1 Introduction

1.1 Burial land as an element of the urban area structure

The current population of the World – 8.05 billion represents about 7% of the total number of humans ever living on Earth. The whole number is estimated to be close to 117 billion (Kaneda et al. 2022). In 2022 67.1 million men died (about 150,000 per day). According to UN projection, the number of humans who will die in 2023 will decrease to about 60.8 million, but will steadily increase in the following years, reaching 91.6 million in 2050 and 122.8 million humans in 2100 (UN 2022). In parallel, the share of the urban population in the total population is increasing, 2020 – 56.2%, 2050 – 68.4%, 2100 – 85% (EC 2020; UN 2022). This means that most of the projected deaths will involve urban residents, who need to be provided with dignified resting places. To obtain new burial sites, current cemeteries are enlarged, generally by no more than 1 ha in area at a time (Długozima and Rej 2014). More space is also being acquired for new burial sites (Scalenghe and Pantani 2020).

Cities existing almost all around the World have a history of many centuries, sometimes thousands of years. This implies a large number of generations that lived and died in each city, resulting in the need to organize burial sites. They were at the very beginning implemented in various ways, occupying sites both inside and outside cities (Długozima 2011; Buell and McEnroe 2018; Ratti 2021; Szuro 2022). The last mentioned were placed near the city limits for reasons of providing easy access, but also far from them, sometimes due to fear of the phenomenon of death and of the dead ones as well. Since burial sites were usually treated as hallowed (with exceptions, resulting, for example, in the disposal of municipal waste on their grounds (Ariès, 1989; Klima et al. 2019; Colleter and Barreau 2021), subsequent burials on every area were carried out for a long time. In the course of urbanization and suburbanization, initially non-urban cemeteries became elements of their internal structure, often already with changed functional and spatial characteristics. The former burial areas in route of a subsequent development became often areas of multifunctional greenery (Wieczorek 2019; Grabalov and Nordh 2021; Nordh et al. 2023). The greenery of cemeteries takes a very different form, occupying different places in the overall establishment. Lawns, which are maintained in very good condition, cover a large part of Scandinavian (Nordh et al. 2023) and German (Długoński et al. 2022) burial land.

Former cemeteries, closed during different periods of the cities' existence, have a special place in the urban space. Their modern form of use depends mainly on the location in relation to the development and the desire to reflect history in the outline of the modern city. It also corresponds with the general approach to the spheres of the sacred and profane. Of the total area of the Ohlsdorf Cemetery in Hamburg, Germany, exceeding 400 hectares, 200 hectares are currently being used, which has provided an opportunity to initiate a functional and spatial change of the remaining part. To this end, implementation of a comprehensive program for the cemetery, dubbed “Ohlsdorf 2050”, has begun (Hamburger Friedhöfe 2023a,b). Other cemeteries have also been transformed into an urban park, i.e.: in the Berlin district of Neukölln the Anita Berber Park was formed on a former burial land (Kowarik 2020), in Zielona Góra, Poland, the Green-Cross Cemetery (Grün-Kreuz Friedhof) was transformed into Millennium Park and the New Holy Trinity Cemetery (Dreifältigkeitsfriedhof II) – into the district pocket park (Greinert and Drozdek 2015). Others, such as the Innocents' Cemetery in Paris, France (Landru 2012), and Holy Trinity Cemetery in Zielona Gora, Poland (Greinert and Drozdek 2015), have been transformed into town squares.

1.2 Soils of urban cemeteries position and characteristics

The history of cities development has been characterized by great dynamism (UN 2018). Hence, many areas, including cemeteries, have changed (sometimes repeatedly) the form of land use. Over time, many cemeteries have disappeared from human consciousness, making them seem absent. Earthworks carried out in settled areas indicate the continued presence of remnants in the modern urban fabric. Others were characterized by repeated use of the same burial sites, which has the effect of systematically transforming the newly forming soils (Cohen 2019; Grabalov and Nordh 2021). The organization of a cemetery has the effect of clearing the surface of various elements of previous development, mainly vegetation. During tree and shrub clearance work, soil profiles are deeply disturbed. The indiscriminate nature of the work in practice makes it impossible to carry out selective management of excavated soil materials. This leads to the mixing of materials with different characteristics. When the terrain is uneven, its levelling is carried out. In the course of it, smaller depressions are backfilled and larger slopes are terraced. Deficiencies in soil materials are made up by applying them from outside the treated area. For an interesting landscape and the effect of "naturalizing the cemetery area", height forms – hills, elevations, embankments – are also piled up (Stockholms Stad 2023). Also by this route, some of the imperfections of the native soil are removed – the sanding of overly compacted soils. Sites for the location of buildings and other architectural structures are prepared by constructing their foundations. Buildings are equipped with utilities. The entire area of the cemetery is also prepared in terms of networking, usually supplying water and electricity, and receiving sewage.

In urban areas, areas even temporarily used as burial grounds have undergone a number of land surface and soil transformations both during the preparation of the burial site, its operation and after its closure (Lins and Lins 2020). From among environmental effects, there are those relating to the transformation of geomorphology:

  • Levelling of the terrain;

  • Terraces formation;

  • Creation of artificial mounds;

  • Local depressions backfilling;


and soils:

  • Soil profile decapitation;

  • Admixture of waste to soil;

  • Deep mixing;

  • Sealing with impervious surface;

  • Covering the soil with human transported materials (HTMs);

  • Compaction;

  • Contamination.

The construction works carried out were of different nature by which the changes affected only topsoil, horizons including subsoil or the entire soil profile. Hence, the soils of former cemeteries more or less resemble Regosols and Technosols today similar to other locations not historically associated with this specific form of land use.

The soils of long-used cemeteries take on characteristics resulting from natural soil-forming processes. A typical feature is the formation of a humic horizon in the topsoil. At the same time, both topsoil, subsoil and bedrock can contain various materials, both natural and anthropogenic. Due to the different course of land use of the cemetery itself, as well as adjacent areas, the following materials may be present in soil: coal, sands or gravel used for road and path construction, mortar, ashes, slag, construction debris and wood residues, metals, gypsum (Schmidt-Bartelt et al. 1990).

