1. Brittany n. Zepernick,1,2 Jeffrey w. krause2,3 and behzad mortazavi2,4
The Influence of Juncus-rhizosphere Dissolved Organic Matter on Coastal Plankton Communities
Brittany n. Zepernick,1,2 Jeffrey w. krause2,3 and behzad mortazavi2,4
1Bowling Green State University, 2Dauphin Island Sea Lab, 3University of South Alabama, 4University of Alabama
Correspondence:
I. Introduction
IV. Results
V. Conclusions
Initial DOC and DON Concentrations
Juncus roemerianus releases significant dissolved organic matter (DOM) within its rhizosphere.
Subsurface water movement (e.g. submarine groundwater discharge, tidal flux) and sediment benthic flux can move rhizosphere DOM into the water column.
We predict this DOM is labile, and will increase net phytoplankton production and bacterial production.
The following metrics will be used to test this hypothesis:
- Chlorophyll a (phytoplankton)
- Oxygen consumption (bacteria)
General respiration Stoichiometry:
(CH2O)106(NH3)16(H3PO4) +138O2 
106CO2 + 16HNO3 + H3PO4 +122H2O
DOC
DON
In DOM treatment, 19.8 µmol/L DOC added
O2 consumption in DOM: 18 µmol/L more than in controls after 24hrs
Suggests 23 µmol DOC consumed … over 100% of DOC addition
In Sample 3, Chlorophyll increase was observed after 48hr period.
Pennock et. al. 1989,1990, 1999
Sample Salinities:
31.02 & psu
Sample Salinities:
31.02 & psu
Treatment Chlorophyll Concentration (±Stdev)
Sample 1
Sample 2
Sample 3
Figure 1: Juncus rhizosphere pore water collection.
II. Field Collection
Figure 5: FlowCam Image
Figure 6: Juncus Rhizosphere water sampling
Figure 7: Flow-Cam Image
Locations of Sample Collection:
-Gulf Shores Pier: °N, °W (Sample 1,2)
-Mobile Bay: °N, ° W (Sample 3)
“Take Home” Points:
Juncus roemerianus rhizosphere DOM appears to be very labile, i.e. rapidly consumed by the heterotrophic community.
DOM stimulation of Chlorophyll only observed in Mobile Bay discharge station (Sample 3).
FlowCam image diagnostics (sample 3) did not suggest a shift in phytoplankton community structure, despite increased chlorophyll.
DOM is directly labile to phytoplankton community or made accessible after remineralization by the heterotrophic community.
Flow Cam Quantitative Data (Sample 3 Only)
Figure 2: Sample Collection Locations. Sample 1,2, Gulf Shores Pier. Sample 3, Mobile Bay.
III. Methods
Treatments (triplicate bottles):
Control, DOM, Labile (C6H12O6+ [(NH4)2SO4])
Quantity/Magnitudes of Treatments:
DOM Treatment:
Extracted using Dittmar et al. (2008, doi:
/lom )
+19.8 µM DOC addition
+ 0.5 µM DON addition
Labile Treatment (i.e. Positive Control):
+1,000 µM Glucose (C) addition
+20 µM Ammonium (N) addition
VI. Future Directions
It remains to be determined if pore water DOM is either directly labile to phytoplankton community or made accessible after remineralization by the heterotrophic community. Future directions include:
Conduct more experiments using Mobile Bay water.
Assess Prokaryote abundance and diversity.
Determine composition of DOM using high-resolution liquid chromatography mass spectrometry.
Respiration as a Function of Time Sample 3
Sample Intervals: 0, 12, 24, 48 & 72hrs (Figure 3).
Sample Analysis:
-Chlorophyll a (acetone extraction)
-Dissolved Oxygen (optical method)
- Fluorescent particle imaging (FlowCam)
Acknowledgements
Linear Regressions
Dauphin Island Sea Lab (DISL) personnel: Rebecca Pickering-Turner, Liesl Cole, Israel Marquez, Sydney Acton, William Dobbins, Laura Linn, Alice Kleinhuizen, and Claire Derby for laboratory and logistical support. This work was funded by the National Science Foundation (OCE , DISL REU).
Labile
[O2] = -3.80(time)
R2= 0.99
DOM:
[O2] = -1.52(time) R² = 0.99
Control:
[O2] = -1.29(time) R² = 0.91
Figure 3: Collection of DOM from pore water utilizing Bonding Agilent Eluts (PPL)
Figure 4. Environmental incubation system containing samples