Almost two years’ worth of phosphorous was leached into a river in Co Wexford following just one heavy rain downpour, Teagasc research has shown.

Monitoring of the 1,200ha Castledockrell water catchment in Co Wexford has been ongoing for 15 years under the Teagasc agricultural catchments programme (ACP).

Last month, the ACP data showed just how much phosphorus can be washed into waterways during heavy rain showers.

Just over 32mm of rain fell on one day - 21 May - with most of it falling over a very short period of time.

Some 20mm fell in 20 minutes and the remaining 10mm over the following 40 minutes, causing the river to flood.

Teagasc has revealed that the river measurements gathered in the following 12 hours showed that the flood event took with it 0.61kg/ha of phosphorous.

That’s almost twice the average level of phosphorous recorded for an entire year in that catchment.

Teagasc said that Castledockrell typically has small phosphorous losses, well below concentrations required required under environmental regulations.

Typical losses

The average amount of phosphorus measured per year in the stream is 0.37kg/ha, but that one day’s rain and subsequent flooding ramped this up to 0.61kg/ha in a single day.

ACP technologist David Ryan said this level of detail would not be possible to record without the co-operation of over 300 farmers across the six locations.

The ACP is funded by the Department of Agriculture, which enables this research to take place.

Read more

What is the Agricultural Catchments Programme and what does it do?

Fast-tracking nitrates action on highest risk farms

Tillage: buffers, liebacks and changes to ACRES rules