Sediment budgets and salt marshes:
a zero-sum game
Neil K. Ganju
U.S. Department of the Interior
U.S. Geological Survey
Sediment budget like a bank account
Blackwater NWR
Direct deposits
Rivers
Estuary
Ocean
Balance
Elevation and areal
coverage of system
Automatic withdrawals
Currents
Waves
Dredging
- System includes marsh plain, mudflats, and channels
- “Stable” system means elevation and areal footprint
of all components is constant
A “stable” system can be upset by sea-level rise
Direct deposits
Rivers
Estuary
Ocean
Balance
Elevation and areal
coverage of system
Automatic withdrawals
Currents
Waves
Dredging
Sea-level rise
- Sea-level rise represents a relative decrease in elevation of the marsh
- More sediment is needed to keep account balance stable
A “stable” system can be upset by sea-level rise
Direct deposits
Rivers
Estuary
Ocean
Automatic withdrawals
Currents
Waves
Dredging
Sea-level rise
- If no additional source of funds, balance gets depleted
A “stable” system can be upset by sea-level rise
Direct deposits
Rivers
Estuary
Ocean
Automatic withdrawals
Currents
Waves
Dredging
Sea-level rise
????
- Once sediment in account is depleted, marsh is “in debt”
- Sediment-based “lifespan” is time left until marsh is in debt
- Debt means scavenging of marsh plain to feed mudflats and channels
Accounting a difficult first step: sediment flux
Sediment flux (kg/s)
What does flux tell us? Sediment budget
What does flux tell us? Sediment portfolio
Wetland sediment fluxes: what have we learned?
Schooner Creek: Suk et al., 1999
Sediment budget is correlated with open water coverage
𝑈𝑈𝑈𝑈𝑈𝑈𝑈𝑈 =
𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶, 𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓, 𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝
𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣 𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚
UVVR excellent indicator of
sediment budget
Optimal UVVR ~ 0.10
UVVR can be measured and
tracked through time with
aerial imagery/satellites
UVVR = 0.1
UVVR = 1
Lifespan is correlated with open water coverage
UVVR good indicator of
sediment-based lifespan
Lifespan an estimate of when
sediment reserves held in the
marsh plain are needed to
satisfy withdrawals
Most vulnerable marshes
have lifespan <200 y
UVVR = 0.1
UVVR = 1
Knowledge gap: Bay-wide sediment budget
USGS NYWSC established sediment
flux site on Marine Parkway Bridge
Nov. 2014
Preliminary results show small import
Rutgers studies show similar results
WHOI numerical modeling of entire
Hudson/JB system agrees
Hudson River Estuary and NY/NJ
Harbor sediments may be only
reliable holding in portfolio
Knowledge gap: marsh-specific sediment budgets
JoCo marsh: UVVR ~ 0.4
Sediment budget?
Lifespan?
Big Egg marsh: UVVR ~ 0.7
Sediment budget?
Lifespan?
Ramifications of sediment budget/UVVR in Jamaica Bay
JB marshes certainly experiencing a
sediment deficit
Lifespan likely < 200 y
Quantifying sediment budget critical if
engaging in sediment replenishment
Quantifying lifespan critical for
planning habitat provision