Water quality survey results from the Afon Cegin

Last week NWRT Project Officers completed a water quality survey of the Afon Cegin as part of our Esmee Fairburn ‘Blue Spaces’ project. The river runs near to Bangor and is known to be impacted by high levels of Phosphorus. The survey aimed to identify general trends in water quality across the catchment and assess the impact of permitted discharges.

Permitted discharges allow companies or properties to release waste to the river within limits specified in the permit. There are 14 permitted discharges on the Afon Cegin, covering treated sewage, CSOs, road run-off, and industrial waste.

The survey measured a range of water quality parameters, but the focus of our analysis was on Nitrates and Oxidation Reduction Potential (ORP).

Nitrates are associated with sewage and agricultural run-off and are often a good indicator of phosphorus, which is more difficult to measure quickly and precisely. Excessive Nitrates and Phosphorus can result in eutrophication and a decline in river oxygen levels. Nitrate levels exceeding 10 mg/L can be harmful to some aquatic organisms. ORP measures the ability of a river to cleanse itself or break down waste products, such as contaminants and organic matter. Low ORP can be an indicator of pollution from sewage, chemicals, or metals. As illustrated in the map below, the survey showed Nitrate concentrations increase in the Afon Cegin with distance downstream, which is a trend generally observed in rivers. Sudden increases in Nitrates were detected below sewage treatment works at Sample Points 2 and 16. Point 16 is the discharge location for a private sewage works on the Llandygai Industrial Estate, and here localised Nitrate levels exceeded the 10 mg/l threshold. The permit is registered to a short brook that enters the main Afon Cegin, and in this brook Nitrates ranged between 29 and 35 mg/L. ORP values also indicate issues at the Llandygai Industrial Estate. A dramatic drop in ORP was recorded in the vicinity of industrial discharges and drainage ditches that enter the river near the estate (Sample Points 11 -13).

Over the coming months we will continue our water quality monitoring on the Afon Cegin to capture data over a wider range of weather and river conditions and further investigate the localised issues indicated in our first survey. As part of the Blue Spaces project, we are developing innovative methods to improve water quality in the area.