How efficient is modern peri-urban nitrogen cycling: A case study

Area of Science:

• Environmental Science
• Urban Ecology
• Nutrient Cycling

Background:

• Urban centers import substantial materials, including nitrogen (N), from their hinterlands.
• A common perception is that urban food production and recycling limit nutrient accumulation, a notion this study investigates.

Purpose of the Study:

• To quantify nitrogen influxes and effluxes in the peri-urban Lower Fraser Valley (LFV).
• To assess the effectiveness of urban food production, composting, and recycling in managing nitrogen accumulation.
• To evaluate the impact of nitrogen transport on coastal waters.

Main Methods:

• Quantified nitrogen influxes from livestock feed, food imports, fertilizer, and atmospheric deposition.
• Quantified nitrogen effluxes from sewage, solid waste, and atmospheric emissions.
• Calculated per capita and per land area nitrogen balances for the LFV.

Main Results:

• Nitrogen influx is dominated by livestock feed (18,000 tonnes N/year), followed by human food imports (9,210 tonnes N/year).
• Nitrogen effluxes are primarily from sewage (10,400 tonnes N/year) and atmospheric emissions (9,460 tonnes N/year).
• The LFV has a net nitrogen influx of 3.1 kg N per person, with significant transport to the ocean via the Fraser River and sewage outfall.

Conclusions:

• The assumption that urban food production and recycling limit nitrogen accumulation in the LFV is not supported by the data.
• Current waste management practices demonstrate low nitrogen use efficiency.
• The substantial nitrogen transport to coastal waters likely impacts marine ecosystems.