Abstract
The biogeochemical impact of 3 long-line mussel farms (M1, M2 and M3) in Lysekil, Sweden, was investigated from before farm establishment until 1.5 yr after operation had begun. Sedimentation, benthic N flux, total oxygen uptake (TOU) and sulfate reduction rate (SRR) were all significantly increased below the mussel lines at all 3 farms. Effects of increased sedimentation rates were revealed by sediment profile imaging and were highest at Stn M2. These effects increased significantly with time of farm operation, indicating the accumulation of organic matter within sediments over time. Furthermore, more total particulate organic N deposited at farm stations was recycled into the water column compared to at reference stations (similar to 45 versus similar to 13%), indicating an increased release of dissolved inorganic N from sediment below the mussel farms. At one station (M2) with the highest increase in sedimentation rate, denitrification seemed inhibited, while at another station (M3), with a less pronounced increase in sedimentation rate, denitrification was in fact stimulated, accounting for 13% of total sediment N removal. Calculations based on estimated values of N removal through mussel harvest and direct measurements of N input through changes in sedimentation, N regeneration from sediment to the water column through benthic fluxes and changes in denitrification showed, in all cases, a net removal of N from the system, as only 26 to 40% of the total amount of harvested N had been added to the sediments during the growth period.
Highlights
Mussel aquaculture is an internationally expanding industry, and currently increasing along the Scandinavian coasts (Smaal 2002)
Six sediment cores for measurement of nutrient the farms were established in July 2005, followed by fluxes, denitrification and total oxygen uptake were a second visit in May 2006 (May06) and a third in collected on each sampling occasion at each station
Values were higher at farm station (FS) than at reference station (REF), while, in other cases, they were lower at FS than at REF (Table 2)
Summary
Mussel aquaculture is an internationally expanding industry, and currently increasing along the Scandinavian coasts (Smaal 2002). The conditions for cultivating blue mussels Mytilus edulis in off-bottom farms are favourable due to the plentiful supply of mussel larvae and plankton in this area. Mussel farms have the potential to permanently remove particle-bound nitrogen (N) and phosphorus (P) from the water column, thereby improving water quality in eutrophic areas (Lindahl & Kollberg 2009). Eutrophication as a result of excess nutrient supply is widespread in Scandinavia, as it is in other coastal areas around the world (Diaz & Rosenberg 2008). Several international agreements (North Sea and OSPAR) have outlined goals to reduce anthropogenic N and P emissions to the sea, these remain unfullfilled (Rosenberg 1990, Anonymous 2001). Blue mussels could have the ability to reduce
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