Urban Agriculture as Blue-Green Infrastructure

woman operating an agricultural experiment.

Urban agriculture is increasing in popularity but is an understudied green infrastructure type in terms of nutrients. 

This project fills part of said knowledge gap in urban ecology and sustainable cities by looking at food gardens and nutrient cycling, focusing our measurements in Linköping.

Why it mattersShow/Hide content

photo of scientist taking samples in the ground. Checking new lysimeter installation before the growing season.Cities are hotspots of nitrogen and phosphorus cycling, and as such play a key role in their management. These nutrients are essential for plants but can pollute waterways when not properly managed. Cities are trying to improve how they manage nutrients, including through the implementation of blue-green infrastructure programs. However, there is a lack of empirical knowledge on how such programs affect the fate of nutrients and the ecosystem services that depend on nutrient flows.

Urban agriculture is increasing in popularity but is an understudied green infrastructure type in terms of nitrogen and phosphorus.

What we are doingShow/Hide content

Photo of water samples in small plastic bottles.Water samples after coming back from field work. Each lysimeter yields very different amounts and colors of water. Photo credit Genevieve MetsonThis project investigates nutrient cycling in food gardens in Linköping Sweden and compares findings with a sister project in Minneapolis USA. We combine discussions with people, field work, and lab work to understand how nutrients are moving around under real-world conditions. For instance, we survey gardeners to document the diversity of management practices they use and calculate the amount of nutrients applied and harvested in these urban agriculture systems.

We are also measuring nutrient losses as leachate for 3 years with over 30 gardeners in Linköping right now! Every week we go out and collect water which accumulates in a bottle underneath our participants’ gardens. We measure how much water is there and bring samples back to the lab. In the lab we look for how much nitrogen and phosphorus are in the water. Soil is also collected once a year to look at nutrients stored there.

At a later stage, workshops and interviews will be conducted to better understand the benefits (and concerns) stakeholders are interested in related to their gardens and how nutrients fit into this picture.

These results can help cities evaluate how to spend limited resources in adapting green space to meet multiple sustainable development goals, especially related to nutrient sustainability.

DataShow/Hide content

This section is under construction. We aim to create interactive plots of the weekly water data we have been collecting since April 2020.

map, urban agricultural sampling in linköping.

Minneapolis sister projectShow/Hide content

Across the Atlantic ocean, in Minneapolis Saint-Paul, USA, a similar project has been measuring the efficiency of nutrient recycling from compost in urban gardens. 

Photo of urban agriculture.In replicated experimental garden plots, different amounts and different types of compost are applied over five growing seasons. Project results have shown that typical phosphorus (P) inputs in the form of compost in far exceed the demand of crops, and that excess P can be lost through leachate.

Targeting compost applications to crop nutrient demand mitigates these losses and increases recycling efficiency, and the application of spent lime (water treatment residual) below gardens can be highly effective at retaining P.

Photo of urban agriculture.We will be comparing these controlled experiments in the USA to the results from real world gardener plot results In Sweden in the years to come.

The work in the USA is led by Dr. Gaston “Chip” Small and has been funded by a US National Science Foundation CAREER grant focused on the effects of urban agriculture expansion and climate on nutrient cycling and loss in urban ecosystems.

Selected publications
Small, G.E., I. Jimenez, M. Salzl, P. Shrestha. 2020. Urban heat island mitigation due to enhanced evapotranspiration in an urban garden in Saint Paul, Minnesota, USA. WIT Transactions on Ecology and the Environment 243: 39-45.

Shrestha, P., G.E. Small, A. Kay. 2020. Quantifying nutrient recovery efficiency and loss from compost-based urban agriculture. PloS one 15: e0230996

Small, G.E., P. Shrestha, G.S. Metson, K. Polsky, I. Jimenez, A. Kay. 2019. Excess phosphorus from compost applications in urban gardens creates potential pollution hotspots. Environmental Research Communications 1 (9): 091007.

Shrestha, P., M.T. Salzl, I. Jimenez, N. Pradhan, M. Hay, H.R. Wallace, J.N. Abrahamson, G.E. Small. Efficacy of spent lime as a soil amendment for nutrient retention in bioretention green stormwater infrastructure. Water 11:1575

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OrganisationShow/Hide content