K, total alkalinity, Cl, SO4, F); nitrogen isotopes (d15NNO3, d18ONO3); characteristic tracers (Br, B); isotopes of water (d18OH2O, d2HH2O); and tritium.Data analysis includes the following: 1) Review field parameters to establish the general chemistry and to identify if conditions are oxidizing or reducing, and to confirm that the water sampled is representative of the aquifer; 2) Review bacteria concentrations, specifically E. coli, as a direct indication of human or animal wastes; 3) Plot characteristic ratios of major ions and mixing plots of major ions, tracers, and nitrate or nitrogen isotopes to confirm recharge and nitrate source mixing and to identify signatures of potential nitrate sources; 4) Prepare piper trilinear diagrams in order to show mixing between major recharge and contamination sources; 5) Plot characteristic ratios of major ions, nitrates, tracers, and nitrogen isotopes to provide signatures of potential recharge nitrate sources; 6) Employ mixing plots to identify significant indicators and mixing between both recharge and contaminant sources; 7) Dual isotope plots of nitrogen and oxygen of nitrates are used to identify original nitrate sources and distinguish nitrification and denitrification; 8) Isotopes of oxygen and hydrogen in water are used to confirm timing and source of recharge; and 8) Tritium age dating provides the age of recharge.

Selective Groundwater Extraction for Agricultural Yield Optimization

Best Environmental Subsurface Science and Technologies (BESST)

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Subsurface quality grading of the groundwater supply throughout California began in earnest about a decade ago through miniaturization of down-hole flow and water chemistry measurement technologies as applied to municipal water supply wells. However, there has been a growing push in the agricultural sector for Selective Groundwater Extraction (SGE) – at least within California. SGE means that municipal groundwater producers and a growing number of agricultural concerns that use large quantities of groundwater now have the ability to pick and choose which subsurface layers of earth they extract groundwater from based in-well, down-hole, water quality grading. Many times, these new miniaturized technologies can be deployed in existing production wells without removing the pump from the well – such that an agricultural production well is catheterized in similar fashion to a patient receiving cardiac assist balloon pumping and angioplasty. In this sense the well is the patient. The line shaft turbine is the heart, the casing is the aorta, the well screen and surrounding formational stratigraphic units the complex of veins feeding groundwater to the well in different amounts and varying quality; where it is all mixed and blended in the casing before reaching the surface. In other cases, the farmer’s primary pump is removed and then reinstalled with small diameter access pipe (1” to 1.25” ID) to allow safe passage of the miniaturized tooling into the well and past the pump bowls and intake. In either case, the cost savings of using miniaturized technologies to diagnose flow and water quality contribution along the screens (perforations) of wells are significant in both the short and long term. Standard alternative approaches to dealing with water quality problems in agriculture are expensive and stem from not knowing how groundwater from the different stratigraphic horizons are blended inside the well before reaching the surface. The typical response for vineyards that experience difficulty with second plantings due to buildup of boron and sodium in the soil as well as walnut, almond and pistachio growers is to use expensive treatment and/or resort to building new wells. This presentation will explain the concept behind SGE including use of manipulated in-well hydraulics and engineered down-hole blending to achieve the desired water quality result through use of miniaturized diagnostic technologies. In one case, arsenic contribution will be examined which is of particular concern for ag facilities delivering potable drinking water to their employees. In another case, subsurface boron distribution will be explained.

Nitrogen surplus key factor in relation between farm practices and water quality

Agricultural Economics Research Institute (LEI)

https://www.youtube.com/watch?v=p2sjFYmCvwk&index=5&list=PLZC-5vj9_JAYC2i99zybgBpF-Iq1U3Tb4

