Ecological Status of Water Quality

Abstract

This chapter gives an overview of environmental quality standards and water quality elements according to the Water Framework Directive and all related guidance documents, Environmental Quality Standards Directive and Water Information System for Europe – WISE GIS Guidance. The chapter explains the main definitions and principles by which surface water and groundwater quality is assessed; it sets out the concepts and procedures that closely drive the development of the aquatic environment protection strategy for the basins for the purpose of preventing the damage to water bodies, as well as protecting, increasing, and rehabilitating the status of all bodies of water, both surface and groundwater ones.

1. Introduction

One of the requirements of Water Framework Directive is that each River/Lake Basin area should have a Management Plan, which needs to be updated each 5–6 years. All River Basin Management Plans implementing the Water Framework Directive in the European Union have as their overriding purpose the maintenance and protection of the aquatic environment. This is achieved through measures to ensure that all waters (surface and groundwater) are of sufficient and sustainable quality and quantity for both environmental and economic needs.

Article 4 of the Water Framework Directive (WFD) [1] defines the core concept of the Directive and the specific purpose of RBMPs, namely, to implement measures as appropriate to:

• Prevent deterioration of the status of all surface water and to achieve good ecological status or good ecological potential.

• Progressively reduce pollution from priority substances and river basin specific pollutants to achieve good chemical status for surface waters.

• Prevent or limit the discharge of pollutants generally to groundwater and reverse negative trends.

• Prevent deterioration of the status of all groundwater, determined by quantitative status and chemical status, and to achieve good chemical status for all groundwater bodies.

• Ensure a sustainable balance of groundwater abstraction against annual recharge.

The European Union (EU) Water Framework Directive (WFD) [1] requires EU member states to set up monitoring and ecological quality classification systems in order to assess the ecological status of surface waters and gauge the extent of human impact on these water bodies. Inland, transitional, and coastal surface waters as well as groundwaters are covered by the WFD. By regulating specific pollutants and establishing corresponding regulatory standards, the directive ensures an integrated approach to water management while respecting the integrity of entire ecosystems.

The reference condition technique, which is what the Directive uses, classifies ecological state by comparing it to reference circumstances. Finding reference conditions, which are understood as the set of conditions to be anticipated in the absence of or under minimum anthropogenic perturbations, is a critical component of the ecological evaluation.

2. Ecological status

The quality of the structure and efficiency of aquatic ecosystems is described by an indicator called the Ecological State of Surface Waters. The ability of the water body to maintain well-organized and balanced animal and plant communities, which are essential biological instruments for supporting the self-purification processes of water, is interpreted as the ecological quality target set forth by Directive 2000/60/EC [1]. Using the physical-chemical and hydro-morphological aspects (such as the water regime and the morphological natural characteristics of the river body) as support for the process of establishing environmental quality, the legislation defines the ecological condition through the research of particular aquatic biological groups. In a high ecological state, or when anthropogenic activities are absent or minimal, the reference conditions define the needs of the biological quality elements. When anthropic activities are absent or of minor significance, as is the case in high ecological states, the reference circumstances define the needs of the biological quality elements. The primary distinction between reference conditions and high ecological status is that the former primarily describe biological quality components, whilst the latter additionally contain chemical-physical, hydro-morphological, and other components (see WFD, appendix II, 1.3) [1]. As a result, particular physical-chemical parameters are established for each kind of transition environment for each form of surface water body, which corresponds to the circumstances of the same in a highly ecological state.

According to Guideline n.13 “Classification of Ecological Status” [2], the degree of correspondence between the present and unaltered physic-chemical conditions only influences the transition between ecological status from high to excellent and from good to sufficient. As a result, the ecological state of the water body will be deemed sufficient if the biological quality components meet the requirements for excellent status, but one or more chemical-physical quality elements do not. As stated in Annex V, 1.1.3 of the WFD [3], both generic elements and particular pollutants are included in the chemical-physical elements.

