Dynamic Growth of “Pioneer Trees” as a Basis for Recreational Revitalization of Old Urban Landfills: A Case Study of Zgierz, Central Poland

Abstract

Urban tree biodiversity represents a valuable natural resource. However, some fast-growing tree species with limited esthetic value play an important ecological role by colonizing degraded areas, such as closed landfills. Our observations indicate that trees like Betula pendula (Roth), Acer negundo (L.), and Populus tremula (L.) reached the size of adult trees in less than 30 years after the landfill’s closure in the 1990s, forming a nature area similar to a natural forest. A resident survey conducted among the inhabitants of Zgierz confirmed that the lack of space provides opportunities for various forms of recreation. The example analyzed indicates a trend that can be replicated in other cities with minimal human intervention and low financial costs for landfill reclamation. The case study presents an ecological approach to managing degraded sites, where nature determines the quality of the soil environment by eliminating pollutants from the residential surroundings. Furthermore, the research framework provides a basis for developing future models for cleaning up urban landfill sites and promoting placemaking. This pilot study shows a model for old landfills in Europe with well-developed spontaneous vegetation that can be transformed into recreation and sports facilities in the urban areas with industrial past times.

1. Introduction

Cities that experience economic growth during periods of dynamic industrial development, driving the national economy, have increased the number of specialized factories that produce large amounts of waste. Both factories and landfill sites were located on the outskirts of the former city boundaries. However, with the territorial expansion of these rapidly developing cities, these sites became part of the urban center, close to residential areas. Over time, some factories were closed due to capitalism, new legislation, legal changes, and the rise of industries—such as the textile industry—in Asia such as in China. This pattern occurred in many cities of the Łódź agglomeration, including the small town of Zgierz, which serves as a case study [1,2,3,4]. The waste dump was closed and its surface, covered with anthropogenic soil, became inhabited by seedlings of locally occurring tree species, in some cases resulting in the area becoming overgrown with natural forest. Unfortunately, the close proximity of the Bzura River and favorable conditions for the development of beaver (Castor fiber) habitats led to the destruction of landfill deposits, mainly on the slopes, posing a threat to the environment [5,6,7].

Urban degraded sites like former landfills constitute significant natural and recreational potential as unused spaces [8,9,10,11,12]. Naturally covered with trees with a forest function, they can support human well-being if proper infrastructure and financial resources are provided [13,14]. Also, the involvement of stakeholders in shaping and improving the landscape around their surroundings can be of great importance in transforming degraded places. We have many examples of well-executed investments in reconstructing degraded areas into parks with a recreational function [6,9,10,11,12,13]. One of the oldest Polish examples is the construction of Silesian Park in the post-mining areas of Upper Silesia. As a 600 ha development, this park remains an essential place of entertainment and rest for the Upper Silesian agglomeration [15]. Another good example is the development of former landfill sites into entertainment areas, such as ski jumps, skate and walking parks, or viewing points, as evidenced by various examples dynamically implemented in Germany (e.g., in the Ruhr area) and in the post-industrial regions of cities in Great Britain [16,17,18,19,20]. Another example can be found in Upper Lusatia in Saxony, Germany, where degraded areas were developed using the topography (hilly mountainous terrain) and the color of the anthropogenically degraded soil affected by toxic impacts, for recreational purposes and regional promotion [21]. Also, in Central Poland, the Łódź agglomeration, including the city of Zgierz, has several landfill sites in the design or implementation phase of sports and recreation development. For example, in the capital of the Łódzkie voivodeship (the city of Łódź), Górka Rogowska and Górka Retkińska, as former construction waste landfills, have been designated as green areas and currently require, thanks to stakeholder involvement, the gradual introduction of new recreational infrastructure. There are also ongoing studies indicating the important role of natural and spontaneous vegetation in shaping the image of cities and their natural value. An example is the right bank of Warsaw and its vegetation (Acer negundo L. and Salix viminalis L.), plants commonly found in the riverside areas of Central Poland [22,23,24,25,26,27]. This trend is also observed in other places. Still, not all researchers share the view of its key role in revalorizing the degraded environments, especially in the case of post-industrial waste landfills, the so-called ticking bombs [28] due to their hazardous status. However, a good example may be the pro-ecological development of the production waste landfill of Charleroi at the former beer factory in southern Belgium using natural vegetation like Alnus glutinosa (L.) or Betula pendula (Roth) [29,30]. Encouraging plant growth while developing pedestrian and recreational routes in the form of roofed squares or viewpoints has turned the site into a tourist attraction and a valuable opportunity to admire the panorama of Belgium, particularly given its relatively flat character. This place, which we visited in 2024 during the ECLAS Conference in Belgium, inspired further reflections on the development of our case study in the lowland area of central Poland [31].

