Nitrogen (N) inputs to developed coastlines are linked with multiple ecosystem and socio-economic impacts worldwide such as algal blooms, habitat/resource deterioration, and hypoxia. This study investigated the microbial and biogeochemical processes associated with recurrent, seasonal bottom-water hypoxia in an urban estuary, western Long Island Sound, that receives high N inputs. A field study spanned two hypoxia events, entailing surface and bottom depth water sampling for dissolved inorganic and organic forms of N and phosphorus, organic carbon (DOC), as well as chlorophyll a, bacterial abundances, and physical water quality. Results showed that dissolved organic matter was highest at the most hypoxic locations, with DOC significantly and negatively correlated with bottom-water dissolved oxygen, indicating an increase in bacterial respiration. Ammonia-N was the dominant DIN form pre-hypoxia and declined throughout hypoxia while nitrate + nitrite depicted the reverse, being minimal pre- then increasing during and post-hypoxia. This indicates that ammonia oxidation, a key pathway in water column nitrification, contributed to the switch in dominant DIN forms. At the most hypoxic location, bottom depth bacterial concentrations peaked pre-hypoxia, declined throughout, and were significantly and positively correlated with ammonia-N, confirming that hypoxia influences bacterially induced N-cycling within LIS. These findings provide novel insight to feedbacks between major biogeochemical (N and C) cycles and has implications for N management in hypoxic urban estuaries.

Primary Presenter: Georgie Humphries, Advanced Science Research Center, NY (georgia.humphries42@qmail.cuny.edu)

Authors:

Georgie Humphries, Advanced Science Research Center & CUNY Queens College  (georgia.humphries42@qmail.cuny.edu)

Jessica Espinosa, Advanced Science Research Center & University of Connecticut   ()

Mariapaola Ambrosone, Advanced Science Research Center  ()

Zabdiel Roldan Ayala, Advanced Science Research Center & CUNY Queens College  ()

Maria Tzortziou, City College Center for Discovery and Innovation  ()

Joaquim Goes, Columbia Lamont-Doherty Earth Observatory  ()

Dianne Greenfield, Advanced Science Research Center & CUNY Queens College  (dgreenfield@gc.cuny.edu)