The WFD in this regard strongly emphasizes the importance of using biological indicator elements (plankton, fish and benthic flora and fauna) in order to assess the ecological quality status and thus maintain the ecological health conditions. These indicators respond in an anticipated manner to anthropogenic disturbances and stressors and make possible long-term classification of ecological quality based on a predictable interaction between pressures and indicators. During the past decades, intensive efforts have been carried out in Europe to standardize and develop biological indicator metrics that can be used rapidly and on a large scale across the continent. WFD gives a framework for developing such scientifically sound and practicably applicable assessments for freshwater ecosystems. Linkage of biological indicators to pressures has been made possible by using a large set of multimeric indices. For fish communities, the multimeric index IBI (Index of Biological Integrity), for benthic macroinvertebrates indices such as Biological Monitoring Working Party (BMWP) and Ephemeroptera, Plecoptera, Trichoptera (EPT) as well as diversity indices, for diatoms several metrics are used, including Trophic Diatom Index (TDI). Many other locally developed indices are also used in specific countries to accommodate the knowledge and the existing set of the existing data.

The Directive stipulates that the ecological quality classification “… shall be represented by lower of the values for biological and physic-chemical monitoring results for the relevant quality elements…” (WFD, Annex V, 1.4.2) [4]. Based on this set of biological indicators the ecological status processing procedure involves, the calculation of the metrics expected for the quality elements monitored and the integration of the results at the water body level. The class of the ecological status of the water body will derive from the lowest class attributed to the different quality elements. The quality, expressed in five classes, can vary from high to bad. The worst ratings (poor and bad) are determined only by EQBs (biological quality elements).

The reference conditions are used to define the limits of the indicators, as shown in Figure 1.

Figure 1.

Link between reference condition and limit definition [5].

The biological quality elements at good ecological status or potential must be supported, relevantly, by the established ranges and levels for the physic-chemical quality element.

It is fair to infer that the ranges and levels defined for the physic-chemical quality components should also be type-specific as the values for the biological quality elements at excellent status will be type-specific. The ranges or values for any or all of the physicochemical quality factors may be the same for several varieties.

Cases (a) and (b), in Figure 2, should be recognized, but for practical reasons, it is proposed to establish only one range or level including both aspects [6].

Figure 2.

The establishment of ranges and levels for the physic-chemical quality elements at a good ecological status potential [6].

2.1 Chemical status

The legislation of the European Union includes safeguards against chemical contamination of surface waterways. Two parts are present. Choosing and regulating compounds of concern to the entire EU (the “priority substances” and “priority hazardous substances”); choosing by Member States substances of concern to their own countries or regions (the “river basin specific pollutants”) for control at the appropriate level. The Environmental Quality Standards Directive (EQSD) 2008/105/EC (as amended by the Priority Compounds Directive 2013/39/EU) [7] establishes the relevant environmental quality standards (EQS) for surface waters, and surface waters are said to be in good chemical condition if their concentrations of “priority substances” [1, 7] do not exceed those EQS. EQSs seek to safeguard both human health and the most vulnerable aquatic animals from direct toxicity. Hazardous compounds must be eliminated for groundwater to achieve the goal of good chemical status.

2.2 Quantitative status

Whereas water quantity was regarded as an ancillary element to overall ecological status in the WFD at publication, water quantity in terms of flow regime is now seen as one of the primary elements of good ecological status [8, 9]. For rivers especially, specific assessments should be made to identify the ‘environmental flow regime’ and to quantify the degree of impact on the waterbody resulting from changes to the flow regime.

For groundwater, quantitative status is determined by a comparison of the rate of annual recharge of the groundwater stock against consumption of the groundwater. Abstractions exceeding recharge even in the short-term will negatively impact on local groundwater level with consequences for (a) surface water flows and ecosystems (b) availability of groundwater for economic uses generally.

2.3 Levels of status

The concept of waterbody status is central to the environmental deliverables of the WFD generally and RBMPs specifically. Status is seen as a relative concept, relative to the ‘reference condition’ which is always type-specific.

The fundamental concepts to keep in mind in the process of identifying the reference conditions can be summarized as follows:

• RCs do not necessarily equal undisturbed conditions; they can include small disturbances, i.e., they can include those anthropic pressures that do not cause ecological effects, or that induce negligible ecological effects;

• RCs equal high ecological status;

• RCs are represented by values of the ecological quality elements relevant in the status classification.

Typically:

• High Status -

  
  - No or very minor anthropogenic alterations to the biological quality, physic-chemical and hydro morphological elements of the waterbody.

