-
OCEAN SCIENCES 2016
Monday, February 22, 2016 TIME: 8:45 AM - 09:00 AM LOCATION:
RO3
#LSURESEARCHFor more information, call the LSU Division of
Strategic Communications at 225-578-8654.
RESEARCH WORKS
Animal dispersal behaviors have both ecological and evolutionary
significance. However, due to the logistical challenges of tracking
animals in the Antarctic marine environment little is known about
the winter dispersal and migration of Antarctic marine predators.
We used a combination of direct tracking (Geolocation sensors; GLS)
and compound-specific stable isotope analysis of carbon in
essential amino acids (CSIA-AA) to describe the winter distribution
of two wide-ranging marine predators, the Adélie penguin
(Pygoscelis adeliae) and chinstrap penguin (P. antarctica) along
the Antarctic Peninsula and Scotia Arc. GLS and CSIA-AA identified
two general migration strategies, with animals overwintering to the
east or west of the Antarctic Peninsula, with CSIA-AA also being
able to discriminate
between ice-free vs. pack-ice habitats. In addition, CSIA-AA
provided the ability to assign non GLS-tracked chinstrap penguins
from multiple breeding sites across the Scotia Arc to specific
over-wintering areas. This provided a first ever, regional-scale
analyses of the winter movements and distributions of the species
and identified a cryptic latitudinal trend that would have been
otherwise undetectable. Breeding colonies farther north were more
likely to have individuals dispersing eastwards relative to
colonies further south where most individual dispersed westwards,
possibly due to a combination of proximity and competition
avoidance. Finally we highlight how CSIA-AA approaches can be
applied to other studies of the distribution and ecology of marine
top predators.
MICHAEL POLITOLSU DEPARTMENT OF OCEANOGRAPHY & COASTAL
SCIENCES
Direct Tracking and Compound-Specific Stable Isotope Analysis
Identifies Dispersal Routes and Cryptic Latitudinal Trends in the
Winter Distribution of Two Antarctic Penguin Species
-
OCEAN SCIENCES 2016
Monday, February 22, 2016 TIME: 12:00 PM - 12:15 PM LOCATION:
220-221
#LSURESEARCHFor more information, call the LSU Division of
Strategic Communications at 225-578-8654.
RESEARCH WORKS
In the past decade, interest in wave attenuation by vegetation
has increased considerably as coastal scientists and engineers
search for sustainable solutions to mitigate the impacts of climate
change and natural hazards. It is well known that vegetation in
wetlands can effectively reduce the flow speed, modify turbulence
structure, attenuate wave energy, and affect sediment dynamics.
Restoring coastal wetlands and reducing flood risks require
improved understanding and better predictive capability of wave and
surge attenuation over inundated coastal landscapes with
vegetation. The interactions of surface waves and natural
vegetation span over a large range of scales, from turbulence and
eddies at the vegetation stem scale to wave generation in vast
inundated wetlands of hundreds of square miles under
hurricane conditions. The study is focused on a phase-averaged
energy-based model and phase-resolving Euler and Navier-Stokes
(N-S) solvers with different representations of submerged
vegetation. We will present recent advances in multi-scale modeling
of wave attenuation by wetland vegetation. Numerical modeling
results ranging from vegetation-resolved large eddy simulation
under idealized conditions to incorporating vegetation-induced drag
forces into conservation laws of momentum and energy for
engineering applications will be shown. Effects of vegetation
flexibility, turbulence closure, and various wave theories on the
prediction of wave attenuation and the choice of vegetation drag
coefficients will be discussed.
QIN JIM CHENLSU DEPARTMENT OF CIVIL & ENVIRONMENTAL
ENGINEERING
Multi-Scale Modeling of Wave Attenuation by Vegetation
-
OCEAN SCIENCES 2016
Wednesday, February 24, 2016TIME: 8:00 AM - 8:15 AM LOCATION:
222
#LSURESEARCHFor more information, call the LSU Division of
Strategic Communications at 225-578-8654.