The soils of cemeteries show a number of transformations typical of activities carried out in settlement areas. However, they also have a special dimension due to the presence of human remains in them. This is not always reflected in the description of these soils, even in well-recognized areas. This causes difficulty in assessing the availability of urban areas associated with former burial land for investors.

Land preparation for new burial sites is characterized by some flexibility only when new cemeteries are established. Existing plots do not always exhibit favourable soil conditions. In this context, the presence of diverse materials (both natural and anthropogenic) with different characteristics, including air and water permeability, is noted (Schmidt-Bartelt et al. 1990; Mengede and Burghardt 2003). Sometimes, due to the movement of fine mineral particles along with infiltrating water, lenses, layers or veins of closely adhering grains are formed, constituting diffusion barriers to air and water. In a consequence the air capacity of such horizons can be extremely low, with pF 0–1,8. In such conditions, gleyic horizons are formed with a clear dominance by reduction and anaerobic decomposition processes, often occurring after intense, prolonged rainfall. In the course of digging a burial pit, the continuity of soil pores is disrupted. Also, when backfilling a grave cavity with mechanical equipment, excessive compaction of soil material can occur (Mengede and Burghardt 2003). On the other hand, the soil profile may contain materials that are highly permeable to air and water, including gravels, stones and coarse sands (Schmidt-Bartelt et al. 1990). The possibility of unrestrained gas exchange, in addition to the grain size composition and degree of compaction, is also limited by the materials presence with a high water capacity, when saturated (Mengede et al. 2001). Environmental problems, including those belonging to the group of sanitation issues, are emerging, hindering and sometimes preventing the normal operation of cemeteries. The example of Bochum indicates that problems caused by waterlogged soils are large in some cases – they have been noted in varying degrees for 17 of the 21 cemeteries in use (Schmidt-Bartelt et al. 1990). Also at the New Communal Cemetery in Zielona Gora, the problem of prolonged sinking of graves after heavy rains was noted, after inadequate preparation of the area covered with grainsize diversified silty sands.

Fundamental considerations for the location of cemeteries are the depth of the soil profile to the level of solid rock (Dippenaar and Brouwers 2018; Dippenaar and Olivier 2018), the nature of this rock (continuity, degree of fracturing, stability), soil characteristics (including its microbial activity and neutral reaction), water relations (including groundwater level variability), location in the relief (slope of less than 15%, but possibly not on completely flat areas due to defects in rainwater runoff), and existing plant communities (Uslu et al 2009; Długozima 2020). Earth burials are placed at a legally sanctioned depth. Single graves are excavated to a depth of up to 1.8 m, and double graves are excavated to a depth of 1.8–2.1(2.2) m. The organization of such a site is ordered to be established before the first burial. In exceptional cases, the pit can be deepened after exhumation (Van Allemann et al. 2019). For the organization of cemeteries, areas with simple sandy soils that are well aerated are most often chosen, which is expected to promote the decomposition of bodies for up to 20 years (Charzyński et al. 2011). At the same time, the decomposition process takes place at a rate that does not allow a large amount of leachate to form in a short period of time. When backfilling graves, it is recommended that the material be not deeply compacted to achieve mechanical stability while ensuring the freedom of movement of water and air in the deposited soil materials (Schmidt-Bartelt et al. 1990). In many countries, the goal of making an earth grave is to dig a pit with average dimensions of 200 × 80 cm, to a depth of 100–150 cm. Approximately 2 m3 of earth is dug during the work. At the same time, the location of burials at a certain depth affects the achievement of the expected air and water conditions. A shallower burial allows the burial to be located in a zone of good aeration and better gas exchange. The depth of the burial generally influences its placement in soil material with higher moisture content (Mengede and Burghardt 2003). After burial, the grave is backfilled with mixed soil material. The tombstone is placed on the surface. The soil surface is not treated with pesticides and insecticides. This does not preclude conducting chemical protection of cemetery plants (Uslu et al. 2009). In pre-war European cemeteries, stelae were made of stone, usually unpolished. After World War II, in Poland and other Central European countries, gravestones and steles were made mainly of cement and terazzo (cement with decorative rock aggregate). Today there has been a return to natural materials (mainly granite and marble), very often imported from distant countries, mainly China and Turkey. These are laid on reinforced concrete bearing elements, after the ground has stabilized. Thus, unlike in Middle Eastern countries, burial pits are usually not masonry. This is the case with large family tombs. Decorations and candles placed on tombstones, made of glass and plastic, are a separate item (Pilarczyk and Nowak 2019).

In the course of burial organization, bodies were deposited in different soils, at different depths and in different numbers. Hence, chemical transformation of ground and surface water caused by leachates is possible. As a consequence of capillary and groundwater level rise, it is also possible for derived substances to enter the soil horizons lying above the burials. Individual elements are released into the environment with the decomposition of the body, showing a systematic decrease in the level of released masses over time, depending on local conditions, the method of implementation of burial and the materials used to cover human remains (Uslu et al. 2009). Sometimes, the presence of metals contained in prostheses, stabilizing elements and tooth fillings, including Co, Cr, Fe, Hg, T, among others, is also associated with the human body (Van Allemann et al. 2019). Mineral residues, mainly bone, are preserved in the soil in the form of hydroxyapatite (Ca10(PO4)6(OH)2) (Żychowski and Bryndal 2015; Dippenaar and Brouwers 2018; Dippenaar and Olivier 2018). There is also a release of chemical compounds from coffins and a range of materials used in burial: fabrics, varnishes, hardware, handles, screws, metal screws and nails, plastics. Heavy metals (As, Cd, Cr, Cu, Hg, Ni, Pb, V, Zn), formaldehyde, phenol, glycerol, pentachlorophenol, among others, enter the soils via this route (Karmakar 2010; Gondal et al 2011; Janin et al 2011; Jonker and Olivier 2012).

