1.4 Watercourses

1.4.1 Location, size and density is believed that it will hereafter remain necessary to operate with several levels of monitoring in or- Danish watercourses, including those in Odense der to achieve a suffi ciently adequate description River Basin, are typically lowland watercourses of watercourse status to enable prioritization of (terrain height under 200 m). In a European environmental initiatives and the selection of the perspective, they are all very small (Figure 1.4.1). most appropriate measures to improve water- The largest watercourse in Odense River Basin is course environmental quality. the River Odense (catchment 630 km2), the main reach of which is just under 60 km long and up to 30 m wide. The density of open watercourses 1.4.2 Typology in the basin as a whole is approx. 1.0 km/km2. The original (natural) density of the watercourse According to the WFD, the watercourses have network was probably somewhat greater (up to to be differentiated into types in order to es- 1.5-fold). However, the density is of the same tablish relatively uniform groupings for which magnitude as in the other Nordic countries and the natural reference conditions are relatively Great Britain (as well as in parts of the USA). homogenous. Annex II of the WFD provides In Odense River Basin, the very small water- two typology systems for differentiating the courses account for a considerable proportion watercourses, namely System A and System B. of the watercourse network (Table 1.4.1). Even As Danish watercourses are so small, the use of though the watercourse system is incomplete, System A in its present form is inappropriate. the relative distribution of the watercourses in Two other systems for differentiating Danish size categories does not differ very much from watercourses have therefore been tested. the expected natural distribution (Horton’s laws One of the systems in principle resembles Sys- of stream number and stream lengths; see Dodds tem A, but contains elements of System B (Table & Rothman, 1999). 1.4.2). This typology, which has been developed Due to resource constraints, the many small by the National Environmental Research Insti- watercourses are relatively under-represented tute, has so far only been notifi ed nationally. in the current monitoring (Table 1.4.1). They According to this system, Danish watercourses encompass both spring brooks, summer-dry are differentiated according to location east or (temporary) watercourses (which should be in- west of the line formed by the Weichsel ice front cluded as watercourses – and not as wetlands) and ditches established in connection with drainage of wetlands. Even though our knowledge of the Width 2 m 2–10 m >10 m Table 1.4.1 small watercourses is generally less than that of Size distribution of Watercourse the larger watercourses, the small watercourses 730 330 42 watercourses and length (km) monitoring stations in are considered to be a very important part of Percentage of Odense River Basin. 66 30 4 the watercourse network. Thus the small wa- total length tercourses together contain just as many species No. of monitoring 101 192 15 of macroinvertebrates as the larger watercourses stations (including also special spring species), just as Percentage of 33 62 5 many small watercourses are important spawn- stations ing and nursery grounds for salmonids. Given that the small watercourses are of Table 1.4.2 such great signifi cance, they, like the larger Typology of Danish watercourses, should also be included when watercourses proposed identifying water bodies (Section 1.4.3). As it is Type 1 2 3 by the National Envi- impracticable to investigate them all, it would be Stream order (Strahler ronmental Research In- 1–2 3–4 >5 appropriate to aggregate them into groups. Ag- system) stitute (M.L. Pedersen, personal communica- gregation could be carried out for each type (Sec- 2 Catchment area (km ) <10 10–100 >100 tion 1.4.2) according to the main threats/pres- tion). The watercourses in Odense River Basin Width (m) 0–2 >2–10 >10 sures. The monitoring and subsequent reporting lie east of the line could thereafter be restricted to a representative Distance to source (km) <2 2–40 >40 formed by the Weichsel fraction of the water bodies within each group. It ice front.

