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• *
A NEW UNDERSTANDING OF PLANKTON DYNAMICS WITHIN ELKHORN SLOUGH: THE IMPORTANCE OF MICROBIAL PROCESSES.
*Nick Welschmeyer*, Lawrence Younan, Sarah Smith, Chris Scianni & Megan Wehrenberg
Moss Landing Marine Laboratories
Main Point• Elkhorn Slough is characterized by two plankton
communities
-Upper slough characterized by algal cryptophytes, high bacterial biomass, active denitrifying bacteria and traces of anoxygenic bacteria
-Lower slough reflects plankton communities of Monterey Bay (source)
Sampling sites: (2002 – present)Kirby Park
Parsons Slough
Highway 1 bridge
0
2
4
6
8
10
12
09/01/02 11/01/02 01/01/03 03/03/03 05/03/03 07/03/03 09/02/03 11/02/03 01/02/04 03/03/04 05/03/04Date
Chl
orop
hyll
a (m
g m-3
)
Lower Elkhorn Slough(mean Stations 1-5)
0
2
4
6
8
10
12
14
16
09/01/02 11/01/02 01/01/03 03/03/03 05/03/03 07/03/03 09/02/03 11/02/03 01/02/04 03/03/04 05/03/04
Date
Chl
orop
hyll
a (m
g m-3
)
Upper Elkhorn Slough(mean of Stations 6-10)
Phytoplankton blooms (Chl a > 5ug/L)Occur anytime except January/February
The pattern is similar for both upper and lower Elkhorn Slough
Elkhorn Slough (Oct 2003)
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.10
0 5 10 15 20 25 30 35 40 45 50
Retention Time (min)
Abs
orba
nce
440n
m (r
elat
ive)
Peridinin (dinoflagellates) Fucoxanthin (diatoms)
Alloxanthin (cryptophytes)
Highw ay 1 Bridge
Kirby Park
Chromatographic analysis of algal pigments (HPLC)
Chl a
y = -0.0595x + 0.6914
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 1 2 3 4 5 6 7 8 9 10 11
Station
Fuco
xant
hin/
Chl
orop
hyll
a (g
/g)
B
y = 0.0418x + 0.0394
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 1 2 3 4 5 6 7 8 9 10 11
Station
Allo
xant
hin/
Chl
orop
hyll
a (g
/g)
C
Phytoplankton Horizontal DistributionsDiatoms vs. Cryptophytes
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 1 2 3 4 5 6 7 8 9 10 11
Station
Fuco
xant
hin/
Chl
orop
hyll
a (g
/g)
0
0.1
0.2
0.3
0.4
0.5
0.6
Allo
xant
hin/
Chl
orop
hyll
a (g
/g)
Fucox/Chl
Allox/Chl
A
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 1 2 3 4 5 6 7 8 9 10 11
Station
Fuco
xant
hin/
Chl
orop
hyll
a (g
/g)
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
Allo
xant
hin/
Chl
orop
hyll
a (g
/g)
Fucox/Chl
Allox/Chl
A
Low Tide
High Tide
PhytoplanktonCommunity
InterfaceShifts w/Tide
Low tideLow Tide
High TideUpper Slough
Cryp75%
Chlor18%
Diat5%
Cyan2%
Dino0%
Lower Slough
Diat70%
Cryp19%
Chlor8%
Dino0%
Cyan3%
Figure 1: An enhanced image, derived form hyperspectral imagery collected by the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS), reveals a discharge plume exiting the mouth of the slough.
In: 12/10/2004 St4
Diat18%
Dino2%Cyan
7%
Chlor16%
Cryp57%
Out: 12/10/2004 St3Diat16%
Dino53%
Cyan1%
Chlor11%
Cryp19%
FL3 FL3 FL3 FL3 FL3
FL3 FL3 FL3FL3FL3
FL2
FL2
FL2
FL2
FL2
FL2
FL2
FL2
FL2
FL2
St. 1 St. 2 St. 3 St. 4 St. 5
St. 6 St. 7 St. 8 St. 9 St. 10
Sample
laser Scattered light Detector
Fluorescence Detector
Waste
Flow Cytometry: Cryptophytes
Bacteria (cells/mL) Elkhorn Slough
0
200000
400000
600000
800000
1000000
1200000
0 1 2 3 4 5 6 7 8 9 10 11Stations
Bac
teria
cel
ls/m
L
18-Mar20048-May200417-Jun2004
Epifluorescence enumeration of bacteria (DAPI)
Water Column Bacteriochlorophyll a
0
2
4
6
8
10
12
14
0 2 4 6 8 10
Station
Bac
terio
chlo
roph
yll a
(ng/
L)
A
Mudflat Bacteriochlorophyll a
0
50
100
150
200
250
300
0 2 4 6 8 10
Station
Bac
terio
chlo
roph
yll a
(ng/
mL
pack
ed s
edim
ent)
B
Anoxygenic Bacteria: characterized by bacteriochlorophyll a (770nm HPLC)
Dissolved organic matter (DOM) in Elkhorn Slough(spectrofluorometric determination)
Nitrate Distribution
0.00
50.00
100.00
150.00
200.00
250.00
300.00
350.00
400.00
450.00
500.00
0 2 4 6 8 10 12
Station
Nitr
ate
(uM
)
Dissolved Nutrient Concentrations in Elkhorn Slough
0.00
20.00
40.00
60.00
80.00
100.00
120.00
140.00
160.00
0 2 4 6 8 10 12
Station
N/P
(mol
e/m
ole)
Nitrate/Phosphate Ratios:
- Redfield C:N:P (106:16:1) - expected Redfield N/P ~ 16 (mole/mole)
Redfield
All Nutrient Data w/ N/P > 20
0
20
40
60
80
100
120
140
160
0 2 4 6 8 10 12
Station
N/P
(mol
e/m
ole)
N/P > 20 79% 21%
All Nutrient Data w/ N/P < 2
0.0
0.5
1.0
1.5
2.0
2.5
0 1 2 3 4 5 6 7 8 9 10 11
Station
N/P
(mol
e/m
ole)
All N/P < 2.09.7% 90.3%
AgriculturalRunoff
BacterialDenitrification
NO3- → N2 (gas)
Abundance of two Acartia species (copepods) in Elkhorn Slough
0
2000
4000
6000
8000
10000
12000
14000
16000
1 2 3station (1-lower, 2-mid, 3-upper)
# an
imal
s/m
^3
Ac Tonsa
Ac Calif
Conclusions:• Upper Elkhorn Slough phytoplankton form a low-diversity
community dominated by Cryptophytes
• Bacterial denitrification is a dominant microbial process in Upper ES, possibly dampening agricultural nitrate levels
• Lower ES phytoplankton are nutrient-saturated and are expected to exchange freely with Monterey Bay via tides
Pigment Distribution in Cores