The soils of cemetery and post-cemetery areas are subject to a number of transformations associated with the various stages of their use. In doing so, they acquire the characteristics of a particular form of land use, but also retain information about earlier stages (related to burial practices). The paper points out the spatial position of modern and historical cemeteries areas against the background of urban development. Thus, the functional and spatial changes taking place were indicated, affecting pedogenesis and, consequently, the properties of soils. The landscape position of soils is now recognized as a very important element in the description of soils, precisely because of the noting of the transformations taking place through this path. In order to illustrate these transformations more closely, it was decided to analyse the soil characteristics of two historical cemeteries, transformed today into a square surrounded by buildings and a pocket park. The scientific goal of this activity was to indicate the position of former cemetery soils with the changed form of land use. At the same time, it was analysed to what extent and in what references the soil characteristics change. The goal of the scientific line thus defined was to finally grasp to what extent the soil characteristics indicate the existence of historical burials. Which of them correlate with old burials, and which are more a resultant of the new form of land use.

2 Materials and methods

2.1 Characteristics of the research area

Zielona Góra is a medium-size town inhabited by about 140 thousand residents, located in the western part of Poland (51°56′07"N, 15°30′13"E). The town's history dates back to the thirteenth century (following German literature, the date of 1222 CE was accepted as the beginning of the city). For most of its existence, the city was small, with only a few thousand residents, mostly engaged in farming, small crafts and trade. Built-up areas occupied a small area for a long period of the city's history. Small cemeteries were organized on the outskirts, mainly as areas accompanying churches. The character of the city changed initially in the 18th century due to significant reconstruction of the city's structure (including the delineation of new cemeteries) and in the mid-19th century due to the development of industry and railroads. In the process, many of the burial sites continued to be used, despite their location inside the city. However, some of them were closed with a change in the form of land use. Today 14 cemeteries are in use, which parts are of historical meaning. The following 21 cemeteries are not-operational. In the area of today’s city was also found the presence of 4 burial sites from the Bronze and Iron Ages, with the current status of archaeological stands. Plan of the city of Zielona Góra with marked contemporary and historical cemeteries has been attached as supplementary material S1.

From the geological and geomorphological point of view, Zielona Góra is located on the Middle-Odra-Land, on two geomorphological forms: the Zielona Góra Moraine Shaft (max. height 221 m a.s.l.) and the Chynów-Płoty Basin (about 80 m a.s.l.). The Moraine Shaft has a latitudinal shape, and is situated between two main ice marginal valleys: Warsaw-Berlin and Głogow-Baruth (Podgajna 2010). Most of geological materials building superficial layers of the Zielona Góra locality are medium and coarse sands of glacial and water origin, gravels and in some areas silts and clays within glacitectonically disturbed moraine structures (Gontaszewska and Kraiński 2007). As a result of this formation of soil parent material, the most soils in the vicinity of Zielona Góra are Podzols and Brunic Arenosols. The inner surfaces of today's city are characterized by both cultivated and technogenic soil transformations, as a result of which they formed, among others: Hortic Anthrosols, Technic Regosols, Mollic Technosols, Urbic Technosols and Ekranic Technosols (Greinert 2003).

Weather conditions are typical of the transition area, influenced by the oceanic and continental climate. During the period of 30 years there were noted average values for: monthly temperatures – 9.1 °C, min. -22 °C (I), max. + 35.3 °C (VII); annual precipitation – 585 mm (with high annual volatility – 385–807 mm from 1980 to 2021); number of rainy days per year – 175.1; winds from the western sector above 50% of wind rose; wind velocity – 3.1 m·s−1, max. 34 m·s−1; number of cloudy days per year – 109 (on a base of data of Provincial Statistical Office in Zielona Góra).

2.2 Research methods

The analysis presented in the paper covered burial sites in the city of Zielona Góra, in its contemporary borders. The provisions of the city's planning documentation – the "Study of Determinants and Directions for Spatial Development of the City" – were analysed (Study 2021). At the time of this paper writing, the city has a bipartite document, with different designations for the former city of Zielona Gora and the municipality of Zielona Gora. Currently, the two mentioned structures are forming a single organism but the documentation has not yet been unified. An example of such differentiation is the delimitation of ZC cemetery areas in the former municipality and C/Z4 in the city.

Buried land within the city was drawn using Esri's ArcGIS PRO and graphically processed in CorelDRAW 2021 software. The location of these areas was linked to the temporal ranges of the changes taking place in the extent of urban development during key periods for the city. Thus, the location of the city's cemeteries in relation to the development and other areas that make up parts of the city and its hinterland is shown. Some of the soils in these areas were uncovered during field work carried out recently. Soil characteristics (full or just a description of the soil profile, depending on the permit obtained) are shown for selected cemeteries. Organized excavations in the course of ongoing municipal projects from 2010–2022 were used for this purpose. Their range was up to 4 m deep. Since the burials were exposed much shallower, the principle of evaluating the soil profile in accordance with the WRB assumptions was maintained in these cases. According to them, material is called soil when deposited up to the 2 m below the ground surface (IUSS WG WRB 2022). The information obtained through this route complemented the former own research, based on field surveys. The soil characteristics were given for two inner-city cemeteries:

  • The Holy Trinity Cemetery – HTC (Dreifältigkeitsfriedhof I), used as a burial ground between 1588 and 1815 (formally closed in 1809); soon after the burials were stopped, it was transformed into a city market place – Neumarkt established in 1815 (Czyżniewski 2014), and after World War II – into a central square between public buildings; the whole area is now called Słowiański Square, located in the immediate back of the Old Town; geographic coordinates of the focal point: 51°56′32"N, 15°31′03"E; the area has been shown on the Fig. 1a;

  • The New Holy Trinity Cemetery – NHTC (Dreifältigkeitsfriedhof II), used as a burial ground between 1817 and 1945; decommissioned in the late 1960s and early 1970s., after that exhumation took place and the entire area was transformed into a pocket estate park, located in the back of the downtown; geographic coordinates of the focal point: 51°56′21"N, 15°29′32"E; the area has been shown on the Fig. 1b.

