Chandra A. Madramootoo

Pollutant removal from municipal sewage lagoon effluents with a free-surface wetland

This research project was initiated to refine the knowledge available on the treatment of rural municipal wastewater by constructed wetlands. To determine the treatment capacity of a constructed wetland system receiving municipal lagoon effluents, the wetland was monitored over one treatment season, from May 19 to November 3, 2000. The wetland system consisted of a three-cell free-surface wetland, phosphorus adsorption slag filters and a vegetated filter strip. Bimonthly water samples at the inlet and outlet of each component of the wetland system were analysed for biochemical oxygen demand, nitrate and nitrite, ammonia and ammonium, total Kjeldahl nitrogen (TKN), total suspended solids (TSS), total phosphorus (TP), ortho-phosphate (ortho-PO(4)), fecal coliforms (FCs) and Escherichia coli. The free-surface wetland cells treating the lagoon effluents achieved removals as follows: biochemical oxygen demand (34%), ammonia and ammonium (52%), TKN (37%), TSS (93%), TP (90%), ortho-PO(4) (82%), FCs (52%) and E. coli (58%). The wetland cells reduced total nitrogen, TP and biochemical oxygen demand to levels below the maximum permissible levels required for direct discharge to nearby receiving waters (TN<3.0 mg x L(-1), TP<0.3 mg x L(-1), BOD(5)<3.0 mg x L(-1)). The vegetated filter strip treating the effluents from the wetland cells achieved removals as follows: biochemical oxygen demand (18%), ammonia and ammonium (28%), TKN (11%), TSS (22%), TP (5%), FCs (28%) and E. coli (22%). It may therefore serve as an additional treatment stage further reducing the concentrations of these mentioned parameters. The slag filters reduced TP in the lagoon effluents by up to 99%, and, in this study, were concluded to be effective phosphorus adsorbers.

EFFECTS OF CONTROLLED DRAINAGE ON NITRATE CONCENTRATIONS IN SUBSURFACE DRAIN DISCHARGE

Abstract A water table management field study was conducted on a Bainesville silt loam soil during 1992 and 1993. The water table levels studied were conventional free outlet subsurface drainage (FD), and controlled water tables (CWT) of 0.50 and 0.25 m above the drain level. The three treatments were replicated thrice resulting in nine plots, each measuring 115 m long by 18.69 m wide. A subsurface drain was installed 1.0 m deep in the centre of each plot. Drain discharge, nitrate concentrations in drainage effluent, rainfall and water table elevations were measured during the two growing seasons. The plots were cropped with grain corn ( Zea mays L.) in 1992, and soybean ( Glycine max (L.) Mill.) in 1993. Controlled drainage had a significant effect on drain discharge quantity and quality. In 1992, the 0.25 and 0.50 m CWT treatments reduced drain flow by 58.7% and 65.3% respectively; and in 1993, by 40.9% and 95%, respectively, compared with the FD treatment. In 1992, there was a 75.9% and 68.9% reduction of nitrate concentration in drain flow with the 0.25 and 0.50 m CWT, respectively, compared with FD. In 1993, the reductions were 62.3% and 95.7% for the 0.25 and 0.5 m CWT, respectively. While it was impossible to maintain the water tables consistently at 0.5 and 0.25 m throughout the growing season, these results show that there are significant environmental benefits with controlled drainage.

APPLICATION OF DECISION TREE TECHNOLOGY FOR IMAGE CLASSIFICATION USING REMOTE SENSING DATA

Abstract Hyperspectral images of plots, cropped with silage or grain corn and cultivated with conventional tillage, reduced tillage, or no till, were classified using the classification and regression tree (C&RT) approach, an innovative intelligent computational algorithm in data mining. Each tillage/cropping combination was replicated three times, for a total of 18 plots. Five hyperspectral reflectance measurements per plot were taken randomly to obtain a total of 90 measurements. Images were taken on June 30, August 5, and August 25, 2000 to reflect three stages of crop development. Each measurement consisted of reflectances in 71 wave bands ranging from 400 to 950 nm. C&RT models were developed separately for the three observation dates, using the 71 reflectances as inputs to classify the image according to: (a) tillage practice, (b) residue level, (c) cropping practices, (d) tillage/cropping (residue) combination. C&RT models could generally distinguish tillage practices with a classification accuracy of 0.89 and residue levels with a classification accuracy of 0.98.

