The effect of rainfall intensity on soil erosion and particulate phosphorus transfer from arable soils

Abstract

Soil erosion, in the form of transported suspended sediment in overland flow, is often associated with high rates of particulate phosphorus (PP) (total P>0.45 μm) transfer from land to watercourses. Particulate P may provide a long-term source of P for aquatic biota. Twenty-two sites for winter overland flow monitoring were selected in south-west England within fields ranging from 0.2–3.8 ha on conventionally-managed arable land. Fields were situated on highly porous, light textured soils, lacking impermeable horizons and often overlying major aquifers. Long arable use and modern cultivation methods result in these soils capping under rain impact. Overland flow was observed when rainfall intensity approached the modest rate of 0.8 mm hr−1 on land at or near to field capacity. Low intensity rainfall (<2 mm hr−1) produced mean suspended sediment losses of 14 kg ha−1 hr−1, with associated PP transfer rates of 16 g ha−1 hr−1. In high intensity rainfall (>9 mm hr−1) mean PP losses of 319 g ha−1 hr−1 leaving the field were observed. As might be expected, there was a good relationship between PP and suspended sediment transfer in overland flow leaving the sites. The capacity of light soils to cap when in arable use, combined with heavy or prolonged rainfall, resulted in substantial discharges, soil erosion and associated PP transfer. Storms with heavy rain, typically of only a few hours duration, were characterised by considerable losses of PP. Such events, with return periods of once or twice a winter, may account for a significant proportion of total annual P transfer from agricultural soils under arable crops. However, contributions from less intense rain with much longer duration (around 100 hours per winter in many arable districts of the UK) are also demonstrated here.

A review of phosphorus and sediment release from Irish tillage soils, the methods used to quantify losses and the current state of mitigation practice

“…Sandy soils are particularly vulnerable to erosion due to low SOM content and poor structural stability, which predisposes the soil to disaggregation under raindrop impact and a subsequent development of a surface crust, reduction of infiltration rate and surface runoff (Quinton and Catt 2004). Long-term arable use and modern cultivation methods can result in light textured soils capping (a surface crust caused by heavy raindrops on finely cultivated soils) under rain impact (Fraser et al 1999). In a review of critical levels of SOC in tillage land in Ireland, Spink et al (2010) concluded that soil function is unlikely to be adversely affected when SOC is above a threshold of 2% (equivalent to 3.4% SOM).…”

“…It has been shown that approximately 90-95% of soil erosion occurs during the most severe 2% of storms (Winegardner 1996). Erosion also occurs over periods of prolonged lower-intensity rainfall (Fraser et al 1999;Robinson 1999). Mean annual precipitation for Ireland ranges from 750-1000mm on the eastern half of the country to 1000-1400mm on the western half (Met Éireann 2012).…”

Climate and land-use changes affecting river sediment and brown trout in alpine countries—a review

“…Torrential rain is widely believed to considerably contribute to sediment erosion (Summer 1989;Acornley and Sear 1999;Fraser et al 1999;Descroix and Gautier 2002). Additionally, both droughts followed by heavy rain events and long consecutive rain events on already saturated soil can trigger erosion; the latter at an even higher extent than single day heavy rainfall events (Prasuhn 2003).…”

The phosphorus transfer continuum: Linking source to impact with an interdisciplinary and multi-scaled approach

“…Soil erosion per se has been described many times (Quinton, 1997) and in the context of P transfer is important for particulate loss (Catt et al, 1994;Fraser et al, 1998). Some studies showed that soil solution and river water contain a continuum of sub-0.45 Am sized particles, often smaller than 10,000 Da molecular weight (Haygarth et al, 1997;Heathwaite et al, in press).…”