Foreign examples of Western European countries (Germany, Belgium, and Great Britain) show good practices of recreational development of formerly degraded areas (with the public’s participation). They may serve as a model in giving appropriate directions for the revitalization of such regions and also for Polish examples, such as the Boruta landfill.

The management and disposal of industrial waste, including hazardous waste, are currently regulated in Poland (Central Europe) by legal regulations harmonized with European Union standards [3,6,7]. Unfortunately, industrial waste landfills created before Poland’s accession to the European Union remain a significant problem, especially the no-man’s landfills left over from industrial plants closed due to the economic and political transformation in 1989. It is assumed that there are currently about 80 such landfills in Poland, five colloquially referred to as “green bombs.” A significant problem is the leakage from the landfill, which contaminates groundwater and enters the Baltic Sea via the local Bzura River and then via the river network, systematically increasing the pollution of the Baltic Sea with toxic substances [5,6,28].

Our research is important in terms of the development of degraded areas. Firstly, they determine the natural and recreational potential by conducting public opinion polls on how degraded places should look in the future and whether they should be eliminated or transformed for recreation and nature protection purposes.

Secondly, we try to pay more attention to areas that are particularly difficult to transform due to their unclear history or the concealment of biological or ecological danger, which we try to explain in more detail in this article. The lack of research in this area also highlights the difficulty of accessing the site due to changes in their management and ownership, as well as the risks of illegal exploration, as these places are used for walks or sample collection. All these factors contribute to making the area a ticking time bomb. It is a significant problem that has persisted for a long time, leading everyone to become accustomed to its presence. Although the issue is not immediately noticeable, it poses a significant risk, as it can easily become biologically contaminated if pollutants enter the soil or the Bzura River [5,6,7]. Currently, there are only three highly dangerous degraded landfill sites in Poland that have already undergone partial or basic revitalization. These are Bydgoszcz Zachem in Kujawy (Northern Poland), Tarnowskie Góry, and Jaworzno in Upper Silesia (Southern Poland). However, these places were previously cleared of tree and shrub vegetation to limit plant succession. The landfill area remains a grassy surface, which corresponds to Western trends [32,33,34,35,36]. However, it is worth emphasizing that each landfill requires separate analysis and field observation. This is a challenging logistical and engineering task not only for urban planners but also for landscape architects or environmental engineers. Although these areas are part of one degraded post-production area, each site should be approached individually [37,38]. Thus, analyzing the current state and further revitalization methods is a challenge of interdisciplinary research, the beginning of which we have tried to outline in this paper. The transfer of ownership of these degraded areas to the municipality of Zgierz has also allowed for scientific cooperation in this area [14]. Recognizing the current development and the challenges of the revitalizing of hazardous landfills, as demonstrated by our case study of the Boruta landfill (including, among other factors, the course of long-term secondary plant succession), may help assess and plan the future implementation of spatial plans that adapt these degraded sites for new recreational and natural functions [39,40].

