ECOSTAT Working Group Discussion Paper

ECOSTAT Working Group Discussion Paper

Draft Principles of Ecological Status Classification in Relation to Eutrophication

Purpose
This paper has been prepared by the UK and German Working Group Leaders to facilitate discussion by the ECOSTAT Working Group at its meeting on 7th July 2004 on some of the key principles relating to ecological status that might be included in CIS Guidance on Eutrophication.
The main aim of the paper is to initiate the development of a common understanding of the meaning of the Directive’s normative definitions in the context of the ecological effects of nutrient enrichment.
Discussions on a more general interpretation of the normative definitions were initiated by the former REFCOND and COAST Working Groups. This work was not completed and is now necessary to support the intercalibration exercise; the development of guidance on eutrophication; and Member States’ preparations for monitoring. The principles for the classification of ecological status are summarised in the Guidance on Ecological Classification prepared by the Ecostat Working Group.
The paper identifies some guiding principles on the interpretation of the normative definitions in relation to nutrient enrichment. These principles are intended to help Member States identify class boundary values for the indicator parameters with which they will monitor and assess the condition of those biological quality elements most sensitive to nutrient enrichment.
The key principles proposed in the paper are in bold blue font

1. Summary of the Water Framework Directive’s requirements

1.1 The Water Framework Directive requires Member States to classify the ecological status of surface water bodies[1] into one of five ecological status classes; high, good, moderate, poor or bad ecological status. The ecological status of a water body is an expression of the quality of the structure and functioning of its aquatic ecosystem.

1.2 The Directive provides general qualitative definitions of each ecological status class, and more detailed qualitative definitions for high, good and moderate ecological status for each surface water category.

1.3 Among other things, the definitions of each ecological status class describe the extent to which biological components of the aquatic ecosystem, called biological quality elements, may differ in that class compared to their reference, or high status, conditions as a result of the effects of human activity.

1.4 The reference conditions relevant to a particular water body depend on the type of water body. They are type-specific. This enables the classification system to take account of the natural variety of aquatic ecosystems across the Community’s different water types.

1.5 The Directive requires the Commission to facilitate an intercalibration exercise. This exercise is designed to ensure that the numeric class boundaries for good ecological status, which have to be set by each Member State to make the classification scheme operational, are consistent with the Directive’s ‘normative’ definitions and comparable between Member States.

1.6 The environmental objectives of the Directive require Member States to prevent deterioration in the status of water bodies. They also require Member States to aim to restore all surface water bodies to good ecological status, except where doing so would be unfeasible or disproportionately expensive. The Directive’s ecological status classification scheme is therefore central to water management across the Community.

1.7 Nutrient enrichment leading to eutrophication is one of the many different anthropogenic pressures on water bodies that may affect their ecological status. As such, management measures may be required to control nutrient enrichment in order to achieve the objectives of the Directive.

1.8 Operational monitoring must be undertaken for water bodies, or groups of water bodies, that are at risk of failing to achieve the Directive’s objectives. The monitoring data obtained must be used to establish the status of those bodies and to assess changes to their status resulting from management measures.

1.9 This monitoring must be designed to ensure that an adequate level of confidence and precision in the classification of ecological status can be achieved. Guideline minimum monitoring frequencies are set out in the Directive. However, the actual frequencies selected must provide sufficient data for a reliable assessment of the status of the relevant quality elements.

1.10 For the purposes of monitoring water bodies at risk because of nutrient enrichment, Member States must monitor parameters indicative of the biological quality element, or elements, most sensitive to the effects of nutrient enrichment as well as the nutrients that are being discharged into the water body in significant quantities.

1.11 Member States may where appropriate group water bodies and use representative monitoring to assess the status of the water bodies in the group.

1. Interpretation of ecological status in the context of the impacts of nutrient enrichment

2.1 The following Sections set out a proposed common understanding of the normative definitions in the context of nutrient enrichment. Such an understanding is necessary to underpin the intercalibration exercise and the design of monitoring programmes. The proposed understanding focuses on those key principles of the normative definitions that are relevant across the water categories.

