Unsealed Soil Research Articles

Engagement with Urban Soils Part II: Starting Points for Sustainable Urban Planning Guidelines Derived from Maya Soil Connectivity

Using the Precolumbian lowland Maya model of urban soil connectivity discussed in Part I, we review how soil connectivity can transition into urban planning policy and, by extension, could ultimately become codified as vantages and guidelines for urban design. In Maya agro-urban landscapes, the interspersion of open and green space with construction and paving provides edges (or interfaces) between sealed and unsealed soils at which the potential for soil connectivity manifests. These edges create an undeniable opportunity for urban planning to determine methods, guidelines, and conditions that can enhance soil connectivity. We argue that adequate attention to soils in urban sustainability goals would counteract misconceptions about the compact city paradigm and compensation for soil sealing in urban practice. Through preserving and increasing urban soil availability, proximity, and accessibility, advisory policies can stimulate shared values and everyday behaviours that reinforce the responsible and productive use of urban soils. Such urban planning can enable and encourage widespread participation in urban soil management. To promote policymaking on urban soils, we assess the importance and challenges of using urban green space as a proxy for the presence of urban soils. Our review suggests that urban green space offers high potential for use in urban planning to develop habit architectures that nurture soil-oriented pro-environmental behaviour. However, we also acknowledge the need for consistent and systematic data on urban soils that match sustainable urban development concepts to assist the effective transition of soil connectivity into urban planning codifications. Formulating adequate soil-oriented planning guidelines will require translating empirical insights into policy applications. To this end, we propose methods for enhancing our understanding and ability to monitor urban soil connectivity, including onsite surveys of land-use and bottom-up experience of soils, the mapping of the edges between sealed and unsealed soils, and using landscape ecological scales of analysis. In conclusion, we position soil care and connectivity as a primary task for urban planning and design and digest our findings and empirical vantages into concrete starting points devised as instruments to support urban planning in achieving soil codification.

The effects of sealing on urban soil carbon and nutrients

Abstract. Urban soils are of increasing interest for their potential to provide ecosystem services such as carbon storage and nutrient cycling. Despite this, there is limited knowledge on how soil sealing with impervious surfaces, a common disturbance in urban environments, affects these important ecosystem services. In this paper, we investigate the effect of soil sealing on soil properties, soil carbon and soil nutrient stocks. We undertook a comparative survey of sealed and unsealed green space soils across the UK city of Manchester. Our results reveal that the context of urban soil and the anthropogenic artefacts added to soil have a great influence on soil properties and functions. In general, sealing reduced soil carbon and nutrient stocks compared to green space soil; however, where there were anthropogenic additions of organic and mineral artefacts, this led to increases in soil carbon and nitrate content. Anthropogenic additions led to carbon stocks equivalent to or larger than those in green spaces; this was likely a result of charcoal additions, leading to carbon stores with long residence times. This suggests that in areas with an industrial past, anthropogenic additions can lead to a legacy carbon store in urban soil and make important contributions to urban soil carbon budgets. These findings shed light on the heterogeneity of urban sealed soil and the influence of anthropogenic artefacts on soil functions. Our research highlights the need to gain a further understanding of urban soil processes, in both sealed and unsealed soils, and of the influence and legacy of anthropogenic additions for soil functions and important ecosystem services.

Assessing soil ecosystem services in urban and peri-urban areas: From urban soils survey to providing support tool for urban planning

