Date of Award

Fall 2012

Degree Type

Masters Thesis

Degree Name

Master of Science (MS)

Department

Marine Science

Committee Chair

Stephan Howden

Committee Chair Department

Marine Science

Committee Member 2

Kjell Gundersen

Committee Member 2 Department

Marine Science

Committee Member 3

Karen Orcutt

Committee Member 3 Department

Marine Science

Committee Member 4

Bruce Spiering

Committee Member 4 Department

Marine Science

Abstract

This study describes the spatial and temporal distribution of net primary productivity (NetPP) and respiration (RESP) in relation to the biogeochemical, optical, and hydrographic variability in the Mississippi Sound and Mississippi Bight over the course of one year. Surface in-situ measurements of NetPP and RESP were regularly determined at two stations by a time-course detection of dissolved oxygen (DO) using novel optode technology. In addition, various biogeochemical, optical, and hydrographic parameters were examined over 14 stations throughout the estuary over a year, using ground and satellite (MODIS Aqua) measurements. In this study, consistently low dissolved inorganic N:P ratios (average N:P < 4.3 for all stations) suggest that rates ofNetPP were nitrogen limited, while the NetPP rates measured in the Mississippi Sound showed periodic growth limitation due to low watercolumn light availabi lity. Measured RESP rates were partially correlated to both allochthonous (POM, r2 = 0.78, p < 0.01 , n = 20) and authochthonous (chlorophyll-a, r2 = 0.74, p < 0.01 , n = 23) proxies for organic matter sources. There was also some evidence that ambient seasonal light levels may have driven some enhanced light-dependent respiration. Time and depth integrations ofNetPP and RESP indicate that net heterotrophic conditions persisted in Mississippi waters through most of the year, and that both integrated rates tended to be higher in the Mississippi Bight compared to the Mississippi Sound. As light availability appears to play an important role in regulating biological activity in this estuary, an empirical model (derived from multiple regression analysis) for predicting the down welling light attenuation coefficient [Kd(P AR)] is proposed for Mississippi waters. The model is based on contributing biogeochemical parameters [suspended particulate matter (SPM), chromophoric dissolved organic matter (CDOM), and chlorophyll-a] and the partitioning of each biogeochemical parameter using the empirical model reveals that SPM was the dominant contributor to Kd(P AR). However, relative contribution of SPM ( as well as values of Kd) diminished in the Mississippi Bight as the fraction of Particulate Inorganic Matter (PIM) to total SPM decreased. Finally, the extrapolation of biologically significant parameters to larger spatial scales via satellite remote sensing was assessed for the study area. Comparisons of measured chlorophyll-a, SPM, CDOM, Kd, euphotic depth (Zeu), and photosynthetically available radiation (PAR) to various products derived from the MODIS time-series showed high con-elations (r2 > 0.8), with the exception of chlorophyll-a (r2 :S 0.6). Overall, a quasi-analytical algorithm (QAA) approach was better suited for measuring the distribution of light (i.e. Kd and Zeu) using satellite remote sensing methods in these optically complex waters, while simpler remote sensing reflectance (Rrs) and band ratios , tended to predict SPM and CDOM distribution better. The results of this study demonstrate that the drivers of biogeochemical variability as well as the balance between NetPP and RESP are determined by a multitude of factors.

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