A nearshore model to investigate the effects of seagrass bed geometry on wave attenuation and suspended sediment transport

Biological nitrogen (N 2 ) fixation is the primary input of new nitrogen (N) to marine systems, and is important in meeting the N demands of primary producers. In this study, we determined whether restoration of the eelgrass Zostera marina L. in a shallow coastal bay facilitated increasing rates of N 2 fixation as the meadows aged. Rates of N 2 fixation were measured in a system that had been devoid of eelgrass following local extinction in the 1930s until restoration by seeding began in 2001. Restored meadows of different ages were compared to nearby bare sediment sites during summer peak metabolism over 2 yr. Nutrient addition by N 2 fixation was enhanced as the meadows aged. Rates of N 2 fixation in the older (7 to 8 yr old) meadows were 2.7 times more than the younger (2 to 3 yr old) meadows (average 390 and 146 µmol N m ). Heterotrophic epiphyte bacteria fixed approximately 90% of the total N 2 in Z. marina meadows of both age classes. Both sediment and epiphyte N 2 fixation were strongly related to Z. marina density and sediment organic content, suggesting that shoot density increases the positive feedback of plant presence on N 2 fixation through the release of organic carbon exudates into the rhizosphere and phyllosphere, and the build up of sediment organic matter also increases. The N provided through fixation represented a large fraction (20.5 to 30%) of the total N demand to support eelgrass aboveground growth during this period of peak summertime production.

Section: Drivers Of N 2 Fixationmentioning

confidence: 71%

Nitrogen fixation in restored eelgrass meadows

Cole¹,

McGlathery²

2012

“…6). At South Bay, the rapid increase in turbidity with flooding tide suggests that in addition to wind-and storm-generated resuspension (Koch et al 2006, Chen et al 2007, Lawson et al 2007, tidal energies were sufficient at the site to re-suspend sediments and reduce water clarity. Much less effect was seen at all 3 Chesapeake Bay sites.…”

Section: Discussionmentioning

confidence: 99%

Eelgrass survival in two contrasting systems: role of turbidity and summer water temperatures

Moore¹,

Shields²,

Parrish³

et al. 2012

“…The effect of shoot density on wave attenuation has been recognised in a number of studies (e.g. Bouma et al 2005, Chen et al 2007, Augustin et al 2009, Prinos et al 2010), but the number of different densities , C. L. Amos used was generally low (2 to 3) and hence insufficient to derive in-depth insight in the relationship between shoot density and wave attenuation. Moreover, this relationship might be complicated by the effect of water depth.…”

Section: Introductionmentioning

confidence: 99%

Wave attenuation by submerged vegetation: combining the effect of organism traits and tidal current

Paul¹,

Bouma²,

Amos³

2012

148

104

Accurate wave height prediction along the shore plays an important role in coastal protection and management. To account for the effect of submerged vegetation in waveattenuation models, it is important to understand how the interaction between vegetation characteristics and hydrodynamic forcing affects wave attenuation. To determine the effect of vegetation characteristics, we used seagrass mimics that varied in (1) blade stiffness, (2) shoot density and (3) leaf length; to investigate the effect of hydrodynamic forcing, we studied wave attenuation in the absence and presence of a tidal current. Results show that wave attenuation is positively correlated with blade stiffness and for a given wave in shallow water, attenuation is dependent on a combination of shoot density and leaf length, which can be described by the leaf area index. The presence of a tidal current strongly reduced the wave-attenuating capacity of seagrass mimics, and this reduction was most pronounced at high shoot densities. Thus, most studies that have been carried out under waves only will structurally overestimate wave attenuation for tidal environments, emphasising that tidal currents need to be taken into account in future studies on wave attenuation by vegetation.