The current practice of urban planning does not pay proper attention to the quality of urban soils, to their multiple functions and to the supply of ecosystem services to the urban population. The purpose of this paper is to contribute to raising awareness about the role of soil in the built-up environment, to provide tools to assess and map urban soils ecosystem services and to highlight the possibility of integrating soil knowledge into urban planning.Within the framework of the EU funded project SOS4LIFE - Save Our Soils for LIFE, we surveyed, sampled, analyzed and mapped the soil of the city of Carpi (NE Italy), integrating the existing knowledge about soils and land use with the urban plan, and providing the basis for the production of a 1:5,000 map of urban soils. Soil data interpolated over the entire case study area provided the inputs for locally calibrated pedotransfer functions whose outputs were used to assess a set of six indicators of ecosystem services supply: soil biodiversity, buffer capacity, carbon storage, agricultural production, water regulation, and water storage. Maps of the six ecosystem services are presented along with an overall urban soil quality map based upon the number of service hotspots per unit area of unsealed soil. Results show that for a number of services, hotspots occur not only in the peri-urban agricultural areas but also in unsealed soils within the urban fabric, and that different soils provide high quality services in diverse constellation depending on soil characteristics and degree of sealing. We estimated that the unsealed soils of the green areas within the city (193 ha) store within the first 30 cm of depth 15,067 Mg of organic carbon (55,246 Mg CO2 eq.) corresponding to an average carbon density of 78.0 Mg ha−1, which is significantly higher than the corresponding average of the agricultural soils of the area (43.4 Mg ha−1). Furthermore, thanks to their high available water capacity they store up to 58,682 m3 of water, corresponding to 304 m3 ha−1.Our approach can contribute to making soils and their ecosystem services an integral part of the urban planning process, and an example of its application is provided in order to highlight the impact of planning decisions of the joint provision of soil ecosystem services.

The Fourth Regime of Open Space

This article reinterprets open space as the theatre of adaptive regimes in the interfering wakes of two major waves of transformation: the agricultural and the urban transformation. The aim of the wave regime concept is to accommodate traditional and emerging land uses in a logical scheme of co-existing regimes separated by transition waves in space and time. Each wave corresponds to a transitional stage from one set to another set of value regime, which by the agents of the transformation is interpreted as a major value increase. The current struggle for space and the difficult interpretations of quality and sustainability can be explained as expressions of competition between value regimes. These value regimes tend to be driven and perpetuated by customary paradigms of land-use planning and management (urban planning, ecology, agronomy, etc.). Land-use sectors ask for rather unambiguous definitions and clear use rights of land use categories and zoning, leaving limited possibility for interaction, mixed regimes and innovative multifunctional land-use. New service demands, new sustainability and resilience urgencies challenge these customary land-use planning paradigms and their rules and instruments. This paper acknowledges a third wave and consequent fourth regime. This regime seeks overall increased sustainability and resilience in open spaces, stressing the strategic importance of unsealed soils and other life conditioning substrates. Different existing land-use models, such as “transition towns”, “agroforestry” and many more, can be interpreted as fourth regime examples, but altogether there is a need for more coordination or integration to turn the third wave concept into a real “wave”. A specific target is to scan territories for characteristics and values according to the prevailing regimes, and assess each unit in terms of third wave transition opportunities, even within active uses that may be at odds with customary rules and expectations. This is illustrated for cases of illegal intake of farmland for non-agricultural activities and for domestic gardens as a missing category in customary rural and land use policy.

Soil sealing and unsealing: State of the art and examples

AbstractSoil sealing for urban and infrastructure development constitutes the most intense form of land degradation and affects all ecosystem services. Researchers and policy makers have become aware of this fact and call for limiting development and compensating for new soil sealing with unsealing measures. In a literature review, we found that the state of research about the impacts of soil sealing is far more advanced than about the potential and prerequisites of unsealing. In practice, soil restoration after mining and construction activities as well as redevelopment or renaturation of abandoned industrial sites are increasingly important issues, but systematic research on the success of soil unsealing and restoration is rare. In particular, the development of soils and vegetation after unsealing and restoration measures as well as their potential to provide ecosystem services need more detailed investigation.In 3 case studies, we demonstrate that replacing a sealed surface with soil to restore ecosystem services is always beneficial for humans and nature. An indicator‐based mapping approach revealed the potential performance of different ecosystem services at former industrial sites in Switzerland. When unsealed sites are transformed to pioneer habitats, the intended vegetation may successfully be regained, but landscape connectivity is hardly enhanced due to increased overall landscape fragmentation. Our investigations show that with the techniques currently applied, the soil physical parameters in a restored agricultural soil developed favourably for crop growth within 15 years. However, unsealed soils are anthropogenic soils with reduced multifunctionality, and protecting natural soil against sealing is always the better option.