Odense PRB Odense Pilot River Basin 21 1.4 Watercourses

Figure 1.4.1 tested in part of Odense River Basin (Figure Map of Odense River 1.4.2) and is fully practicable when appropriate N Basin showing the calculation methods are used to defi ne catchment complete watercourse network. boundaries and to determine watercourse length. Watercourse width (if possible the winter width of the water surface, otherwise the summer width of the water surface) and the catchment area are the parameters that are easiest to work with. That stream order and distance to source are more diffi cult to work with is due to the fact that it can be diffi cult to locate the source (often piped) and to differentiate artifi cial reaches from natural reaches in the upper parts of the watercourse systems. For Danish watercourses, it has been shown that the composition of the plants, macroinvertebrates and fi sh is closely correlated with watercourse size (Fyn County, 2000a; Wa- terFrame, 2003). The macroinvertebrate fauna also correlates with the watercourse slope, which in turn is negatively correlated with watercourse size (Wiberg-Larsen et al., 2000). The second system (Table 1.4.3) is based in 0 5 10 km part on theoretical considerations, according to which the magnitude and variation of water fl ow and the watercourse slope considerably infl uence and thereafter according to size. The typology conditions for the fl ora and fauna. Thus many of each individual locality is assessed from four reaches can more or less regularly dry out in appropriate (and mutually positively correlated) summer, especially the very small watercourses size components. A locality is assigned a type and the upper reaches of the larger watercourses. in accordance with the dominance principle. In Furthermore, the slope is decisive for fl ow rate cases of equal distribution between two types, and the composition of the bottom substrate. the size of the catchment area is the decisive de- Runoff is described from the median minimum terminant of type. This principle is employed to value. For Fyn County as a whole this is deter- ensure that the system can be used throughout mined with an average density of 1 location per 5 Denmark irrespective of regional or local dif- km2. For Odense River Basin, the corresponding ferences in topography. The method has been density is 1 location per 4.4 km2. The project part- ner, DDH, has tested this method in the Lunde Stream system and concluded that the selected Table 1.4.3 Alternative type 1 2 3 parameters can be accurately determined, and An alternative typol- that the method is easy to use and not very time- ogy of Danish water- 2 Catchment area (km ) <10 10–100 >100 consuming (DDH, 2003). The relationship to the courses proposed by DDH (2003). In this Runoff, median min biological conditions still remains to be tested, 2 <0.2 0.2–2,0 >2.0 system the three vari- (l/s • km ) though. There is no doubt, however, that at least the naturally summer-dry watercourse reaches ables should be consid- Slope (m/km) <0.25 0.25–0.75 >0.75 ered independently of have reference conditions that differs markedly each other.

Table 1.4.4 Physical pressure Specification of extent Physical modiﬁ cations initially examined in Piped reaches km (and pipe diameter) the Ryds Stream catch- Other regulation (straightening, deepening) Grade 0–3 ment and the main Bank stabilization (stones/fascines) +/- course of the River Maintenance (weed cutting/dredging) Grade 0–3 Odense. Obstructions for fish Number (height and upstream damming effect) Stormwater discharges (hydraulic stress) Number (and frequency) Sand transport Grade 0–3 Drainage (flood plain) Grade 0–3

Odense 22 PRB Odense Pilot River Basin 1.4 Watercourses

Figure 1.4.2 N Map indicating the N watercourse typology for the Ryds Stream catchment and the upper parts of the River Odense system.

Type 1

0 1 2 3 km Type 2

Type 3 from that of permanently ﬂ owing watercourse Basin reaches. Moreover, the reference conditions of watercourse reaches with a naturally very gentle slope can be expected to differ markedly from that of those with a steeper slope.

