De-vegetated marshes may contribute reactive nitrogen to urban estuaries"..pptx

what effect does a de-vegetated marsh have on an urban estuary in terms of nitrogen release

1. De-vegetated Marshes May
Contribute Reactive Nitrogen
to Urban Estuaries

Beryl C.M. Kahn,
Baruch College/The Graduate Center, City University of New York

Jamaica Bay Task Force Meeting
18 June 2024

BaruchcOLEGE

2. Jamaica Bay Marsh Restoration
Allows for Ecosystem Service
Recovery

Marshes naturally provide:
* Protection against flooding/wave action

* Carbon storage
+ Habitat for birds, fish, invertebrates
* Nitrogen (N) removal through denitrification

+ Over time, restored marshes in Jamaica Bay
perform comparable services to natural marshes

e
Photo by C. Zarnoch

3. With time, denitrification rates in restored marshes
resemble natural marshes

Jamaica Bay

Hempstead Bay (Zamoch et al, NYSG)
Other studies:
White and Howes 1994 = ~75 umol N m2 hr
(Cape Cod, MA)

Piehler and Smyth 2011 = ~100ymol N m2 h*
(Bogue Sound, NC)

Zarnoch et al. 2016

4. In restored marshes: denitrification rate corresponds with
belowground biomass

Site
Yellow Bar
Elders West
Elders East

e Joco

Belowground Biomass (g m“)

Zarnoch et al. 2017

5. Restored marshes act as a sink for dissolved
inorganic nitrogen (DIN)

Yellow Bar (YB) = 3 y/o
Elders East (EE) = 9 y/o

* Negative flux =
DIN uptake

* Marsh sediment
is a DIN sink

e
=
z
3
a y
=
[re
Z
a

Oct 2015

Zarnoch etal. 2016

6. Jamaica Bay Marshes Experience Rapid Erosion and
Loss

+ Estimates of ~85% of area lost over
the past century

Losses driven by multiple potential factors:
o Sea level rise
o Nloading

o Changes to sediment deposition

* Subsequent changes to N cycling
processes?

7. How do N cycling processes differ between degraded and intact
(vegetated) marsh sediments?

Eroding Marsh Edge

Nitrification-
Denitrification

8. Intact (Vegetated) Marsh
(n= 4/site)

Eroded (De-vegetated) Marsh
Peat (n = 4/site)

RSS

9. Methods: Continuous-Flow
Sediment Core Incubations
and Analysis

Cores fitted with airtight seals

Site water pumped through cores
Compare nutrient content, dissolved
gases between inflow/outflow

Dissolved gases measured on
membrane-inlet mass spectrometer
(MIMS)
+ Dissolved nutrients measured on auto-
analyzer

10. Results: Denitrification Response to Marsh
Loss

+ Denitrification did not
differ between
vegetated/de-vegetated
marshes

No Flux (umol N m?h-")

11. Rate (umol N mh-1)

Lenitrinicauon

Keacuve N EMUX

600;

400;

200:

-200

BB

+ De-vegetated marshes:
reactive N efflux ~2x as
high as denitrification

Possible explanations:

+ Lower microbial
assimilation in de-vegetated
sediment

Changes to chemistry
because of decomposition

12. DIN Flux (umol N m2h-')

2
8
=

300;

>
>

20 30 40
Belowground Biomass (g dry wt)

50

site
88
© swe

MarshType
A Degraded
O intact

Belowground biomass is
significantly lower in
degraded marsh sediments
(p < 0.001)

Reactive N flux negatively
correlates with belowground
biomass (p = 0.015)

13. Management Takeaways: Marsh Loss and N Release

Net N released: ~250 pmol m?h?
+ 1,400 acres of Jamaica Bay marshes lost over the past century

Daily reactive N contributions from degraded former marsh
areas in summer: 1,100 lbs N day”

+ Continued losses likely to perpetuate eutrophic conditions

« Marsh restoration will likely recover N sink capacity

14. Appendix