Hydroclimatic influences and physiographic controls on phosphorus dynamics in prairie pothole wetlands

While wetlands are known as long-term storages or sinks for contaminants, not all are equally effective at trapping phosphorus (P). The prevalence of P-sink behavior in prairie pothole wetlands remains unclear, especially across gradients of human disturbance. The objectives of the current study were three-fold: (1) characterize the spatiotemporal variability of wetland hydrology and wetland water P concentration across a range of prairie potholes; (2) establish the propensity of different pothole wetlands to act as sources or sinks of P; and (3) assess the potential controls of climatic conditions, landscape characteristics, wetland soil physiochemical properties and local hydrology on source versus sink dynamics. Ten intact and three consolidated (i.e., drained) wetlands located in southwestern Manitoba, Canada, were monitored for water level fluctuations and water soluble reactive P (SRP) concentration over two years with contrasting antecedent wetness conditions. Soil cores were also collected to measure soil physiochemical properties such as the equilibrium phosphorus concentration (EPC). Water column SRP concentrations were compared to EPC values to infer the time-variable source versus sink behavior of each of wetland. Statistical analyses were then performed to assess whether the source versus sink behavior of individual wetlands could be linked to their physiographic or hydrologic characteristics. Results show that some wetlands persistently acted as P sinks while others switched between source and sink behavior. Persistent P-sink behavior was more common with intact wetlands, as opposed to consolidated wetlands. Wetland soil texture, storage volume and short-term water level fluctuations appeared to control the source versus sink behavior of individual wetlands. The dominant controls on P-sink behavior identified under dry conditions were, however, different from those identified under wetter conditions. This study therefore highlights the importance of considering the non-stationary nature of P-sorption dynamics and their controls, even at sub-annual timescales, in the prairie pothole region.