Extracellular enzymatic activity and secondary production in free-living and marine-snow-associated bacteria

Abundance, production (measured as thymidine incorporation) and extracellular enzymatic activity in free-living and marine-snow-associated bacteria were measured in the northern Adriatic Sea. Although bacterial density and production were similar in both free-living and marine-snow-associated bacteria, hydrolytic activity (- and -glucosidase and l-aminopeptidase) was significantly higher in marine-snow-associated bacteria, in terms of both absolute and per-cell rates. As concentrations of dissolved total and monomeric carbohydrates and free amino acids in marine snow were very close to those in the ambient water, we suggest that the observed differences between free-living and marine-snow-associated baycteria do not simply reflect catabolic repression of enzyme expression in one of the bacterial components. Whether substrate induction is responsible for the observed higher hydrolase activity in marine-snow bacteria and/or whether there are distinct bacterial species obligatorily associated with marine snow remains unknown.     

Effects of multiple but low pesticide loads on aquatic fungal communities colonizing leaf litter

In the first tier risk assessment (RA) of pesticides, risk for aquatic communities is estimated by using results from standard laboratory tests with algae, daphnids and fish for single pesticides such as herbicides, fungicides, and insecticides. However, fungi as key organisms for nutrient cycling in ecosystems as well as multiple pesticide applications are not considered in the RA. In this study, the effects of multiple low pesticide pulses using regulatory acceptable concentrations (RACs) on the dynamics of non-target aquatic fungi were investigated in a study using pond mesocosm. For that, fungi colonizing black alder (Alnus glutinosa) leaves were exposed to multiple, low pulses of 11 different pesticides over a period of 60 days using a real farmer''s pesticide application protocol for apple cropping. Four pond mesocosms served as treatments and 4 as controls. The composition of fungal communities colonizing the litter material was analyzed using a molecular fingerprinting approach based on the terminal Restriction Fragment Length Polymorphism (t-RFLP) of the fungal Internal Transcribed Spacer (ITS) region of the ribonucleic acid (RNA) gene(s). Our data indicated a clear fluctuation of fungal communities based on the degree of leaf litter degradation. However significant effects of the applied spraying sequence were not observed. Consequently also degradation rates of the litter material were not affected by the treatments. Our results indicate that the nutrient rich environment of the leaf litter material gave fungal communities the possibility to express genes that induce tolerance against the applied pesticides. Thus our data may not be transferred to other fresh water habitats with lower nutrient availability.     

Examining Source-Receptor Relationships for Mercury in Scandinavia Modelled and Empirical Evidence

The atmosphere remains the major source of mercuryin Swedish ecosystems. Since the late eighties,atmospheric emissions of mercury have drasticallydecreased in Europe. Wet deposition of mercury hasdecreased over the last decade but still exhibitsa clear south-to-north gradient, greatlyinfluenced by source areas in northern and centralEurope. The decreases in emissions can beattributed to both direct measures to close knownpoint sources and a declining economy and energyconsumption in many East European countries.Further reductions of mercury emissions willrequire that other source categories such asindirect emissions from mercury-containingproducts and crematories are be considered.