Development of a method for estimating the likelihood of crack flow in Canadian agricultural soils at the landscape scale

Abstract

Development of a method for estimating the likelihood of crack flow in Canadian agricultural soils at the landscape scale. Can. J. Soil Sci. 90: 129Á149. Indicators of risk of water contamination by agricultural pollutants are developed in Canada to assess sustainability of agriculture. Crack flow (CF), a key pathway for sub-surface contaminant transport, is part of the transport-hydrology algorithm used in two of these risk indicators. The objective was to develop a methodology for predicting the likelihood of CF in Canadian agricultural soils at the landscape scale. The algorithm considers soil clay content, crack development followed by a runoff event based on water budget, tile drainage, and crops. More than 40% of Canadian farmlands had moderate to very high likelihood of CF, mainly in Manitoba, Ontario and Quebec, due to frequent runoffs on cracked clay soils potentially contributing to groundwater contamination. In Ontario and Quebec, farmlands with high CF likelihood correspond to regions under intensive tile drainage, which increases the risk of lateral translocation of contaminants to surface water bodies. Besides being a component of risk indicators of water contamination by phosphorus and coliforms, the CF algorithm and maps can be used to identify areas at risk of subsurface water contamination. Best management practices, adapted to reduce CF can then be targeted to these areas.

Components of Phosphorus Loss From Agricultural Landscapes, and How to Incorporate Them Into Risk Assessment Tools

“…The tile drains reduce the amount of surface runoff, diverting that water into the tile drains, but also carrying the portion of the sediment that is carried with the portion of tile flow that has reached the tile through macropores rather than soil matrix flow. The partitioning of water between surface runoff and tile flow is predicted using the hydrology module of the DNDC model (Kröbel et al, 2010;Dutta et al, 2016;Guest et al, 2017), and the fraction of tile flow from macropores is derived from the probability of burrow flow (through anecic worm burrows) (Dadfar et al, 2010a) and crack flow (Dadfar et al, 2010b). In general, the macropore flow is highest for the fine and medium textured soils, and lowest for the coarse textured soils.…”

A phosphorus index for use in intensive irrigated areas

“… Preferential flow is a key pathway for subsurface contaminant transport. However, only a few P indices do incorporate PF (Dadfar et al. , 2010), possibly due to the large number of factors affecting this process.…”

“…Preferential flow is a key pathway for subsurface contaminant transport. However, only a few P indices do incorporate PF (Dadfar et al, 2010), possibly due to the large number of factors affecting this process. The phosphorus index developed by Beaulieu et al (2006) and Goulet et al (2006) included PF in a simple way, assuming that PF was only related to soil texture.…”

Vertisolic soils of Canada: Genesis, distribution, and classification

“…Thus, even though clay soils are characteristically described as having a low infiltration rate, if surface cracks are present, shallow water tables are susceptible to contamination with excess nitrates, phosphates, herbicides, pesticides etc., through bypass flow. Dadfar et al (2010) developed a risk methodology to assess the likelihood of soil landscapes containing finetextured parent materials (40% clay) to initially form surface cracks resulting in subsequent ground water contamination. Vertisolic soils in Canada contain more than 60% clay and surface cracks to depths of more than 60 cm have been regularly recorded, so these soils qualify as potential high-risk areas (Brierley et al 1996).…”