Clean & Protect

Water Quality and Pollution

Pollution

Anna Harlow, researcher at Exeter University, measures diffuse pollution

As pollution from specific sources is gradually tackled and brought under control, so the relative importance of the diffuse sources, (those from no particular specific point of source), will increase.

What do we mean by pollution?

Rain is the main source of the water in the estuary. It travels over and under the ground as it drains down into the river. By the time it reaches the tidal section of the river the nature of the water has changed - though we would hardly call it polluted.

Pollution in the River Dart catchment comes from two sources, point-source and diffuse.

Point sources are those that can be traced back to specific discharge points, which can be both from public and private.

When a discharge comes from a combination of sources such as land and the atmosphere it is called diffuse pollution.

Not all sources or discharges constitute pollution.

The nature and quantity of what is put into the water defines what we would call a pollutant.

The estuary system requires nutrients in order to thrive but some substances can be toxic in minute concentrations (e.g. TBT, organo-phosphates). Other substances only become a problem if there is too much or too little of them present. It is all a question of maintaining an ecological balance. No-one wants a river 'clean' to the point of sterility, it wouldn't be desirable.

Why is diffuse pollution a problem on the Dart?

Diffuse pollution is a problem in the Dart Estuary because it can have an impact on the environmental well-being and ecological balance of the estuarine ecosystem. One of the major factors, which makes the problem worse is simply the very steep sided nature of the Dart Valley itself.

The Dart Valley has what is known as a 'flashy' catchment. This means that immediately rain falls on the land surrounding it, the effects are almost instantly seen in the river. Unlike rivers that have a large flood plain there is no time for pollutants, or excess nutrients, to be absorbed before they turn up in the river.

" The Dart Valley has what is known as a 'flashy' catchment. "

Another problem in the Dart is that there are many examples where farmland is used right down to the water's edge. This means there are not many buffer zones around the edges of our estuary, where run-off can be naturally filtered before it reaches the river.

There has been an increase in intensive methods of farming, which means more slurry is produced and stored on farms causing a disposal problem for the farmer.

In recent years, many more farms have switched to organic production and in the Dart catchment this switch has been quite dramatic. Organic methods make great use of natural fertilisers which, if not carefully applied, can produce run-off with lots of bacteria.

Another factor is that since the end of 1998, disposing sewage sludge (the concentrated by-product of sewage treatment works) at sea has been stopped. More sludge is being spread on land, which may raise the natural levels of bacteria on the land.

All these factors give rise for concern.

It does also seem to be raining more. One of the phenomena predicted in association with global warming is wetter winters for this part of the world. Perhaps this should be included in our list of factors to consider relating to diffuse pollution.

The Dart is regularly monitored for its water quality; by both the Environment Agency and the Environmental Health Service of SHDC. In particular, Environmental Health Officers have monitored the shellfish of the Dart, under the Shellfish Hygiene Regulations, since the introduction of those Regulations about a decade ago.

Sewage from ships

The question of sewage discharge from boats can be highly contentious. It is also very dificult to quantify.

Compared to that from towns and villages, the volume of sewage produced by boats is extremely small. However it is considered a high profile form of pollution. As boating activities have increased in recent years so has concern about this form of pollution.

" The question of sewage discharge from ships can be highly contentious "

There are approximately 2800 boat moorings from Dartmouth to Totnes on the Dart Estuary. Only a small percentage of those relate to boats of a size likely, or capable of, having a toilet on board. The majority of larger boats are moored in the marinas in the Dartmouth area. These boats have shore side facilities available for their crews - but are they used ?

Each year, mostly in the summer months, visitors spend around 12,000 yacht/nights at Dartmouth. Not all yachts are in use all the time but there are obviously peaks at the weekends. Only a handful of people permanently live aboard.

Another important sector on the Dart is the commercial sector, which includes cruise ships and the local tripper boat trade, as opposed to the leisure yachts.

Cruise ships are relatively straightforward. They are fitted with holding tanks and the Harbour Authority Waste Management Policy prohibits any discharge into the harbour.

