TY - JOUR

T1 - Living on the edge

T2 - How traits of ecosystem engineers drive bio-physical interactions at coastal wetland edges

AU - LG, Gillis

AU - Maza, M.

AU - Garcia-Maribona, J.

AU - Lara, J. L.

AU - Suzuki, T.

AU - Argemi Cierco, M.

AU - Paul, M.

AU - Folkard, A. M.

AU - Balke, T.

N1 - Funding Information: This study (H+DHI-10-HyWEdges) received funding from European Union , Hydralab+ . The authors would like to thank DHI for the use of their total environmental stimulator flume and the support staff. M. Maza is sincerely grateful to the Spanish Ministry of Science and Innovation for the funding provided in the grant RTI2018–097014-B-I00 of Proyectos de I+D+I Retos Investigación 2018 funded by MCIN / AEI / 10.13039/501100011033 and by “ ERDF A way of making Europe ”.

PY - 2022/8

Y1 - 2022/8

N2 - Salt marshes and mangrove forests provide critical ecosystem services such as reduced sediment erosion and increased hydrodynamic buffering. Sediment transport and hydrodynamics can be influenced by specific functional traits of the plants (for example, flexibility vs. rigidity) and community traits (for example, spatial density). While there is a growing body of literature on plant trait and hydrodynamic interactions, direct comparative studies of sediment transport and scour development in and around intertidal wetland edges are scarce. In this study we systematically compared the effects of plant traits on sediment budgets around the lateral edges of intertidal wetlands under controlled hydrodynamic and sedimentary conditions using full scale vegetation mimics with contrasting flexibilities and densities. Experiments were carried out in a large-scale flume, using two spatial densities each of flexible and rigid vegetation mimics. We measured unconsolidated sedimentary bed-level changes in experimental runs using waves only, currents only, and waves combined with currents. Both mimic types dampened the energy of the incoming flow, highlighting the role of rigid and flexible aquatic vegetation in providing coastal protection. The rigid vegetation mimics’ lateral edge experienced larger velocities, more energetic turbulence, and local scour around individual stems. Scour around stems could influence the lateral expansion of the rigid vegetation ecosystem by reducing sediment stability and thus decreasing seedling establishment success. The flexible plant mimics produced lower turbulence at their leading edge, which resulted in sediment being deposited over a shorter distance into the patch than in the rigid mimics. Decreased vegetation density caused reduced sediment erosion at the leading edge and less sediment accumulation within the vegetation patches for both the rigid and flexible mimics. The hydrodynamic and sedimentary processes identified for both ecosystems are linked to different feedbacks. A positive feedback was identified in which vegetation attenuates hydrodynamic energy allowing sediment accumulation within the patch. A negative feedback was identified where large velocities caused flow divergence and erosion outside of the vegetation, and would therefore compromise its lateral expansion. High densities of rigid vegetation enhance this negative feedback. Lower density flexible vegetation, however, combined with less energetic hydrodynamic conditions facilitate the expansion of vegetation patches as they cause less flow divergence and therefore less erosion. The strong flow divergence observed in the rigid vegetation cases highlight their importance for buffering hydrodynamics but at the cost of increased erosion within the front end of patches and along their lateral edges.

AB - Salt marshes and mangrove forests provide critical ecosystem services such as reduced sediment erosion and increased hydrodynamic buffering. Sediment transport and hydrodynamics can be influenced by specific functional traits of the plants (for example, flexibility vs. rigidity) and community traits (for example, spatial density). While there is a growing body of literature on plant trait and hydrodynamic interactions, direct comparative studies of sediment transport and scour development in and around intertidal wetland edges are scarce. In this study we systematically compared the effects of plant traits on sediment budgets around the lateral edges of intertidal wetlands under controlled hydrodynamic and sedimentary conditions using full scale vegetation mimics with contrasting flexibilities and densities. Experiments were carried out in a large-scale flume, using two spatial densities each of flexible and rigid vegetation mimics. We measured unconsolidated sedimentary bed-level changes in experimental runs using waves only, currents only, and waves combined with currents. Both mimic types dampened the energy of the incoming flow, highlighting the role of rigid and flexible aquatic vegetation in providing coastal protection. The rigid vegetation mimics’ lateral edge experienced larger velocities, more energetic turbulence, and local scour around individual stems. Scour around stems could influence the lateral expansion of the rigid vegetation ecosystem by reducing sediment stability and thus decreasing seedling establishment success. The flexible plant mimics produced lower turbulence at their leading edge, which resulted in sediment being deposited over a shorter distance into the patch than in the rigid mimics. Decreased vegetation density caused reduced sediment erosion at the leading edge and less sediment accumulation within the vegetation patches for both the rigid and flexible mimics. The hydrodynamic and sedimentary processes identified for both ecosystems are linked to different feedbacks. A positive feedback was identified in which vegetation attenuates hydrodynamic energy allowing sediment accumulation within the patch. A negative feedback was identified where large velocities caused flow divergence and erosion outside of the vegetation, and would therefore compromise its lateral expansion. High densities of rigid vegetation enhance this negative feedback. Lower density flexible vegetation, however, combined with less energetic hydrodynamic conditions facilitate the expansion of vegetation patches as they cause less flow divergence and therefore less erosion. The strong flow divergence observed in the rigid vegetation cases highlight their importance for buffering hydrodynamics but at the cost of increased erosion within the front end of patches and along their lateral edges.

KW - Currents

KW - Mangrove forest

KW - Positive and negative feedbacks

KW - Salt marsh

KW - Scale-dependant feedbacks

KW - Sediment transport

KW - Waves

UR - http://www.scopus.com/inward/record.url?scp=85132939783&partnerID=8YFLogxK

U2 - 10.1016/j.advwatres.2022.104257

DO - 10.1016/j.advwatres.2022.104257

M3 - Article

AN - SCOPUS:85132939783

VL - 166

JO - Advances in water resources

JF - Advances in water resources

SN - 0309-1708

M1 - 104257

ER -