Degradation of the urban ecosystem function due to soil sealing: involvement in the heat island phenomenon and hydrologic cycle in the Tokyo metropolitan area

ABSTRACT We reviewed the role of the soil function of urban green space in mitigating the heat island phenomenon and urban flood damage, which are important issues in the modern urban environment. Urban sprawl has progressed remarkably in the southern part of the Kanto District of Japan, especially since the 1960s. The grassland/bare land area ratio in the center of Tokyo was more than 70% in the 1930s but less than 40% in 1990. On the other hand, the paving area ratio was ~2% in the 1930s but more than 10 times that amount in 1990. Thus, cities, such as Tokyo, in the southern part of the Kanto District have been significantly sealed soil throughout time, and the heat island phenomenon has intensified. Urban green space helps to mitigate the heat island phenomenon based on the water retention and heat dissipation function of plants and unsealed soil. A cool island effect was reported during summer days in urban green spaces in Tokyo. The mitigation of the heat island effect seems to be large, even when conditions, such as the park area, land use, afforestation area ratio, and soil type, differ. Soil sealing and compaction affect urban flooding by hindering the penetration of rainwater and increasing surface runoff. According to a survey in the hilly basin (1 km2) of the western part of Tokyo, the proportion of farm- and forestland decreased due to development. The urban area increased from ~10% in the 1970s to ~60% in the 1980s. As a result, the flood arrival time shortened. Green spaces have a high rainwater permeability. The forest soil structure and presence of O horizons further increase the permeability. By promoting permeability to the underground, it is possible to reduce and delay the water runoff on the land surface. To develop urban green space as green infrastructure, it is necessary to accumulate more information on the current situation and agenda for the future of urban green space.

Environmental and geochemical assessment of sealed soils in the Eastern Moscow

Sealed with road coverings soils in the Eastern Administrative District (EAD) of Moscow were studied, their morphological and physico-chemical properties have been established in various landuse zones, their ecological and geochemical state and level of readily soluble salts and priority organic pollutants - petroleum products (PP) and benzo(a)pyrene (BaP) as compared with background and open urban soils. The article is based on the results of soil-geochemical survey of ekranozems in September 2016 and previously obtained analytical data from an unsealed territory in the southern part of the EAD. A mapping technique was developed and a map of degree of soil sealing in the EAD was compiled. The morphological features and the basic properties of ekranozem’s horizons in different land-use zones of the EAD were determined. They have a low content of organic matter (2,24%), an alkaline pH (8,0), light loamy texture. Despite the use of de-icing salts and mineral fertilizers, the upper part of the profile of the sealed soils is not saline, salts accumulate mainly in the middle and lower parts of the profile, forming maxima in the RAT horizon. Screening of soils with asphalt concrete is not an obstacle to the penetration of technogenic flows of polluting substances - salts, PP, BaP, capable of accumulating in increased concentrations and forming pronounced technogenic anomalies. The average BaP content in the sealed soils exceeds the background level by 56 times, and the MPC - by 9,6 times. The permissible content of PP in ekranozems is exceeded by 9,5 times. However, in comparison with unsealed soils, the content of BaP and PP in ekranozems is 3,5 times less. The vertical distribution of the BaP is, as a rule, uniform, with the exception in the industrial zone, and for the PP it is accumulative with several well-defined maxima in different parts of the profile. As a result of lateral migration, BaP and PP accumulate in the sealed soils of the lower parts of the slopes, where they form accumulations on organomineral and sorption-sedimentative geochemical barriers. High-level man-made accumulations of hydrocarbons are formed mainly in the sealed soils of industrial and transport zones. When opening the asphalt, risks associated with the migration of hydrocarbons to other components of the landscape, including them in the biological cycle and food chains may appear.

