Uniform TitleAssessing multiple indicators of nutrient limitation in marine phytoplankton on the Louisiana continental shelf
NameSylvan, Jason B. (author), Ammerman, James (chair), Kerkhof, Lee (internal member), Seitzinger, Sybil (internal member), Vetriani, Costantino (internal member), Dyhrman, Sonya (outside member), Rutgers University, Graduate School - New Brunswick,
Nutrient pollution of water--Louisiana,
DescriptionEutrophication on the Louisiana continental shelf is driven by excess nitrogen (N) and phosphorus (P) delivered by the Mississippi River. While the eutrophication is driven primarily by excess nitrogen, scattered data going back to the early 1990's suggests that the ecosystem on the Louisiana shelf may be seasonally P-limited in the spring and early summer during high runoff periods, primarily in areas of intermediate salinity. These intermediate salinity zones are also the areas where chlorophyll biomass and primary productivity are often maximal. This production likely drives the annual bottom water hypoxia in the region, known in the popular press as the "dead zone." Three very different methods were used to address the question of nutrient limitation on the Louisiana shelf. In July 2002, a Fast Repetition Rate fluorometer (FRRf) was used in conjunction with nutrient addition bioassays and mapping of surface water parameters to examine the response of the phytoplankton community to eutrophication. In incubations, chlorophyll a biomass responded to phosphorus additions, but not those of N alone and FRRf parameters indicated a positive response to P additions in the way of higher efficiency in photosystem II. The mapping data was more heterogeneous in nature, but overall patterns indicated that P limited phytoplankton biomass. Three cruises in March, May and July 2004 were conducted in order to investigate seasonal patterns of dissolved inorganic, dissolved organic, and particulate nutrients on the Louisiana shelf. The combination of low P concentrations, high inorganic and total N:P ratios and high alkaline phosphatase activities indicated P limitation of phytoplankton biomass on the Louisiana shelf during the spring and early summer of 2004. A study of pstS, a gene induced under P-stress, revealed that its distribution in oceanic waters is related to location of the sample. The pstS gene in Synechococcus spp. taken from various sites around the world clustered on a phylogenetic tree closest to other sequences taken nearby. The combination of FRRf, nutrient data, enzyme assays and molecular markers of P-limitation strongly confirm seasonal P-limitation on the Louisiana continental shelf in the spring and early summer, driven by extreme N loads during these seasons.
NoteIncludes bibliographical references (p. 108-121).
CollectionGraduate School - New Brunswick Electronic Theses and Dissertations
Organization NameRutgers, The State University of New Jersey
RightsThe author owns the copyright to this work.