Featured Research

from universities, journals, and other organizations

Aquatic species decline at dams and weirs documented

Date:
September 14, 2011
Source:
Technische Universitaet Muenchen
Summary:
Dams and weirs have a stronger impact on watercourse ecosystems than was previously realized. Species diversity in the dammed area upstream of weirs shows a significant decline: one-quarter lower on average among fish, up to 50 percent lower among invertebrates. Scientists have demonstrated this through a survey of five rivers. Theirs is the first such analysis to consider both abiotic and biotic factors.

A comprehensive analysis reveals the extent and complexity of dams' effects on ecosystems.
Credit: TUM

Dams and weirs have a stronger impact on the ecosystem of watercourses than was previously realized. Species diversity in the dammed area upstream of weirs shows a significant decline: the diversity of fish species is one-quarter lower on average, and species diversity among invertebrates is up to 50 percent lower. The interruption of a river course thus has greater effects on the biodiversity than the geological origin of the river itself.

Scientists from the Technische Universitaet Muenchen have demonstrated this on the basis of a survey of five rivers in the catchment areas of the Elbe, Rhine/Main, and Danube. Their analysis records, for the first time, both abiotic factors, for example chemical composition, current, and river bed substrate, and biotic factors, such as the number, size, and diversity of all important animal and plant groups on the two sides of weirs. The TUM researchers will present their findings, which have already been published online in the Journal of Applied Ecology, at the annual conference of the German Limnological Society, which takes place from September 12 to 16, 2011.

Whether it is done for the generation of electricity, for flood protection, or collection of drinking water, the damming of a river represents a drastic intervention in its ecosystem. Weirs and dams alter the chemical and physical characteristics of the water and the riverbed. Their construction is accompanied by a clear decline in upstream species diversity, and this is exacerbated by successive damming. This phenomenon, which is known as "serial discontinuity," has now been measured for all important animal and plant groups by system biologists from the TUM for the first time; the information available up to now concerned only individual taxonomic groups or species. The scientists carried out a systematic survey of the aquatic organisms on both sides of the weirs in five rivers of different geological origins. Their survey revealed a significant reduction in the number, biomass and variety of periphyton, invertebrates, and fish species upstream of the weirs. Compared with downstream areas, the diversity of fish species measured upstream of weirs was 25 percent lower on average; a threefold decline in biomass was also observed.

Current-loving fish species, many of which are on the "Red List" of endangered species, are particularly severely affected. "Brown trout, grayling and Danube salmon are demanding fish species that require oxygen-rich water and spawn in coarse gravel areas. As typical residents of the upper reaches of rivers, they are unable to find suitable habitats in dammed areas," explains Juergen Geist, Professor of Aquatic Systems Biology at TUM. "These river sections are often dominated instead by bream, chub, and even carp -- generalist species that are actually adapted to stagnant waters. The ecological impoverishment of rivers is particularly dramatic when series of dams prevent the sufficient interlinking of different habitat types," says Geist. According to the Bayerische Landesamt für Umwelt (Bavarian Environmental Agency) there are more than 10,000 weirs in Bavaria's rivers alone.

According to the researchers, the main reason for the species decline is not the impermeability of the barrier to migrating fish species. Instead, the deciding factor is the chemical and physical alteration of the river itself which leads to a reduction of biodiversity. If the current is decelerated or interrupted, the flow rate upstream of the weir declines, and this is accompanied by increased water depth. In all of the surveyed dammed areas, the TUM scientists also recorded major differences in the oxygen content and temperature of the water and the sediment in the river bed, which hinders reproduction in current-loving fish species. The situation is compounded by differences in the structure of the sediments. The particles in the sediment found downstream of weirs are twice as large on average as those upstream, providing more and better quality spawning grounds.

River sections in the direct proximity of weirs should, therefore, be given greater consideration in ecological quality assessments, notes Prof. Geist: "During the evaluation of new weirs or modernization of hydroelectric power plants, attention should no longer be focused exclusively on the migration of fish species, but on the consequences of the structure and function for the river ecosystem as a whole." To ensure this, affected river sections must be covered by the relevant laws or regulations, such as the European Union Water Framework Directive. "A set of instruments for the quantification of the effects of weirs is now available, which records both the quality of the habitat and its biodiversity," says the TUM scientist.


Story Source:

The above story is based on materials provided by Technische Universitaet Muenchen. Note: Materials may be edited for content and length.


Journal Reference:

  1. Melanie Mueller, Joachim Pander, Juergen Geist. The effects of weirs on structural stream habitat and biological communities. Journal of Applied Ecology, 2011; DOI: 10.1111/j.1365-2664.2011.02035.x

Cite This Page:

Technische Universitaet Muenchen. "Aquatic species decline at dams and weirs documented." ScienceDaily. ScienceDaily, 14 September 2011. <www.sciencedaily.com/releases/2011/09/110914143638.htm>.
Technische Universitaet Muenchen. (2011, September 14). Aquatic species decline at dams and weirs documented. ScienceDaily. Retrieved July 25, 2014 from www.sciencedaily.com/releases/2011/09/110914143638.htm
Technische Universitaet Muenchen. "Aquatic species decline at dams and weirs documented." ScienceDaily. www.sciencedaily.com/releases/2011/09/110914143638.htm (accessed July 25, 2014).

Share This




More Earth & Climate News

Friday, July 25, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Goma Cheese Brings Whiff of New Hope to DRC

Goma Cheese Brings Whiff of New Hope to DRC

Reuters - Business Video Online (July 24, 2014) — The eastern region of the Democratic Republic of Congo, mainly known for conflict and instability, is an unlikely place for the production of fine cheese. But a farm in the village of Masisi, in North Kivu is slowly transforming perceptions of the area. Known simply as Goma cheese, the Congolese version of Dutch gouda has gained popularity through out the region. Ciara Sutton reports. Video provided by Reuters
Powered by NewsLook.com
Bill Gates: Health, Agriculture Key to Africa's Development

Bill Gates: Health, Agriculture Key to Africa's Development

AFP (July 24, 2014) — Health and agriculture development are key if African countries are to overcome poverty and grow, US software billionaire Bill Gates said Thursday, as he received an honourary degree in Ethiopia. Duration: 00:36 Video provided by AFP
Powered by NewsLook.com
Higgins Breaks Record at Mt. Washington

Higgins Breaks Record at Mt. Washington

Driving Sports (July 24, 2014) — Subaru Rally Team USA drivers David Higgins and Travis Pastrana face off against a global contingent of racers at the annual Mt. Washington Hillclimb in New Hampshire. Includes exclusive in-car footage from Higgins' record attempt. Video provided by Driving Sports
Powered by NewsLook.com
Storm Kills Three, Injures 20 at Virginia Campground

Storm Kills Three, Injures 20 at Virginia Campground

Reuters - US Online Video (July 24, 2014) — A likely tornado tears through an eastern Virginia campground, killing three and injuring at least 20. Linda So reports. Video provided by Reuters
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

    Health News

      Environment News

        Technology News



          Save/Print:
          Share:  

          Free Subscriptions


          Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

          Get Social & Mobile


          Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

          Have Feedback?


          Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
          Mobile iPhone Android Web
          Follow Facebook Twitter Google+
          Subscribe RSS Feeds Email Newsletters
          Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins