September 7, 2023

Tidal wetland groundwater: the flood from below

by S-FX.com

marsh wetland

Tidal wetlands flood twice a day in the Barnegat Bay. As nature intended, tides rise, water floods the surface, and then drains as the tide falls. But as above, so below; the same tidal rise, fall, and flooding above ground also happen underground. The soil can occasionally flood underground because of tidal wetlands’ low-lying elevation.


Peat and plant roots that serve as the base of these wetlands are like sponges that soak in water. Although these plants are adapted to wet conditions, their roots still need oxygen and should not be too wet. Tidal wetlands that are too wet are vulnerable to drowning as sea-level rises. For the past year, the Barnegat Bay Partnership with Partnership for the Delaware Estuary have been plumbing the depths of tidal marshes to divine what information it holds.

PA051727 Copy Scaled
Flooded Wetlands


Last year, the team installed wells at four tidal marshes in Barnegat Bay to study and understand groundwater patterns, shallow groundwater levels, and what factors cause groundwater levels to rise higher than usual. This information will help them track how waterlogged ground affects tidal wetlands and perhaps design better future restoration plans for tidal wetlands.


One tactic that tidal wetland managers are exploring, called thin-layer placement, casts clean dredge material onto the tidal wetland surface to raise elevations. Groundwater levels show how underground flooding happens at the dredged material locations during this process. So far, the team has found that some sites are more saturated than others.


Barnegat Bay Partnership and Partnership for the Delaware Estuary will continue to monitor these wetland sites through this summer and hopefully beyond. Their findings will help practitioners, such as state and federal wetlands specialists, design wetland restoration projects.

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UNKNOWN

There is limited data available to quantify Wetland and Riparian Buffer Preservation, or updated data to quantify Wetland Acreage. The BBP has obtained funding and will begin assessment efforts for both targets, in the next few years.

 

 Hard Clam abundance has not been updated since 2012. Recovery of the stock will be guided by the Fishery Management Plan for Hard Clams, which is under development with the NJDEP, BBP, and other organizations. Reclam the Bay and other partners have continued to plant clams for restoration purposes. Continued plantings in strategic locations which maximize survival and reproduction is one strategy to pursue in the coming years. This work can use a model developed by Rutgers with BBP funding which identified areas where planted clams could have the greatest dispersal of their larvae and thus potentially maximally contribute to the recovery of the stock.

 Water Withdrawals were over the target in the 2021 report; USGS has not yet completed its latest update, so a definitive determination of status is not available. However, additional NJDEP data show that it is likely that we continue to not meet the target. Per capita water use has gone down, demonstrating the effectiveness of water-saving appliances and practices, but that decrease has been offset by population gains. 


IN PROGRESS

New maps quantifying Submerged Aquatic Vegetation extent were developed, but poor image clarity resulted in a high degree of uncertainty in the total acreage. NJDEP and Rutgers are working to resolve the uncertainty of these maps, and improve the total acreage estimate. Funding has also been obtained for further research and restoration activities. Several groups are developing potential restoration actions.

The USGS has completed the first phase of its study to identify minimum ecological flows in select Barnegat Bay tributaries. USGS scientists compared streamflow statistics between historical and current time periods to better understand trends in watershed flow conditions. This work provides a foundation for developing ecological flow targets in the Barnegat Bay watershed.  Similar to SAV extent, funding (approximately $450K) has been obtained by the BBP to complete the remaining phases necessary for threshold determination.

 

TARGETS ACHIEVED

No targets can be considered “Achieved” at this time.

 

NOT ACHIEVING

Several Public Swimming Beaches exceeded their safe swimming standards more frequently than during their baseline time period (2016-2018).

While most beaches are routinely safe for swimming, several problematic areas such as Beachwood, Hancock, Windward, and several lake beaches need track-down studies and restoration to pinpoint and address sources of bacteria.

Acres of Approved Shellfish Waters decreased from the last report. While this decrease was small, it represents a loss of previously approved waters. Similar to public beaches, track-down studies and restoration work are needed to pinpoint and address sources of bacteria.

 

Tidal wetland groundwater: the flood from below

Tidal wetlands flood twice a day in the Barnegat Bay. As nature intended, tides rise, water floods the surface, and then drains as the tide falls. But as above, so below; the same tidal rise, fall, and flooding above ground also happen underground. The soil can occasionally flood underground because of tidal wetlands’ low-lying elevation.

Peat and plant roots that serve as the base of these wetlands are like sponges that soak in water. Although these plants are adapted to wet conditions, their roots still need oxygen and should not be too wet. Tidal wetlands that are too wet are vulnerable to drowning as sea-level rises. For the past year, the Barnegat Bay Partnership with Partnership for the Delaware Estuary have been plumbing the depths of tidal marshes to divine what information it holds.

PA051727 Copy Scaled
Flooded Wetlands

Last year, the team installed wells at four tidal marshes in Barnegat Bay to study and understand groundwater patterns, shallow groundwater levels, and what factors cause groundwater levels to rise higher than usual. This information will help them track how waterlogged ground affects tidal wetlands and perhaps design better future restoration plans for tidal wetlands.

One tactic that tidal wetland managers are exploring, called thin-layer placement, casts clean dredge material onto the tidal wetland surface to raise elevations. Groundwater levels show how underground flooding happens at the dredged material locations during this process. So far, the team has found that some sites are more saturated than others.

Barnegat Bay Partnership and Partnership for the Delaware Estuary will continue to monitor these wetland sites through this summer and hopefully beyond. Their findings will help practitioners, such as state and federal wetlands specialists, design wetland restoration projects.

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marsh wetland