RESEARCH WORKS
Deltas and estuaries are productive and fertile links between
the land and the sea. Deltas occupy only about 5% of the Earth’s
surface but sustain over a half billion people all around the
world. Many river deltas are endangered because of extensive dam
and levee construction, declining sediment supply, groundwater
withdrawal, relative sea level rise and severe coastal erosion,
leading to a variety of threats to natural, economic and social
systems. About 630 million people now live at an elevation of 10 m
or less above mean sea level, and maintaining sustainable land with
a rising sea will be a challenging problem for many major deltaic
coasts and cities in the next century. Stemming from 20 years of
LOICZ (Land-Ocean Interactions in the Coastal Zone), Future Earth
Coasts is a new global initiative that seeks to enable
the scientific and social scientific communities to build
knowledge through collaborative processes to better understand and
address the profound and urgent changes occurring in vulnerable
coastal zones. The topics of this comparative study are the
Mississippi and Yangtze (Changjiang) Rivers, the largest in the
United States and China, respectively. We use these two rivers as
examples to evaluate current conditions and catalyze future
discussion. The Mississippi and Yangtze both have had long-term
observations of physical and biological processes that affect human
activities, making it possible to quantify both natural and
anthropogenic impacts. We also consider the limits to the concept
of sustainability for the Earth’s biosphere and human civilization,
and emphasize biophysical constraints and demographic
challenges.
CHRIS D’ELIALSU COLLEGE OF THE COAST & ENVIRONMENT
Future Earth Coasts: The Mississippi and Yangtze Rivers as
Examples
-
OCEAN SCIENCES 2016
Wednesday, February 24, 2016 TIME: 9:30 AM - 9:45 AM LOCATION:
222
#LSURESEARCHFor more information, call the LSU Division of
Strategic Communications at 225-578-8654.
RESEARCH WORKS
The shelf offshore Louisiana is characterized by a dominantly
muddy seafloor with a paucity of restoration-quality sand proximal
to shore. Discrete sand deposits associated with ancient rivers
that incised the shelf during lower sea-level positions occur close
to shore. These shelf channel sands have been targeted for coastal
restoration projects resulting in significant cost savings over
more distal deposits. Several recent projects targeted shelf
paleo-fluvial deposits comprising relatively deep (10 m) channel
sands underlying a muddy overburden. Because of contrasting
characteristics of cohesive mud vs. non-cohesive sand and potential
modern fluvial mud supply from the Mississippi and Atchafalaya
Rivers, long term pit evolution is poorly understood relative to
their more common sand-only counterparts. Alterations to seafloor
topography from dredging shelf sediment resources can potentially
affect oil and gas infrastructure or other resources of concern
(i.e. historic
shipwrecks) located proximal to dredge pits. Site-specific data
required to make accurate predictions and empirical measurements to
test and validate predictive models were only available for Peveto
Channel offshore Holly Beach, Louisiana. Here we present new
geophysical and geological data (bathymetry, sidescan, subbottom,
and radionuclide of sediment cores) and physical oceanographic
observations (hydrodynamics and sediment dynamics) collected at
Raccoon Island (dredged in 2013) dredge pit in Louisiana. These
field data collections along with pre-existing data provide a
time-series to capture evolution at Raccoon Island post-excavation.
Conceptual morphological models will be developed for dredge pit
evolution and testing effectiveness of setback buffers protecting
pipelines, habitats, and cultural resources. Our results will
increase decision making ability regarding safety and protecting
environmental and cultural resources, and better management of
valuable sand resources.
KEHUI XULSU DEPARTMENT OF OCEANOGRAPHY & COASTAL
SCIENCES
Assessment of Mud-Capped Dredge Pit Evolution Offshore
Louisiana: Implications to Sand Excavation and Coastal
Restoration
-
OCEAN SCIENCES 2016
Wednesday, February 24, 2016TIME: 9:45 AM – 10:00 AM LOCATION:
222
#LSURESEARCHFor more information, call the LSU Division of
Strategic Communications at 225-578-8654.
RESEARCH WORKS
Many fluvial channels incised the Northern Gulf of Mexico inner
continental shelf during the late Quaternary. Mud-capped dredge
pits (MCDPs), which are generally elongate and deep (8-10 m)
excavations, target sandy fluvial channel deposits for coastal
restoration projects. The morphological evolution of dredge
excavations in noncohesive sandy substrate is well studied, but
MCDPs have up to a several-meter-thick veneer of Holocene shelf mud
overlying sandy channel deposits. This stratigraphy is hypothesized
to result in more complex post-dredge morphology than pit walls
simply slumping to the angle of repose shortly after excavation.
