Contrasting sensitivities to toxicants of the freshwater amphipods Gammarus pulex and G. fossarum

Amphipods are an important component of freshwater ecosystems. They are very often used in ecotoxicology, particularly the freshwater amphipod Gammarus pulex. However, there is scarce information on the sensitivity to toxicants of other species within the genus Gammarus. The present study aims to: (1) to compare sensitivities to ivermectin and cadmium between two species of freshwater amphipods (G. pulex and G. fossarum); (2) to compare sensitivities to these toxicants between juveniles and adults within each species; and (3) to assess whether the sensitivity to toxicants of these co-generic species is related with the wideness of their natural distribution area. Eight independent short-term bioassays (96 h) were conducted to assess sensitivity for ivermectin and cadmium for juvenile and adult life stages for each species. The LC50 (mortality) and EC50 (mortality plus immobility) were calculated to 48 and 96 h of continuous exposure. Our results showed that G. pulex was less tolerant to ivermectin than G. fossarum, the reverse being true for cadmium. In general, juveniles of both species were less tolerant to cadmium than adults. In the case of ivermectin, only for G. fossarum EC50 values were different between life stages. These results suggest that the risk assessment of toxicants to freshwater amphipods should include bioassays with the most sensitive species and life stag

Winterweer kan effectiviteit van KRW-maatregelen beinvloeden

Experimentele studies tonen aan dat drijvende planten meer profiteren van klimaatverandering dan submerse planten. Een analyse van langjarige (1981-2006) meetgegevens afkomstig uit sloten onderschrijft deze bevindingen: milde winters leiden tot hogere kroosbedekking in de zomer, terwijl koude winters leiden tot meer submerse planten. Daarnaast toont onze analyse aan dat overwinterings- en groeistrategie van planten, bodemsoort en de weersomstandigheden in de winter de plantenbedekking in het groeiseizoen kunnen verklaren. Analyses van langjarige meetreeksen kunnen een belangrijke bijdrage leveren aan het begrijpen van het functioneren van ecosystemen, nu en in de toekomst. Dit kan bijvoorbeeld gebruikt worden voor de planning van het uitvoeren van voorgenomen (KRW-)maatregelen

Benthic macroinvertebrates and multiple stressors : quantification of the effects of multiple stressors in field, laboratory and model settings

Organisms are always exposed to several simultaneously operating stressors in nature. It appears that the combined effects of multiple stressors cannot be understood as a simple product of their individual effects. To understand how multiple stressors affect the composition and functioning of ecosystems it is necessary to know their quantitative contributions but also to explore their interactions. The central theme of this thesis is the quantification of the combined effects of multiple stressors on benthic aquatic macroinvertebrates and their communities. The statistical analyses of data sets in this thesis demonstrate that effects of multiple stressors in field situation can be quantified and that the benthic macroinvertebrate communities are affected by micropollutants. Furthermore, the modeling and laboratory studies show that the type of interaction between stressors can be analyzed and also that the effect of a certain stressor depends on the impact of all other stressors. Energy budgets and scope for growth seem powerful tools for improving the knowledge on the distribution and abundance of organisms. Finally, this thesis provides a foundation for differentiated standard setting

Population dynamics of free-swimming Annelida in four Dutch wastewater treatment plants in relation to process characteristics

Free-swimming Annelida occasionally occur in very high densities in WWTPs (WasteWater Treatment Plants) and are nowadays applied for waste sludge reduction, but their growth is uncontrollable. In order to get more insight in the population dynamics of these free-swimming Annelida, and relate their presence to process characteristics, nine ATs (Aeration Tanks) of four Dutch WWTPs were regularly sampled over a 2.5-year period. For each species, peak periods in worm population growth were defined and population doubling times and half-lives calculated. Peak periods and doubling times were compared to those in natural systems. Process characteristics were obtained from the plant operators and related to the worm populations by multivariate analysis for the first time in large-scale WWTPs. The species composition in the WWTPs was limited and the most abundant free-swimming Annelida were in decreasing order Nais spp., Aeolosoma hemprichi, Pristina aequiseta, Aeolosoma variegatum, Chaetogaster diastrophus, and Aeolosoma tenebrarum.This latter species had never been found before in WWTPs. Worm absence sometimes coincided with the presence of anoxic zones, but this was possibly overcome by higher temperatures in the WWTPs. Worms were present all year round, even in winter, but no yearly recurrences of population peaks were observed, probably as a result of stable food supply and temperature, and the lack of predation in the WWTPs. Peak periods were similar between the ATs of each WWTP. The duration of the peak periods was on average 2¿3 months for each species and the population doubling times in the peak periods were short (on average 2¿6 days), which also corresponds to a stable favorable environment. The disappearance of worm populations from the WWTPs was presumably caused by declining asexual reproduction and subsequent removal with the waste sludge. Multivariate analysis indicated that 36% of the variability in worm populations was due to spatial and temporal patterns only. In addition, no more than 4% of the variability in worm populations was related to variations in process characteristics only and worm presence was usually associated with better sludge settleability. In conclusion, our data from large-scale WWTPs suggest that growth of free-swimming Annelida still seems uncontrollable and that their effects on treatment processes are unclear, which makes stable application in wastewater treatment for sludge reduction difficult

