David M. Oliver

Assessing the potential for pathogen transfer from grassland soils to surface waters.

Contamination of surface waters with pathogenic micro-organisms is an area of growing importance in the context of diffuse agricultural pollution. Hydrological pathways linking farmed land to receiving waters may operate as vectors of disease transmission. Runoff from grassland systems may be particularly important. In this chapter, we synthesize and evaluate recent and contextual studies relating to the issue. The chapter is necessarily wide ranging and interdisciplinary but we have focused largely on the hydrological, soil-based, and microbiological perspectives. The potential for pathogen presence in livestock wastes is demonstrated through prevalence studies, and subsequent loading of grasslands with contaminated wastes generates a potential surface store of pathogens. These microbes may then be transferred to the wider environment when source and transport drivers are combined in, for example, precipitation events. The delivery of contaminated agricultural drainage waters into first order streams may impact the quality and ecological balance of watercourses if the micro-organisms of concern are still viable. This chapter evaluates both die-off and transfer processes operating from source through to the end point receptors in surface waters. Gaps in knowledge are identified and appear to be due to the contribution of heterogeneity and hydrological complexity of agricultural catchments and the complications of prevalence data derived via a range of methodologies.

Valuing local knowledge as a source of expert data: Farmer engagement and the design of decision support systems

Engagement with farmers and landowners is often undertaken by the research community to obtain information relating to typical land, livestock and enterprise management and generally centres on responses to questionnaire surveys. Farmers and land managers are constituted as expert observers of ground-level processes and provide diverse information on farming practices, enterprise economics and underpinning attitudes towards risk. Research projects designed to inform policy and practice may rely on such data to understand better on-the-ground decisions that can impact on environmental quality and the rural economy. Such approaches to eliciting local-level expert knowledge can generate large quantities of data from which to formulate rules relating to farm enterprise types. In turn, this can help to inform the structure of Decision Support Systems (DSS) and risk-based tools to determine farming practices likely to impact on environmental quality. However, in this paper we advocate the need for integrated farmer participation throughout the whole research process - from project inception through to community qualitative validation and legitimation - and thus not just for the elicitation of questionnaire responses. With farm questionnaire surveys being adopted widely by the research community, it is an opportune time to highlight a recent case study of the Taw catchment, Devon, UK. This serves as an example of co-construction of a DSS via a co-ordinated and integrated approach to expert elicitation with a farmer questionnaire survey as a central methodology. The aim of the paper is to detail the core aspects of an iterative cycle of participatory environmental management and DSS development for water quality protection and consider the multiple benefits of co-ordinated programmes of engagement with the farming community in this process.

Scale appropriate modelling of diffuse microbial pollution from agriculture

The prediction of microbial concentrations and loads in receiving waters is a key requirement for informing policy decisions in order to safeguard human health. However, modelling the fate and transfer dynamics of faecally derived microorganisms at different spatial scales poses a considerable challenge to the research and policy community. The objective of this paper is to critically evaluate the complexities and associated uncertainties attributed to the development of models for assessing agriculturally derived microbial pollution of watercourses. A series of key issues with respect to scale appropriate modelling of diffuse microbial pollution from agriculture is presented, and these include: (1) appreciating inadequacies in baseline sampling to underpin model development; (2) uncertainty in the magnitudes of microbial pollutants attributed to different faecal sources; (3) continued development of the empirical evidence base in line with other agricultural pollutants; (4) acknowledging the value of interdisciplinary working; and (5) beginning to account for economics in model development. It is argued that uncertainty in model predictions produces a space for meaningful scrutiny of the nature of evidence and assumptions underpinning model applications around which pathways towards more effective model development may ultimately emerge.

Mitigation and Current Management Attempts to Limit Pathogen Survival and Movement Within Farmed Grassland

To successfully curb microbial contamination of surface waters we need to understand, and holistically evaluate, the range of mitigation strategies that have been designed to protect watercourses from non-point agricultural sources, so as to use them to best effect. A cost-effective and pragmatic approach is to improve knowledge of farm management operations capable of (i) reducing potential pathogen numbers in livestock manures and (ii) reducing subsequent transfer (through the environment) of fecal micro-organisms derived from livestock manures that are recycled to land. This will prove important for supporting farmer decision making, devising policy and implementing mitigation practices to limit fecal micro-organism delivery from land to water. In this chapter, we consider a diverse suite of manure, animal and land management options that range from simple manure composting techniques and the use of slurry additives, through to land management engineering approaches and the design of constructed wetlands to protect watercourses from microbial contamination. The choice as to which strategy to use, if any, is ultimately made by the farmer and is likely to be influenced by a complex range of factors which may include, for example, tradition, convenience and farm economics. We conclude that the inherent complexity associated with heterogeneous landscapes confounds the likelihood that a single management strategy will provide complete protection of receiving waters from microbial contamination. Instead, the coupling of different strategies alongside improved education and considerable vigilance by farmers and land-owners is needed for a more sustainable approach to limiting diffuse microbial (and, crucially, other contaminant) pollution from agriculture.

