The International Interdisciplinary Conference on Land Use and Water Quality Conference took place in Aarhus, Denmark from June 3 – 6, 2025. ADMC member Chris Hay of Hay Water Solutions, LLC attended the conference and posted a great summary of the field tours on LinkedIn. Chris was kind enough to provide his posts for a guest blog to ADMC for a showcase of international practices. These posts are to show practices that others are using in conservation drainage and are not an endorsement on any policies or programs. For any questions or more information please contact Chris.
Following the LuWQ conference in Aarhus Denmark, a group of us were treated to a tour of #ConservationDrainage practices for nutrient mitigation on the Jutland peninsula led by Flemming Gertz of SEGES Innovation. At stop one, we visited a constructed surface flow wetland established in 2024.
Also at the site are some low-lying organic soils used for grass production for the dairy operation. These areas will be rewetted as part of the “Aftale om et Grønt Danmark” (Agreement on a Green Denmark) which has a target for rewetting 140,000 ha (approx. 346,000 acres) of drained carbon-rich soils to reduce CO2 emissions. Approximately $1.4B are set aside for this rewetting initiative. The farmer is trying to get ahead of the curve in finding replacement land before the market heats up more or carbon taxes take effect in 2028.
Second stop on our #ConservationDrainage tour of Denmark was another constructed surface flow wetland. Called “mini wetlands”, these field-scale wetlands capture and convert N and P from tile drainage. They include a sedimentation basin, deep open basins, and shallow vegetation zones. Requiring about 1% of the contributing drainage area, they take more area than saturated buffers or bioreactors but provide more habitat, biodiversity, and hunting benefits.
Established in 2010, this 0.75 acre wetland treats drainage from 94 acres. Over four years of monitoring, it removed an average of 628 lbs of N (28% of inflow) and 8 lbs of P (47% of inflow) per year. The habitat and biodiversity benefits were evident compared to the newly established wetland at the first site.
Our third stop of the #ConservationDrainage tour of Denmark was an Integrated Buffer Zone. This first of its kind practice was the one I was eager to see, since it’s not something we have in the US. Similar in concept to a saturated buffer, the field drains are directed into an open water surface ditch (instead of an underground distribution pipe) running parallel to the stream. Water infiltrates from the ditch and flows through the buffer before discharging to the stream. Nitrate in the water is removed by denitrification in the buffer.
I’m not sure how well this concept would play in the US, but potential use cases could be: (1) buffers with existing trees or where trees are desired to avoid the potential plugging of an underground distribution pipe by tree roots or (2) fields with multiple outlets to avoid the need for multiple control structures and the potentially more complicated plumbing of connecting distribution lines.
Fourth stop on our Denmark #ConservationDrainage tour was a bioreactor (or wetland with biofilter). In this design, the drainage water is directed into a sedimentation pond first (to the left of the autosampler circled in red) before flowing into the bed of woodchips (to the right of the autosampler).
An oxygenation well re-oxygenates the water before it is released to the stream. Like many conservation drainage practices, the action happens underground, so there’s not a lot to see.
Despite early promise, bioreactors have fallen out of favor in Denmark (see Laura C.’s post for more discussion on this: https://lostdropraider.wordpress.com/2025/06/10/seges-tour-day-1/). In addition to some of the concerns that Laura discusses, a big blow to bioreactors in Denmark has been the market for woodchips for biomass energy production making woodchips too pricey for use in bioreactors. While issues/concerns with bioreactors in the US don’t reach the same level, the discussions about bioreactors in Denmark were valuable, especially as we think about managing and maintaining aging bioreactors in the US.
Stop 5 on the #ConservationDrainage tour of Denmark was a saturated buffer zone. All the action is happening underground (even more so than the bioreactor site), so there’s not much to see except for a nice forested riparian buffer along a small grain field (something we don’t see much of in Iowa) until you see the monitoring wells for measuring nutrient reduction.
Just as it was cool to see the integrated buffer zone that was pioneered in Denmark and think about applications in the US, it was also cool to see saturated buffers, which originated in Iowa, being successfully applied in Denmark. The conclusions they’ve reached from saturated buffer monitoring sound spot on with our experience here, “Overall, SBZs show strong potential for nutrient mitigation in tile-drained landscapes, but site-specific conditions are critical for success” (Zak, D.H.).
Sixth stop (last stop of day 1) of our Denmark #ConservationDrainage tour was a compact filter system for phosphorus removal. It’s not as attractive to look at compared to the nature-based solutions for nitrogen removal, but dealing with phosphorus, particularly dissolved P, is trickier. So, some of these more engineered solutions may be critical for reducing P losses from tile drainage, especially where there are hot spots.
Posts from Day 2 are soon to come!