Carol Francis

Catchment microbial dynamics: the emergence of a research agenda:

Parallel policy developments driven in the USA by the Clean Water Act and in Europe by the Water Framework Directive have focused attention on the need for quantitative information on the fluxes of faecal indicator bacteria in catchment systems. Data are required on point and diffuse source loadings, fate and transport of these non-conservative parameters, on the land surface, within soil systems, in groundwater, streams, impoundments and nearshore waters. This new information is needed by regulators to inform Total Maximum Daily Load estimates in the USA and Programmes of Measures in Europe both designed to prevent impairment of water quality at locations where compliance is assessed against health-based standards for drinking, bathing or shellfish harvesting. In the UK, the majority of catchment-scale activity in this field has been undertaken by physical geographers although microbial flux analysis and modelling has received much less attention from the research and policy communities than, for example, the nutrient parameters. This paper charts the policy drivers now operative and assesses the evidence base to support current policy questions. Finally, gaps and priority research questions are identified.

Faecal indicator organism concentrations and catchment export coefficients in the UK.

Characterisation of faecal indicator organism (FIO) concentrations and export coefficients for catchments with particular combinations of land use and under specific climatic regimes is critical in developing models to predict daily loads and apportion sources of the microbial parameters used to regulate water quality. Accordingly, this paper presents a synthesis of FIO concentration and export coefficient data for the summer bathing season, with some comparative winter data, for 205 river/stream sampling points widely distributed across mainland UK. In terms of both geometric mean (GM) FIO concentrations and export coefficients (expressed as cfu km(-2) h(-1)), the results reveal (1) statistically significant elevations at high flow compared with base flow, with concentrations typically increasing by more than an order of magnitude and export coefficients by about two orders; (2) significantly higher values in summer than in winter under high-flow conditions; and (3) extremely wide variability between the catchments (e.g. four orders of magnitude range for GM faecal coliform concentrations), which closely reflects land use-with urban areas and improved pastures identified as key FIO sources. Generally, these two most polluting land uses are concentrated in lowland areas where runoff (m3 km(-2) h(-1)) is low compared with upland areas, which in the UK are dominated by rough grazing and forestry. Consequently, contrasts in export coefficients between land use types are less than for FIO concentrations. The GMs reported for most land use categories are based on 13 sites and exhibit quite narrow confidence intervals. They may therefore be applied with some confidence to other catchments in the UK and similar geographical regions elsewhere. Examples are presented to illustrate how the results can be used to estimate daily summer base- and high-flow FIO loads for catchments with different land use types, and to assess the likely effectiveness of certain strategies for reducing FIO pollutant loadings in areas with extensive areas of lowland improved pasture.

Results of field investigations into the impact of intermittent sewage discharges on the microbiological quality of wild mussels (Mytilus edulis) in a tidal estuary.

Field surveys were designed to examine the effects of sewage contamination from storm overflow effluent on faecal coliform and Escherichia coli concentrations in the flesh of wild mussels (Mytilus edulis). Bags containing 30 mussels each were fixed at known inter-tidal locations and retrieved at intervals following discharge from a nearby combined sewer overflow (CSO). Concentrations of faecal coliform bacteria and E. coli were measured in the shellfish flesh and in samples of overlying water prior to collection of the mussel samples. Faecal coliform and E. coli concentrations in shellfish increased rapidly after CSO discharge. E. coli concentrations exceeded the European shellfish hygiene class C limit of 46,000 100g(-1), and decayed during subsequent CSO discharge-free periods. The concentration and depuration response was independent of the magnitude of CSO spill volume. First-order exponential decay functions were fitted to the data. Decay rates were lower than those found in corresponding microcosm experiments. This relates to the repeated pattern of inundation and exposure associated with the tidal cycles in the estuary. Relationships between E. coli and faecal coliform concentrations in the shellfish and overlying water samples were relatively weak (r<0.60), a pattern often seen with data from uncontrolled environmental experiments.

