Implications of Different Nitrogen Input Sources for Primary Production and Carbon Flux Estimates in Coastal Waters
Abstract
The coastal Gulf of Mexico (GOM) and Coastal Sea off Korea (CSK) both suffer from
eutrophication and/or hypoxia, both of which are driven mainly by humans. We compared two
different regions with different nitrogen input sources to estimate organic carbon fluxes and predict
future carbon fluxes based on our model scenarios. This research focuses on how we take
advantage of carbon-nitrogen cycling and ecological consequences to estimate the effects of future
nutrient inputs.
We tested the Rowe and Chapman (RC02) three-zone hypothesis of hypoxia using two
different methods. We found that RC02 applied only in certain seasons and that a major nutrient
input source is necessary. We used both nutrient/salinity relationships and a N-mass balance
model to identify three different zones, each with different productivity and carbon fluxes. We
define the brown zone as having a linear nutrient/salinity relationship, where physical forcing
(river flow) dominates over local production, and defined the blue zone as having nutrient (N or
Si) concentrations < 1 μM. The green zone, with variable nutrient concentrations, occurs between
them. Based on our N-mass balance model results, we could set the potential primary production
rate in the brown zone of the GOM and CSK, respectively, as over 2 (GOM) and over 1.5 gC m^-2
day^-1 (CSK). In the green zone, production was between 0.1 to 2 (GOM) and 0.3 to 1.5 gC m^-2
day^-1 (CSK) and in the blue zone less than 0.1and 0.3 gC m^-2 day^-1, respectively. From our results, we have estimated the fluxes of nitrogen via the atmosphere, groundwater, and river to the ocean, based on observational and literature data.
The coastal Gulf of Mexico receives nitrogen predominantly from the Mississippi and
Atchafalaya Rivers and AN-D is only a minor component in this region. However, in the coastal
sea off Korea, either groundwater or atmospheric nitrogen deposition is more important controlling
factors of our model results. In the future, we need to consider collecting data on both groundwater
and AN-D inputs in investigations of chemical cycling in the coastal ocean
Citation
Kim, Jongsun (2018). Implications of Different Nitrogen Input Sources for Primary Production and Carbon Flux Estimates in Coastal Waters. Doctoral dissertation, Texas A & M University. Available electronically from https : / /hdl .handle .net /1969 .1 /173902.