Drainage: management options to mitigate nutrient export
Within the prairies we’re used to dryness. Yet, in key periods, there is a lot of water, which can move quickly. We manage our agricultural landscapes to help manage this water – adopting reduced tillage to help manage soil quality, and maintain soil moisture, and using drainage to move water away from where we don’t want it.
Recent wet conditions in the prairies have reminded us of the challenges of water management and of drainage. While this decades-old practice is part of prairie agriculture, it has a myriad of benefits, and negative impacts. One of the negative impacts is the potential impact on water quality.
By draining prairie lands, we can increase nutrient loads to downstream ecosystems – by connecting areas of the watershed that typically wouldn’t lead to flow, by removing wetlands, which can function as nutrient sinks, by reducing the capacity of the landscape to store water, and in some areas, and by contributing to erosion, as more water may leave more quickly, taking soils along.
Can we manage ditches to help manage water quality? Research is underway:
Vegetation residues can be an important source of nutrients on prairie agricultural fields. This is because vegetation residues can release nutrients when they are frozen and thawed during long, cold winters. In our work, we’re experimenting with managing the vegetation in ditches, to see if removing vegetation is enough to impact nutrient loads downstream. We’re also assessing the sediments of ditches to better understand if they will function as sources of nutrients, or if they could indeed help trap nutrients.
To do this, we’re combining small scale experiments with larger scale monitoring. We’re sampling for nitrogen and phosphorus in water, and monitoring how much water and nutrients move through ditches. Then, we’re looking at what happens to nutrient export when we hold water back in ditches – a common practice to help manage floodwaters. We want to know if holding this water back will have added benefits in terms of water quality of downstream lakes and rivers.
This work is just one area of research we’re engaged in to help manage water quality in our agricultural landscapes. We’re looking for options that work, in our working landscape – and can help maintain strong agricultural production, while protecting water quality.
What else can we do to mitigate effects of drainage on water quality?
In wet periods, the impacts of drainage on nutrient export can be very large — potentially more than doubling nutrient loads to downstream ecosystems, and contributing to problems of harmful algal blooms. Managing this impact in our landscape is challenging. The most important advice is managing inputs. For more information, please see:
The prairies are rich agricultural land, dotted with many wetlands that vary in their size and permanence. These wetlands are often seen as a hindrance to agriculture. Many producers on the prairies use drainage to improve efficiency of field operations. Drainage is also a tool to help adapt to wet conditions, and support higher yields by increasing arable acres. Some believe areas of the prairies would not be arable without wetland drainage.
Though drainage has agronomic benefits, it also has several environmental downsides. These include:
- increasing runoff and the frequency of flooding
- reducing infiltration of water into shallow groundwater, which may affect well water supplies,
- reducing wildlife habitat,
- decreasing carbon storage in wetland soils, and
- increasing nutrient runoff.
Although the extent of drainage varies across the prairies, estimates suggest that since agricultural expansion began, 40-70% of prairie wetlands have been removed (Watmough and Schmoll 2007; Davidson 2014). Drainage is ongoing.
What should I know about drainage and nutrient management in the prairies?
Drainage connects areas of the catchment that would not normally be connected. That is, in normal years, some areas of prairie landscapes do not contribute water or nutrients to streams. However, in drained areas, ditches increase connectivity and likewise increase the area of a landscape contributing nutrients and water downstream. This reduces the water storage capacity of wetlands, as well as the capacity of wetlands to process and retain nutrients.
Drainage can more than double water and nutrient export. Because downstream ecosystems are incredibly sensitive to phosphorus, this increase in nutrient export can have a major impact contributing to increased algal growth, and algal blooms.
If drainage is an important part of managing your farm, consider ways you can mitigate the impacts
Strategically maintain or construct wetlands: Wetlands store agricultural nutrients that can cause problems downstream. These storage wetlands are most important when they’re able to catch runoff from high-nutrient areas: for example, when they’re immediately downstream of a bale grazing field. Wetlands lower in the watershed play a key role in limiting nutrient transport into regional river channels, which protects downstream ecosystems. Consider maintaining a wetland on your low-elevation sites to reducekeep nutrients from entering area streams.
Avoid over-applying nutrients and decrease soil surplus nutrients: You can help mitigate the impacts of drainage by implementing 4R nutrient management practices. Careful management of nutrients, particularly near areas where water accumulates or flows, can help better manage nutrients and lessen the effects of drainage on water quality.
Drainage has been ongoing in the prairies for more than a century, and extensive drainage is underway in some areas. While this can have agronomic benefits, environmental concerns associated with drainage merit consideration.
To solve downstream nutrient problems, the best options are to keep water on the land in wetlands and reservoirs, and to manage nutrients at the source — for example, by carefully managing phosphorus inputs to your land. Keeping wetlands may not always be an option. However, maintaining as much water storage capacity as you can in wetlands will help manage water quality in downstream lakes.
Badiou, P., B. Page, and W. Akinremi. (2018a). Phosphorus Retention in Intact and Drained Prairie Wetland Basins: Implications for Nutrient Export. J. Environ. Qual. 47: 902–913. doi:10.2134/jeq2017.08.0336
Baulch, H., Elliott, J., Cordeiro, M., Flaten, D., Lobb, D., & Wilson, H. (2019). Soil and water management practices: Opportunities to mitigate nutrient losses to surface waters in the Northern Great Plains. Environmental Reviews, 27(4), 447-477.
Davidson, N. C. (2014). How much wetland has the world lost? Long-term and recent trends in global wetland area. Marine and Freshwater Research 65: 934–41. doi:10.1071/MF14173.
Watmough, M. D., and M. J. Schmoll. (2007). Environment Canada’s Prairie & Northern Region Habitat Monitoring Program Phase II: Recent habitat trends in the Prairie Habitat Joint Venture. Technical Report Series No. 493. Environment Canada, Canadian Wildlife Service, Edmonton, AB, Canada. 135 pp.
Wilson, H.F., N.J. Casson, A.J. Glenn, P. Badiou and L. Boychuk. (2019). Landscape controls on nutrient export during snowmelt and an extreme rainfall runoff event in northern agricultural watersheds. J. Environ. Qual. 48:841–849 (2019) doi:10.2134/jeq2018.07.0278