Aquatic%20Microbial%20Ecology%20and%20Biogeochemistry%20at%20Ole%20Miss:

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Aquatic Microbial Ecology and Biogeochemistry at
Ole Miss  An Overview of On-going Research
Projects

• Dr. Clifford Ochs
• Department of Biology
• University of Mississippi
• 20 November 2003

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Projects

• Nutrient Competition Between Bacteria and
  Phytoplankton Under Varying Conditions of UV
  Exposure - NSF
• Effects of Wintertime Flooding of Mississippi
  Delta Agricultural Fields on Soil Chemistry and
  Microbiological Properties EPA
• Effects of multiple interacting stressors in
  agricultural ecosystem wetlands EPA
• North Mississippi GK-8 Project - NSF

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Nutrient Competition Between Bacteria and
Phytoplankton Under Varying Conditions of UV
ExposureU.S. NSF (Ecology) 0212710 PI C.A.
Ochs2002-2004
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Conceptual model of fluxes of C and P in the
plankton environment
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The Question
Does ambient solar UVR affect competition for
limiting nutrients between bacteria and
phytoplankton?
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What was measured?

• ? Bacterial production protein synthesis?
  Bacterial biomass microscopy? Bacterial growth
  rate Production/Biomass
• ? Algal biomass Chlorophyll a C content?
  Algal growth rate µ (InNt InNo)/time ?
  Relative growth rate responses of bacteria and
  phytoplankton response index (RI)

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• Response index (RI)
• (µx(b) (µo(b)) - (µx(a) µo(a))
• µo(b) and µx(b) bacterial GR in control and
  each nutrient/light
  manipulations.
• µo(a) and µx(a) phytoplankton GR in control
  and each nutrient/light
  manipulations.
• RI bacteria favored
• - phytoplankton favored
• Chrzanowski and Grover, 2001

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Predictions for Response Index
Nutrient Levels R.I. UVR R.I. -UVR Analysis of Interaction
Control (no addition) low C/low P Baseline weak coupling commensalism for C competition for P
high C/high P C and P enriched -- - uncoupling no commensalism for C no competition for P
high C/low P P-limited uncoupling no commensalism for C competition for P
low C/high P organic C-limited --- -- coupling commensalism for C no competition for P
Assumes bacteria GR more reduced than phyto
GR by UVR
bacteria favored - phytoplankton favored
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Significant Effects Analyzed by Day
DAY (2002) GR phytoplankton GR bacteria RI
6 AUG Light (No UVR gt W/ UVR) Nutrients Light X Nutrients
8 AUG Nutrients Nutrients
10 AUG Light (No UVR lt W/ UVR) Nutrients
12 AUG Light (No UVR gt W/ UVR)
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Effects of Wintertime Flooding of Mississippi
Delta Agricultural Fields on Soil Chemistry and
Microbiological PropertiesU.S. EPA
C9994866-96-1 C.A. Ochs and S.A Milburn
1997-1999
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The Question
Does winter flooding of agricultural fields
affect soil and water chemistry, microbial
metabolism, or microbial community composition?
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Wetlands N Cycle
N2
Denitrification (anoxic)
Nitrogen Fixation
Organic N
NO3-
Nitrification (oxic)
Ammonification
NH4
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Predictions

• Flooding will reduce rates of nitrification,
  microbial respiration and organic matter
  decomposition.
• Winter-time flooding will enhance rates of
  denitrification.
• Flooding will reduce losses of N and P from
  agricultural fields compared to non-flooded
  fields.

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Field Locations
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What was measured?

• Chemical parameters measured in soil
• Ammonium, nitrate, total N, organic C, total P,
  and percent organic matter
• Chemical parameters measured in overlying water
• Ammonium, nitrate, and total P
• Microbial community parameters
• Microbial biomass and abundance of denitrifying
  bacteria, denitrification and respiration rates.

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Conclusions

• Nitrate was lower and ammonium was higher in
  flooded soils.
• No detectable effect on soil nutrient
  concentrations in post-treatment soils.
• Denitrification and soil respiration rates were
  low and unaffected by winter flooding.
• Losses of N and P during flooding were
  insignificant relative to soil N concentrations,
  and less than losses by erosion from bare
  cotton-field soils

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Effects of multiple interacting stressors in
agricultural ecosystem wetlands
U.S. EPA R826595-01-0 S.Threlkeld, C. Britson,
S. D'Surney, G. Easson and C. Ochs 1998 - 2002
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Treatment factors and levels for factorial
mesocosm experiment
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? ag. ponds (n25) ? non-ag. ponds (n75)
Y 5.5014 x 5.6571 r2 0.07 (?)
Y15.354-5248 r2 0.60 (?)
Y 0.1132x 8.1433 r2 0.07 (?)
Y -0.304x 17.04 r2 0.02 (?)
Y1.4278x r2 0.30 (?)
Y 0.2631x 59.727 r2 0.01 (?)
Y6.8719x r2 0.30 (?)
Y 5.9552x 15.585 r2 0.30 (?)
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Spatial patterns in bacterial productivity
Bacterial productivity (thymine/L/hr)
low
high
Chlorpyifos (estimated use in kg/acre)
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Phytoplankton Pigment Biomass and Spectral
Signature
low
high
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Mississippi River Projects

• Historical patterns in algal community structure
  as a measure of water quality changes.
• Sources of organic matter The relative
  importance of allochthonous vs. autothonous
  inputs.
• Controls on bacterial and algal productivity
  light vs. nutrients limitation.
• Nitrogen transport and transformations
  mechanisms, rates and sites of activity.
• Spatial patterns in bacterial community structure
  relative to water chemistry (nutrients, metals,
  organic and inorganic pollutants).

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The North Mississippi GK-8 Project
U.S. NSF DGE-0231751 J. OHaver, C.A. Ochs, D.
Rock, M. Eftink2003-2006
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The Biology Analytical Laboratory
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Microscope and Nucleic Acid Sequencing Resources
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The University of Mississippi Field Station