Fig. 1
figure 1

Contemporary appearance of the former Holy Trinity Cemetery – central part of the new established square with fountain (a) and New Holy Trinity Cemetery – one of the former cemetery alleys; today a park path (b)

Full size image

2.3 Analytical methods

Soil samples weighing approximately 2 kg were collected from the soil profiles, from each horizon in cardboard boxes, transported to the certified Central Laboratory of the Institute of Environmental Engineering in Zielona Góra (Certificate no. AB 772), air-dried (35 °C) and then passed through a system of sieves (2, 10 and 20 mm; Geolab, Poland), using LPzE-2e shaker (Morek Multiserv, Poland). After separating the soil skeletal fraction, the fraction below 2 mm was used to analyse a grain-size composition and physicochemical and chemical properties of the soils. In the skeletal fraction, the content of anthropogenic materials was determined. The colour of the soil in each horizon was determined visually, using Munsell Soil Color Charts (Munsell Color division, X-Rite Inc.), in dry and moist states. Particle size distribution was determined for both the > 2 mm and sand fractions by sieving, and for silt and clay particles using the hydrometer method. The pH-H2O and pH-0.01 M CaCl2 values were measured with a glass electrode WTW SenTix 41 in the 1:2.5 soil/supernatant suspension. Electrical conductivity (EC) of the soil–water extract was determined using the conductometric method. Sorption properties of soils were determined according to the Pallmann method. Carbon content in forms: TC, TOC, IC were determined using a Shimadzu TOC-V CSN analyser with solid sample module SSM-5000A (Shimadzu, Japan). For the determination of the content of carbonates in the soil samples, the ISO 10693 method was used, based on the displacement of carbon dioxide by hydrochloric acid addition. Extracts of soil samples were prepared in aqua regia (a mixture of concentrated acids HCl/HNO3 in the proportion of 3:1) according to ISO 11466, extracts in 0.1 M HCl according to Baker and Amacher (1982). This fraction is potentially available to plants. Additionally, water extracts using soil and water ratio of 1:10 were made, where the mixing time was 2 h of mixer rotations at 100 RPM and a temperature of 23 °C. The content of heavy metals in the soil samples was determined by ICP-OES method (Perkin Elmer Optima 8000). All statistical analyses were conducted using Statistica for Windows 13. The basic statistical figures were defined together with correlations between soil condition indices at levels α = 0.01 and 0.05.

3 Results

3.1 Distribution of cemeteries in the city space

In the area of the present-day city of Zielona Gora 42 burial areas are existing, representing the different object types (Table 1).

Table 1 The burial grounds in Zielona Gora, divided using general legal position
Full size table

The cemeteries being currently in use (Fig. 2), distinguished in urban plans (CC), also have parts of historical significance (HC), preserved to varying degrees. Some cemeteries in today’s use are organized with the same range as historical ones or in areas adjacent to them. Thus, the historical sites exist together or independently of the current cemeteries. In this case mentioned as second one, they are often have been located right outside the fence of the operational area.

Fig. 2
figure 2

Division of urban cemeteries according to their types; CC – contemporary cemeteries, HC – historical cemeteries, AHR – abandoned historical cemeteries with visible structure, AHC – abandoned historical cemeteries without visible structure (covered by other forms of land use), AB – archaeological burial sites

Full size image

The contemporary location of the areas under investigation varies greatly, depending on where they are located on the city plan and the development history of the site. The 3 of them are covered by the building structures and 3 by the traffic development, 14 are distinguished cemeteries, 13 are present in forest areas, 2 in urban parks, 2 under the squares, and 3 regarding to the land use are wastelands. The immediate surroundings of cemeteries, considered in the context of planning protection of the zone of 50 m from the limits of the burial area have been established by Polish spatial planning law (Table 2).

Table 2 Landscape position of Zielona Gora burial grounds in distance of spatial planning protection zone – 50 m from the cemetery limits
Full size table

The forms of urban development, located close to the cemeteries are mainly constructed (totally or partly) of: mixed buildings (11 cases), single-family buildings (12 cases), services (18 cases), and manufacturing (6 cases).

In a strategic spatial plan for the city of Zielona Góra 14 of the investigated areas have been described with a “C” (areas of extensive urbanization), with only one zone distinguished – Z4 (cemetery) or directly ZC (cemetery), the next 6 as the “A” (downtown area, with a following detailed division on S1 (downtown functions domination) and Z5 (urban park) zones. The following 2 areas have been described using “B” letter (area of intensive urban development), with division to M1 (dominance of single-family residential development) and Z5 zones. As many as 14 sites are designated as ZL (forest) in the planning documentation. Three areas have been described as MN/MU (dominance of single-family and service development), two as UK (areas of religious services) and one as P (dominance of production development) land use forms (Fig. 3).

Fig. 3
figure 3

Forms of a land use of the cemeteries described related to the spatial planning classification in Poland; A/S1 – area of downtown functions domination, A/Z5 – downtown/urban park, B/Z5 – area of intensive urban development/urban park, B/M1 – area of intensive urban development/dominance of single-family residential development, C/Z4 – areas of extensive urbanization/cemetery, ZC – cemetery, MU – residential area with a dominance of service development, MN – residential area with a dominance of single-family development, U/UK – dominance of service development/religious services, P – dominance of production development, ZL – forest

Full size image

Detailed data on individual cemeteries in the city are provided in Table S2, included in the supplementary material.

