1.8 Transitional waters and coastal waters

1.8 Transitional waters and coastal waters

1.8.1 Odense Fjord Northern Belt Sea Figure 1.8.1 ODF22B Map of Odense Fjord Odense Fjord is a shallow (average depth 2.25 indicating the bound- m) mesohaline estuary located in the northern aries of the inner fjord part of Fyn (Figure 1.8.1). The submerged area (Seden Strand) and outer fjord. The three encompasses 63 km2. The fjord can be subdivided monitoring stations, into a smaller inner fjord, Seden Strand, which SS8 in Seden Strand, has an average depth of 0.8 m and accounts for a ODF17 in the outer little less than 1/4 of the submerged area, and an part of the fjord and E g outer part which has an average depth of 2.7 m e n ODF22B in the boun- s G OTTERUP e a D b and accounts for the remaining approx. 3/4. e Odense e dary zone outside the e t p Fjord fjord are indicated. By far the major source of riverine runoff to the Outer fjord is the River Odense, which fl ows into the fjord inner part of Seden Strand. The water exchange ODF17 between the fjord and the open sea (Northern MUNKEBO Belt Sea) takes place via Gabet, the narrow mouth KERTEMINDE Seden Ø

Strand e g i of the fjord. Using a hydrodynamic model it has t S SS8 l been calculated that the residence time of River Depth na Ca 30-40 m se n l R Odense water is short, around a yearly average 20-30 m de a n i O a v 10-20 m C e ld r of 17 days for the fjord as a whole and 9 days for 6-10 m O O d 4-6 m e n Seden Strand. 0 5 km 2-4 m s ODENSE Odense Harbour e Nutrient loading of the fjord from anthropo- 0-2 m genic sources is high due to the large size of the catchment (1 060 km2), which corresponds to one third of the area of Fyn and is characterized by intensive agricultural production and a high fl uorescence are measured electronically every population density (see Section 1.1). Thus in 2001, 10–20 cm along the water column; the oxygen for example, total loading from the catchment and concentration is alternatively measured using the the atmosphere amounted to approx. 32 g N (or Winkler technique. Transparency is measured 2.3 mol N) and approx. 0.88 g P (or 0.03 mol P) using a Secchi disc. per m2 of fjord, with atmospheric deposition only Nutrient concentrations – total nitrogen, am- accounting for 5% or less. Given this high level of monium, nitrate (+nitrite), total phosphorus, loading, Odense Fjord can be characterized as a orthophosphate and silicate – are measured in eutrophic water body. surface water samples and in the bottom water at Both national and local initiatives initiated in the deeper stations. the late 1980s have helped reduce this high level Phytoplankton conditions are evaluated by of loading, and the point-source dominated P load measurement of chlorophyll a at several depths has since been reduced by a factor of 6–7. The N and of primary production (C-14 method). At load, which is predominantly attributable to dif- ODF17 in addition, carbon biomass is measured fuse loading from farmland, has only been reduced at species and taxa level. by around 1/3 though, (see also Section 3). A number of other variables are monitored concomitantly with these pelagic activities, but Monitoring programme with varying frequency. These are: Benthic in- Pelagic variables are monitored weekly at three vertebrate number, biomass and fi ltration capac- stations representative of the fjord and its border ity; macroalgal and rooted macrophyte species zone: SS8 (depth 0.8 m) in the shallow inner composition, coverage and (to a lesser extent) fjord, Seden Strand, ODF17 (depth 8.5 m) in the biomass; nutrient and oxygen exchange across outer deep part of the fjord, and ODF22B (depth the sediment-water interface; continual hydro- 17 m) in the border zone outside the fjord (Figure graphic measurements for use in a deterministic, 1.8.1). hydrodynamic 3D-model, which is coupled to a The physical variables monitored are salinity, dynamic eutrophication model; and the content temperature and light attenuation, which togeth- and effects of hazardous substances in water, er with oxygen concentration and chlorophyll sediment and biota.

Odense PRB Odense Pilot River Basin 55 1.8 Transitional waters and coastal waters

Hydrographic conditions and nutrient condi- due to the high runoff, and are highest (median tions in Odense Fjord 3 500–4 000 µg N/l) in the inner fjord near the The seasonal variation in the salinity of the fjord main freshwater outfl ow, decreasing towards the and border zone is illustrated in Figure 1.8.2 open sea, i.e. approx. 1 400 µg N/l in the outer based on data for the past seven years. The sa- fjord and approx. 350 µg N/l outside the fjord. In linity in Seden Strand varies during the year be- the summer the concentrations of total nitrogen tween approx. 10 and 15 PSU (monthly median), are lower, the median values being around 650, being lowest in winter/spring when riverine run- 450 and 250 µg N/l, respectively. off is highest. The salinity is higher in the outer Corresponding estuarine winter gradients also fjord (16–21 PSU), and highest outside the fjord occur for total phosphorus (Figure 1.8.4). In this (16–24 PSU). The water temperature at the three case the winter median is approx. 110, 50 and 30 stations varies between approx. 0 and 25ºC. µg P/l in the inner fjord, outer fjord and border The estuarine gradient in nutrient concentra- zone, respectively. A special feature of the nutri- tions is illustrated in Figure 1.8.3 (nitrogen) and ent cycle in the fjord is the almost bell-shaped 1.8.4 (phosphorus). The concentrations of total course of phosphorus concentration over the nitrogen are generally higher in the winter period summer, which also comprises the yearly maxi-

