# Exploring the formation and function of anthropogenic soils > Dr. Yamina Pressler > Cal Poly, San Luis Obispo > Developed for the Western Chapter of the International Society of Arboriculture, Oct 6th 2023 # Learning Objectives >[!abstract] In this lecture we will... >- define anthropogenic and urban soils and their features >- evaluate the processes by which anthropogenic and urban soils form >- identify field observations and tools useful for interpreting anthropogenic and urban soils # Human impacts to soils are immense and ubiquitous General examples include: - agriculture - urbanization - climate change Specific examples: NRCS list of how humans impact urban soils[^1] [^1]: https://www.nrcs.usda.gov/conservation-basics/natural-resource-concerns/soil/urban-soils#research - dredge materials - accelerated erosion - land filling - land leveling - surface removal - contamination - sedimentation - windblown deep plowing/logging - severe compaction by machinery - artificial saturation # Agricultural land uses have led to net loss of soil organic carbon - Sanderman et al. 2017[^sanderman] estimated that 133 Pg C lost due to agriculture in the top 2 m of soil in the last 12,000 years, with losses increasing most dramatically in the last 200 years - There is potential to store more carbon in soils in regions where high "soil organic carbon debt" is present [^sanderman]: Sanderman, J., Hengl, T., & Fiske, G. J. (2017). Soil carbon debt of 12,000 years of human land use. _Proceedings of the National Academy of Sciences_, _114_ (36), 9575-9580. # Urbanization influences pedodiversity - Pedodiversity is the diversity of soil types in a region, typically defined by soil classification systems - An analysis by Amundson et al. 2003[^amundson] estimated rare and endangered soil types across the US and found evidence for loss of endemic soil types due to urbanization and agriculture - Rare soil types are common in California due to geologic and climatic diversity - Influence of urbanization on pedodiversity depends on the spatial scale at which you quantify urbanization. At a large regional scale, urbanization decreases pedodiversity[^amundson], but within a given city, urban development can increase pedodiversity due to the formation of novel urban soil types[^pindral] [^amundson]: Amundson, R., Guo, Y., & Gong, P. (2003). Soil diversity and land use in the United States. _Ecosystems_, _6_, 470-482. [^pindral]: Pindral, S., Kot, R., & Hulisz, P. (2022). The influence of city development on urban pedodiversity. _Scientific Reports_, _12_(1), 6009. # Humans as a soil forming factor soil = f (climate, organisms, topography, parent material, time, humans) - Human impacts to soil are unique compared to other soil forming factors - Humans also indirectly influence soil formation by altering soil forming factors (climate change, invasive species, agricultural crops, mining, etc) # Humans influence soil formation via altering the soil forming processes Four processes of soil formation are: - additions (material added to soil) - losses (material lost from soil) - translocations (movement of material within soil) - transformations (materials changing form within soils) # This leads to the formation of novel soil types Anthropogenic soil (aka Anthrosols*) - any soil body whose formation has been significantly influenced by long-term human activities (usually agricultural) Urban soil (aka Technosols*) - A soil that is dominated by human artifacts where materials have been moved by humans. Often occur in (sub)urban, industrial, and military settings. \* Anthrosols and Technosols are terms used in the [World Reference Base](https://www.fao.org/soils-portal/data-hub/soil-classification/world-reference-base/en/) system for soil classification More examples of Anthrosols: https://edepot.wur.nl/17686 # Urban soils arise from diverse human influences Human-altered and human-transported (HAHT) materials are formed by: - dredge materials - accelerated erosion - land filing - land leveling - surface removal - contamination - sedimentation - windblown deep plowing/logging - severe compaction by machinery - artificial saturation This was list compiled from [NRCS urban soil resources](https://www.nrcs.usda.gov/conservation-basics/natural-resource-concerns/soil/urban-soils#research) # Compared to "natural" soils, urban soils have... - higher bulk density (from