Influence of the soil sealing on the geoaccumulation index of heavy metals and various pollution factors

Soil sealing belongs to the most destructive and damaging processes to the soil environment. Soil sealing interrupts or greatly restricts the exchange of matter and energy between the biosphere, hydrosphere, and atmosphere and the soil environment. The aim of this study was to compare the content of heavy metals (Cd, Cr, Cu, Hg, Fe, Ni, Pb, Zn) of Ekranic Technosols by applying indicators such as geoaccumulation index (Igeo), enrichment factor (EF), and pollution load index (PLI), which allowed to determine quantitatively the impact of the soil sealing degree on the content of heavy metals and to distinguish natural from anthropogenic sources of origin of heavy metals. In general, 42 soils from different parts of the city of Toruń (NW Poland) were sampled and divided into three groups according to the degree of soil sealing: completely sealed with asphalt or concrete (A), semi-permeable (partially sealed with cobblestones and concrete paving slabs (B)), and reference (non-sealed) (C). The results indicate that the artificial sealing in urban areas slightly affects the content of heavy metals in soils. However, based on PLI, Igeo, and EF, it was found that the sealing has influence on soil properties and unsealed soil is the most exposed to the accumulation of pollutants.

The effect of soil surface sealing on vegetation water uptake along a dry climatic gradient

Soil surface sealing is a widespread natural process occurring frequently in bare soil areas between vegetation patches. The low hydraulic conductivity that characterizes the seal layer reduces both infiltration and evaporation fluxes from the soil, and thus has the potential to affect local vegetation water uptake (VWU). This effect is investigated here using experimental data, 2-D physically based modeling, and a long-term climatic data set from three dry sites presenting a climatic gradient in the Negev Desert, Israel. The Feddes VWU parameters for the dominant shrub at the study site (Sarcopoterium spinosum) were acquired using lysimeter experiments. The results indicate that during the season surface sealing could either increase or decrease VWU depending on initial soil water content, rainfall intensity, and the duration of the subsequent drying intervals. These factors have a marked effect on interannual variability of the seal layer effect on VWU, which on average was found to be 26% higher under sealed conditions than in the case of unsealed soil surfaces. The seal layer was found to reduce the period where the vegetation was under water stress by 31% compared with unsealed conditions. This effect was more pronounced for seasons with total rainfall depth higher than 10 cm/yr, and was affected by interseasonal climatic variability. These results shed light on the importance of surface sealing in dry environments and its contribution to the resilience of woody vegetation.

The soil–water system as basis for a climate proof and healthy urban environment: Opportunities identified in a Dutch case-study

One of the effects of climate change expected to take place in urban areas in the Netherlands is an increase in periods of extreme heat and drought. How the soil can contribute to making cities more climate proof is often neglected. Unsealed soil and green spaces increase water storage capacity and can consequently prevent flooding. The planning of public or private green spaces can have a cooling effect and, in general, have a positive effect on how people perceive their health. This paper reviews existing guidelines from Dutch policy documents regarding unsealed soil and green spaces in the Netherlands; do they support climate adaptation policies? Scientific literature was used to quantify the positive effects of green spaces on water storage capacity, cooling and public health. Finally we present a case study of a model town where different policy areas are linked together. Maps were made to provide insight into the ratio of unsealed soil and the number of green spaces in relation to existing guidelines using Geographical Information Systems (GIS). Maps marking the age and social-economic status of the population were also made. The benefits of green spaces are difficult to express in averages because they depend on many different factors such as soil properties, type of green spaces, population characteristics and spatial planning. Moreover, it is not possible to provide quantifications of the benefits of green spaces because of a lack of scientific evidence at the moment. Based on the maps, however, policy assessments can be made, for example, in which site a neighborhood will most benefit from investment in parks and public gardens. Neighborhoods where people have a low social-economic status have for example fewer green spaces than others. This offers opportunities for efficient adaptation policies linking goals of several policy fields.