Salinity, surface Total N, surface PSU µg N/l Figure 1.8.2 (left) 90% quantile SS8 7 000 90% quantile SS8 Surface water salinity 24 Median 1996-02 Median 1996-02 at three stations inside 10% quantile 6 000 10% quantile and outside Odense 20 Fjord (see Figure 1.8.1) 5 000 16 for the period 1996– 4 000 2002. The median and 12 10% and 90% quan- 3 000 8 tiles are shown together 2 000 with all the data. 4 1 000

0 0 JFMAMJJASONDJ JFMAMJJASONDJ

PSU µg N/l Figure 1.8.3 (right) Surface water con- 90% quantile ODF17 90% quantile ODF17 28 Median 1996-02 Median 1996-02 4 000 centration of total 10% quantile 10% quantile nitrogen at three 24 stations inside and 3 000 outside Odense Fjord 20 (see Figure 1.8.1) for 2 000 the period 1996–2002. 16 The median and 10% 1 000 and 90% quantiles are 12 shown together with all the data. 8 0 JFMAMJJASONDJ JFMAMJJASONDJ

PSU µg N/l

90% quantile ODF22B 700 90% quantile ODF22B 32 Median 1996-02 Median 1996-02 10% quantile 600 10% quantile 28 500 24 400 20 300 16 200

12 100

8 0 JFMAMJJASONDJ JFMAMJJASONDJ

Odense 56 PRB Odense Pilot River Basin 1.8 Transitional waters and coastal waters

Total P, surface mum. The highest median concentrations are µg P/l found in the inner fjord, reaching a maximum Figure 1.8.4 90% quantile SS8 Surface water con- of approx. 200 µg P/l as compared with approx. 500 Median 1996-02 centration of total 100 µg P/l in the outer fjord. The concentration 10% quantile phosphorus at three 400 peak is primarily attributable to release from stations inside and the sediment iron-bound phosphorus pool and outside Odense Fjord 300 (to a lesser extent) point-source discharges of (see Figure 1.8.1) for phosphorus and poorer water exchange during 200 the period 1996–2002. the summer. The phosphorus peak is not seen in The median and 10% the surface water outside the fjord; on the other 100 and 90% quantiles are hand, oxygen defi cit-dependent accumulation of shown together with all phosphorus (and nitrogen) often occurs through- 0 the data. out the summer and autumn in the bottom layer JFMAMJJASONDJ of these stratifi ed open marine waters. µg P/l During the growth season, nutrient concentra- 90% quantile ODF17 tions in the fjord are potentially limiting for the 160 Median 1996-02 phytoplankton, although exhibiting temporal 10% quantile and spatial variation (data not shown). Potential P limitation generally exists in the spring, and 120 potential N limitation in the summer. Moreover, nutrient limitation of the phytoplankton is gen- 80 erally more pronounced in the outer fjord (where silicate can also be potentially limiting for dia- 40 toms) than in Seden Strand. Not surprisingly, the greatest potential nutrient limitation exists at the 0 considerably lower nutrient levels found in the JFMAMJJASONDJ open marine waters outside the fjord. µg P/l 90% quantile ODF22B Biological conditions in Odense Fjord 50 Median 1996-02 Despite the high nutrient loading of the fjord, 10% quantile pelagic phytoplankton biomass, which is domi- 40 nated by diatoms, is relatively low (data not shown). At the same time, the seasonal devel- 30 opment of the phytoplankton biomass is very 20 dynamic, with rapidly shifting concentrations of chlorophyll a. 10 Apart from the fact that water exchange is high, one of the main reasons for the relatively 0 low phytoplankton abundance and the dynamic JFMAMJJASONDJ seasonal development is that the diverse benthic invertebrate fauna of Odense Fjord is dominated by fi lter feeders, i.e. polychaetes and mussels (Figure 1.8.5), which fi lter the phytoplankton from the water column. It is calculated that alone the daily fi ltration capacity of the dominant polychaete Neries diversicolor is several times Benthic fauna Figure 1.8.5 that of the water volume in Seden Strand, and Benthic fauna in approximately half the water volume in the outer Apportioned by species Apportioned by individuals Odense Fjord appor- tioned by number of fjord. To what extent the fi ltration potential is 29% 41% species and individu- expressed is highly dependent on the physical als. Mean of 50 sta- mixing of the water bodies. 24% tions, 1998–2001. That nutrient loading of the fjord is high gen- 10% erally favours growth of the rapidly growing Molluscs ephemeral macroalgae: For example, sea lettuce 2 % Crustaceans 11% Echinoderms (Ulva lactuca) dominates in Seden Strand. In 13% Polychaetes step with a demonstrated fall in nutrient loading 36% Other since the 1980s (see Figure 4.5.1), the abundance 34%

