Robert Gordon

Dalhousie University, Halifax, Nova Scotia, Canada

Are you Robert Gordon?

Claim your profile

Publications (22)29.24 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Treatment wetlands can be a viable wastewater treatment option, especially in rural and remote regions where centralized wastewater treatment is not feasible. Bacteria fate and transport modeling within wetlands requires further development if they are to become a more reliable and predictable form of wastewater treatment. The goal of this paper was to calibrate and test an unsteady state numerical model for the simulation of E. coli fate and transport within full-scale surface flow (SF) wetlands treating domestic wastewater. The Water Quality Analysis and Simulation Program (WASP) was used to develop the model. Accurately predicting E. coli effluent concentrations using WASP was difficult due to the dynamic nature of the wetland environment including hydraulics, seasonal variability, and wetland maturity. WASP was successful in predicting average E. coli effluent concentrations but did not accurately forecast maximum and minimum values. The model produced better fits with observed E. coli effluent concentrations during the summer months, when observed effluent concentrations were less variable. Hydraulic tracer studies and model results suggest that preferential flow pathways may be affecting E. coli removal due to reduced retention times. Flow channelling or short circuiting may have been caused by high flow conditions and/or dense cattail growth. A more detailed understanding of treatment wetland hydraulics is required before we can accurately predict treatment performance.
    Journal of Environmental Science and Health Part A Toxic/Hazardous Substances & Environmental Engineering 06/2011; 46(7):680-91. DOI:10.1080/10934529.2011.571576 · 1.14 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Four years of performance data from a free-water surface constructed wetland receiving dairy wastewater in Nova Scotia was used to compute first order reaction rate constants (Ka) for several parameters including BOD5, TP, TKN, NH4+-N, FC, and TSS. Flow rates at the inlet and outlet of the 5 m wide × 20 m long wetland were continuously measured to assess how external hydrologic influences affected the water budget of the wetland and the system treatment performance. The Ka values were calculated using inlet and outlet concentrations and an assumption of plug flow hydraulics. Adjusted rate constants (Kac) were also computed, in which the effects of dilution and concentration on pollutant concentrations were considered. Precipitation, runoff, and evapotranspiration had a large influence on the wetland water budget. Values of Ka were higher than Kac for all wastewater parameters, illustrating the effects of dilution on outlet pollutant concentrations and the importance of accurately characterizing wetland hydrology when determining or using rate constants. The Kac values did not appear to be influenced by temperature or solar radiation, but were positively correlated with the hydraulic loading rate for most parameters. Rate constants were lower than those reported in the literature for livestock wastewater treatment wetlands operating in warmer climates. This could be due to differences in climate, but could also be attributed to the relatively high strength wastewater and low hydraulic loading rate (0.1 m month–1) used in this study. Key words: treatment wetlands, cold climate, agricultural wastewater, design, rate constants.
    Journal of Environmental Engineering and Science 02/2011; 6(1):65-72. DOI:10.1139/s06-028 · 0.67 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: There is growing interest in Nova Scotia's Environmental Farm Plan (NS EFP) program among farmers and policy makers because of several reasons. First, effectiveness of standardized or uniform beneficial management practices in mitigating the negative environmental impacts from agriculture is limited by inherent heterogeneities in agricultural production systems. In addition, there is heightened interest in farmers generating ecological goods and services to society. This study investigates the determinants of participation in the NS EFP program. A discrete choice model of NS EFP participation was applied to a sample of 83 farmers (representing a 31% response rate). To increase relevance of the study to program administrators, the study also examined farmers’ use of various channels and sources of information on farm conservation practices. The most used sources of information on farm conservation practices include a mix of interpersonal sources and government agencies. Although online information (especially those available for free) appears to be gaining popularity in usage, overall, electronic and computer channels of information (especially radio and television) were used less compared with traditional channels of communicating farm conservation information (such as newsletters and agricultural magazines). Regression analysis suggests that farm characteristics (i.e., farm type, farm size, farm income) and farmer capacity variables (i.e., specialized training and knowledge from EFP program information sessions and workshops, and on-farm stewardship demonstrations) were significant determinants of environmental farm planning.
