Effects of Acidification and Habitat Loss on Coastal Nitrogen Cycling Dynamics

Author

Beryl M. Kahn, CUNY Graduate CenterFollow

Date of Degree

6-2025

Document Type

Doctoral Dissertation

Degree Name

Doctor of Philosophy

Program

Biology

Advisor

Chester Zarnoch

Committee Members

J. Stephen Gosnell

Peter Groffman

Mary Alldred

Monica Palta

Subject Categories

Ecology and Evolutionary Biology | Environmental Chemistry | Marine Biology | Natural Resources Management and Policy | Other Ecology and Evolutionary Biology

Keywords

urban ecology, Jamaica Bay, biogeochemistry, salt marsh ecology, eelgrass, estuarine ecology

Abstract

Excess nitrogen (N) in urbanized coastal waterways from wastewater or agricultural inputs causes widespread habitat decline due to harmful algal blooms, poor water quality, and changes to seawater chemistry. For example, during an algal bloom, nocturnal respiration and seasonal decomposition of algal biomass release carbon dioxide (CO₂) into the water column, which lowers seawater pH in a process known as coastal acidification. Additionally, high N loading leads to the death of salt marsh vegetation communities, in turn leading to salt marsh erosion and loss, with implications for coastal stability. Estuarine habitats such as seagrass beds and salt marshes are known as hotspots of microbially-mediated nutrient cycling, but it has been unclear how stressors caused by N loading (i.e., coastal acidification, macroalgal blooms, and salt marsh erosion/loss) impact vital biogeochemical processes in these habitats. This dissertation explored the effects of acidification on nutrient cycling in eelgrass beds and salt marshes (in Shinnecock Bay, Long Island and Jamaica Bay, New York City, respectively), as well as the impacts of salt marsh loss on N dynamics in eutrophic urban estuaries. Results show that lower seawater pH shifted sediments in eelgrass beds from net sources of reactive N to net N sinks, with implications for water quality mitigation. In salt marshes, acidification appeared to have no effect on nutrient cycles. Instead, N cycling in salt marshes is likely to respond to erosion and increasing inundation. De-vegetated marsh sediments showed net N release compared to still-intact vegetated marsh areas, suggesting that losses in salt marsh habitat may contribute to water quality decline and algal bloom conditions, as well as perpetuate further habitat loss. This body of research addressed critical gaps in understanding the processes that underpin coastal habitat function under various N loading-related stressors, such as acidification-induced impacts on nitrification and denitrification in eelgrass beds and changes to sediment N cycling as marshes erode. The former finding may suggest that N loading may be at least partially mitigated during a coastal acidification event, while the latter finding suggests that marsh restoration may prevent loss of N removal services. The applications of this research are likely to become increasingly critical, as these habitats serve as vital natural infrastructure against sea level rise, storm surges, and coastal change.

Recommended Citation

Kahn, Beryl M., "Effects of Acidification and Habitat Loss on Coastal Nitrogen Cycling Dynamics" (2025). CUNY Academic Works.
https://academicworks.cuny.edu/gc_etds/6267