Odense PRB Odense Pilot River Basin 57 1.8 Transitional waters and coastal waters

of other ephemeral macroalgae with a lower Optional factors: nutrient requirement has been increasing in 4) Wave exposure Seden Strand, and the abundance of perennial 5) Mean depth macroalgae such as bladderwrack (Fucus vesicu- 6) Further geomorphological subdivision of losus) and of rooted macrophytes such as eelgrass fjords: Inner fjords, sill fjords and sluice (Zostera marina) and widgeon grass (Ruppia mar- fjords. itima) has been increasing in the outer fjord. The macrophyte community in the fjord is still very This typology yields 18 types of coastal water, of unstable, though, and still exhibits large interan- which 16 are found in Denmark. nual variation in coverage. Among other things, According to the proposed national typology eelgrass has virtually disappeared in Egense Deep Odense Fjord has to be differentiated into two in the northwestern part of the outer fjord since types of water body based on data from the the mid 1990s, and the overall eelgrass coverage monitoring stations SS8 in the inner fjord and was found to be very low during the last survey ODF17 in the outer fjord: in 2002 (see also Section 4.5.2). • Odense Fjord, inner part, denoted Seden Strand: Inner fjord, mesohaline (7–18 PSU). 1.8.2 Typology • Odense Fjord, outer part: Shallow (0–3 m mean depth), mesohaline (7–18 PSU) fjord. Ecoregion The Danish coastal waters are located within The border zone of Odense Fjord located outside two of the ecoregions defi ned in the WFD, the the mouth, Gabet, will be incorporated in the North Sea ecoregion and the Baltic Sea ecoregion description and establishment of quantitative cri- (cf. WFD Annex XI, map B). The boundary be- teria for Odense Fjord. According to the national tween the two regions runs from Sjællands Odde geomorphological subdivision of fjords, this zone through the southern Kattegat to Djursland. In is comprised of a third type of water body when the Habitats Directive, the boundary between using monitoring data from station ODF22B: the Atlantic bioregion and the Baltic bioregion runs along the Weichsel ice front line, i.e. from • Odense Fjord, border zone: “Inner marine Hirtshals to the southern coast of Norway. In water between Djursland/Sjællands Odde and the context of both the WFD and the Habitats Fyns Hoved/Røsnæs, depth <15m, salinity Directive, Odense Fjord will thus belong to 15–20 PSU”. Ecoregion 5, the Baltic Sea ecoregion, but with close association with the North Sea ecoregion in Three types of coastal water have thus been iden- the context of the WFD. The international ma- tifi ed in the Odense River Basin. rine convention OSPAR encompasses both open Delineation of water bodies outside the fjord marine waters and fjords, while the Helsinki cannot be fi nalized until the geographic bounda- Convention only encompasses open marine wa- ries of the new administrative units “River ba- ters. In Danish marine waters the OSPAR Con- sins” with associated coastal waters have been vention encompasses the area north of the WFD established for the forthcoming River Basin outer boundary (North Sea ecoregion), while the District Fyn County (Annex 0.2). The area Helsinki Convention encompasses the Baltic Sea will be encompassed by the WFD’s administra- region as well as the whole of the Kattegat up to tive delineation of fjords and/or coastal waters a line between Skagen and the western coast of within one nautical mile of the so-called baseline Sweden at Gothenburg. The two conventions from which the breadth of territorial waters are thus overlap in the Kattegat area. measured (cf. Nielsen et al., 2001; Danish En- vironmental Protection Agency, 1983b; Annex Typology 0.2). The status of these water bodies has to be The provisional national proposal for a typology classifi ed relative to reference conditions estab- of coastal waters (Nielsen et al., 2001) follows lished on the basis of biological quality elements. System B, with a number of optional factors, and The remainder of the border zone between 1 and operates with the following descriptors: 12 nautical miles from the baseline might have to be assigned to a coastal water body that, pursuant Obligatory factors: to the WFD, only has to be characterized relative 1) Geomorphological differentiation into main to physical/chemical quality elements. coastal waters 2) Tidal range 3) Salinity.

Odense 58 PRB Odense Pilot River Basin 1.8 Transitional waters and coastal waters

1.8.3 Delineation of water bodies Figure 1.8.6 Delineation and area In the context of the WFD a surface water body of the fi ve marine has to be a “discrete and signifi cant” element of Boundary zone water bodies encom- surface water that can be characterized and as- 74 km² passed by Odense sessed in relation to the environmental objectives River Basin, the inner fjord, NW, mid and set. A water body may only consist of a single NE outer fjord, and N type of water body, and can only hold a single the boundary zone. See ecological status class. According to the EU also Table 1.8.2. Guidance Document “Identifi cation of water ODF NW bodies”, protected areas have also to be taken OTTERUP 14 km² into account, and subdivision into several water ODF NE 19 km² bodies can be considered in cases where only part ODF mid of a water body is designated as a protected area. 13 km² The application of the above-mentioned typol- ODF inner/ MUNKEBO ogy based on morphological/hydrographical KERTEMINDE Seden Strand criteria yields three types of coastal water in 17 km² Odense River Basin and hence a minimum of three water bodies. Odense Fjord is also encom- passed by both international and regional protec- tion provisions. The borders of these areas do not ODENSE follow either the geographical subdivisions of the 0 1 2 3 km fjord or the above-mentioned morphological dif- ferentiation into types of fjord (Figure 1.8.8). Further subdivision of the outer part of Odense Fjord into three water bodies will thus Northern Belt Sea Figure 1.8.7 be necessary in order to be able to assess status Map of Odense Fjord and to assess whether the fjord meets the various indicating formerly submerged but now re- degrees of objective. claimed areas, location In all, fi ve coastal water bodies have thus been of the dykes and major identifi ed in Odense River Basin, namely Seden physical installations Strand, the outer fjord subdivided into Odense such as harbours, pow- Fjord northwest, Odense Fjord mid and Odense er stations, shipyards, Fjord northeast, and fi nally the border zone ad- Egense Harbour fairways, etc. E g e joining Odense Fjord. The delineation and areas n G OTTERUP s e a Reclaimed areas D Odense b of the fi ve individual water bodies are indicated e e e t p Fjord in Figure 1.8.6. Outer Dykes fjord Bregnør Harbour Klintebjerg Harbour Physical installations Boelsbro 1.8.4 Physical modifi cation Lindø Terminal Lindø ShipyardMUNKEBO Odense KERTEMINDE North landfill Seden Strand Harbours and navigation Stige Ø landfill Odense Fjord is connected to Denmark’s third largest city, Odense, via Odense Canal (Figure Fynsværket, CHP Plant 1.8.6). Since ancient times it has been a hub for Odense Harbour maritime trade and transport. Thus there are ODENSE 0 5 km a number of minor harbours and quays on the fjord. Odense Harbour, Lindø Shipyard and Lindø Terminal represent installations of con- siderable size that have entailed major physical in the form of large amounts of resuspended changes to the fjord’s natural coastline (Figure sediment that reduces the transparency of the 1.8.7). Moreover, shipping fairways have been water column and causes sedimentation on the excavated in connection with the harbours, and seabed. Periodic intensive navigation to and from these have to be dredged every few years (Figure Odense Harbour and Lindø Shipyard with large 1.8.7). This dredging work periodically places vessels also causes resuspension of sediment and marked physical pressure on the fjord, especially reduces the transparency of the water.

