Impact of bottom trawling on sediment biogeochemistry: a modelling approach

Abstract. Bottom trawling in shelf seas can occur more than 10 times per year for a given location. This affects the benthic metabolism, through mortality of macrofauna, resuspension organic matter from sediment, and alterations physical sediment structure. However, impacts on carbon mineralization associated processes are not well known. Using modelling approach, effects increasing frequencies early diagenesis were studied five different sedimentary environments, simulating deeper-penetrating gear (e.g. tickler chain beam trawl) versus shallower, variable penetrating an electric pulse trawl). Trawling events strongly increased oxygen nitrate concentrations surface layers led to significantly lower amounts ammonium (43 %–99 % reduction) top cm (62 %–96 reduction). As result, total rates decreased by up 28 %. The effect differed both between types frequencies. shallow-penetrating had slightly smaller denitrification gear, but there no statistically results all other parameters. Denitrification was reduced 69 fine sandy whereas nitrogen removal nearly doubled highly eutrophic mud. suggests that even relatively low penetration depths bottom fishing gears generate significant biogeochemical alterations. Physical trawl-induced sediments, exacerbated bioturbating identified as main cause changes process.