Numerical modeling of MCDP post-dredge response conducted prior to
excavation indicates pit walls may retrogressively fail, which is
accounted for in pit design by assigning no-dredge setback buffers
from pipelines or cultural and environmental resources. To validate
model results and test effectiveness of setback buffers, a
geophysical survey of the Sandy Point MCDP (20 km west of the
Mississippi River Delta in 10m deep water), where 1.7 million m3 of
sandy sediment was excavated in 2012, was conducted May 2015. A
total of 84 line-km of high-
resolution chirp subbottom and a 27 km2 grid of swath bathymetry
and sidescan sonar were collected.
The data indicate the dredge pit walls are differentially
slumping, with the western pit wall in a more active state of
failure than the eastern wall. The western failures morphologically
resemble features observed along the muddy Mississippi River Delta
Front at water depths of 20-100 m, including bowl-shaped collapse
failures and retrogressive stair-stepped slumps; these failures may
play a key role in evaluating the distance of setback buffer zone
to pipelines. These features indicate the cohesive mud overlying
the sandy infill has a prominent role in pit wall stability. A
0.5-1 m thick acoustically transparent package overlies the entire
pit floor (interpreted as a possible fluid mud layer), overlying
1-3 m of post-dredge deposition that is concentrated along the
western wall and center of the pit. The Sandy Point MCDP lies
within a clockwise gyre, and its relief may serve as a significant
trap of suspended sediment. These findings emphasize the role MCDPs
play in sediment dynamics as well as their potential for submarine
geohazards.
JEFFREY OBELCZLSU COASTAL STUDIES INSTITUTE
Evolution of Mud-capped Dredge Pits Following Excavation:
Sediment Trapping and Slope Instability
-
OCEAN SCIENCES 2016
Wednesday, February 24, 2016TIME: 2:30 PM – 2:45 PM LOCATION:
231-232
#LSURESEARCHFor more information, call the LSU Division of
Strategic Communications at 225-578-8654.
RESEARCH WORKS
Sediment-water interface represents an important exchange
surface that regulates the cycling and transfer of many elements
and nutrients between sediments and overlying water. Traditionally,
rate of transfer across the sediment–water interface is determined
by deploying benthic chambers or modeling the depth profiles of a
dissolved species of interest in the sediment. In this study we
utilize224Ra: 228Th disequilibrium in the sediment to determine
solute transport rates in coastal Louisiana sediments. In marine
sediments, 224Ra (half-life = 3.66 d) is continuously produced by
alpha decay of its parent nuclide, 228Th (half-life = 1.91 y).
While 228Th is strongly bound to sediments, 224Ra tends to remain
in dissolved phase in the interstitial water, and migrate across
the
sediment–water interface into the overlying water. This results
in a deficit of 224Ra with respect to 228Th in near-surface
sediments that can be utilized to calculate solute transport rates.
Depth profiles of dissolved and surface-bound 224Ra and 228Th in
the upper 10 cm sediment column indicate significant deficit of
224Ra relative to 228Th. By modeling the 224Ra depth profiles in
the sediment using the general diagenetic equation along with 234Th
bioturbation rates we demonstrated that molecular diffusion and
bioturbation together accounts for less than 50% of the measured
fluxes of 224Ra in this region. The solute transport derived from
this method are also utilized to understand transport/consumption
of other species like O2 and Fe
2+ in these sediments.
WOKIL BAMLSU DEPARTMENT OF OCEANOGRAPHY & COASTAL
SCIENCES
224Ra: 228Th Disequilibrium in Sediments as a Tracer for Solute
Transfer across the Sediment-Water Interface in Coastal
Louisiana
-
OCEAN SCIENCES 2016
Thursday, February 25, 2016TIME: 9:00 AM – 9:15 AM LOCATION:
206
#LSURESEARCHFor more information, call the LSU Division of
Strategic Communications at 225-578-8654.
RESEARCH WORKS
Gulf hypoxia has received considerable scientific and policy
attention because of its large size (up to 22,000 square km),
potential ecological and economic effects, and the need to
understand the implications of various nutrient management
strategies in the large Mississippi River watershed. Over the past
20 years, a number of different models have been developed to
simulate the severity and areal extent of hypoxia in the northern
Gulf of Mexico, and to predict the consequences of management
actions. The models range from simple statistical models to complex
three-dimensional fully coupled hydrodynamic-biogeochemical models.