Odense PRB Odense Pilot River Basin 59 1.8 Transitional waters and coastal waters

Other physical installations Outer parts of Odense Fjord The physical environment of the fjord is also The main physical changes in the form of dyking affected by a number of other large installa- and harbour construction have long been com- tions located on the fjord. Stige Ø Landfi ll pleted, and the water balance in the fjord can has considerably increased the area of Stige Ø thus be expected to have reached equilibrium. peninsula which, after cessation of landfi lling In themselves, these changes do not hinder the and subsequent re-establishment, now forms a fjord in meeting the WFD objective of good eco- hilly peninsula projecting into the inner part of logical status. Moreover, as the recurrent work of Seden Strand. Since its construction, the intake dredging the fairways is carried out at intervals of cooling water by Fynsværket Combined Heat of many years, its impact is not expected to be and Power (CHP) plant has caused changes to the suffi cient to hinder attainment of good ecological physical environment in the form of temperature status either. and salinity changes, altered water exchange and enhanced mortality of planktonic organisms in Seden Strand. 1.8.5 Reference conditions

Dyking and land reclamation As described in Section 1.8.3, differentiation and Due to the shallow nature of the fjord and the fl at delineation resulted in Odense Fjord being subdi- topography of the catchment, major dyking and vided into an inner fjord (Seden Strand), an outer land reclamation works have been carried out in fjord comprised of three discrete water bodies, the fjord right up to the 1960s. This considerably and a border zone. reduced the area of the fjord, and long portions According to the WFD and the Guidance of the physical coastline were replaced by dykes Document on classifi cation of coastal waters (Figure 1.8.7). In addition to the physical chang- (GD 2.4), establishment of the reference condi- es, drainage and dyking considerably reduced tions can be based on data from existing water the capacity of the fjord and catchment to retain bodies assessed as being in an undisturbed state, nitrogen input from the catchment. on historical data, on modelling of historical and other data and on expert judgement. There are Shell mining no coastal water bodies in Denmark that can be The great abundance of calcareous oyster shells presently characterized as “undisturbed”. The in the seabed of the shallow parts of the fjord establishment of reference conditions for Odense were exploited right up to the 1970s. The min- Fjord has therefore been based partly on 3D mod- ing was conducted in large parts of Seden Strand elling of Odense Fjord carried out in connection right down to a depth of 4 m, and thus undoubt- with the cooling water intake and discharge edly comprised a major physical pressure. permits for Fynsværket (CHP) plant, partly on historical data on the macrophyte vegetation in Heavily modifi ed water bodies Odense Fjord around 1900, at which time an- Seden Strand thropogenic nutrient loading of the outer part Based on the guidelines given in the EU Guid- of Odense Fjord and the border zone, but not ance Document “Heavily modifi ed water bodies” Seden Strand, is considered to have been low, and it is concluded that the above-mentioned physi- partly on empirical modelling of these historical cal pressures are not of suffi cient magnitude to data. Selection of the variables described below justify classifi cation of all or part of the fjord as was thus based on what was rendered possible by heavily modifi ed. historical data and modelling within the provi- The intake and discharge of cooling water sions of the WFD concerning biological vari- by Fynsværket (CHP) plant cause changes in ables and supporting physico-chemical variables. the hydromorphological conditions in Seden It should be noted that the variables described Strand. In particular, water exchange, salinity below should not be considered as the fi nal list of and temperature are raised relative to the natural criteria for establishing objectives. In the further state (see Section 1.8.5). It is estimated that these work, the description of reference conditions changes are not of suffi cient magnitude to hinder will be supplemented with additional criteria for the fjord in meeting the objective of good ecolog- biological variables, especially pertaining to phy- ical status, however. This assessment will have to toplankton and benthic invertebrates, as well as be revised, though, if the above-mentioned con- additional criteria for supporting physico-chemi- ditions change, i.e. if the power station’s current cal variables to describe hazardous substances, discharge permit is altered. heavy metals, etc.