    Land Use Policy 10/2010; 27(4):1097-1106. DOI:10.1016/j.landusepol.2010.02.006 · 3.13 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The forest litter decomposition model (FLDM) described in this paper provides an important basis for assessing the impacts of forest management on seasonal stream water quality and export of dissolved organic carbon (DOC). By definition, models with annual time steps are unable to capture seasonal, within-year variation. In order to simulate seasonal variation in litter decomposition and DOC production and export, we have modified an existing annual FLDM to account for monthly dynamics of decomposition and residual mass in experimental litterbags placed in 21 different forests across Canada.The original annual FLDM was formulated with three main litter pools (fast, slow, and very slow decomposing litter) to address the fact that forest litter is naturally composed of a mixture of organic compounds that decompose at different rates. The annual FLDM was shown to provide better simulations than more complex models like CENTURY and SOMM.The revised monthly model retains the original structure of the annual FLDM, but separates litter decomposition from nitrogen (N) mineralization. In the model, monthly soil temperature, soil moisture, and mean January soil temperature are shown to be the most important controlling variables of within-year variation in decomposition. Use of the three variables in a process-based definition of litter decomposition is a significant departure from the empirical definition in the annual model. The revised model is shown to give similar calculations of residual mass and N concentration as the annual model (r2=0.91, 0.78), despite producing very different timeseries of decomposition over six years. It is shown from a modelling perspective that (i) forest litter decomposition is independent of N mineralization, whereas N mineralization is dependent on litter decomposition, and (ii) mean January soil temperature defines litter decomposition in the summer because of winter-temperatures’ role in modifying forest-floor microorganism community composition and functioning in the following summer.
    Ecological Modelling 08/2010; 221(16):1944-1953. DOI:10.1016/j.ecolmodel.2010.04.015 · 2.33 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Treatment wetlands can be a viable alternative for rural wastewater treatment where conventional centralized methods of treatment may not be feasible. The seasonal treatment performance associated with two surface-flow domestic wastewater treatment wetlands located at the Bio-Environmental Engineering Centre in Truro, Nova Scotia was investigated between October 2007 and April 2009. Each wetland had a surface area of ≈ 100m2, was loaded with ≈ 1,400L of domestic septic tank effluent d−1, and had a theoretical hydraulic retention time (HRT) of ≈ 25d. The wetlands achieved average% reductions on a concentration basis of 95% E. coli, 69% BOD5, 78% TSS, 46% TKN, 42% NH3, 39% TP, and 34% SRP. Average% mass reductions based on monthly flows were 92% E. coli, 59% BOD5, 65% of TSS, 23% TKN, 21% NH3, 8% TP, and 2% SRP. First order removal rate constants averaged 0.19 d−1 for E. coli, 0.08 d−1 TSS, 0.07d−1 BOD5, 0.03d−1 TKN, 0.04d−1 NH3, and 0.03d-1 for both TP and SRP. Treatment performance was highly variable and appeared to decrease over time. Seasonal variability, hydrologic loading, and long term performance must be considered during the design stage to ensure adequate treatment capacity. KeywordsContaminant removal-Rural wastewater management-Water quality
    Wetlands 08/2010; 30(4):795-804. DOI:10.1007/s13157-010-0067-1 · 1.44 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: : Microbial contamination of surface waters is one of the most important water quality issues affecting the agricultural sector in Nova Scotia, Canada. Most farmers who irrigate in the province draw their source water directly from streams and rivers. One mode of pathogen transmission is the irrigation of horticultural crops with contaminated water. The extended storage of irrigation water prior to crop application could minimize this risk. Natural inactivation processes could, depending on the source water characteristics and length of storage time, reduce bacteria levels to acceptable use standards. The purpose of this project was to study bacterial population dynamics, specifically those of Escherichia coli, in shallow irrigation water reservoirs. Experiments, involving a series of dialysis tube survival studies, were conducted from May through September of 2006 in an operational farm reservoir to examine microbial inactivation kinetics. It was found that E. coli populations in the cool, lower layer (depth ≈ 3 m) did not decline, while populations in the warm upper layer (depth ≈ 1.0 m) experienced significant reductions over a period of several days. An inactivation model was calibrated and used to develop conservative estimates of T90, T99, and T99.9 values for environmental conditions typical of the Annapolis Valley of Nova Scotia. If a shallow reservoir was well mixed to prevent gradients in temperature and dissolved oxygen, storage of irrigation water for a period of at least two weeks would reduce bacterial numbers by at least three logs during the growing season in Nova Scotia.
