Entity

Time filter

Source Type

Apeldoorn, Netherlands

Van De Vijver B.,Botanic Garden Meise | Van De Vijver B.,University of Antwerp | Mertens A.,Grontmij Nederland B.V. | Van Dam H.,Consultancy for Water and Nature
Phytotaxa | Year: 2016

During an extensive analysis of the diatom flora of the Port of Antwerp (Belgium) in 2008, an unknown naviculoid taxon was observed. Detailed morphological investigations using light, scanning electron and transmission electron microscopy resulted in the description of this unknown taxon as Olifantiella elisabethiana Van de Vijver sp.nov. This new small-celled, biraphid species is characterized in having a typical internal process named buciniportula, opening externally by a pore or slit, unseriate striae composed of one single transapically elongated areola and a siliceous hymenous velum extending internally from the valve mantle to halfway the valve margin and the axial area. The morphological observations allowed to precise the characterization of the genus Olifantiella. A modification of the original description is proposed with regard to the internal structure. The presence of this Olifantiellaspecies in the northern hemisphere is briefly discussed as all other known taxa of this genus have only been found in the tropical coastal waters of the Indian and Pacific Ocean. © 2016 Magnolia Press.


Hussner A.,Heinrich Heine University Dusseldorf | Van Dam H.,Consultancy for Water and Nature | Vermaat J.E.,Norways University for Environmental and Life science | Hilt S.,Leibniz Institute of Freshwater Ecology and Inland Fisheries
Fundamental and Applied Limnology | Year: 2014

Global warming is expected to accelerate the invasive success of non-native plants. Long-term data on aquatic macrophytes confirming this hypothesis, however, are scarce. In this study we analyzed the development of native and neophytic aquatic macrophyte species number and abundance in a geothermally warmed river (Erft, North-western Germany) during a 4-year period and compared it to a dataset from thermally normal channels of a similar climatic region (The Netherlands). Total native species numbers declined in both systems, but only in the warmed river, this trend was accompanied by an increase in the relative plant mass of neophytes. Strong changes became apparent at the species level. In the warmed river, the subtropic neophyte Vallisneria spiralis was assumed to have displaced the formerly dominant and highly competitive native species Sparganium emersum, Potamogeton pectinatus and Ceratophyllum demersum based on negative correlations between changes in their plant mass in 52 river sections. The evergreen V. spiralis expanded particularly in winter after dieback of the native species. In thermally normal channels, a small increase in neophyte plant mass (Azolla filiculoides) did not account for losses of native submerged species. We thus conclude that higher water temperatures, especially in winter, potentially accelerate the displacement of native species by warm-water wintergreen neophytes. © 2014 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany.


Goldenberg Vilar A.,University of Amsterdam | Van Dam H.,Consultancy for Water and Nature | Vonk J.A.,University of Amsterdam | Van Der Geest H.G.,University of Amsterdam | Admiraal W.,University of Amsterdam
Ecological Indicators | Year: 2014

The extensive network of waters in the lower part of the Dutch delta is loaded with nutrients and accordingly a uniform ecological classification 'moderate' has been derived. The present study sets out to typify the diatom communities in this apparently homogenous environment via self-organizing maps of diatom species composition. Clusters of diatom communities were characterized through the representation of ecological guilds (high and low profile, motile and planktonic) and via a RDA analysis based on either species, genus or ecological guilds together with environmental drivers. Five clusters of diatom communities were identified despite the prominence of omnipresent species. The clusters had different profiles of ecological guilds and were associated with water transparency and sediment type (peat/clay) in addition to the well-established environmental drivers related to eutrophication, but with distinct roles for nitrogen and phosphate concentration. The clusters were interpreted as functional types of community, e.g. communities with a substantial share of planktonic diatom species were found in peat ditches with turbid water. The high consistency found between diatom community classification using species, genus or guilds may allow for a simplified water quality assessment while retaining valuable ecological information. The typology, based on species, genus and ecological guilds underpins the robust use of diatoms as water quality indicators in nutrient rich lentic waters and supports steps to improve ecological conditions. © 2014 Elsevier Ltd.


Goldenberg Vilar A.,University of Amsterdam | Vonk J.A.,University of Amsterdam | Bichebois S.,University of Amsterdam | van Dam H.,Consultancy for Water and Nature | And 2 more authors.
Hydrobiologia | Year: 2014

Mineral particles in rivers have been shown to cover adnate algal species, promoting motile and filamentous species. Such effects and the role of detrital particles have not been studied in stagnant waters. In degraded peat lands, detrital particles are very prominent and therefore we studied the interaction of organic particles and attached algae. Field grown communities were translocated to microcosms and exposed to organic particles in the laboratory. Colonization of substrate was also studied in field enclosures that allowed settlement of particles. We compared algal settlement under low particle regime (enclosures) with settlement at high particle concentrations (outside). Suspended particles were found to be trapped by attached algae in proportion to the concentration of particles. The presence of particles in the incubations and field enclosures modified species composition, reducing the share of low-profile forms. These experimental results were verified in a field survey with a wide range of turbidity. The share of low-profile species was lowest in turbid ditches while motile and planktonic algae dominated, in agreement with the results from experiments. It is argued that the strong interactions of attached algae and suspended organic matter found in peat land ditches is a characteristic feature of detritus rich waters. © 2014, Springer International Publishing Switzerland.


Goldenberg Vilar A.,University of Amsterdam | Van Dam H.,Consultancy for Water and Nature | Van Loon E.E.,University of Amsterdam | Vonk J.A.,University of Amsterdam | And 2 more authors.
Freshwater Biology | Year: 2014

Summary: The distance-decay relationship has been claimed to be a predictor for biological diversity because it unites several ecological phenomena such as dispersal ability and environmental structure. The effect of long-term disturbances on distance decay, however, has been widely overlooked, especially for microorganisms. We examine the effect of eutrophication on the distance-decay relationship in communities of attached diatoms in three peatland areas: mesotrophic, eutrophic and hypertrophic. The study follows a spatially explicit sampling scheme, collecting evenly spaced samples along 6-km sampling tracks. The three areas shared 24% of the total number of species, but the different nutrient levels in the three areas are reflected by the prominence of low profile and planktonic diatom species. Our study demonstrates that eutrophication can affect distance-decay relationships by decreasing turnover rates in microorganisms. Diatom communities are shown to be constrained by both environmental and spatial features, whose relative importance depends on the degree of eutrophication. Under eutrophic conditions, species are filtered from the regional species pool and community structure responds strongly to environmental factors (water chemistry variables and depth), while in mesotrophic environments, purely spatial processes play a prominent role in structuring diatom communities. These findings reveal that homogenisation of communities triggered by environmental disturbance is an ecological phenomenon of importance in the microbial world. © 2014 John Wiley & Sons Ltd.

Discover hidden collaborations