We present an overview of high nitrogen deposition effects on coastal dune grasslands in NW-Europe (H2130), especially concerning grass encroachment in calcareous and acidic Grey Dunes. The problem is larger than previously assumed, because critical loads are still too high, and extra N-input from the sea may amount to 10 kg ha− 1 yr− 1. Grass encroachment clearly leads to loss of characteristic plant species, from approximately 16 in open dune grassland to 2 in tall-grass vegetation.

Nitrogen deposition and grass encroachment in calcareous and acidic Grey dunes (H2130) in NW-Europe

Restoration measures in raised bog remnants frequently include the construction of dams, intended to retain rainwater and decrease fluctuations in the water table. However, comparative research in various bog remnants has provided strong indications that there are risks for macroinvertebrates. Risks include (i) rapid changes causing a disturbance, and (ii) similar changes at a large scale leading to a loss of heterogeneity, and consequently to a loss of species. This paper directly examines the risks associated with rewetting measures in bog remnants by investigating and comparing the macroinvertebrate assemblages in the same area before and after measures took effect.

Changes in macroinvertebrate richness and diversity following large scale rewetting measures in a heterogeneous bog landscape.

Watercrassula is een uit Australië en Nieuw-Zeeland afkomstige water- en moerasplant. De eerste verwilderingen in Engeland dateren van 1956. Sindsdien is ze achtereenvolgens ook in Ierland, Duitsland, België, Nederland en Frankrijk verwilderd. Omdat ze zich in uiteenlopende biotopen weet te vestigen en daar de samenstelling van de vegetatie ingrijpend doet veranderen, plaatst Watercrassula terrein- en waterbeheerders in veel West-Europese landen voor problemen. Wat zijn de perspectieven om deze plant onder de duim te houden?

Watercrassula: Watercrisis in het waterlichaam

In natuurgebied de Groote Heide is acht jaar geleden de knikkende schroeforchis ontdekt. De soort verspreidt zich erg snel, zowel door miljoenen stofzaden als door uitlopers van de wortels. In het huidige tempo zijn er zorgen over de negatieve effecten op inheemse soorten en verdere verspreiding naar andere natuurgebieden. Hebben we te maken met een nieuwe invasieve exoot?

Opkomst van de knikkende schroeforchis in de Nederlandse natuur.

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.

Reducing nutrient availability and enhancing biotic resistance limits settlement and growth of the invasive Australian swamp stonecrop (Crassula helmsii)

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.

Lessons learned from rapid environmental risk assessments for prioritization of alien species using 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.

Salinization lowers nutrient availability in formerlybrackish freshwater wetlands; unexpected resultsfrom a long-term field experiment

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.

Effects of Groundwater Nitrate and Sulphate Enrichmenton Groundwater-Fed Mires: a Case Study