Effectiviteit KRW herstelmaatregelen in de rijkswateren. Analyserapport meestromende nevengeulen en eenzijdig aangetakte strangen

Met de komst van de KRW (EP 2000) en stroomgebiedbeheersplannen met bijbehorende maatregelpakketten is er veel aandacht voor de wijze waarop maatregelen uitgevoerd kunnen worden. Vragen die hierbij centraal staan zijn: welke inrichting levert het hoogste ecologische rendement en hoe kunnen beheer en onderhoud tot een minimum beperkt worden? In opdracht van Rijkswaterstaat voert Deltares daarom studies uit die gericht zijn op de ontwikkeling en montage van kennis over de ecologische effectiviteit van maatregelen in Rijkswateren, in samenhang met hydromorfologische stuurvariabelen. De hier besproken studie wordt in 3 delen opgesplitst: - een oevertypologie aan de hand van bestaande natuurvriendelijke oeverconstructies; - een literatuuronderzoek naar de huidige kennis met betrekking tot (ecologisch effectieve) inrichting van natuurvriendelijke oevers; - een literatuuronderzoek naar de huidige kennis met betrekking tot beheer en onderhoud

Effectiviteit KRW herstelmaatregelen in de rijkswateren. Analyserapport meestromende nevengeulen en eenzijdig aangetakte strangen

Met de komst van de KRW (EP 2000) en stroomgebiedbeheersplannen met bijbehorende maatregelpakketten is er veel aandacht voor de wijze waarop maatregelen uitgevoerd kunnen worden. Vragen die hierbij centraal staan zijn: welke inrichting levert het hoogste ecologische rendement en hoe kunnen beheer en onderhoud tot een minimum beperkt worden? In opdracht van Rijkswaterstaat voert Deltares daarom studies uit die gericht zijn op de ontwikkeling en montage van kennis over de ecologische effectiviteit van maatregelen in Rijkswateren, in samenhang met hydromorfologische stuurvariabelen. De hier besproken studie wordt in 3 delen opgesplitst: - een oevertypologie aan de hand van bestaande natuurvriendelijke oeverconstructies; - een literatuuronderzoek naar de huidige kennis met betrekking tot (ecologisch effectieve) inrichting van natuurvriendelijke oevers; - een literatuuronderzoek naar de huidige kennis met betrekking tot beheer en onderhoud

Functional response of Anodonta anatina feeding on a green alga and four strains of cyanobacteria, differing in shape, size, and toxicity

We studied the functional response of the freshwater unionid bivalve Anodonta anatina, feeding on five phytoplankton strains differing in food quality: the small green alga Scenedesmus obliquus, a toxic and a non-toxic strain of the filamentous cyanobacterium Planktothrix agardhii and a toxic and a non-toxic strain of the coccoid cyanobacterium Microcystis aeruginosa. On S. obliquus, A. anatina had a type II functional response with a maximum mass-specific ingestion rate (IRmax) of 5.24 mg C g DW−1 h−1 and a maximum mass-specific clearance rate (CRmax) of 492 (±38) ml g DW−1 h−1, the highest values for all the phytoplankton strains that were investigated. On toxic and non-toxic P. agardhii filaments, A. anatina also had a type II functional response, but IRmax and CRmax were considerably lower (IRmax 1.90 and 1.56 mg C g DW−1 h−1; CRmax 387 (±97) and 429 (±71) ml g DW−1 h−1, respectively) than on S. obliquus. Toxicity of P. agardhii had no effect on the filtration rate of the mussels. On the non-toxic M. aeruginosa (small coccoid cells), we also observed a type II functional response, although a type I functional response fitted almost as good to these data. For the colonial and toxic M. aeruginosa, a type I functional response fitted best to the data: IR increased linearly with food concentration and CR remained constant. CRmax and IRmax values for the (colonial) toxic M. aeruginosa (383 (±40) ml g DW−1 h−1; 3.7 mg C g DW−1 h−1) demonstrated that A. anatina filtered and ingested this cyanobacterium as good as the other cyanobacterial strains. However, on the non-toxic M. aeruginosa we observed the lowest CRmax of all phytoplankters (246 (±23) ml g DW−1 h−1, whereas IRmax was similar to that on toxic M. aeruginosa. The high maximum ingestion rates on S. obliquus and M. aeruginosa indicate a short handling time of these phytoplankton species. The high clearance rates on S. obliquus, toxic M. aeruginosa and P. agardhii reflect a high effort of the mussels to filter these particles out of the water column at low concentrations. The low clearance rates on non-toxic M. aeruginosa may be explained by the small size and coccoid form of this cyanobacterium, which may have impaired A. anatina to efficiently capture the cells. Although A. anatina had relatively high maximum clearance rates on non-toxic and toxic P. agardhii, this cyanobacterium does not seem to be a good food source, because of the observed high rates of pseudofaeces production and hence low ingestion rates.

Risicobeoordeling en uitzetcriteria voor de uitheemse quaggamossel (Dreissena rostriformis bugensis) in Nederland

Contains fulltext : 150764pos.pdf (postprint version ) (Open Access)87 p

Comparing grazing on lake seston by Dreissena and Daphnia: lessons for biomanipulation

Biomanipulation measures in lakes, taken to diminish algal blooms, have mainly been restricted to the reduction of zooplanktivorous fish with the aim to stimulate the grazing pressure by native filter feeders such as Daphnia. However, larger filter feeders like the exotic zebra mussel, Dreissena polymorpha, have been suggested as an optional tool because of their high filtering capacity. We compared grazing by two filter feeders, D. polymorpha and Daphnia galeata, offered seston from Lake IJsselmeer, the Netherlands in two consecutive years: 2002 and 2003. The seston in both years was dominated by the colony-forming cyanobacterium Microcystis aeruginosa. The grazing studies were performed under controlled conditions in the laboratory and samples were analyzed on a flow cytometer, making it possible to quantify grazing on different seston components and size fractions, including cyanobacteria, other phytoplankton (green algae, diatoms, etc.), and detritus. No differences in clearance rates, on a per weight basis, were found between the two grazer species. The clearance rate on cyanobacteria (especially <20 µm) was lower in 2003 than in 2002. In 2003, the microcystin concentration of cyanobacteria was higher than in 2002, suggesting that the observed lower clearance rate in 2003 was due to the enhanced toxin content of the cyanobacteria. Zebra mussels, although indiscriminately filtering all seston groups out of the water, positively selected for phytoplankton in their mantle cavity, irrespective of its toxicity, and rejected detritus. Since no differences in clearance rates were found between the two grazer species, we conclude that for biomanipulation purposes of shallow lakes, native species like the daphnids should be preferred over exotic species like zebra mussels. When the seston is dominated by phytoplankton that cannot be filtered out of the water column by Daphnia, however, the use of zebra mussels may be considered. Care should be taken, however, in the choice of the lakes since the mussels may have severe ecological and economic impacts.