Which factors determine spring biological bloom in the China Sea?

Xiaohong Yao

Key Laboratory of Marine Environment and Ecology

(Ministry of Education), Ocean University of China,

Qingdao, 266100, P.R. China

2012.5.10, SOLAS OPENSCIENCE CONFERENCE

Objectives

• 1) In the China Sea, which factors determine spring biological bloom (not always occur)? This is a “yes” or “no” question

• 2) In the China Sea, which factors enhance spring biological bloom? This is “how much” question

• 3) Roles of Asian dust deposition on spring biological bloom in the China Sea

Fertilization incubation experiments in the Yellow Sea in March 2011

Surface sea water

200μm filtering

bottles

Dust and nutrientscontrol

Photo of incubation box, each of bottle is 16 L , recycling sea water is used for controlling temperature

Route of incubation experiment in March, 2011

Sea water was collected in the mid of the Yellow sea (red star), then direct to East China sea;

Atmospheric deposition, including nature and anthropogenic pollutants, was reported to be the major source of nutrients in the Yellow sea.

Initial nutrients in sea water:

NO3-=1.05 umol/L; NH4

+=0.31 umol/L; PO4

3-=0.15 umol/L;NO2

-=0.09 umol/L.

Nutrients added in incubation experiment in March, 2011

ID Nutrients added Amount or concentration

A control No

B dust 20 mg/L based on episodic observations

C FeSO4 2nmol/L just a guessD NaH2PO4 0.2μmol/L close to sea waterE FeSO4+NaH2PO4 2nmol/L+0.2μmol/LF NaNO3 2μmol/L close to sea water

G rainwater 2ml/L assuming 10 cm rainfall in a 50 m mixed layer

20 mg/L dust contains 0.14 umol/L Fe (total, Fe2+ could be much less than 2 nmol/L) + 0.005 umol/L PO4

3-+ (0.14 umol/L NO3-+0.08

umol/L NH4+);

Chemical composition of Rainwater was not measured.

What determined spring biogenic bloom in the Yellow Sea?

A weak biogenic bloom was observed at A2 station from satellite data;

Much strong biogenic bloom occurred in the control incubation experiment ;

Temperature and PAR (photosynthetically active radiation) were likely the most important limitation factors for biogenic bloom.

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6.00

9.00

12.00

15.00

18.00

0 2 4 6 8 9 10 11 13 15

Cho

loph

yll-

a (μ

g/L

)

Days

Control

Dust in 20mg/L

NO3- in 2umol/L

What can enhance spring biogenic bloom?

In Dust and NO3- fertilization

incubation experiments, CHLA was statistically higher than in the control experiment

A net increase of CHLA in dust experiment relative

to the control was 1/3 of that in NO3- experiment

1) Doubling NO3- in sea

water doubles the concentration of CHLA;

2) Added 20 mg/L dust to sea water increased the concentration of CHLA by about 30% relative to the control;

3) Bio-availability Nitrogen in Dust experiment was only 1/10 of that in NO3

- experiment;

4) What caused high efficiency in dust fertilization experiment?

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0 2 4 6 8 9 10 11 13 15

Cho

loph

yll-

a (μ

g/L

)

Days

Control

Fe in 2nmol/l

P in 0.2umol/L

Fe in 2nmol/L+ P in 0.2umol/L

Can Fe, P, Fe+P and rainwater enhance spring biogenic bloom?

In Fe, P, (Fe+P) and Rain water fertilization incubation experiments, CHLA was higher than that in the control during the most of experiment times;

However, the difference was not statistically significant;

More experiments might be needed.

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0 2 4 6 8 9 10 11 13 15

Cho

loph

yll-

a (μ

g/L

)

Days

Control

Rain

Why dust has a high efficiency?-Nutrients in dust

fertilization experiment

Fe2+ was not measured in this study

Dust increased concentration of NH4

+;

Dust decreased PO4

3- at the initial stage, then released;

Minor influences on NO3

- and NO2- too

much;

Overall, unexpected increase of NH4

+ relative to NH4

+ in sea water; is high efficiency of dust associated with NH4

+ input?

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NH

4+ con

cent

ratio

n, μ

mol

L-1

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0.04

0.08

0.12

0.16

0 2 4 6 8 9 10 11 13 15Days

PO43-

con

cent

ratio

n, μ

mol

L-1

0.00

0.03

0.06

0.09

0.12

0 2 4 6 8 9 10 11 13 15Days

NO

2- con

cent

ratio

n, μ

mol

L-1

0.00

0.40

0.80

1.20

1.60

0 2 4 6 8 9 10 11 13 15Days

NO

3- con

cent

ratio

n, μ

mol

L-1 Control

Dust20

Nutrition in NO3- and PO4

3- fertilization experiment

Only about 50% of added NO3

- and PO43-

were detected in experiments;

Reverse daily variations of NH4

+ between the control and the NO3

- experiment;

More NH4+ was

released in the NO3-

and PO43- experiment

than in the control.