1.4.3 Delineation of watercourse reaches

The complete method for delineating watercourse reaches was initially tested on the Ryds Stream 2 catchment (area 46 km ) and the main course of 0 5 10 km the River Odense (length 60 km) calculated from the source of Rislebæk Brook to the outlet in Odense Fjord (Figure 1.4.3). In addition, part of the physical conditions is available it is compared the identifi cation process (excluding assessment with the results of the biological monitoring. In of physical modifi cation) has been tested in the addition, the presence of different forms of na- Lunde Stream catchment (area 70 km2) (DDH, tional and regional protection is incorporated in 2003). Applying the criteria in the EU horizon- the assessments. Delineation of water bodies has tal guidance “Identifi cation of water bodies” to thus primarily been based on knowledge of the these three test areas together with the criteria watercourses’ current status assessed from the ex- for identifying heavily modifi ed water bodies isting knowledge about the physical and biologi- (Section 1.4.4) yields 13, 16 and 14 water bodies, cal quality. It should be noted that the biological respectively, i.e. an average of 1 water body per 4 status is primarily described from the existing km of watercourse. The individual water bodies Danish assessment system, whereby macroin- vary in length from 1 to 12 km. If the present vertebrates are utilized as “indicators” for the level of detail is maintained, an estimated 280 biological conditions in general (Danish Stream water bodies should be identifi able in Odense Fauna Index; Skriver et al., 2000). The status is River Basin solely from the watercourse systems. measured as fauna classes on a scale from 1 (poor- This fi gure is preliminary and could be revised as est) to 7 (best). According to the guidelines, the experience with the pilot project progresses. Fur- riparian zone is counted as a biological quality el- thermore, aggregation of the smaller watercourse ement. No decision has been made as to how this reaches in particular is being considered. zone should be delineated from wetlands along To facilitate the identifi cation of the water bod- the watercourses, though, and consequently the ies, watercourse physical conditions have been zone has not been included as an element in their charted on the basis of information from the identifi cation. watercourse regulations (only county and municipal watercourses), preliminary investigations in connection with wetland projects and moni- 1.4.4 Physical modifi cation toring results (see also Section 1.4.4). The whole process of assessing the physical conditions is An analysis of large watercourses in Fyn County very time-consuming, among other reasons (county watercourses) reveals that approx. 46% because much of the data is usually only avail- are regulated, and have thereby been shortened able in paper form or has to be collected from by 5–10%. The extent to which the minor wa- the municipal authorities. When information on tercourses have been regulated is unclear, among

Odense PRB Odense Pilot River Basin 23 1.4 Watercourses

Figure 1.4.3 Map indicating the wa- N RWB 3 N ter bodies in the Ryds RWB 4 RWB 2 Stream catchment and RWB 5 RWB 13 RWB 11 the main course of the River Odense. RWB 10 RWB 12

RWB 1 RWB 8 RWB 7 RWB 6 RWB 9 OWB 16

0 1 2 3 km OWB 14 OWB 15

OWB 13 OWB 12 other reasons because many changes of course OWB 11 and length were made long ago (before 1850). A general phenomenon, though, is that the upper sections of the watercourses are more heavily OWB 10 modifi ed than the lower sections. In many plac- es, the upper sections are piped, often including OWB 8 OWB 9 OWB 7 the natural source. An analysis of known piped sections in the whole of Odense River Basin OWB 4 OWB 6 Lake Arreskov OWB 5 shows that approx. 25% of the total watercourse OWB 3 network is piped, although the real fi gure is un- OWB 2 doubtedly signifi cantly higher. Of the remaining OWB 1 open watercourses in Odense River Basin, 60% 0 5 10 km are estimated to be regulated. All in all, the majority of the watercourses are therefore modifi ed by man to some extent. At the same time, of physical modifi cation, an analysis has been though, it is clear that some of these modifi ca- made of the main physical pressures affecting tions are very old such that the environmental a number of sub-reaches (Table 1.4.4). It should quality of at least some reaches have considerably be noted that it has not been possible to identify improved in the course of time through “natural actual artifi cial reaches in the areas tested with re-establishment” (Brookes, 1984), and hence can certainty, even among the smaller, upper ends no longer be considered as heavily modifi ed. of watercourses. Different forms of artifi cially The procedure for the provisional identifi ca- established bypasses through which part of the tion of heavily modifi ed water bodies (Guid- watercourse water passes, for example at dams ance Document 2.2) has in the fi rst instance and weirs in the main course, are thus included been tested on the Ryds Stream catchment and as part of a modifi ed water body. the main course of the River Odense (see also Table 1.4.4 is based on work with two test lo- Section 1.4.3). For use in assessing the degree calities. It is not complete with regard to either