3.2 Soil profile descriptions

The described soil profiles of former burial grounds show a wide variety of a structure, which is mainly related to their use after the closure of cemeteries. With the closure of HTC, a second cemetery of the same name was established in a new location. As a result, some families decided to move the remains of their loved ones to this new area. Analogous soil transformations are also evident at transmission network sites. This has resulted in the re-shuffling of soil profiles at the sites of former graves of exhumed persons – this means simplifying the structure of the soil profile to an A(AC)-C arrangement (Fig. 4, left side). In the part of the site with a clear picture of ancient burial practices, the soil profile has a different structure (Fig. 4, right side). The superficial soil horizons are significantly cluttered, especially the ACca. All these materials are covering the horizons: AC-C of some darker colour, bearing signs of partial mixing of humus material with sandy soil matrix and the native sand C2. Immediately below this material the C3 horizon is located, in which human remnants are still preserved. According to the WRB soil classification, the soil profile cannot be named Technosol, because of a low artefacts content (IUSS WG WRB 2022). However, due to the pronounced technogenic anthropogenic transformations, it cannot be scaled up in any other group, except for the one dedicated for other soils – Regosols. The described soil meets the requirements set for the one only principal qualifier Relocatic (a soil has been certainly remodelled in situ or within the immediate vicinity by human activity to a depth of ≥ 100 cm). Supplementary qualifiers able to be used are in this case: Arenic (consisting of mineral material and having, single or in combination, a texture class of sand or loamy sand), and Technic (having ≥ 10% artefacts by volume, weighted average, related to the whole soil; located in the upper 100 cm from the soil surface or to a limiting layer, whichever is shallower). As a result we can obtain the description of soil section: Relocatic Regosols (Technic, Arenic).

Fig. 4
figure 4

Necrosol of the Holy Trinity Cemetery being under use in Zielona Góra between 1588 and 1815; visible nested mechanical transformation of soil and human remains in levels of 1.0–2.0 m below ground level (right side and center of the photo; left side clear deep mixing of soil material with sharp spatial edges, perhaps during past exhumation); classified as: Relocatic Regosols (Technic, Arenic)

Full size image

Other materials were left in place despite a radical change in the functionality of the site. Further transformation of the soils occurred during the construction of public buildings (court, school) in the areas bounding the market square (Fig. 5). The most readily apparent in this regard is the lime mortar layer of varying thickness in the soil profile (Cca horizon). Nevertheless, from the construction period, the soil profile also states the presence of brick fragments, gravel and small stones and cement mortar (horizons: Aca, C and IIC1). All these materials are covering the horizon IIC2, in which human remnants are still preserved and practically not changed the native sandy rock (IIC3). From the point of view of modern soil classification, this section represents Technosols, because it is a soil having a layer, ≥ 10 cm thick and starting ≤ 50 cm from the soil surface, with ≥ 80% (by volume, related to the whole soil) artefacts. At the same time, the criteria 1b and 1c of the Technosols description are met (IUSS WG WRB 2022). The described soil meets the requirements set for the principal qualifier Urbic, showing the presence of rubble and domestic wastes in a layer ≥ 20 cm thick with ≥ 20% artefacts within 100 cm of the soil surface, with ≥ 35% of which consist of rubble and refuse of human settlements. The supplementary qualifiers can be used in case of this soil section are: Relocatic (a soil has been certainly remodelled in situ or within the immediate vicinity by human activity to a depth of ≥ 100 cm), Arenic (consisting of mineral material and having, single or in combination, a texture class of sand or loamy sand), and Terric (all of the criteria for the mineral materials described are fulfilled). As a result we can obtain the description of soil section: Urbic Technosols (Relocatic, Arenic, Terric).

Fig. 5
figure 5

Deposition of construction waste on the post-cemetery surface and in the surface layers of former necrosols used as a building surface, Zielona Góra (Poland); deposit of lime mortar, municipal and construction waste covering necrosol of the Holy Trinity Cemetery site (human bones visible on left side of the soil section; 90–150 cm), Zielona Góra (Poland); classified as: Urbic Technosols (Relocatic, Arenic, Terric)

Full size image

The newer NHTC area was differently located in the city space – away from intense development. Also in modern times, it has not been developed, but only transformed into an estate pocket park. The soils of the area were significantly transformed in the 1960s during the ongoing exhumation of human remains and reconstruction of plantings (including massive tree cutting). In the course of this work, there was also significant deposition in the soil of various waste materials of a construction nature, partly related to the existence of various structures in the former cemetery, partly brought to the soil during the construction of nearby housing and technical infrastructure. As a result of the described work, the structure of the soil profile was simplified to an A-AC-C arrangement (Fig. 6). Level A is related to the nature of land use and the deposition of plant residues with limited surface maintenance. At the same time, it is rich in construction and municipal waste. Below, the overlying AC horizon is clearly mixed, with a high proportion of gravel-diameter waste. C horizons are largely mixed, nevertheless sublevels have been separated showing their different characteristics and colour. According to the WRB soil classification, the soil profile cannot be called Technosol, due to its low artifact content (IUSS WG WRB 2022). One can, of course, look for similar soil profiles in wooded areas outside of urban areas. However, due to the clear technogenic anthropogenic transformations, this would not be reasonable. This leaves a group of other soils – Regosols. The described soil meets the requirements specified for the only main qualifier Relocatic (the soil has certainly been transformed in situ or in the immediate vicinity as a result of human activity to a depth of ≥ 100 cm). In this case, an supplementary qualifier can be used: Arenic (consisting of mineral material and having, singly or in combination, the texture class of sand or loamy sand). The Technic supplementary qualifier is problematic due to the presence of 9.3% artifacts only (the classification description resurrects the presence of ≥ 10% artifact volume, weighted average, related to the whole soil; located in the upper 100 cm from the soil surface or to the boundary layer, whichever is shallower). In our opinion, however, the fact of the presence of so many artifacts cannot go unnoticed in this case. As a result, we can obtain a description of the soil section: Relocatic Regosols (Technic, Arenic).

