characteristic behaviour and potential mitigation of some diffuse pollutants in England and Wales: A review of Ammonium, nitrite, some potential pathogens and Biological Oxygen Demand
A review prepared as part fullfillment of defra project es0121 ‘cost-dp: cost effective diffuse pollution management’
project team:
Haygarth, P.1, Chadwick, D.1, Granger, S.1, Chambers, B.2, Anthony, S.3, Smith, K.3 and Harris, D.3
1Institute of Grassland and Environmental Research (IGER), North Wyke Research Station, Okehampton, Devon, EX20 4LR.
2ADAS, Gleadthorpe, Meden Vale, Mansfield, Notts, NG20 9PF.
3ADAS, Wolverhampton, Woodthorne, Wolverhampton, WV6 8TQ.
Executive summary
This review fulfils milestones 1-4 of project ES0121 ‘COST-DP: Cost effective diffuse pollution mitigation’. This project follows on from Defra projects PE0203 and NT2511 which reviewed P and NO3- respectively. Project ES0121 reviews the remining significant diffuse pollutants; these are Ammonium (NH4+), Nitrite (NO2-), Pathogens and Biological oxygen demand. The review of each pollutant has been broken down into:
· An introduction to the pollutant
· Defining the problem in terms of Source, Mobilisation and Delivery
· Mitigation measures
· Pollution swapping
Pollutant summary:
· Ammonium
Ammonium (NH4+) is applied to agricultural land to promote plant growth and optimise agricultural yields. It can be applied in inorganic forms as fertilisers or via animal manures and other organic residues and effluents. Ammonium can also be released from organic nitrogen forms through the process of mineralization. Ammonium transfers to watercourses can cause eutrophication while dissolved ammonia (NH3) is directly toxic to fresh water fish, and the nitrification of NH4+ to NO3- can cause oxygen depletion.
· Nitrite
Nitrite (NO2-) is seldom measured in aquatic systems and often included in nitrate values. The two dominant processes involved with NO2- turnover in the environment are nitrification of NH4+ and the reduction of NO3- during denitrification. Nitrite is highly toxic and high concentrations can adversely affect plants and soil micro-organisms, while in watercourses NO2- poses a threat to fish and some species of invertebrates.
· Pathogens
The rumen and digestive tract in farm livestock is host to a rich diversity of microflora and can act as a reservoir for pathogenic micro-organisms i.e. E. coli. O157, Salmonella, Listeria, Campylobacter, Cryptosporidium and Giardia. Pathogen presence in manures is affected by factors such as animal type, age, diet and management, as well as regional and seasonal influences. Pathogenic micro-organisms may be transmitted from animals to humans either directly or indirectly through water and food chain contamination.
· Biological oxygen demand
Most agricultural organic wastes contain substantial quantities of biologically degradable material, which means considerable potential for pollution once these effluents gain access to watercourses. The presence or absence of micro-organisms influences the pollution potential of the waste. The main effect of loading surface waters with organic matter is the rapid depletion of available oxygen as a result of the increased microbial activity stimulated. In fast-flowing waters, a rapid restoration of aerobic conditions can quickly follow (as long as the pollution source is blocked), but in stagnant or slow-moving waters, anaerobic conditions quickly develop associated with the generation of foul odours and, in the longer term, the reduction in biodiversity of the system.
The mitigation matrix
A mitigation matrix has been developed (Appendix I) to help provide Defra and the project team with a provisional ‘guide’ to key pollutant behaviour properties and mitigation options. This lists the main mitigation measures currently available to agriculture and relevant to the pollutants of interest in this study. Each measure is rated according to how effective it is considered to be at mitigating each pollutant. The cost-effectiveness of each measure within the matrix has also been scored and the ease of implementation is also rated. Other measure characteristics that have also been rated include public and farmer acceptability, potential for pollution swapping, potential for conflicts with other measures, and the uncertainty of effectiveness of the measure. As part of this process, a list of typical farm systems has been created (Appendix II). This has been based upon livestock/cropping system, soil type and drainage system, manure system, and grazing regime.