The
size and the complexity of these models have been steadily
increasing due to developments in computer technology and
computational techniques, and also in response to new scientific
paradigms that have emerged over time forcing modelers to broaden
the scope of their original models. We present an overview of
hypoxia models developed for the Gulf of Mexico hypoxic zone and
discuss the lessons learned, and some fundamental differences
between simple and complex models in evaluating the effectiveness
of nutrient management strategies for reducing hypoxia.
DUBRAVKO JUSTICLSU DEPARTMENT OF OCEANOGRAPHY & COASTAL
SCIENCES
Reducing Hypoxia in the Northern Gulf of Mexico: Lessons from
Simple and Complex Models
-
OCEAN SCIENCES 2016
Thursday, February 25, 2016TIME: 8:15 AM – 8:30 AM LOCATION:
222
#LSURESEARCHFor more information, call the LSU Division of
Strategic Communications at 225-578-8654.
RESEARCH WORKS
Coastal wetlands in southern Louisiana are vanishing rapidly due
to a host of environmental stressors including sea level rise,
subsidence, and lack of sediment deposition. Since these wetlands
provide significant environmental and economic value, their
stability and preservation are critical issues for scientists and
policyholders. A key question concerns the spatial and temporal
variability of wetland accretion rates, particularly the role of
hurricanes as an agent in wetland sedimentation. Since 1996,
thousands of wetland accretion measurements have been determined at
390 sites across South Louisiana as a result of a regional
monitoring network (Coastal Reference Monitoring System, or CRMS),
under the collaboration of the Louisiana Office of Coastal
Protection and Restoration (CPRA) and the United States Geological
Survey (USGS). We utilized this voluminous dataset to analyze the
spatial and temporal
patterns of wetland accretion by mapping the rates during three
time periods around the landfall of Isaac, a category 1 hurricane,
in August 2012. By analyzing sites with sampling dates no more than
7 months from establishment, the results indicate that wetland
accretion rates averaged about 2.89 cm/yr from stations sampled
before Isaac, 4.04 cm/yr during the period containing Isaac’s
impact, and 2.38 cm/yr from sites established and sampled after
Isaac. Wetland accretion rates determined from the period
containing Isaac’s impact were 40% and 70% greater than rates
before and after the hurricane, respectively. Wetland accretion
rates associated with Isaac were highest at sites along the
Mississippi River and its tributaries instead of along the path of
the hurricane, suggesting that freshwater flooding from rivers and
streams, rather than storm surge, is the main mechanism responsible
for increased wetland accretion.
THOMAS BIANCHETTELSU DEPARTMENT OF OCEANOGRAPHY & COASTAL
SCIENCES
Wetland Accretion Rates along Coastal Louisiana: Spatial and
Temporal Variability in Light of Hurricane Isaac’s Impacts
-
OCEAN SCIENCES 2016
Thursday, February 25, 2016TIME: 8:30 AM – 8:45 AM LOCATION:
222
#LSURESEARCHFor more information, call the LSU Division of
Strategic Communications at 225-578-8654.
RESEARCH WORKS
The modern Mississippi River Delta plain has been largely
disconnected from the main distributary by a highly engineered
system of levees and floodways. This vast and fragile landscape is
experiencing land-loss and is increasingly susceptible to
inundation. Intense debate exists in the scientific community as to
whether direct fluvial or hurricane-driven re-suspension and
sedimentation are the present dominant sources of mineral sediment
to the wetland surfaces of the modern delta complex. The relative
importance of these sources remains a matter of public discussion
and scientific debate, and this lack of clarity strongly influences
development of tools, strategies, and policies to conserve coastal
Mississippi River Delta lands.
Research fueling this debate has been restricted both spatially
and temporally thus far. Furthermore, the contribution of organic
production is unknown at these scales. A comprehensive study of the
Lafourche and Plaquemine-Balize Mississippi River Delta
complexes
at a temporal scale similar to that of natural deltaic cycles
(102 - 103years) is being completed to address the deficiencies in
our current understanding. A suite of 38 5m vibracores and 33
co-located 1m piston cores are being analyzed at moderate- to high-
resolution for bulk density, grain-size, organic matter, magnetic
susceptibility, and X-ray fluorescence to create the recognition
criteria necessary to distinguish sedimentary sources for this time
period.