Most sensitive biological quality elements

2.2 For water bodies subject to nutrient enrichment, it is likely that for operational monitoring purposes the most sensitive biological quality element, or elements, will be aquatic plants that derive their nutrients from the water column (Table 1).

Table 1: Biological quality elements likely to be among the most sensitive to nutrient enrichment
Rivers / Lakes / Transitional Waters / Coastal Waters
Phytoplankton[2] / Phytoplankton / Phytoplankton / Phytoplankton
Phytobenthos[3] / Phytobenthos3 / Macroalgae / Macroalgae

2.3 Macrophytes and angiosperms which derive their nutrients from sediments are likely in most cases to be less sensitive to the primary effects of increases in nutrient concentrations in the water column than are phytoplankton, macroalgae and phytobenthos. The initial impact of nutrient enrichment on macrophytes and angiosperms may be secondary due to changes in water transparency caused by increases in algal biomass.

2.4 Some macrophytes can obtain nutrients from both sediments and water. Nevertheless, their ability to obtain nutrients from sediments means that their response to nutrient enrichment tends to be slower and more complicated than that of phytobenthos or phytoplankton. Operationally, although changes in the macrophyte community would indicate that deterioration from good to a worse ecological status has occurred, phytobenthos are likely to be the more sensitive (e.g. faster responding) quality element in most cases.

2.5 General interpretations of the normative definitions for the quality elements phytoplankton, phytobenthos and macroalgae at high, good and moderate ecological status are summarised in Annex I. The moderate status conditions for these elements are summarised below. A common understanding of the degree of anthropogenic alteration represented by moderate ecological status is important. Such an understanding will help the intercalibration exercise assess whether the good-moderate boundary values identified by Member States are consistent with the normative definitions and comparable between Member States. It will also allow comparison of the ecological status classes with the two categories of nutrient sensitive areas identified under the Urban Waste Water Treatment Directive.

2.6 The condition of phytoplankton in a river, lake, transitional or coastal water body is described as consistent with moderate status if nutrient enrichment has resulted in:

(a) A moderate change from reference conditions in the taxonomic composition of phytoplankton;

(b) A moderate change in the biomass/abundance of phytoplankton;

(c) A moderate increase in the frequency and intensity of phytoplankton blooms or in the summer persistence of those blooms[4].

2.7 The condition of macroalgae in a transitional or coastal water body is described as consistent with moderate status if nutrient enrichment has resulted in:

(a) A moderate change from reference conditions in the taxonomic composition of macroalgae;

(b) A moderate change in the cover of macroalgae

2.8 The condition of phytobenthos in a river or lake water body is described as consistent with moderate status if nutrient enrichment has resulted in:

(a) A moderate change from reference conditions in the taxonomic composition of phytobenthos;

(b) A moderate change in the average abundance of phytobenthos;

(c) Bacterial tufts or coats interfering with or, in some areas, displacing the phytobenthic community

Role of the normative definitions in the development of ecological assessment methods

2.9 Where a water body is at risk of failing to achieve good status because of nutrient enrichment, the Directive requires Member States to select and monitor an appropriate parameter, or group of parameters, indicative of the condition of the most sensitive biological quality element or elements to nutrient enrichment (see Section 2.2). Member States may combine the results for several indicator parameters in a way that improves confidence in assessments of the effects on the quality element of nutrient enrichment.

2.10 Further guidance on selecting and combining parameters into ‘multi-metrics’ for use in assessing the condition of biological quality elements is provided in the CIS Guidance on Ecological Status Classification. The normative definitions are the basis for identifying suitable boundary values for each of the indicator parameters (see Figure 1)[5].

Figure 1: The conditions described by the normative definitions are the basis for identifying appropriate boundary values for the parameters selected to indicate the condition of the biological quality elements

Shared principles in the normative definitions for the different water categories

2.11 The type-specific conditions for good and for moderate status in rivers, lakes, transitional waters and coastal waters represent equivalent levels of anthropogenic alteration to the ecosystems.