Effect of Rainfall-Induced Soil Seals on the Soil Water Regime: Drying Interval and Subsequent Wetting

The effects of rainfall-induced soil seals on drying processes and on infiltration following drying intervals are simulated for two different soils, a loam and a sandy loam. The simulated drying processes include water content redistribution without evaporation and under a constant evaporation rate of 5 mm day−1. During evaporation, the water content at the seal surface decreases rapidly. A high water content gradient develops within the seal, which increases along the drying interval. It indicates that, at least during the first hours of drying, the seal layer fulfilled all the evaporation demand and therefore dries faster that an unsealed soil where the evaporation is supplied by a much deeper zone of the soil profile. This phenomenon is more accentuated in the loam than in the sandy loam soil. Considering the subsequent infiltration curves during rainfall following different drying intervals, the ponding time and the post-ponding infiltration rates increase when the antecedent drying period is longer, but no significant effect on the final infiltration is found following drying intervals of few days. Also, the water content at the sealed soil surface before rainfall seems to play a major role on infiltration. Very close infiltration curves were obtained after different drying intervals that ended with similar surface water content.

Infiltration during soil sealing: The effect of areal heterogeneity of soil hydraulic properties

The combined effects of soil surface sealing and areal heterogeneity of the soil hydraulic properties on the mean infiltration curve are studied here for the first time. Seal formation during rainfall is simulated according to the dynamic model of Assouline and Mualem [1997]. Areal heterogeneity is represented by lognormal distribution of the saturated hydraulic conductivity of the initially undisturbed soil and by related distributions of the other soil parameters. The mean infiltration curve of the heterogeneous field is evaluated presuming that horizontal fluxes are negligible. It is found that when soil surface sealing is taken into account in a heterogeneous field, the ponding time is only slightly affected. However, significantly more runoff is produced compared to nonsealing field (mulched), with the relative area contributing to surface runoff being increased from 65 to 95%. The relative effect of field heterogeneity on the infiltration curve increases for higher rainfall intensity. The formation of soil surface seal apparently reduces the effect of the field areal variability on the steady infiltration rate. The infiltration rate after 60 min of rainfall distributes lognormally under sealing conditions, while it distributes normally in the case of the unsealed soil. The final infiltration rate resulting from the assumption of a sealed uniform field is underestimated compared to sealed heterogeneous field, with the relative effect being larger for a loam soil (−51%) than for a sandy loam soil (−26%). Also, the approximation that the infiltration curve is a unique function of cumulative rainfall independent of rainfall intensity is not valid in a sealing heterogeneous field, and its application in such a case would be more erroneous than in uniform fields. On the other hand, one may disregard the variability of all soil parameters, except the hydraulic conductivity, when calculating infiltration.

Compaction, Aging, and Raindrop‐Impact Effects on Hydraulic Properties of Saline and Sodic Vertisols

AbstractVertisols markedly swell and disperse when wet because of the high percentage of montmorillonite in the soil. We hypothesized that soil bulk compaction, time since soil wetting (aging), and raindrop impact affect seal formation, soil permeability, and salt leaching of Vertisols. Vertisol (Typic Chromoxererts) samples with exchangeable Na percentages (ESP) of 0.4 and 11.8 were subjected to simulated rainfall of deionized (DW) and saline (SW) (electrical conductivity [EC] = 5 dSm‐1) waters with 0 and 18.1 J mm‐1 m‐2 impact energies. In a Vertisol without aging (0.5 h of prewetting) and under zero compaction, subjected to DW and SW rainfall, seal formation controls the soil permeability. Under DW rainfall, the final infiltration rates (FIR) of the sealed and unsealed Vertisol samples were 6 and >44 mm h‐1 at ESP 0.4, and 5 and 17 mm h‐1, respectively. Four days of aging without compaction, followed by DW rainfall, increased the FIR of unsealed soil to 37 and to >44 mm h‐1 at high and low ESP, respectively, and that of sealed soil to 12 and 14 mm h‐1 at high and low ESP, respectively. Subjecting wet soil to pressure up to 800 kg m‐2 decreased the unsealed Vertisol FIR under DW rainfall to 8.9 and 27 mm h‐1 at high and low ESP, respectively. Seal formation and bulk compaction had little effect on salt leaching in the low‐ESP soil. Under bulk compaction or seal formation, the high‐ESP soil leachate EC decreased from 10.7 to 9.0 dS m‐1 after 300 mm of DW rain.