210Pb and 137Cs data show that despite rapid subsidence and
sea-level rise, many studied wetlands are still able to maintain
their elevations. Sedimentary accumulation rates in the subaerial
components of the Lafourche complex would seem to indicate that
following distributary abandonment/cutoff and the elimination of
pre-levee and overbank flooding and crevasse sediments,
resuspension by cold fronts and hurricanes has become the primary
sediment source for affected wetlands.
CRAWFORD WHITELSU DEPARTMENT OF GEOLOGY & GEOPHYSICS
Influences of Hurricanes, Floods, and Organic Production on
River-Delta Evolution
-
OCEAN SCIENCES 2016
Thursday, February 25, 2016TIME: 9:00 AM – 9:15 AM LOCATION:
217-219
#LSURESEARCHFor more information, call the LSU Division of
Strategic Communications at 225-578-8654.
RESEARCH WORKS
Arctic storms in the late summer and early fall can produce
severe weather conditions for the seasonally unfrozen coastal
waters. The alternating wind directions due to the movement of
Arctic high pressure systems and atmospheric low pressure frontal
systems produce a low frequency subtidal oscillation of water
levels, causing flushing and through flows in Arctic lagoons with
multiple inlets. From 2013 to 2015, we conducted surveys in late
summer and early fall with bottom deployed acoustic Doppler current
profilers (ADCP) in a 16-m deep tidal pass of the Elson Lagoon, and
ship based surveys in the nearshore Barrow region of Alaska.
Atmospheric, CTD, water level, and wave data were also obtained
during this period. An atmospheric
Weather Research and Forecasting (WRF) model was run to resolve
the evolution of the high pressure movement and wind regime
changes. A coastal ocean hydrodynamics model was run to illustrate
the dynamical processes as shown by the observations. Our results
have shown the sensitivity of the flushing and through flow
oscillations in the multi-inlet lagoon to the atmospheric pressure
systems, which also can be used to explain the great inter-annual
variabilities and impact on ice movement in and out of the lagoons.
This variability in hydrodynamic conditions, driven by
meteorological phenomenon, is believed to play a significant role
in structuring the nearshore ecology of the region.
CHUNYAN LILSU DEPARTMENT OF OCEANOGRAPHY & COASTAL
SCIENCES
Summer Time Flushing of an Arctic Multi-inlet Lagoon under
Storms from 2013 to 2015
-
OCEAN SCIENCES 2016
Thursday, February 25, 2016TIME: 9:45 AM – 10:00 AM LOCATION:
222
#LSURESEARCHFor more information, call the LSU Division of
Strategic Communications at 225-578-8654.
RESEARCH WORKS
Dujiangyan, also known as the Dujiangyan Project, is a hydraulic
engineering complex built more than 2,260 years ago on the
Mingjiang River near Chengdu in China’s Sichuan Province. The
complex splits the river into two channels, a so-called “inner
river” (Leijiang) and an “outer river” (Waijiang) that carry
variable water volumes and sediment loads under different river
flow conditions. The inner river and its numerous distributary
canals are primarily man-made for irrigation over the past 2000
years, while the outer river is the natural channel and flows
southward before entering into the Yangtze River. Under normal
flow, 60% of the Mingjiang River goes into the inner river for
irrigating nearly 1 million hectares of agricultural land on the
Chengdu plain. During floods, however, less than 40% of the
Mingjiang River flows into the inner river. Under both flow
conditions, about 80% of the riverine sediments is carried by the
outer river and continues downstream. This hydrology is achieved
through a weir work complex that comprises three major components:
a V-shaped bypass dike in the center of the Mingjiang River, a
sediment diversion canal in the inner river
below the bypass dike (the Feishayan Floodgate), and a flow
control in the inner river below the sediment diversion canal (the
Baopingkou Diversion Passage). Together with ancillary embankments,
these structures have not only ensured a regular supply of
silt-reduced water to the fertile Chengdu plain, but have provided
great benefits in flood control, sediment transport, and water
resources regulation over the past 2,000 years. The design of this
ancient hydraulic complex ingeniously conforms to the natural
environment while incorporating many sophisticated techniques,
reflecting the concept that humankind is an integral part of
nature. As we are urgently seeking solutions today to save the
sinking Mississippi River Delta, examination of the ancient
engineering marvel may offer insights into sustainable practices in
river engineering of the lower Mississippi under climate change and
sea level rise. This paper will introduce the Dujiangyan Project
and will discuss possibilities of applying Dujiangyan’s fundamental
concept for sediment diversions in the Lower Mississippi River.
