Could changing weather patterns alter the way we use fertiliser?

The Agricultural Catchments Programme (ACP) was originally established to monitor water quality in 2009, with 300 farms involved across six catchments. It was set up to evaluate the environmental and economic effects of the Nitrates Directive on water quality while developing solutions for the pressure coming from farms.

The water quality in these catchments is continually being monitored by a team of researchers. The water is automatically tested every 10 minutes for phosphorus and nitrogen levels, among other aspects.

Eddie Burgess, manager of the programme, has been involved since the beginning. “There are six catchments and they were chosen to represent different farming systems, different soils types and to have as low a housing density as possible. They weren’t chosen at random. This way we could see what effect agriculture is having on water quality,” Eddie said.

Catchment science

“The main sources of nutrients that we look at are nitrogen and phosphorus. We examine the source and mobilisation of the nutrients, the pathways that they take through the soils and the delivery point, or where they end up,” said Eddie.

“The soil type determines which of these nutrients is the biggest issue, in conjunction with the weather. Phosphorus is more likely to be a problem on heavy soils where you have a runoff scenario, where soils are waterlogged.

“Nitrogen is the complete opposite to that. It would be more of a problem where you have free-draining soils. If you have that type of soil and a farmer goes organic and doesn’t spread any chemical nitrogen, it could still be as much of an issue as on an intensive dairy farm on heavy soils.

Buy-in

“At this stage, there is good buy-in from the farmers as they are so well aware of the programme. It has been going for nine years,” according to Dr Per-Erik Mellander, chief scientist leading a team of researchers within the programme.

“They know what we are about. They have seen the benefits of the programme and, from our point of view, the farmer’s insight helps us as they know their land better than anyone. The catchments are about 10 sq km. Because it is a small area, we can know everything about it in depth. We can see the processes and see how nutrients are moving.”

When it comes to Ireland retaining its nitrates derogation, one of the first things that is looked at is if water quality has deteriorated. The intensification that has resulted from an expanding dairy industry has meant more pressure is coming on our water quality.

Per-Erik said: “There is certainly a lot more pressure on the catchment in Cork due to dairy intensification, than the one in Mayo, for example. However, our understanding of nutrients has helped improve efficiency in these areas, so I think that we are managing to cope with that pressure better. We have dedicated advisers on site with the programme who help to communicate what is coming out from the research.”

Research

The latest piece of research that has come out of the programme looks at the changing weather patterns and how they could affect water quality. It could potentially lead to a change in the way that farmers use fertiliser, while it could also play a part in policy decisions that are made at European level.

“I was looking at nitrates concentrations in ground water and surface water in one of the catchments. I know that the nitrate sources had remained steady over the years and travel times (the time taken for nutrients to move from source to water point) are relatively quick in this catchment so we knew what we were monitoring very much reflected what was happening at least maybe two years ago,” Per-Erik said.

“The only thing that had changed was the weather but then looking at the weather data there wasn’t really more rainfall, but there certainly was a different pattern. There were more of these really big, intense rainfall events.

“So I started looking into it and thought that maybe these weather patterns are having an effect on what we are monitoring – that was my working hypothesis. Weather changes are not usually considered in policy reviews so it is an important component to bring into the conversation and that is what this paper does. All scientists working in catchments would know that weather is having an effect on water quality, but it is not as easy to show it,” Per-Erik continued.

“The difficulty is that they are studied on such different scales compared to water quality. We are monitoring water quality at really high resolution. Every 10 minutes we are getting information on it, for a defined area of 10 sq km. Then we are looking at a weather system which covers the whole Atlantic; how do you link these two very different scales?

“Luckily there is an index which measures the intensity of these weather events. During the time that the catchments have been monitored there has been a sharp increase in this index reflected in more intense weather events.

“I correlated the yearly water quality results with this index and the results were striking. It just all lined up. There was a strong correlation in most of our catchments where there was a higher concentration of high-rainfall events coinciding with an increased level of nitrates in the water. But we thought that we cannot isolate this to only Ireland. We thought we should look broader so we collaborated with scientists monitoring catchments in both Norway and France and the results were consistent.”

Management

Management will always have a considerable role to play in ensuring that we improve our water quality. “There are different aspects in each catchment that will influence water quality. Firstly, management that will affect the nutrient pool. Soil chemistry has a large part to play too as some soils will hold the nutrients better than others,” Per-Erik said.

“Hotter summers will lead to more mineralisation of nutrients which means they are more vulnerable to being lost. Then you get heavy showers which will wash them out. As the programme moves on, I would like to create water vulnerability maps that could be useful for farm management decisions. So far, we haven’t really looked at what effects these results could have on management yet.

These vulnerability maps could be a useful tool to highlight areas that farmers may have to be more careful of when spreading fertiliser, for example. “Everyone would love if it was a short clear answer as to where the main source pressures are coming from when it comes to nutrients entering waterways but it is not that simple,” said Eddie.

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