Engaging with the water sector for public health benefits: waterborne pathogens and diseases in developed countries

When viewed from a public health perspective, water is typically considered in terms of drinking, bathing and waste disposal but other activities, particularly food production, inshore fisheries and recreation, form important points of hu-man contact. The water sector is diverse, comprising environmental sciences, engineering, the water supply industry, regulatory authorities and government policy-makers. A new level of engage-ment to involve the water sector in public health objectives is therefore dependent upon establishing a basis for dialogue and collaboration between these stakeholders, who bring widely differing conceptual approaches and practical concerns. In support of this aim, we present here a perspective on waterborne pathogens and diseases from a multidisciplinary expert group from the environmental science, microbiology, water industry, regulatory and health protection communities in the United Kingdom of Great Britain and Northern Ireland. Details of the group participants, funding and activities are available from the corresponding author.

Re-shaping models of E. coli population dynamics in livestock faeces: Increased bacterial risk to humans?

Dung-pats excreted directly on pasture from grazing animals can contribute a significant burden of faecal microbes to agricultural land. The aim of this study was to use a combined field and modelling approach to determine the importance of Escherichia coli growth in dung-pats when predicting faecal bacteria accumulation on grazed grassland. To do this an empirical model was developed to predict the dynamics of an E. coli reservoir within 1ha plots each grazed by four beef steers for six months. Published first-order die-off coefficients were used within the model to describe the expected decline of E. coli in dung-pats. Modelled estimates using first-order kinetics led to an underestimation of the observed E. coli land reservoir, when using site-specific die-off coefficients. A simultaneous experiment determined the die-off profiles of E. coli within fresh faeces of beef cattle under field relevant conditions and suggested that faecal bacteria may experience growth and re-growth in the period post defecation when exposed to a complex interaction of environmental drivers such as variable temperature, UV radiation and moisture levels. This growth phase in dung-pats is not accounted for in models based on first-order die-off coefficients. When the model was amended to incorporate the growth of E. coli, equivalent to that observed in the field study, the prediction of the E. coli reservoir was improved with respect to the observed data and produced a previously unquantified step-change improvement in model predictions of the accumulation of these faecal bacteria on grasslands. Results from this study suggest that the use of first-order kinetic equations for determining land-based reservoirs of faecal bacteria should be approached with caution and greater emphasis placed on accounting for actual survival patterns observed under field relevant conditions.

Establishing relative release kinetics of faecal indicator organisms from different faecal matrices

Aims:  A laboratory assay for comparative characterization of various faecal matrices with respect to faecal indicator organism (FIO) release using, artificial rain water.

Modeling Fate and Transport of Fecally-derived Microorganisms at the Watershed Scale: State of the Science and Future Opportunities

Natural waters serve as habitat for a wide range of microorganisms, a proportion of which may be derived from fecal material. A number of watershed models have been developed to understand and predict the fate and transport of fecal microorganisms within complex watersheds, as well as to determine whether microbial water quality standards can be satisfied under site-specific meteorological and/or management conditions. The aim of this review is to highlight and critically evaluate developments in the modeling of microbial water quality of surface waters over the last 10 years and to discuss the future of model development and application at the watershed scale, with a particular focus on fecal indicator organisms (FIOs). In doing so, an agenda of research opportunities is identified to help deliver improvements in the modeling of microbial water quality draining through complex landscape systems. This comprehensive review therefore provides a timely steer to help strengthen future modeling capability of FIOs in surface water environments and provides a useful resource to complement the development of risk management strategies to reduce microbial impairment of freshwater sources.

Seaweeds and plastic debris can influence the survival of faecal indicator organisms in beach environments

The revised Bathing Water Directive (rBWD) introduces more stringent standards for microbial water quality and promotes more pro-active management of the beach environment through the production of a bathing water profile (BWP). The aim of this study was to determine whether living seaweeds in the littoral zone are colonised by faecal indicator organisms (FIOs), and to quantify the survival dynamics of waterborne Escherichia coli in microcosms containing senescing seaweeds. Living seaweed (Fucus spiralis) was not associated with FIO colonisation, although could be providing a protected environment in the underlying sand. Senescing seaweeds enhanced waterborne E. coli survival compared to plastic debris, with the brown seaweed Laminaria saccharina facilitating greater E. coli persistence than either Chondrus crispus or Ulva lactuca. This has important implications for FIO survival on bathing beaches as the majority of beach-cast biomass is composed of brown seaweeds, which could support significant levels of FIOs.

Predicting microbial water quality with models : over-arching questions for managing risk in agricultural catchments.

The application of models to predict concentrations of faecal indicator organisms (FIOs) in environmental systems plays an important role for guiding decision-making associated with the management of microbial water quality. In recent years there has been an increasing demand by policy-makers for models to help inform FIO dynamics in order to prioritise efforts for environmental and human-health protection. However, given the limited evidence-base on which FIO models are built relative to other agricultural pollutants (e.g. nutrients) it is imperative that the end-user expectations of FIO models are appropriately managed. In response, this commentary highlights four over-arching questions associated with: (i) model purpose; (ii) modelling approach; (iii) data availability; and (iv) model application, that must be considered as part of good practice prior to the deployment of any modelling approach to predict FIO behaviour in catchment systems. A series of short and longer-term research priorities are proposed in response to these questions in order to promote better model deployment in the field of catchment microbial dynamics.