YI-JUN XULSU SCHOOL OF RENEWABLE NATURAL RESOURCES
Dujiangyan: Could Ancient Hydraulic Engineering be a Sustainable
Solution for Mississippi River Diversions?
-
OCEAN SCIENCES 2016
Wednesday, February 24, 2016TIME: 3:30 PM - 3:45 PM LOCATION:
231-232
#LSURESEARCHFor more information, call the LSU Division of
Strategic Communications at 225-578-8654.
RESEARCH WORKS
Photosynthetic microbial mats produce organic matter, cycle
nutrients, bind pollutants, and stabilize sediment in sandy marine
environments. Here, we investigate the influence of bedforms and
wave motion on the growth rate, composition, and spatial
variability of microbial mats by growing cyanobacterial mats on a
rippled bed of carbonate sand in a wave tank. The tank was forced
with an oscillatory flow with velocities below the threshold for
sediment motion yet able to induce a porewater flow within the
sediment. Different spatial patterns developed in mats depending on
the initial biochemistry of the water medium. When growing in a
medium rich in nitrogen, phosphorous, and micronutrients, mats grew
faster on ripple troughs than on ripple crests. After two months,
mats covered the bed surface uniformly, and the microbial
communities on the crests and in the troughs had similar
compositions. Differences in bed shear stress and nutrient
availability between crests and troughs
were not able to explain the faster growth in the troughs. We
hypothesize that this growth pattern is due to a “strainer” effect,
i.e. the suspended bacteria from the inoculum were preferentially
delivered to troughs by the wave-induced porewater flow. In the
experiments initiated in a medium previously used up by a microbial
mat and thus depleted in nutrients, mats grew preferentially on the
ripple crests. This spatial pattern persisted for nearly two years,
and the microbial composition on troughs and crests was different.
We attribute this pattern to the upwelling of porewater in the
crests, which increased the delivery of nutrients from sediment to
the cyanobacteria on the bed surface. Thus, the macroscopic
patterns formed by photosynthetic microbial mats on sand ripples
may be used to infer whether mats are nutrient-limited and whether
they are recently colonized or older than a month.
GIULIO MARIOTTILSU DEPARTMENT OF OCEANOGRAPHY & COASTAL
SCIENCES
Spatial Patterns of Cyanobacterial Mat Growth on Sand
Ripples
-
OCEAN SCIENCES 2016
Thursday, February 25, 2016TIME: 3:45 PM – 4:00 PM LOCATION:
206
#LSURESEARCHFor more information, call the LSU Division of
Strategic Communications at 225-578-8654.
RESEARCH WORKS
The northwestern Gulf of Mexico (USA) currently experiences a
large hypoxic area (“dead zone”) during the summer. The
population-level effects of hypoxia on coastal fish are largely
unknown. We developed a spatially-explicit, individual-based model
to analyze how hypoxia effects on reproduction, growth, and
mortality of individual Atlantic croaker could lead to
population-level responses. The model follows the hourly growth,
mortality, reproduction, and movement of individuals on a 300 x 800
spatial grid of 1 km2 cells for 140 years. Chlorophyll-a
concentration and water temperature were specified daily for each
grid cell. Dissolved oxygen (DO) was obtained from a 3-D water
quality model for four years that differed in their severity of
hypoxia. A bioenergetics model was used to represent growth,
mortality was assumed stage- and age-dependent, and movement
behavior was based on temperature preferences and avoidance of low
DO. Hypoxia effects were imposed using exposure-effects sub-models
that converted time-varying
exposure to DO to reductions in growth and fecundity, and
increases in mortality. Using sequences of mild, intermediate, and
severe hypoxia years, the model predicted a 20% decrease in
population abundance. Additional simulations were performed under
the assumption that river-based nutrient loadings that lead to more
hypoxia also lead to higher primary production and more food for
croaker. Twenty-five percent and 50% nutrient reduction scenarios
were simulated by adjusting the cholorphyll-a concentrations used
as food proxy for the croaker. We then incrementally increased the
DO concentrations to determine how much hypoxia would need to be
reduced to offset the lower food production resulting from reduced
nutrients. We discuss the generality of our results, the hidden
effects of hypoxia on fish, and our overall strategy of combining
laboratory and field studies with modeling to produce robust
predictions of population responses to stressors under dynamic and
multi-stressor conditions.
