Understanding the impact of farming on aquatic ecosystems

Use of biomarkers as early warning systems for farming-related activities

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Understanding the impact of farming on aquatic ecosystems

Use of biomarkers as early warning systems for farming-related activities

Biomarkers are broadly defined as a change in a biological response (ranging from molecular through cellular and physiological responses) that can be related to exposure to, or toxic effects of, environmental chemicals.^¹⁷⁸ In recent years, selected markers measured in indigenous aquatic organisms have been shown to be sensitive indices or early warning signals of environmental degradation caused by pollutants. These indices are typically those that can be measured with an acceptable level of precision and accuracy, so that spatial and temporal trends can be monitored, and that measure a response which can be linked with more traditional measures of effects on the reproduction, development and growth of the organisms and the resulting effects on populations (i.e. they are indicators of effect). Such biomarkers are more valuable as early warning tools that those which are considered to be simply indicators of exposure to specific pollutants.
Table 2 provides an indication of the types of biomarkers that may be useful in measuring the effects of pressures which result from farming-related activities, particularly pesticides and endocrine disrupting chemicals.
With increasing activity in the fields of environmental genomics and proteomics, it is likely that additional tools will become available that are linked mechanistically to effects in individuals. However, irrespective of the tools developed, it will be necessary to use biomarkers as a tool within a broader assessment framework and they may be best used in the coming years as mechanistic “signposts” (e.g. to guide further monitoring) rather than as “traffic lights” in the environmental risk assessment of pollutants.^¹⁷⁹^,^¹⁸⁰
Table 2 Types of biomarkers that may be useful in measuring the effects of pressures which result from farming related activities

Biomarker	Description	Type of chemical to which biomarker responds
Biochemical markers
Acetylchlolinesterase (AChE)	Inhibition of acetylcholinesterase activity in exposed organisms	Organophosphorus pesticides
Phytochemical pattern	Changes in different groups of compounds (e.g. amino acids, lipids and terpenes, phenolic compounds) in exposed plants	Herbicides
Vitellogenin (VTG)	Increased levels of the protein vitellogenin are measured in exposed male fish	Natural and synthetic steroids
Histological markers
Imposex	Masculinisation of reproductive organs in exposed clams and gastropods	Tributyltin
Intersex	Feminisation of reproductive organs in exposed male fish	Natural and synthetic steroids

Summary

1. A number of ecological indicators show statistical significant relationships with pressures which are relevant to farming-related activities. However, in many instances there is a high degree of variability associated with the relationships which limits their wide-scale application. Relationships may, therefore, have to be water body type-specific rather than generic.

2. There is evidence that changes in abundance of certain key aquatic flora and/or fauna species may be valuable in providing an early warning of the impacts of certain pressures associated with farming-related activities. However, further research is needed to determine how applicable the relationships would be across a particular water type (e.g. rivers, lakes, transitional and coastal waters) and what procedure should be used to minimise the effects of potentially confounding factors.

3. There may be a role for biomarkers in assessing the impacts of pressures resulting from farming-related activities. However, irrespective of the tools developed, it will be necessary to use biomarkers as a tool within a broader assessment framework.

4. It is unlikely that a single indicator can be used evaluate the impacts of specific pressures (e.g. nutrient enrichment, organic enrichment, exposure to pesticides or veterinary medicines). Instead, the outputs from a series of indicators will be needed.

Understanding the impact of farming on aquatic ecosystems
1. Introduction

The previous Sections of the report have described the current understanding and knowledge base on the impact of farming on aquatic ecosystems in the context of current policy and practices. It is clear that some farming activities and processes leading to impacts on aquatic ecosystems are better understood than others. Control of these activities and processes should lead to improvements in the status of some impacted water bodies. But as the more dominant pressures (e.g. point sources of phosphorus and diffuse sources of nitrate) are reduced then the importance of other pressures (e.g. veterinary medicines and endocrine disrupting chemicals) may be revealed and become more important in terms of achieving good ecological status of some water bodies. There are significant gaps in the current knowledge base which will have to filled if the impact of farming is to be better understood, and more importantly identify what is required to achieve good ecological status in impacted water bodies in as cost-effective way as possible.
Table 3 below summarises the main findings of Sections 2 and 3 in terms of the knowledge of how farming may lead to impacts on aquatic ecosystems (e.g. activities, pathways, apportionment of loads, processes, effects) and the quantification of scale and importance of the impact through information on the significance (e.g. status of water bodies and proportion of water bodies affected) and the geographic scale of the impact (e.g. local, regional, national). Both aspects have to be quantified in order to fully understand the impact of farming on aquatic ecosystems.
Information on the status of water bodies and proportion of water bodies affected comes from several available sources: results of the WFd Article 5 risk assessments, results of current monitoring programmes, preliminary classification of the ecological status of waters according to the proposed Environmental Standards for the implementation of the WFD, and recorded pollution incidents arising from farming activities and sources. The aim is also to summarise knowledge gaps that must be filled to improve understanding.
The significance of the gaps will also need to be assessed to define priorities for research and development. Significance may relate to the potential severity of the effects of the different pollutants, the scale (e.g. local, regional or national) of the farming activity leading to the impact, the size and nature of the gap in current knowledge and the availability of existing cost effective mitigation measures. Based on the evidence obtained from this review the most significant impacts arising from farming are caused by phosphorus, nitrate, soil sediment, pesticides, organic matter and ammonia (in decreasing order of the number of water bodies potentially impacted). However, it should be noted that there is currently no representative overview of the significance of the potential impact from veterinary medicines and non-regulated endocrine disrupting chemicals.
Table 3 Summary of knowledge of the how farming may lead to impacts, and on information for the quantification of scale and importance of the impact of farming on aquatic ecosystems

