Carbon and Wildlife in the Restored Marshes of the Nisqually River Delta

The reference marsh at spring high tide (A) and summer low tide (B), and the restoration marsh at summer low tide (C). High tides in the restored marsh can stand more than a meter above its plain, because the land sank after being diked and drained for farming. USGS.

Since 1996 the U.S. Fish and Wildlife Service and the Nisqually Indian Tribe have restored 902 acres of tidal marsh in the Nisqually River Delta (NRD) — the largest estuary restoration in the Pacific Northwest to date. Restoring marsh helps the estuary support more wildlife, and boosts the plant carbon that feeds food webs and can be stored in marsh soils for the long term.

The study

In 2015 a USGS team began studying the delta's carbon, with three goals:

1. find which carbon sources feed the food webs of juvenile Chinook salmon and build peat, now and in the past;
2. measure the net ecosystem carbon balance (NECB) of a reference marsh and a restoration marsh;
3. model how both marshes will fare under sea-level rise, alongside historical vegetation change.

This fact sheet covers the NECB: carbon taken up by photosynthesis, lost through plant and soil respiration, released as methane, and carried off or brought in by tides.

The net ecosystem carbon balance: CO₂ uptake by photosynthesis, against CO₂ lost to respiration, methane emissions, and dissolved organic and inorganic carbon and sediment exchanged with the tides. USGS.

Why marshes matter for climate

Rising atmospheric CO₂ is changing weather and climate worldwide. One response is to preserve, restore and create ecosystems that pull carbon from the air and lock it into soil organic matter.

• Fast-growing marsh plants take up carbon into leaves, stems and roots.
• Waterlogged soils slow decay, so carbon builds up — under the right conditions forming peat that holds it for hundreds to thousands of years.
• Preventing marsh loss and restoring marshes both maximize long-term storage and bring other benefits, of great interest to resource managers and policymakers.

Measuring it

• Two sites: a natural reference marsh and a restoration marsh — historical marsh diked for farming and reopened to the tides in 2009. Comparing them shows how uptake differs and helps quantify carbon stocks for carbon markets.
• Meteorological stations at each site: instruments measure CO₂ and methane concentrations 10 times a second, with wind speed (which carries the gases), to calculate net carbon exchange with the air — and how it varies with plant type, hydrology, salinity and season.
• Light footprint: station sites are coordinated with the Billy Frank Jr. Nisqually National Wildlife Refuge and the Nisqually Indian Tribe, with solar panels and batteries placed to minimize disturbance and preserve the scenery.

The Nisqually River Delta: historical marsh (green) and marsh under restoration (gray). USGS.

A meteorological tower: CO₂ and methane analyzers, a wind anemometer, temperature, humidity and radiation sensors, and a field camera. USGS.

The tides complicate things

Tides can carry away a lot of carbon — plant carbon exported as litter or dissolved organic carbon (DOC) — and bring some in as dissolved carbon and sediment. All of it must be counted. So hydrology stations beside each meteorological station, at the edge of the marsh channel, will continuously measure dissolved carbon and particles in the water moving in and out. Together, the air and water measurements give the net carbon stored in each marsh.

Sources

Based on Assessing Wildlife Benefits and Carbon Storage from Restored and Natural Coastal Marshes in the Nisqually River Delta: Determining Marsh Net Ecosystem Carbon Balance, by Frank Anderson, Brian Bergamaschi, Lisamarie Windham-Myers, Isa Woo, Susan De La Cruz, Judith Drexler, Kristin Byrd and Karen Thorne, USGS Fact Sheet 2016–3042 (June 2016), U.S. Geological Survey (DOI); a work of the United States government in the public domain. The photographs, diagram and map come from the fact sheet's PDF. Partner: Billy Frank Jr. Nisqually National Wildlife Refuge.