Biogeochemistry of Indian estuaries: Influence of Human Interferences

V.V.S.S. Sarma National Institute of Oceanography

India

2-4th April 2012

GEOSS, Miraikan, Japan

An estuary is… “a transition zone between river and sea in which fresh water gets mixed with seawater and tidal influence Is strongly felt ”

River

Fresh water

Seawater

Estuary Sea

A section along the main channel

A bird’s view of estuarine system

Estuaries significance… •  important in hydrological cycles •  sediment supplies to ocean •  habitats for a large variety of life •  highly productive among aquatic systems •  food resources of socioeconomic relevance •  influence ocean dynamics in the neighbourhood

Influence of different river discharges on oceans in our neighbourhood

INDIAN SUBCONTINENT

Bay of Bengal

Arabian Sea

1.6x1012 m3/y WATER 0.3x1012 m3/y

1.4x109 tons/y SPM 0.2x109 tons/y

River and estuarine systems facilitated human settlements on

their banks through the civilizations

However, human interference with these systems is a cause for worry!

ENVIRONMENTAL ISSUES IN ESTUARIES

•  Changes in sediment load and water caused by clearing forests for agriculture and development

•  Construction of dams •  Waste disposal •  Commercial fishing •  Dredging •  Shipping •  Habitat destruction

Indian monsoonal river systems

Dis

char

ge (m

3 s-1

)

Dry Wet Dry Wet

Modification of organic matter in the Dam reservoir

DA

M

Dry Wet Dry Wet

ESTU

ARY

Influence on inorganic carbon system

Sarma et al., 2011; 2012

pCO2 (matm)

Enhanced coastal CO2 fluxes…

Sarma et al., 2011

Winter monsoon - -0.66 Intermonsoon - +0.06

Summer monsoon +7.8

Fluxes in mmolC m-2 d-1

4918

5798

8231

5806

1573

7262

3673

9608  721  17751  

293  

8616  

686  516  

1245  

2423  

10415  

289  408  

3388  1691

4126  

2352

pCO2 in the Indian estuaries

CH4-Flux(µmole m-2 Day-1)

1.06

1.07

0.44

-0.04

-0.04 0.61

0.04

-0.37

1.24 0.04 -0.03

2.13

11.8 4.03

114

1.39

0.3

1.27

5.33

11.8

10.2

0.26 2.97 1.14

Fluxes of CH4 and N2O from the Indian Estuaries

-0.01 -0.03

-0.08

-0.17

0.16

-0.03

-0.17 -0.11

0.02

-0.04

0.08

-1.11

-0.03 -0.04

7.9

0.19

0.75

1.12

3.60

-0.6

0.16

1.27 1.05 0.71

N2O-Flux(µmole m-2 Day-1)

Estuaries (107 g y-1) East coast 1300 0.82 0.20 1.80 West coast 2300 1.04 8.43 0.80 TOTAL 3600 1.86 8.63 2.60 Coastal region (1012 g y-1) Bay of Bengal 1.30 -0.03 0.08 0.04 Arabian Sea 5.03 0.33 0.09 0.006 TOTAL 6.33 0.30 0.17 0.046

Region CO2 N2O CH4 DMS Fluxes of trace gases

Yearly  Average  Discharge  (m3/sec)

Discharge versus phytoplankton blooms

Acharyya and Sarma, 2012

Magnitude and pattern of discharge has significant impact on phytoplankton bloom. Modification of this pattern may lead to change so far healthy Indian estuaries into eutrophicated.

Discharge versus phytoplankton

Impact of Fertilizer usage on Phytoplankton diversity in the

Indian estuaries

Estuarine systems under threat … Fertilizer washings – biological productivity

eutrophication & oxygen deficiency

Fertilizer usage in India

Source: Ministry of Agriculture

N. India S. India

74% 26%

Parameter N. India S. India

Nitrate 26.2±8 4.3±1 Ammonium 3.8±1 2.1±1 Silicate 32.8±8 157±48 DIN:DIP 8.3±2 1.9±2 Chl-a 2.1±1 4.3±1

Variable nutrients composition

9.0

9.9

9.0

9.7

3.7 1.8

3.5

0.9

1.9 4.1 2.5

3.9

16.6 5.8

5.2

5.8

9.7

6.5

8.1

8.6

15.0

10.2 9.1 9.9

d15NPN (per mil)

Nitrogen isotopic ratios in the Indian estuaries

2.9 8.8

Mean

3.61

0.79

0.49

0.58 0.67

0.41

0.06

0.09 1.09 0.16

8.96

0.49

1.01

0.15

0.05

0.25

0.00

0.31

0.13

0.07

0.02

0.04 1.36

0.12

1.36

2.95 0.27

0.08

0.54

0.16

0.21

0.78

0.24

0.46

0.15 1.06 0.15

0.05

0.41

0.53 0.5

Bacillariophy. Blue-green Alg. Fucoxanthin b-carotinoids

0.75 0.48 mg/L 0.28 1.68 mg/L

Variability in pigments composition in Indian estuaries

Fucoxanthin (mg/L) b-Carotinoid (mg/L)

Sarma et al, 2012

XII Five Year Plan (2012-2017)

Ocean Science for Forecasting Indian Marine Living Resource

Potential (OCEAN FINDER)

Forecasting Potential Fishery Zones (PFZ) : connection between sea surface temperature, chlorophyll & fish catch

What is the basis for this connection?

Forecast of PFZ for central west coast of India (2008)

From INCOIS

Schematic of an ecosystem model

Mesocosm (Expedition to Experiment) ‏

Observations ‏

Modelling ‏

Glider Acoustic Doppler Current Profiler

Forecasting living resources Organism Habitat

Benthic/Pelagic

ü  Expedition to experiment ü  Spatial & temporal observations (to supplement information for

ecosystem analyses & forecasting)

Time-series locations

Estuarine time-series Coastal time-series

Coastal time-series ADCP moorings Sediment traps Profilling buoys Gliders Ship-based observations Mesocosm experiments

Thanks!