    Canadian Water Resources Journal 01/2010; 35(1):69-78. DOI:10.4296/cwrj3501069 · 1.22 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Standard analysis of the economic feasibility of on-farm biogas energy production tend to emphasize primarily on direct financial benefits to farmers, and abstracts from the nonmarket cobenefits associated with anaerobic digestion of livestock manure and other biomass feedstock. This shortcoming of the standard feasibility analysis raises a fundamental question: How is the economic feasibility of on-farm anaerobic biogas energy production affected by the associated nonpecuniary cobenefits? Incorporating key nonmarket cobenefits from biogas energy production extends the standard economic feasibility analysis, and provides important insights. When nonmarket cobenefits were excluded, on-farm biogas energy production was generally not financially feasible for the dairy and swine farm size ranges studied (except for 600- and 800-sow farms). Overall, results of the financial feasibility analysis did not change compared to a base scenario (without nonmarket cobenefits) when an estimated annual total nonmarket cobenefits of CND$5000 was incorporated into the analysis, for both dairy and swine farms. Biogas energy production was generally financially viable for small-size dairy (i.e., 50-cow) and swine (i.e., 200-sow) farms when the nonmarket cobenefits were valued at CND$15,000 (or higher). Improvements in financial feasibility were more dramatic for dairy than for swine farms.
    Energy Policy 02/2009; DOI:10.1016/j.enpol.2008.11.018 · 2.70 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A paired stream approach was used to assess ecosystem health in two rural Nova Scotia streams (Thomas Brook and Sharpe Brook) with varying land-use practices. The objectives of the study were to assess stream health within an agricultural catchment, the Thomas Brook Watershed, and to identify parameters that could be used to characterize the impacts of agricultural land use on stream ecosystem health within intensively farmed watersheds in Nova Scotia. General water quality (nutrient concentrations, turbidity, pH, temperature) and the hydrology of both watersheds were monitored from May to October 2006. In addition, continuous dissolved oxygen (DO) and chlorophyll a data were collected in both streams, and benthic invertebrate populations were characterized during the study period. Diurnal DO data were analyzed to determine photosynthesis and respiration ratios. Macroinvertebrate data provided information on productivity, and on a number of other relevant metrics. Findings determined that agricultural land-use generally led to high nutrient concentrations, large dissolved oxygen variability, turbid waters, high chlorophyll a content, and impacted macroinvertebrate populations in streams. Forested land-use demonstrated typically unimpacted conditions. It was concluded that DO dynamics and macroinvertebrate metrics would be very useful for providing a generalized assessment of stream health in agricultural watersheds.
    Journal of Environmental Engineering and Science 09/2008; 7(5). DOI:10.1139/S08-016 · 0.94 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Constructed wetlands are cost effective wastewater treatment systems being increasingly used in agriculture. Efficient phosphorus (P) treatment by wetlands can however, be a challenge due to slow removal mechanisms. As a result, extended contact times are often required to achieve desired treatment. There are also concerns related to the long-term sustaina bility of P treatment. Therefore, a five year dataset from a surface flow constructed wetland located in Bible Hill Nova Scotia, Canada was examined to: 1) determine the effects of continued loading on P treatment and 2) evaluate hydrological impacts on P treatment. The wetland was intensively monitored year-round from November, 2000 through April, 2005 for total P (TP) and soluble reactive P(SRP). Dairy wastewater (milkhouse wash water and liquid manure) was loaded at 1.5 ± 1.0 kg ha−1 d−1 for TP and 1.0 ± 0.9 kg ha−1 d−1 for SRP. Mass reductions for the entire monitoring period were 53.7% and 52.7% for TP and SRP, respectively. Soils in this wetland appeared to have a sustained P adsorption capacity, with treatment being largely influenced by hydrology and fluctuations in wastewater loading rates. Linear regression of monthly TP and SRP mass reductions, with monthly outflow volumes resulted in decreased mass reductions with increased outflow. Monthly mass reductions were > 50% when corresponding outflows were < 100 mm. When monthly outflow exceeded 100 mm, however, mass reductions became highly variable. To maintain effective P management by constructed wetlands, the use of approaches that prevent high external hydrological loadings are recommended.
