Acidification has led to a strong decline of species characteristic of shallow soft-water lakes. In spite of reductions in acidifying deposition, natural recovery of biodiversity is modest or even absent, suggesting that the impact of acidification is difficult to reverse. We compared recovery from acidification in non-restored and restored lakes using data from 1983 and 2004. In restored lakes, accumulated organic matter was removed and alkaline water was supplied, resulting in an increase in pH and alkalinity and a decrease in ammonium, sulphur and aluminium. For evaluation of biotic changes we selected chironomid larvae (Diptera). In non-restored lakes, chironomid response did not indicate a recovery, despite an improved water chemistry in terms of decreased acidity and sulphur (not ammonium and aluminium).

Natural recovery and restoration of acidified shallow soft-water lakes: Successes and bottlenecks revealed by assessing life-history strategies of chironomid larvae

De brede geelgerande waterroofkever wordt beschermd via de EU-Habitatrichtlijn Annex II en IV. Maar welke maatregelen zou je als terreinbeheerder kunnen treffen om de leefomstandigheden voor deze soort te behouden en te verbeteren? Die vraag is niet gemakkelijk te beantwoorden. De kever wordt namelijk onder zeer verschillende omstandigheden aangetroffen en de ecologische kennis over de soort bevat veel hiaten.

Habitateisen van brede geelgerande waterroofkever ontrafeld door af te dalen langs de voedselketen.

Strong population development of the pumpkinseed appears to be facilitated by nature management practices in existing ponds (the removal of accumulated organic matter and macrophytes) and by creating new ponds. These measures enhance suitable breeding habitats that are free of competitors and predators. Isolated waters harbouring pumpkinseed were more often situated close to human habitation and infrastructure than could be expected based on the distribution of randomly selected isolated waters, identifying introductions as an important dispersal mechanism. Currently there is little experience with pumpkinseed control. However, options to be explored include: decreasing depth of colonized waters by filling them with soil allowing them to occasionally dry up, introducing native competitors and predators and the use of biodegradable piscicides. In addition, limitation of the sale of pumpkinseed is required as well as public education on the consequences of introducing exotic species.

Pumpkinseed sunfish (Lepomis gibbosus) invasions facilitated by introductions and nature management strongly reduce macroinvertebrate abundance in isolated water bodies

Het aantal uitheemse soorten in Nederland blijft groeien. Sommige van deze soorten worden dermate talrijk dat zij schadelijk zijn voor andere soorten, ecosystemen en economie. Deze worden invasieve exoten genoemd. Het bestrijden van invasieve exoten is vaak niet effectief en vormt daarmee een jaarlijks terugkerende en groeiende kostenpost. Wellicht zijn er beheermaatregelen die een duurzame oplossing bieden voor het exotenbeheer? Om antwoord te kunnen geven op deze vraag, gaan we op zoek naar de achterliggende oorzaak van invasiviteit en proberen deze te vertalen naar beheermaatregelen waarmee het mogelijk is de aantallen van uitheemse probleemsoorten onder controle te houden. Beheermaatregelen die leiden tot natuurlijke abiotische en biotische standplaatscondities – systeemgericht beheer – lijken geschikt om plagen van uitheemse soorten te voorkomen.

Systeemgericht beheer als duurzame oplossing tegen invasieve exoten.

De uitheemse watercrassula (Crassula helmsii) is in Nederland bezig met een razendsnelle opmars in vennen, vijvers, poelen, duinplassen en watergangen. Omdat de exoot vaak woekert in voedselarme natuurgebieden, zorgt het voor grijze haren bij menig beheerder. Het besproeien met kokendheet water wordt regelmatig genoemd als kansrijke methode voor de bestrijding van watercrassula en als alternatief voor ingrijpende alternatieven als afdekken met folie en afgraven. Met een veld- en kasexperiment is ervaring opgedaan met deze methode. Het onderzoek moest allereerst inzicht geven in de efficiëntie van heet water als bestrijdingsmaatregel tegen woekerende watercrassula. Verder is nagegaan of na behandeling met heet water de bodem geschikt zou zijn voor de ontwikkeling van voedselarme natuur.

Effectiviteit van kokend water bij bestrijding en beheer van watercrassula in natuurgebieden.

Species differ in their life cycle, habitat demands and dispersal capacity. Consequently different species or species groups may respond differently to restoration measures. To evaluate effects of restoration measures in raised bog remnants on aquatic microinvertebrates, species assemblages of Rotifera and microcrustaceans were sampled in 10 rewetted and 10 non-rewetted sites, situated in 7 Dutch raised bog remnants.

Effects of rewetting measures in Dutch raised bog remnants on assemblages of aquatic Rotifera and microcrustaceans.

Brent goose colonies around snowy owl nests have been studied near Medusa Bay (73 ° 21 ‘ N, 80 ° 32 ‘ E) and in the lower reaches of the Uboinaya River (73 ° 37 ‘ N, 82 ° 10 ‘ E), the northwestern Taimyr Peninsula, from 1999 to 2006. All brent nests within 680 m from an owl nest have been regarded as an individual colony. The results show that the area of the colony is always larger than the protected area around the owl nest. In years of low abundance of lemmings, brent geese nest generally closer to the owl nest than in years of high abundance. When arctic foxes are abundant, however, brent geese nest significantly closer to owls than when the foxes are scarce, irrespective of lemming abundance. The mechanism of brent colony formation around owl nests is based on a number of stimuli.

Brent goose colonies near snowy owls: Internest distances in relation to abundance of lemmings and arctic foxes.

To evaluate the potential invasiveness of pumpkinseed Lepomis gibbosus introduced to northwestern European inland waters, growth and reproduction traits were examined in ten populations along a trajectory spanning northwestern Europe (Norway, England, Holland, Belgium and France) and evaluated in light of published dataset from Europe.

Life-history traits and potential invasiveness of introduced pumpkinseed Lepomis gibbosus populations in northwestern Europe.

Pristine freshwater fens harbour many species of aquatic macroinvertebrates. Effects of eutrophication and desiccation have strong negative impacts on macroinvertebrate assemblages. To restore degraded fens, the removal of accumulated organic sludge by dredging seems a necessary step. However, degraded fens may harbour relic populations of rare and characteristic species as was found for raised bogs and shallow soft water lakes. This study investigates the effectivity of dredging by comparing dredged and undredged water bodies in two areas (SW & MP). To help interpret the observed differences, a third least impacted area is sampled in addition (WD).

Restoring fen water bodies by removing accumulated organic sludge: what are the effects for aquatic macroinvertebrates?