Sustainable and Holistic Food Chains for Recycling Livestock Waste to Land

Funder: RELU

Cost: £430k

Duration: 2005-2008

Project Details

Justification for inclusion of risk factors within the index framework

Site Source Characteristics

Aged faecal material.

The soil matrix can sustain FIO survival, especially if bacteria are incorporated in association with faecal material. Indeed some studies have detailed cell survival in excess of several months (Unc and Goss, 2006). This can be due to protective microsites and protection from desiccation and UV radiation. The inclusion of aged faecal material within the FIO risk indexing framework reiterated that it is not only fresh additions of manures to land that may be capable of impacting on the microbial quality of watercourses, and allowed for bacterial die-off to be built into the risk index in a basic manner.

Manure type (untreated), application method and application rate.

Slurries, solid manures and faeces all harbour different numbers of FIOs and all impact on differential FIO die-off patterns (Oliver et al., 2006). Furthermore, the consistency of each manure type (e.g. dry matter content) allows for differing degrees of mobility of FIOs accommodated within. Regarding application methods, broadcast-applied manures are likely to be considered more risky than injected or ploughed manures because of the opportunity for incidental contaminant losses from land to water (Preedy et al., 2001). However, broadcast applied slurry is likely to lead to a more rapid destruction of associated bacteria through UV radiation and desiccation (Hutchison et al., 2004). Finally, application rate is a logical inclusion based on the likelihood that more FIOs will be present on land where a higher application rate has been used.

Animal type, grazing density and grazing duration.

Animal type is an important risk factor to include within FIORIT because it governs the number of organisms per gram of faeces excreted onto pasture but also dictates the daily excretion rates to farmed land (Chambers et al., 2001) and the differential release of FIOs from various types of livestock faeces (McDowell, 2006) at different times of the year. Grazing density is included because it has been shown that the concentration of FIOs in streams in sub-catchments with high stocking densities can be 4 to 8 times higher compared to sub-catchments accommodating low stocking densities (Aitken, 2003) and grazing duration is potentially important based on the accumulating impact of faecal excretion to land through time.

Site Transfer Characteristics

Runoff potential.

Rainfall and resulting runoff from farmed land is critical for the transfer of agricultural pollutants such as phosphorus and sediments from land to water (e.g. Preedy et al., 2001; Bilotta et al., 2007). Likewise, runoff has been shown to act as a carrier of FIOs from land to water (Oliver et al., 2005). The inclusion of field runoff potential within the FIO risk index was thus considered a key risk factor to be weighted and was defined as a function of slope length (impacting on runoff momentum), shape (convex and concave slopes allowing for runoff to accelerate and decelerate, respectively, with increasing distance downslope), vegetation type (affecting surface roughness) and soil type (impacting on soil structure and compaction).

Preferential flow potential.

A range of hydrological pathways permit the transfer of FIOs from land to water (Oliver et al., 2005b). Within the risk indexing framework we opted to include those pathways that are likely to allow for rapid water (and associated FIO) flows. Consequently, the potential of soils to facilitate preferential flow through soil cracks and fissures was built into the risk index to complement runoff potential (Heathwaite and Dils, 2000), though it is constrained to certain soil types with higher clay content.

Erosion potential.

Though linked to runoff potential, this transfer risk factor was included to account for the ability of FIOs to be transferred with particulate material. Association of FIOs with soil particles has been discussed (e.g. Muirhead et al., 2006a; Pachepsky et al., 2006) though there is a large degree of uncertainty regarding �vehicles� for cell transfer under environmental settings (Tyrrel et al., 2003).

Site Connectivity Characteristics

Subsurface drainage.

The presence of subsurface drains (e.g. mole and tile drains) effectively increases subsurface connectivity provided that the age and condition of the features is such that the pathway still functions efficiently as a hydrological conduit. Field drains have been reported to be a rapid route of nutrient export from agricultural land (Heathwaite et al., 2006) and have also been shown to export E. coli from land to water during storm events (irrespective of surface runoff) at similar loads to that of undrained fields (Oliver et al., 2005).

Overland flow distance.

Overland flow that directly connects with a watercourse has been shown to deliver substantial loads of FIOs to the stream network (Collins et al., 2005). It is likely that a greater uninterrupted overland flow distance and contributing area will enhance the potential for accumulated carriage and delivery of FIOs to the watercourse.

Cattle access to streams.

Livestock exclusion from streams prevents their direct defecation into a watercourse. Stream fording by a dairy herd has been shown to produce appreciable increases in stream FIO concentrations (Davies-Colley et al., 2004) highlighting the potential benefits of fencing off watercourses. Livestock access to streams needs to be considered as a route of connectivity to surface waters when moving from plot to larger scale research (Vinten et al., 2004).

Tracks and tramlines perpendicular to contours.

We can speculate that animal tracks and farm machinery tramlines that cut across contours may provide rapid delivery pathways for FIOs because they are known to promote runoff and contaminant transfers (Nguyen et al., 1998; Quinton and Catt, 2004). The extent to which they impact on FIO loss from land to water relative to other delivery risk factors is largely unknown and more anecdotal.

Gateway location.

Gateways located downslope of a contributing area and close to a point of drainage can potentially increase hydrological connectivity from land to water by permitting overland flow to move rapidly across the often compacted (and contaminated) soil surface and between fields The contribution of such poorly located gateways to FIO delivery, per se, to watercourses is relatively unknown though it is identified as a contributor to increased connectivity between land and water (Cuttle et al., 2007).