    Wetlands 09/2008; 28(3):715-723. DOI:10.1672/07-163.1 · 1.44 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper describes the performance of six lateral flow sand filters (LFSFs) for their treatment of septic tank effluent in Truro, Nova Scotia, Canada. This report presents LFSF performance data collected during the first year of monitoring (Sept. 2004-Sept. 2005). The objectives of this initial study were to: (i) Evaluate the performance of LFSFs in field conditions and determine the influence of temperature and external hydrologic processes on treatment processes; (ii) evaluate the effects of slope and sand characteristics on LFSF performance; and (iii) characterize the hydraulic operation of LFSF systems in field conditions. Six LFSFs were constructed according to the Nova Scotia Department of Environment and Labour's (NSDEL) design guidelines. Fine (d(10)=0.15 mm), medium (d(10)=0.17 mm), and coarse (d(10)=0.30 mm) sands were tested at 5 and 30% slopes. The hydraulic conductivity of these sands ranged from 1.5x10(-4) to 1x10(-3) m s(-1). Each LFSF was loaded with approximately 100 L d(-1) of septic tank effluent for 1 year and samples were collected monthly. Average removal efficiencies for all LFSFs met NSDEL requirements: biological oxygen demand (>98.5%), total suspended solids (>95.5%), and E. coli (>5.4 log reduction). Phosphorus removal ranged from 98% in the fine sand to 71.2% in the coarse sand filter. Nitrification was favored because the filters were operating under aerobic and unsaturated conditions. Therefore, denitrification was limited causing elevated nitrate effluent concentrations. Total nitrogen removal ranged from 60 to 66%. The LFSFs provided consistent year-round treatment and did not appear to be impacted greatly by slope, temperature, or external hydrologic influences.
    Journal of Hydrologic Engineering 08/2008; 13(8). DOI:10.1061/(ASCE)1084-0699(2008)13:8(720) · 1.62 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Most agricultural beneficial management practices (BMP) require not only investment of money and forgone opportunities for farmers, but can also result in reduced farm returns, especially in the short-run, thereby making such BMP adoption costly for farmers. Two approaches were used to assess the detailed on-farm costs, and important non-economic and less quantifiable decision considerations associated with establishing and maintaining two structural BMPs and one nonstructural BMP in the Thomas Brook Watershed, Nova Scotia, Canada. Labour cost and technical consultancy fees as a percentage of total BMP cost was higher for the stormwater diversion drainage system (60%) than for fencing to exclude livestock from a waterway (32%). In contrast, material costs as a proportion of total cost was higher for livestock exclusion fencing (47%) than for the stormwater diversion drainage system (6%). Results of the analysis demonstrate the complementarity of the two methods. The case study in-depth interviews on key farm and BMP specific factors considered in implementing the BMPs are consistent with the empirical economic cost analysis. Furthermore, the qualitative analysis revealed that besides economic costs, other important factors and motivations influence farmers' decisions to implement and maintain environmental conservation-compatible practices, which agricultural administrators and policy makers should not ignore.
