SEAGRASS RESTORATION STIMULATES NITROGEN CYCLING (E)
Following the wholesale loss of seagrass in Virginia’s coastal bays in the 1930s, large-scale restoration has lead to the establishment of over 25 km2 of seagrass meadow by 2016. We measured a suite of nitrogen processes in the restored meadow and in adjacent bare sediment in order to understand the effects of this state change on nitrogen (N) cycling. We used in situ push-pull incubations to measure denitrification and DNRA and laboratory incubations to measure N fixation. We measured dissolved N fluxes across the sediment-water interface using benthic chambers and calculated burial rates from the N content and accretion rates of the sediment. In addition to processes, we measured standing stocks of N in the sediment and in seagrass biomass, using the leaf marking technique to measure changes to the biomass stock over time. Our results showed that N processes were enhanced in the meadow compared to adjacent bare sediment, likely due to increased sedimentation and release of oxygen and labile carbon from seagrass roots. In particular, N storage and removal were enhanced in the meadow. Denitrification rates were 25.4 µmol N m-2 h-1 and 7.3 µmol N m-2 h-1 in the meadow and bare sediment respectively, and burial rates were 30.7 µmol N m-2 h-1 and 2.9 µmol N m-2 h-1. Standing stocks were orders of magnitude greater than fluxes; the meadow stored 2.13 mol N m-2 in sediment and 0.60 mol N m-2 in seagrass biomass (in summer), compared to 1.29 mol N m-2 in bare sediment. The stimulation of N removal and storage in the restored meadow may buffer increased N loading to the coastal bays as Virginia’s Eastern Shore experiences increased development and agricultural intensification.
Aoki, L. R., University of Virginia, USA, email@example.com
McGlathery, K. J., University of Virginia, USA, firstname.lastname@example.org
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