Rivers and Their Catchments Physical Impacts of Agriculture

Many features of the dynamic river channel are mutually adjusting (Church 2002), the present rate at which human activities alter water or sediment supply has destabilized the existing channel shape, setting off a complex cascade of changes that have disrupted geomorphic processes and ultimately degrading the river habitat (Junk et al., 1989). Such actions, called potentially destabilizing phenomena (PDP) – or factors that are the most likely causes of management problems – must be tackled in developing sustainable river channel management solutions (Downs &amp. Priestnall, 2003).

All river systems are vulnerable to the potentially deleterious impacts of agricultural activities but this report is focused on regions of humid mid-latitude climates mostly because of the exacerbating factors such as winter, frequent thunderstorms, and mid-latitude cyclones (Pidwirny, 2006) that contribute to detrimental effects of some aspects of agricultural practices and to emphasize the necessity of proper mitigation and management actions (Clark, n.d.). These destabilizing actions of agricultural activities are summarized in Table 1 and their causative relationship is discussed in detail in the following sections.

Agriculture requires the clearing of riparian vegetation and plowing to cultivate the soil (Clark, n.d.). Riparian vegetation allows the gradual infiltration of water that comes down as precipitation into the soil and without it, surface run-off increases (Odum, 1993). The increased surface run-off coupled with the loose soil due to cultivation results to increased sediment transport and soil erosion (Clark, n.d.. Allan, 2004). this effect is more pronounced during winter when soils are more exposed and transport is aggravated by&nbsp.stronger winds (Clark, n.d.).&nbsp.&nbsp.The increased run-off is usually mitigated by land drainage but this has resulted in the faster rise and fall of the water levels where the drainage is discharged (Clark, n.d.).&nbsp. The trampling of livestock, on the other hand, causes soil compaction which increases surface run-off further (Quinn 2000).&nbsp.