PROSPERITY BASED ON WATER NOT COAL

In the concluding part of his article on the redevelopment of Cardiff Bay Darren Hanson highlights the work that has been undertaken to keep the water clean enough for salmon the thrive.

Salmon are unable to survive in water that is low in dissolved oxygen and this was undoubtedly a factor in choosing dissolved oxygen as the main indicator of water quality. However, a wide range of other water quality parameters are also monitored.

Dissolved oxygen levels are affected by a number of different factors. For example, windy weather helps to aerate the water and cold water is able to hold higher levels of dissolved oxygen than warm. As a result, warm windless summer days pose the greatest threat.

However, pollution discharges, such as combined sewer overflows, can also reduce dissolved oxygen levels. Algae have the potential to lower dissolved oxygen levels following death and eutrophication, but it is thought algae in Cardiff Bay, on balance, have a positive effect on dissolved oxygen as a result of photosynthesis.

The Cardiff Harbour Authority employs two methods with which to combat low dissolved oxygen levels. An aeration system extends across the floor of the bay and provides an opportunity to circulate and aerate the water. This system is fed by air compressors which feed over 600 diffusers through a network of 20 kilometres of pipes. However, in conditions of extremely low dissolved oxygen, the Cardiff Harbour Authority is able to deploy an oxygen barge that feeds pure oxygen directly into the worst affected water.

YSI multiparameter water quality monitoring sondes have been deployed in Cardiff Bay since the beginning of the construction of the barrage. Initially, these were strategically placed logging instruments from which data was collected manually at regular intervals. But as Steve Ellery of the Cardiff Harbour Authority explains: 'This was labour intensive and only provided an historical view of water quality, which meant that our ability to respond to poor water quality was limited and often delayed. We therefore installed six YSI buoys in 2000 and began to collect data via radio.'

The radio telemetry provided Cardiff Harbour Authority staff with access to live data, which transformed their ability to respond quickly to low dissolved oxygen. However, the radio systems had to contend with interference and line of sight issues, so in 2008, the buoys were connected to YSI's EcoNet system, which automatically publishes live data to a dedicated website.

A map showing the location of the YSI buoys is shown on the home page of www.ysihydrodata.com and provides any web user with access to live water quality data. This data is collected at 15 minute intervals from the buoys via GSM and stored on a secure server that hosts the web data.

Two of the buoys are fitted with water quality monitoring sondes at both a metre below the water surface level and a metre above the floor of the bay. The remaining seven buoys have one sonde monitoring at a metre below the surface.

The sondes are compact, rugged, battery powered instruments, capable of logging data from a broad selection of sensors that have been designed specifically to withstand the harshest of aquatic environments. The sondes in Cardiff Bay are fitted with sensors for dissolved oxygen, pH, conductivity, salinity, temperature and turbidity, but many other sensor options are possible.

Commenting on the reliability of the sondes, Steve Ellery says: 'We have been delighted with the performance of the sondes, because they have enabled us to demonstrate extremely high levels of compliance with the dissolved oxygen requirement.'

He continues: 'The initial sondes were replaced after about six or seven years and we now run eight spare sondes so that when recalibration is due we can simply swap sondes without incurring any downtime in data collection.

The ability of the monitoring network to deliver live data means that we are able to respond to low dissolved oxygen levels very quickly and accurately, and as a result, over the last five years our compliance performance with the five milligrams per litre of dissolved oxygen has been over 99.9 per cent every year.'

Users of the YSI EcoNet system do not always opt for live web data display but Steve Ellery has never regretted the decision to do so. He says: 'If the sondes were less reliable we would not wish to display inaccurate data, but since their performance has been so good, it has been great to be able to provide the data to anybody with an interest.'

In addition to the buoy based monitoring network, the Cardiff Harbour Authority also takes monthly water samples from six locations for the laboratory analysis of a wide variety of parameters, including phosphate, nitrate, ammonia, biological oxygen demand and bacteria.

Looking back over the changes that have taken place in water quality in recent decades, Peter Gough of the Environment Agency believes that the Taff may be the only capital city river in Europe with salmon spawning within the city and says: 'This is testament to what has been achieved in a relatively short period of time.'

The YSI water quality monitoring network has enabled the Cardiff Harbour Authority to provide live data to the public and to ensure the protection of water quality in the bay. This has ensured that the area has become an attractive environment for all forms of life, including human beings.

David Hall of the Cardiff Harbour Authority has lived in Cardiff for the whole of his life and believes that the protection of water quality has been key to the success that the city has enjoyed in recent years. He says: 'If you include the housing, pubs, restaurants and sports facilities etc, the development of the Cardiff Bay area represents a total investment of about £2billion.  The overwhelming success of this area hinges on the aesthetic quality of the bay; the water is clean, wildlife is thriving and many thousands of people enjoy a wide variety of leisure activities. Prosperity has once more returned to Cardiff, and this time, it's not coal we have to thank… it's water.'

Darren Hanson is a director of YSI Hydrodata

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