Table 1.4.5 WB No. HM FC Remarks Water bodies (WB) in the main course of the 1 + 4 Regulated, restoration planned, mean slopes 1.2–2.9 m/km River Odense indicat- 2 - 7 Unregulated, sinuous, mean slopes 2.8–6.9 m/km ing the occurrence of 3 + ? Regulated, mean slopes 0.1–4.6 m/km heavy modiﬁ cation 4 - - Lake Arreskov (HM), biological status (FC = fauna 5 + 3–4 Regulated, affected by fluctuation in water level (periodic outflow of water from the lake) class) assessed from the 6 - 5–6 Regulated, but with a rather varied bottom substrate macroinvertebrates 7 - 5–6 (pre) Under restoration (remeandering) (Danish Stream Fauna 8 + ? Regulated, affected by damming, technical structures Index), and remarks 9 - 5–7 Unregulated, sinuous 10 - 5–7 Regulated, but with a rather varied bottom, restoration planned concerning physical 11 - 5–7 Unregulated, sinuous potential. 12 + 3–4 Affected by damming, technical structures 13 - 5–6 Regulated, but with a rather varied bottom substrate 14 + 3–5 Regulated, several technical structures 15 - 4–6 Slightly regulated 16 + 4 Affected by salt water, cooling water and impoundment

Odense 24 PRB Odense Pilot River Basin 1.4 Watercourses

watercourses in Fyn County or in Denmark as dams, weirs, etc. that cause signifi cant impound- a whole. For example, it lacks groundwater ab- ment of the water or the formation of upstream straction, which in some cases can considerably lakes are also a major physical modifi cation. In affect watercourse fl ow and hence also hydro- the main course of the River Odense, 7 out of 15 morphology (especially in the watercourses of reaches corresponding to 33% of the main course eastern Denmark, to which those of Fyn County (20 km) have thus been provisionally designated belong, and which are affected by water abstrac- as heavily modifi ed (Table 1.4.5). The main tion to supply the major towns). In general, course also contains other reaches that have been though, the analysis is a good tool for use in the severely regulated over the years, but where most subsequent design of restoration scenarios and of them have a fauna class >5 (i.e. good status or for prioritization of efforts to improve the status better) and a relatively varied bottom substrate. It of the water bodies. During the work process it has been decided not to designate these reaches as transpired that information about drainage of the heavily modifi ed water bodies. fl oodplain is diffi cult to obtain, and only sporadic While subdivision of the main course is in prin- information is available about sand transport and ciple “quite simple”, this is not the case with the bank stabilization. In addition, it is characteristic minor watercourses due to the fact that they are that the data material is best for the major wa- often very fragmented by piped sections/dams tercourses, whereas knowledge about the small or other forms of regulation (straightening/ watercourses is more limited. With two of the deepening). Subdivision into sub-reaches accord- tributaries of Ryds Stream catchment it has been ing to physical status might therefore result in necessary to make a fi eld inspection. In these an enormous number of water bodies, which is cases it will be necessary to clarify the degree of naturally undesirable. Conversely, merging of detail to be recorded, and to draw up unambigu- too many sub-reaches into a single water body ous operational methods for assessing the extent entails that it will be possible to designate them of physical modifi cation at the national level. all as heavily modifi ed irrespective of the fact The most extensive physical modifi cations are that some sub-reaches could have a very good piping and straightening/deepening, where the status as assessed from fauna class and physical form of the watercourse and drainage status of conditions. There is therefore a general need to the surroundings are radically altered, and where draw up more exact criteria for what is meant by efforts are subsequently made to maintain this “heavily modifi ed”. status through intensive watercourse mainte- The water bodies in the Ryds Stream catch- nance (frequent weed cutting and dredging of ment have provisionally been designated as heav- bottom substrate). The establishment of major ily modifi ed according to the criteria in Table

Table 1.4.6 Physical pressure Extent (percentage of reach length) Criteria for prelimi- Piped reaches >50 nary identiﬁ cation of Regulation (grade 2–3) >75 heavily modiﬁ ed water Piped reaches and regulation (grade 2–3) >75 bodies. Maintenance (grade 3) >50 Hydraulic stress (considerable pressure) >50