CONTENTS
1. Introduction and content.
2. Ammonium.
1. Introduction.
2. Defining the Problem.
2.1. Sources.
2.1.1. Managed Manures.
2.1.2. Outdoor Livestock.
2.1.3. Inorganic Fertilizers.
2.1.4. Silage Clamps.
2.1.5. Atmospheric Deposition.
2.1.6. Mineralisation.
2.2. Mobilisation.
2.3. DELIVERY.
2.3.1. Surface Pathways.
2.3.2. Preferential Pathways.
2.3.3. Through-flow Pathways.
2.4.4. Field Runoff and Leaching of Inorganic Fertilizers.
3. MITIGATION MEASURES.
3.1. Hard Standings.
3.2. Manure Stores.
3.3. Grazing/Outdoor Livestock.
3.4. Land Spreading of Manures, Dirty Water and Other Organic …...Residues.
3.5. Silage Clamps and Big Bales.
3.6. Septic Tanks.
3.7. ‘Upstream’ Measures.
4. POLLUTION SWAPPING.
3. NITRITE.
1. Introduction.
2. Defining the Problem.
2.1. Sources.
2.1.1. Direct Sources.
2.1.2. Indirect Sources.
2.1.3. Processes of NO2- Formation in Soil.
2.1.4. Relative Contributions of Nitrification and …………Denitrification to Soil NO2-.
2.1.5. Causes of NO2- Accumulation.
2.2. MOBILISATION.
2.3. DELIVERY.
3. MITIGATION MEASURES.
4. POLLUTION SWAPPING.
4. PATHOGENS.
1. Introduction.
2. Defining the Problem.
2.1. Sources.
2.1.1. Microbial Pathogens.
2.1.2. Protozoa.
2.1.3. Viruses.
2.1.4. Summary
2.2. MOBILISATION.
2.3. DELIVERY.
2.3.1. Field Losses Following Manure Spreading.
2.3.2. Field Losses Following Livestock Grazing.
2.3.3. Losses During Slurry Storage.
2.3.4. Farmstead Runoff.
2.3.5. Livestock Access Direct to Water Courses.
2.4. PATHOGEN LOSS RISK MATRIX.
3. MITIGATION MEASURES.
3.1. Dietary AND MICROBIAL MANIPULATION.
3.1.1. Cattle.
3.1.2. Pigs.
3.1.3. Poultry.
3.1.4. Summary.
3.2. MANURE STORAGE AND TREATMENT.
3.2.1. Storage.
3.2.2. Slurry Treatment.
3.2.3. Solids Composting.
3.3. MANURE SPREADING AND GRAZING ANIMALS.
3.3.1. Spreading Method.
3.3.2. Direct Deposition to Water Courses.
3.3.3. Die-off in the Soil Environment.
3.4. METHOD EFFECTIVENESS.
3.2.1. Storage.
3.2.2. Slurry Treatment.
3.2.3. Solids Composting.
4. POLLUTION SWAPPING.
5. BIOLOGICAL OXYGEN DEMAND.
1. Introduction.
2. Defining the Problem.
2.1. Sources.
2.2. MOBILISATION.
2.3. DELIVERY.
2.3.1. Outdoor Grazing.
2.3.2. Manure and Dirty Water Land Applications.
2.3.3. Summary.
3. MITIGATION MEASURES.
3.1. STORAGE.
3.1.1. Management of Manure.
3.1.2. Management of Dirty Water.
3.1.3. Management Benefits.
3.2. GOOD MANAGEMENT PRACTICE.
3.2.1. Manure Application Practice.
3.2.2. Manure Application and Soil Management.
3.2.3. Solids or Liquids Manure Management Systems.
3.3. MANURE EXPORTS.
3.4. TREATMENT SYSTEMS.
3.4.1. Mechanical Separation.
3.4.2. Anaerobic and Aerobic Digestion.
3.4.3. Solids Composting.
3.4.4. Use of Treatment Additives.
3.4.5. Manure Processing.
3.4.6. Soil Treatment Processing.
3.4.7. Constructed Wetlands.
4. POLLUTION SWAPPING.
6. A conceptual model for diffuse pollutant behavior: a measure centric approach.
1. A measure centric approach.
2. the mitigation matrix.