Surface seal micromorphology as affected by fluidized bed combustion bottom-ash

Amendments that alter clay dispersion and aggregate disintegration also change soil porosity and sealing. Soils selected for this study had increased (Mollisol, Oxisol, and Vertisol), decreased (Oxisol), or non-affected (Oxisol and Ultisol) water infiltration when fluidized bed combustor bottom-ash (FBCBA) was surface applied to decrease dispersion. Soil was sieved to pass 8-mm, packed into small erosion pans, prewetted by capillarity, and subjected to 110 mm h −1 simulated rain until steady state infiltration. Image analysis was used to quantify crust morphology, porosity and characteristics of the seal and the unsealed soil below it. A conspicuous feature was a structural crust at the surface with a continuous dense layer of lesser porosity and smaller pores than uncrusted soil. The seal showed no evidence of a “washed-in” zone of illuvial clay in the control treatment, although dispersed clay was observed in the percolating water for some soils. Where FBCBA was effective in increasing water infiltration, an increase in total porosity attributed to planar pores was observed. A sandy loam Oxisol was the least prone to sealing. For this soil, a considerable amount of dispersed clay was observed in the control, while FBCBA rapidly flocculated clay and formed an illuvial clay layer, lowering infiltration. A layer of eluvial silt and fine sand was observed at the surface of soils where considerable dispersion occurred on non-treated soils. Differences in steady-state infiltration could not be explained by the variation in total porosity or pore shape. Spatial variability, pore continuity, and expansion/contraction of clays obscure any relationship with an averaged infiltration even on a small plot.

The hydrological response of soil surfaces to rainfall as affected by cover and position of rock fragments in the top layer

AbstractRainfall experiments have been conducted in the laboratory in order to assess the hydrological response of top soils very susceptible to surface sealing and containing rock fragments in different positions with respect to the soil surface. For a given cover level, rock fragment position in the top soil has an ambivalent effect on water intake and runoff generation. Compared to a bare soil surface rock fragments increase water intake rates as well as time of runoff concentration and decrease runoff volume if they rest on the soil surface. For the same cover level, rock fragments reduce infiltration rate and enhance runoff generation if they are well embedded in the top layer. The effects of rock fragment position on infiltration rate and runoff generation are proportional to cover percentage. Micromorphological analysis and measurements of the saturated hydraulic conductivity of bare top soils and of the top layer underneath rock fragments resting on the soil surface reveal significant differences supporting the mechanism proposed by Poesen (1986): i.e. runoff generated as rock flow or as Horton overland flow can (partly) infiltrate into the unsealed soil surface under the rock fragments, provided that they are not completely embedded in the top layer. Hence, rock fragment position, beside other rock fragment properties, should be taken into account when assessing the hydrological response of soils susceptible to surface sealing and containing rock fragments in their surface layers. A simple model, based on the proportions of bare soil surface, soil surface occupied by embedded rock fragments, and soil surface covered with rock fragments resting on the soil surface, describes the runoff coefficient data relatively well.

Micromorphological study of surface seals developed under simulated rainfall

Soil surface seals were formed on microplots of homogeneous soil in the laboratory using simulated rainfall. The soil horizons studied varied in texture and organic matter content. The surface sealing was quantified by monitoring changes in infiltration rate, splash detachment and near-surface shear strength with time. The porosity of the resulting surface seals and unsealed soil material was studied in the laboratory using image analysis of thin sections. Various sealing indices demonstrated that the A horizons of the soil sealed to a greater extent than the corresponding Bt horizons. In general, as sealing increased, soil loss decreased from the microplots. Total porosity of the soil surface seal did not explain differences in infiltration rate, splash detachment or strength well; however, the percentage of planar pores was more related to the final infiltration rate. Different morphological types of surface seals could be found in the soils that were representative of various sealing processes. Even though some soils had a considerable amount of water-dispersible clay, the downward translocation of clay was a minor process. A more important process was the physical breakdown of aggregates and the accompanied compaction of the surface resulting in a zone with a lower percentage of planar pores. The primary particle size of the soil was a poor indicator of the soils' susceptibility to surface sealing, whereas, the water dispersible particle size, particularly the silt size distribution, was a good indicator of its sealing behavior.