Eendenkroos: van afval tot veevoer = Duckweed from waste to animal feed

Kroosdekken op sloten en vaarten zijn ongewenst voor de waterkwaliteit. Door kroos frequent te verwijderen wordt de waterkwaliteit sterk verbeterd, maar dit brengt voor waterschappen hoge kosten met zich mee. Kroos is geschikt als eiwitrijk veevoer en door stijgende voerprijzen is een alternatieve eiwitbron voor grondstoffen als sojaschroot. In 2007 is een pilot uitgevoerd om ervaring op te doen met de mogelijkheden van verzamelen en verwerken van kroos, maar ook om de gezondheidsrisico’s en de voederwaarde in beeld te brengen. Op twee locaties is in september 2007 kroos geoogst: bij Stolwijk in het buitengebied en bij Spakenburg aan de rand van de stedelijke bebouwing. Deze twee locaties zijn gekozen om te bepalen of er verschil in kwaliteit bestaat tussen gebieden met een landbouwkundige omgeving en een stedelijke omgeving. Daarnaast is op de beide locaties met een verschillende oogstmethode gewerkt. Direct na het oogsten is het natte product afgevoerd naar een drogerij, waar het kroos in droogkamers is gedroogd

Zijn sloten en meren vergelijkbaar?

De opgedane kennis over het ecologisch functioneren van meren kan relevante aanknopingspunten bieden voor het begrip van het functioneren van sloten. Daarom zijn de twee ecosystemen met elkaar vergeleken. Na een karakterisering van verschillen en parallellen worden belangrijke mechanismen in sloten benoemd en in een schema met terugkoppelingen weergegeven. De vergelijking geeft een beeld van het nut van de kennis over meren voor onderzoek in sloten en hoe de mechanismen die in sloten een rol spelen inzichtelijk gemaakt kunnen worde

Effects of aquatic vegetation type on denitrification

In a microcosm 15N enrichment experiment we tested the effect of floating vegetation (Lemna sp.) and submerged vegetation (Elodea nuttallii) on denitrification rates, and compared it to systems without macrophytes. Oxygen concentration, and thus photosynthesis, plays an important role in regulating denitrification rates and therefore the experiments were performed under dark as well as under light conditions. Denitrification rates differed widely between treatments, ranging from 2.8 to 20.9 µmol N m-2 h-1, and were strongly affected by the type of macrophytes present. These differences may be explained by the effects of macrophytes on oxygen conditions. Highest denitrification rates were observed under a closed mat of floating macrophytes where oxygen concentrations were low. In the light, denitrification was inhibited by oxygen from photosynthesis by submerged macrophytes, and by benthic algae in the systems without macrophytes. However, in microcosms with floating vegetation there was no effect of light, as the closed mat of floating plants caused permanently dark conditions in the water column. Nitrate removal was dominated by plant uptake rather than denitrification, and did not differ between systems with submerged or floating plant

Toxiciteit van oliefracties in sediment voor Corophium volutor

Naar aanleiding van toxiciteitexperimenten zijn milieu risicogrenzen voor minerale olie afgeleid, waarbij onderscheid wordt gemaakt naar fracties op basis van kookpunt (lengte van de koolstofketens). In dit onderzoek is onderzocht in hoeverre de voorgestelde risicogrenzen overeenkomen met waargenomen toxiciteit in veldsedimenten. Het oliegehalte werd in deze sedimenten bepaald door middel van XAD-extracties, waarmee het snel desorberend gehalte werd bepaald. Toxiciteit werd bepaald met een 10-daagse test met de slijkgarnaal Corophium volutator