Justification for the Swedish method for BQE Macroalgae and angiosperms

Transcription

1 Justification for the Swedish method for BQE Macroalgae and angiosperms Mats Blomqvist, Hafok AB Introduction In the JRC document Method compliance checking: which methods can be included in the intercalibration exercise. Version May 2011 there is a discussion about compliance of national assessment methods and a conclusion not to include methods that only include the depth limit of 1 (or several) species or are not validated against a pressure. The Swedish method is according to this a candidate for exclusion since it can appear to only include depth limit of several species and since it was not validated against a pressure. In this document I will argue that the method can be regarded as compliant and validated against a pressure and describe our method. Argumentation for compliance Our method is based on depth distribution (abundance) of 3 9 (dependent on national type) selected common conspicuous perennial eutrophication sensitive species (disturbance sensitive taxa). We have a rule that says if one of these species disappears from an area due to anthropogenic reasons it will get a low score (0.2) and hence our indicator will react to decrease (worse depth limit) and disappearance of disturbance sensitive taxa. We believe that this is in line with the normative definition in Annex V of the WFD. Argumentation for validation against pressure It is a well known fact that depth limit and abundance of seagrasses and macroalgae in deeper waters show significant responses to eutrophication pressure (Krause Jensen et al. 2008). Since our method is based on these variables we have a strong theoretical support for validation against a pressure. We have not yet validated our indicator based on field data from our common types. We will try to do this during late summer In the work with phase 1 Boundary Setting Protocol there are data from Norway on the relation between nutrient load and secchi depth against lower depth limits of species used in our assessment method that can be used as a validation (see Figure 1).

2 Figure 1 Relationships between Secchi depth (m) and lower depth limits (m) of selected macroalgae (left) and total nitrogen concentration (µg N l 1) and depth limits (m) of the same macroalgae (right). Depth limits are defined as the deepest occurrence with cover values >5%. R2 is the coefficient of determination. P is significance level. POW = power analysis at a significance level of 0.05 (0.90 means 90%). Note that some relationships are not significant at the 0.05 levels and 2 power analyses are below 80% when calculating against Secchi depth. The lines represent least square regression lines on not transformed data. Abbreviations: PHYLQ = Phyllophora pseudoceranoides + Coccotylus truncata, LAMSA=Laminaria saccharina, FURLU= Furcellaria lumbricalis, RHOCO= Rhodomela confervoides, DELSA = Delesseria sanguinea, PHYRU = Phycodrys rubens, HALSI = Halidrys siliquosa. Data from Are Pedersen, NIVA. Our method relies on several studies on changes in depth distribution over time in different areas of Sweden (e.g. Eriksson et al. 1998, 2002, Kautsky et al 1986). In these studies changes in depth distribution are discussed in relation to eutrophication. Description of method The fact that depth distribution of perennial species is affect by shading from overgrowth of opportunistic species, increased phytoplankton amounts and increased siltation following eutrophication is the basis for our assessment method. Method was developed in 2006 (Kautsky et al. 2007, in Swedish) and implemented in Swedish law 2008 (NFS 2008:1). Method description exists in Wiser data base (id 74) and are explained here in another way.

3 Background The Swedish coastline is long (> 7600 km) and spans over a salinity gradient from almost limnic to fully marine conditions (see Figure 2). To handle this large variation the coast is divided into 25 different national types (see Figure 3 and Table 1). Salinity, exposure, substrate and amount of winter ice cover are important factors in the type definitions. Figure 2 Bottom layer salinity in PSU (map from Leonardsson et al. 2009). Figure 3 National typology (map from Leonardsson et al. 2009). Table 1 National typology of Sweden Type Name 1 Archipelago of the West Coast, inner parts 2 Fjords of the West Coast 3 Archipelago of the West Coast, Skagerrak, outer parts 4 Archipelago of the West Coast, Kattegat, outer parts 5 Coastal waters of south Halland and north Öresund 6 Coastal waters of Öresund 7 Coastal waters of Skåne 8 Archipelago of Blekinge and Kalmarsund, inner parts 9 Archipelago of Blekinge and Kalmarsund, outer parts 10 Coastal waters of east Öland and south and east Gotland including Gotska Sandön 11 Coastal waters of northwest part of Gotland 12 Archipelago of Östergötland and Archipelago of Stockholm, middle parts 13 Archipelago of Östergötland, inner parts 14 Archipelago of Östergötland, outer parts 15 Archipelago of Stockholm, outer parts 16 Coastal waters of south Bothnian Sea, inner parts 17 Coastal waters of south Bothnian Sea, outer parts 18 Coastal waters of north Bothnian Sea, Höga kusten, inner parts 19 Coastal waters of north Bothnian Sea, Höga kusten, outer parts 20 Coastal waters of the Quark, inner parts 21 Coastal waters of the Quark, outer parts 22 Coastal waters of north Bothnian Bay, inner parts 23 Coastal waters of north Bothnian Bay, outer parts 24 Göta Älvs and Nordre Älvs estuary

