Worms and submersed macrophytes reduce methane release and increase nutrient removal in organic sediments

Organic sediments are greenhouse gas and nutrient hotspots. They may display lower methane (CH4) emissions and increase nutrient retention when macrophytes and macrofauna are present, due to oxygen leakage from roots and bioirrigation. We tested this hypothesis via incubations of microcosms reproducing four treatments: bare sediment, sediment with oligochaetes, sediment with macrophytes, and sediment with both organisms. Along a 12-d experiment, CH4 ebullition in bare sediment (470 ± 13 mmol m−2) decreased by 67%, 88%, and 97% in the presence of plants, oligochaetes, and both organisms, respectively. Oligochaetes increased N2 production by ~ 200 mmol N m−2 and nitrate consumption by a factor of 4, whereas macrophytes reduced nitrogen losses by ~ 65 mmol N m−2. All treatments acted as phosphate sink. Results suggest that the maintenance of vegetation and associated macrofauna in organic sediments promotes their combined ecosystem services, resulting in significant reduction of greenhouse gas emission and nutrient release to the water column.