Rivers are important. They provide water for economic development and human consumption; they provide recreational facilities - fishing, boating etc.; they support a large variety of wildlife and they are part of our natural scenic heritage. Industrial development, improvements in living standards and changes in agricultural practices, especially since the 1960s, have resulted in an increased demand for good quality water. However, such developments have produced increased amounts of sewage, industrial wastewater, agricultural discharges and agricultural run-off. A comprehensive river water quality monitoring programme is necessary in order to safeguard public health and to protect our valuable fresh water resources for present and future generations. The monitoring programme is based on discussions between local authorities and the Environmental Protections Agency (EPA) Regional Managers and reflects the priority for each river and the statutory monitoring obligations which must be fulfilled.

How the Quality of a River is Measured

There are two systems used for assessing the quality of a river: chemical analysis, where samples of the water are tested in a laboratory for a range of parameters, and biological assessment which involves looking at the different species which live in the water. Chemical analysis can identify specific pollutants and they show conditions in the river at the time the sample is taken. Biological assessment, however, shows the effect of pollutants on the aquatic organisms at the time of sampling and it also reveals the longer-term effects of changing water quality. Water quantity data are also collected from rivers both for abstraction and discharge purposes.

Chemical Testing.

Parameters tested can be divided into those showing the general characteristics or type of water (e.g. whether it is hard or soft, acid or alkaline), and quality characteristics which give an indication of whether or not the water is polluted.

Tests for general characteristics include pH, conductivity, colour, alkalinity, hardness and temperature. Tests indicating possible pollution are dissolved oxygen (DO), biochemical oxygen demand (BOD), ammonia, phosphate, nitrate & nitrite and chloride.

pH is a measure of the acidity/alkalinity of a river and normally varies in unpolluted waters between 6.0 and 9.0 depending on the geology of the river catchment. Water from acid, peaty upland areas can have a pH as low as 4.5 and pH values over 10 can occur in waters where there is intense photosynthetic activity by algae; the latter values indicate pollution.

Conductivity is a measure of the amount of material dissolved in the water. conductivity generally increases over the lenght of a river but an unusual increase in conductivity can indicate the presence of polluting matter.

Colour is present in all surface waters at low levels and is generally caused by the leaching of natural coloured compounds from vegetable matter such as peat, leaves, branches, etc.

Hardness and Alkalinity in natural waters are due mainly to the presence of calcium and magnesium salts and bicarbonate formed in reactions in the soil and rock through which the water percolates. Water with low alkalinity or hardness may be susceptible to pH reduction by 'acid rain'.

Temperature is significant because biochemical reactions, e.g. uptake of oxygen by bacteria, proceed more rapidly at higher temperatures. Temperature also affects the solubility of oxygen in water with less oxygen available for aquatic life at higher temperatures. This means the aquatic life is more vulnerable during the summer period when flows are low and water temperatures are high. Elevated temperatures can occur where there are thermal discharges (e.g cooling water from power stations).

Dissolved Oxygen (DO) Is the amount of oxygen in the water. Oxygen is essential for the survival of fish and other aquatic life and the DO test is one of the most important indicators of pollution in rivers. It can also indicate whether there is excessive plant growth present. Normally water is 100% saturated with oxygen but if the oxygen is used up, either by polluting material or by plants that live in the water, the oxygen levels can decrease. If the levels fall too low a fish kill can result. The presence of excessive plant life can result in supersaturation (>100% DO) of the water as oxygen is given off during photosynthesis. This is often accompanied by low night-time levels of DO as the plants respire; these can result in fish kills.

Biochemical Oxygen Demand (BOD) Any organic waste matter entering a river/lake acts as a food source for the micro-organisms living in the water. These micre-organisms use the dissolved oxygen present in the water in breaking down the food. The amount of oxygen used up by the micro-organisms is measured using the Biochemical Oxygen Demand (BOD) test and provides a measue of whether the water is clean or polluted. The test is carried out under standard conditions for 5 days at 20 degrees C in the dark. Unpolluted river waters are likely to have a BOD value <3mg/1 O2 and values significantly above 4-5 mg/1O2 indicate possible pollution. The BOD value in rivers can also be affected by high flows or floods.

Ammonia.

Ammonia is naturally present at very low levels (<0.1mg/l N) in surface waters. Domestic sewage and animal slurries are high in ammonia, as are some industry processes. River levels are higher that 0.2mg/l N are usually indicative of pollution. The un-ionised form of ammonia (i.e. NH3 as opposed to NH4+) is very toxic to fish.

Phosphate.

Phosphorous occurs naturally in plants and micro-organisms. It is present in animal wastes, in agriculture fertilisers and in detergents. Run-off from agricultural land and sewage and agriculture discharges are the main contributors of phosphorous to surface waters. The significance of phosphorous is that it is essential for the growth of algae and is usually the limiting factor in algal growth.

Oxidized Nitrogen.

Most of the nitrate found in surface waters comes either directly from waste discharges or from run-off from land treated with artificial fertilisers. Nitrate levels in river waters vary on an annual basis and are generally lowest in July?August and highest in January/February ( when the river flows are normally higher). Nitrate concentrations in some rivers are increasing mainly as a result of intensive farming and high river nitrate levels are generally associated with tillage areas.

Nitrite.

Nitrite levels in unpolluted waters should be low (< 0.05 mg/l N). It is an intermediate in the oxidation of ammonia to nitrate because many effluents, including sewage, are rich in ammonia high levels of nitrate in river waters may indicate recent pollution.

Chloride.

Chloride occurs in all natural waters and background levels in inland waters are low 10 - 30 mg/l Cl. Sewage contains large amounts of chloride as do some industrial effluents so raised levels can indicate contamination of waste discharges : however, they can also be due to sea spray near the coasts.

Biological Testing.

Biological classification of river water quality is carried out by examining the different types of macroinvertebrates - crustaceans, insects worms. molluscs, leeches etc. that live in the river - but not all fish. Some species are sensitive and some are tolerant to pollution and a system for classifying water quality depending on the different numbers of the various macroinvertebrate species has been developed. Biologists sample in fast flowing areas of rivers and collect all specimens found in the area, lifting stones and kicking up sediments etc. The creatures found are identified and counted. Depending on the diversity of species found in the community and their numbers, the river is classified on a scale of Q1 to Q5 with 5 the cleanest water and 1 the most polluted. This scale is called the Biotic Index or Biological Qaulity Rating. The relationship between Biotic Indices (Q values) and water quality is given in the following table.

Hydrometric Information

Information on river flows and loadings is acquired from a network of water level recorders and guages placed at strategic points on most rivers in the country. The information form this network is collated and verified by teams of EPA hydrometric technicians who are located in 8 centres around the country.