ALBERT

Description: In order to monitor recovery from acidification caused by acid atmospheric deposition, desmids and water chemistry were sampled in three Dutch moorland pools regularly from 1978 to 2014. Reference desmid samples from the early twentieth century were retrieved from old collections. Changes of the desmid assemblages were assessed by analyses of traits, including indicator values for pH and total phosphate, conservation value, cell volume and surface/volume (s/v) ratio. Direct correspondence analysis (DCA) traced relations between desmids and environmental variables. Between 1916 and 2014, species composition altered due to changes in acidifying atmospheric deposition: The change was most pronounced in pools with relatively flat shores exposed to the atmosphere in extremely dry summers. After the dry summer of 1921, changes were slight, but after the dry summer of 1976, changes were dramatic, when the sulphur and nitrogen compounds stored in the water bottom oxidized and acidified the water. The conservation value declined sharply but increased again until the 1990s, partly due to the decrease in acidifying deposition. Although the acid atmospheric deposition continued to decline until the early 21th century, the conservation value declined again, as did the stability of the desmid assemblages. It is likely that internal eutrophication (nutrients), presence of toxic substances (such as hydrogen sulphide), the decline of aquatic macrophytes (substrate), shading by afforestation (light) and/or reduced supply of carbon dioxide (due to decreased local seepage) play a role. The chemical dynamics due to the large stock of sulphur and nitrogen compounds will hamper the development of rare desmids, bound to stable environmental conditions.

Description: Cosmarium denboeri wordt vanuit Nederland beschreven als een voor de wetenschap nieuwe sieralgsoort. De soort is goed te herkennen aan de karakteristieke celwandsculptuur, maar wordt vanwege de geringe celafmetingen gemakkelijk over het hoofd gezien. Tot nu toe is C. denboeri bekend van drie locaties, gelegen in de provincies Zuid-Holland, Overijssel en Noord-Brabant.\nDe vindplaatsen in kwestie betreffen eutrofe wateren, waar ondergedoken waterplanten ontbreken.\nAangezien een dergelijke habitat in westerse, ontwikkelde landen veel kan worden aangetroffen, is het aannemelijk dat C. denboeri een wijd verspreidingsgebied zal blijken te hebben.\nCosmarium denboeri spec. nov. is described from the Netherlands as a new, planktic desmid species, well to be recognised by its characteristic cell wall sculpturing. The species in question may be readily overlooked because of its small cell dimensions. Up to now, C. denboeri is known from three sites, located in the Dutch Provinces of Zuid-Holland, Overijssel and Noord-Brabant. All three sites are eutrophic in nature, without any submerged aquatic weeds. As such a habitat is much encountered in western, developed countries, C. denboeri is likely a widely distributed species.