    07/2008; 4(3):1-32.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Water quality within the Thomas Brook watershed, a 750 ha mixed land-use catchment located in the headwaters of the Cornwallis River drainage basin, was assessed using an integrated monitoring program. The research objective was to examine spatial and temporal characteristics of fecal bacteria loading from a watershed during the growing season. Fecal coliform, Escherichia coli, total suspended solids (TSS) concentrations and stream flow were monitored at five points in the watershed during a six growing season period (May to Oct, 2001-2006). A nested watershed monitoring approach was used to determine bacterial loading from distinct source types (residential vs. agricultural). Daily loading was further differentiated into stormflow and baseflow. Bacterial loading per hectare increased in each nested watershed moving downstream through the watershed and were highest in the three subcatchments dominated by agricultural activities. Upper watershed bacterial loading from an agricultural subcatchment (Annual Avg 8.92x1010 CFU/ha) was consistently higher than a residential subcatchment (Annual Avg 8.43x109 CFU/ha). Annual stormflow bacterial loads were higher than baseflow loads. The highest daily fecal bacteria load per annum ranged from 8.1 to 20.1% of the total annual growing season load and were all preceded by at least 38 mm of precipitation. Annual fecal bacteria loads were found to be greater during growing seasons with greater annual precipitation. A positive linear relationship was observed between E. coli and TSS loading during the 2005 and 2006 growing seasons when both parameters were monitored. The E. coli and TSS loading relationship was weakest during baseflow periods (R2=0.40), higher for stormflow periods (R2=0.50), and strongest (R2=0.60) when all flow conditions were included in the regression. Further year round watershed and intensive stormflow monitoring are required to expand the understanding of fecal bacteria loading in the Thomas Brook watershed.
    21st Century Watershed Technology: Improving Water Quality and Environment Conference Proceedings, 29 March - 3 April 2008, Concepcion, Chile; 01/2008
  • [Show abstract] [Hide abstract]
    ABSTRACT: The economic feasibility of on-farm biogas energy production was investigated for swine and dairy operations under Nova Scotia, Canada farming conditions, using net present value (NPV), internal rate of return (IRR), and payback period (PP) economic decision criteria. In addition, the effects of selected environmental and “green” energy policy schemes on co-generation of on-farm biogas energy production and other co-benefits from anaerobic digestion of livestock manure were investigated. Cost-efficiencies arising from economies of scale for on-farm anaerobic biogas production were found for swine farms, and less so for dairy production systems. Without incentive schemes, on-farm biogas energy production was not economically feasible across the farm size ranges studied, except for 600- and 800-sow operations. Among single policy schemes investigated, green energy credit policy schemes generated the highest financial returns, compared to cost-share and low-interest loan schemes. Combinations of multiple policies that included cost-share and green energy credit incentive schemes generated the most improvement in financial feasibility of on-farm biogas energy production, for both swine and dairy operations.
    Energy Policy 09/2007; 35(9-35):4597-4610. DOI:10.1016/j.enpol.2007.03.023 · 2.70 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Nuisance odours emanating from livestock operations are a major concern to the non-farming public. Several field experiments were conducted to evaluate the effect of management strategies and meteorological conditions on odour emissions from hog slurry applied to grass. Management strategies included slurry application rate, soil water status, slurry dilution with water and rainfall simulation shortly after field application. It was found that doubling (120,000 L ha-1) the application rate had no impact on odour emissions. Tripling (180,000 L ha-1) the application rate, however, increased emissions, relative to a conventional (60,000 L ha-1) application rate. Applying slurry to soil that received rainfall prior to application increased emissions in one of the experiments, compared to soil that did not receive water. On average, diluting slurry with water decreased emissions by only 11%. Meanwhile, rainfall immediately after application increased odour emissions by 17%. Odour fluxes increased with higher windspeed, net radiation and evapotranspiration. Odour emissions can therefore, be reduced by following proper application rates, but most importantly, by applying slurry during calm, cool days. However, such stable weather conditions may increase odour persistence due to lack of vertical mixing, reduced transfer rates and slow drying of the slurry.
    2007 Minneapolis, Minnesota, June 17-20, 2007; 01/2007
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The association of microorganisms with sediment particles is one of the primary complicating factors in assessing microbial fate in aquatic systems. The literature indicates that the majority of enteric bacteria in aquatic systems are associated with sediments and that these associations influence their survival and transport characteristics. Yet, the nature of these associations has not been fully characterized. In this study, a combination of field experiments and mathematical modeling were used to better understand the processes which control the fate and transport of enteric bacteria in alluvial streams. An experimental procedure, involving the use of a tracer-bacteria, was developed to simulate the transport and deposition of bacteria-laden bed sediments in a small alluvial stream during steady flow conditions. The experimental data and mathematical model were used to determine dispersion coefficients, deposition rates, and partitioning coefficients for sediment-associated bacteria in two natural streams. The results provided evidence that bacterial adsorption can be modeled as an irreversible process in freshwater environments. Net settling velocities of fine sediments and associated bacteria were typically two orders of magnitude lower than those predicted from Stokes equation, due to re-entrainment of settled particles. The information presented in this study will further the development of representative microbial water quality models.