Table 1.4.7 WB No. HM FC Remarks Water bodies (WB) 1 + 4 Upper parts piped, mean slopes 4.4–5.6 m/km in the Ryds Stream 2 + 5 Partially piped, with spring, mean slopes 6.4–20 m/km catchment indicat- 3 + ? Highly regulated, lower part piped, mean slope 0.9 m/km ing the occurrence of 4 + - Completely piped heavy modiﬁ cation 5 + - Completely piped (HM), biological status 6 + 4–5 Several piped/regulated sections, lower part sinuous, mean slopes 5.4–11 m/km (FC) assessed from the 7 - 4–6 Upper parts piped, remainder sinuous, many small obstructions, mean slope 10 m/km macroinvertebrates 8 + 4–5 Upper parts piped, with springs, mean slope 9.2–13 m/km (Danish Stream Fauna 9 + ? Upper parts piped, mean slopes 1.5–3.2 m/km Index) in the open part 10 - 5 Unregulated, sinuous, mean slope 9.0 m/km 11 - 5–7 Unregulated, slightly sinuous, mean slope 2.4 m/km of the watercourse, and 12 - 6–7 Regulated, but sinuous, mean slopes 1.2–1.8 m/km remarks concerning 13 + 4 Unregulated, sinuous, very affected by hydraulic stress, mean slope 3.8 m/km “physical potential”.

Odense PRB Odense Pilot River Basin 25 1.4 Watercourses

1.4.6. As a consequence, 9 out of 13 water bodies ing to the expected conditions if undisturbed by can be considered to be heavily modifi ed (Table human activity. For each watercourse reach of 1.4.7), corresponding to 65% of the total water- known type, an assessment has to be made of course network in the catchment. It is empha- the extent to which the current status deviates sized that the criteria established are provisional, from the “natural background conditions”. There and that changes can occur as the pilot project are several possibilities for describing the refer- progresses. ence conditions, namely using current data from No attempt has been made to identify heavily virtually undisturbed Danish watercourses or physically modifi ed watercourse reaches in the comparable foreign watercourses, historical and Lunde Stream system. palaeolimnological data, or, if necessary, data Based on experience to date, and applying the from expert judgements. criteria in Table 1.4.6, it must be presumed that Assessment of the extent to which suitable around 60% of the total watercourse network in reference stations exist is primarily based on Odense River Basin will be provisionally desig- the macroinvertebrate fauna, for which the data nated as heavily modifi ed. material is generally greatest. For natural reasons (cf. the island biogeographic principles on spatial 1.4.5 Reference conditions extinction and immigration), there are clear differences between the macroinvertebrate fauna Under the provisions of the WFD, reference con- in Jutland, Fyn + Zealand, and Bornholm. In ditions must be established for each type of wa- addition, man has enhanced this difference in tercourse (Guidance Document 2.3) correspond- various ways.

Table 1.4.8 Data series Watercourse Locality Type No. of data sets (yr) Stations assessed as being suitable as Historical Lindved Main road A1 2 4 (1947–1950) reference stations for biological conditions Stavis Upstream of Lærkehus 2 4 (1951–1952) in watercourses in Fyn Stavis Lake Langesø forest 2 1 (1952) County. The data in Stavis Morud forest 2 1 (1947) (3 outliers excluded) question primarily Stokkebæk Mullerup forest 2 1 (1945) concern macroinverte- Stokkebæk Skrams Vænge 2 1 (1945) brates and are included Odense Lykkensprøve 3 5 (1942–1955) in the analysis shown in Figure 1.4.4. Rislebæk Sollerup 1 Several (2001 selected) Present-day Stamperenden Idyllendal 1 Several (2001 selected) Ørredbæk Forest road 1 Several (2001 selected) Brende Tanderup 2 Several (2001 selected) Hattebæk Upstream of fish farm 2 3 (1996–1998) Hattebæk Faldsled–Jordløse road 2 Several (2001 selected) Hågerup Downstream of Hågerup 2 Several (2001 selected) Kongshøj Ågård 2 Several (2001 selected) Lindved Main road A1 2 Several (2001 selected) Stokkebæk Dyregård 2 Several (2001 selected) Tange Downstream of Skovmøllen 2 Several (2001 selected) Traunskov-afløb Vissenbjerg–Morud road 2 Several (2001 selected) Vindinge Rønninge 2 Several (2001 selected)

Odense Vibæk 3 Several (2001 selected)

Table 1.4.9 Objective Classification (Danish EPA, 1983a) Required FC Existing system of objectives used in Fyn Reference area for scientific studies A (Areas of special scientific interest) >5 County and the requirements stipulated Salmonid spawning and nursery waters B1 and B2 (Salmonid waters) >5 for fulﬁ lment of the Fish waters for angling/fishery B (Cyprinid waters) >5 objective. 3 Aesthetically satisfactory, etc. C–F (Eased objectives) >4

