Northern Gulf Institute, BP GRI Funds
Phase Two Proposal: Does the “Primer effect” caused by the DWH oil-spill result in
increased microbial and zooplankton consumption of labile and refractory DOC?
Co-PIs: Drs. William (Monty) Graham and Robert Condon, Dauphin Island Sea Lab, Biological
Oceanography Laboratory
Students & Technical Support: N. Shelton (U. Kansas, DISL, REU Student), one Research
Technician (position to be filled)
1. Overview
The Deepwater Horizon (DWH) oil spill delivered huge quantities of carbon (C) into the coastal
waters of the northern Gulf of Mexico. Regular two-week monitoring by the FOCAL program as
part of BP NGI Phase 1 funding (see progress report attached), documented marked changes in
labile C pools, and in microbial and zooplanktonic processes in response to the presence of oil in
coastal waters of Alabama. The most significant results were:
(1) Up to 60% increase in DOC concentrations at offshore sites (T10, T20 & C3) in June and
July that coincided with surface oil slicks and oil-derived material, as determined with the
Wetstar CDOM probe in the field and CDOM excitation-emission matrices in the
laboratory;
(2) Correlations between oil-derived DOC, CDOM and light isotopic del 13C signatures in
DIC pools supports microbial respiration of oil C at offshore locations (see Graham et al.
poster presented at IMBER conference, Greece);
(3) Isotopically light del 13C signatures in both the microplankton (<200 µm) and
mesozooplankton (>200 µm) fractions suggested oil C was consumed and assimilated by
at least two plankton trophic levels (see Graham et al, In Press)
These findings alone clearly suggest major short-term to monthly changes to biogeochemical
cycling and ecosystem functioning due to the DWH oil spill, but how much oil and the
mechanisms by which oil-derived C were transferred from organic pools into zooplankton
biomass still remain unclear. These findings would not have been possible without a rapidly
ramped and intensive field sampling effort in part by Phase I of NGI-BP funds. Moreover, these
findings indicate that ecosystem perturbations, the focus of Phase II oil spill funding by NGI,
were likely substantial at the base (i.e., microbes to zooplankton) of the very productive northern
Gulf ecosystem.
2. Does the “primer effect” caused by the DWH oil-spill result in increased microbial and
zooplankton consumption of labile and refractory DOC?
Despite huge quantities of oil-derived C in northern Gulf of Mexico coastal waters, comparison
of bulk DOC concentrations between pre- (2007 & 2008) and post-oil spill years suggests that
post-spill standing stocks were well below previous years (Fig. 1). This result is counterintuitive
particularly as (1) application of dispersants likely degraded and dissolved high quantities of oil
into the water column, and (2) inputs of freshwater DOM sources, such as humics, into coastal
waters were likely higher than normal due to higher than average river runoff.
Recently, it has been hypothesized that increased bioavailability of labile C sources will promote
microbial diversity and cell activity, which in turn will stimulate high uptake of refractory DOM
(e.g., humics, high fractionated components of crude oil). This process has been termed the
“primer effect” but to date studies have focused on terrestrial systems with little to no emphasis of
these effects in marine or estuarine systems. Assuming this effect occurred during the DWH oil
spill, there are important implications of the primer effect for ecosystem functioning, including:
(1)
(2)
(3)
(4)
a major shift towards oligotrophic conditions and nutrient limitation in coastal waters
greatly reduced DOC export from shelf to open ocean environments
increased gas fluxes to/from the atmosphere, and
increased C bioavailability for planktonic food webs from both oil- and
refractory/freshwater organic sources.
The latter point is particularly important as it has the potential to make “extra” energy
bioavailable for planktonic food webs because DOM pools primarily comprised of refractory
material were not likely utilized as readily by pre-spill microbial communities. Whether the
additional C is consumed by zooplankton or lost from the planktonic food web is dependent upon
how microbes partition this material for their production (growth and protein synthesis) and
respiration/cell maintenance relative to total C consumed, with production being the primary
mechanism to introduce more energy to lower trophic levels. Therefore, the key to understanding
the primer effect hypothesis and oil-mediated planktonic C pathways, and ultimately how this
alters ecosystem structure and functioning, hinges primarily on determining how microbial
community composition and metabolic processes relate to the quality and quantity of DOM pools.
Figure 1. Bulk DOC
concentrations (µM) against
number of days since 20 April
(as the date of the DWH
accident) in surface waters at
T20 for two pre-spill (2007 &
2008) and the post-spill (2010)
year. No data exists for 2009.