Odense 60 PRB Odense Pilot River Basin 1.8 Transitional waters and coastal waters

Under the WFD, a status class is only con- ous criteria for reference conditions are examined sidered to be attained if the criteria for all the below and in Table 1.8.1. biological variables are met (one out, all out prin- ciple). As a result of this strict requirement, the Reference conditions for the inner fjord, Seden EU guidance documents propose that variables Strand subject to large natural variation – which is often Macrophytes the case with the marine waters – can be excluded In 1957 there was a well-developed community from the array of variables included in the defi ni- of eelgrass (Zostera marina), widgeon grass (Rup- tion of reference conditions. As the data material pia maritima) and sago pondweed (Potamogeton for coastal waters is inadequate to establish many pectinatus) in the northern part of Seden Strand, detailed criteria for their biological state, it is while in the southern part there was an abun- essential to maintain that the criteria in combi- dance of sea lettuce (Muus, 1967). The present- nation must still provide the same broad picture day distribution of vegetation in Seden Strand is of the biological status, and that all the criteria examined in Sections 1.8.1 and 4.5.2, and illus- established must be fulfi lled. trated in Figure 4.5.3. The WFD does not specify over which time Based on historical data from other similar period these established criteria must be fulfi lled, fjords (Petersen, 1892; 1901), 3D modelling (DHI, however. As demonstrated in Roskilde Fjord, for 2002; 2003) and the studies of Muus (1967) and example (Andersen et al., in press), assessment Larsen (unpublished manuscript), it is concluded of status based on a single monitoring year will that reference conditions entail a considerably often lead to random variation in status clas- lower abundance of eutrophication-dependent sifi cation. Assessment of status should therefore ephemeral macroalgae (in Seden Strand, primari- be carried out in accordance with statistically ly sea lettuce and fi lamentous algae) concentrated well-founded guidelines that provide the best in the immediate vicinity of the main freshwater possible assessment over time in relation to the inputs than is presently the case. Using 3D mod- coming six-year reporting period, cf. also the rec- elling the reference conditions for macroalgae ommendations based on the existing experience has been quantifi ed for two different years (1998 with quantitative quality criteria and assessment and 2002) in so-called “Natural state scenarios”. of objective fulfi lment in the current recipient Based on these values the reference conditions quality planning (Nielsen et al., 2001). The vari- for ephemeral macroalgae has been established

Table 1.8.1 Odense Fjord Reference conditions Water body Type Reference status criteria for the fi ve ma- rine water bodies en- Secchi Macrophytes Nutrients compassed by Odense depth River Basin. Coverage (%) Biomass Depth distri- Total N Total P 2 (m) (depth interval) (g C/m ) bution (m) (µg/l) (µg/l) Filamentous Eelgrass Widgeon grass algae and Eelgrass sea lettuce Inner fjord (Se- 1 >80 (1.5–4 m) >80 (0.5–1.5 m) <10**** >4 <660* <30* - den Strand)

Outer fjord NW 2 >80 (1–6 m) >80 (0.5–1 m) <3*** >6 <370** <10** >7.2

Outer fjord NE 2 >80 (1–6 m) >80 (0.5–1 m) <3*** >6 <370** <10** >7.2

Outer fjord mid 2 >80 (1–6 m) >80 (0.5–1 m) <3*** >6 <370** <10** >7.2

Boundary zone 3 >80 (1–10 m) >80 (0.5–1 m) <3*** >10 <146 <5 >10.6

Remarks: The values apply for the individual water bodies as a whole. * The nutrient criteria are set at a salinity of 12.2 PSU. ** The nutrient criteria are set at a salinity of 18.1 PSU. Total N is up- and down-regulated by 49.3 µg/l total N per PSU with a decrease or increase in salinity, respectively. Total P is up- and down-regulated by 3.4 µg/l total P per PSU with a decrease or increase in salinity, respectively. *** Only anchored filamentous algae; freely floating filamentous algae must not be present. **** New calculations could lead to the value being lower.

Odense PRB Odense Pilot River Basin 61 1.8 Transitional waters and coastal waters

