The impact of historic marsh farming on Delaware Bay tidal marshes
The impact of historic marsh farming on Delaware Bay tidal marshes
MARSH FARMING ON THE DELAWARE BAY • Extensive in the Delaware Bay
• Gradually became unsustainable and unprofitable • Passive restoration of tidal flow to the majority of formerly diked marshes • No accounting of the extent of diked marsh in the Delaware Bay
Cedar Swamp Creek
Cedar Swamp Creek Meadow Company
1815
1909
Elevation
Elevation
GOALS OF STUDY • Describe the scale of impoundment • Quantify the impacts • Put these impacts in context with other marsh losses and gains.
APPROACH
APPROACH
• historically impounded marsh • unimpounded marsh • forest
• • • • • • • • •
Spartina alterniflora high marsh freshwater tidal Phragmites impounded forest interior open water coastline edge erosion tidal channel expansion
• historically impounded marsh • unimpounded marsh • forest
• • • • • • • • •
Spartina alterniflora high marsh freshwater tidal Phragmites impounded forest interior open water coastline edge erosion tidal channel expansion
EXTENT OF MARSH FARMING
51% of marsh historically impounded for farming = 45,793 acres
farmed not farmed
Impacts of farming: elevation
Historically farmed marsh is lower in elevation
meters NAVD88
1.2 1.0 0.8 0.6 0.4 0.2 0.0
farmed
still diked farms
not farmed
Historically farmed marsh is lower in elevation
meters NAVD88
1.2 1.0 0.8 0.6 0.4 0.2 0.0
farmed
still diked farms
not farmed
Impacts of farming: vegetation
Nearly all interior marsh loss is in historically farmed areas 30 25 20
Conversion of interior marsh to open water
15 10 5 0
farmed
never farmed
Nearly all high marsh vegetation is in areas that were never farmed. 25 20 15
Amount of high marsh
10 5 0
farmed
never farmed
FARM IMPACTS IN CONTEXT Conversion of interior marsh to open water: 10,022 acres (11%) Bay shoreline erosion: 4,242 acres (5%) Creek and ditch expansion: 5,236 acres (6%) Total: 19,500 out of 90,288 (22%)
NET MARSH LOSS 12,542 ACRES 6000 4000
6,958
Hectares
2000 0 -2000 -4000 -6000
10,022
4,242
5,236
SUMMARY Past impoundment is responsible for considerable marsh loss and degradation An even greater area is at low elevations, threatening further losses from sea level rise
THE BRIGHT SIDE Degradation is the result of direct human impacts – easier to address.
Dredge material can offset elevation deficits = more diverse wildlife habitat + greater resilience to sea level rise.
MARSH FARMING ON THE DELAWARE BAY • Extensive in the Delaware Bay
• Gradually became unsustainable and unprofitable • Passive restoration of tidal flow to the majority of formerly diked marshes • No accounting of the extent of diked marsh in the Delaware Bay
Cedar Swamp Creek
Cedar Swamp Creek Meadow Company
1815
1909
Elevation
Elevation
GOALS OF STUDY • Describe the scale of impoundment • Quantify the impacts • Put these impacts in context with other marsh losses and gains.
APPROACH
APPROACH
• historically impounded marsh • unimpounded marsh • forest
• • • • • • • • •
Spartina alterniflora high marsh freshwater tidal Phragmites impounded forest interior open water coastline edge erosion tidal channel expansion
• historically impounded marsh • unimpounded marsh • forest
• • • • • • • • •
Spartina alterniflora high marsh freshwater tidal Phragmites impounded forest interior open water coastline edge erosion tidal channel expansion
EXTENT OF MARSH FARMING
51% of marsh historically impounded for farming = 45,793 acres
farmed not farmed
Impacts of farming: elevation
Historically farmed marsh is lower in elevation
meters NAVD88
1.2 1.0 0.8 0.6 0.4 0.2 0.0
farmed
still diked farms
not farmed
Historically farmed marsh is lower in elevation
meters NAVD88
1.2 1.0 0.8 0.6 0.4 0.2 0.0
farmed
still diked farms
not farmed
Impacts of farming: vegetation
Nearly all interior marsh loss is in historically farmed areas 30 25 20
Conversion of interior marsh to open water
15 10 5 0
farmed
never farmed
Nearly all high marsh vegetation is in areas that were never farmed. 25 20 15
Amount of high marsh
10 5 0
farmed
never farmed
FARM IMPACTS IN CONTEXT Conversion of interior marsh to open water: 10,022 acres (11%) Bay shoreline erosion: 4,242 acres (5%) Creek and ditch expansion: 5,236 acres (6%) Total: 19,500 out of 90,288 (22%)
NET MARSH LOSS 12,542 ACRES 6000 4000
6,958
Hectares
2000 0 -2000 -4000 -6000
10,022
4,242
5,236
SUMMARY Past impoundment is responsible for considerable marsh loss and degradation An even greater area is at low elevations, threatening further losses from sea level rise
THE BRIGHT SIDE Degradation is the result of direct human impacts – easier to address.
Dredge material can offset elevation deficits = more diverse wildlife habitat + greater resilience to sea level rise.
