https://doi.org/10.2134/jeq2019.03.0103

Kokulan, V., Macrae, M. L., Lobb, D. A., & Ali, G. A. (2019b). Contribution of overland and tile flow to runoff and nutrient losses from Vertisols in Manitoba, Canada. Journal of environmental quality, 48(4), 959-965. https://doi.org/10.2134/jeq2019.03.0103.

This study quantified the contributions of overland and tile flow to total runoff (sum of overland and tile flow) and nutrient losses in a Vertisolic soil in the Red River valley (Manitoba, Canada), a region with a cold climate where tile drainage is rapidly expanding. Most annual runoff occurred as overland flow (72–89%), during spring snowmelt and large spring and summer storms. Tile drains did not flow in early spring due to frozen ground. Although tiles flowed in late spring and summer (33–100% of event flow), this represented a small volume of annual runoff (10–25%), which is in stark contrast with what has been observed in other tile-drained landscapes. Median daily flow-weighted mean concentrations of soluble reactive P (SRP) and total P (TP) were significantly greater in overland flow than in tile flow (p < 0.001), but the reverse pattern was observed for NO3–N (p < 0.001). Overland flow was the primary export pathway for both P and NO3–N, accounting for >95% of annual SRP and TP and 50 to 60% of annual NO3–N losses. Data suggest that tile drains do not exacerbate P export from Vertisols in the Red River valley because they are decoupled from the surface by soil-ice during snowmelt, which is the primary time for P loss. However, NO3–N loading to downstream water bodies may be exacerbated by tiles, particularly during spring and summer storms after fertilizer application.

https://doi.org/10.2134/jeq2019.03.0103