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Digging worms for remediation of sediments impacted by mussel farms

Författare och institution:
Marianne Holmer (-); Marita Carlsson (-); Per Bergström (Institutionen för biologi och miljövetenskap, Tjärnö marinbiologiska laboratorium); Jens Kjerulf Petersen (-)
Antal sidor:
Sammanfattning (abstract):
Mussel farms affect the biogeochemical conditions in the sediments underneath the farms due to organic enrichment by mussel biodeposits and by mussels falling of the long-lines, which is an unwanted effect of mussel farming (Carlsson et al. 2009). Organically-enriched sediments have high oxygen consumption rates contributing to oxygen depletion events. High efflux rates of nutrients such as ammonium and phosphate, contributing to eutrophication, are also observed together with accumulation of sulphides, which prevent benthic infauna from colonizing and surviving in the sediments. Thus, a low biodiversity is in general observed in this environment. Burrowing polychaetes have the potential to stimulate the decomposition of mussel biodeposits in a similar way as has been observed underneath fish farm (Heilskov et al. 2006, Sanz-Lazaro et al. 2011). This increases the assimilative capacity of the sediments (Hargrave et al. 2008) and avoids deterioration of the sediment conditions. In this study, the prediction that polychaetes counteract the negative effects of organic enrichment in mussel farms are addressed by conducting a number of field and laboratory studies using the organic tolerant polychaete, Capitella sp., and the less tolerant but larger polychaete Hediste diversicolor, which are added to sediments affected by organic enrichment from mussel farms. Both polychaetes are native in the study area and Hediste diversicolor has commercial potential as fish feed and as bait for anglers (Bischoff et al. 2009). Sediment oxygen uptake, nutrient fluxes and pools of sulphides were measured in the field 5 weeks after the two polychaetes were added in different densities to mussel farm sediment and compared to reference sediment. In the lab experiment, sediments were collected from a reference site and manipulated with different densities of polychaetes and doses of mussel biodeposits. Short-term (hours, days) dynamics in sediment oxygen uptake and nutrient fluxes were measured. The results showed that H. diversicolor may be a strong candidate for remediation of mussel farm sediments, as it enhances the decomposition of organic matter to a larger extent than observed for other types of organic matter (dried yeast, fish farm waste products). This is probably due to direct consumption of the fecal pellets by the worms as well as mixing of the fecal pellets into the sediments by bioturbation. At the same time, the sediments were oxidized which reduced the accumulation of particular pore water sulphides as well as the iron-bound sulphides (the AVS pool). This may create favourable sediment conditions for recolonization of other infaunal species. In the lab experiment, the positive effects of H. diversicolor occurred within the first day of deposition of organic matter and then rapidly declined, when no further organic matter (fecal pellets) was added. It can be expected that the rates will remain high upon continuous addition as observed in the field, where rates were generally higher in mussel farm compared to reference sediments over the study period. The effects of addition of H. diversicolor on nutrient fluxes were more complex. It did to some extent follow the enhanced decomposition with enhanced release of nutrients from the sediments, in particular right after the organic matter was added, but fluxes of phosphate were more controlled by the biogeochemistry of the sediments, where an uptake was observed in all treatments, probably due to a reoxidation event at the study site. In these experiments H. diversicolor was added at relatively low densities (91-444 m-2) and the trends with increasing density suggests that larger densities, e.g. up to 1000 m2 may enhance the decomposition of biodeposits even further. Compared to H. diversicolor, the effects of Capitella sp. were limited. In the highest densities, the effects on sediment oxygen uptake and nutrient fluxes were similar to the low density of H. diversicolor and there were no apparent effects on the organic matter decomposition under enriched conditions by Capitella. This suggests that Capitella may have limited effects on the decomposition of mussel biodeposits, as compared to H. diversicolor, probably due to the difference in bioturbation activity between the two species. However, to further evaluate the potential of this species, higher densities of Capitella compared to what was used in this experiment should be used.
Ämne (baseras på Högskoleverkets indelning av forskningsämnen):
Biologiska vetenskaper ->
Ekologi ->
Marin ekologi
Ytterligare information:
A report from project Hav möter Land Rapportnummer: 34 Rapportnummer hos Länsstyrelsen: 2013:80 ISSN: 1403-168X
Postens nummer:
Posten skapad:
2014-04-14 12:35

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