    Water Research 08/2005; 39(12):2665-75. DOI:10.1016/j.watres.2005.04.040 · 5.32 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Nitrous oxide (N2O) is primarily produced as intermediate in denitrification and, to a lesser extent, through nitrification processes. Nitrous oxide emission and, consequently, its atmospheric impacts depend on the extent to which N2O is reduced to dinitrogen gas (N2) by denitrifiers. Field experiments were conducted from 1998 through 2000 growing seasons at St. Emmanuel, Quebec, Canada, to investigate the combined impact of water table management (WTM) and N fertilization rate on the soil denitrification (N2O + N2) rate, rate of N2O production, and the N2O:N2O + N2 ratio. Water table treatments included subirrigation (SI) with a target water table depth of 0.6 m and free drainage (FD) with open drains. The tile drains (75 mm diameter) were laid at a 1.0 m depth from the soil surface. Nitrogen fertilizer was applied at two rates:120 and 200 kg N ha−1 as ammonium nitrate (34-0-0). The N2O + N2 evolution rates were greater in SI (12.9 kg N ha−1) than in FD (5.8 kg N ha−1) plots. The percentages of N2O relative to overall N2O + N2 evolution were 35 and 11% for 1998, 29 and 8% for 1999, and 37 and 20% for 2000, under FD and SI, respectively. The reduced N2O production under SI was due to a greater reduction of N2O to N2. Results indicate that greater N2O + N2 evolution under shallow water tables are not necessarily accompanied by higher N2O emissions.
    Nutrient Cycling in Agroecosystems 07/2005; 72(3):229-240. DOI:10.1007/s10705-005-2920-9 · 1.73 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The recognition of the environmental impacts of untreated wastewater has lead to the investigation of effective and low cost treatment technologies. Constructed wetlands have not been widely adopted in Atlantic Canada and Local issues pertaining to the integration of these systems need to be addressed including their cold climate operation and treatment efficiencies. The objective of this research was to evaluate a subsurface flow wetlands ability to treat multi source waste for Atlantic Canada. A subsurface flow wetland was designed to treat wastewater generated from a dairy farm in Nova Scotia. These wastewaters include: (i) milkhouse washwater from approximately 55 cows, (ii) leachate from four silage silos, (iii) solid manure runoff from a concrete pad, and (iv) domestic sewage from two households. The size of wetland is 8 m x 25 m with the main body being 0.6 m in depth and constructed with the combinations of course and fine gravel. Cattails (Typha sp.) are planted in the center of the wetland. Samples from both the inlet and outlet are taken on a weekly basis from April 2003 through December 2004 and analyzed for Total Kjeldalh Nitrogen, Ammonia Nitrogen, Nitrate Nitrogen, Soluble Reactive Phosphorus, and Total Phosphorus, pH, Total Suspended Solids, Five Day Biological Oxygen Demand, and E. coli. Results showed that the wetland was not capable of reducing high levels of pollutants from the silage leachate and its low pH. After its diversion from the wetland, Biological Oxygen Demand and Phosphorous removal efficiencies increased to moderate levels. However, nitrogen removals showed high variability and low treatment. These findings suggest that constructed wetlands may be limited in there ability to treat nitrogen in wastewater and sizing may need to be reconsidered for cold climate regions.