• Good Status -

  
  - Slight levels of distortion of the composition and abundance of biological quality elements, with physic-chemical and hydro morphological conditions consistent with the achievement of good biological quality.

• Moderate Status -

  
  - Modest deviation of biological quality elements relative to High Status, with physic-chemical and hydro morphological conditions consistent with the achievement of moderate biological quality.

• Poor Status -

  
  - Waters showing evidence of major alterations to the values of the biological quality elements.

• Bad Status -

  
  - Waters showing evidence of severe alterations to the values of the biological quality elements.

For groundwater, status is defined only by the lesser of quantitative status and chemical status, thereby being either:

• ‘Good’ -

  

• or ‘Fail’ -

  

Figure 3 illustrates various components associated with an ecological status assessment generally. The comprehensive list of all quality elements is shown in Technical Appendix 1. Biological assessment results need to be expressed using a numerical scale between 0.00 and 1.00, the ‘Ecological Quality Ratio’ (EQR) [11]. An EQR value = 1.00 represents type-specific reference conditions (i.e., fully natural conditions). Values close to 0.00 = Bad Ecological Status (BES) [11].

Figure 3.

Quality elements in waterbody ecological status [10].

The objective of the EQR is to ensure comparability between different assessment methods i.e., to provide a common scale of ecological quality between different river basins. The EQR intervals shown in Figure 3 are indicative only and may vary depending on the BQE under assessment.

Flow abstraction has a direct impact on ecological status, even in modest quantity. Figure 3 shows that typically, permanent, or very extended abstraction quantities >30% of the mean flow are likely to result in the hydro morphological quality element achieving only Moderate status [8]. Due to the importance of flow regime generally, it is probable that the ecological status of the waterbody would also be classed as Moderate.

2.4 Environmental objectives for surface waterbodies

To progress the determination, the status of individual waterbodies must be compared to a ‘type-specific reference condition’.

For each surface waterbody type, type-specific biological, hydro morphological and physic-chemical conditions should be established representing values of the elements specified for that surface water body type at high ecological status [12]. ‘Status’ is therefore a condition relative to the reference condition, generally defined as the waterbody type in ‘high status’.

Determination of the biological reference condition for each waterbody type is a matter for national/country procedures, although some EU standard criteria are fixed, especially with respect to ‘priority substances’ as set out in Directive 2008/105/EC [13].

2.4.1 Reference conditions for biological quality elements

Numerous approaches have been used in Europe to assess surface water biological quality conditions by evaluating taxonomic data. The general approach is to use the composition (defined as diversity + abundance) of the community at each site to infer water quality conditions. Some macro-invertebrates tend to be tolerant of poor water quality conditions e.g., order Diptera and the class Oligochaeta. Other organisms, for example, the orders Ephemeroptera, Plecoptera, and Trichoptera, are more sensitive to pollution.

Specific to the type of waterbody sensitive taxa are expected to be found only at sites with ‘good water quality’, varying according to specific national conditions. It can be generally inferred that if any of the specific ‘quality elements’ of waterbody status i.e., physic-chemical, specific pollutants, hydro morphological and/or priority substances are significantly adverse, then the biological quality elements (BQEs) can be expected to show a lower ecological quality ratio, as per Figure 1 and Table 1.

Biotic index score range	Equivalent EQR	Expected water quality status	Degree of organic or chemical pollution	Degree of hydromorphological disruption1
e.g., 0.00–4.50	e.g., > 0.8	e.g., HIGH	e.g., slight	e.g., none
4.51–5.50	0.8–0.6	Good		e.g., slight
	0.6–0.4	Moderate		Moderate
	0.4–0.2	Poor		High
	< 0.2	Bad		Severe

Table 1.

Relationship between biotic index and BQE ecological quality ratio.

¹

Hydro morphological disruption encompasses physical habitat destruction, longitudinal discontinuity and/or significant disturbance to the hydrological flow regime through e.g., abstraction, mining, or hydropeaking, and can be objectively quantified through the use of European Standard EN 15843 [14].

The hydro-morphological, physic-chemical, and biological quality components represent undisturbed or nearly undisturbed circumstances, therefore strictly speaking the normative definition supplied by the WFD needs the development of reference conditions in relation to the values of the quality elements. At first glance, it would seem that the limitations of these quality element values may serve as the foundation for the reference requirements for the biological quality element. These values are unknown, nevertheless, until the development of reference circumstances. Hence, the crucial element in defining reference conditions for biological quality elements is the understanding of the range of values of the biological quality elements in healthy (entirely undisturbed) ecosystems and the amount of deviation allowed.