The tripper boats operate throughout the year with the bulk of their traffic concentrated in the summer season. Estimates of the number of passengers vary between 500,000 and 750,000 per annum. All of the tripper boats are fitted with flushing toilets. As far as we know, none of the tripper boats make use of holding tanks.

Legislation

Historically vessels have been exempt from the legislation governing the discharge of sewage into tidal waters. In fact the Merchant Shipping Acts specifically exclude them, which many people see as a massive loophole.

There is no existing legislation requiring the fitting of holding tanks or any reception facilities where boats can discharge sewage. Nor is there any such legislation anticipated at the national or inter-national level.

There is, though, the Recreational Craft Directive (RCD). This is an EU Directive, applicable to U.K. craft, but it only applies to newly built vessels (not retrospectively) and only requires as a minimum that the vessels should have provision for the fitting of a holding tank.

Is it Sewage or is it Algae ?

We often receive reports about sewage in the water. Very occasionally, as with accidental spillages, this may be the case - but in most instances, it is not. It is marine algae.

Microscopic plants

" Not all marine algae are harmless "

In the summer months you may have seen creamy brown coloured foam floating on the sea. This is the result of a bloom, a rapid growth, of marine algae.

Marine algae are microscopic plants that grow naturally in the sea. They use sunlight for energy to grow and reproduce. Marine algae are vital for the natural health of our waters.

Stinking water blooms

Algal blooms are not new but some believe that they are occurring more frequently and lasting longer. Increased levels of nutrients in coastal waters and substances such as nitrogen and phosphorous will cause the algae to grow faster. Global warming, with its higher temperatures, might also cause the algae to multiply rapidly.

Toxic algae

Not all marine algae are harmless. Some can cause health risk for both marine life and humans. Cases such as these are rare but hit the headlines when shellfish become contaminated.

The toxicity in the algae is in such low concentrations that humans are unaffected by direct contact with water. You would have to eat such large volumes of algae that you would die of drowning long before the toxicity had any effect! However, the toxic algae can become concentrated in filter feeders such as shellfish and if any toxic marine algae are detected in the waters, then shellfish harvesting will be rapidly, temporarily suspended to prevent problems arising by human consumption of the shellfish.

In some cases certain algae cause discoloration of the water known as 'red tides'. If you see one of these rare events it should be reported as soon as possible to the Environment Agency (see contact number below).

If you notice foam on the water it is likely to be the result of algae dying off and breaking down. It is unlikely to be sewage. The Environment Agency has produced some useful indicators to help you tell the difference:

Algal blooms generally occur between April and August. Surface foams are likely to be due to algae or other natural processes between these dates.
Algal foam can often be seen in long streaks off headlands on the open coast lying parallel to the shore.
Sewage will generally have other litter associated with the slick, such as cotton buds and panty liners.
Sewage slicks tend to cause brown or grey discoloration of the water.
Untreated sewage rarely forms foam or scum on the surface of the water. However, washing powders and detergents can cause localised foaming around discharge pipes.
Both sewage and algal breakdown can lead to unpleasant smells, typically that of rotten eggs or vegetables.
Environment Agency Emergency Hotline: 0800 80 70 60.
Call Free, 24hrs a day, 7 days a week

Find out how DEEM works to improve the Dart's water quality and deal with pollution problems by reading this extract from the Management Plan. The full plan can be downloaded at the end of the extract.

The plan's guiding principles provide the context in which the aims are achieved and the actions carried out.

Guiding Principles
To work towards establishing the Dart Estuary as a model for others to follow as an example of a clean estuary.
Strategic Objectives
To work with, and assist where appropriate, the Environment Agency and other bodies in improving the water quality of the Estuary
To raise public awareness of water quality issues through a process of education
To work towards the elimination of all harmful wastes entering the estuarine system and, where elimination is not possible harmful wastes should be rendered innocuous to the ecosystem
To work towards the elimination of all forms of sewage discharged from vessels
To further protect the quality of the Dart Estuary waters though enhanced status designations under EC Directives
To improve existing knowledge of sources and sinks of pollution within the estuary