Fig. 6
figure 6

Necrosol of the New Holy Trinity Cemetery being under use in Zielona Góra between 1817 and 1945; clear impact of park land use, including deep rooting of plants on the construction of the soil profile; in addition, construction waste artifacts are visible in individual soil horizons; Zielona Góra (Poland); classified as: Relocatic Regosols (Technic, Arenic)

Full size image

3.3 Soil physicochemical and chemical characteristics

In the soil profiles analysed, the distribution of artefacts related to construction processes (debris deposition) and residential activities (domestic waste deposition) mainly reflects contemporary activities. Therefore, in post-cemetery areas, most of them have been gathered in the topsoil horizons – above burials previously organised. This situation has been changed as a result of earthworks, resulting in deep mixing of soil horizons. Nevertheless, the presence of artefacts in the 0–20 cm horizons usually does not reach 10%. In the area where no earthworks have been carried out, by far the more abundant of municipal and construction waste (up to 22–24%) is the next horizon, lying at depths of up to 40 cm below the ground surface. A significant difference was noted in this regard between two areas with a different position in the city and form of a land use (Fig. 7a). The square area HTC was enriched with waste materials in horizons lying below 10–15 cm, while the pocket park NHTC was not. Only in the area under heavy construction pressure, with the effect of significant admixture of construction materials during the work conducted, it was observed reaching the 20% artefacts content, established in the WRB classification as the limit for determining Technosols (Fig. 7b). The burial horizons (respectively in the following profiles: C3, IIC2) contained relatively small amounts of artefacts, mainly related to the presence of human remains and a small amount of other materials. One soil horizon (IIC3) doesn’t contain any artifacts, representing pure native sand material. Next 6 horizons were characterised by the artefacts content less than 2%, 3 horizons – 2% and slightly above, 3 – 2,5–10%, 2 – 22–23%, and 1 – 95%. The average artefacts content of the analysed soils is 11.2 ± 22.7% (5.6 ± 7.2% not counting the layer of practically pure lime-mortar), with a median of 2.0%.

Fig. 7
figure 7

a Artefacts content in soil of the former Holy Trinity Cemetery in Zielona Góra; darker colours representing the soil horizons containing human remnants. b Artefacts content in soil of the former New Holy Trinity Cemetery in Zielona Góra; darker colours representing the soil horizons containing human remnants

Full size image

The most uniform features of the soils described were their pH, CaCO3 content and the total carbon conten. Soil reaction close to neutral was caused by anthropogenic pressure. For this characteristic, pH measurements in H2O ranged from 6.2–7.7, with a median of 7.0. A comparatively higher pH characterized the soils of the part of HTC less transformed by construction activities (median 7.11) and the park NHTC (median 7.55). The square HTC, in its part more transformed by construction was characterized by a median of pH in H2O 6.54 (Fig. 8a and b).

Fig. 8
figure 8

a The pH, CaCO3 and TC content in soil of the former Holy Trinity Cemetery in Zielona Góra; CaCO3 and TC content are presented in %; darker colours representing the soil horizons containing human remnants. b The pH, CaCO3 and TC content in soil of the former New Holy Trinity Cemetery in Zielona Góra; CaCO3 and TC content are presented in %; darker colours representing the soil horizons containing human remnants

Full size image

The accumulation of CaCO3 in soil of HTC is complex in nature. Its highest content in the first soil profile is characterized by the Aca horizon of 15–40 cm. This horizon contains 3.4% carbonate, while the accompanying ones: A (0–10 cm) 2.4% and Cca (40–55 cm) 1.9%. Subsequently, the carbonate content decreases to 150 cm below the ground surface to rise again to 2.6% in the IIC3 horizon (150–200 cm), directly below the burial layer in the IIC2 (80–150 cm) soil horizon. To some extent, a similar distribution of carbonates was noted in the second soil profile of the HTC site. Admittedly, there the highest value characterized the Aca (0–10 cm) horizon, but below it there was a decrease in content up to the soil horizon of the C3 (110–200 cm) burial layer. Different pattern characterizes the highly mechanically transformed area of the NHTC. In the following horizons lying in the soil profile up to 100 cm below ground surface, the uniformity of soil carbonate content is evident. Significantly higher carbonates content was found in the C3 horizon (100–2000 cm) associated with the implementation of burials, as well as the presence of construction debris (Fig. 8a and b).

With respect to total carbon accumulation, a relatively higher concentration characterizes the topsoil horizons. Comparing the two sites, the NHTC is characterized by almost 3 times higher TC concentration than a soil of the HTC site. The presence of elevated TC content in buried layers is unclear. In the first soil profile of the HTC site, the higher TC content in IIC3 soil horizon (below the burial layer) was noted. In the second profile in the same site, the elevated TC content in the C3 soil horizon (burial layer) in relation to the above occurring C2 is clear. In the NHTC site a burial layer representing by the soil horizon C3ca is characterised by the lower TC concentration than the higher occurring C2ca horizon, but higher than the subsoil horizons ACca and Cca (Fig. 8a and b).

Detailed data related to the soil physicochemical and chemical characteristics are presented in tables and figures attached as a supplementary material – S3–S5.

Phosphorus was an element whose content showed high variability. The minimum concentration was 69 mg·kg−1, and the maximum was 1260 mg·kg−1. The average P content was relatively low, 342 ± 278 mg·kg−1, and the median was 230 mg·kg−1. In the HTC area the presence of 250 and 414 mg P·kg−1 in soil horizons IIC2 and C3 was adjacent to considerably smaller, respectively 135–180 and 180 mg P·kg−1. In both cases, humus horizons and those showing deposition of domestic waste were characterized by a higher concentration of phosphorus, correspondingly reaching 535 and 463 mg P·kg−1. In the NHTC area A horizon was characterised by even higher P content – 1261 mg P·kg−1. But the P content in the burial horizon C3 was still higher than for native material with building debris 69–196 mg P·kg−1 (Fig. 9a and b).

Fig. 9
figure 9

The P content in soil of the former New Holy Trinity Cemetery in Zielona Góra; darker colours representing the soil horizons containing human remnants

Full size image

Detailed data related to the soils chemical characteristics are presented in tables and figures attached as a supplementary material – S3 and S4.

