The invasive Australian swamp stonecrop,Crassula helmsii, is a perennial amphibious herboriginating from Australia and New Zealand. In freshwater wetlands of North-western Europe, this alien plant species is invasive due to its efficient colonization of empty niches. The establishment of dense C. helmsii growth is threatening native biodiversity and functioning of freshwater ecosystems, especially oligotrophic wetlands with high disturbance and nutrient enrichments. As the effects of these potential drivers of ecosystem degradation are generally difficult to determine in the field, we tested the competitive strength of C. helmsii in a greenhouse experiment with two native competitor species of the same habitat type, Pilularia globulifera and Littorella uniflora. In addition, the effect of nutrient enrichment by water bird feces on competition was studied by adding waterfowl droppings.
Limiting the spread and impacts of invasive alien species (IAS) on biodiversity and ecosystems has become a goal of global, regional and national biodiversity policies. Evidence based management of IAS requires support by risk assessments, which are often based on expert judgment. We developed a tool to prioritize potentially new IAS based on their ecological risks, socio-economic impact and feasibility of management using multidisciplinary expert panels.
Worldwide, coastal freshwater wetlands arefacingsalinizationat anincreasingrate duetolarge-scaleland use change, freshwater extraction, climate-drivensea level rise, droughts and land subsidence. Although itis known that increased surface water salinity doesinfluence wetland functioning, effects on nutrientdynamics reported in literature are contradictory andevidence from controlled, long-term field experiments isscarce. We therefore tested the effects of 4 levels ofincreased surface water salinity, from oligohaline tomesohaline conditions (0.9, 2.25, 4.5, 9 PSU), onbiogeochemical and physicochemical processes in thesediment of a formerly brackish freshwater wetland.
Mires and peatlands in general are heavilyinfluenced by anthropogenic stressors like acidification,eutrophication, desiccation and fragmentation.Groundwater-fed mires are, in contrast to rainwater-fedmires, often well protected against desiccation due toconstant groundwater discharge. Groundwater-fedmires can however be influenced by groundwater pol-lution such as groundwater nitrate enrichment, a threatwhich has received minor attention in literature. Thepresent case study demonstrates how groundwater ni-trate enrichment can affect the biogeochemical function-ing and vegetation composition of groundwater-fedmires through direct nitrogen enrichment and indirectnitrate-induced sulphate mobilisation from geologicaldeposits.
Deze brochure biedt handvatten hoe in het terreinbeheer en bij de ontwikkeling van nieuwe natuur met watercrassula omgegaan kan worden.
Na 25 jaar werd een zweefvliegentelling in het Bargerveen weer herhaald.