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No. 260: Streams 2016. Ecological state, environmentally hazardous substances and heavy metals and natural habitats and species

Rasmussen, J.J., Andersen, D.K. & Alnøe, A.B. 2018. Vandløb 2016. Økologisk tilstand, miljøfremmede stoffer og tungmetaller samt naturtyper og arter. NOVANA. Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi, 64 s. - Videnskabelig rapport fra DCE - Nationalt Center for Miljø og Energi nr. 260


This year’s report focuses on the ecological status of streams, including the development of the ecological status at selected stream monitoring sites. Furthermore, it presents a state of the art account of environmentally hazardous substances and stream habitats included in the EU Habitats Directive. All data were gathered within the framework of the National Monitoring Program for the Aquatic Environment and Nature (NOVANA) in 2016.  

Ecological status 

The ecological status of streams is described based on various biological quality elements: benthic macroinvertebrates, fish and plants. As to invertebrates, the Danish Water Fauna Index (DVFI), which has been applied for more than 20 years, is used, while the indices for fish (DFFVa and DFFVø) and plants (DVPI) have only been used for a few years. Only DVFI allows a description of the development of ecological status for a longer period based on a relatively limited number of sampling sites where benthic sampling is conducted every year (including 250 sites). The number of sites for which DVPI and DFFV data were gathered in 2016 was 61 and 111, respectively. 

Focusing on these annually monitored sites, the ecological status has generally improved significantly since 1994. Thus, the percentage of sites with faunal classes 1-3 decreased from 22-26% in the period 1994-1998 to 5-10% in the period 2011-2015, and the percentage of sites with faunal class 4 declined from 45-58% to 27-37%. In contrast, the number of sites with faunal classes 5-7 (i.e. “good” to “high” ecological status) increased from 19-32% in 1994 to 56-65% in 2015. Especially, the percentage of faunal classes 6 or 7 has increased markedly. In 2016, there was a minor decline in the percentage of sites with faunal class 7 and a slight increase in the number of sites with faunal class 4. Comparing faunal class values at the site level between 2015 and 2016, the faunal class decreased from 5-7 to 4 at 18 sites indicating a negative development. However, no strong conclusions can be made on basis of faunal class values in two subsequent years, as natural between-year variation may be responsible for this observed decline in ecological status. Furthermore, the declining amount of sites with faunal class 7 is primarily owed to missing samples at sites that historically were characterized by faunal class 7. 

Ved sammenligning af DVFI for de enkelte stationer mellem 2015 og 2016 ses, at der har været en negativ udvikling, hvor faunaklassen er faldet fra 5-7 til 4 på 18 stationer. Denne udvikling er dog baseret på DVFI målinger for kun to år, og derfor kan der ikke drages konklusioner om den generelle udvikling i DVFI, da der kan forekomme almindelige år til år variationer. Endvidere skal det nævnes at den faldende andel af stationer med DVFI 7 primært et udtryk for at en række stationer der i tidligere år havde en faunaklasse 7 ikke er blevet prøvetaget i 2016. 

The primary reason for the observed ecological progress based on DVFI is improved efficiency of municipal wastewater treatment plants and reduced pollution from fish farms. With this improvement in the water chemical state, there is a gradual recolonisation by benthic macroinvertebrates, indicators of “good-high” ecological status, of stream reaches with physical favourable conditions. This recolonisation exhibits a natural delay relative to the increase in the number of suitable habitats as the recolonisation by macroinvertebrates of the new habitats partly depends on overland dispersal during their adult life stages. The stagnation in the increase of the number of sites with faunal classes 5-7 during the past approx. 5 years is probably due to the fact that other environmental conditions, including poor physical conditions in many regulated streams, set the lower limit for how many macroinvertebrate species indicative of “good-high” ecological status may establish sustainable populations along the stream reaches.  

Based on DFFVa and DFFVø, the number of sites with at least “good” ecological status was 47% and 38%, respectively. DFFVa was calculated for all streams where minimum three or more species were caught, while DFFVø was applied to the remaining sites. Based on DVPI, the number of streams with minimum “good” ecological status was 64%. While the entire network of NOVANA stream monitoring sites is selected so as represent the dominant influencing factors on Danish streams, it cannot be assumed that the sites included in the 2016 monitoring (approx. 1/6 of the total stream network) are representative of the gradients in these influencing factors. Thus, the results from these sites cannot be extrapolated to describe the general ecological status of Danish streams determined with DFFFv and DVPI. 

Hazardous substances and heavy metals 

For 2016, the data on environmentally hazardous substances and heavy metals come from two stream monitoring sites. Most metals had a detection frequency of 100% in the stream water, and the specified environmental quality standard for zinc was exceeded at both sites and for copper and nickel at one site. To the extent that environmental quality standards have been specified for the individual hazardous substances, no exceedance of the prevailing standards was observed.  

For stream sediments, environmental quality standards have only been speified for very few substances. Of these, the standard was exceeded in one of the two streams for lead, cadmium and anthracene (PAH).  

Habitat types and species 

The NOVANA program for habitat types and species has the purpose of providing a representative picture of the status and development of habitat types specified in Appendix I of the Habitats Directive and species included in Appendices II and VI, as well as describing connections between influencing factors, status and development. 

This year’s report includes a presentation of the status and development of three habitat types and three species associated with streams based on mapping and reference monitoring data. For two habitat types (“Streams with intermittently exposed mud and annuals” and “Fringes with tall herbs and shadowy forest”) and the fish species river lamprey and sea lamprey, only a status is given as these were only included in the most recent monitoring period. For the habitat type “Streams with macrophytes” and the species brook lamprey, a presentation of both status and development is given as these were monitored in both periods. The report has particular focus on tendencies in the status and development of selected indicators of the three stream habitat types and on the distribution of the three lamprey species. 

The distribution of brook lamprey seems stable between the two periods, while the development of the other two lamprey species cannot be assessed as they are rare on a nationwide scale and have only been monitored during the most recent period. Herb fringes occur regularly throughout the country and are dominated by common competitive species and several grasses, while streams with intermittently exposed mud have only been recorded a few times during the monitoring period. Streams with macrophytes are a common habitat type throughout the country. Invasive species were recorded at more than one third of the total number of sites. A small reduction was observed in the value for the Danish Stream Fauna Index and a small increase of the Ellenberg indicator values for humidity and reaction rate/pH from the period 2004-2000 to the period 2010-2016. No changes were found for the other indicators.