4 Discussion

4.1 Location of cemeteries in contemporary city

The cemeteries in the city of Zielona Gora have a different history of use. They were established at different times (from the XIIIth to the XXth Centuries), when different rules for their organization were legal. Today, some of these areas are still in use, while others were formally closed in the past. They were also located in a variety of landscapes – in rural areas, in the middle of fields, in suburbs, along roads leading out of cities or at the churches (Ariès, 1989; Dziobek-Romański 1999; Zajęcki 2005; Długozima 2011; Brather 2014). The place and period of foundation largely determines the layout and state of preservation of the described objects (Scalenghe and Pantani 2020). Modern cities contain ancient cemeteries within their boundaries, with varying contemporary functionality. Many of the historic cemeteries unfortunately show a defective location in the modern spatial structure of the city. They are objects directly adjacent to residential and commercial developments, and are also areas separating other uses of urban space (Grabalov and Nordh 2021). Operational cemeteries are demarcated by fencing, which traditionally separates the world of the living from the world of the dead and facilitates control of the cemetery area (Capels and Senville 2006; Greenfield 2011). Most of the described historical areas are not protected, which promotes their systematic destruction. As the consequence, the state of preservation of these objects is unfortunately generally bad. Many such areas resemble the appearance of debris covered with ruderal vegetation (Greinert 2017; Mathey et al. 2018).

Most of the Zielona Góra cemeteries fall into the categories of contemporary areas with usually small historical parts and forgotten cemeteries in forested areas. They both account for 33.3 of all listed cemeteries. The surroundings of contemporary cemeteries is very diverse, however, showing the predominance of typically urban development in the area adjacent directly. They are mostly made up of single-family residential buildings, built at various times in the second half of the 20th century and the early 21st century, with the introduction of service buildings. This implies a potentially large interaction due to the short distance, with decidedly different land uses (Lazar et al. 2009). Unfortunately, such proximity also means littering of cemetery areas mainly with municipal waste, including those from cleaning up home gardens (Lepaon et al. 2018). The forest areas are predominantly in the hands of the state manager – the State Forests. They play both a productive and a soil- or water-protective function. As these cemeteries have not been used since 1945, the development of their ecosystems is analogous to other suburban forest areas. Also, impacts on the land surface and soils are mainly due to tree-stand development. However, since graves in the 19th and 20th centuries were arranged with building materials, their remains are still present in the described cemeteries.

Urban burial areas with a very ancient history have disappeared beneath historic and modern development elements. In Zielona Gora, they make up 26.2% of the total number of cemeteries. These areas are now built up, mainly by large tenement buildings and modern apartment buildings, as well as covered by roads, sealed squares and sidewalks. In many cases, the change in the form of development has occurred long ago and/or has gone so far that the former cemetery function is invisible. The removal of a cemetery located in the city, with partial exhumation of human remains is not a contemporary process. The history of Le Cimetière des Saints-Innocents in Paris, created in 1130 and finally closed in 1780, has been perfectly described (Share 2014; de Saint Sauveur 2018). Later, it was a city market – Viktualienmarkt, as was the case with HTC in Zielona Góra – Neumarkt (Czyżniewski 2014). Similarly, the Jewish cemetery in Breslau was closed in 1856 and leveled and built over in the 2nd half of the 20th century (Banasiewicz-Ossowska 2020). Impacts in the areas of such history should therefore be considered typically urban, bearing the hallmarks of technogenization of the environment. They in no way reflect the ceremonial activities associated with the original form of land use. The anonymity of many urban cemeteries is also an inherent feature of developing communities forgetting the past, especially the distant past (McDougall and Vines 2004; Grabalov and Nordh 2021; Rugg 2021). Their contemporary use is debatable – they are generally wastelands with a peripheral location, and urban planning documents often do not provide for changes in such a situation.

Some post-cemetery areas were decided to be turned into parks and city green areas. The latter bear the features of pocket parks or expanded multipurpose squares. The past of these sites is betrayed by the individual architectural forms left behind, related to the early existence of cemeteries there, as well as the preserved historical layout of the alleys. The functioning of the described areas in the municipal green system evidently reduces negative impacts on the land surface (the areas are supervised and kept in order), resulting in the preservation of planned layout as soil deposits as well. Cemetery arrangements favor a new function as peculiar urban parks, often with unique aesthetic features and diverse biosphere (Uslu et al. 2009; Kjøller 2012; Skår et al 2018; Kowarik 2020; Grabalov and Nordh 2021; Nordh et al 2023). The use of old cemetery areas in such a capacity, combining rest with reflection and historical education is extremely valuable and should be widely promoted (McDougall and Vines 2004; Grabalov and Nordh 2021; Rugg 2021).

4.2 Main characteristics of cemetery soils

Both of the cemeteries described in the paper were organized in their time outside the strict city limits. The location of The Holy Trinity Cemetery seems to us now to even be a part of the old city. In practice, it was in the 16th century an area outside the city walls. The New Holy Trinity Cemetery, established in the early 19th century, was located among orchards and farmland for its entire time of use. In a short time, as early as the mid-19th century, it found itself in the vicinity of many, even exponentially emerging industrial plants. In both cases, areas covered with poor sandy soils were chosen, at a short distance from urban development. The Holy Trinity Cemetery was established in the period of time, when the first regulations and guidelines concerning burial practices were implemented. They indicated both the conditions of the location of cemeteries, their internal organization and the manner in which burials were conducted (Dziobek-Romański 1999; Długozima 2011). These regulations (as well as developed on their basis) were still in use at the time of the establishment of the second cemetery described. Closed city cemeteries were put to other uses. Also, the organization of marketplaces was not foreign to such areas. This is evidenced by the example of Paris' Le Cimetière des Innocents (Ariès, 1989; ACAM 2023). Hence, the varying pressure of human activity against the soils of burial grounds should be considered a wide-scale phenomenon. In both described post-cemetery areas the presence of soil skeleton, partly in the form of artefacts was noted. The presence of artefacts is particularly evident in the superficial horizons, which is a characteristic feature of urban areas. In the areas of urban cemeteries, there was deposition of construction and household waste while they were still in use. Littering of cemeteries was a reality as in ancient, medieval and modern periods as well. This was described, among other things, for Le Cimetière des Innocents, which was littered with different wastes from its beginnings in the Middle Ages (Ariès, 1989; ACAM 2023). The problem is also illustrated by the legal prohibitions that have been enforced, including grazing animals, laundering, washing dishes, and conducting commerce in cemeteries (Ariès, 1989; Klima et al. 2019; Colleter and Barreau 2021). Historically, therefore, the soils of cemetery areas were apparently heavily laden with various deposits. In addition, it should be taken into account that the backfilling of the graves was done with this material, which was dug on the site. No one cleaned it during this process. Waste materials appeared in cemeteries as a result of building processes taking place in cemetery areas themselves (headstones, monuments, chapels and roads constructing), in post-cemetery areas (after the change of land use form) and as delivered from adjacent areas. The presence of construction debris and household waste was described in cemetery soils by the Gerasimova et al. (2003) and Charzyński et al. (2011). Also, the dominance of gravel and rubble fragments in the soil skeleton in the studied soils from Zielona Góra corresponds to the data for Toruń (Charzyński et al. 2011).