A simple modified membrane filtration medium for the enumeration of aerobic spore-bearing bacilli in water

Aerobic spore-bearing bacilli have been proposed as a surrogate indicator for the removal of Cryptosporidium by drinking water treatment processes. Pasteurisation of samples followed by culture on non-selective media is the method of choice. Using white membranes for filtration of water samples makes colony counting difficult. Vital dyes such as neutral red or trypan blue can help when added to the growth medium but these dyes tend to colour the membrane and reduce the contrast between the colonies and the background. The incorporation of bromothymol blue at a concentration of 0.005% (w/v) into nutrient agar facilitated colony counting without inhibiting colony formation compared with unsupplemented nutrient agar. Statistical analysis of the data (ANOVA) confirms this observation. The modified technique was found to be satisfactory with spore suspensions of Bacillus globigii and B. cereus as well as with samples of surface water, settled water and drinking water.

Chapter 4:Impacts of Agriculture on Water-borne Pathogens

Microbial indicators of water quality are used to quantify the risk derived from faecally contaminated surface and drinking waters. The historical focus in this area has centred on human-derived sewage contamination of bathing, shellfish and drinking waters. However, emerging catchment-scale water legislation in North America and Europe, in particular, is driving a more holistic approach in which quantification of microbial pollution from all sources is undertaken, to inform and prioritise appropriate remedial action designed to ensure health risk is minimised. This involves integrated management of agricultural livestock-derived pollution alongside sewage effluents to ensure compliance of impacted sites with appropriate regulatory standards. The evidence-base for the design of best management practices by farmers which will remove and/or attenuate microbial flux from catchment systems is very limited when compared to the chemical parameters associated with ecological impairments, such as phosphorus and nitrogen. However, early empirical investigations do suggest the potential to realise very significant water quality benefits from simple interventions, such as stock exclusion fencing of stream banks and well-designed constructed wetland systems. Further process-based investigation of these areas is underway and this research effort is becoming imperative as emerging experience of catchment-scale legislation strongly suggests the importance of microbial pollution as the principal reason for non-compliance with water quality standards in North America.

Faecal Indicators and Pathogens: Expanding Opportunities for the Microbiology Community

Water regulation world-wide is moving to a new and challenging paradigm characterised by integrated assessment and management of multiple pollution loadings within drainage basins. This is seen in the European Water Framework Directive and the United States Clean Water Act. Implementation lessons of the latter suggest the principal water quality concern at the continental scale is microbial pollution by faecal indicators and pathogens. This presents a major new challenge to the microbiological community and presents major opportunities of joint working with catchment scientists, modellers, engineers and the farming community. To date, very little catchment-scale science has addressed microbial flux measurement, modelling and prediction when compared to other parameters such as the nutrients, oxygen demand and sediments. The engineering community has made excellent progress on point-source pollution control from sewage works but, parallel progress on agricultural best management practices to limit diffuse-source pollution from agriculture is less evident and the science evidence-base for the efficacy of such measures remains equivocal. This contribution presents a clear set of research challenges and management priorities designed to stimulate further involvement by the microbiological community in this emerging area.

Microbiology of Sustainable Water Systems; Rainwater Harvesting – A UK Perspective

Pressure on water resources, along with a need to reduce the risk of surface water flooding, have led to an increased interest in the adoption of a variety of sustainable water systems. This paper looks at the microbiology of rainwater harvesting in a UK context. While harvested rainwater is not generally used as drinking water in the UK, it is used to replace water (e.g. for toilet flushing) which is currently of potable quality, thus it is important to assess the potential infection risks incurred by residents of properties using such systems. A review of the literature suggests that there may, on occasion, be a number of pathogens present in harvested rainwater. This finding was confirmed in a small-scale empirical study of three rainwater harvesting tanks located in England and Wales, with Campylobacter spp. being isolated from up to 50% of the samples, with a maximum concentration of 91 per litre. An exploratory quantitative microbial risk assessment, based on exposure scenarios derived from the empirical data suggests that if consistently high levels of Campylobacter are present in the harvested rainwater there could be an increase in the number of cases of campylobacteriosis in population. However, a more conservative estimate of Campylobacter concentration and frequency of contamination (based on median figures) suggests a virtually negligible risk of infection.