To forecast modest (acceptable) levels of change in the hydro-morphological, chemical, and physicochemical factors supporting the biological elements, criteria must be developed. The criteria that will be used to anticipate unimpaired circumstances need not be the same for various taxonomic groups due to the significant ecological differences between the taxonomic groups that may be utilized in monitoring operations (e.g., fish, phytoplankton, etc.). However, it must be ensured that the characteristics listed below, each of which can be connected to one or more pressure types, are of utmost significance when characterizing and maintaining biological reference conditions and then comparing various locations to these sites. These elements are all included in Annex V 1.2.1 of the WFD [1, 15].

Hydro morphological elements supporting the biological elements:

• hydrological regime

• quantity and dynamics of water flow

• connection to ground water bodies

• river continuity

• morphological conditions

• river depth and width variation

• structure and substrate of the riverbed

• structure of the riparian zone

Chemical and physicochemical elements supporting the biological elements:

• General

  • thermal conditions

  • oxygenation conditions

  • salinity

  • acidification status

  • nutrient conditions

• Specific pollutants

  • pollution by all priority substances identified as being discharged into the body of water.

  • pollution by other substances identified as being discharged in significant quantities into the body of water.

The WFD defines the following biological characteristics for use as indicators of ecological state for the quality element “fish”: species composition, abundance, sensitive species, age structure and reproduction.

Several metrics are used all over Europe to describe these elements. For benthic invertebrate fauna beside taxonomic composition, the abundance and ratio of disturbance sensitive taxa to semi sensitive and tolerant ones are taken into consideration. For macrophytes and Phyto-benthos taxonomic composition and average abundance are taken into consideration. Reference conditions, representing biological communities in high status waterbodies, should be defined for each individual metric, and for each area and river type. An example of Biological Quality Element is given herein below (Figure 4).

Figure 4.

Example of benthic invertebratefauna as one of biological quality elements.

The European Water Framework Directive (WFD) [1] mandates that an intercalibration process be used to reconcile national classifications of excellent ecological state. Because different geographical areas in Europe harbor different conditions in terms of biological indicators, geography, substrate and climate.

In this effort, the good status limits of the national evaluation techniques are compared and, if required, adjusted in order to harmonize the major disparities in status categorization among the states. Distinct freshwater categories are intercalibrated, with an emphasis on a few different types of water bodies (intercalibration types), human stresses, and biological quality elements. The WFD Common Implementation Strategy Guidance paper on the intercalibration process outlines the steps that must be followed when conducting intercalibration exercises. These exercises are conducted in Geographical Intercalibration Groups, which are bigger geographical entities made up of Member States with comparable water body types.

According to the WFD/Annex II, 1.3 [12], the reference sites and conditions are designated based on the following options and requirements:

• Spatially based reference conditions using data from monitoring sites;

• Reference conditions based on predictive modeling

• Temporally based reference conditions using either historical data or paleo-reconstruction or a combination of both;

• A combination of the above approaches.

In cases when it is not possible to imply the abovementioned methodology, according to the WFD, reference conditions can be established based on the expert judgment taking into consideration the country specificities.

2.4.2 Reference conditions for physic-chemical elements

Together with knowledge about water users and site-specific elements, water-quality criteria serve as a starting point for setting water-quality targets. Information is acquired, among other things, based on the following to determine water-quality objectives:

• Inventories of current and potential new water uses;

• Inventories of emission sources including point and non-point sources, and of sites of production, use, storage and disposal of hazardous substances which could accidentally be emitted into aquatic ecosystems;

• Results of water-quality monitoring and/or water-quality assessments and classifications;

• Surveys of specially protected waters such as drinking-water reservoirs and groundwater, and specially protected areas such as wetlands;

• Results of hydrological measurements and related information (e.g., run-off, hydraulic characteristics of water bodies).

