Managing headwater catchments to reduce downstream flood risk

There is increasing concern about flood risk associated with climate change, and an interest in means of addressing this that complement traditional flood defence measures in flood-prone areas.  Since 2016, we have been installing permeable timber dams in the Eye Brook headwater within our Water Friendly Farming project.  The intention has been to create low cost barriers to hold water back in ditches and small streams, without any negative consequences for farming, so as to reduce downstream risks of flooding.  Most of the dams are designed to hold water back within the channel, but some are extended into small floodplains to increase the storage capacity where the land is otherwise unproductive from an agricultural perspective, or not used for access.

Initially, these dams were made with lengths of cordwood sourced from local woods that were being thinned to improve timber production or wildlife habitat.  They were intended to be easily constructed by a local contractor or farmer.  Although we wanted to hold water back during storm events, we did not want to impede baseflow so a gap was left at the base of the dam.

The dams worked well until the really heavy storms arrived and six of the dams on the main stream were badly damaged.  As a result, we redesigned and rebuilt these larger dams so that they were made from long lengths of timber that spanned the whole channel width, without the need for joins or in-channel support posts.  We selected larch to prolong the life of the dams.

We also raised the base of the dams so that they were above winter baseflow.  This reduced the frequency with which water backed up behind the dams, but improved their performance during the larger events which are the ones we are most concerned about in terms of flood risk.  These dams have held up well to the largest storms and the flow monitoring at the base of the catchment allows us to evaluate their performance. With our partners at the Freshwater Habitats Trust, we have produced a guidance document on the practical design and installation of permeable dams which is available as a pdf here.

York University's hydrological modelling reveals that for the most commonly occurring storm events (those occurring at up to one in a hundred-year intervals), the 28 dams across the 1,000ha catchment reduced peak flow at the base of the headwater catchment by 19-24%.

For very severe events (those occurring only once in a thousand years), the reduction in peak flow was 11%.  Although encouraging, this is a reminder that we are less able to adapt to the more severe events that climate change is expected to confront us with more frequently in future.  This is one of many reasons why, as well as investigating approaches to adaptation, our research is also focusing on ways in which we can mitigate climate change through the management of agricultural land.

Permeable dam outside the study area at our research and demonstration farm at Loddington

Soil and climate change research

It is hard to know how this summer will turn out.  An exceptionally wet autumn and winter completely prevented the establishment of autumn-sown crops at Loddington and other local farms.  There was just about time to drill spring varieties in those fields where we needed to do so for research, or considered that it would still be economically viable to do so for our farm business.  Then the drought hit.

By June, livestock farmers were searching around for additional grazing as pasture and leys withered, recalling memories of the prolonged drought just two years ago.  Social media were scattered with posts from normally successful arable farmers sharing images of drought stressed crops and professing that the continuing weather uncertainties and extremes were now making it impossible to maintain a viable business.  Recent rain has provided a reprieve by increasing surface soil moisture, at least for now.

Loddington soil moiture deficit to June 2020, including the 2018 drought and exceptionally wet autumn/winter of 2019/20

Our research aims to contribute to our understanding of this issue.  We want to see continuing economically viable food production on farms such as ours, to understand better how to reduce our greenhouse gas emissions and to sequester carbon in our soils.

Global warming potential of CO2 and N2O in compacted SoilCare project plots

Monitoring of greenhouse gas flux in compacted soils as part of our contribution to the EU-funded SoilCare project reveals that carbon dioxide flux is higher in ploughed plots than in direct drilled plots.  In these compacted conditions, nitrous oxide flux is higher in direct drilled plots.  The amounts involved are very low, but because nitrous oxide has a global warming potential that is nearly 300 times that of carbon dioxide, the implications for climate change are that much greater.  Looked at together, the global warming potential of greenhouse gases associated with ploughed and direct drilled plots is roughly equivalent.  The additional emissions associated with multiple field operations in the ploughed plots mean that direct drilling has the lower impact.

Mean Soil Organic Carbon from ten Water Friendly Farming project fields

Reduced soil disturbance, whether through direct drilling or other practices such as incorporation of leys into the rotation, also has the potential to increase soil organic carbon.  Data from local fields in the Water Friendly Farming project study area reveal that this is currently around 3%, and typically, declines with soil depth.  Increasing soil carbon helps to improve soil moisture retention during drought.  It also has the potential to deliver public benefits such as improved water infiltration during storms, resulting in better water quality and ecology, and reduced downstream flood risk.  At depth, stable forms of carbon represent an important potential carbon store, contributing to climate change mitigation.