Note low DOC concentrations
in 2010 despite oil spill and
high river runoff. Also high
fluctuations in DOC around
day 50 due to presence of
surface oil slicks.
Approach and Budget Summary: We would like to use the DWH oil spill as a natural
experiment specifically testing the primer effect hypothesis as a means of evaluating how much
oil vs. other sources of organic C (e.g., refractory material) entered the planktonic food web. On
a larger scale, we are interested in examining whether the ecosystem baseline (e.g., historical
trends in DOC) recovers to pre-spill conditions in the year following the DWH oil spill (the null
hypothesis) or whether alterations in microbial processes have caused long-term (> 1 yr) changes
in biogeochemical cycles, resulting in increased zooplankton and potentially fisheries production.
Our primary research approach will be a series of controlled laboratory experiments and
modeling to examine how the DWH oil spill impacts short- and long-term DOM cycles and how
this relates to microbial-mediated ecosystem functioning in the coastal waters of Alabama. In
turn, we will align our research effort and groundtruth our experimental and model results with
the ongoing FOCAL sampling program. Please note that this LOI is separate to our pending
request for MESC-BP funding to perform several oil impact mesocosm experiments in 2011, but
results from the proposed NGI Phase II research will serve to compliment this other study by
addressing a key objective of this program in “gaining a better understanding of microbialzooplankton linkages”.
We will conduct a series of laboratory experiments to simultaneously measure uptake rates of oil
and humic material (as a chemical model for refractory DOM) by microbes and to assess whether
the primer effect hypothesis holds under oiled conditions. The inclusion of various of micro-,
meso- and gelatinous zooplankton treatments combined with stable isotope, CDOM and DOC
analyses will allow us to identify source-sink dynamics of oil and DOM pools and allow us to
evaluate whether increased supply of labile C frees-up additional refractory organic resources for
zooplankton. The results of these experiments combined with historical and post-spill field
measurements will be used in a PARAFAC model to evaluate short- and long-term effects of the
DWH oil spill on DOM cycles and zooplankton production.
Radioisotopes and a Fibox Optode Oxygen probe system will be used to measure microbial
production and respiration, and these rates compared to flow cytometry, DOC, CDOM and DI13C
results to determine source material and how this relates to DOM cycles. We currently have on
loan a Picarro DIC isotope analyzer from a colleague, Dr. L. McAllister (Virginia
Commonwealth University), and the purchase of a Picarro Liaison unit with NGI Phase 1 funds
allows us near real-time information on particulate 13C fractions. In phase 2, funding is requested
to cover costs for consumables associated with microbial and zooplankton analyses. We also
request funds to conduct four supplementary water sampling research trips on the RV EO Wilson
between March and September in 2011.
Co-PI Graham’s role will be to experimentally assess microbe-to-zooplankton linkages and to
advise Ms. Shelton in her graduate studies. Co-PI Condon’s role in this project will primarily be
to oversee day-to-day laboratory and field exercises, and to co-advise Ms. Shelton. He has
requested 1 mo. salary. Due to the additional sampling effort we request 12 mo. salary for one full
time technician to be dedicated to maintenance of experiments and processing of samples. In
support of this work, we request funds for a MSc student (Ms. N. Shelton). Ms. Shelton is
returning to DISL in January 2011 to work as a technician, and will be applying to graduate
school at University of South Alabama. A portion of our NGI-BP phase two funds will support
her thesis.
Travel costs are requested for presentation of these results at a major scientific conference by Drs.
Graham and Condon, and Ms. Shelton. We also request some travel funds for our colleagues
(e.g., Dr. McAllister) to continue our collaboration on oil related projects.
Graham/Condon NGI-BP Phase 2
Budget
A. Senior Personnel
Senior Research Scientist (Condon)
MSc Student (Shelton)
Research Technician
Fringe benefits
C. Travel
D. Research Support
E. Supply & Analysis Costs
1 mo. @ $42,000 p.a.
12 mo. @ $16,000 p.a.
12 mo. @ $ 25,000 p.a.
Combined
Conferences, colleague travel
E.O. Wilson – 4 trips @ $2,500
1 x Tech Support – 12 hr day @ $20/hr
Flow cytomtery
DOC consumables, vials etc…
Bacterial Production supplies
Computer & Back-up hard drive
Software for model, statistical analyses
Publication costs, Communication
TOTAL
$
$
$
$
$
$
$
$
$
$
$
$
$
3,500
16,000
25,000
18,889
6,000
10,000
960
3,000
3,000
2,000
3,000
2,500
1,500
$ 95,349