Ecological Stressors - Rocky Coastlines, Mangroves, Marshes, Droughts, and Storms

Science Center Objects

Coastal estuaries that contain marshes and mangroves are currently being reshaped by changing ocean and atmospheric conditions through prolong drought, sea-level rise and increased extreme storm events. Many projected increases in sea-level are expected to result in loss of tidal wetlands and their component species. In addition, changing sediment loads, extreme tide and storm events, and shifting salinity levels will affect tidal marshes by altering the plant community and structure that provide critical habitat for endangered species. Efforts to anticipate coastal ecosystem change have largely relied on global or regional data, and therefore it remains unknown how these ecological stressors will impact nearshore habitat at local scales. Dr. Karen Thorne and her team of researchers are monitoring and investigating how ecological stressors impact wetlands and habitat along the Pacific coast.

Tidal Marsh Processes

Our coastal monitoring network is focused on involving managers in collecting tidal wetland data at several local sites along the Pacific coast. We use this data for both site-specific sea-level rise ecosystem response projections, and for interpreting across the entire latitudinal gradient of the Pacific coast. Some methods we use to collect this information are outlined below.

WERC Tidal Marsh Processes
For more information on Sediment Elevation Tables (SETs): domain.)

Water Level Monitoring: Storm impacts

Members of WERC study the impact of extreme storm flooding events on marsh wildlife habitats and on sediment accumulation in coastal marshes.  Water level and salinity loggers are deployed at a network of wetland sites in San Francisco Bay and along the Pacific coast.  Inundation and salinity patterns help inform flooding trends during tidal cycles, seasons and El Nino and other extreme storm events. For a time lapse video of inundation during a king tide:

WERC marsh during a storm
Marsh during a storm (Public domain.)

Storm Impacts and Marsh Wildlife Habitat

An objective for large-scale wetland restoration efforts in the San Francisco Bay Estuary is to be successful in ensuring the persistence of endangered species. In order to accomplish this goal, land managers will need to understand how habitat availability and quality for these wildlife species will be affected by sea-level rise, particularly in relation to elevated water levels during storm events. We projected the effects of increased storm frequency and intensity on breeding habitats availability and in San Francisco Bay marshes. Our results suggest instead of focusing only on marshes with suitable habitat structure, restoration efforts should also be focused on high-elevation marshes, as they provide greater protection from nest flooding during high tides than low-elevation marshes.

Storm Impacts on Sediment and Accretion

Tidal marsh ecosystems are dynamic systems that respond to changes in oceanic and freshwater processes and sea-level. Therefore, how sea-level rise will impact these coastal and estuarine systems is dependent on local flooding conditions within each site. Projected sea-level rise and changes in storm frequency and intensity will affect tidal marshes by altering the supply of suspended sediment, the length of inundation of the marsh platform, and plant and wildlife communities. Lower energy storms that coincide with high tides can create extreme sea-levels and cause extended periods of flooding which can substantially reduce habitat availability for wildlife, but can also increase the potential for marsh sediment accumulation, which is essential for marsh stability and persistence. The objective of this research is to evaluate how regional weather conditions resulting in low-pressure storms change local tidal conditions. Using site-level measurements of elevation, plant communities, and water levels, we study the impacts these storms and projected sea-level rise will have on the structure and function of tidal marshes, and how they may affect hydro-geomorphic processes and marsh biotic communities.

WERC technician deploying water level logger
USGS WERC technician deploying water level logger (Public domain.)

Inundation Patterns

To understand current tidal flooding patterns and cycles at local salt marsh locations, we deployed water-level loggers at large channel networks throughout our estuary study sites. The loggers measured water depth and duration, temperature, and conductivity at 6-minute intervals. This type of water level monitoring provides detailed information on tidal marsh flooding and drainage patterns, including depth during tidal cycles, inundation periods for the salt marsh plain, and characteristics of flooding during storm events. Site-specific tidal data are tied to established tide gauges to allow understanding of historic patterns of extreme tidal events which can be related to projected future conditions.

A photo of a USGS employee monitoring turbidity in an eelgrass bed.
USGS employee monitoring turbidity in an eelgrass bed, Seal Beach National Wildlife Refuge.(Credit: Katherine Powelson, USGS Western Ecological Research Center. Public domain.)

Predator Prey Relationships

Numerous publications have suggested that high tides can potentially negatively impact prey populations in tidal marshes through increased predation risk, primarily by forcing prey species to temporarily emigrate from their flooded habitat. In California many of these prey species are of management concern, such as the endangered salt marsh harvest mouse and Ridgway’s Light-footed rails. However, few studies have explicitly examined this hypothesis that endangered species are at greater risk during floods from predators. We monitor flooding patterns and habitat availability during high tides, Atmospheric River storms, and El Nino events which all result in longer and deeper flooding in tidal marsh habitats.  We hypothesized that predator effort and efficiency would increase with increasing water level.

Program Objectives:

  • Development of sea-level rise impact models for the Pacific estuarine tidal gradient.
  • Monitor the effects of storms on availability of tidal marsh habitat to wildlife.
  • Incorporate wildlife movements and population monitoring into sea-level rise modeling.
  • Inventory and monitor current species presence and develop a better understanding of species requirements.
  • Model sedimentation accretion processes on the marsh platform.