Guiding salt marsh restoration through sediment budgets and integrative metrics
Dates
Start Date
2016-10-01
End Date
2018-09-30
Summary
USFWS Region 5 Refuges manage approximately 24,000 hectares of coastal wetlands, ecosystems that are undergoing drastic change under accelerating sea-level rise and changing climatic forcing. In response to signs of marsh destabilization, such as widening channels, water logged platforms, accelerating erosion, and internal disintegration, Refuges have invested > $100 million in restoration projects to enhance resiliency. However, more data is needed on the long-term viability of salt marsh units in order to direct limited resources to sites that are likely to persist with sea level rise. Fifteen coastal refuges or refuge complexes in Region 5 participate in Salt Marsh Integrity (SMI) monitoring, to assess ecological condition, and [...]
Summary
USFWS Region 5 Refuges manage approximately 24,000 hectares of coastal wetlands, ecosystems that are undergoing drastic change under accelerating sea-level rise and changing climatic forcing. In response to signs of marsh destabilization, such as widening channels, water logged platforms, accelerating erosion, and internal disintegration, Refuges have invested > $100 million in restoration projects to enhance resiliency. However, more data is needed on the long-term viability of salt marsh units in order to direct limited resources to sites that are likely to persist with sea level rise.
Fifteen coastal refuges or refuge complexes in Region 5 participate in Salt Marsh Integrity (SMI) monitoring, to assess ecological condition, and to determine where management or restoration is needed. SMI is monitored on 130 salt marsh management units, encompassing 23,777 ha. SMI includes a suite of 11 salt marsh attributes, mainly using rapid field assessment methods. SMI does not include sediment transport-based metrics, which geophysicists have recently indicated are vital indicators of marsh trajectory.Studies by the USGS (e.g., Ganju et al., 2013) have shown that the sediment budget is critical to wetland long-term viability. Most wetland assessments rely on point measurements of suspended-sediment concentration (SSC), accretion, and/or elevation change which can be misleading. Recent work from eight marshes nationwide (Ganju et al., in preparation) shows that the sediment budget within a marsh complex scales with the unvegetated-vegetated marsh ratio (UVVR), an integrative metric of marsh condition. It is critical to use more spatially and temporally integrative measures of stability, such as sediment budgets and the UVVR, to guide management and restoration priorities.
For this proposal, we will determine the sediment flux budget for selected Parker River NWR and Plum Island Estuary marsh complexes, to guide restoration strategies under consideration. We will also develop rapid-assessment metrics of marsh stability that can be applied across broader landscapes, and other salt marsh management units. These include the UVVR and a monitoring protocol for sediment flux. Plum Island Sound is characterized by low riverine sediment input; as a result the salt marshes of the Parker River NWR are potentially vulnerable to sea-level rise, as there might not be enough sediment for overall stability. It is therefore a priority to determine the resilience/vulnerability of salt marshes in Region 5 using the sediment budget protocol developed by the USGS (Ganju et al. 2013).
Objectives:
Our first objective is to determine the sediment budgets of tidal creeks at different points within the refuge. These results will directly inform wetland restoration efforts by providing boundary conditions for numerical models (e.g. MEM) as well as expected rates of sediment import/export from the system. Before planning a major restoration project such as sediment augmentation (thin-layer deposition) it is critical to quantify the pre-restoration sediment budget to understand potential future outcomes. Based on this knowledge, we will instrument 2 new sites in the Parker River NWR, likely sites with larger UVVRs than the PIE-LTER sites.
Our second objective is to use these data to expand coverage of a new, physically based national wetland assessment. Through Sandy Supplemental funding, the USGS is developing such a product for Forsythe NWR (New Jersey). That product synthesizes physical, geomorphic, and ecological drivers of wetland change, based on data collected through Sandy-funded efforts. The deliverable product is a GIS-based portal that displays drivers (e.g. wave attack, sediment supply, SLR, salinity intrusion, etc.) and derived vulnerability indices. Through this SSP project, we aim to expand coverage to wetlands within Parker River NWR and throughout the Plum Island Estuary.
Our third objective is to develop rapid assessment metrics that can be applied by USFWS and other conservation organizations on a regional-scale to assess salt marsh persistence. Additional data collected from the Rowley marsh and Newbury marsh will augment existing data from other sites with sediment flux measurements to compare intensive field data to (1) UVVR and (2) reduced field measurements using turbidity and directional velocity meters alone. These metrics will allow USFWS to conduct region-wide vulnerability assessment and focus future research, management, restoration, and acquisition funds where it is needed.