The effects of the EU Nitrates Directive Action Programme are monitored in The Netherlands via standard programmes for groundwater and surface water, and a special programme known as the Dutch Minerals Policy Monitoring Programme (LMM) based on a national network for measuring the effects of the Manure Policy. LMM uses an effect monitoring approach to assess the contribution of nitrate from agriculture to receiving waters and the effects of changing agricultural practice on these losses. LMM monitors therefore both water quality and the farm management that might influence this quality. LMM data on water quality and farm management showed the importance of N-surplus on the soil as an indicator for water quality. Therefore within the LMM-programme there is a strong focus on farm management factors that effects N-surplus. For this a solid method is needed in order to assess comparable N-surpluses for different farm types and soils. This contribution describes the assessment of N-surplus based on a soil balance method. Furthermore it presents the relation between N-surplus and water quality and the relation with the Dutch policy on manure and the amount of N-fertilization for the period 1991-2013.The surplus on the farm gate balance is first calculated by determining the total annual input (for instance inorganic fertiliser, feedstuffs) and output (for instance animal products, crops and other plant products) of nutrients as registered in the farm records. Stock changes are taken into account when calculating this surplus. The calculated nitrogen surplus on the farm gate balance is then corrected to account for input and output items on the soil surface balance. Allowance is made for net mineralisation of organic substances in the soil, nitrogen fixation by leguminous plants, ammonia emission and atmospheric deposition. The phosphate surplus on the soil surface balance is equal to the surplus on the farm gate balance. A state of equilibrium is assumed when calculating nutrient surpluses on the soil surface balance, except for peat soils. On Dutch peat soils a net mineralisation occurs. For different farm types the method and data is useful to calculate the nutrient surplus on the soil balance. Comparisons can be made between farm types and within one type between regions. For dairy farms the soil surpluses for nitrogen and phosphate amount to 181 kg of N and 12 kg of P2O5 per hectare (Figure 1, phosphate is not shown). The nitrogen surplus has remained at the same level for the past few years, while the phosphate surplus is still decreasing as a result of the Usage Standard System. The soil surpluses for nitrogen and phosphate at arable farms amounted to 110 kg of N and 19 kg of P2O5 per hectare (Figure 1, phosphate is not shown). The nitrogen surplus has more or less stabilised since 2008, while the phosphate surplus continues to decrease. N-surpluses as well as nitrate concentrations differ between farm types and between regions (not shown). Dry-matter yields of grass are hardly changed despite a lower fertilization level, due to better farm management. Figure 1 Nitrogen applied (kg/ha) and Nitrogen surplus (kg/ha) for Dutch dairy and arable farms in the 1991-2013 period

Nitrate sensitive salinity management

University of California Davis

https://www.youtube.com/watch?v=fT9iBNFKHnM&index=4&list=PLZC-5vj9_JAYC2i99zybgBpF-Iq1U3Tb4

The majority of growers in California have adopted their irrigation system to micro-irrigation systems (drip and micro-spray) in response to the need for improving the management practices for both irrigation and fertigation toward a sustainable agricultural practice. Whereas providing water and nutrient to plants through micro-irrigation system offer a great opportunity to move toward Best Management Practices by reducing the water and nutrient loss through runoff and deep percolation, leaching is an undeniable part of irrigated agricultural practices, since salt accumulation in the root zone adversely affects crop growth and yield. Irrigation strategies, fertigation management, nitrate leaching and salinity management are therefore linked and strategies must be developed that optimize productivity while minimizing nitrate leaching and avoiding salt-induced stress. Perennial species and micro-irrigation impose unique challenges for salinity management and strategies developed for annual crops are not optimized for tree crops. Specifically, 1) for salt sensitive crops (e.g., almond) as water quality diminishes greater leaching volumes will be required, 2) micro-irrigation results in local salt deposition at the lateral and vertical margin of the wetting pattern, and thus water and nitrate within this high salt margin will not be available for uptake, 3) if not conducted properly, strategies that optimize salt leaching to the periphery of the rooted zone will simultaneously leach nitrate. Given the complexity of solute management under micro-irrigation and the lack of information on crop response to salinity and the lack of information on the effects of salinity on root distribution and nitrate uptake it is virtually impossible for growers to make informed irrigation management decisions that satisfy the dual goal of minimizing root zone salinity while simultaneously minimizing nitrate leaching. Therefore, proper irrigation/fertigation management guidelines for grower require a more detailed understanding of patterns of root growth and N uptake in response to non-uniform water and salt distribution. The application of irrigation water and fertigated nutrients, as well as root distribution, and nutrient and water uptake all clearly interact with soil properties and fertilizer source in a complex manner that cannot easily be resolved with ‘experience’ or experimentation alone. we aim to employ an existing and widely used modeling platform, HYDRUS, to conduct numerical simulation for different scenarios for a variety of almond cultivar, soil types, and different level of salinity and combine it with data obtained field/lysimeter experiments to be used as an integrated water and nitrate management tool. This will provide a means to transfer outcome of the treatments and findings of this project to other orchards with other soil types, tree root systems, crop salinity threshold, etc.