compaction) - higher pH (from liming effect of building materials like concrete) - higher surface organic carbon content (from irrigation and amendments) - elevated concentrations of contaminants (heavy metals, organic pollutants) Based on Riddle et al. 2022[^riddle] [^riddle]:Riddle, R. L., Siebecker, M. G., Weindorf, D. C., Shaw, R. K., & Scharenbroch, B. C. (2022). Soils in urban and built environments: Pedogenic processes, characteristics, mapping, and classification. _Advances in Agronomy_, _173_, 227-255. # Even though urban soils are degraded, they can still provide ecosystem services - Morel et al. 2015[^morel] suggest that there is decreasing potential for urban soils to provide ecosystem services when soil are used as dumping sites, paved, or sealed, compared to soils that have pseudo-natural or engineered vegetation. - Ecosystem services provided by urban soils include provisioning of food and plant biomass, filtration of water, sequestration of pollutants and nutrients, storage of genetic materials, and recreational uses[^pindral] [^morel]:Morel, J. L., Chenu, C., & Lorenz, K. (2015). Ecosystem services provided by soils of urban, industrial, traffic, mining, and military areas (SUITMAs). _Journal of soils and sediments_, _15_, 1659-1666. # Soil biodiversity supports multiple ecosystem functions in urban greenspaces - Fan et al. 2023[^fan] conducted a study of 56 greenspaces (parks) around the world and found a positive relationship between soil biodiversity and multifunctionality of ecosystem services [^fan]: Fan, K., Chu, H., Eldridge, D. J., Gaitan, J. J., Liu, Y. R., Sokoya, B., ... & Delgado-Baquerizo, M. (2023). Soil biodiversity supports the delivery of multiple ecosystem functions in urban greenspaces. _Nature Ecology & Evolution_, _7_(1), 113-126. # How do we evaluate soil features in the field? - the soil profile is the basic unit of soil investigations - describing the soil profile allows for comprehensive assessment but isn't always possible due to logistical and expertise constraints - use of an auger or soil corer, or making surface assessments can also be useful # What should we look for in the field? When evaluating anthropogenic and urban soils, look for - abrupt and discontinous horizons - strongly contrasting colors & textures - clayey textures at the surface (indicating movement of subsurface material) - artifacts - evidence of compaction Based on Riddle et al. 2022[^riddle] # Abrupt horizon boundaries indicate recent human-aided transport When materials have been moved and deposited recently, obvious boundaries will persist between strongly contrasting materials Example: [Ladyliberty series](https://soilseries.sc.egov.usda.gov/OSD_Docs/L/LADYLIBERTY.html) (photo in Riddle et al. 2022[^riddle]) # Soil color indicates materials present - Minerals and organic matter are common pigmenting agents in soils - urban soils often have horizons with very different colors because the origins and mineralogy of materials are diverse - color can be used as a clue to the types of materials present in the soil # Soil color indicates environmental conditions - soils are darker when wet - saturated soils = reduced iron = gleyed (gray) colors - aerated soils = oxidized iron = reddish colors # How do we measure soil color in the field? - Color is identified visually using [Munsell color book](https://munsell.com/color-products/color-communications-products/environmental-color-communication/munsell-soil-color-charts/) - For more about soil color, check out my essay [[Soils are colorful natural wonders]] # Terra Preta soils form from long-term human organic matter inputs - Terra Preta soils form in the Amazon after long-term additions of partially combusted organic matter (e.g. charcoal). These soils harbor greater fertility than adjacent unamended tropical soils[^glaser] - Terra Preta soils spurred the interest in biochar as a soil amendment [^glaser]:Glaser, B., Haumaier, L., Guggenberger, G., & Zech, W. (2001). The 'Terra Preta' phenomenon: a model for sustainable agriculture in the humid tropics. _Naturwissenschaften_, _88_, 37-41. # Soil texture is one of the most important physical properties of the soil - texture is considered a "permanent property" of the soil because it arises from the processes of soil formation (weathering of rocks and minerals) - texture is difficult to change with management, so