Birger Bjerkeng

The Response of Experimental Rocky Shore Communities to Nutrient Additions

The aim of this study was to determine whether the experimental nutrient enrichment of littoral rocky shore communities would be followed by a predicted accumulation of fast-growing opportunistic algae and a subsequent loss of perennial benthic vegetation. Inorganic nitrogen (N) and potassium (P) was added to eight concrete mesocosms inhabited by established littoral communities dominated by fucoids. The response to nutrient enrichment was followed for almost 2 1/2 years. Fast-growing opportunistic algae (periphyton and ephemeral green algae) grew significantly faster in response to nutrient enrichment, but the growth of red filamentous algae and large perennial brown algae was unaffected. However, these changes were not followed by comparable changes in the biomass and composition of the macroalgae. The biomass of opportunistic algae was stimulated only marginally by the nutrient enrichment, and perennial brown algae (fucoids) remained dominant in the mesocosm regardless of nutrient treatment level. Established rocky shore communities thus seem able to resist the effects of heavy nutrient loading. We found that the combined effects of the heavy competition for space and light imposed by canopy-forming algae, preferential grazing on opportunistic algae by herbivores, and physical disturbance, succeeded by a marked export of detached opportunistic algae, prevented the fast-growing algae from becoming dominant. However, recruitment studies showed that the opportunistic algae would become dominant when free space was available under conditions of high nutrient loading and low grazing pressure. These results show that established communities of perennial algae and associated fauna in rocky shore environments can prevent or delay the accumulation of bloom-forming opportunistic algae and that the replacement of long-lived macroalgae by opportunistic species at high nutrient loading may be a slow process. Nutrient enrichment may not, in itself, be enough to stimulate structural changes in rocky shore communities.

Modeling the fate of polychlorinated biphenyls in the inner Oslofjord, Norway.

A dynamic, segmented, multimedia fate and transport model has been developed, evaluated, and applied to gain insight regarding the behavior of seven polychlorinated biphenyl (PCB) congeners in the Inner Oslofjord (Norway). A comparison with a dated sediment core reveals that the model is not capable of reproducing some key features of the observed, historical, long-term trend in sediments, although better agreement is observed for six of seven PCB congeners over the last two decades. The model also underestimates the concentrations of PCBs in surface sediments in areas adjacent to the city of Oslo (Norway). In general, deviations between modeled and observed concentrations indicate that the historical emissions and discharges of PCBs are not sufficiently characterized and described. Net fluxes predicted by the model suggest that several congeners may have experienced a reversal of air-water and seawater-sediment exchange during the last decade or even earlier. The present study further suggests that the benefit of the proposed removal of the most contaminated sediments of the Inner Oslofjord needs to be assessed, with consideration of the relative contribution of current atmospheric inputs as well as the leaching of PCBs from less contaminated sediments.

Polychlorinated Dibenzo-p-Dioxins (PCDDs) and Dibenzofurans (PCDFs) in the Grenland Fjords (Norway)—Disposition, Levels, and Effects

Polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) are regarded as highly toxic. Their lipophilicity and persistence also render them subject to bioaccumulation. The Grenlandfjords (southern Norway) have long been polluted by PCDD/Fs through the magnesium production at Herøya (1951–2002). Therefore, extensive environmental monitoring was performed in the area, and the project “Dioxins in the Grenlandfjords—DIG” was launched to study abiotic mass balances, biotic processes and ecological risk. This article describes some results from DIG on the dispositions of PCDD/Fs in the food web and biological effects. Furthermore, data from the Norwegian monitoring of the Grenlandfjords are described. Differences in cod liver PCDD/F levels were found between stations, with the highest concentrations in the inner fjord (the Frierfjord), closest to the pollution source. Furthermore, considerable decreases in the concentrations followed the large discharge reductions (1975 and 1990). Contrary to earlier food web studies on other organochlorines, it was found that the concentrations of PCDD/Fs decline with higher trophic level. Higher chlorinated congeners also constituted a lower percentage of ∑PCDD/Fs higher in the food chain. The results indicated a limited bioaccumulation of PCDD/Fs, especially of higher chlorinated congeners, likely due to reduced membrane permeability (high molecular size), and possibly slow transport through intestinal aqueous phases. Hepatic cod 7-ethoxyresorufin O-deethylase (EROD) activities differed between the Frierfjord and the Eidangerfjord, showing the different PCDD/F exposure in the two fjords. Furthermore, seasonal variations in cytochrome P-450 (CYP) 1A activity were shown, with different responses between genders. The differences were likely linked to the reproductive cycle of the fish.