2.12 The same key status conditions apply to phytoplankton, phytobenthos or macroalgae across the different water categories. However, the conditions are sometimes expressed in the Annex V normative definitions using different wording. For example, according to the normative definitions, phytoplankton biomass in coastal waters would be expected to be impacting on other biological quality elements if the water body were at moderate status. It is also clear that the likelihood of these impacts being significant would increase from very low at the boundary between good and moderate status to a high probability at poor status. This understanding is compatible with the condition for phytoplankton biomass at moderate status in the other surface water categories. The normative definitions for rivers, lakes and transitional waters indicate that at moderate status phytoplankton biomass may be such as to result in significant impacts on other biological quality elements. This indicates that, as with coastal waters, there is a higher probability at poor status of significant impacts on other biological quality elements occurring than there is at the good-moderate boundary (see Section 2.14, Figure 2 and Tables 3a-c).

Type-specific reference conditions

2.13 Relevant sub-types of the general typologies of surface water bodies may be identified when establishing type-specific biological reference conditions for particular quality elements.

2.14 The use of sub-types may be necessary to adequately take account of the way in which a particular biological quality element naturally varies across surface waters and hence enable the reliable assessment of that element’s status. For example, operationally the reference phytoplankton conditions for some lakes may best be derived using modelling predictions or palaeolimnological studies that are specific to the particular lake.

Description given for phytoplankton biomass, macroalgal cover and average phytobenthic abundance

2.15 A moderately changed phytoplankton biomass, macroalgal cover or average phytobenthic abundance is one that has some potential to (i.e. “may be such as to..”) give rise to a significant undesirable disturbance [See Table 2] in the condition of other biological quality elements or in the physico-chemical quality of the water (or sediments).

2.16 The condition of phytoplankton, macroalgae or phytobenthos would not be consistent with good status unless there was a negligible probability (i.e. risk) that accelerated algal growth (i.e. an increasing phytoplankton biomass; macroalgal cover or average phytobenthic abundance due to nutrient enrichment) would result in a significant undesirable disturbance to the aquatic ecosystem (Figure 2).

2.17 As nutrient enrichment increases, both the probability of undesirable disturbances occurring and the severity of those disturbances will increase. At poor and bad ecological status, undesirable disturbances would be expected to occur frequently and the impacts of these disturbances on the aquatic ecosystem and the quality of the water and sediment would be expected to be major or severe.

2.18 Moderate status is therefore the ‘transition’ class between good status, in which significant undesirable disturbances resulting from nutrient enrichment are not present, and poor status, in which such significant undesirable disturbances would be expected to be common place.

Figure 2: Once phytoplankton biomass; macroalgal cover or average phytobenthic abundance has reached levels at which the probability of a significant undesirable disturbance to the aquatic ecosystem is no longer negligible, the condition of phytoplankton, macroalgae or phytobenthos would not be consistent with good status

Undesirable disturbance

2.19 A significant undesirable disturbance is a direct or indirect anthropogenic impact on an aquatic ecosystem that appreciably degrades the health or threatens the sustainable human use of that ecosystem. Table 2 provides a general list of significant undesirable disturbances

Table 2: Significant undesirable disturbances that may result from accelerated growth of phytoplankton, macroalgae or phytobenthos
(a) Causes the condition of other elements of aquatic flora in the ecosystem to be moderate or worse
(b) Causes the condition of benthic invertebrate fauna to be moderate or worse
(c) Causes the condition of fish fauna to be moderate or worse
(d) Compromises the achievement of the objectives of a Protected Area for economically significant species
(e) Compromises the achievement of objectives for a Natura Protected Area
(f) Compromises the achievement of objectives for a Drinking Water Protected Area
(g) Causes a change that is harmful to human health (e.g. shellfish poisoning)
(h) Causes a significant impairment of, or interference with, amenities and other legitimate uses of the environment
(i) Causes significant damage to material property

Description given for taxonomic composition of phytoplankton, macroalgae and phytobenthos

2.20 In many water bodies in the Community, the changes resulting from increases in the biomass of phytoplankton; the cover of macroalgae; or the average abundance of phytobenthos will be the most ecologically significant effects of nutrient enrichment.

