Effects Based Acidification Abatement Strategies:

Effects Based Acidification Abatement Strategies:

Current Criteria and Proposed Approach

Alan Jenkins

CEH Wallingford

Report produced in fulfilment of deliverable 7a under the

RECOVER: 2010 project

Table of Contents

1. Introduction

2. Current approaches and criteria

2.1 Critical loads for freshwaters

2.2 Other EU legislation

3. Proposed aproach in RECOVER: 2010

3.1 Ecological risk assessment

3.2 Uncertainty

3.3 End-users and RECOVER: 2010

4. Required targets and end-points

5. References

1. Introduction

Within RECOVER: 2010, Work Package 7 (PROFFER) aims to Provide Relevant Output For Formulating End-user Requirements. The policy context for this work is that despite international instruments to control S and N emission being almost complete with the signing of the Multi-pollutant, Multi-effect Protocol (Gothenberg Protocol) in 1999 and the potential to consider that no further action is necessary, the instruments are not ambitious and reviews are already planned for 2004. There is, therefore, a need to maintain momentum and to exploit the opportunity to rectify shortfalls in the currently used instruments.

The first step in this process is to review current methods and criteria and so identify shortfalls and improvements that could be made in the future. This report documents the existing methods and criteria, reports the conclusions of the end-user meeting held in Abingdon, UK, on 22-24 May 2000 and documents the approach planned within RECOVER: 2010.

2. Current approaches and criteria

Chemical criteria for water have been defined to protect biota and humans for adverse toxic effects. These criteria are based upon the use to which the water is intended and these have formed the basis for much EU legislation relating to water. In addition, chemical criteria have been used with the framework of the UN-ECE Convention on Long Rang Transboundary Air Pollution to identify acidified and acid-sensitive waters and to underpin S and N emission reduction strategies. In this case, these chemical criteria are related to biological characteristics of the water body.

2.1 Critical loads for freshwaters

For the work under the LRTAP Convention a critical load has been defined as 'a quantitative estimate of an exposure to one or more pollutants below which significant harmful effects on specified sensitive elements of the environment do not occur according to present knowledge' (Nilsson and Grennfelt 1988). Originally, critical loads were calculated for acidity and a 'sulphur fraction' was used to derive a critical load for sulphur (eg in the 1994 Oslo Protocol). For the 1999 Gothenberg Protocol, critical loads of N were also required since this was a 'multi-pollutant, multi-effect' protocol. The critical loads are defined for:

(i) the maximum critical load of sulphur as the net input of (seasalt corrected) base cation minus a critical leaching of acid neutralisation capacity (see later),

CL_max(S)=BC^*_dep - CL^*_dep + BC_w - BC_u - ANC_de(crit) (1)

(ii) the minimum critical load of N, where N deposition is all consumed by sinks of N (immobilisation and uptake),

N_dep d N_I + N_u=CL_min(N) (2)

(iii) the maximum critical load for nitrogen acidity in the case of no S deposition which accounts for N sinks and deposition-dependent denitrification,

CL_max(N)=CL_min(N) + CL_max(S)/(1 - F_de) (3)

Both S and N contribute to acidification, but one equivalent of S contributes, in general, more to excess acidity than one equivalent of N. Clearly, no unique acidity critical load can be defined, but combinations of N_dep and S_dep not causing 'harmful effects' lie on the 'critical load function' of the ecosystem as defined by the three critical loads from equations (1) to (3) (Figure 1). Harmful effects, in the case of freshwaters are defined in terms of some level of ANC_le(crit (see later).

Figure 1 Example of a critical load function for S and acidifying N. Every point of the shaded area represents depositions of N and S which do not lead to the exceedance of the critical load

Example of a critical load function for S and acidifying N.

For negotiations under the protocol, information describing critical loads is used within an integrated assessment model (RAINS model; Amann et al. 1999) to optimise emission reductions and lead to a closing of the gap between N and S deposition and critical loads (Posch et al. 1999).

