Variability of interrill erosion at low slopes

Abstract

Numerous models and risk assessments have been developed in order to estimate soil erosion from agricultural land, with some including estimates of nutrient and contaminant transfer. Many of these models have a slope term as a control over particle transfer, with increased transfer associated with increased slopes. This is based on data collected over a wide range of slopes and using relatively small soil fl umes and physical principals, i.e. the role of gravity in splash transport and fl ow. This study uses laboratory rainfall simulation on a large soil fl ume to investigate interrill soil erosion of a silt loam under a rainfall intensity of 47 mm h −1 on 3%, 6% and 9% slopes, which are representative of agricultural land in much of northwest Europe. The results show: (1) wide variation in runoff and sediment concentration data from replicate experiments, which indicates the complexities in interrill soil erosion processes; and (2) that at low slopes processes related to surface area connectivity, soil saturation, fl ow patterns and water depth may dominant over those related to gravity. Consequently, this questions the use of risk assessments and soil erosion models with a dominant slope term when assessing soil erosion from agricultural land at low slopes.

Quantifying sources of suspended sediment in three size fractions

“…Erosion processes are size selective during the supply, transport and storage steps of sediment movement (see Koiter et al 2013 for size selectivity of erosion and transport processes). A number of factors including flow condition, soil aggregation, soil type, erosion type and rainfall parameters can affect the degree of selectivity in a particular catchment (Hairsine et al 1999;Martinez-Mena et al 1999;Schiettecatte et al 2008;Armstrong et al 2011).…”

Controls over nutrient dynamics in overland flows on slopes representative of agricultural land in North West Europe

“…These data were collected during the same experiments as Armstrong et al (2011). A laboratory rainfall simulator and a 3.9 m long by 1.4 m wide soil flume were used.…”

“…All of the models relate an increase in sedimentassociated nutrient transfer with slope through its correlation with sediment transfer. Moreover, recent experiments undertaken by Armstrong et al (2011), along with close examination of the low slope data in Helming et al (1998), Römkens et al (2002) and Assouline and Ben-Hur (2006) suggest that the assumption of increased sediment transfer with increased slope does not hold at low slopes, which are representative of agricultural land in North West Europe. It follows that there may not be a positive relationship between sediment-associated nutrient transfer and slope at low slopes.…”

“…Despite these explicit slope controls related to the relative dominance of rainfall and runoff erosion, limited studies have examined the impact of slope on nutrient dynamics and instead rely on studies examining the effect of slope on sediment transfer (Ben-Hur et al, 1992). Moreover, as for studies examining the impact of slope on sediment transfer, summarised in Armstrong et al (2011), those which do examine the role of slope use slope ranges which are steeper than typical of agricultural land in North West Europe (Kleinman et al, 2006;Regan et al, 2009).…”

“…There is most concern regarding nitrogen (N) and phosphorus (P) transfer, with more emphasis currently placed on P as it is commonly the limiting nutrient for eutrophication in surface waters (Jarvie et al, 1998). Consequently, many laboratory, field and modelling studies have been undertaken to further the understanding of processes responsible for particulate and solute nutrient transfer within overland flow and to develop mitigation options (Armstrong et al, 2011;Deasy et al, 2009).…”