Variations in chemical and phase speciation of phosphorus during estuarine mixing in the Bay of Saint Louis. Laodong Guo and Peng Lin

Transcription

1 Variations in chemical and phase speciation of phosphorus during estuarine mixing in the Bay of Saint Louis Laodong Guo and Peng Lin Department of Marine Science University of Southern Mississippi

2 Acknowledgements Lab experiment/analysis: Zhengzhen Zhou, Kusumica Mitra Field sampling: Kevin Martin, Xuri Wang Funding support: NGI/NOAA

3 Phosphorus and phosphorus cycle Particulate-P Oxygen Organic P Aquatic P species: Dissolved: DIP + DOP = TDP Colloidal: CIP + COP = TCP Particulate: PIP + POP = TPP Hydrogen (reducing) Redox chemistry

4 Motivation Phosphorus (P) is an essential nutrient for all living organisms in aquatic environments. Nutrient (N, P, Si) concentrations are usually higher in rivers than in coastal waters, causing seasonal eutrophication and hypoxia in the northern Gulf of Mexico; In the Bay of Saint Louis, phosphate has been found to be higher in coastal waters than in river waters, but the role of particulate and organic P and their behavior during estuarine mixing remain poorly understood.

5 Comparison of DOC/DIC ratio between rivers in MS-LA Gulf Coast Mostly DIC Equally important between DOC and DIC Atchafalaya (AR), Mississippi (MR), Pearl River at Bogalusa (PRB), Pearl River at SSC (PR-SSC), Jordan River (JR)

6 Questions What are the sources of DIP (phosphate) in the lower estuary of the Bay of Saint Louis? What is the mixing behavior of P species and their transport and transformation processes in the BSL estuary? The relative importance between physicochemical and biological processes in controlling the dynamics of P in the BSL estuary?

7 Approach Phase and Chemical Speciation dissolved, colloidal and particulate phases Organic and inorganic species, including dissolved inorganic P (DIP), dissolved organic P (DOP), colloidal inorganic P (CIP), colloidal organic P (COP), particulate inorganic P (PIP) and particulate organic P (POP) Combine field studies and laboratory mixing experiments

8 Study area and sampling locations during 2008 and 2009 : River and seawater end-member stations;

9 Riverwater-Seawater Mixing Exp River Water S=0 Dissolved Measurements of DIP and DOP Seawater S= 35 Diff. S 0.45µm Filter Particulate Measurements of PIP and POP DIP - Molybdenum blue standard method TDP - Oven-assisted persulfate oxidation PIP - Acid hydrolysis method TPP- High temp combustion & acid hydrolysis

10 Partitioning of phosphorus between organic and inorganic phases in MS-LA Gulf Coast rivers A progressive decrease in DIP but increase in DOP from MR to PR to JR/WR, indicating distinctive river chemistry related to land-use and anthropogenic impacts between river basins in the NGM

11 Results from field studies Variations in DIP and DOP concentrations with salinity in the Bay of St. Louis (BSL) Elevated DIP and DOP concentrations at mid-salinity stations during both sampling years; Higher DIP and DOP during 2008 compared to 2009

12 Results from field studies Dynamic changes in DIP% and DOP% in the BSL during 2008 and 2009 DOP DOP DIP DIP Intensive transformation between P species: Lower salinity region: DOP dominant; Mid-salinity estuary: DIP dominant; High salinity coastal waters: DOP dominant again

13 Results from field studies Variations in P species during estuarine mixing in the Bay of Stain Louis Particulate Dissolved Showing intensive transformation between dissolved and particulate phases during estuarine mixing and dynamic changes in P speciation in BSL

14 Comparison between field and lab mixing experiments Field study (Sept 2009) Mixing Exp (Jan 2010)

15 Results from lab mixing experiments Dissolved and Particulate P Lab experiments could mimic estuarine mixing even though river end-member was sampled at diff time; The quasi-negative correlation between dissolved and particulate P again suggests a dynamic transformation of P between particulate and dissolved phases during estuarine mixing; Without measurements of organic and particulate species, river export fluxes of P can be considerably under-estimated. Part Dissolved Part Dissolved Part Dissolved Inorganic Organic Total P

16 Colloidal phosphorus Colloidal inorganic (CIP) and organic (COP) phosphorus CIP COP Low salinity stations: High colloidal P in both inorganic and organic phases; Mid-salinity stations: Low in colloidal P; High salinity region: No colloidal inorganic P (river source only), but high COP again (also marine derived)

17 Distribution coefficient (K d ) between dissolved and particulate phases K d = [C P ]/[C D ]/SPM (in ml/g) High log{kd} values indicate that P is a particle-reactive element; Low Kd values in mid-salinity region correspond to high dissolved P; Higher Kd values in both upper and lower estuarine regions correspond to low dissolved P concentration.

18 Particle Concentration Effect K d vs. SPM A particle concentration effect was observed, consistent with the presence of high colloidal P concentration in the BSL

19 C/P ratio as an index of source and diagenetic status of natural organic matter terrestrial Marine Very high C/P ratio compared to Redfield Ratio (106) Terrestrial organic matter: high OC, low P & high C/P ratio; Marine organic matter: high P and low C/P ratio

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21 Ongoing Research on Phosphorus Sequential leaching technique to determine the different forms of P in particulate samples The effect of sediment re-suspension on the distribution and speciation of phosphorus in estuarine waters. Comparison between large river and small river (e.g., Mississippi River vs. Pearl/Jourdan Rivers)