Odense 26 PRB Odense Pilot River Basin 1.4 Watercourses

The fi rst step taken was to examine which MDS for stream macroinvertebrates Type 3_ref_old regional data could be used to describe the refer- Type 3_ref_new Figure 1.4.4 Type 3_other_new Multidimensional ence conditions for watercourses in Fyn County Type 2_ref_old Type 2_ref_new scaling (MDS) for ma- (Table 1.4.8). As is apparent, the data material Type 2_other_new is generally rather sparse (7 old and 14 new sta- Type 1_ref_new croinvertebrates in the Type 1_other_new watercourses of Fyn. tions). Comparison of the macroinvertebrate The data derive partly fauna by multidimensional scaling (MDS) on from new (new) and the basis of the Bray Curtis similarity shows that historical (old) refer- there is a clear difference between old (histori- ence stations (ref, see cal) and new data sets (Figure 1.4.4). In making Table 1.4.8), and partly the analysis, attempts were made to compensate from remaining (other) for the fact that the methods employed earlier new watercourse sta- in time differ from those currently employed tions where the com- (quantitative data have been normalized, a few position and density of macroinvertebrates species have been aggregated; in addition, species have been comprehen- composition was tested for alone, with the same and 3.000 years ago, respectively (Klink, 1989; sively investigated. result.) Overall, the results indicate that it is not Wilkinson, 1987). Such studies are also feasible The distance between possible – even using the best stations currently in Denmark, for example in the fl oodplain of the points refl ects the available – to fi nd a macroinvertebrate fauna the River Odense. The method has already been difference in the fauna quite resembling that which previously existed tested on 10 300 year-old watercourse sediments between the individual (certain species have become extinct, and with from the Great Belt (Wiberg-Larsen et al., 2001). stations. The stress of others immigration can be expected to take a A good initial suggestion for the reference the ordination is 0.14 very long time). The same undoubtedly applies conditions for watercourses in Fyn County is (i.e. a useful 2-dimen- sional picture). to plants, for which the data material is even reaches with a natural course, good hydraulic smaller (e.g. Riis et al., 1999). contact with the surroundings, no or very ex- As impoverishment of the watercourse fl ora tensive utilization of the surrounding land, gen- and fauna due to human activities has been con- erally varied physical conditions in and around siderable, especially over the past 100 years (e.g. the watercourses, clean water with a low nutrient Riis & Sand-Jensen, 2001; Jensen & Jensen, 1980), content and a naturally varied fl ora and fauna the lack of suitable reference data is expected to both in and around the watercourses. These apply to large parts of the country. There is thus conditions will be close to that described as high a need to establish a suitable network of reference ecological status in Section 1.4.6. stations in Danish watercourses, and it will probably also be necessary to utilize data from reference stations abroad (southern Sweden, northern 1.4.6 Provisional establishment of Germany, southern Baltic countries, northern objectives Poland). There is a particular lack of data for all relevant biological quality elements (plants, Fyn County’s current Regional Plan stipulates a macroinvertebrates and fi sh), and knowledge of quality objective stating the use for which each the hydromorphological quality elements under watercourse should be suitable (Table 1.4.9). reference conditions also needs to be improved. Whether a watercourse fulfi ls its quality objec- For comparative purposes, consideration should tive is determined biologically from the fauna be given to the use of independent expert judge- class (Danish Stream Fauna Index). Since the ment for selected quality elements, for example fauna class at a given location can vary from year for part of the macroinvertebrate fauna (regional species lists) and fl ora (regional species lists). Finally, it is possible to gain an impression of Ecological Required FC Requried FC Table 1.4.10 the composition of the macroinvertebrate fauna status (slope >0.1 m/km) (slope 0–0.1 m/km) Summary of how the fauna class (cf. DSFI) and fl ora in watercourses of the past – before the High 6–7 5 (if possible) impact of human activities became extensive – by can initially be used to employing palaeolimnological methods. Investi- Good 5 4 assess watercourse ecological status. It should gations of subfossil insect remains in “old” water- Moderate 4 3 be noted that a greater course sediments have thus been successfully uti- number of quality ele- lized to describe the macroinvertebrate fauna in Poor 3 2 ments will be included the lower part of the Rhine (Germany/Holland) Bad 1–2 1 in the assessment in and the River Avon (England) for 100–250 future.

