Land use and climate affects wetland dynamics and productivity

Background/Question/Methods

Wetlands in the Prairie Pothole Region (PPR) are important components of the northern prairie ecosystem. The PPR experiences wet-dry cycles that cause water levels to fluctuate which drive productivity of aquatic invertebrates and plants.  However, the landscape in the PPR is altered by consolidation drainage, where smaller wetlands are drained into larger, more interconnected wetlands. We hypothesized that (1) current water levels of remaining wetlands are higher and respond less to climate cycles than historically and (2) that these changes are due to consolidation drainage. We digitized water levels from aerial photography for 141 semi-permanent and permanent sample wetlands across the PPR in North Dakota during historic (1937-1969) and current (2003-2010) eras. We defined wetland catchments as the portion of land in which water flows toward the sample wetland and may include other smaller wetlands and their discrete catchments; we delineated catchments for sample wetlands using high-resolution elevation data. We also developed a climate index to estimate expected moisture conditions. Within each catchment, we quantified drained wetlands, other remaining wetlands, row crops, and roads. We used mixed-effects regressions to evaluate a change in water level from historic to current eras and to test if that change was influenced by drainage. 

Results/Conclusions

On average, current water levels are 97% higher than they were historically and the dynamics in response to climate has decreased 51%. Water-level differences can be attributed to consolidation drainage; wetlands in highly-drained catchments are 209% larger than those with low drainage and the dynamics in response to climate has decreased 83%. However, a higher amount of other remaining wetlands in the catchment decreases water levels. Stabilization of water levels can lead to lower productivity of plants and invertebrates, reducing potential food sources for wetland wildlife. Stable, interconnected wetlands likely promote invasive species because these wetland communities evolved in a hydrologically dynamic and isolated system. Semi-permanent and permanent wetlands provide important foraging habitat for waterbirds during dry periods if water levels decrease beyond emergent vegetation; our results suggest that these types of wetlands in modified landscapes rarely do this and thus, cannot serve as drought refuge as they did in the past. Lastly, our results indicate a loss of nesting habitat for the federally listed piping plover, which nests on bare wetland shorelines during drought periods. Our results indicate that consolidation drainage is widespread across the PPR and could be altering wetland ecosystems throughout the region.