Catchment News

The Suir Estuary and its catchment

What does the marine area tell us about upstream conditions? Can the Suir estuary function as a  ‘canary’ for it’s catchment?

The Suir and associated rivers join up to create one of the largest estuarine systems in Ireland. The tidal limits extend up the Three Sisters to Carrick on Suir on the Suir river, Saint Mullins on the Barrow, and Inishtioge on the Nore. The main channels of the Suir and the Barrow-Nore system converge at Cheekpoint and continue towards the sea past the Passage East ferry, Dunmore East, and finally at Hook Head out into the Celtic sea.

Given the importance of this estuary at a local scale and to the larger marine environment, the EPA, Inland Fisheries Ireland and Marine Institute undertake monitoring of water quality and ecology from the mouth of Waterford harbour up to the tidal limits and beyond. This information allows us to get a holistic picture of the general ecology of the estuarine area, but also allows us to use the estuary as an indicator of what things are like upstream.

Estuaries as indicators

In many freshwater systems, the nutrient that is of most concern for its effects on the biological communities is phosphorus (P). Measures have been in place to reduce loading of phosphorus into our catchments and these have proved quite effective, with inputs of phosphorus from the Three Sisters into the Suir Estuary decreasing by 60 % since 2000, and concentrations of this nutrient in the estuary are now considered to be acceptable. As less emphasis is placed on nitrogen (N) reduction this nutrient has only shown a 15 % decrease in the same time frame. Not surprisingly, this nutrient is above the levels which are acceptable for Irish estuarine systems. This has resulted in more of the nitrogen in the catchment being available for plant growth. While this is not immediately obvious in the upstream freshwater areas, once this nitrogen reaches the estuary biological effects can be observed.

As the ultimate receptors of all the inputs upstream, the estuarine and coastal areas can tell us a lot about what is happening in the overall catchment. We can use the biological communities to tell us about nutrients in the water, or chemical pollutants. Useful indicators to look at nutrient pressures are the seaweeds. We use the presence and abundance of certain seaweeds, such as sea lettuce, to tell us about the nutrient conditions in the estuary. In areas where nitrogen inputs increase these green seaweeds can grow in huge quantities causing an environmental impact.

Other indicators of nutrient pressures are the phytoplankton communities (small plants that grow suspended in the water column) which can change depending on the balance of nutrients coming downstream. In severe cases this can result in large harmful algal blooms that can affect the other marine communities, such as shellfish or the bottom dwelling animals.

In the Suir we have seen some disturbances to the marine plants with elevated levels of phytoplankton in the water suggesting that the nutrient conditions are too high. We can use this information, along with the other data from our monitoring programmes, to work out what has to be done to improve the situation. By looking at the estuary and coastal areas we can develop an idea of the sort of changes that need to take place in the whole catchment for improvement across all our waters.

Robert Wilkes, EPA and Sorcha Ni Longphuirt, Aquafact Environmental and Hydrographic Consultants