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0.05

0.10

0.15

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0.25

0 2 4 6 8 9 10 11 13 15Days

PO

43- c

once

ntra

tion,

μm

ol L

-1

Control

PO43- in 0.2 umol/L

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0.50

1.00

1.50

2.00

2.50

0 2 4 6 8 9 10 11 13 15Days

NO

3- con

cent

ratio

n, μ

mol

L-1

Control

NO3- in 2umol/L

0.00

0.20

0.40

0.60

0.80

0 2 4 6 8 9 10 11 13 15Days

NH

4+ con

cent

ratio

n, μ

mol

L-1

Control

NO3- in 2umol/L

0.00

0.20

0.40

0.60

0 2 4 6 8 9 10 11 13 15Days

NH

4+ con

cent

ratio

n,

μm

ol L

-1

Control

PO43- in 0.2umol/L

Daily variations of NH4+ implied: grew and degrade, then grew and degrade…

NO3- and NH4

+ were used to synthesize organic, then decomposed into NH4+,

NH4+ was further used to synthesize organic, then decomposed into NH4

+ …

Nutrients in rain water fertilization experiment

Rainwater did not add the detectable amount of PO4

3-;

Added rainwater increased N by 50%; When considered only 50% of added nutrients can be detected, N added by rainwater could be close to that in NO3

- fertilization experiment ; then why low CHLA?

NO3- could be

partially converted to NH4

+? and vice verse?

NO3- NH4

+ ?

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0.40

0.80

1.20

1.60

0 2 4 6 8 9 10 11 13 15Days

NO

3- con

cent

ratio

n, μ

mol

L-1

Control

Rain

0.00

0.30

0.60

0.90

1.20

0 2 4 6 8 9 10 11 13 15Days

NH

4+ con

cent

ratio

n, μ

mol

L-1

0.00

0.04

0.08

0.12

0.16

0 2 4 6 8 9 10 11 13 15Days

PO43-

con

cent

ratio

n, μ

mol

L-1

0.00

0.03

0.06

0.09

0.12

0 2 4 6 8 9 10 11 13 15Days

NO

2- con

cent

ratio

n, μ

mol

L-1

Experiment in the East China Sea in summer

No bloom for the control and no synthesized effect by DustMuch low concentration of CHLA, only three days for CHLA reaching the maximum.

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0 2 4 5 6 7 8 9 10 11 12 13 15

Days

Chl

-a c

once

trat

ion,

μg/

L

Control

Dust20

NO3-2

2

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Days

Chl

-a c

once

trat

ion,

μg/

L

Control

Dust20

NO3-2

20

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Days

Chl

-a c

once

trat

ion,

μg/

L

Control

Dust20

NO3-2

T

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0.40

0.60

0.80

1.00

1.20

1.40

0 2 4 5 6 7 8 9 10 11 12 13 15

Days

Chl

-a c

once

trat

ion,

μg/

L

Control

Dust20

NO3-2

N limitation; not limited by Fe, P and Fe+P (not shown)

<0.2 um CHLA

>20 um CHLA

2-20 um CHLA

Total CHLA

Conclusion

• 1) Temperature and PAR were likely the most important limitation factors for biogenic bloom in the Yellow sea;

• 2) Since the ratio of N/P is less than 10 at the ocean zone, the concentration of chlorophyll-a was very sensitive to the external input of N; the concentration also increased with increasing external input of P, but not statistically significant;

• 3) N in Dust fertilization experiment was only 1/10 of that in NO3-

fertilization experiment, but the net increase of CHLA in the former experiment relative to the control was 1/3 of that in the later experiment; Does this imply that any unknown X could enhance bloom?

• 4) In the rainwater fertilization experiment, N increased by about 100%. However, relative to the control, no significant increase of the concentration of chlorophyll-a was observed. Again, Does this imply any unknown X limitation? X appeared to be absent in rainwater and it seems to play a key role for the use of NH4

+.

Acknowledgement

• This study is a team work by my colleagues and students, they are Prof. Huiwang Gao, Jinhui, Shi, Jianhua Qi, students include Tianran Zhang, YangFan, Ying Liu,…

Not SiO32-

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SiO

32- c

once

ntra

tion,

μm

ol L

-1 Control

Dust in 20mg/L

SEEDSSERIES

EisenEx SOIREE

, II

SOFeX

IronEx I

In situ Fe fertilizer experiments in N.Pac

SAGE

SEEDS II

LNLC

Most of areas in China Sea is subject to EOZ

HNLC

LNLCEOZ

Surface Chl.a concentration

EOZ: Eutrophic Ocean Zone; HNLC: High-Nutrient Low-Chlorophyll; LNLC: Low -Nutrient Low-

Chlorophyll

China

Biological bloom in the China Sea occurred frequently in spring, but not yet well understand; the process could provide a clue to understand dynamics of carbon transfer in the China sea.

US