Pollutant	Knowledge of activities, pathways, processes, apportionment and impacts	Quantification of scale and importance of impact
		Water bodies at risk: WFD Article 5	Status of impacted water bodies	Pollution incidents	Geographic scale
Nitrate	Pathways and processes relatively well known. 60.6% of total nitrogen load in E&W from agriculture. Eutrophication: some further research required. Acidification: farming contribution unknown. Toxicity: not fully assessed.	37.9% river, 19.9% estuary, 13.1% coastal WBs: sources: agriculture, atmospheric deposition for rivers	28% rivers high nitrate concentrations (all sources). 39% of 60 estuaries/coastal WBs less than good ecological status in E&W	Not relevant	Highest concentrations tend to be in arable areas
Phosphorus	Pathways and processes relatively well known. 23-28% of TP and 19% SRP loads in GB from agriculture. Eutrophication: some processes (e.g. role of sediment bound P in some rivers) not well quantified.	47.4% river, 36.8% lake WBs: diffuse agriculture.	63.3% river and 67% of lake WBs less than good ecological status in England: 12.8% rivers and 80% lake WBs in Wales: all sources.	Not relevant	Higher concentrations found in urban and arable areas
Ammonia	Pathways and processes relatively well known. 80% of emissions to air, water and soil from agriculture. Eutrophication: indirect effect, some further research required. Acidification – indirect effect. Toxicity – direct effect.	2.9% rivers, 20.8% lakes, acidification, atmospheric deposition of emissions (including ammonia) from all sources.	17.3% of rivers in England and 2.7% in Wales predicted to be less than good ecological status when applying proposed standards for WFD. This will relate mainly to direct emissions of ammonia to water bodies from point and diffuse sources.	No information	Acidification: Upland areas. Highest water concentrations in North West
Sediment	Some processes and pathways not fully quantified e.g. chronic releases to water. 75% of sediment input to rivers from agriculture. Siltation and increased turbidity.	21% of river WBs at risk from agriculture	Salmonid reproduction affected by siltation at 2 of 43 sites. Up to 101 out of 161 chalk streams possibly affected by siltation. Half of 62 principal salmon rivers in E&W possibly affected. No representative assessment of suspended sediment or siltation levels in rivers	No information	Regional differences, NW, NE, Anglian, Severn and South East worst
Pesticides	Pathways and processes relatively well known. No source apportionment. Toxic effects.	20.8% river WBs at risk: agriculture and sheep dip	Sheep dip chemicals caused third of EQS failures, and cypermethrin exceeds EQSs at 21% sites in England and 19% sites in Wales. Between 6 and 8% of samples (taken at 2500 sites, mainly rivers) exceeded 0.1 µg/l between 1998 to 2006: mainly diuron (mainly amenity use), isoproturon and mecoprop. Monitoring not necessarily representative of acute exposure pathways or of all water bodies.	43 out of 49 significant pollution incidents from agricultural use	Sheep dip failures mainly Wales and north of England.
Veterinary medicines	Pathways and processes not fully quantified. No source apportionment. Toxic effects.	Not assessed	Four sites representing worst case of potential contamination generally had concentrations below PNECs. Assessment of impact of other priority medicines required. Information not necessarily representative of all water bodies.	No information	No information, only very limited case studies undertaken.
Faecal pathogens	Pathways and processes relatively well known. No source apportionment. No effects on aquatic organisms found.	Not assessed	Contribution to failure of Bathing water standards for example in two of three known 'problem areas'.	Not relevant	Problem (failing) bathing waters
Organic material	Pathways and processes relatively well known. No source apportionment. Oxygen depletion, smothering.	13.4% of estuaries, and 0.2% of coastal water bodies at risk of organic enrichment (direct and riverine inputs)	18.7% of rivers in England and 3.7% in Wales predicted to be less than good ecological status when applying proposed standards for WFD.	55 significant pollution incidents in 2006: slurry accounted for 75% of incidents	Highest BOD in North England, worst quality rivers from GQA in Anglian region.
Endocrine disrupting chemicals	Pathways and processes not fully quantified. Hormone disruption (e.g. intersex in fish, mainly roach). No information on impact on other fish species and invertebrates, and the implications to fish populations as a whole.	Not assessed	At eight of the 11 (worst-case) farms surveyed oestrogenic activity exceeded at least once the PNEC for 17β-oestradiol in water. Only limited data on concentrations of agriculturally related EDC in fresh and marine waters.	Not relevant	Only Intensive livestock farms and small streams surveyed
Other pollutants - oil	Pathways and processes relatively well known. No source apportionment. Toxic effects.	Not assessed	No information	Oil and fuel most important type of pollution: 89 (14.7%) of 605 significant incidents in 2006. Proportion from agriculture not publicly available.	Localised

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Understanding the impact of farming on aquatic ecosystems

Use of biomarkers as early warning systems for farming-related activities

Use of biomarkers as early warning systems for farming-related activities

Summary

Understanding the impact of farming on aquatic ecosystems

Introduction