Nitrogen (N) is an essential biological element, so optimizing N use for food production while minimizing the release of N and co-pollutants to the environment is an important challenge. The Nooksack-lower Fraser Valley, spanning a portion of the western interface of British Columbia, Washington state, and the Lummi Nation and the Nooksack Tribe, supports agriculture, fisheries, diverse wildlife, and vibrant urban areas. Groundwater nitrate contamination affects thousands of households in this region. Fisheries and air quality are also affected including periodic closures of shellfish harvest. To reduce the release of N to the environment, successful approaches are needed that partner all stakeholders with appropriate institutions to integrate science, outreach and management efforts. Our goal is to determine the distribution and quantities of N inventories of the watershed. This work synthesizes publicly available data on N sources including deposition, sewage and septic inputs, fertilizer and manure applications, marine-derived N from salmon, and more. The information on cross-boundary N inputs to the landscape will be coupled with stream monitoring data and existing knowledge about N inputs and exports from the watershed to estimate the N residual and inform N management in the search for the environmentally and economically viable and effective solutions.
We will estimate the N inputs into the Nooksack-lower Fraser Valley and transfers within the watershed originating from energy use, transportation, fertilization, wastewater treatment plants (WWTP), animal feeding and manure production, and others. Here we present some preliminary results on the U.S. side using available data: About 11% of the watershed is farmed land, and 87% of the production acres in 2015 consisted of forage grass, silage corn, caneberries, blueberries, and potatoes. Using the existing SPAtially Referenced Regression On Watershed attributes (SPARROW) model, we estimated that the manure N input to the watershed from dairy and livestock operations ranged between 17 metric ton (MT) N to 300 MT N in 2002. SPARROW result also indicated that individual WWTP sites contributed between 3 to 220 MT N to the watershed in 2002, and fish hatcheries 0.2 to 28 MT N. We will supplement and update the existing data for more recent years and improve the results by reaching out to local groups to quantify crop-specific N data and animal feed inputs. This project will reach out to other stakeholders on both sides of the international border for a first comprehensive, quantitative characterization of all N inventories across this international watershed.