One of the most important bellwethers for the health of Ireland’s environment is the status of our water bodies. As Ireland’s agriculture sector has expanded production over the last decade, the scrutiny of our water quality standards has rightly intensified.

Water quality is one of the most regulated areas when it comes to farming as nutrients can leech via multiple routes into our streams, rivers, lakes and other water courses.

While the impact of nitrates and phosphorus on water ecology is widely understood, research on the impact of sediment in water is still in its early days.

Webinars

Speaking on Friday morning as part of the latest "Signpost Series" of online webinars on sustainable agriculture, Teagasc water quality researchers Owen Fenton and Daire O’hUallachain said the key to stopping nutrient and sediment leeching into our water systems is to break the pathway.

“In our research we try to understand where do all the nutrients go. But if we know where the water goes from our soils then we know where the nutrients go because water is what carries the nutrients,” said Fenton.

Rainfall

The Teagasc researcher said Ireland’s rainfall pattern has a distinctive U-shape over the year, with higher rainfall in the shoulders of the year (Oct-Dec and Jan –Mar). However, Fenton said the U-shaped pattern of rainfall levels in Ireland was becoming shallower as we now receive higher amounts of rainfall in the summer in Ireland.

The impact of increased summer rain is that it can lead to increased water run-off in soils at a time when farmers apply the bulk of their nutrients – be it slurry or chemical fertiliser. Despite this increased risk of nutrient loss from our soils, there are actions that farmers can take to effectively mitigate nutrient losses from heavy rainfall.

One of the most effective ways to stop nutrient losses is to break the pathway or flow of water from our soils to water bodies. This can be done by introducing riparian strips or buffer zones close to streams, rivers, lakes or other water bodies.

While many farmers close to rivers and lakes may have already implemented these buffer zones, O’hUallachain says our use of riparian strips and buffer zones needs to become much more targeted to match the flow of water, particularly when it comes to sediment flows.

Using LiDAR technology to map the terrain, researchers can visualise the flow of water within the farm landscape to see where water run-off will take place. By understanding the flow of the water, the farmer can then make an informed decision to introduce a riparian strip or buffer zone that will be most effective to prevent nutrient and sediment loss into a nearby water body.

Sediment

In terms of sediment losses in water, Daire O’hUallachain said initial research in Ireland showed the volume of sediment lost can range from as little as 3t/km2 in extensive farming systems to highs of 25t/km2 in more intensive farming enterprises operating off poorly drained soils.

For example, 75% of sediment losses on a poorly drained tillage field will come from the topsoil, whereas in a well-drained soil this figure will be much lower at less than 25%.

Early research into sediment suggests it can be very damaging for water ecology as it creates clogging gravel, reduces oxygen levels in the water as well as increasing the turbidity (cloudiness) of the water. These factors all have a negative impact on aquatic ecology.

To stem sediment loss into waterways, O’hUallachain says we need to develop more innovative and diverse riparian strips to stop nutrient run-off and halt soil erosion/sediment losses. However, O’hUallachain cautions that these advanced level buffer zones mean increased complexity from a management perspective and do bring additional costs for the farmer.

The more complex and costly the buffer zone becomes, the level of buy-in from farmers and policy makers is likely to reduce. Therefore finding the right balance that works for both sides is key.

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