Odense PRB Odense Pilot River Basin 27 1.4 Watercourses

Table 1.4.11 Water Physical Surroundings Size Biology Variables included in chemistry conditions the data analysis for Percentage of farmland in Catchment NH -N, mean Degree of shading No. of species/taxa: 103 monitoring sta- x catchment area NO -N, mean Percentage Macrophytes tions in watercourses Woodland, nearest 25 m Winter width x stone+gravel Macroinvertebrates PO -P, mean in Fyn County. The Trees/bushes, nearest 2 m Max depth 4 Degree of sinuousity Fish physical index is cur- High (>0.5 m) herbaceous BOD5, mean Pools + riffles Coverage: rently calculated as a plants, nearest 2 m Roots All macrophytes modiﬁ ed Aarhus Index Herbaceous plant diversity, Degree of regulation Submerged (after Kaarup, 1999; nearest 2 m Physical index macrophytes but with plants, cf. the Fauna class (DSFI) unpublished proposal Fish index drawn up by the Physi- cal Index Working Group), and the ﬁ sh index is calculated according to WaterFrame (2003).

Table 1.4.12 BOD NH -N NO -N PO -P Status Physical index DSFI Fish index 5 x x 4 Summary of how dif- mg/l (mg/l) (mg/l) (mg/l) ferent variables can High >33 6–7 55–60 <0.5 <0.05 <0.8 <0.020 be used to assess the Good 25–33 5 47–54 0.5–2.0 0.05–1.0 0.8–2.0 0.020–0.040 ecological status of Moderate 17–24 4 38–46 2.1–3.5 1.1–2.5 2.1–5.0 0.041–0.090 watercourses. It should Poor 8–16 3 24–37 3.6–5.0 2.6–5.0 5.1–7.5 0.091–0.170 be noted that these Bad <8 1–2 12–23 >5.0 >5.0 >7.5 >0.170 considerations are only preliminary. The basis for the classifi cation is as follows: Physical to year, among other reasons due to differences over, the WFD prescribes the use of considerably index: Kaarup (1999); in precipitation and hence runoff, the objective more quality elements, including both physico- Fish Index: Water- is only considered to be fulfi lled in regional envi- chemical elements and other biological elements Frame (2003); Water chemistry: Prelimi- ronmental administration if the minimum fauna (Guidance Document 2.3). nary data and for high class requirement has been met for at least fi ve In order to determine what consequences status among others consecutive years. this can have, a more detailed analysis has been Kristensen & Hansen Under the provisions of the WFD, watercours- made of data from 103 monitoring stations in (1994). es have henceforth to be subdivided into fi ve Fyn County for which more detailed informa- classes of ecological status. The objective here is tion is available, for example on land use and that all water bodies should achieve good ecologi- physico-chemical and biological conditions. As cal status by 2015 at the latest, while at the same regards size and fauna class, the stations turned time preventing deterioration in the existing sta- out to be reasonably representative for the whole tus. A simple and manageable means of convert- regional station network, as well as for the sta- ing to the new system is to initially continue to tion network in Odense River Basin, although, employ the macroinvertebrate fauna to assess ful- as mentioned earlier, the smallest watercourses fi lment of the objective (Table 1.4.10). This is not are under-represented in the monitoring (Section without problems, though, as the DSFI employs 1.4.1). The analysis encompassed an initial selec- a 7-step scale and the WFD a 5-step scale. More- tion of the strongest descriptive variables in the Table 1.4.13 data set (Table 1.4.11) and subsequent statistical Watercourse total N analysis of these variables (see Annex 1.4). From and total P concen- Ecological Total N Total P this it is apparent that there is a positive correla- trations for different status (mg/l) (mg/l) tion between the selected biological variables and ecological status classes. High <1.0 <0.030 watercourse size, the presence of natural, varied This also gives the physical conditions in the watercourse and the requirements that wa- Good 1-0–2.5 0.030–0.060 presence of woodland around the watercourse, tercourses will have to respectively. Correspondingly, there is a nega- Moderate 2.6–6.0 0.061–0.125 meet in order to attain tive correlation to the degree of anthropogenic high and good ecologi- Poor 6.1–9.0 0.126–0.250 cal status in lakes and pressure described by land use for agriculture, watercourse regulation and input of easily me- coastal waters, respec- Bad >9.0 >0.250 tively. tabolizable organic matter (BOD5) and nutrients

