“Have we forgotten something?”. Summary of afternoon discussion 21 June 2010 at Gustafsberg, Uddevalla

General discussion
Per Hall informed the group that the Byfjord cruise in June went overall fairly well and that the analysis will be carried out in July. BOX now has collected samples from all seasons of the year. It was also asked if Åke Granmo could add his measurements from the control programme into the dataset.

Anders Stigebrandt pointed out that Länsstyrelsen (the county administrative board) wants us to publish numbers of hydrogen sulphide (H2S) concentrations on our website. They want to follow what happens when oxygenating the fjord and particularly if the levels of H2S fall significantly, or disappears all together. BOX’s field campaigns have sampled H2S, and also take samples for that every month. These samples are later sent to SMHI for analysis. SMHI is also in the Byfjord collecting samples for a wide range of parameters, for example H2S, the first week every month.

Questions were raised whether or not we need to report H2S concentrations in the Byfjord even after the pumps have been started and the bulk of it has been oxidised. This is presently unknown and we need to check with Länsstyrelsen. However, we may ask SMHI to continue carry out those analyses as before.

Loreto De Brabandere pointed out that she didn’t smell any H2S on the field campaign in June. However, there was an inflow in the middle of March that seems to have oxidised most of the H2S. Mikhail Kononets wondered if the BOX-project could start measuring H2S directly, and Lena Viktorson filled in that it would be very useful for the flux measurements. Per Hall said that the alternative was either to buy a sensor or use the laboratory sensor that Lars Rahm has bought.

In addition, Lena Viktorsson wondered if total dissolved phosphorous should be measured. Per Hall addressed the issue saying that it will be done in the coming field campaigns. In addition, analysis of it could also be done on samples taken in June, provided that there is enough water left in the bottles after running the other analyses.

Weekly measurements campaign
SMHI takes monthly measurements and CTD-profiles, usually in the first week of every month. According to preliminary model studies, monthly resolution is too coarse to reliable resolve changes and variability in the fjord. During the BOX project, samples and CTD-profiles at the official SMHI coastal station in the Byfjord and the Havstensfjord are also collected once a month, approximately two weeks after SMHI has visited the fjord. However, during about ten weeks, BOX will visit the fjord once per week. Anders Stigebrandt suggested that we may utilise SMHI since they are in the fjord every month. Thus, we can sample on three consecutive weeks, then SMHI takes their samples on the fourth week, and we resume with another three weeks of sampling. This is then repeated over the ten-week period. It was also suggested that samples only were collected down to sill depth since the deep-water is subject to only minor changes, while the surface layer exhibits far greater variability.

RV Alice will be used for taking the samples and CTD-profiles. Bengt will steer the ship and Daniel and Madeleine will assist during the campaign. However, due to teaching for both, predominantly in October, Per Hall, Lena Viktorsson and Anders Stigebrandt volunteered to help out when needed. The weekly campaign will start in the second week of September.

Anders Stigebrandt also informed the participants that Länsstyrelsen have a project in the Stigfjord, between Orust and Tjörn. They are interested in that we measure at two shallow locations in that fjord during our weekly field campaign.

The control programme, carried out by Marine Monitoring, can probably to another survey during the autumn since the Byfjord probably is at least partly oxygenated by early September if the pumps are turned on in early July at latest.

Future campaigns
Per Hall said that four more field campaigns could be done using RV Skagerrak, or a similar vessel, by the end of 2011. The next campaign is planned to October 2010. Regarding measuring, two moorings are deployed in the Byfjord and Havstensfjord, and will continue to be throughout the project. The one in the Byfjord transmits data every 4 hours and publish them as a plot on the marsys.se-webpage. In addition, at least one ADCP is located in the sill entrance throughout the project. Both moorings and ADCPs need to be serviced about once every six months. Thus, the data stream will be interrupted for a few hours, up to a few weeks, around that time.

A planar optode is also deployed in the Byfjord, taking daily 2D-images of oxygen in sediments and near sediment water.

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