In Zielona Góra, the soil reaction was found to be close to 7,0, while in Toruń it was slightly alkaline (pH 7.2–8.1). Burials do not seem to have influenced this situation, as confirmed by the results of Schotsmans et al. (2015), who found a non-permanent elevation of soil pH even when the human remains were backfilled with lime. Showing significant clutter in both cases is clearly the dominant cause of the alkalisation of the soils described. The presence of carbon in the following horizons of the soil profiles was mainly the effect of surface deposition of horticultural substrate, carbonates and plant debris. The content of organic carbon only in A horizon of the park soil was high (10.5%), with significantly less in the other horizons and in the location of the post-cemetery square. Investigations made in Toruń showed the maximal content of 1.62% TOC (Charzyński et al. 2011). The higher content in Zielona Góra is straight related to the differences in post-cemetery land use, respectively city market and park.

The phosphorus content, often described as indicative of burial sites, can only partially be described as such for the post-cemetery areas of Zielona Góra. Analysing the horizons containing human remains and adjacent mineral levels, such a conclusion is as legitimate as possible. The same trends were noted by Charzyński et al. (2011) analysing the characteristics of the cemetery soils of Toruń. However, the high P content is also associated with organic matter deposited in soils from a variety of sources, as indicated by both its presence in topsoil and subsoil. The content of Ca in urban soils is a tenuous determinant due to the multitude of sources of its introduction into soils. The content of this element in the burial horizons of soils of HTC (IIC2 and C3) and NHTC (C3) areas indicates their enrichment caused by human burial. This is evident by comparing the Ca content with that characterizing neighbouring horizons, respectively for HTC IIC1, IIC3 and C2, and for NHTC C2. Of course, it is difficult in this context to indicate trends in the shape of the entire soil profile, due to the deposition of construction waste. Studies at the Chudeřín (Czech Republic) cemetery, dating back to 2800–2500 BC, located in the Arenosols complex even now indicate that soils are enriched in P and Ca, especially at the level of the deposited remains and below. The peak in Ca (3.8 ± 1.0%) and P content (1.7 ± 0.6%) applies to sites of modern bones and soil material up to 5 cm from them (Asare et al. 2020), they contain 99% Ca and 80% P of the human body (Mann and Truswell 2002). Most studies indicate that the soils of burial areas are significantly enriched in carbon, nitrogen, calcium and phosphorus (Burghardt 1994; Charzyński et al. 2011; Majgier and Rahmonov 2013; Asare et al. 2020).

5 Conclusions

The issue of cemetery sites and their environmental dimension relating to the formation of specific soils is very complex. The result is a different approach to historical and modern cemeteries. Since, in the general perception, they are hallowed places, they should be well recognized, which is the basis for their protection. A practice commonly found in the world is the burial of human bodies or ashes in the ground, hence their remains should be referred to soil formations. Proper identification of soil profiles at the described sites is the first step for further action. Another should be the designation of the soils of cemetery sites in planning documentation. This, in turn, requires classifying them in a way that allows clear and precise interpretation of the records. Conclusions of both a general nature and strictly directed at a new approach to soil science of anthropogenically altered areas are drawn from the presented work:

  • The long history of European cities results in the appearance of burial sites with different original locations and in modern spatial layout. Many of the ancient cemeteries are covered by younger forms of land use, making their presence unclear. Cemeteries organized on the outskirts of cities and outside them, due to lack of interest from local communities, become wastelands or undergo spontaneous reforestation.

  • Under favourable conditions, human remains can remain in the soils for a very long time making areas with a changed (sometimes several times) form of use continue to fulfil the cemetery function. In general, it becomes clear as a result of an in-depth analysis of the city's development, as well as meticulous observation of soils during earthworks.

  • The soils of historical cemeteries usually do not present the profile typical for this form of land use. This is due to a number of transformations typical for urban investment activities. As a result, the characteristics of urban Technosols and Regosols are developed.

  • The burial layers in soils and those adjacent to them are generally characterized (apart from the presence of human remains) by elevated levels of TC, CaCO3 and phosphorus content. However, they are also being greatly altered by the introduction of various wastes and earthworks carried out on former cemetery sites.

  • Many of the soil characteristics of former cemeteries show a direct correlation with the form of land use. Covering the area after a former cemetery with a solid surface or organizing a green space covered with low vegetation perpetuates the characteristics of cemetery soils. High park plantings produce the effect of greater changes in the soil profile, generated by the deposition of litter and deep penetration of soil by roots.

Further research should clearly define regional differences in the presence of burial sites of historic and contemporary significance, in designed urban space, rural and naturally developed areas (e.g., in forests). With the assumption of a common trait of necrosols, the principal and complementary qualifiers for existing and preferably new taxa should be refined through this action. In my view, we owe this to the soil science, urban studies, and to the generations of humans who preceded us, with an eye toward similar feelings of future generations toward our mortal remains.