Estuaries – an introduction

M. Dileep Kumar

www.nio.org

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

Indian river systems

Sediment discharge (Actual)

<1���1-10���10-25���25-50���50-100���100-200

200-400���

>400 Million tons

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

Estuaries are highly dynamic systems with strong variability in physical and biogeochemical properties in time and space. Circulation results in

•  fresh, brackish and seawater conditions

•  vertically well mixed conditions to density driven layered structure

Creates conditions conducive to large biodiversity and food resources

Healthy estuaries perform many important functions

•  Nursery areas •  Migratory stopovers •  Feeding grounds •  Production of biomass

•  Safe harbour •  Recreation

River and estuarine systems facilitated human settlements on

their banks through the civilizations

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

Estuary/River Major city Population (106)

Waste water discharge (106 m3 / day)

Sabarmani Ahmedabad, Gandhinagar

4.7

14 Narmada Jabalpur, Bharuch 1.3

Tapi Surat 2.8

Mahim, Ulhas, Thane

Mumbai 16.5 2.8

Cochin Backwaters

Kochi 1.4 0.1

Cauvery Thiruchirapalli, Erode

1.3 ~0.1

Ennore, Adyar Chennai 6.7 0.01

Krishna Hyderabad, Vijaywads

6.7 N.A.

Hooghli Kolkata 13.2 15.3

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

Estuarine systems under threat …

Dams not only alter water and sediment discharges but also timeliness and time scales of estuarine processes

Agriculture and urbanization impacts on Global nitrogen fluxes !through rivers

UNH Green et al. 2003

•  The global N fluxes (tot N) have increased more than 3 times"•  Regionally the fluxes have increased more than 10 times"

Estuarine systems under threat … Fertilizer washings – biological productivity eutrophication & oxygen deficiency

Estuarine systems under threat … Bio-invasion due to nutrient supplies…

This is how Kochi backwaters now look

This is how Kochi backwaters should look

Estuarine systems under threat … Sewage – domestic effluents high organic loading & infectious cells

ICMAM Project Directorate Report, June 2010

•  Though monsoon and the intense runoff it brings has helped to keep the system cleaner than what it would be otherwise, the problem has now reached levels where active intervention is needed.

•  The biggest problem seems to be coming from raw sewage that lands in estuarine channels. Awareness of this problem is poor.

The need for focus…

•  Needed is an effort aimed at correcting our interference in a few systems to show feasibility of correcting damaged systems through prevention and rehabilitation.

•  While we understand the physical behaviour of the estuarine systems, biogeochemistry of these systems is still in its infancy. Cleanup in those systems where sediments might have turned toxic will require active intervention of biochemists, toxicologists, etc. to bring back the systems to a healthy state.

Summary

Indian estuaries have a special flavour that is derived from occurrence of monsoon. Progress has been made in understanding the physics of these systems.

However, understanding of implications to biology, chemistry, etc. is in its infancy.

We need concerted efforts to clean up the estuaries that are known to be damaged. This will need a multidisciplinary effort that must begin with awareness of the problem.

Symposium on ‘Indian Estuaries’ has been conceived

To increase the awareness to protect and manage health of our estuarine systems

The following presentations are scheduled:

D. Shankar freshwater influx S. R. Shetye monsoonal estuaries V. V. S. S. Sarma biogeochemistry A. C. Anil estuarine ecosystem V. Purnachandra Rao suspended sediments M. D. Zingde pollution status

Thanks!