Food, health and wildlife security

It is remarkable to think that the Covid-19 pandemic that is causing so much personal, political and economic disruption stems from a food market the other side of the globe.  Virus transmission from wild animals to people has highlighted the trade in wildlife for food in other parts of the world.  While the mode of transmission from wild species to people remains uncertain, there is clear evidence that this trade in species such as pangolins is unsustainable. The fact that such trade is now in the spotlight can only strengthen conservation efforts for these species, although this is dependent on secure income and food supplies for the people who would otherwise be doing the trading. The pandemic makes that more difficult to achieve.

Let's be clear though.  The justification for cessation of trade in endangered species for food is not that we find the consumption of wildlife culturally abhorrent. To follow that argument would lead us onto a slippery ethical slope.  It might also lead us to question the consumption of abundant species such as deer, rabbits and woodpigeons whose control is important to protect food crops and wildlife habitats in the UK, while also providing a source of food in their own right.

In fact, as well as reminding us of the moral imperative for conservation of our own wildlife species, food shortages associated with the pandemic have brought into question our food system and highlighted the need for domestic production at local, regional and national levels, alongside international trade.  The need to understand the relationship between food production and environmental objectives, including wildlife conservation, has never been greater.

Gemma Fox and team prepare for water infiltration assessments in our grass plots

Despite the national lockdown, our research into economically and environmentally sustainable farming methods continues, strictly within the constraints imposed by social distancing.  Where data collection requires more than one person to conduct fieldwork at the same time, we have been fortunate in being able to recruit other members of the same household to help out.

There have been numerous other challenges to overcome though.  With the implications for food producton of the 2018 drought still fresh in our minds, the intense rainfall over the most recent autumn and winter was exceptional. The very wet ground conditions completely precluded the establishment of autumn-sown crops, preventing food production from our land, creating economic problems for our farm business and for many others across the country, and leaving us with no arable experimental plots for research.  Fortunately, it has been possible to drill some spring-sown crops this month, albeit under difficult conditions.  Our research is increasingly focusing on these climate related challenges.

While potentially distracting from the over-riding need to address climate change, in common with climate change mitigation objectives, the Covid-19 pandemic highlights the need to act individually and collectively, locally and globally to address the challenges that affect us all.

New clean water ponds increase landscape scale aquatic biodiversity

We have just seen the publication of another journal paper from the Water Friendly Farming project, our collaborative project with the Freshwater Habitats Trust. The paper demonstrates for the first time the effect of creating new ponds on the number of aquatic plant species present in the landscape.

Creating new clean water ponds in low input pasture in 2013

Following discussions with land owners, we created twenty new ponds in one of our two 'treatment' catchments in 2013.  We selected sites very carefully so that the new ponds were in low input pasture or open areas of woodland where runoff into them was not affected by domestic or agricultural sources of nutrients. The selection of these non-productive areas also made the ponds aceptable to farmers; in fact the introduction of ponds onto farms was regarded as improving the landscape and creating additional interest.

Freshwater Habitats Trust researchers conducted a rigorous annual census of aquatic plants, not just in the new ponds but across multiple other small ponds, ditches and streams within the 3,000ha study area to provide a comprehensive understanding of the plant species present and their distribution across the various habitats.

Ponds generally proved to be a key habitat.  Adding our new clean water ponds brought substantial benefits: increasing total-catchment plant species richness by 26%, and the number of rare plant species by 181%. Populations of spatially restricted species also increased. Creating clean-water ponds specifically targeted for biodiversity could therefore hold considerable potential as a tool to help stem, and even reverse, ongoing declines in freshwater plant biodiversity across agricultural landscapes.

You can access our journal paper as a free pdf for a limited period here.

Integrating crop production at the catchment scale

Some research we carried out within the Water Friendly Farming project in 2017 has just been published in the Journal of Environmental Management.  We use a herbicide that is used to control black-grass in arable crops as an initial focus for exploring broad catchment management issues with farmers in the study area.

