Evaluating the relationships between watershed physiography, land use patterns, and phosphorus loading in the bay of Quinte basin, Ontario, Canada

The Bay of Quinte, a Z-shaped embayment at the northeastern end of Lake Ontario, represents a characteristic case of an area of concern (AOC) where scientific uncertainty underlies management efforts to address eutrophication problems. The present study attempts to examine the relationships between total phosphorus (TP) (i.e., concentrations from point and non-point sources, net export, and yield) and watershed attributes, including land use cover and physiographic characteristics. Dynamic linear modeling is applied to assess temporal trends in the flow rates in five major tributaries of the area. Urbanized catchments near the Bay of Quinte show more dynamic flow patterns with significant within- and among-year variability and stronger response to local precipitation patterns. The “flashy” behavior of urban land is characterized by relatively high net TP export and TP yield. Self-organizing map analysis, classified the watershed into six distinct spatial clusters, representing two agricultural, one forested, one urban, one pasture-dominated, and one transitional area. Our study shows that agricultural and urban sites profoundly shape riverine TP dynamics. We also provide evidence that tributaries draining agricultural areas exhibit considerable variability, depending on management practices and soil properties. Excessive fertilizer or manure application in croplands, management practices (e.g., crop types and tillage methods) and soil hydrological characteristics (e.g., hydraulic conductivity and permeability) generally determine soil phosphorus level and consequent losses through erosion and runoff from agricultural sites. In a similar manner, pasture-based grazing systems appear to play an important role in modulating the fate and transport of phosphorus in the Bay of Quinte watershed.