A Flow and Transport Model Developed as a Salt and Nitrate Management Analysis Tool for a Management Zone in California’s Eastern Kings Subbasin

Luhdorff & Scalmanini Consulting Engineers

https://www.youtube.com/watch?v=ksBoiX_ICl8&list=PLZC-5vj9_JAYC2i99zybgBpF-Iq1U3Tb4&index=3

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For the purposes of Salt and Nitrate Management Plans (SNMP), management zones (MZ) are created that cover a spatial area within which salt and nitrate can be managed by one or more entity. As an archetype for the Central Valley SNMP, an MZ was defined for Alta Irrigation District (AID), located in the eastern portion of the Kings Subbasin. Groundwater quality data are used to estimate the salt and nitrate occurrence for different zones of the saturated subsurface. Separately modeled loading of surface recharge (mass and volume) allows the assessment of the effects of various management regimes on groundwater quality (e.g., changes in irrigation efficiency and fertilization rates, artificial recharge projects, improving POTW effluent quality, etc.). A groundwater flow and transport model was developed using MODFLOW and MT3D to investigate the effects of different management practices on underlying groundwater over time.A local AID model was developed by extracting a portion of the Kings Subbasin from the USGS’s large-scale Central Valley Hydrologic Model (CVHM) (Faunt et al., 2009). Several transformations occurred to adapt the CVHM parent model into the smaller-scale local AID MZ Model. Previous efforts using CVHM for salt and nitrate movement assessments concluded that transient flow simulation durations were not sufficient to evaluate the impacts of management regimes on groundwater used for municipal drinking water purposes. Therefore, the AID MZ model was converted into a steady state model using averaged hydrologic conditions over a selected baseline hydrologic period for model inputs, including initial heads, general head boundaries on model edges, streamflow and stage data, diversion data, pumping data, and recharge data. The local steady-state AID MZ model was further refined by increasing the vertical and horizontal discretization. The baseline groundwater flow model was calibrated using water levels in monitored wells and contour maps of groundwater elevation. Management conditions were developed to represent ongoing shifts in land and water management. The Baseline condition involved historical surface application of N fertilizers and surface irrigation (i.e., before current regulatory program); Scenario 1 involved increased irrigation efficiency and artificial recharge projects; Scenario 2 involved lower fertilization rates in response to regulatory programs; and Scenario 3 combines the changes from Scenario 1 and 2. MT3D transport (transient) modeling included assignment of initial salt and nitrate concentrations to all cells, boundaries, and streams. Simulated recharge concentrations were provided on a cell-by-cell basis for the entire model area for each surface management condition. Transport modeling was run forward in time for 100 years to assess the effects of surface loading changes on different zones in the saturated subsurface.

Reducing environmental N losses and increasing N uptake on grazed dairy farms with simple, low cost detection and treatment of fresh cow urine patches

Pastoral Robotics Ltd

https://www.youtube.com/watch?v=Mejr6_2-fsw&list=PLZC-5vj9_JAYC2i99zybgBpF-Iq1U3Tb4&index=1

Dairy products produced from cows gaining most of their food intake grazing pastures are becoming increasingly preferred by consumers who are seeking more natural food.A significant environmental concern under grazing, especially under intensive farming under higher rainfall or irrigation is the significant nitrogen (N) losses to the environment from cow urine patches, as nitrate leaching and/or as emissions of nitrous oxide greenhouse gas.These losses come about essentially as a result of the very high concentrations of N applied to the urine 'patch' or deposition area, mainly as urea. Within any one patch, the N application rate typically ranges from 500-1200 kgN/ha, far greater than the amount that can be recovered by the pasture before significant losses to the environment occur.This presentation describes the development of new technology which, towed behind a 4-wheel motorbike or other vehicle, enables the farmer to detect fresh cow urine patches and simultaneously treat them with various products such as N inhibitors and growth promotants, greatly increasing the recovery of urine-N by the pasture and reducing losses of N to the environment.The equipment developed, known as 'Spikey', uses a row of light, spiked metal wheels spaced 10 cm apart to measure the electrical conductivity of the top few mm of the soil, as well as the soil surface resistance, to locate fresh (1-3 days old) urine patches with a very high degree of certainty and accuracy.The ionic content of urine is very much higher than that of the soil solution; each urination is typically applying a 10mm 'irrigation' with urine, which saturates the topsoil, and causing easily detectable 'spikes' in soil conductivity for typically 3 days.Treatment of individual fresh urine patches in this way has been found to increase pasture N recovery by up to 70%, and as a consequence sigificantly reduce N losses to the environment.The Spikey equipment can be scaled up to whatever is the most appropriate for the farmer to do on a given farm. For New Zealand, this is like to be a width of 8m initially. Many farmers follow the cows' paddock rotation or electric fence-controlled strip-grazing with applications of fertilizer N to whatever area has been grazed in the last 1-3 days. For these farmers, the fertilzer hopper and spreader can easily be mounted on the Spikey equipment. For these farmers, the additional time requirement to detect and treat urine patches is minimal. For those that do not, the time requirement is typically 20-30 minutes per day.Treatment of the urine-affected area only, which is typically only 2-5% of the area grazed on any one occasion or area, means that the use of chemicals such as urease and/or nitrofication inhibitors and growth promotants is greatly reduced compared to technologies that involve treating the entire area grazed. The period of the year for which Spikey is used will be a function of local climate and soil conditions, farm mangement practises such as irrigation, and the sensitivity of local receiving waters to nitrate enrichment.The Spikey technology, when combined with fertilizer N application, will allow prevention of fertilizer N to urine patches, with consequent calculated savings in N requirements of 5-15%.

