WFD Intertidal Seagrass Assessment

Transcription

1 WFD Intertidal Seagrass Assessment (TW and CW - Germany) Summary prepared by: Kerstin Kolbe, Wilfried Heiber Lower Saxony Water Management, Coastal Defense and Nature Conservation Agency Contact: Kerstin.Kolbe@nlwkn-ny.niedersachsen.de Wilfried.Heiber@nlwkn-bra.niedersachsen.de 1

2 INDEX: 1 - General information 2 - Description of the method 3 - Necessary information 4 - Reference conditions 5 - Indicators description 6 - How to apply the index 2

3 1 - General information Acronym: SG-DE Method name: Assessment Tool for Intertidal Seagrass in Coastal and Transitional Waters Original name: Verfahren zur Bewertung der eulitoralen Seegrasbestände in Küsten- und Übergangsgewässern WISER ID: 131 GIG: NE Atlantic Category: Transitional Waters/Coastal Waters BQE: Angiosperms (TW), Macoalgae and Angiosperms (CW) Country: Germany Scientific literature: Kolbe, K. (2007): Intercalibration Report (NEA GIG). Assessment of German Coastal Waters (NEA1/26, NEA3/4) and Transitional Waters (NEA11) by Macroalgae and Angiosperms. NLWKN, Wilhelmshaven. Adolph, W. (2010): Praxistest Monitoring Küste 2008 Seegraskartierung. Niedersächsischer Landesbetrieb für Wasserwirtschaft Küsten- und Naturschutz (Ed.). Küstengewässer und Ästuare 2/2010: 58 S. 3

4 2 - Description of the method The EQR for submerged Angiosperms EQR_SG derives from the calculation of two EQR-components, which are based on three metrics of the intertidal Zostera stock : a) Zostera acreage / bed extent (hectares) EQR_SG_acre. b) Zostera coverage / bed density (%) a) Zostera species (no.) } EQR_SG_density/spec. EQR_SG = ( EQR_SG_acre. + EQR_SG_density/spec. )/2 4

5 2 - Description of the method EQR_SG_acreage Class boundaries Seagrass acreage (ha) EQR_SG_acre.* EQS Reference bed extent ±10% 0.8 High >10 30% loss** Good >30 50 % loss** Moderate >50 70 % loss** Poor >70 % loss** <0.20 Bad *The EQRs that match acreage data are calculated by means of linear interpolation within the respective equidistant EQR-class ranges ** compared with reference 5

6 2 - Description of the method EQR_SG_/species Class boundaries EQR_SG Seagrass density (%) density./ spec* Reference** density ±10% >10 30% loss*** >30 50% loss*** >50 70% loss*** >70% loss*** species (No.) No spec. lost < spec. recorded 1 spec. lost No spec. coverage = 0% <0.20 < * The EQRs that match coverage data are calculated by means of linear interpolation within the respective equidistant EQR-class ranges ** reference density value depends on dominant species *** compared with reference 6

7 3 - Necessary information To apply the index the following information, collected during august-september in the field, is needed for each waterbody (WB) to be evaluated: extent of seagrass beds (ha) and seagrass density (%) within each seagrass bed on intertidal flats within the WB number of seagrass species (1 or 2) 7

8 4 - Reference conditions (RC) Reference Conditions (RC) for Seagrass acreage /bed extent were defined from historical data: the highest ever recorded bed extent is set as reference for each waterbody individually A loss/gain of 10% from the reference extent of the seagrass beds is considered an expression of natural variability Waterbody code RC Zostera bed extent (ha) % of current intertidal DE_CW_N2_3100_ ,5 DE_CW_N2_4900_ ,0 DE_CW_N4_3100_ ,3 DE_CW_N4_4900_01/ ,7 Table II- Reference condition Zostera bed extent DE_CW_N4_5900_01 > 0? DE_TW_T ,2 DE_TW_T ,4 8

9 4 - Reference conditions (RC) Reference Conditions (RC) for Seagrass bed density (%) were defined from historical data and expert judgement and differ with respect to the species: Zostera noltii and mixed beds: 60% Zostera marina: 30% Fig. 1: Patchily distributed Zostera noltii 9

10 4 - Reference conditions (RC) Reference Conditions (RC) for Seagrass species number were defined from historical data Two seagrass species, Zostera marina and Zostera noltii, are present in each waterbody Fig. 2: Zostera marina Fig. 3: Zostera noltii 10

11 Seagrass monitoring: 5 - Indicators description The presence of Zostera species, the extent and density of Zostera beds in the intertidal zone are assessed by means of field surveys every 6 years. Fig. 4: Field survey of intertidal Zostera stocks 11

12 5 - Indicators description Seagrass acreage /bed extent (ha): The total extent of seagrass beds in the intertidal zone is assessed by means of field surveys (GPS-tracking) Definition of seagrass bed : Zostera marina and/or Zostera noltii in coherent stands or clusters of patches on intertidal flats (Fig.1) distance of seagrass patches within a bed 25 m average density 5% within a seagrass bed 12

13 5 - Indicators description Seagrass coverage / bed density (%): The Seagrass bed density for one bed is calculated from two measurements which are visually determined at 10 sites within each seagrass bed during the field surveys : cover : proportion : area of seagrass-covered patches in relation to the total seagrass bed area (%) area covered by seagrass within the patches (mean density, %) Seagrass bed density (%) = ( cover x proportion )/

14 6 - How to apply the index Seagrass acreage /bed extent: 1. Enter GPS-field-data into a geographic infomation system (GIS) 2. Calculate total Zostera-acreage (ha) for each waterbody (WB) 3. Check current acreage (ha) against WB-specific reference value 4. Calculate EQR_SG_acreage for WB according to classification-matrix Seagrass density / Species number: 1. Collect data of Zostera density (%) and presence of species 2. Calculate mean Zostera density for each WB 3. Check actual density (%) against reference value 4. Calculate EQR_SG_density/species for WB according to classification matrix EQR_SG = ( EQR_SG_acre. + EQR_SG_density/spec. )/2 14