Search

Følgende artikel præsenterer data fra en analyse udarbejdet af ”Arbejdsgruppen vedrørende vandkvalitet i relation til recipientudledninger”, som er nedsat under Spildevands-komitéens Faglige Udvalg (tidl. Regnudvalget).

Med ADCP-udstyr (Accustic Doppler Current Profiler) kan grødensbetydning for vandføringsevnen i vandløb dokumenteres.

Udgivelsesdato: September

Bekæmpelsesmiddelforskning fra Miljøstyrelsen 69

Intensive measurements of the fluxes of phosphorus (P) and of P retention were carried out in a Danish lowland watershed (Gjern A) during two hydrological years (June 1987 to May 1989). Seasonal and short-term variations of P concentrations were measured by intensive automatic sampling covering P fluxes from the entire Gjern A watershed and two subcatchments: the Gelbaek and Lake Sobygard. Moreover, infrequent sampling was performed in all major tributaries of the river system. Transport of P compounds (dissolved and particulate P) exposed a seasonal pattern which was highly affected by flow conditions, instream processes, as well as point and non-point sources. Stormflow P transport during the two study years (1987-8 and 1988-9) constituted 56 and 61% in the Gelbaek, respectively, compared with 25 and 23% in the Gjern A, respectively. Particulate P transport in the Gelbaek constituted 56 and 75% of annual total P transport during the two years compared with 77 and 75% in the Gjern A. The magnitude of monthly baseflow and stormflow total P loads was significantly correlated with the mean monthly discharge during baseflow and stormflow in the Gelbaek, whereas only stormflow loads were correlated to discharge in the Gjern A. In situ measurements of retention showed that the maximum amount of P stored in the Gelbaek during summer (June to August) was 22gPm−2 (1988) compared with 27gPm−2 (1987) in the Gjern A. Lake Sobygard was a P source during summer but a P sink during winter and on an annual basis the net P released was 810 and 1420 kg, which corresponded to 7 and 20% of the annual P export from the watershed, respectively. Retention constituted about 30% of gross P transport in the Gelbaek during summer compared with 20% in the Gjern A. Resuspension of retained P during stormflows in September 1987 constituted 94% of the stormflow P transport and 54% of the total P transport. Monthly total P and dissolved reactive P (DRP) mass balances for the main channel of the Gjern A revealed a significant DRP retention over 17 months (p < 0.05) caused by P adsorption on sediments and biological uptake. On an annual basis the main channel was a sink of DRP (1220 and 1660 kg P) but a source of total P (3440 and 1000 kg P). implying that the channel is an important source of particulate P. Bank erosion proved to be a significant P source in the main channel of Gjern A, whereas P delivery from soil erosion was possibly of minor importance. The annual non-point P export from two intensively sampled catchments was significantly higher (0.89 and 0.45 kg Pha−1 yr−1) than from the five extensively sampled subbasins (0.43 and 0.17 kg Pha−1 yr−1). No significant relationship could be established between non-point P export and the proportion of arable land and soil type. Only for the wet year of 1987-8 was a significant relationship established between non-point P export and the P load from scattered dwellings outside sewage areas in five subbasins.

Rapporten er: Prepared for European Environment Agency Task Force. Directorate General Environment, Nuclear Safety and Civil Protection. The Commission of the European Communities. Contract no: B92/B4-3209.31/-006884. B92/B4-3200.11/013939

SUMMARY 1 This paper introduces the Lowland Streams Restoration Workshop that was held in Lund, Sweden in August 1991. 2 Attenders at the Workshop participated in working groups which discussed and reported on the state of knowledge of stream restoration and identified critical areas of information need. Currently, most restoration efforts are emission-orientated (i.e. waste-water management), while the imitation of the geomorphology or of the riparian vegetation of a quasi-natural or natural reference channel receives less attention. 3 Successful stream restoration requires a multidisciplinary approach within a holistic system framework. Monitoring the outcome of past, existing and future steam-restoration projects is required for information on the feasibility of alternative techniques and approaches. 4 It was recommended that systems in pristine condition serve as a point of reference and not as a goal for most stream restoration projects. Restoration goals must be carefully defined so that everyone at every level understands the aim of the project. At the very least, all restoration programmes should consider geomorphic, hydrological, biological, aesthetic, and water quality aspects of the system. 5 Restoration programmes should aim to create a system with a stable channel, or a channel in dynamic equilibrium that supports a self-sustaining and functionally diverse community assemblage; it should not concentrate on one species or group, except at the local level. Preserving the terrestrial -aquatic interface by setting aside riparian land corridors is critical to all stages of restoration. Additional information on the temporal and regional variability in important system processes and functions is needed.

EWPCA = The European Water Pollution Control Association. ISWA = International Soild Wastes Association