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Assessing the Circularity of Nutrient Flows in the Okanagan Bioregion, BC Canada

Recent years have seen a steep rise in the interest in ‘nutrient circularity’, ‘closing the nutrient loop’, ‘circular nutrient solutions’, and ‘circular nutrient economy’. As part of a broader food system design project in the Okanagan Bioregion, BC Canada, we took the opportunity to help stakeholders in the bioregion better understand current levels of nutrient circularity and how it could be improved.

The notion of nutrient circularity seems to generally encompass the reduction of nutrient losses – during agricultural production, processing, distribution, and consumption – along with comprehensive recovery of nutrients from organic residuals, for reuse in agricultural production. Nutrient circularity has been defined, for example, with a focus on waste management – as the fraction of nutrients in waste streams that are recycled to agricultural production. This circularity indicator could be referred to as ‘output circularity’. Nutrient circularity has also been defined with a focus on agricultural biomass production – as the fraction of total nutrient inputs that are supplied from waste streams. This circularity indicator could be referred to as ‘input circularity’.

Due to the trade of feed and food, nutrient inputs to crop production in one place may make their way into organic residuals in another place. When assessing the level of nutrient circularity for a bioregion like the Okanagan, simply comparing nutrient need and availability may thus give a distorted picture.

To account for the effect of feed and food trade on nutrient circularity in the Okanagan, our analysis went beyond nutrient need and nutrient availability in the bioregion exclusively. Insofar as nutrient flows relate to food consumption (much of which is imported) and production (much of which is exported) in the Okanagan bioregion, the analysis also included nutrient need and nutrient availability outside the bioregion. This approach enabled a separate discussion of four kinds of nutrient circularity – internal and external input and output circularity – as well as how they relate to one another and to system openness.

Distinction of four types of nutrient circularity – internal and external input and output circularity.

We assessed nutrient circularity separately for nitrogen (N), phosphorus (P) and potassium (K) – for the baseline year 2016 and four scenarios that explore various possible food system futures in terms of the extent of cultivated land, the structure of the food system, and dietary preferences.

List of scenarios considered in addition to the 2016 baseline.

Our analysis revealed that nutrients flow from the periphery of the bioregion towards the center – where population and livestock densities are highest – and from outside the bioregion into the bioregion. For N and P, feed and food trade were found to increase the nutrient availability compared to nutrient need in in the bioregion as a whole by about 50 percent. This comes at the cost of reducing nutrient availability elsewhere. This pattern of nutrient accumulation in the Okanagan can be expected to be more pronounced in 2050 and also apply to K. This is due to the projected population increase and the possibility for increased local livestock production and thus more feed imports.

System openness for the 2016 baseline. Spatial variation across the Okanagan, and for the Okanagan as a whole (INT = internal, EXT = external).

With current organic residual management practices and infrastructure, nutrients recovered from organic residuals are insufficient to meet crop nutrient needs in the bioregion. If nutrient recovery efficiency was increased from current levels to 70 percent – which reflects a conservative estimate of the recovery rates that full-scale recovery technologies can be realistically expected to achieve in the long run – there would be a surplus for N and P in the bioregion but still a deficit for K. If livestock production and feed imports were to be increased in the future, there would also be a surplus for K.

At first sight, the high nutrient availability compared to nutrient need in the bioregion may suggest that comprehensive nutrient recovery may not be needed in the Okanagan. But the nutrient increased nutrient availability in organic residuals is due to system openness associated with feed and food trade. In other words, the increased nutrient self-reliance internal to the bioregion comes at the expense of a reduced nutrient self-reliance external to the bioregion. Our analysis quantified the extent to which different food system scenarios aggravate or mitigate this pattern.

Provided that the goal of nutrient management is to maximize nutrient circularity, across all scenarios, it will be necessary to re-distribute nutrients both within and across the spatial boundaries of the Okanagan. This would help to at least partially compensate for nutrient depletion external to the bioregion in the places from where feed and food are imported. Our analysis estimated the tons of NPK that would need to be moved outside the bioregion to compensate for system openness. Alternatively, if nutrients are not moved from areas where they are accumulating, they are likely to have adverse environmental impacts and aggravate anticipated future nutrient scarcity.

Read more:

Find out more about the Bioregion Food System Project here and read more about nutrient management in the Okanagan in our technical research report. A suite of scientific papers are currently under review and will be released later this year.