Assessments and classifications of water quality are often based on a reference system that is used to measure and compare the present water quality. A reference base’s objective is to characterize, as accurately as feasible, the natural characteristics of a water body or the fundamental demands that various water users place on water quality. The establishment of such a reference base presents various challenges, particularly concerning watershed regions that have experienced anthropogenic stress for decades and the use category “aquatic life.” These days, a lot of nations utilize water quality standards for that. To develop a suitable reference basis, other nations conduct detailed hydro-chemical examinations of the relevant catchment region. However, establishing a reference standard for all water-quality metrics is almost impossible.

2.4.3 Reference conditions for priority hazardous substances

Good chemical status is attained for a water body when it conforms with the EQS for all priority compounds and other pollutants specified in Annex I of the EQSD, in accordance with WFD Annex V, 1.4.3 [16] and the EQSD Article 1 [7]. The total concentrations in the entire water sample are how the water environmental quality standards (EQS) are stated. When it comes to cadmium, lead, mercury, and nickel, however, the water EQS relates to the dissolved concentration, or the dissolved phase, of a water sample that was produced by filtering via a 0.45 m filter or other comparable pre-treatment.

When assessing the monitoring results against the relevant EQS, the following can be considered: natural background concentrations for metals and their compounds where such concentrations prevent compliance with the relevant EQS and hardness, pH, dissolved organic carbon or other water quality parameters that affect the bioavailability of metals.

2.4.4 Reference conditions for other specific pollutants

For assessment of the status of a surface water body regarding the other specific pollutants, 12 water samples per year (monthly sampling) should be taken at a representative monitoring point. For classification, the following principles apply:

1. The assessment is conducted per water body, using the monitoring data collected for one calendar year.

2. The 95-percentile value of the monitoring data is used for comparison with the environmental quality standards per pollutant and the results classify the water quality as:

   • high,

   • good,

   • moderate

   • poor, and

   • bad

3. The final class is determined by the poorest score for one or more individual parameters.

2.4.5 Reference conditions for heavily modified and artificial waterbodies

According to WFD Article 2(9) [1], there are two components to the definition of a HMWB. To be a HMWB a water body must be:

• physically altered by human activity

• substantially changed in character

A waterbody may only be designated as heavily modified if it has passed through the designation procedure involving both tests as specified under WFD Article 4(3)(a) & (b) [1]. The tests must be waterbody specific since they are intended to guarantee that HMWBs are only recognized in cases where there are no plausible chances for obtaining excellent status within a water body. The designation and the reasons for it must be specifically mentioned in the RBMP.

As for natural waterbodies, the environmental objectives for HMWBs and AWBs are defined relative to a reference condition, which is the maximum ecological potential (MEP) of the waterbody. The MEP is the condition where, taking into account the altered properties of the waterbody, the biological status most closely resembles that of the nearest similar surface waterbody. With regards to its biological status, Good Ecological Potential (GEP) accommodates “slight changes” from the MEP.

Once designated as HMWB or AWB, the environmental objectives are “good ecological potential” (GEP) and good chemical status. Because it accounts for the ecological effects of physical changes required to support a given purpose, such as flood protection or hydropower, GEP is a less strict target than GES.

2.4.5.1 Hydro morphological impacts of hydropower and HMWB designation

The objective determination of the extent of potential hydro morphological impact from HPPs is highly relevant with respect to waterbody status. The hydro morphological condition of the waterbody is integral to its overall status. As confirmed by EU CIS Guidance 31 [8], flow regime has a preeminent controlling effect on ecosystem health, and therefore waterbody status.

The relevance of hydropower operation is that very frequently, the downstream flow regime is entirely disrupted, either in terms of the magnitude of the flow abstracted relative to the mean flow at the point of abstraction, and/or the duration of time that the flow abstraction takes place. This flow regime disruption is additional to the mainly morphological (physical) impacts implied by EU CIS Guidance 4 [10].

An objective test to determine the level of impact of hydropower is essential within the context of Heavily Modified Waterbody (HMWB) designations.

Clearly, construction of major weirs, barrages or dams have a substantial physical impact on the waterbody, altering the longitudinal continuity and ecosystem integrity. The length of the depleted reach for offline HPP systems is a critical factor in ecosystem impacts. A depleted reach is defined as the length of the river waterbody between the point of abstraction and the point of flow discharge. Long depleted reaches arise when the hydropower Operator is seeking to maximize the hydraulic head (H) operating at the turbine, thus maximizing the power output. If the HPP system is offline, then this maximization of Head invariably means excessively long depleted reaches.

