Vegetation and soil properties as indicators of the hydrology and ecological health of northern prairie wetlands in native and agricultural landscapes.

摘要

Prairie wetlands are designed to withstand, if not thrive, on the climatic instability common to the prairies. It is often the human alteration of their hydrology that impacts wetland productivity. Surrounding land use such as cultivation can potentially alter the dynamics of wetland in-flows and the amount of water entering a wetland. This then alters the hydro-ecological processes of spring rise, summer drawdown, length of dry periods, and vegetative reproduction and establishment. Cultivation can also physically damage or destroy wetland vegetation and impact riparian and wetland soils. Most of the prairie wetlands that have escaped drainage in the prairie pothole region (PPR) now lie in watersheds devoted primarily to agricultural crop production. As a result, human activities have affected nearly every prairie wetland directly or indirectly.;The objective of study 1 was to assess the impact of agricultural land-use on the distribution and diversity of vegetation in seasonal and semi-permanent wetlands. Vegetation surveys were conducted in 21 wetlands in Manitoba and Saskatchewan. Agricultural croplands surrounded 18 wetlands, while native grasslands surrounded three wetlands. No significant differences in total, invasive, weed, exotic or native species were observed between seasonal and semi-permanent wetlands in agricultural landscapes. Native grassland wetlands had more total and native plant species in outer vegetation ' zones compared to wetlands surrounded by croplands and virtually no invasive, exotic or weed species in their shallow marsh zones. In comparison, invasive, weed and exotic species were more prevalent in wetlands surrounded by croplands, with the numbers of invasive and weed species significantly higher in shallow marsh and wet meadow zones, and exotic species higher in wet meadow zones. The loss of native species and the increase of invasive, weed and exotic species in wetlands surrounded by agriculture can be partly attributed to the loss of the low prairie and wet meadow zones. Research shows that agricultural impacts, such as excess sediment and nitrogen additions from soil erosion and changes in soil moisture and soil compaction, also favor the growth of invasive species in the outer vegetative zones of prairie wetlands. These factors help explain why the restoration of native species in the outer wetland vegetation zones is so difficult. Our ability to successfully restore and protect impacted wetlands in agricultural landscapes will be limited if these vegetative margins are not protected from further degradation.;The first objective of study 2 was to examine the accuracy and predictions of a single-basin hydrologic model designed to simulate spring snowmelt events into wetlands. The model was applied to nine seasonal and semi-permanent wetlands in Saskatchewan and Manitoba. Water level data for the ponds and the spatial distribution of the vegetation within all study wetlands indicate that 30% of the average annual snowmelt equivalent that occurs from December to April enters study wetlands. This 30% snowmelt event was consistent in all wetlands regardless of basin size, wetland class, surrounding land-use, or regional location.;The second objective of study 2 was to investigate the spatial extent of the effective transmission zone and its relationship to landscape features and wetland attributes, such as wetland water chemistry. Solute differences observed in the soils surrounding study wetlands were the result of two distinct ionic dominance patterns in wetland water chemistries. Calcium, bicarbonate and calcite precipitate reflected the influence of snowmelt chemistry in seasonal wetlands, while gypsum and other soluble salts in the soils surrounding semi-permanent wetlands reflected the influence of evapotranspiration and the concentration of solutes in more permanently flooded habitats. Results indicate that lateral soil water movement and the effective transmission zone are important in both seasonal and semi-permanent prairie wetlands. A similar spatial pattern for the effective transmission zones was displayed in both seasonal and semi-permanent ponds, with the outer extent of the zone around each wetland type located at a specific and consistent upland elevation relative to the basin itself. The outer extent of the zones were located closer to the wetland edge where slopes were steep and extended further away from the wetland edge where slopes were more gradual. Little is known about the landscape or wetland factors influencing the extent of the effective transmission zone in wetlands and further investigation is warranted.;The overall objectives of this research were to explore the influence of surrounding land-use on wetland vegetation and to better understand spring snowmelt and soil characteristics in wetlands of varying hydrological permanence. The main purpose is to improve our predictive capability for wetland restoration in prairie Canada and to provide recommendations for the future management and protection of wetlands in agricultural landscapes.