Decomposition of grain-corn residues (Zea mays L.): A litterbag study under three tillage systems

This study was undertaken to obtain litterbag decomposition data for grain-corn residues in eastern Canadian conditions, to determine tillage and/or depth effects on residue mass loss, and to compare decomposition patterns for the different plant parts that constitute the residue (cobs, stems, leaves, husks). Mesh bags containing residues were buried or left on the soil surface in grain-corn plots under no-till, reduced tillage, and conventional tillage, and retrieved over a 2-yr period. Data were obtained separately for each plant part, then used to calculate pooled totals for all residues combined, for all residues except cobs, or for stems and leaves only, to facilitate comparison with studies based on different residue mixes. Buried residues lost mass faster than surface residues. Despite low overwinter temperatures, residue mass decreased substantially between placement in November and first sampling in mid- May. Surface litterbag residues lost 20% of initial mass during this period, residues buried ...

Application of geographic information systems in watershed management planning in St. Lucia

The use of geographic information systems (GIS) to develop conservation-oriented watershed management strategies on St. Lucia is presented. A soil loss model was executed within a GIS environment to evaluate agricultural management strategies in terms of soil loss on two agricultural watersheds. The GIS provided a fast and efficient means of generating the input data required for the model and allowed for easy assessment of the relative erosion hazard over the watersheds under the different land management options. The model predicted substantial declines in soil loss under conservation-oriented land management compared to current land management for both watersheds. The results of this study indicate that soil loss potential on the Soufriere watershed is approximately four times higher than on the Marquis watershed. This study represents the first attempt in the application of GIS technology to watershed conservation planning for St. Lucia. The procedures developed will contribute to the evolution of a decision support system to guide agricultural and forestry land planning in St. Lucia.

GEOSTATISTICAL METHODS FOR PREDICTION OF SPATIAL VARIABILITY OF RAINFALL IN A MOUNTAINOUS REGION

Reliable estimation of rainfall distribution in mountainous regions poses a great challenge not only due to highly undulating surface terrain and complex relationships between land elevation and precipitation, but also due to non-availability of abundant rainfall measurement points. Prediction of rainfall variability over mountainous islands is a logical step towards meaningful land use planning and water resources zoning. In this context, geostatistical techniques were developed for mapping the rainfall variability over the island of St. Lucia in the Caribbean, using the elevation information extracted from a Digital Elevation Model (DEM) and long-term mean monthly rainfall (MMR) data of 40 raingauge stations spread over 616 km2. The ordinary co-kriging (OCK) and collocated co-kriging (CCK) methods of interpolation were applied for the standardized rainfall depths associated with elevation, as the primary variate, and the surface elevation values as the secondary variate. The best semivariogram model algorithm generated, using either of the above co-kriging (CK) methods, was used to predict standardized values for the elevation points extracted from the DEM for which the rainfall depths were not known. The predicted values were further destandardized to generate the rainfall depth at the unmeasured locations. Ordinary kriging (OK) was then performed for the destandardized and observed rainfall depths to generate the prediction map of MMR over the entire island. These sequential steps were repeated for the MMR data of all twelve months to generate rainfall prediction maps over the island. The spherical semivariogram model fit well (0.84 < R2 < 0.98) for both the OCK and OK methods. The cross-validation error statistics of OCK presented in terms of coefficient of determination (R2), kriged root mean square error (KRMSE), and kriged average error (KAE) were within the acceptable limits (KAE close to zero, R2 close to one, and KRMSE from 0.55 to 1.45 for 40 raingauge locations) for most of the months. The exploratory data analysis, variogram model fitting, and generation of MMR prediction map through kriging were accomplished through use of ArcGIS and GS+ software.

Water and fertilizer nitrogen management to minimize nitrate pollution from a cropped soil in Southwestern Quebec, Canada

Nitrate-N (NO3--N) pollution of water resources is a widely recognized problem. Water and nitrogen fertilizer are the two most important factors affecting NO3--N movement to surface and groundwater. Field trials were conducted from 1998 to 2000 growing seasons to investigate the combined impacts of water table management (WTM) and N fertilization rate on NO3--N concentration in the soil profile and in drain discharge. There were two water table treatments: free drainage (FD) with open drains at a 1.0 m depth from the soil surface and subirrigation (SI) with a target water table depth of 0.6 m below the soil surface, and two N fertilizer rates: 120 kg N ha-1 (N120) and 200 kg N ha-1 (N200) in a split-plot design. Compared to FD, SI reducedNO3--N concentration in the soil by up to 50% averaged over the two N rates. Concentrations of NO3--N in drainage water fromSI plots were lower than those from FD by 55 to 73%. These findings suggest that SI can be used as a means of reducing soil NO3--N pollution and drainage water NO3--N concentrations.