as an average for the whole of Seden Strand as solely established for the period 01/03–31/10, the the sum of the seasonal maximum biomass of the total N values derived have to be corrected for various species. The reason for operating with an the higher winter concentrations. This has been average value for the whole of Seden Strand is the done on the basis of ratios calculated from meas- physically determined passive mobility of these urements made by Fyn County over the period macroalgae. The resultant reference value is 7 g 1981–2002. C/m2 for 2002 and 10 g C/m2 for 1998, which In addition, total N concentrations have been is in good agreement with calculations based on calculated by DHI (2002; 2003) in “Natural state data in Larsen (unpublished manuscript). scenarios” based on two different meteorological The distribution of the rooted macrophyte situations in 1998 and 2002. The annual mean vegetation in reference conditions is considered concentration of total N at station SS8 was cal- not to differ markedly from the current distribu- culated to be 670 µg N/l in 1998 and 730 µg N/l tion, but the biomass and stability of vegetation in 2002. These values are comparable with the coverage would be considerably greater than is empirically determined value used as the crite- presently the case, and the rooted macrophytes rion for reference conditions, i.e. 660 µg N/l (see should thus occur in dense stands. The variables below). operated with for the rooted macrophytes are No corresponding empirical relationships ex- depth distribution and coverage. The reference ist for total phosphorus (total P). However, as values have been established on the basis of with total N, 3D modelling of “Natural state vegetation surveys made by Fyn County and his- scenarios” yields an annual mean concentration torical data from Odense Fjord (Ostenfeld, 1908; for total P at station SS8 of 30 µg P/l in 1998 and Fyn County, 1990; 2003b), as well as historical 50 µg P/l in 2002. However, new calculations are data from corresponding fjord waters (Nielsen et currently being made with the model in which al., 2003a). riverine nutrient loading has been corrected. It is expected that these calculations will yield a Macrophyte criteria for reference conditions: somewhat lower “natural state” nutrient level in • Depth distribution (main community) of eel- the fjord. For total P, the lower of the two above- grass: ≥4 m where depth in the area permits. mentioned values has therefore been selected as • Coverage of eelgrass: >80% in the depth inter- the criterion for reference conditions. val 1.5–4 m. As the nutrients fl ow into the fjord with the • Coverage of widgeon grass: >80% in the fresh water, and fl ow out of the fjord with water depth interval 0.5–1.5 m. consisting of a mixture of fresh water and the sea • Biomass (seasonal maximum) of sea lettuce water fl owing into the fjord, the nutrient content and freely fl oating fi lamentous algae (average in the fjord follows an estuarine gradient and for the whole of Seden Strand): <10 g C/m2 varies markedly depending on the actual mixing conditions at the time of measurement (see also Nutrients Section 1.8.1). It will therefore be necessary to Seden Strand is presently overfertilized by nutri- relate the nutrient criteria for reference condi- ents from the catchment (Sections 3.4 and 4.5.2, tions to salinity, i.e. to normalize the nutrient Figure 4.5.1). concentrations for differences in salinity. This With respect to nutrient concentrations, the also eliminates “noise” from variation in salinity reference conditions for Seden Strand should be when interpreting the monitoring results. The established such that the requirement for undis- relationships established for variations in total P turbed or virtually undisturbed biological state and salinity are not as good as those established can be met. for total N and salinity, primarily due to sedi- The criteria established for eelgrass depth dis- ment release of phosphorus during summer. It tribution in Seden Strand (and in the outer fjord has been decided to also employ the relationship and border zone; see below) of an undisturbed/ established for total P, though, as it is considered virtually undisturbed state is based on data for that the establishment of the operational criteria the depth distribution of eelgrass early last cen- would be problematic without the correction. tury (Ostenfeld, 1908). For total nitrogen (total N), the reference Nutrient criteria for reference conditions: conditions are hereafter calculated by empirical • At an annual mean salinity of 12.2 PSU at modelling of the relationship between total N station SS8 in Seden Strand, the annual mean and the depth distribution of eelgrass (Nielsen et concentration of total N must not exceed 660 al., 2002). As the empirical relationship has been µg N/l (empirical modelling for the period

Odense 62 PRB Odense Pilot River Basin 1.8 Transitional waters and coastal waters

01/03–31/10 regulated 40.5% up to an annual fjord), but that this is not used in establishing the mean value based on measurements over the reference conditions as the presence of such algae period 1981–2002). is incompatible with the historical data. • Total N is regulated up or down by 49 µg N/l for each PSU change in salinity relative to the Macrophyte criteria for reference conditions: baseline of 12.2 PSU (the 3D model yields • Depth distribution (main community) of eel- comparable values for salinity correction of grass: ≥6 m. 57–58 µg N/l per PSU). • Coverage of eelgrass: >80% in the depth inter- • At an annual mean salinity of 12.2 PSU at val 1–6 m. station SS8, the annual mean concentration of • Coverage of widgeon grass: >80% in the total P must not exceed 30 µg P/l (dynamic 3D depth interval 0.5–1.0 m. modelling, 1998 scenario). • Eutrophication-dependent algae must not oc- • Total P is regulated up or down by 3.4 µg P/l cur in a freely fl oating state. for each PSU change in salinity relative to the • Coverage of anchored fi lamentous algae: baseline of 12.2 PSU. <10% at all depth intervals. • Biomass of anchored fi lamentous algae (aver- Reference conditions for Odense Fjord, outer age for the whole outer fjord): <3 g C/m2. part The reference conditions for the three water bod- Nutrients ies into which the outer fjord has been subdivid- Nutrient loading of the outer fjord from the ed (see Section 1.8.4) is considered to be common catchment is presently considerable (Sections 3.4 as their hydrography are common and loading and 4.5.2, Figure 4.5.1). mainly derives from diffuse sources rather than With respect to nutrient concentrations, the point sources. reference conditions for the outer fjord should be established such that the biological state of Macrophytes the water body will be undisturbed or virtually Petersen (1892; 1901) and Ostenfeld (1908) de- undisturbed. scribed the depth distribution of eelgrass in the For total N, the reference conditions are outer fjord early in the last century and found hereafter calculated by empirical modelling of this to be 6–7 m. In reference conditions, eelgrass the relationship between total N and the depth thus covered the majority of the outer fjord, in- distribution of eelgrass (Nielsen et al., 2002). The cluding the deep northeastern basin and the deep resultant values for total N have been corrected channel Egense Deep in the northwestern part. as described above for Seden Strand. In addition, the rooted macrophytes should gen- The total N concentration has also been erally occur in dense communities. calculated by DHI (2002; 2003) for the above- The current distribution of vegetation in the mentioned “Natural state scenarios”. The annual outer fjord is described in Sections 1.8.1 and mean concentration of total N at station ODF17 4.5.2. (1 m) was calculated to be 260 µg N/l in 1998 It is assessed that the reference conditions and 320 µg N/l in 2002. These values are lower will correspond to the distribution of rooted than the empirically determined value used as the macrophytes early in the last century and that criterion for reference conditions, i.e. 370 µg N/l the occurrence of fi lamentous algae will also be (see below). limited to anchored specimens, such as described No corresponding empirical relationships exist for other corresponding fjords (Petersen, 1898). for total P. However, as with total N, 3D model- The biomass of anchored fi lamentous algae in ling of “Natural state scenarios” yields an annual reference conditions has been established on the mean concentration for total P at station ODF17 basis of measurements made by Fyn County in (1 m) of 10 µg P/l in 1998 and 20 µg P/l in 2002. such areas, as well as quantitative quality criteria New calculations currently being made with cor- established for other Danish fjords. The biomass rected riverine nutrient loading are expected to was converted to C from dry matter using the yield a somewhat lower calculated “natural state” relationships in Larsen (unpublished manuscript) nutrient level in the fjord. For the time being, and Fyn County (unpublished data). It should be the lower of the two above-mentioned values for noted that 3D modelling of “Natural state sce- total P is therefore used. This is supplemented narios” (DHI, 2002; 2003) yields a relatively low with correction of the nutrient concentrations seasonal peak biomass of freely fl oating macro- for salinity as described for Seden Strand. algae of 1.2–1.5 g C/m2 (average for the outer

