Department of Estuarine and Ocean Sciences MS Thesis Defense
When: Tuesday,
October 10, 2017
11:00 AM
-
12:00 PM
Where: > See description for location
Description: The School for Marine Science and Technology
Department of Estuarine and Ocean Sciences
MS Thesis Defense
"Temporal Evolution of Nitrogen Loading in Long Island Sound Using Stable Isotope Geochemistry: A Role for Dissolved Organic Nitrogen (DON)"
by
Sheel Hasmukhbhai Prajapati
advisor
Mark Altabet
Tuesday, October 10, 2017
11:00 am
SMAST East, Room 102
836 S. Rodney French Blvd
New Bedford, MA
Abstract:
Anthropogenic nitrogen loading to Long Island Sound (LIS) is the primary cause of its eutrophication and occurrence of summertime hypoxia. Two-layered gravitational circulation in the LIS estuary helps promote this eutrophication and summertime hypoxia which can ultimately disrupt coastal marine eco-systems. Regulatory efforts have been made by government and private organizations to reduce nitrogen loading but dissolved organic nitrogen (DON), which is ~65% of total dissolved nitrogen in LIS, has been ignored till now because of its difficulty in analysis and previous scientific studies considered it as a refractory component. Recent studies showed that DON could be bioavailable and biodegradable and its utilization by phytoplankton can affect or probably stimulate eutrophication. This study focuses on the stable isotopic composition of nitrogen (δ15N), specifically DON, which can offer a natural means to directly follow and trace DON biogeochemical cycling and determine if it plays an important role in nitrogen cycling specifically providing nutrition to the eutrophication causing phytoplankton.
In 2015- 2016 samples were collected monthly from 17 stations in LIS and were analyzed for NO3-, NH4+ and TDN. TDN was analyzed using the persulfate method. Aliquots for stable nitrogen isotope determination (δ15N-TDN and δ15N-NO3-) were prepared using nitrate reducing bacterial method and were analyzed on an isotope-ratio mass spectrometer (IRMS). DON and δ15N-DON were calculated from those results. We observed DON consumption during August- September in the western end and central basin, where the anthropogenic nitrogen loading is the maximum. DON also observed to be re-mineralizing into. Ammonia and/or nitrate which is more dynamic than DON itself. This can lead to an increased concentration of those nutrients in water, prolonging eutrophication and summertime hypoxia in LIS coastal water. Furthermore, this study suggested that considering DON while making policies for anthropogenic nitrogen loading by SWTP in LIS is as important as regulating nitrate and ammonia.
For additional information, please contact Sue Silva at s1silva@umassd.edu.
Department of Estuarine and Ocean Sciences
MS Thesis Defense
"Temporal Evolution of Nitrogen Loading in Long Island Sound Using Stable Isotope Geochemistry: A Role for Dissolved Organic Nitrogen (DON)"
by
Sheel Hasmukhbhai Prajapati
advisor
Mark Altabet
Tuesday, October 10, 2017
11:00 am
SMAST East, Room 102
836 S. Rodney French Blvd
New Bedford, MA
Abstract:
Anthropogenic nitrogen loading to Long Island Sound (LIS) is the primary cause of its eutrophication and occurrence of summertime hypoxia. Two-layered gravitational circulation in the LIS estuary helps promote this eutrophication and summertime hypoxia which can ultimately disrupt coastal marine eco-systems. Regulatory efforts have been made by government and private organizations to reduce nitrogen loading but dissolved organic nitrogen (DON), which is ~65% of total dissolved nitrogen in LIS, has been ignored till now because of its difficulty in analysis and previous scientific studies considered it as a refractory component. Recent studies showed that DON could be bioavailable and biodegradable and its utilization by phytoplankton can affect or probably stimulate eutrophication. This study focuses on the stable isotopic composition of nitrogen (δ15N), specifically DON, which can offer a natural means to directly follow and trace DON biogeochemical cycling and determine if it plays an important role in nitrogen cycling specifically providing nutrition to the eutrophication causing phytoplankton.
In 2015- 2016 samples were collected monthly from 17 stations in LIS and were analyzed for NO3-, NH4+ and TDN. TDN was analyzed using the persulfate method. Aliquots for stable nitrogen isotope determination (δ15N-TDN and δ15N-NO3-) were prepared using nitrate reducing bacterial method and were analyzed on an isotope-ratio mass spectrometer (IRMS). DON and δ15N-DON were calculated from those results. We observed DON consumption during August- September in the western end and central basin, where the anthropogenic nitrogen loading is the maximum. DON also observed to be re-mineralizing into. Ammonia and/or nitrate which is more dynamic than DON itself. This can lead to an increased concentration of those nutrients in water, prolonging eutrophication and summertime hypoxia in LIS coastal water. Furthermore, this study suggested that considering DON while making policies for anthropogenic nitrogen loading by SWTP in LIS is as important as regulating nitrate and ammonia.
For additional information, please contact Sue Silva at s1silva@umassd.edu.
Contact: > See Description for contact information
Topical Areas: School for Marine Sciences and Technology, SMAST Seminar Series