The RAINS model can then be used in a 'scenario analysis' mode to estimate future trends in deposition over time (Schöpp et al. 2000) and this in turn can be used as input to dynamic bio-geochemical models to predict changes in soil and surface water chemistry in response to the protocol. Given suitable relationships between chemistry and biota, it is then possible to use the models to assess the timescale of recovery of the ecosystem. In addition, this process can be reversed such that ecological targets can be prescribed for a given point in time and the dynamic bio-geochemical models can estimate the deposition target required to achieve it.

The relationship between ANC and biology can be generated by field or laboratory experiments focusing on individual biological targets, for example, some fish species (Baker et al. 1987). An alternative approach is to derive empirical regression models relating biological status to chemical conditions using field survey data (eg Reckhow et al. 1987, Ormerod 1993, Lien et al. 1996; Henriksen et al. 1999). In general, most organisms show a graded response to ANC rather than a step change and so response curves can be fitted using logistic regression. In this way, appropriate chemical targets can be defined to protect or establish a required biological status. For example, describing the occurrence of the diatom Achnanthes minutissima, the macroinvertebrate Baetis rhodani, non-impoverished macroinvertebrate assemblages, number of mayfly species and the density of trout/salmonid populations in relation to surface water chemistry, and in particular ANC, has been collated from surveys undertaken in England, Scotland and Wales (Juggins et al. 1995). The results provide response curves for ANC (Figure 2) and critical ANC values for mayflies and trout (Table 1). In this example, to ensure a 0.5 probability of occurrence, the ANC should not fall below 23 m eq l^-1 for the diatom species and below 36 m eq l^-1 for Baetis rhodani. A more detailed survey of fish status and water chemistry has been undertaken in Norway (Lien et al. 1996). The results of which demonstrate the probability of a change in the status of brown trout population in relation to ANC (Figure 3). This analysis has been taken further to determine the relationship between fish status and critical load exceedance (Henriksen et al. 1999).

Figure 2 Response curves derived using logistic regression and showing the relationship between ANC and the probability of occurrence of (a) A.minutissima, (b) B.rhodani and (c) non-impoverished macroinvertebrate assemblage. Ticks show original data and dotted lines represent 95% confidence limits for predicted probability (after Juggins et al. 1995)

Brown trout curve

Figure 3 Brown trout population status in relation to surface water ANC for 827 lakes in Norway (after Lien et al. 1996)

Brown trout v ANC

Table 1 Biological status and ANC predicted from regression relationships (Juggins et al. 1995)

ANC

No of mayfly species

Trout density (nos 100 m^-2)

-100

-50

-20

100

200

2.2 Other EU legislation

The Council Directive of 16 June 1975 concerned the quality required of surface water intended for the abstraction of drinking water in the Member States (75/440/EEC). This Directive classifies the quality of surface water intended for drinking into three categories (Al, A2, A3) according to the extent of the treatment required to render them fit for that use (Table 2). Only pH, NO₃ and SO₄ are considered here within the subject area of RECOVER: 2010.

Table 2 Guide (G) and mandatory (I) concentrations of NO₃ and SO₄ and pH for three categories of water treatment (A1=lowest level of treatment)

Parameters

Nitrate (mg/l NO₃)

Sulphate (mg/l SO₄)

6.5 to 8.5

150

50 (0)

250

5.5 to 9

150

50 (0)

250 (0)

5.5 to 9

150

50 (0)

250 (0)

The Council Directive of 18 July 1978 concerned the quality of freshwaters needing protection or improvement in order to support fish life (78/659/EEC). This directive deals with the quality of water required to support salmonid and cyprinid species of fish and lists, for each of these species, guide and mandatory values for a wide range of parameters. Within the subject area of RECOVER: 2010, pH is the only relevant parameter and this is given a mandatory range of 6 to 9 for both salmonid and cyprinid fish. This pH is based on an annual 95 percentile value for samples taken at a minimum of monthly frequency.