Odense PRB Odense Pilot River Basin 63 1.8 Transitional waters and coastal waters

Nutrient criteria for reference conditions: relationships in Larsen (unpublished manuscript) • At an annual mean salinity of 18.1 PSU at and Fyn County (unpublished data). station ODF17 (1 m) in the outer fjord, the an- nual mean concentration of total N must not Macrophyte criteria for reference conditions: exceed 370 µg N/l (empirical modelling for • Rooted macrophytes must be present in dense the period 01/03–31/10 regulated 34% up to communities (>80% coverage): an annual mean value based on measurements • Depth distribution (main community) of eel- over the period 1981–2002). grass: ≥10 m. • Total N is regulated up or down by 49µg N/l • Coverage of eelgrass: >80% in the depth inter- for each PSU change in salinity relative to the val 1–10 m. baseline of 18.1 PSU. • Coverage of widgeon grass: >80% in the • At an annual mean salinity of 18.1 PSU at depth interval 0.5–1.0 m. station ODF17 (1 m) in the outer fjord, the an- • Eutrophication-dependent algae may not oc- nual mean concentration of total P must not cur in a freely fl oating state. exceed 10 µg P/l (dynamic 3D modelling, 1998 • Coverage of anchored fi lamentous algae: scenario). <10% at all depth intervals. • Total P is regulated up or down by 3.4 µg P/l • Biomass of anchored fi lamentous algae (aver- for each PSU change in salinity relative to the age for the whole of the outer fjord): <3 g baseline of 18.1 PSU. C/m2.

Secchi depth Nutrients The reference conditions for Secchi depth are With respect to nutrient concentrations in the also established from the relationship between water, the reference conditions for the border the depth distribution of the vegetation early in zone should be established such that the biologi- the last century (Ostenfeld, 1908) and the empiri- cal state of the water bodies will be undisturbed cal relationship between this depth distribution or virtually undisturbed. and the necessary transparency of the water dur- The reference conditions for total N were ing the growth season (Nielsen et al., 2002). The established on the basis of empirical modelling Secchi depth is presently approx. 3 m (summer as described above (although without any correc- mean). tion for salinity) In the 3D modelling of the “Natural state Secchi depth criterion for reference conditions: scenarios” the nutrient concentrations in the • 7.2 m (mean, March–October). marine border (i.e. the present border zone) were reduced relative to the current concentrations by Reference conditions for the border zone backwards extrapolation of N and P values from Macrophytes Kieler Bight for the period 1960–1989 (Helsinki Petersen (1892; 1901) and Ostenfeld (1908) de- Commission, 1990). For nitrogen the reduction scribed the depth distribution of eelgrass in the was 67%, thus yielding total N values of 94–97 border zone north of Odense Fjord early in the µg N/l for the modelling years 1998 and 2002 last century and found this to be 9–10 m. In (33% of the actual annual mean values measured reference conditions, eelgrass thus occurred in a those two years in the surface water at station dense, broad belt around the coast and reached ODF22B). This is somewhat lower than the out to a depth of approx. 10 m. empirically determined value used as the crite- It is assessed that the reference conditions will rion for reference conditions, i.e. 146 µg N/l (see correspond to the distribution of rooted macro- below). phytes early in the last century, and that the oc- Useful empirical relationships do not exist for currence of fi lamentous algae will be limited to establishing the reference conditions for total P. anchored specimens, such as described for other Using a similar backwards extrapolation for total corresponding fjords (Petersen, 1892; 1901). The P at station ODF22B (1 m) as that used for total biomass of anchored fi lamentous algae in refer- N above in the “Natural state scenarios” yielded ence conditions has been established on the basis an annual mean concentration of 25% of the of measurements made by Fyn County in such measured value (75% reduction), corresponding areas, as well as quantitative quality criteria es- to a very low level of 5–6 µg P/l for the two tablished for other Danish fjords. The biomass years. was converted to C from dry matter using the New calculations are currently being made,

