Quantifying the Value of Wetlands on Pastureland

Background

Globally, temperate grasslands are among the most modified ecosystems and conversion of these ecosystems continues today. Most remaining grasslands in the Canadian prairies exist on privately owned land largely used to support beef cattle production. Understanding and quantifying the ecosystem services associated with the grassland landscapes that support the Canadian beef industry is critical especially when it comes to public trust conversations. Beef production in the Canadian prairies overlaps the Prairie Pothole Region of western Canada where small isolated wetlands can comprise a significant portion of the landscape. These wetlands play important roles in carbon cycling and climate regulation, water quality and quantity regulation, and are hotspots for biodiversity. Although many Canadian studies are looking at ecosystem services provided by grazing cattle few focus specifically on wetlands.

Objectives

• To quantify the extent of wetlands in beef production landscapes and to quantify the ecological benefits of these wetlands including water quality, waterfowl production and carbon cycling

What they Did

Using flux towers, researchers measured carbon sequestration, evapotranspiration and heat changes from two wetlands. One was located on a grazing landscape and the other on cropland in southern Manitoba and were compared to crop and grazing land without wetlands. Flux towers are able to collect a large number and variety of  data from a specific wetlands meaning the measurements taken are able to me more accurate. However, mass installation of these towers are limited due to their cost. To address this, researchers collected water samples and GHG samples from 60 wetlands (half in pasture half in cropland) across the prairie provinces to assess differences between wetlands embedded in grazing landscapes and cropland landscapes. This information was compiled into a comprehensive geodatabase that documents the extent of wetlands in beef production landscapes and their associated ecosystem services across the Canadian Prairies.

What They Learned

Our extensive monitoring work over the last three years has substantially advanced our knowledge with respect to the range of greenhouse gas (GHG) emissions associated with freshwater mineral soil wetlands in agricultural landscapes and their drivers. In particular, we have demonstrated that wetlands embedded in perennial cover associated with beef production landscapes emit significantly less methane relative to wetlands embedded in cropland. This difference appears to be mostly attributed to lower phosphorous (P) concentrations and higher sulfate (SO₄) concentrations observed in wetlands embedded in perennial cover relative to cropland. These findings based on our extensive monitoring and dissolved gas analyses were further confirmed by the measurements collected at the two first ever Eddy Covariance flux towers deployed in prairie wetlands. In addition to better understanding GHG emissions from wetlands and their impact on climate we continue to learn about the biophysical impact of wetlands on regional climate, and our early results indicate that prairie wetlands likely play a substantial role in regional summer cooling which could provide substantial mitigation benefits for both croplands and rangelands under a changing climate.

Our project has provided the first estimate of the areal extent of wetlands embedded in beef production landscapes of the Canadian Prairies and demonstrates that a substantial portion of wetlands in this region (~2M ha) are embedded in these landscapes. As such, these wetlands are generally protected from conversion, and this is evidenced but the noticeable differences observed in both their water quality and GHG emissions.

Lastly, in addition to quantifying the differences between GHG emissions and climate impact of these wetlands we have provided the first estimates for the broader set of ecosystem services associated with wetlands in beef production landscapes of the Canadian Prairies. Using our environmental metrics calculator, we estimate that these wetlands are:

• Storing 5,157,563,904 m³ of water
• Retaining up to 6,467,102 kg of P per year and 24,115,641 kg of nitrogen per year
• Storing 423,464,202 tonnes of CO₂eq that are vulnerable to conversion if drained.

What It Means

The results of our research suggest that beef production landscapes are important for maintaining wetlands on the landscape and the ecosystem services associated with them. Our work also suggest that wetland embedded in perennial landscapes, like those associated with beef production, result in wetlands with significantly lower methane and overall GHG emissions (expressed as CO₂eq). Our research has identified key drivers of methane emissions from wetlands which will help inform future wetland conservation and restoration efforts to minimize GHG emissions while maintaining other important ecosystem services. Lastly, our work is contributing to our understanding for how beef production landscapes contribute to biodiversity while also moderating local/regional climate.