State of the Bay Report 2011-Final.pdf - Anchor Environmental

State of Saldanha Bay & Langebaan Lagoon 2011
Background to monitoring
2 BACKGROUND TO ENVIRONMENTAL MONITORING AND
WATER QUALITY MANAGEMENT
2.1 Introduction
Pollution is defined by the United Nations Convention on the Law of the Sea as ‘the introduction by
man, directly or indirectly, of substances or energy into the marine environment, including estuaries,
which results in such deleterious effects as harm to living resources and marine life, hazards to
human health, hindrance to marine activities, including fishing and other legitimate uses of the sea,
impairment of quality for use of the sea water and reduction of amenities’. A wide variety of
pollutants are generated by man, many of which are discharged to the environment in one form or
another. Pollutants or contaminants can broadly be grouped into five different types: trace metals,
hydrocarbons, organochlorines, radionuclides, and nutrients. Certain metals, normally found in very
low concentrations in the environment (hence referred to as trace metals) are highly toxic to aquatic
organisms. These include for example Mercury, Cadmium, Arsenic, Lead, Chromium, Zinc and
Copper. These metals occur naturally in the earth’s crust, but mining of metals by man is increasing
the rate at which these are being mobilised which is enormously over that achieved by geological
weathering. Many of these metals are also used as catalysts in industrial processes and are
discharged to the environment together with industrial effluent and waste water. Hydrocarbons
discharged to the marine environment include mostly oil (crude oil and bunker oil) and various types
of fuel (diesel and petrol). Sources of hydrocarbons include spills from tankers, other vessels,
refineries, storage tanks, and various industrial and domestic sources. Hydrocarbons are lethal to
most marine organisms due to their toxicity, but particularly to marine mammals and birds due to
their propensity to float on the surface of the water where they come into contact with seabirds and
marine mammals. Organochlorines do not occur naturally in the environment, and are
manufactured entirely by man. A wide variety of these chemicals exists, the most commonly known
ones being plastics (e.g. polyvinylchloride or PVC), solvents and insecticides (e.g. DDT). Most
organochlorines are toxic to marine life and have a propensity to accumulate up the food chain.
Nutrients are derived from a number of sources, the major one being sewage, industrial effluent,
and agricultural runoff. They are of concern owing to the vast quantities discharged to the
environment each year which has the propensity to cause eutrophication of coastal and inland
waters. Eutrophication in turn can result in proliferation of algae, phytoplankton (red tide) blooms,
and deoxygenation of the water (black tides).
It is important to monitor both the concentration of these contaminants in the environment
and their effects on biota such that negative effects on the environment can be detected at an early
stage before they begin to pose a major risk to environmental and/or human health.
2.2 Mechanisms for monitoring contaminants and their effects on the
environment
The effects of pollutants on the environment can be detected in a variety of ways as can the
concentrations of the pollutants themselves in the environment. Three principal ways exists for
assessing the concentration of pollutants in aquatic ecosystems - through the analysis of pollutant
concentrations in the water itself, in sediments or in living organisms. Each has their advantages and
disadvantages. For example, the analysis of pollutant concentrations in water samples is often
problematic owing to the fact that even at concentrations lethal to living organisms, they are
difficult to detect without highly sophisticated sampling and analytical techniques. Pollutant
concentrations in natural waters may vary with factors such as season, state of the tide, currents,
extent of freshwater runoff, sampling depth, and the intermittent flow of industrial effluents, which
complicates matters even further. In order to accurately elucidate the degree of contamination of a
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