KENNETH ROSELSU DEPARTMENT OF OCEANOGRAPHY & COASTAL
SCIENCES
Modeling the Population-level Effects of Hypoxia on a Coastal
Fish: Implications of a Spatially-explicit Individual-based
Model
-
OCEAN SCIENCES 2016
Friday, February 26, 2016TIME: 8:45 AM – 9:00 AM LOCATION:
225-227
#LSURESEARCHFor more information, call the LSU Division of
Strategic Communications at 225-578-8654.
RESEARCH WORKS
Coastal regions of eutrophication-driven oxygen depletion are
widespread and increasing in number. Also known as dead zones,
these regions take their name from the deleterious effects of
hypoxia (dissolved oxygen less than 2 mg/L) on shrimp, demersal
fish, and other animal life. Dead zones result from nutrient
enrichment of primary production, concomitant consumption by
chemoorganotrophic aerobic microorganisms, and strong
stratification that prevents ventilation of bottom water. One of
the largest dead zones in the world occurs seasonally in the
northern Gulf of Mexico (nGOM), where hypoxia can reach up to
22,000 square kilometers. To explore the underlying genomic
variation and metabolic potential of microorganisms in hypoxia, we
performed metagenomic and metatranscriptomic sequencing on six
samples from the 2013 nGOM dead zone from both hypoxic and oxic
bottom waters. Over 217 Mb of sequence was assembled into contigs
of at
least 3 kb with IDBA-UD, with 72 greater than 100 kb, and the
largest 495 kb in length. Annotation by IMG recovered over 224,000
genes in these contigs. Binning with tetra-ESOM and quality
filtering based on relative coverage of sample-specific reads led
to the recovery of 83 partial to near complete (31 over 70%)
high-quality genomes. These metagenomes represent key microbial
taxa previously determined to be numerically abundant from 16S rRNA
data, such as Thaumarcheaota, Marine Group II Euryarchaeota,
SAR406, Synechococcus spp., Actinobacteria, and Planctomycetes.
Ongoing work includes the recruitment of metatranscriptomic data to
binned contigs for evaluation of relative gene expression,
metabolic reconstruction, and comparative genomics with related
organisms elsewhere in the global oceans. These data will provide
us with detailed information regarding the metabolic potential and
activity of many of the key players in the nGOM dead zone.
CAMERON THRASHLSU DEPARTMENT OF BIOLOGICAL SCIENCES
A Metagenomic Assembly-based Approach to Decoding Taxa in the
Dead Zone
-
OCEAN SCIENCES 2016
Friday, February 26, 2016TIME: 8:45 AM – 9:00 AM LOCATION:
211-213
#LSURESEARCHFor more information, call the LSU Division of
Strategic Communications at 225-578-8654.
RESEARCH WORKS
Orbicella (formerly Montastraea) faveolata is an Atlantic
massive coral species used by paleoclimatologists to reconstruct
monthly- and annually-resolved sea surface temperature (SST)
variations. Previous studies found discrepancies in coral
strontium-to-calcium ratios (Sr/Ca) among colonies separated by
meters to kilometers possibly attributed to either biological
processes inherent to each colony, environmental differences at
each coral site, and/or sampling-analytical methods. Here we
examine coral Sr/Ca variations in five O. faveolata colonies
offshore from Veracruz, Mexico (19.06ºN, 96.93ºW), two colonies
from different water depths (3 and 6 m) in the same local reef
environment (Santiaguillo) and three colonies in nearby reefs
closer to the mainland (water depth of 4, 6, and 12 m); all
colonies were cored in 1993. We control for sampling-analytical
methods by using a refined sampling protocol that follows a
corallite thecal wall that is parallel to the coral slab surface
(i.e., optimal alignment) and we use the same analytical
method and instrument for all colonies. Coral annual growth
rates decrease by 44% for colonies in deeper water (12 m) with no
significant correlation in annual growth rates among the colonies.
