Changes in ecosystem nitrogen and carbon allocation with black mangrove (Avicennia germinans) encroachment into Spartina alterniflora salt marsh

Date 2019-11-21
Temporal extent 2016-06-02 -2018-05-18
Author(s) Macy AaronORCID, Osland MichaelORCID, Cherry JuliaORCID, Cebrian JustORCID
DOI 10.17882/70428
Publisher SEANOE
Keyword(s) wetlands, coastal, sequestration, Louisiana, tropicalization, migration, climate change, ecosystem services, filtration, blue carbon
Abstract

Increases in temperature are expected to facilitate encroachment of tropical mangrove forests into temperate salt marshes, yet the effects on ecosystem services are understudied. Our work was conducted along a mangrove expansion front in Louisiana (USA), an area where coastal wetlands are in rapid decline due to compounding factors, including reduced sediment supply, rising sea level, and subsidence. Marsh and mangrove ecosystems are each known for their ability to adjust to sea-level rise and support numerous ecosystem services, but there are some differences in the societal benefits they provide. Here we compare carbon and nitrogen stocks and relate these findings to the expected effects of mangrove encroachment on nitrogen filtration and carbon sequestration in coastal wetlands. We specifically evaluate the implications of black mangrove (Avicennia germinans) encroachment into Spartina alterniflora-dominated salt marsh. Our results indicate that black mangrove encroachment will lead to increased aboveground carbon and nitrogen stocks. However, we found no differences in belowground (i.e., root and sediment) nitrogen or carbon stocks between marshes and mangroves. Thus, the shift from marsh to mangrove may provide decadal-scale increases in aboveground nitrogen and carbon sequestration, but belowground nitrogen and carbon sequestration (i.e., carbon burial) may not be affected. We measured lower pore water nitrogen content beneath growing mangroves, which we postulate may be due to greater nitrogen uptake and storage in mangrove aboveground tissues compared to marshes. However, further studies are needed to better characterize the implications of mangrove encroachment on nitrogen cycling, storage, and export to the coastal ocean.

Licence CC-BY-NC-SA
Acknowledgements We thank the many folks who gave their time and effort in the field and in lab: J. Goff, E. Wellman, G. Martin, A. Moorhead, T. Gruninger, N. Snyder, G. MacManus, L. Puishys, S. Lindhardt, N. Moreno, L. Linn, P. Chanton, B. Mortazavi, A. Robertson, E. Waddell, H. Ehrmann. The Louisiana Department of Wildlife and Fisheries (Grand Isle, LA) provided regular lodging, as well as additional lodging support from the USDA Plant Materials Center (Golden Meadow, LA). We are thankful to ConocoPhillips for access to their property. Funding for this project was provided by the Dauphin Island Sea Lab Fellowship, the University of South Alabama’s Department of Marine Sciences Fellowship, with additional support from The Wetland Foundation and the Birmingham Audubon Society. MJO’s participation was supported by the DOI Southeast Climate Adaptation Science Center, USGS Ecosystems Mission Area, and the USGS Land Change Science Program Climate R&D Program. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Data
File Size Format Processing Access
Avicennnia germinans root biomass 884 bytes CSV Raw data Open access
Spartina alterniflora and Avicennia germinans tissue and sediment concentrations of nitrogen and carbon 173 KB CSV Raw data Open access
DIC, DOC, and TDN of pore waters of Avicennia germinans and Spartina alterniflora 16 KB CSV Raw data Open access
spartina alterniflora aboveground biomass 5 KB CSV Raw data Open access
stocks of N and carbon for Avicennia germinans and Spartina alterniflora 99 KB CSV Processed data Open access
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How to cite 

Macy Aaron, Osland Michael, Cherry Julia, Cebrian Just (2019). Changes in ecosystem nitrogen and carbon allocation with black mangrove (Avicennia germinans) encroachment into Spartina alterniflora salt marsh. SEANOE. https://doi.org/10.17882/70428