Sustainable Agriculture Student Research Project

Introduction

Garden City Lands

• 55 ha of municipal parkland in Richmond
  • Purchased from federal government in 2010
  • Included in Agricultural Land Reserve in 1973
  • Used as a rifle range between 1904 and 1928, leading to soil contamination
  • Within the traditional territories of the Musqueam, Kwantlen, Semiahmoo, and Tsawwassen people, who likely harvested berries and medicinal plants from the site and used occasional controlled burns to prevent tree establishment
• Surrounded by dense urban development on three sides
• Situated at the western edge of the Greater Lulu Island peat bog
  • Peat is dominant soil
    • Shallow on west side
    • Deeper on east side

Image

• Bisected by dyke (Fig. 1)

  • Agricultural production on west side (18 ha)
    • Gradually being layered with clean, imported mineral soil fill
      • Address contamination concerns
      • Protect underlying peat from drainage and oxidation
  • Bog restoration on east side (31 ha)

Soil respiration

• Carbon dioxide (CO₂) emissions from soil, due to plant and microbial life below soil surface
  • Autotrophic respiration: CO₂ emitted by living plant roots
    • Dominant component of soil respiration when plants are sequestering carbon through photosynthesis, countering climate change (Rankin et al. 2022)
  • Heterotrophic respiration: CO₂ emitted by microbial decomposition of soil organic matter
    • Dominant component of soil respiration when soil is losing sequestered carbon, contributing to climate change
    • Positively correlated with soil temperature, aeration, and organic matter content (Wang et al. 2014)
    • Negatively correlated with water table depth (high water table reduces aeration) (Wang et al. 2014)

Objective

• Elucidate effects of the following management tactics on soil respiration at the Garden City Lands:
  • Dyking
  • Layering organic and mineral soil fill
  • Mowing vegetation

Methods

• Soil respiration was measured along the dyke at the Garden City Lands
  • Each sample measured CO₂ accumulation over 120 s in a 10 cm diameter chamber (SRC-2, PP Systems) connected to an infrared gas analyzer (CIRAS-3, PP Systems) on October 7, 2025

  • Image

    

    Samples collected from 18 replicate blocks, spaced at least 20 m apart, with 4 samples per block (n = 72)

    • 10 and 30 m east of dyke center (bog side)
    • 10 and 30 m west of dyke center (agriculture side)
  • Conditions sampled:
    • Bog side (n = 36)
      • Mowed (n = 12)
      • Unmowed (n = 24)
    • Agriculture side (n = 36)
      • Imported fill layered over peat (n = 20)
        • Peat layered over peat (n = 8)
        • Vegetated mineral soil layered over peat (n = 12)
      • Mowed vegetated peat without fill (n = 16)
  • Qualitative observations of vegetation and soil quality recorded at each sample site
• Soil volumetric water content measured in top 20 cm (FieldScout soil moisture meter, Spectrum Technologies) at each sample location in eight southern replicates (n = 32)
  • Mean calculated from five measurements per sample location
  • Sampled replicates excluded sections of dyke adjacent to filled areas 

Results

• Soil respiration rates (Fig. 3):
  • Mean: 8.8 ± 8.3 µmol m^-2 s^-1
  • Range: 0.9 - 45.3 µmol m^-2 s^-1

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• Higher soil respiration on west (agricultural) side of dyke than on east (bog) side (Fig. 4)
  • West side mean: 4.6 µmol m^-2 s^-1
  • East side mean: 9.5 µmol m^-2 s^-1

  • Image

    

• Higher soil respiration over organic fill than unfilled areas (Fig. 5)
• Higher soil respiration over mineral fill than mowed bog (Fig. 5)
  • Farm area planted with mowed grass over mineral fill had intermediate respiration between organic fill area and unfilled area
• No significant difference between:
  • Mowed and unmowed areas of bog
  • Unfilled areas on either side of dyke

Image

• Mean soil volumetric water content: 28.6 ± 6.3 % (Fig. 6)
  • No difference between dyke sides
  • No difference between mowed and unmowed areas of bog

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Discussion

• Our soil respiration observations did not distinguish between autotrophic and heterotrophic contributions to total respiration rate, but qualitative observations of soil quality and vegetation support several hypotheses for future testing:
  • High respiration rate from the areas covered in organic fill likely resulted from heterotrophic respiration of the freshly-deposited, aerobic soil, rich in organic matter
    • Some areas of organic fill had high emissions but no surface vegetation, suggesting low autotrophic respiration at those locations
  • Although peat has a high organic matter content, total soil respiration rates in the bog and in the unfilled agricultural areas were much lower than in the farm section filled with organic soil
    • Suggests that the bog is anaerobic, despite the similar volumetric water content on either side of the dyke
    • Low emissions suggest that bog is retaining peat
  • Most areas were vegetated, but the agricultural areas more often had green (i.e. actively photosynthesizing) plants when the study was conducted, suggesting that autotrophic respiration may have been higher these areas
  • Mowing had little or no effect on total respiration in the bog, suggesting that heterotrophic respiration was a large component of total respiration in the bog
• Further studies are needed at this site to distinguish between autotrophic and heterotrophic respiration and determine the site's overall contributions to climate change

Conclusion

• Vegetated fill on the agricultural side of the dike bisecting the Garden City Lands has higher respiration than bare peat on the bog side
  • The relative contributions of autotrophic and heterotrophic respiration are not known, but circumstantial evidence suggests that heterotrophic respiration is higher from the organic fill than from the peat bog
  • Sequestered carbon is more stable in the peat bog
  • Carbon in the organic fill was recently brought to the site, so its respiration does not represent loss of long-sequestered carbon from on-site photosynthesis
• Because this is an observational study we cannot make definitive statements about cause and effect, but the differences in soil respiration observed between different management zones suggest areas for further study:
  • Time series data are needed to determine whether differences persist seasonally, and whether emissions fall as the fresh organic fill settles and ages
  • Studies designed to distinguish between autotrophic and heterotrophic respiration will provide insight into likely effects of different management tactics on climate change
• These data provide a valuable baseline for future comparisons

Acknowledgements

• Talia Parfeniuk and Rue Bandanic received a KPU Student Research and Innovation Grant to support this work

References

1. Rankin TE, Roulet NT, Moore TR. 2022. Controls on autotrophic and heterotrophic respiration in an ombrotrophic bog. Biogeosciences. 19(13):3285–3303. doi:https://doi.org/10.5194/bg-19-3285-2022.
2. Wang X, Liu L, Piao S, Janssens IA, Tang J, Liu W, Chi Y, Wang J, Xu S. 2014. Soil respiration under climate warming: differential response of heterotrophic and autotrophic respiration. Global Change Biology. 20(10):3229–3237. https://doi.org/10.1111/gcb.12620

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