1. Ecological classification using eelgrass Zostera marina as an example Jesper Andersen, National Environmental Research Institute, Denmark
Thanks:
Dorte Krause-Jensen, Tina Maria Greve, Kurt Nielsen & Gunni Ærtebjerg
National Environmental Research Institute
Per Nilsson
Tjärnö Marine Biological Station, Göteborg University, Sweden
Sponsors: Danish EPA, CHARM (EU), RETRO (NCM)

2. Background
From Jackson et al. 2001

3. Eutrophication in coastal waters
From Ærtebjerg et al. 2003

4. EELGRASS - A CASE STUDY Overall aim
Analyse depth limits of eelgrass according to the WFD in order to test the WFD in practice
Specific aims
Assess “reference conditions” in “water body types”
Evaluate the use of “type-specific” reference conditions and suggest an number (2) of “type-specific” classification schemes

5. Background: Why eelgrass?
Eelgrass is a promising quality element
Responds to eutrophication
Nielsen et al. 2002
Widely distributed
A key element
Historic data - reference conditions (e.g. DK)
Depth Limits (m)
Nielsen et al. 2002
Data from the marine monitoring program shows that eelgrass depth limits are coupled to Secchi depths: The clearer the water, the deeper eelgrass grows.
Secchi depths are largely determined by chlorophyll concentrations and chlorophylle concentrations are coupled to nitrogen concentrations. As a consequence, depth limits of eelgrass are also coupled to nitrogen concentrations.
Key element: Nursery for fish fry, coastal stability, nutrient buffer
Historic data: To be used for evaluation of reference conditions

6. Procedure Definition of water body types (crude!)
Identification of reference/historic depth limits
Identification of actual depth limits
Definition of status classes
Assessment of ecological status
Evaluate the use of “type-specific” reference conditions and “type-specific” classification schemes
Reference data - define status classes
Actual data - assess actual depth limits

7. Water body types
Definition of estuarine types based on mean water depth, salinity, sluices/tresholds..
Historic data
Actual data: National Danish Monitoring programme

8. Historic and actual depth limits
Historic data: conservative estimates - Actual data: maximum estimates
Depth limits larger under reference conditions than at present
Wide range in depth limits - even under reference conditions. Due to broadly defined classes. (Wide ranges also appear if changes in the quality elements do not parallel changes in salinity and depth used to define the water body types.)

9. Classification - 2 examples
Non-restrictive: Good ES - Moderate ES = 25%
Restrictive: Good ES - Moderate ES = 15%
2 examples for defining status classes:
- Non-restrictive definition: High/good-limit: EQR=0.90, good/moderate limit: EQR=0.75.
- Restrictive definition: High/good-limit: EQR=0.95, good/moderate limit: EQR=0.85.

10. Eelgrass depth limits: status classes
With non-restrictive criteria, depth limits required for high ecological status vary from a minimum of 3.8 m in water bodies of type A1 and B2 to a maximum of 7.7 m in D1

11. With restrictive criteria, depth limits required for high ecological status vary from a minimum of about 4 m in water bodies of type A1 and B2 to a maximum of about 8 m in D1
Depth limits defining status classes vary markedly depending on whether nonrestrictive or restrictive criteria are used.

12. Environmental status A1 = 0-3 m depth, 7-18 PSU
C1 = > 8 depth, 7-18 PSU
For 2 water body types, we assessed ecolocical status by comparing actual depth limits with those defining the status classes.
BUT as historic estimates are conservative while actual estimates are maximum estimates, we overestimate the actual ecological status. The analysis therefore ONLY serves to illustrate some principles concerning classification according to the WFD:
1. Nonrestrictive and restrictive criteria gives markedly different assessments of environmental status.With non-restrictive criteria more areas fulfilled the requirements of good or high ecological status. Pronounced for C1
2. There is a risc of classification errors which we will illustrate by an example. .

13. Problems! Defines ref. conditions
BUT also historically, many areas had larger or smaller depth limits
Type-specific classifica-tion may create serious classification errors:
false-negative classification
false-possitive classification
This happens is spite of the fact that we have access to an unusually large reference material!
Ref.
Example based on waterbody type A1.
Possible classification errors:
1) Water bodies with small actual depth limits obtains relatively bad ecological status though they may not in historic times have had high depth limits. Some of these areas will never receive a high status because that would require that depth limits> water depth for the water body.
- Water bodies with relatively large actual depth limits obtain a high ecological status though they may, historically, have had much larger depth limits.

14. Type- vs. site-specific classification
The classification varies markedly depending on whether type- or site-specific criteria are used
The Directive demands that a water body must be capable of being assigned to a single ecological status class with sufficient confidence and precision. This is not posssible using type-specific criteria!

15. Conclusions
Reference conditions may vary markedly within a given water body type
Type-specific reference conditions therefore imply a risk of misinterpretation of ecological status:
Site-specific reference conditions might be a robust alternative
The draft typology (mean depth + salinity) should be replaced with at typology based on salinity (PSU) and residence time (R) and include ‘sub features’ similar to ‘Habitat classification’

16. WFD and the Habitats Directive
from ‘Nutrients and Eutrophication in Danish Marine Waters. A Challenge for Science and Management’ edited by Ærtebjerg et al. (2003)

17. Thank you for your attention ...