## 4 Discussion
Likewise, sediment descriptors (Turbidity = 7.66 NTU, TSS = 8.84 mg/L) in our study were also similar to measures reported in streams from other agricultural catchments containing a variety of BMPs (e.g., [PERSON] _et al._[18]: Turbidity = 8.10 NTU, TSS = 21.3 mg/L). Although differences are noted between phosphorus and TSS parameters, this may be attributed to the type of agricultural practice, and BMP characteristics within the catchments. Our study found BMP abundance and location metrics to be unassociated with rates of stream metabolism. The lack of association is not surprising in light of the fact that BMPs were not associated with summer concentrations of major nutrient forms and that nutrient concentrations were not related to stream metabolism. Our finding that both stream metabolism residuals and water quality parameters are not associated with BMP metrics may be attributable to one, or a combination, of three potential hypotheses: (1) BMP implementation has not exceeded the threshold required to initiate an ecosystem response; (2) limited connection between BMPs and the hydrologic system during the summer season; and (3) legacy effects of past agricultural activities and practices. Stream ecosystems often display a threshold response to a variety of environmental factors [1, 55], including management practices [18]. Although our study catchments comprised a substantial range of BMP implementation, a significant change in stream ecological condition was not associated with the increases in abundance or improved location of BMPs attained in the Grand River Watershed. As such it may be that the combined effects of BMPs in our study area are insufficient to reduce nutrient losses to streams and initiate a measurable change in water quality and stream metabolism. This explanation is supported by predicted nutrient loss reductions from models testing BMP implementation strategies in Great Lakes river basins [56]. In this past study, a scenario of BMP implementation levels considered feasible through conservation efforts similar to the Rural Water Quality Program were insufficient to generate substantive reductions in nutrient losses. However, a scenario of more extensive and more targeted BMP implementation was found to generate significant reductions in nutrient yield. Based on these findings the Rural Water Quality Program may need to adopt strategies that encourage more intensive implementation and improved targeting of BMPs toward hydrologically connected areas in order to enhance the condition of streams in the Grand River watershed. BMPs assessed in past studies have been shown to reduce nutrient levels in agricultural streams (e.g., [57, 58, 59, 60, 61, 62]). However, results from our study did not suggest that BMPs were enhancing water quality in the studied streams. The absence of associations between BMPs and water nutrients may be attributed to seasonal climate variation [63, 64]. Greater evapotranspiration rates in summer months can remove soil water and dry out the land resulting in precipitation infiltrating the soil in all but the largest of events. Under these warm, dry conditions the land is less likely to generate significant surface runoff and BMPs designed to capture nutrients and sediments in runoff have less influence on surface water quality. Furthermore, the availability of nutrients on the landscape is abated during the summer season from actively growing crops and reduced agricultural inputs. In contrast, during spring and autumn agricultural inputs intensify and soils are more often saturated due to lower evapotranspiration rates and large amounts of precipitation or melt water. Saturated conditions will result in greater overland connection between the land and hydrologic system where structural BMPs may more effectively reduce transport of contaminants. Indeed, [PERSON] [65], found significant negative associations between instream nutrient concentrations and BMP abundance and location metrics based on samples collected in November from similar sized catchments in the GRW.