Monthly coral Sr/Ca determinations co-vary among colonies up to 16
km apart suggesting a common environmental signal. Means in coral
Sr/Ca among the colonies is similar until 1986 when a divergence
occurs that does not follow the expected differences due to water
depth and growth rate. The two colonies farthest from the mainland
(Santiaguillo) have similar means and coral Sr/Ca variations from
1986–1993. In the mid-1980s, Veracruz experienced changes in land
use with increased river runoff delivering more sediment to the
ocean that could shift seawater chemistry in coastal waters causing
the observed coral Sr/Ca divergence in the near shore colonies.
Increased sedimentation could stress coral colonies causes
different biological responses evident in the coral Sr/Ca
records.
KRISTINE DELONGLSU DEPARTMENT OF GEOGRAPHY &
ANTHROPOLOGY
Assessment of Coral Sr/Ca Variations in Orbicella faveolata
Colonies in Veracruz, Mexico
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OCEAN SCIENCES 2016
Friday, February 26, 2016TIME: 2:00 PM – 2:15 PM LOCATION:
RO5
#LSURESEARCHFor more information, call the LSU Division of
Strategic Communications at 225-578-8654.
RESEARCH WORKS
It has been well established that the composition of oil, when
spilled into the marine environment, undergoes substantial changes
caused by weathering. The general sequence of this compositional
change begins with straight chain alkanes (the fastest to degrade),
followed by low molecular weight branched and cyclic alkanes and,
finally the aromatics. Most resistant to weathering are the higher
molecular weight cyclic and branched alkanes (i.e., the “forensic
biomarker compounds” such as the hopanes and steranes) and
tri-aromatic ringed steroids. The composition of these biomarker
compounds is particularly resistant to change because they are not
affected by evaporative weathering,
are not water soluble, and are not readily degraded by microbial
and/or photo-oxidation. However, after extensive time in the
environment, being subjected to numerous weathering factors,
biomarker compositional patterns are beginning to exhibit
significant changes. This presentation will describe the general
weathering patterns of petroleum residues in sediment samples
collected from marsh areas of coastal Louisiana over a five year
period. Particular attention will focus on compositional changes
that have been observed in the steranes and diasteranes compounds
that traditionally have been considered the most resistant to
compositional changes due to weathering.
EDWARD OVERTONDEPARTMENT OF ENVIRONMENTAL SCIENCES
Weathering Patterns of Forensic Biomarker Compounds and PAHs in
Coastal Marsh Sediment Samples since the 2010 Deepwater Horizon Oil
Spill
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OCEAN SCIENCES 2016
Friday, February 26, 2016TIME: 3:30 PM – 3:45 PM LOCATION:
RO5
#LSURESEARCHFor more information, call the LSU Division of
Strategic Communications at 225-578-8654.
RESEARCH WORKS
On April 20, 2010, the Macondo well in Mississippi Canyon 252
blew and the well gushed oil uncontrollably into the sea and
subsequently into the saltmarsh. Aromatics were measured and found
to increase until May 2011. In Sept 2012, Hurricane Isaac
remobilized oil in the marsh further increasing aromatics once
again and oiled areas of marsh that were previously not
contaminated with Macondo oil. Over the course of the next year,
monthly samples were taken and the aromatics decreased. Also, a
large number of extracted oil samples emerged in the marsh that
matched the Macondo oil, but differed significantly from the
original patterns seen which we started calling “Pattern A” and
“Pattern B.” Additionally, in 2013 an uptick in aromatic compounds
was observed at previously-oiled sites and lesser so at some
previously-unoiled sites. Associated with this increase in
aromatics was a shift from mostly Pattern A oil to
more Pattern B oil or a combination of Pattern AB.
Previously, we’ve shown that the ants in the marsh are
intimately connected to the terrestrial food web and that they are
good indicators of the presence of stressors that affect food
availability for vertebrates such as fish and birds. Initially
populations of ants survived the oiling of the marshes but the
population crashed in the summer of 2011 in response to the
decreased food availability in the marsh. We started to see
recovery of ants in the oiled areas in August 2012, but the
populations were annihilated by hurricane Isaac. The ants largely
recovered in the unoiled plots, but not in oiled plots in 2013,
which matches the uptick in the aromatic compounds measured at the
same sites. In 2015, we started to measure recovery of the ant
population in the oiled areas but lack hydrocarbon data at this
time to associate with the recovery.
LINDA HOOPER-BUIDEPARTMENT OF ENVIRONMENTAL SCIENCES
Tracking Macondo Oil in the Marsh: Sampling Directly via
Sediment and Indirectly via Ants