The Full Picture

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Global water quality monitoring

Steven R. Greb, Wisconsin Department of Natural Resources;

Antti Herlevi, World Meteorological Organization; Paul DiGiacomo, National Oceanic and

Atmospheric Administration, National Environmental Satellite

Data and Information Service

onitoring of water quality is critical to the future health

of the human population as well as the health of the

ecosystem.

Monitoring of inland and coastal areas is a

particular concern with the majority of the world’s population

living in these riparian and coastal areas. In addition, half of the

earth’s available freshwater is currently appropriated. Concurrent

with increased demand on freshwater, the supply of ‘clean’ water

continues to dwindle as a result of contamination from pollutants

in municipal and industrial discharges and non-point source

runoff. This contamination affects coastal receiving waters, inland

water bodies and groundwater. Further, increased sedimentation

can adversely affect fisheries, shellfish, plant life and coral reefs.

Large influxes of nutrients can potentially lead to harmful algal

blooms, decreased dissolved oxygen and hypoxia in coastal areas.

Another major water quality issue is water-borne pathogens. Every

year, over two billion people suffer from water-borne illnesses,

and water-related diseases account for five million deaths. More

than one-fifth of the world’s people do not have access to safe

drinking water and one-half of the population does not have

adequate sanitation.

Monitoring plays a critical role in determining the current status of

water quality conditions and helps anticipate and hopefully avoid

future water catastrophes. Given the great number of global issues

directly or indirectly linked to water resources, or more specifically

here, water quality, this priority area has been identified by the Group

on Earth Observation (GEO) as one of the key societal benefit areas,

and it seeks advances in earth observation capabilities.

Water quality monitoring and assessment is generally grouped into

two approaches, either remotely sensed (satellite, airborne or ground-

based) or in situ (collected by field staff). These multiple approaches,

sometimes in concert, can address water quality on local, regional or

global scales. Many water quality monitoring programmes are defi-

cient. For example, many countries lack the technical, institutional,

financial resources and infrastructure, and sometimes the political

stability, to conduct proper water quality assessments on a long-term

basis. Today, the United Nations Environment Programme (UNEP)

archives freshwater quality data from national and international coop-

erators around the world in its Global Environmental Monitoring

System (GEMS).

Remote sensing technology is an emerging capability that can

greatly bolster traditional in situ methods, but the field is relatively

new, especially in addressing optically complex waters. Satellite

remote sensing potentially offers a promising alternative for scien-

tists and managers to use for assessment of a large

number of water bodies in an economical and timely

fashion. Today, global-scale aquatic satellite remote-

sensing systems are generally limited to oceanic

products, e.g. daily and also composite eight-day and

monthly composite chlorophyll images generated from

the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) to

address a variety of biogeochemical and ecosystem

issues. With respect to coastal products, increasing inter-

est in the monitoring of coastal areas has led to new and

ongoing regional efforts such as the ChloroGIN Africa,

Antares (South America) and European Space Agency

(ESA) GMES Services Element (GSE), MarCoast (Baltic

Sea) initiatives and networks. Objectives of these and

other similar efforts include mapping of turbidity,

chlorophyll, primary productivity and forecasting of

harmful algal blooms (e.g., NOAA HAB Bulletin).

Monitoring of inland water quality using remote sensing

is virtually non-existent on a global operational level.

There are some unique challenges to the application of

remote sensing to water quality in inland and coastal

regions. These waters are a complex mixture of

constituents, the composition of which varies across water

bodies, regions and globally. Unlike open-ocean surface

waters, which are generally clear and typically contain

only low concentrations of phytoplankton, inland and

coastal waters contain a myriad of both dissolved and

particulate matter. In addition, they can exhibit signifi-

cantly heterogeneous patterns of water quality. These

patterns and associated processes and phenomena are

frequently dynamic, short-lived and small-scale, and may

be missed by satellites with inadequate spatial and/or

temporal observing capabilities. Small water bodies such

as lakes are irregularly distributed across the terrestrial

landscape, often representing only a few pixels in a satel-

lite image, and confounded by a number of ‘edge’ pixels.

In addition, remote sensing generally only represents

surface conditions, and it can be difficult to relate what the

satellite can actually ‘see’ (e.g. ocean colour) versus those

properties primarily of interest to a manager or decision-

maker (e.g. bacteria).

Remote sensing has attempted to quantify a number

of water quality parameters, with varying degrees of

success and utilization. These include biological,

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