The proposed 'Council Directive establishing a framework for Community action in the field of water policy' (the Water Framework Directive; European Council 1999) differs significantly from the earlier mentioned Directives and others of the 1970s and 80s which were either targeted to protect particular uses of the aquatic environment (eg water for abstraction for drinking, for protection of fisheries etc) or to address specific threats to environmental quality (eg the Dangerous Substances Directive: 76/464/EEC).

The WFD provides instead a framework covering groundwater, wetlands, rivers, lakes, estuaries and coastal waters using environmental objectives which will aim to prevent further deterioration and protect and enhance the status of aquatic ecosystems. The WFD repeals seven existing Directives:

standards for protection of drinking water (75/440/EEC and 79/869/EEC)
freshwater fisheries (78/659/EEC)
shellfish waters (79/923/EEC)
groundwaters (80/68/EEC)
control of dangerous substances (76/464/EEC)
reporting to the Commission (77/795/EEC)

These are replaced by environmental objectives with the primary aim for surface waters and groundwaters of achieving good status. Good surface water status depends on a waterbody achieving at least good chemical status and good ecological status. Member states must aim to achieve these environmental objectives by 2016 (?).

Good chemical status is determined mainly by compliance with Environmental Quality Standards (EQS) set for priority substances, which replace the Dangerous Substances list I. None of these are relevant to RECOVER: 2010.

Good ecological status is derived from a combination of measurements of biological and physico-chemical (excluding priority substances) parameters. The most important physico-chemical parameter for upland lakes and rivers in areas subject to acidic deposition, in RECOVER: 2010, is acidification status which is to be defined in terms of pH and acid neutralisation capacity (ANC). In this respect, an EQS for ANC should be set by Member States to ensure that good biological status can be maintained. Good biological status being defined in terms of deviation from pristine (or relatively undisturbed) reference conditions. Compliance with both the EQS and good biological quality is required to achieve good ecological status. The definition of high, good and moderate status for biological and physico-chemical quality elements relevant to RECOVER: 2010 are given in Table 3.

Table 3: Definitions for high, good and moderate ecological status in rivers and lakes

1. RIVERS (BIOLOGICAL QUALITY ELEMENTS)

Element

High Status

Good Status

Moderate State

Phytoplankton

The taxonomic composition of phytoplankton corresponds totally or nearly totally to undisturbed conditions.

The average phytoplankton abundance is wholly consistent with the type-specific physico-chemical conditions and is not such as to significantly alter the type-specific transparency conditions.

Planktonic blooms occur at a frequency and intensity which is consistent with the type-specific physico-chemical conditions

There are slight changes in the composition and abundance of planktonic taxa compared to the type-specific communities. Such changes do not indicate any accelerated growth of algae resulting in undesirable disturbances to the balance of organisms present in the water body or to the physico-chemical quality of the water or sediment.

A slight increase in the frequency and intensity of the type-specific planktonic blooms may occur.

The composition of planktonic taxa differs moderately from the type-specific communities.

Abundance is moderately disturbed and may be such as to produce a significant undesirable disturbance in the values of other biological and physico-chemical quality elements.

A moderate increase in the frequency and intensity of planktonic blooms may occur. Persistent blooms may occur during summer months.

Macrophytes and phytobenthos

The taxonomic composition corresponds totally or nearly totally to undisturbed conditions.

There are no detectable changes in the average macrophytic and the average phytobenthic abundance.

There are slight changes in the composition and abundance of macrophytic and phytobenthic taxa compared to the type-specific communities. Such changes do not indicate any accelerated growth of phytobenthos or higher forms of plant life resulting in undesirable disturbances to the balance of organisms present in the water body or to the physico-chemical quality of the water or sediment.

The phytobenthic community is not adversely affected by bacterial tufts and coats present due to anthropogenic activity.

