• *

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

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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)

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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

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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