it is instead important to understand the limitations of a site given the inherent texture of the soil # How do we estimate soil texture in the field? - using texture by feel method to create ribbons of soil - longer ribbons = higher clay content estimate - sand feels gritty, silt is smooth, clay is sticky - practicing with many different soil types is the best way to get better at this skill # Soil texture controls behavior Soil texture controls the behavior of the soil including - water holding capacity - ability to store plant nutrients - susceptibility to erosion - drainage rate - pollutant leaching potential - compactibility among many others (see Brady and Weil 2019[^brady] for more) [^brady]:Brady and Weil. 2019. The Nature and Properties of Soil. Pearson. # Urban soil and prone to compaction - Compaction occurs in urban soils when material is moved, mixed, and compressed (e.g. during construction) - Compaction occurs in anthropogenic soils in agricultural context when soils are repeatedly tilled for may years and soil structure is broken - Compaction is an increase in bulk density, decreases aeration, and limited water infiltration # Human artifacts and debris Artifacts found in urban soils can include bricks, concrete and other building materials, ash, fibers, cloth, metals, and any other human-derived products Example: [Laguardia series](https://soilseries.sc.egov.usda.gov/OSD_Docs/L/LAGUARDIA.html), see photo from [Urban Soil Institute](https://urbansoils.org/nyc-soil-survey-profiles) # We can restore soil patches within urban landscapes Soils can be restored in small, but meaningful, patches - sidewalk trees - community gardens - green roofs - filled in swimming pools - rain gardens in parking lots Based on Byrne 2021[^byrne] [^byrne]:Byrne, L. B. (2021). Socioecological soil restoration in urban cultural landscapes. In _Soils and Landscape Restoration_ (pp. 373-410). Academic Press. # The land use history of a site should inform current restoration decisions - When it comes to urban soils, knowing the short term land use history of a site is as important as understanding the geologic context in which materials formed[^byrne] - Examples to consider: - abandoned gas stations - scrap yards - industrial areas # How can we restore degraded urban soils? Start by de-compacting and adding organic matter (e.g. compost)[^byrne] An urban afforestation experiment conducted in New York City by Oldfield et al. 2015[^old] found that compost increased stem volume and tree survival compared to non-composted sites. This effect depended on tree species and presence of shrubs. [^old]:Oldfield, E. E., Felson, A. J., Auyeung, D. N., Crowther, T. W., Sonti, N. F., Harada, Y., ... & Bradford, M. A. (2015). Growing the urban forest: tree performance in response to biotic and abiotic land management. _Restoration Ecology_, _23_(5), 707-718. # How can we use soil maps in urban areas? Urban soil mapping is limited but improving In CA, detailed urban soil maps are available for Los Angeles, San Francisco, San Mateo, San Jose Otherwise ^ indicates human-transported materials u indicates artifacts Access soil maps at https://casoilresource.lawr.ucdavis.edu/soilweb-apps/ Based on Riddle et al. 2022[^riddle] # Guiding questions for soil interpretations in urban contexts - What is the land use history of the site? - From where do the soil materials originate? - What are the physical, chemical, and biological properties of the soil? - What kinds of ecosystem services are we expecting the soil to provide? - Does the soil have the potential to provide these services? - How might inherent soil properties constrain tree selection, growth, or other restoration interventions? # Take home messages - Anthropogenic and urban soils are subject to the same soil forming processes, but have unique origins & properties due to human activities - Many soil properties are inherent. Knowing your soil allows you to understand potential constraints for plant growth and make decisions. - Quick field measurements (horizons, texture, color) and existing tools (soil web app) can aid soil interpretations # Additional Resources - NRCS urban soil fact sheet https://www.nrcs.usda.gov/sites/default/files/2022-11/Urban-Soils-Fact-Sheet.pdf - Presentation about urban soil survey in LA https://www.treepeople.org/wp-content/uploads/2020/09/Soil-Survey-in-Greater-Los-Angeles.pdf