2.21 However, in some naturally oligotrophic water bodies, an ecologically significant change in phytoplankton, macroalgal or phytobenthic composition may occur at a level of nutrient enrichment that is insufficient to produce a phytoplankton biomass, a macroalgal cover or an average phytobenthic abundance that has potential to give rise to significant undesirable disturbances (Figure 3). In such cases, the condition of phytoplankton, macroalgae or phytobenthos may be considered moderate on the basis of the effects of nutrient enrichment on taxonomic composition.

Figure 3: Ecologically significant changes in taxonomic composition may occur earlier along an increasing nutrient enrichment gradient than ecologically significant changes in biomass in some types of water bodies (e.g. some naturally oligotrophic lakes)

Ecologically significant changes in the composition of aquatic flora

2.22 The condition of phytoplankton, phytobenthos or macroalgae would not be consistent with good ecological status where, as a result of anthropogenic nutrient enrichment:

(a) An entire functional group of taxa, or a keystone taxon, normally present at reference conditions is absent;

(b) A nutrient-tolerant functional group of taxa not present under reference conditions is no longer rare

(c) A substantial change in the balance of functional groups of taxa has occurred;

(d) A group of taxa, or a taxon, of significant conservation importance normally present at reference conditions is missing

General physico-chemical quality elements

2.23 At good ecological status, the normative definition’s type-specific conditions for nutrient quality elements, such as phosphorus and nitrogen, state that:

 Concentrations should not exceed levels established (by the Member State) so as to ensure the functioning of the ecosystem[6] and the achievement of the values specified for the biological quality elements at good ecological status

2.24 The relative significance of nitrogen and phosphorus in different surface water categories and types of surface waters will vary. In transitional and coastal waters anthropogenic nitrogen enrichment could be the most important cause of eutrophication whereas in many fresh surface waters, phosphorus enrichment is likely to be more important.

2.25 For the purposes of operational monitoring, the nutrient, or nutrients, being discharged in significant quantities (i.e. causing the water body to be at risk of failing to achieve good status) should be monitored. This monitoring may be undertaken using appropriate parameters, such as, for example, total-P; or soluble reactive P.

2.26 If the monitoring results for (a) the biological quality element or elements most sensitive to nutrient enrichment and (b) the nutrient or nutrients thought to be being discharged in significant quantities meet the relevant type-specific conditions required for good ecological status, the level of nutrient enrichment in the water body will be consistent with good ecological status.

2.27 However, if either (a) one of the most sensitive biological quality elements to nutrient enrichment; or (b) one of the nutrients being discharged in significant quantities do not meet the conditions required for good ecological status, the ecological status of the water body will be moderate or worse.

2.28 Further guidance on classification and, in particular, the role of general physico-chemical quality elements is provided in CIS Guidance on the Classification of Ecological Status. The guidance describes a checking procedure aimed at helping to ensure that the good status type-specific levels established by Member States for nutrient concentrations are neither more stringent nor less stringent than required to support the achievement of the type-specific conditions for the biological quality elements and the functioning of the ecosystem.

Annex 1: General interpretation of normative definitions

The definition of high, good and moderate ecological status for phytoplankton[i] are summarised in Table 3a.

Table 3a: Key components of the type-specific conditions described in the normative definitions for phytoplankton (all water categories)
Ecological status class
Type-specific conditions / High / Good / Moderate
Taxonomic composition / If corresponds totally, or nearly totally, to undisturbed conditions / If differs slightly from reference (i.e. high status) conditions / If differs moderately from reference conditions
Biomass / If consistent with reference physico-chemical conditions, including transparency / If differs slightly from reference conditions but not to the extent that it has the potential to cause an undesirable disturbance to the balance of organisms or to the physico-chemical quality of the water or sediment / If differs moderately from reference conditions such that it may produce a significant undesirable disturbance in the condition of other biological quality elements and the physico-chemical quality of the water or sediment
Frequency and intensity of planktonic blooms / If consistent with reference physico-chemical conditions / If showing a slight increase compared to reference conditions / If showing a moderate increase compared to reference conditions or if persistent summer blooms occur

The definition of high, good and moderate ecological status for macroalgaei are summarised in Table 3b.