Bromide redistribution as influenced by landscape morphology and pedogenic properties in a variable glacial till landscape: A quantitative examination

Abstract

The spatial and temporal variability of soil properties with depth in the profile and across landscape positions results in diverse patterns of water and solute distribution over the landscape. Vertical and lateral movement of soluble nutrients within the soil profile influences the availability of nutrients required for crop growth, and the entry of nutrients into groundwater and surface water systems. However, commonly used geomorphic concepts such as crest and depression are not rigorously, quantitatively defined. The objective of this study was to determine the influence of quantitative topographic variables and zones of relative surface flows on vertical and lateral redistribution of a bromide tracer under field conditions in a variable glacial till landscape under zero tillage agricultural management. Tracer plots were established on three representative soil-slope associations and digital terrain models (DTM) were produced for determining slope gradient (G), horizontal curvature (Kh), vertical curvature (Kv), mean curvature (H) and accumulation curvature (Ka). Models of accumulation, transit and dissipation (ATD) zones of surface flows were produced for each digital elevation model (DEM) using data on mean and accumulation curvatures. Topographic variables and soil properties had mixed ability to predict bromide redistribution parameters. Soil profile development indicators were negatively correlated with bromide recovery, indicating that increased profile development resulted in more redistribution and lower recovery rates. Pedogenic indicators were significantly different between ATD zones, with depth to calcium carbonate, A horizon thickness, solum thickness and profile development indicator all significantly greater at accumulation zones relative to dissipation or transit zones, indicating that profile development was greatest at accumulation zones. However, the concept of ATD zones did not correlate significantly with bromide redistribution parameters. The utility of ATD zones as a predictive tool for static soil properties is limited by differing hydrologic regime and pedogenic processes occurring at lower slope positions, as a result of near-surface, dynamic water tables. Previous research, however, has shown that topographic variables and concepts of landscape element complexes have some utility in determining spatial variability of deep solute percolation and determination of potential for groundwater impacts. This study indicates that increased N application in convergent portions of the landscape may result in higher rates of deep percolation and removal of N from the crop rooting zone, in areas of depression-focused recharge, when environmental conditions are favourable for such. Key words: Solute redistribution, bromide tracer, digital terrain model, topography, landscape