Odense 64 PRB Odense Pilot River Basin 1.8 Transitional waters and coastal waters

however, and it is expected that these calcula- Northern Belt Sea Figure 1.8.8 tions will yield a somewhat lower “natural state” Map of Odense Fjord level for the nitrogen concentration in the border indicating areas E g e n encompassed by the zone, but not for the phosphorus concentration. s G OTTERUP e a D b quality objective e Odense e e t p Nutrient criteria for reference conditions: Fjord "Reference area for Outer scientifi c studies" in • The annual mean concentration of total N at fjord Fyn County's Regional station ODF22B (1 m) must not exceed 146 Plan for 2001–2013. µg N/l (empirical modelling for the period Areas designated as MUNKEBO 01/03–31/10 regulated 3.7% up to an annual KERTEMINDE international protec- Seden mean value based on measurements made by Strand tion sites (Natura 2000 Fyn County over the period 1981–2002). sites, which in Odense Fjord encompass sites • The annual mean concentration of total P at Depth station ODF22B (1 m) must not exceed 5 µg 30-40 m protected under the 20-30 m Habitats Directive and P/l (dynamic 3D modelling, 1998 scenario). 10-20 m 6-10 m Birds Directive) are 4-6 m ODENSE 0 5 km 2-4 m also indicated. Secchi depth 0-2 m The reference conditions for Secchi depth are Reference site also established from the relationship between Natura 2000 site the depth distribution of the vegetation early in the last century (Ostenfeld, 1908) and the empiri- cal relationship between this depth distribution and the necessary transparency of the water dur- ing the growth season (Nielsen et al., 2002). The tion Agency’s remarks on the draft bill on imple- Secchi depth is presently approx. 7.5 m (summer mentation of parts of the WFD and the Habitats mean). Directive, the overall aim for the marine waters is to transfer the current objectives directly such Secchi depth criterion for reference conditions: that areas with a general (basic) quality objective •9.0 m (mean, March–October). shall in future have to fulfi l “good ecological status” pursuant to the WFD. With regard to areas assigned a stringent quality objective in the 1.8.6 Provisional establishment of objec- current recipient quality plans, or areas where tives the state is actually better than the criteria for good status, the county authorities shall ensure Due to the natural qualities of Odense Fjord, the that these higher objectives are preserved. For northwestern part at Egense Deep has been des- Odense Fjord, this will entail that the area at ignated as a “reference area for scientifi c studies” Egense Deep that is currently assigned a high (stringent quality objective) in Fyn County’s Re- (stringent) quality objective will have to fulfi l the gional Plan for 2001–2013. The quality objective WFD requirements for “high ecological status”, for the remainder of the fjord is “fi sh waters for while the remainder of the fjord will have to ful- angling and/or fi shery” and, where the natural fi l the requirements for “good ecological status”. conditions permit, “spawning and/or nursery A large part of the fjord is presently designated grounds for fi sh” (general/basic quality objec- as a Natura 2000 site pursuant to the Habitats Di- tive). rective and Birds Directive, yet is only assigned a Moreover, the whole of the inner fjord, Seden general quality objective in the Regional Plan. Strand, and the western part of the outer fjord, In order to ensure adequate protection of the has been designated as an international nature nature qualities that justifi ed designation as a protection area (Natura 2000), see Figure 1.8.8. Natura 2000 site, i.e. achievement of good pres- The fjord is also encompassed by a number of ervation status for species and habitat types se- other protection regulations (see Section 2 on lected pursuant to the Habitats Directive or Birds protected areas, Figure 2.6 and 2.7). Directive, these areas will in future have to meet The quality objectives stipulated in the Re- at least “good ecological status” pursuant to the gional Plan serve as the basis for establishing WFD. It is as yet unclear whether consideration environmental objectives pursuant to the WFD. for the species that comprise the basis for designa- According to the Danish Environmental Protec- tion of sites in the fjord pursuant to the Habitats

Odense PRB Odense Pilot River Basin 65 1.8 Transitional waters and coastal waters

Table 1.8.2 Area Present Future Water body Type 2 HM The fi ve marine water (km ) objective objective bodies encompassed by Inner fjord (Seden Strand) 1 14 No General, P G Odense River Basin in- dicating type and area ODF NW 2 14 No Stringent, P H and present and future objective. See Figure Outer fjord ODF NE 2 19 No General G 1.8.6 for delineation of ODF Mid 2 13 No General, P G the water bodies. Boundary zone 3 74 No General G

P: International Natura 2000 protected site (Habitat Site, EC Bird Protection Site). H: High ecological status. G: Good ecological status. General: Regional Plan objective that all coastal waters should be suitable as fish waters for angling/fishery and, where the natural conditions permit, suitable as spawing and/or nursery areas for fish. Stringent: Regional Plan objective that the recipient should be a reference area for scientific studies. HM: Heavily modified water body. Type 1: Inner fjord, salinity <18 PSU. Type 2: Fjord, salinity 7–18 PSU, mean depth 0–3 m Type 3: Inner marine waters between Djursland/Sjællands Odde and Fyns Hoved/Røsnæs, salinity 15–20 PSU, depth <15 m.

Directive and the Birds Directive, as well as for preservation status (Dahl et al., in press; see also their habitat conditions such as food resource in Section 2). the form of macrophyte vegetation, water level Areas of Odense Fjord that are designated as in wetlands etc. can entail requirements different Natura 2000 sites, but which have not been as- from those that have otherwise to be fulfi lled to signed the highest quality objective in the cur- meet good ecological status (Søgaard et al., 2003). rent recipient quality plans, are thus assigned In the case of certain marine habitat types, it is the provisional environmental objective “good considered necessary to achieve “high ecologi- ecological quality” (i.e. Seden Strand and ODF cal status” in order to be able to achieve good mid; Table 1.8.2 and Figure 1.8.6).

“LIV II” Fyn County’s surveillance vessel.

Photo: Fyn County

Odense 66 PRB Odense Pilot River Basin