Water Quality Modeling of Two Agricultural Fields in Southern Quebec Using SWAT

To study the dynamics of nutrient transport at the field scale, we collected data from two tile-drained agricultural fields in the Pike River watershed of southern Quebec. A two-year data set was used to calibrate and validate the Soil and Water Assessment Tool (SWAT) for sediment, nitrate, and phosphorus loads exiting the field through surface runoff and tile drainage. We found that SWAT output on water quality required an accurate estimation of the timing and form of field management practices employed. After calibration, the monthly coefficients of performance (Cp) over four site-years varied from 0.23 to 0.89 for sediment loads, from 0.48 to 1.35 for nitrate loads, and from 0.38 to 0.67 for total phosphorus loads. Subsurface nitrate loads accounted for 97.7% and 86.7% of the total nitrate yield, while particulate phosphorus accounted for 61.2% and 87.7% of total phosphorus load on sites 1 and 2, respectively. SWAT underestimated nitrate loads in subsurface drainage during spring snowmelt and large storms. Sediments and particulate phosphorus predictions were most accurate of all simulated parameters, whereas dissolved phosphorus was marginally overestimated year-round. Overall, SWAT satisfactorily reproduced field observations for sediment and nutrient transport and could be used to compare the impacts of implementing different best management practices (BMP) on individual fields for the study site.

PHOSPHORUS LOSSES IN SURFACE RUNOFF AND SUBSURFACE DRAINAGE WATERS ON TWO AGRICULTURAL FIELDS IN QUEBEC

Concentrations of phosphorus (P) above the water quality guideline of 0.03 mg L-1 are commonly found in rivers draining agricultural lands in Quebec. This gives rise to eutrophication, which has become quite problematic in some parts of Quebec. Agricultural nonpoint source pollution is the dominant source of this P. While the links between P losses, surface runoff, erosion and manure management are reasonably well understood, there is far less information available on the movement of P via subsurface tile drainage systems. Since the majority of intensively managed agricultural lands in Quebec are subsurface drained, this represents a major knowledge gap. Two field sites, located in the Pike River Watershed of Southwestern Quebec, which drains into Lake Champlain, have been instrumented to measure and sample surface runoff and tile drainage waters. Monitoring has been ongoing since October 2000. Results are reported here for the six site-years of data. Subsurface drainage was the dominant pathway by which water left the fields. On average, tile drainage accounted for 81% of the total annual drainage. Surface runoff was responsible for majority of the annual P losses. It accounted for 60% of the annual total, which was on average 1.09 kg/ha. The flow weighted average annual P concentration in subsurface drainage waters ranged between 0.06 mg L-1 and 0.37 mg L-1. The flow weighted average annual P concentration in surface runoff waters ranged between 0.20 mg L-1 and 2.15 mg L-1. On average, P concentrations in surface runoff were 10.9 times higher than those found in subsurface drainage waters, indicating that subsurface drainage may reduce annual P losses. These results also reveal that soil test P and percent P saturation are, on their own, inadequate indicators of potential for P pollution.

Review: Reducing residual soil nitrogen losses from agroecosystems for surface water protection in Quebec and Ontario, Canada: Best management practices, policies and perspectives

Rasouli, S., Whalen, J. K. and Madramootoo, C. A. 2014. Review: Reducing residual soil nitrogen losses from agroecosystems for surface water protection in Quebec and Ontario, Canada: Best management practices, policies and perspectives. Can. J. Soil Sci. 94: 109-127. Eutrophication and cyanobacteria blooms, a growing problem in many of Quebec and Ontarios lakes and rivers, are largely attributed to the phosphorus (P) and nitrogen (N) emanating from intensively cropped agricultural fields. In fact, 49% of N loading in surface waters comes from runoff and leaching from fertilized soils and livestock operations. The residual soil nitrogen (RSN), which remains in soil at the end of the growing season, contains soluble and particulate forms of N that are prone to being transported from agricultural fields to waterways. Policies and best management practices (BMPs) to regulate manure storage and restrict fertilizer and manure spreading can help in reducing N losses from agroecosystems. However, reduction of RSN also requires an understanding of the complex interactions between climate, soil type, topography, hydrology and cropping systems. Reducing N losses from agroecosystems can be achieved through careful accounting for all N inputs (e.g., N credits for legumes and manure inputs) in nutrient management plans, including those applied in previous years, as well as the strategic implementation of multiple BMPs and calibrated soil N testing for crops with high N requirements. We conclude that increasing farmer awareness and motivation to implement BMPs will be important in reducing RSN. Programs to promote communication between farmers and researchers, crop advisors and provincial ministries of agriculture and the environment are recommended.