Lake sediment phosphorus and relationships to soils and chemistry across the Boreal Plains and Prairie ecozones

Within the Prairie region of Canada, rates of internal phosphorus (P) loading are high, and lakes are nutrient rich. However, there is important variation in lakes of the region which span two ecozones (the Boreal Plains and Prairies; an area of >1 000 000 km 2 ). Using a survey-based approach, we characterized the variation in lake sediments (including sequential fractionation and porewater analysis), water chemistry, and lake and watershed attributes expected to affect sediment P cycling. Principal components analysis suggests that lake sediments of this vast region have a gradient between areas with luvisolic soils and greater forestry (Boreal Plains), characterized by higher labile organic phosphorus, sediment total phosphorus, and residual phosphorus, to watersheds with more chernozemic soils and agriculture (Prairies ecozone) where sediments have greater calcium-bound phosphorus. Lake trophic status, salinity, and dissolved sulfate were higher in Prairie ecozone lakes than in the Boreal Plains. However, the ecozones were not associated with significant differences in porewater P; porewater P was better predicted by chemical variables especially iron. While ecozones can be a tool to understand differences in lake chemistry and sediment P, soil types may be the most important geospatial factor predicting P storage in lake sediments.