    2005 Tampa, FL July 17-20, 2005; 01/2005
  • [Show abstract] [Hide abstract]
    ABSTRACT: The denitrification process and nitrous oxide (N2O) production in the soil profile are poorly documented because most research into denitrification has concentrated on the upper soil layer (0-0.15 m). This study, undertaken during the 1999 and 2000 growing seasons, was designed to examine the effects of water table management (WTM), nitrogen (N) application rate, and depth (0.15, 0.30, and 0.45 m) on soil denitrification end-products (N2O and N2) from a corn (Zea mays L.) field. Water table management treatments were free drainage (FD) with open drains and subirrigation (SI) with a target water table depth of 0.6 m. Fertility treatments (ammonium nitrate) were 120 kg N ha(-1) (N120) and 200 kg N ha(-1) (N200). During both growing seasons greater denitrification rates were measured in SI than in FD, particularly in the surface soil (0-0.15 m) and at the intermediate (0.15-0.30 m) soil depths under N200 treatment. Greater denitrification rates under the SI treatment, however, were not accompanied with greater N2O production. The decrease in N2O production under SI was probably caused by a more complete reduction of N2O to N2, which resulted in lower N2O to (N2O + N2) ratios. Denitrification rate, N2O production and N2O to (N2O + N2) ratios were only minimally affected by N treatments, irrespective of sampling date and soil depth. Overall, half of the denitrification occurred at the 0.15- to 0.30- and 0.30- to 0.45-m soil layers, and under SI, regardless of fertility treatment level. Consequently, sampling of the 0- to 0.15-m soil layer alone may not give an accurate estimation of denitrification losses under SI practice.
    Journal of Environmental Quality 01/2005; 34(2):446-54. DOI:10.2134/jeq2005.0446 · 2.35 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Integrated water quality assessments that pertain not only to crop production systems but also public health at the watershed level are growing in popularity. The Thomas brook is a small (760 ha) tributary of the Cornwallis river located in the Annapolis Valley of Nova Scotia, Canada. The Annapolis valley is the most intensively managed agroecosystem in the province, characterized by both agricultural and residential land uses. The objective of this research was to: (i) quantify concentration and loading levels of nutrients (nitrogen and phosphorus) and total coliform bacteria in the surface waters and (ii) attempt to identify the primary sources of pollution within the Thomas brook. Five sampling stations were strategically stationed in the watershed based on the different land uses within the watershed. Water quality and stream flow were monitored at these monitoring stations during a three year period (May to November from 2001 to 2003). Water quality indicators monitored included total phosphorus (TP; 0.09 mg L-1), soluble reactive phosphorus (SRP; 0.09 mg L-1), nitrate-nitrogen (NO3 --N; 2.28 mg L-1), ammonium-nitrogen (NH4+ -N; 0.24 mg L-1) and E. coli (403 cfu 100ml-1). Results show that P concentrations were greatest in a section close to an adjacent dairy farm. The largest mass loadings of nitrogen to the stream were observed in the lower reaches of the watershed, which is surrounded by agricultural cropping systems. Whereas fecal coliform loading along stream reaches were affected by both livestock operations and residential dwellings. These findings support the suggestion that integrated water quality assessment is a key to develop management strategies that minimize health and environmental risks through the contamination of water.
    2004, Ottawa, Canada August 1 - 4, 2004; 01/2004
  • [Show abstract] [Hide abstract]
    ABSTRACT: Denitrification rate in the soil profile is poorly documented because most research into denitrification has concentrated on the upper soil layer (0-0.15 m). This study was designed to examine the effects of water table management (WTM), nitrogen (N) application rate, and depth (0.15, 0.30, and 0.45 m) on denitrification processes from a corn (Zea mays L.) field. Water table management treatments were free drainage (FD) and subirrigation (SI). Fertility treatments (ammonium nitrate) were 120 kg N ha-1 (N120) and 200 kg N ha-1 (N200). Greater denitrification rates were measured in SI than in FD, particularly in the surface soil (0-0.15 m) and at the intermediate (0.15-0.30 m) soil depth under N200 treatment. Denitrification rates were only minimally affected by N treatments, irrespective of sampling date and soil depth. Overall, half of the denitrification occurred at the 0.15-0.30 m and 0.30-0.45m soil layers combined under SI, regardless of fertility treatment level. Consequently, we conclude that sampling of the 0-0.15 m soil layer alone may not give an accurate estimation of denitrification losses under SI practice.
    2004, Ottawa, Canada August 1 - 4, 2004; 01/2004

Publication Stats

200 Citations
29.24 Total Impact Points

Institutions

  • 2011
    • Dalhousie University
      • Department of Biological Engineering
      Halifax, Nova Scotia, Canada
  • 2009–2011
    • University of Guelph
      • School of Environmental Sciences
      Guelph, Ontario, Canada
  • 2003–2010
    • Nova Scotia Agricultural College
      XLZ, Nova Scotia, Canada