The deficient hydro-morphological status will apply for the full length of the depleted reach, albeit on a ‘reducing balance’ basis. At the point of hydropower discharge, the river flow is restored and for ‘run of river’ systems, equilibrium is restored.

However, for the worst-case design of a major Dam + an offline HPP system (i.e., HPP not at the Dam), then at the point of discharge (where turbine operation is a function of storage, not of river flow), the disrupted regime may then continue for a further significant distance downstream, as the turbines discharge significantly more than the expected natural flow, the degree of impact depending on the downstream hydrology.

A single large storage based offline HPP system may therefore significantly impact on e.g., 20 km + of waterbody, depleting flow in the upper reaches, and over-compensating in the lower reaches, and thoroughly disrupting if not completely destroying the aquatic ecosystem.

2.4.6 Final status determination of surface waterbodies

The final or overall status of each delineated waterbody is derived through a complex evaluation of elements shown in Figure 5 [6]. According to WFD CIS guidance [6, 10], the final status of the waterbody should derive from the lowest classed element in each group.

Figure 5.

Procedure for determination of waterbody overall status (European Commission-CIS Guidance 13 – Approach to the classification of ecological status) [6].

2.5 Environmental objectives for groundwater bodies

The WFD requires Member States to designate separate groundwater bodies and ensure that each one achieves ‘good chemical and quantitative status’ (WFD Article 2(24) (25)) [1]. Determination of groundwater status is not as complex as those for surface water bodies. However, groundwater protection is the subject of numerous interacting Directives, including principally Directives 2006/118/EEC and 91/676/EEC [17, 18]. Primarily through Directive 2006/118/EC [19], a management regime should be established which sets groundwater quality standards and introduces measures to prevent or limit inputs of pollutants into groundwater. Member States should establish standards at the most appropriate level and consider local or regional conditions [5].

The standard procedure for determination of the overall status of groundwater bodies is shown in the Figure 6.

Figure 6.

Standard procedure for determination of groundwater overall status.

3. Conclusions and recommendations

• According to WFD, EU member countries are obliged to prepare management plans for each River/Lake Basin area. The non-EU countries and those aiming to adhere to EU, depending on their status of pre-accession are recommended to align their national water related legislation with the EU legal framework.

• The EU pre-accession countries should harmonize and adopt EU water monitoring plans, strategies and practices for the periodical assessment of water quality, maintenance and achievement of good quality status of water.

• The water basin management plans should be updated each 5–6 years.

• Under the framework of integrated management of water resources, for each water basin should be identified a number of water bodies in different categories, based on geographical features and pressures/socio-economic activities within a water body.

• The countries should apply monitoring and ecological quality classification systems to assess the ecological status of waterbodies.

• Per each waterbody hydro-morphological, physic-chemical, chemical and biological quality component should be monitored and assessed.

• For the biological quality elements assessment, locally developed indices may be also used in specific countries accommodate the knowledge and the existing set of the existing data.

• For rivers especially, specific assessment should be made to identify the ‘environmental flow regime’ and to quantify the degree of impact on the waterbody resulting from changes to the flow regime.

• For groundwater, quantitative status is determined by a comparison of the rate of annual recharge of the groundwater stock against consumption of the groundwater.

• The definition of the ecological status per water body should be based on the comparison of real quality results with type specific reference condition.

• Reference condition should be defined per each group of quality elements. Reference conditions of a waterbody represent undisturbed or nearly undisturbed circumstances for that water body.

Acronyms and abbreviations

AWB	artificial waterbody
BES	bad ecological status
BQEs	biological quality elements
BMWP	biological monitoring working party
CIS	common implementation strategy
EPT	Ephemeroptera, Plecoptera, Trichoptera
EQR	environmental quality ratio
EQS	environmental quality standard
EQSD	environmental quality standards directive
EU	European union
GWB	groundwater body
GEP	good ecological potential
IBI	index of biological integrity
HMWB	heavily modified waterbody
HPP	hydropower plant
MEP	maximum ecological potential
PE	population equivalent
RC	reference conditions
RBMP	river basin management plan
SWB	surface water body
WFD	water framework directive
WISE	water information system for Europe