Nearly double the annual phosphorous (P) loss on an area of land in Co. Wexford occurred after one night of rain.
On May 21 this year, David Ryan of the Agricultural Catchments Programme (ACP) detailed that there were very localised torrential downpours in Co. Wexford.
He said that one such shower occurred in Castledockrell, Co. Wexford, which is one of six areas in the country being closely monitored by Teagasc’s ACP.
The catchment area of 1,200ha has numerous pieces of automated equipment that continuously monitor rainfall, river flow and nutrient content, and there is now over 15 years of data collected.
In Castledockrell for example, phosphorous losses are small and concentrations are usually below that required under environmental regulations (WFD).
The average amount of P measured/year in the stream is 0.37 kg/ha.
On May 21, just over 32mm of rain fell on the land that day, most of it over a very short period of time.
Some 20mm fell in 20 minutes and the remaining 10mm over the following 40 minutes.
In the following 12 hours, the flood event took with it 0.61 kg/ha of P, which Ryan said was “close to twice what would normally leave in a year”.
He added that this level of detail would not be achievable without the up-to-date and functioning equipment installed in the catchment with the co-operation of over 300 farmers across the six locations.
Ryan stated: “The ACP would like to acknowledge the funding from the Department of Agriculture, Food and the Marine which enables this research to take place.”
The ACP commenced in 2008 and is coordinated and managed from the Teagasc environmental research centre in Johnstown Castle.
Ryan, a technologist with the ACP said that “many people are surprised to hear the amount of phosphorous (P) that we measure which is lost to our rivers and streams.
“From an agricultural perspective it is very small, but is often significant from an ecological impact in rivers and lakes,” he added.