Selecting the right model to simulate a specific watershed has always been a challenge, and field testing of watersheds could help researchers to use the proper model for their purposes. The performance of three popular Geographic Information System (GIS)-based watershed simulation models (European Hydrological System Model (MIKE SHE), Agricultural Policy/Environmental Extender (APEX) and Soil and Water Assessment Tool (SWAT)) were evaluated for their ability to simulate the hydrology of the 52.6 km² Canagagigue Watershed located in the Grand River Basin in southern Ontario, Canada. All three models were calibrated for a four-year period and then validated using an independent four-year period by comparing simulated and observed daily, monthly and annual streamflow. The simulated flows generated by the three models are quite similar and closely match the observed flow, particularly for the calibration results. The mean daily/monthly flow at the outlet of the Canagagigue Watershed simulated by MIKE SHE was more accurate than that simulated by either the SWAT or the APEX model, during both the calibration and validation periods. Moreover, for the validation period, MIKE SHE predicted the overall variation of streamflow slightly better than either SWAT or APEX.

Constructed wetlands (CW) are a treatment option for agricultural wastewater. Their ability to adequately function in cold climates continues to be evaluated as they are biologically active systems that depend on microbial and plant activity. In order to assess their performance and to highlight regional specific design considerations, a review of CWs in Eastern Canada and the Northeastern USA was conducted. Here, we synthesize performance data from 21 studies, in which 25 full-scale wetlands were assessed. Where possible, data were separated seasonally to evaluate the climatic effects on treatment performance. The wastewater parameters considered were five-day biochemical oxygen demand (BOD₅), total suspended solids (TSS), E. coli, fecal coliforms, total Kjeldahl nitrogen (TKN), ammonia/ammonium (NH₃/NH₄⁺-N), nitrate-nitrogen (NO₃⁻-N), and total phosphorus (TP). Average concentration reductions were: BOD₅ 81%, TSS 83%, TKN 75%, NH₄⁺-N 76%, NO₃⁻-N 42%, and TP 64%. Average log reductions for E. coli and fecal coliforms were 1.63 and 1.93, respectively. Average first order areal rate constants (k_a, m·y⁻¹) were: BOD₅ 6.0 m·y⁻¹, TSS 7.7 m·y⁻¹, E. coli 7.0 m·y⁻¹, fecal coliforms 9.7 m·y⁻¹, TKN 3.1 m·y⁻¹, NH₄⁺-N 3.3 m·y⁻¹, NO₃⁻-N 2.5 m·y⁻¹, and TP 2.9 m·y⁻¹. In general, CWs effectively treated a variety of agricultural wastewaters, regardless of season.

Constructed wetlands (CW) have gained recognition as a management option for the treatment of various agricultural wastewaters. This study involved the design, construction, and initial evaluation of a wetland-reservoir-irrigation (WRI) system. The system was established in Truro, Nova Scotia, Canada, with the goal to capture, treat, and re-use agricultural sub-surface drainage water. It consisted of a 1.8-ha area of a cropped field that was systematically tile drained. Drainage water was directed through a 2-cell CW and then into a reservoir-irrigation pond. Flow rate hydraulics, residence time distributions, and treatment efficiencies for nitrate-nitrogen (NO₃⁻-N) and Escherichia coli (E. coli) were monitored for 14 months. Mass reductions of NO₃⁻-N and E. coli from the CW were 67.6% and 63.3%, respectively. However, average E. coli concentrations increased to 178 CFU 100 mL⁻¹ in the reservoir during the warm season. It may therefore be best to use reservoir water for irrigation of crops that are not consumed raw. To aid in the future design of similar systems, mean first-order rate constants (k_s) for NO₃⁻-N and E. coli were calculated to be 8.0 and 6.4 m y⁻¹, respectively. The volume of water collected in the reservoir exceeded typical irrigation requirements of the drained land and could therefore provide irrigation to additional land beyond the drainage area.

The Watershed Analysis Risk Management Framework (WARMF) model is adapted to simulate flow and nitrate-N transport in an agricultural watershed in Quebec, Canada. The model was evaluated for the St. Esprit Watershed (24.3 km2), which is a part of the 210 km2 St. Esprit river basin, a tributary of the L'Assomption Watershed (4,220 km2). WARMF's hydrologic calibration and validation was performed using data from the gauge station located at the outlet of the watershed. Water-quality data collected were used to guide water quality calibration/validation. Simulations were carried out from 1994 to 1996; data from 1994 and 1995 were used for model calibration and data from 1996 were used for model validation. The model performed reasonably well in simulating the hydrologic response and nitrate losses at the outlet of the watershed. The R2 between the observed and simulated monthly stream flow for calibration was 0.92, and that for validation was 0.94. The corresponding coefficients of efficiency (E) were 0.89 and 0.91. The R2 and E values for calibration/validation of NO3−-N loads simulation were 0.89/0.84 and 0.86/0.75, respectively. Thus, the model simulated monthly flow and nitrogen losses with a good degree of accuracy over the entire year.