4 25 Archipelago of Stockholm, inner parts and Hallsfjärden Due to the same factors the composition of the benthic macroalgae and angiosperm communities varies around the coast. Species used for assessment Depending on national type we have chosen 3 9 conspicuous common perennial eutrophication sensitive species to use in the assessment of changes due to eutrophication. In Table 2 the selected species in each national type are shown. Table 2 Selected perennial eutrophication sensitive taxa in each national type having an assessment method for BQE macroalgae and angiosperms in Sweden. Type 13, 24 and 25 lack assessment method due to lack of data. North East Atlantic Group Taxon Delesseria X X X X X Rhodophyceae sanguinea Rhodophyceae Phycodrys rubens X X X X X Rhodomela Rhodophyceae confervoides X X X X X X X X X X X X X X X X Furcellaria Rhodophyceae lumbricalis X X X X X X X X X X X X X X X X X X Baltic Rhodophyceae Chondrus crispus X X X X X X Phyllophora X X X X X X X X X X X X X X X X Rhodophyceae pseudoceranoïdes Phaeophyceae Halidrys siliquosa X X X X X X Phaeophyceae Fucus X X X X X X Phaeophyceae Fucus serratus X Phaeophyceae Fucus vesiculosus X X X X X X X Saccharina Phaeophyceae latissima X X X X X X Sphacelaria Phaeophyceae arctica X X X X X X X X X X X X X Aegagropila Chlorophyceae linnaei X X X X X X X X Cladophora Chlorophyceae rupestris X X X X Characeae Chara baltica X X Characeae Nitella X X Characeae Tolypella nidifica X X X X X X X X Potamogeton X X X X X X Magnoliophyta perfoliatus Magnoliophyta Zostera marina X X X X X X X X X No of taxa Multi Species Maximum Depth Index (MSMDI) Cover of macroalgae and angiosperms along a transect perpendicular to depth curves are monitored by a diver. Maximum depth of each species is one of the variables noted by the diver in the field. Each selected species from the national type of the transect is given a score based on it s maximum depth along the transect. The index is calculated by taking an average of the scores of selected species found in a transect. To get a score a species depth distribution should be limited by light and not by lack of suitable substrate. Each selected species can get a score of 1, 0.8, 0.6 or 0.4 based on maximum depth distribution in relation to the reference depth limit for that species in the present national type. The reference depth limit and the scoring boundaries are set for each species in each national type based on historical data and relations between depth distribution, secchi depths, chl a and

5 nutrients. The final values are set by expert judgment. If a species has disappeared from an area due to anthropogenic reasons it is given a score for this species of 0.2 in each transect in that area where the species has previously occured. An example of calculation of MSMDI is given in Figure 4. Figure 4 Example of calculation of MSMDI. Each bar show the scoring depths for the selected species in national type 3 Skagerrak outer coastal waters. The black lines on four bars show an example where four of the selected species were found in a transect. The scores 1, 0.8, 1 and 0.6 gives a MSMDI value of 3.4/4=0.85. Water body assessment The average MSMDI values for all transects within a water body are used for assessment against an equidistant 5 class status scale. The adjustment against a reference is done in the scoring system for each species and not for the whole index. The boundaries are also given in the scoring system for each speces rather than derived from a relationship between the whole index and a pressure. These two layers of boundaries (scoring system and status classes) are a complication when filling in milestone reports etc. Hopefully this document will make it easier to understand our method. References Eriksson B.K., G. Johansson, P. Snoeijs Long term changes in the sublittoral zonation of brown algae in the southern Bothnian Sea. Eur. J. Phycol. 33: Eriksson, B.K., G. Johansson, P. Snoeijs Long term changes in the macroalgal vegetation of the inner Gullmar Fjord, Swedish Skagerrak coast. Journal of Phycology 38: Kautsky, L. C. Wibjörn, H. Kautsky Bedömningsgrunder för kust och hav enligt krav i ramdirektivet vatten makroalger och några gömfröiga vattenväxter. Report to Swedish EPA (Naturvårdsverket). In Swedish with English summary. Kautsky, N., H. Kautsky, U. Kautsky, M. Waern Decreased depth penetration of Fucus vesiculosus (L.) since the 1940s indicate eutrophication of the Baltic Sea. Mar. Ecol. Prog. Ser. 28: 1 8. Krause Jensen, D., S. Sagert, H. Schubert, C. Boström Empirical relationships linking distribution and abundance of marine vegetation to eutrophication. Ecol. Indicat. 8:

6 Leonardsson, K., M. Blomqvist, R. Rosenberg Theoretical and practical aspects on benthic quality assessment according to the EU Water Framework Directive examples from Swedish waters. Marine Pollution Bulletine 58: NFS 2008:1. Naturvårdsverkets föreskrifter och allmänna råd om klassificering och miljökvalitetsnormer avseende ytvatten. In Swedish.