Biogeochemical consequences of an oxygenated intrusion into an anoxic fjord.

BACKGROUND: This paper is based on the studies of the biogeochemical structure of the water column in the anoxic Fjord Hunnbunn (south-eastern Norway) performed in 2009, 2011 and 2012. This Fjord is an enclosed basin of brackish water separated by a narrow and shallow outlet to the sea with a permanently anoxic layer. We show how an oxygenated intrusion could lead to both positive and negative effects on the ecosystem state in Hunnbunn due to a change in the biogeochemical structure. RESULTS: During the stratified periods in 2009 and 2012 the anoxic layer amounted to approximately 10% of the total water volume in the Fjord, while dissolved oxygen (DO) was present in 80-90% of the water. In the autumn of 2011 the water chemistry structure observed in Fjord Hunnbunn was clearly affected by a recent oxygenated intrusion defined by abnormal salinity patterns. This led to a shift of the DO boundary position to shallower depths, resulting in a thicker anoxic layer comprising approximately 40% of the total water volume, with DO present only in approximately 60% of the water. The oxygenated water intrusions led to a twofold decrease of the concentrations of hydrogen sulphide, ammonia, phosphate and silicate in the deep layers with a simultaneous increase of these nutrients and a decrease of the pH level in the surface layers. The concentrations of manganese, iron, and mercury species changed dramatically and in particular revealed a significant supply of iron and methylmercury to the water column. CONCLUSIONS: Oxic water intrusions into anoxic fjords could lead not only to the flushing of the bottom anoxia, but to a dispersal of sulphidic and low oxygen conditions to the larger bottom area. The elevation of the hydrogen sulphide to the shallower layers (that can be rapidly oxidized) is accompanied by the appearance in the subsurface water of methylmercury, which is easily accumulated by organisms and can be transported to the surrounding waters, affecting the ecosystem over a larger area.

PCB-containing paint and plaster caused extreme PCB-concentrations in biota from the Sørfjord (Western Norway)--a case study.

The Sørfjord (Western Norway) has a long history of industry and pollution, and has been monitored for several decades. The environmental monitoring has comprised analyses of different contaminants in sea water, mussel, fish, seaweed and sediments. Measurements of polychlorinated biphenyls (PCBs) in blue mussels (Mytilus edulis) some 17 years ago indicated a local source. In 2001 severe concentrations were measured in blue mussels and further investigations disclosed the primary source of PCBs in the Sørfjord. In 2002, extreme PCB-concentrations were found in cod (Gadus morhua) from the same area. However, no induction of EROD activity was detected, indicating the limitations of this assay as marker for PCB contamination. A future scientific challenge will be to understand the specific mechanisms and effects of such PCB accumulation in fish.

Deploying a metal adsorbent in situ: a technique for indicating bioavailable Cd(II) in marine waters.

This paper reports a study into the deployment of a metal adsorbent in situ to estimate bioavailable Cd(II) in marine waters. Eight adsorbents were screened in the laboratory to test their ability to accumulate Cd(II) from deionised water and artificial seawater, and an oxidised activated carbon was selected for further investigation. The adsorption isotherm at Cd(II) concentrations 0.16-38 microgl(-1) and at salinity 15 followed the Freundlich equation. The adsorbent was contained in nylon bags (pore size 35 microm) and dialysis tubes (membrane pore size 2 nm) to produce deployable devices and to investigate the effect of housing material on Cd(II) accumulation. The devices were tested in the laboratory and deployed at four field sites for up to 3 weeks. The adsorbent in the nylon bags reached equilibrium towards the end of this period and the measured contents were in good agreement with expected contents predicted from known seawater Cd(II) concentrations and the adsorption isotherm. The dialysis tubes accumulated significantly lower amounts of Cd(II) than the nylon bags, probably due to an initial lag as Cd(II) diffused into the dialysis bag and due to biofouling which reduced diffusion. The relationship between concentrations of Cd(II) accumulated by the mussels (indicating the bioavailable Cd(II) fraction) and the devices at different field sites could be described by the Freundlich model. The goodness of fit of this relationship was better for the dialysis tubes than the nylon bags. The adsorbent in the nylon bags may have collected small particles from seawater which affected the Cd(II) analysis. Both devices demonstrate potential as indicators of the relative bioavailable fraction of Cd(II) to Mytilus edulis in marine waters.

Post World War II orcharding creates present day DDT-problems in The Sørfjord (Western Norway)--a case study.

The Sørfjord has a long history of agriculture and industry, and environmental monitoring has been conducted for decades, comprising analyses of contaminants in mussel, fish and sediments. DDT was used as an insecticide in orchards surrounding the fjord between World War II and 1970. Since the early 1990 s, elevated concentrations of DDT were found in mussels and fish. Unexpectedly, DDT-concentrations increased towards present day, despite the discontinuation of use. The highest concentrations in mussels (in 2006) corresponded to about two orders of magnitude higher than background. Analyses of sediment core sections also indicated increased input towards present day. Shifts in climatic parameters, as well as increased amounts of soil dissolved organic carbon following a decline in atmospheric sulphate deposition may have contributed to this phenomenon. We warrant the need for increased knowledge of the effects of alterations in variables acting regionally and globally on the disposition of contaminants in ecosystems.