The composition of macrophytic and phytobenthic taxa differs moderately from the type-specific community and is significantly more distorted than at good status.

Moderate changes in the average macrophytic and the average phytobenthic abundance are evident.

The phytobenthic community may be interfered with and, in some areas, displaced by bacterial tufts and coats present as a result of anthropogenic activities.

Benthic invertebrate fauna

The taxonomic composition and abundance correspond totally or nearly totally to undisturbed conditions.

The ratio of disturbance sensitive taxa to insensitive taxa shows no signs of alteration from undisturbed levels.

There are slight changes in the composition and abundance of invertebrate taxa from the type-specific communities.

The ratio of disturbance sensitive taxa to insensitive taxa shows slight alteration from type-specific levels.

The level of diversity of invertebrate taxa shows slight signs of alteration from type-specific levels.

The composition and abundance of invertebrate taxa differ moderately from the type-specific communities.

Major taxonomic groups of the type-specific community are absent.

The ratio of disturbance sensitive taxa to insensitive taxa, and the level of diversity, are substantially lower than for good status.

Fish fauna

Species composition and abundance correspond totally or nearly totally to undisturbed conditions.

All the type-specific disturbance sensitive species are present.

The age structures of the fish communities show little sign of anthropogenic disturbance and are not indicative of a failure in the reproduction or development of any particular species.

There are slight changes in species composition and abundance from the type-specific communities attributable to anthropogenic impacts on physico-chemical and hydromorphological quality elements.

The age structures of the fish communities show signs of disturbance attributable to anthropogenic impacts on physico-chemical or hydromorphological quality elements, and, in a few instances, are indicative of a failure in the reproduction or development of a particular species, to the extent that some age classes may be missing.

The composition and abundance of fish species differ moderately from the type-specific communities attributable to anthropogenic impacts on physico-chemical or hydromorphological quality elements.

The age structure of the fish communities shows major signs of anthropogenic disturbance, to the extent that a moderate proportion of the type-specific species are absent or of very low abundance.

2. RIVERS (PHYSICO-CHEMICAL QUALITY ELEMENTS)

General conditions

The values of the physico-chemical elements correspond totally or nearly totally to undisturbed conditions.

Nutrient concentrations remain within the range normally associated with undisturbed conditions.

Levels of salinity, pH, oxygen balance, acid neutralising capacity and temperature do not show signs of anthropogenic disturbance and remain with the range normally associated with undisturbed conditions.

Temperature, oxygen balance, pH, acid neutralising capacity and salinity do not reach levels outside the range established so as to ensure the functioning of the type-specific ecosystem and the achievement of the values specified above for the biological quality elements.

Nutrient concentrations do not exceed the levels established so as to ensure the functioning of the ecosystem and the achievement of the values specified above for the biological quality elements.

Conditions consistent with the achievement of the values specified above for the biological quality elements.

3. LAKES (BIOLOGICAL QUALITY ELEMENTS)

Phytoplankton

The taxonomic composition of phytoplankton corresponds totally or nearly totally to undisturbed conditions.

The average phytoplankton abundance is wholly consistent with the type-specific physico-chemical conditions and is not such as to significantly alter the type-specific transparency conditions.

Planktonic blooms occur at a frequency and intensity which is consistent with the type-specific physico-chemical conditions

A slight increase in the frequency and intensity of the type-specific planktonic blooms may occur.

The composition of planktonic taxa differs moderately from the type-specific communities.

Abundance is moderately disturbed and may be such as to produce a significant undesirable disturbance in the values of other biological and physico-chemical quality elements.

A moderate increase in the frequency and intensity of planktonic blooms may occur. Persistent blooms may occur during summer months.

Macrophytes and phytobenthos

The taxonomic composition corresponds totally or nearly totally to undisturbed conditions.

There are no detectable changes in the average macrophytic and the average phytobenthic abundance