Groundwater remediation for nitrate contamination in public supply wells: Challenge of the non-point source

University of Waterloo

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Elevated nitrate concentrations in public supply wells are being reported on an increasing frequency globally. Long term agricultural nutrient management practices are often identified as a principal cause. Best management practices (BMPs) designed to limit the regional loss of nutrients on agricultural land in the vicinity of the supply wells are frequently implemented to reduce the groundwater nitrate concentrations. Due to the intrinsically slow movement of groundwater both through the saturated and unsaturated zones, the influence of the BMP activity is often slow to arrive at the wellheads and during this time the concentration of nitrate in the drinking water supply remains high. As an approach to temporarily reduce the nitrate concentrations in the wells prior to the point when the BMPs become fully effective, enhancing the natural process of denitrification in situ offers promise. In this study, denitrification is stimulated through the injection of a carbon amendment (acetate) the production aquifer of a well field in southern Ontario where nitrate concentrations exceed the drinking water limit. The acetate is introduced to the subsurface through an injection-extraction well doublet within a zone of high nitrate mass flux where the groundwater flow field converges near the wellheads. The acetate amendment is pulsed on a regular basis over a period of 60 days and the groundwater geochemistry down gradient of the injection site is monitored in detail to track the fate of nitrate and by-products of the denitrification reaction. The data indicate that the upstream nitrate concentrations averaging 13 mg/l are reduced to below 2 mg/l as a result of the enhanced in situ denitrification. Concentrations of nitrite and other redox products remain very low. The extended field trial illustrates the potential value of enhanced denitrification as a temporary remedial option until the permanent influence of the regional BMPs become fully effective.

Sensitive Catchments – Managing Nutrient Pathways and their Attenuation in NZ Agricultural Catchments

Massey University

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Productive farms and their associated processing industries make a significant contribution to New Zealand’s economic and social welfare. However, grazed pastoral systems and other intensive landuses are inherently leaky with respect to nitrogen (N), the key nutrient implicated in the deterioration of surface and ground water quality in New Zealand’s agricultural catchments. Current N management efforts in sensitive agricultural catchments are focused within the farm boundary and concentrate on identifying and reducing N loss from the root zone of farms. In many regions, the predicted farm rootzone N loss must comply with a set limit or allocation. Farm N loss allowances, as specified in regional council rules, are generally derived using assumptions about the attenuation of nitrate-nitrogen (NO3-N) as it passes from the paddock root zone to rivers and lakes. This approach ignores the spatial and temporal dynamics of the transport and transformations of NO3-N along flow pathways from farms to rivers and lakes as relatively little is known about these processes in NZ agricultural catchments. This information is increasingly being sought to derive a robust understanding of the contribution farming systems make to water quality outcomes, as is required by New Zealand’s National Policy Statement for Freshwater 2014. Our research in the Manawatu River catchment suggests that N loads measured in the river are significantly smaller than the estimates of N leached from the root zone. The on-going field observations, surveys and experiments indicate that denitrification is a key NO3-N attenuation process in the catchment. This N attenuation capacity appears to vary among the sub-catchments within the catchment. We, therefore, suggest that more cost-effective improvements in water quality can be achieved by selecting landuse practises and mitigation options according to the N attenuation capacity in the subsurface environment (below the root zone) in sensitive agricultural catchments. Further research to understand and quantify this N attenuation capacity in NZ agricultural catchments is important for a number of reasons. Firstly, by taking a catchment perspective, we will be able to help redesign landuse practices in a coordinated fashion by spatially aligning intensive landuse practices with high N attenuation pathways, i.e. ‘matching landuse with land suitability’, to increase agricultural production while reducing environmental impacts. Secondly, we will be able to align the spatial and temporal variation in N loss with built or enhanced attenuation to improve water quality outcomes.