3. conclusions.
7. aPPENDIX i. Mitigation Matrix.
8. aPPENDIX ii. Model Farm Scenarios.
9. rEFERENCES.
1. INTRoduction and content
Tackling water pollution over the last 40 years has targeted easily controllable point sources within a catchment such as sewage treatment works and industrial outfalls. Significant progress has been made across the UK addressing these sources of pollution but as further point source control becomes less cost effective, attention is now being directed towards the contribution of diffuse pollution from agriculture.
Diffuse pollution from agriculture and urban areas is now recognised as one of the most significant water quality problems facing the world. In 1995, the US Environment Protection Agency (USEPA) reported that 40% of US rivers, lakes and estuaries did not meet water quality requirements (USEPA, 1995) and that diffuse pollution was identified as the primary cause of this problem.
In recognition of this growing problem, the EU Water Framework Directive (EC, 2000) was adopted by the EU parliament in December 2000. This Directive marks a shift away from effluent based controls to water quality based controls and total maximum daily loads. The directive puts the emphasis on river basin management plans similar to those that were developed in the US during the 1990s.
The terms ‘point source’ and ‘non-point source’ pollution are often used to describe the difference between easily identifiable, generally controllable point sources of pollution from the more diffuse pollution within a catchment, such as runoff from fields and roads. Pollution sources within a catchment tend to be closely linked to land uses (i.e. the application of manures to farmland) and the changes to land use that cause the mobilisation of pollutants (i.e. ploughing of fields or road construction).
Agriculture covers 76% of the land area of England and Wales (Defra, 2001) and as such is a key generator of diffuse pollution. An example of this is nitrogen; it has been estimated that agriculture contributes 70% of the diffuse nitrogen inputs to inland surface waters (The Royal Society, 1983). Activities such as ploughing, the spreading of manures and inorganic fertilisers, and the application of agrochemicals can all give rise to the inadvertent contamination of water supplies.
Pollutants of concern originating from diffuse sources are presented in Table 1. However, the most troublesome pollutants from agriculture are sediments, nutrients, faecal pathogens and pesticides. Future policy for managing water quality requires an understanding of the measures that can decrease losses of pollutants and the costs of implementing them. Defra projects PE0203 and NT2511 (P and N cost curve respectively) highlighted mitigation measures and their associated costs for phosphorus and nitrogen. These projects initiated this Defra project; ES0121 (COST-DP: Cost effective diffuse pollution mitigation) which deals with many of the remaining diffuse pollutants. It aims to provide hard scientific information on the processes involved in diffuse, ammonium, nitrite, pathogenic (E. coli. and Cryptosporidium) and biological oxygen demand (BOD), pollution. The project has prioritised options for mitigating each of these pollutants in terms of costs, pollution reduction, practicalities and applicability in England and Wales. This review contributes in part to fulfilment of project ES0121 by meeting the milestones (1-4):
1. To undertake a ‘bottom up’ literature review of the potential mitigation options available for nitrite, ammonium, pathogens (E. Coli as a bacterial indicator and Cryptosporidium) and BOD.
2. To produce an objective system for classifying the functional behaviour of diffuse pollutants.
3. To prepare a mitigation matrix for diffuse pollutants.
4. To construct typical ‘model farm’ scenarios that can be used to explore mitigation options.
Table 1. Diffuse pollution concerns (modified from D’Arcy et al., 2000).