Propyzamide is applied to the oilseed rape stage of the rotation and while being a crucial means of controlling black-grass also creates a problem for drinking water supply as it often exceeds the 0.1µg/L limit set by the EU Drinking Water Directive.  This puts its use at risk of restriction.  The herbicide moves to water mainly adsorbed to soil particles, so as well as being linked to the stage of the crop rotation, its mobility is reduced by soil management practices that reduce erosion and subsequent sedimentation of water courses.

We found that the concentrations in water were influenced largely by the area of oilseed rape in the catchment, and by rainfall.  Modelling suggested that, to keep below the 0.1µg/L limit, the rape area would need to be restricted to just 2-3% of the catchment.  This is something that participating farmers felt was not practical to manage across the catchment, given that there were multiple farms and the rape area grown was up to 30% of the land area.  Oilseed rape was considered to be an important part of the rotation.  A higher limit for headwater catchments that are distant from drinking water abstraction points might be more manageable but would require coordination of, and collaboration between farmers.

Pest problems now make establishing rape more difficult

The farmers were more enthusiastic about the use of hybrid barley, a crop which supresses blackgrass, extends the rotation, and provides an early entry for a following rape crop.  Rape is the stage in the rotation which requires least soil disturbance and is often direct-drilled, with potential benefits to soil and water.  Reduced tillage and direct drilling reduce the risk of herbicide loss to water while also delivering other public benefits such as reduced sedimentation of watercourses, reduced nutrient concentrations in water, and enhanced aquatic biodiversity.  Farmers were also more generally accepting of reduced tillage and direct drilling for other stages in the rotation, but they identified practical constraints and economic barriers which prevented a wholesale switch to this system on our clay soils.

Since our research in 2017, oilseed rape has become a slightly less popular crop.  The ban on the use of neonicitinoid insecticides has made the control of cabbage stem flea beetle (a major pest of rape) a substantial challenge.  Alternative pyrethroid insecticides, applied as a spray to the crop, rather than as a seed dressing, reduce numbers of a wide range of other invertebrates, including beneficial predators and parasitoids of flea beetles.  It is especially important to encourage these beneficial invertebrates as flea beetles are developing resistance to pyrethroids.

The area of oilseed rape, its yields and profitability have therefore all declined in the past couple of years.  Up until that time, rapeseed and oil were imported and exported to and from the EU but the UK was essentially self-sufficient.  Reduced production in future could mean increased imports of vegetable oils from other countries.  If rape or sunflower are imported from the EU, the crops are currently subject to the same environmental standards as our own, but if from other countries we may find ourselves using oil and animal feed produced using methods which we would not permit in the UK, while simultaneously disadvantaging UK farmers.  Substitution with palm oil from Indonesia and Malaysia has even greater environmental implications.

The use of a herbicide and an insecticide in oilseed rape crops may seem to be independent activities to be considered in isolation, but our research on propyzamide, and the more recent developments with neonicitinoids demonstrate the integration of a wide range of associated activities across and beyond the production of the crop.

Our journal paper is available here as a free download until 18 March.

Should we be feeding trees to ruminants?

Collecting willow leaves at Loddington

Turn sheep or cattle into a field of fresh grass and some of them invariably prefer to eat the hedge!  And why are livestock so determined to eat the young trees we have planted to give them shade in hot weather and shelter in strong winds? If tree leaves are so palatable to ruminants, perhaps we should know why?

That was the rationale for a short project in which we and our Nottingham University partners joined forces with the Organic Research Centre and Bangor University, with funding from the Woodland Trust.  We wanted to understand better the potential nutritional value of tree leaves to ruminants.

We sampled oak, alder and willow leaves in early and late summer across three sites, the Henfaes research farm in North Wales, the Organic Research Centre in Oxfordshire, and our own farm at Loddington.  The leaves were analysed for minerals known to be important to ruminant nutrition.

Cobalt and zinc concentrations were higher in willow than in the other two species.  More importantly, concentrations of these minerals were higher in the willow leaves than in grass swards, and well above the nutritional requirements of growing lambs.  This is particularly important for cobalt, the availability of which declines through the summer in grass swards. For selenium, another important mineral, the sampling site had a greater influence than the tree species or sampling date.  More detailed results are now available as a pdf here.

There are clearly practical challenges to feeding willow leaves to sheep or cattle on a large scale, but these results provide a useful insight into the potential role of trees, and willow in particular, in meeting the nutritional requirements of livestock. We are investigating this further at Loddington, in partnership with the Vet School at Nottingham University.