Saturated and Integrated buffer zones

In a saturated buffer zone, drainage water and riparian soil are reconnected by a buried, lateral perforated distribution pipe running parallel to the stream, which redirects the piped subsurface drainage water into the riparian zone. The infiltrating water saturates the riparian soil and creates anoxic conditions. For denitrification to occur, the soil carbon content must be sufficient. In areas limited by carbon, the integrated buffer zone overcomes this limitation.

Example of a saturated buffer zone to treat water discharged from an agricultural field with subsurface artificial drainage.
Image source: Carsten et al., 2020.

In integrated buffer zones, the drainage water is first retained in a pond designed to capture sediment particles and increase the retention time of the water. This also allows for interception of overland flow. After the pond, the water infiltrates a vegetated shallow zone (constructed wetland) where the topsoil has been removed. In this infiltration zone, anoxic conditions develop and carbon is added from the vegetation or plant litter.

Example of an integrated buffer zone to treat water discharged from an agricultural field with subsurface artificial drainage.
Image source: Carsten et al., 2020.

Why

Saturated and integrated buffer zones were recently developed and tested in North-western Europe with the aim to improve the nutrient reduction capacity of traditional riparian buffer zones bypassed by subsurface drainage pipes. The designs promote multi-functionality, increasing biodiversity and biomass production in the riparian zone.

Saturated and integrated buffer zones provide the ideal conditions for soil microbes to remove nitrate from water through denitrification. Microbes use organic carbon to derive energy and under anoxic conditions, nitrate is removed in the process. Temperature can be a limiting factor when it comes to denitrification rates. Denitrification occurs at all temperatures but is slower in colder conditions and faster as it gets warmer.

Water retention time can also be a limitation. In cooler climates, the integrated buffer zone is recommended due to the ability to store water prior to entering the saturated buffer zone. This also can reduce suspended sediment loads when water is able to pond.

See SCIENCE – CHEMICAL PROCESSES for more information about denitrification.

References

Carstensen, M. V., Hashemi, F., Hoffmann, C. C., Zak, D., Audet, J., & Kronvang, B. (2020). Efficiency of mitigation measures targeting nutrient losses from agricultural drainage systems: A review. Ambio, 49, 1820-1837.

Fahrner, S. (2002). Groundwater Nitrate Removal using a Bioremediation Trench. Honours Thesis. University of Western Australia, Perth.

Jaynes, D.B., & T.M. Isenhart. (2014). Reconnecting tile drainage to riparian buffer hydrology for enhanced nitrate removal. Journal of Environmental Quality 43: 631–638.

Jaynes, D.B., & T.M. Isenhart. (2019). Performance of saturated riparian buffers in Iowa, USA. Journal of Environmental Quality 48: 289–296.

Schipper, L. A., Robertson, W. D., Gold, A. J., Jaynes, D. B., & Cameron, S. C. (2010). Denitrifying bioreactors - an approach for reducing nitrate loads to receiving waters. Ecological engineering, 36(11), 1532-1543.

van Driel, P.W., Robertson, W.D., Merkley, L.C. (2006b). Upflow reactors for riparian zone denitrification. J. Environ. Qual. 35, 412–420.

Zak, D., B. Kronvang, M.V. Carstensen, C.C. Hoffmann, A. Kjeldgaard, S.E. Larsen, J. Audet, S. Egemose, Jorgensen, C.A., Feuerbach, P. and Gertz, F. (2018). Nitrogen and phosphorus removal from agricultural runoff in integrated buffer zones. Environmental Science and Technology 52: 6508–6517.