Pollutant / Example Source / Environmental ProblemSediments / Runoff from agricultural land; upland erosion; forestry; construction sites / Destruction of gravel riffles; sedimentation of natural ponds and pools; carrier of nutrients and toxic compounds
Nitrogen / Agricultural fertilisers; atmospheric deposition / Eutrophication; contamination of potable waters; acidification
Phosphorus / Soil erosion; agricultural fertilisers; urban runoff (detergents, organic material) / Eutrophication of fresh waters:
· Ecological degradation
· Blue green algae
· Increased need for filtration
Costs for potable reservoirs/rivers
Organic Wastes / Agricultural wastes (slurry, silage effluent, dirty water); sewage sludge; industrial wastes for land application / Oxygen demand; nutrient enrichment
Faecal Pathogens / Septic tank system failures; animal faeces; application of organic wastes to land / Health risks; non-compliance with recreational water standards
Pesticides / Golf course maintenance; municipal applications; agriculture; private properties / Toxicity; contamination of potable supplies
Oil and Hydrocarbons / Car maintenance; disposal of waste oils; spills from storage and handling, traffic emissions; road runoff; industrial emissions / Toxicity; contamination of urban stream sediments; groundwater contamination; nuisance (surface waters); taste (potable supplies)
Trace Metals / Urban runoff; application to land of industrial and sewage sludge / Toxicity
Iron / Water table rebound following mining / Toxicity; aesthetic nuisance
Initially, a literature review on pollutant behaviour and its mitigation has been undertaken. Within this, pollutants have been described in terms of three conceptual locations at which mitigation measures may be applied. These are the ‘SOURCE’ of the pollutant, the processes by which the pollutant is ‘MOBILISED’, and how the pollutant is ‘DELIVERED’ to surface waters. Mitigation options for targeting the pollutants within England and Wales have then been highlighted which is followed by the potential problem of pollution swapping when tackling the pollutants.
Using the source, mobilisation and delivery concepts (Haygarth et al., in press), and the information drawn from the literature review, a conceptual model describing diffuse pollutant on the basis of their characteristics has been proposed. Using this model, a mitigation matrix (Appendix I) has been produced. Mitigation measures targeting pollutants in their source, mobilisation and delivery conceptual locations have been scored for their effect on pollutants, cost per hectare, public and farmer acceptability, conflicts with other measures, pollution swapping and uncertainty of the effect of the measure. A list of farm systems is presented in Appendix II. The systems that each measure can be applied to are also included within the mitigation matrix.
2. AMMONIUM
1. INTRODUCTION
Ammonium (NH4+) is applied to agricultural land to promote plant growth and optimise agricultural yields. It can be applied in inorganic forms as fertilisers or via animal manures and other organic residues and effluents. When applied at times and rates to satisfy crop demands, NH4+ is a valuable resource. However, if applied when there is little or no crop demand and at rates greater than the crop can utilise, then there is increased risk of transfer to watercourses. An added complication is that NH4+ is released from organic nitrogen (N) forms (from soil or from added organic residues) by the process of mineralization. Hence, high rates of organic N additions can also result in release of NH4+ in excess of crop demands.
Ammonium transfers to watercourses can supply the aquatic environment with a limiting nutrient for algal growth, and thus encourage eutrophication problems. Also, dissolved ammonia (NH3) is directly toxic to fresh water fish. The Freshwater Fish Directive (E.C., 1978: 78/659/EEC) was implemented to protect and improve the quality of fresh waters in order to support fish life, particularly Salmonids and Cyprinids. Fresh water quality is assessed according to pH, temperature and concentrations of dissolved oxygen, suspended solids, biological oxygen demand (BOD), total phosphorus, nitrites, phenolic compounds, petroleum hydrocarbons, chlorine, zinc, copper, non-ionised NH3 and ammonium-nitrogen (NH4+-N).
When one molecule of NH3 dissolves in water it reacts to form ammonium hydroxide, which dissociates completely to give an NH4+ ion and a hydroxyl ion.
NH3 + H2O Û NH4+ + OH-