Odense 28 PRB Odense Pilot River Basin 1.4 Watercourses

Ecological status from the surroundings, respectively. It should 100 Fauna class (DSFI) Figure 1.4.5 be noted that even though BOD5 is of relatively minor signifi cance in this data set (Annex 1.4), an 80 Distribution of 103 analysis of small watercourses alone would show watercourse stations 60 according to ecological that its signifi cance for biological conditions is 40 status classes for the considerably greater (Fyn County, 2001c). physical, chemical and When the indices employed for the 103 moni- 20 biological variables toring stations are distributed according to eco- listed in Table 1.4.12. 100 logical status classes it is seen that the status is Fish index These variables were generally assessed as being poorer for fi sh and 80 selected on the basis of physical conditions than for macroinvertebrates the statistical analysis 60 (Figure 1.4.5; Table 1.4.12). That the fi sh index described in Annex 1.4. indicates a relatively greater share of watercours- 40 es with bad status than the physical index is in 20 part attributable to the fact that certain forms of physical disturbances – for example dams, weirs 100 Physical index and drying-out – are not included in the physical 80 index (just over 40% of all the stations rated by the fi sh index as having bad status are affected 60 by one or more of these). At the same time it is 40 emphasized that speedy completion of the fi nal physical index is vital, and that the development 20 of a suitable index for plants is highly desirable. 100 Attempts have also been made on a trial basis BOD5 to subdivide into status classes for the water 80 chemistry variables that were included in the 60 statistical analysis (Figure 1.4.5; Table 1.4.12; Annex 1.4). It should be noted that even though 40 nitrogen and phosphorus are usually input to 20 the fl owing water in such large amounts that the 100 watercourse plants are not limited by them, and NH x-N the macroinvertebrates and fi sh are hardly likely 80 to be affected either (Section 4.2), the input of (%) stations watercourse of Proportion 60 these substances is of great signifi cance for the status of other categories of water body (lakes, 40 coastal waters, etc.) fed by the watercourses. In 20 many cases it will therefore be necessary – out of consideration for these water bodies – to include 100 NO x-N nitrogen and phosphorus as an important part of 80 the assessment of watercourse status. A suggestion for the distribution of the total content of 60 these substances across the status classes is shown 40 in Table 1.4.13. Apart from the above-mentioned methods, the status of Danish watercourses can 20 be assessed from other variables such as maxi- 100 mum temperature and pH, as well as the content PO 4-P of oxygen, ochre (especially in Jutland) and 80 various hazardous substances, and the necessary 60 amount of water (see also Figure 4.2.1). In any 40 event, it will be necessary to decide how these variables should be weighted against each other 20 in the fi nal system for determining the ecological status of the watercourses. High Good Moderate Poor Bad Part of the River Odense system, including large parts of the main course and the tributaries Hågerup, Sallinge and Lindved Streams, are

Odense PRB Odense Pilot River Basin 29 1.4 Watercourses

Ryds Stream – a reach surrounded by woodland.

Photo: Bjarne Andresen, Fyn County

encompassed by the Habitats Directive. It is would otherwise have to fulﬁ l in order to achieve therefore important that there is a good corre- good watercourse ecological status. lation between the two ways of assessing status Concrete suggestions for the provisional estab- that accompany the two Directives. Thus high lishment of objectives for the watercourse reach- and good status pursuant to the WFD should es in the two test areas – Ryds Stream catchment correspond to the designation “favourable con- and the main course of the River Odense – are servation status” pursuant to the Habitats Direc- given in Section 4.2.3, together with an assess- tive. However, it is presently uncertain whether ment of the likelihood that the environmental consideration for special habitat species can lead quality objectives will not be achieved by 2015. to requirements different from those that they

Odense 30 PRB Odense Pilot River Basin