The aim is to identify environmental threats and revitalization directions for former degraded sites, such as an inactive hazardous waste landfill in Zgierz. The aim of the work is also to show a developing tendency of transforming degraded places, such as the old Boruta landfill (case study) in Zgierz, into forest recreation areas, using plant succession and landfill bioremediation as a scenario model to address the question of how well the proposed model aligns with the needs of the population. This ecological direction is considered a positive development trend in the current era of sustainability. Reversing the negative transformation of degraded sites and preventing their further deterioration is possible thanks to remote sensing methods, satellite image analysis, and access to online opinions of residents. Many Polish cities struggle with the absence of decisive actions to improve the environmental conditions and to develop postindustrial areas. This is often due to a lack of financial resources for reclamation, unclear legal regulations, or poor management of urban infrastructure.

To answer the research objective, we asked ourselves four main research questions:

(1)

Can the ecological succession of plants cause the creation of a recreational area with a forest character on the site of a former landfill?

(2)

What plant species are suitable for the recultivation of degraded areas and, at the same time, promote recreation in these areas?

(3)

What is the public opinion of the local population on the functioning of the so-called hazardous areas? Are there any ecological bombs, and can they be converted for active recreation?

(4)

Can the presence of a river along a waste disposal site significantly limit revitalization processes and halt environmental transformation and improvement?

Hypothesis 1.

We hypothesize that the primary succession of plants, especially trees that reach maturity, is a guarantee of improving the environmental conditions of old, inactive landfills.

Our research analyzes the development of the Boruta landfill in Zgierz, focusing on three key areas: the identification of contaminants, an assessment of visitor and resident perceptions through a survey, and a description of possible revitalization measures. These measures include conservation actions (such as the use of ecological engineering to protect the landfill’s slopes and the creation of a nature and landscape protection area) and passive or active forms of recreation, as informed by public opinion surveys and landscape architecture research methods.

2. Materials and Methods

2.1. Case Study

The industrial waste landfill covers an area of approximately 10 ha (Figure 1A,B) and is located in the southern part of the city of Zgierz in Central Poland. The study area borders the Bzura River (Figure 1B). The landfill slopes range from 4 to 6.5 m in height. The landfill has been in operation since the early 1960s, with the last waste deposited in 2014. The chemical composition of the waste has not been precisely identified. It is assumed that it largely consists of paints, dyes, and other industrial waste produced by the former Boruta dye factory in Zgierz, whose buildings remain degraded [5,41,42,43,44]. Industrial waste was placed in various containers at the landfill, and, during storage, was covered with rubble, ashes from furnaces, municipal waste of varying thickness, and sand. There are nine piezometers in the area surrounding the industrial waste landfill to monitor groundwater contamination. Leachates from the postindustrial waste landfill are discharged from the west, south, and east sides (Miroszewska Street) into the industrial sewage system and the Sewage Treatment Plant in Zgierz. There is no discharge from the north side of the landfill (the expansion had been planned), which results in the accumulation of leachates in the depression at the foot of the northern slope, causing erosion of the landfill slope [45,46]. According to the local land-use plan for the Boruta landfill site [44], the degraded area is designated to serve as a green space with recreational facilities. However, the document does not specify the methods and means for adapting the property to its new function. This is to be the subject of further specialized studies and regulations on landfill waste management, which are considered in the current environmental impact forecast for the Boruta landfill and the environmental protection program for the city of Zgierz [7,41,42,43].

2.2. Materials

The work uses thematically differentiated source materials concerning the Borta landfill and plant in Zgierz. These are specialized studies:

• Forecast for the environmental impact of the Boruta landfill site and the environmental protection program of Zgierz city [42,43];
• Report on the state of the landfill environment and its impact on the environment commissioned by the city of Zgierz [47,48];
• Report on vegetation and contaminants in the landfill area cut by ALS (Eng. Airborne Laser Scanning) method from the aerial ceiling [49,50,51];
• Local land use plan for Boruta landfill site [44];
• Regional Environmental Protection Inspectorate (Wojewódzki Inspektorat Ochrony Środowiska, WIOŚ) and General Environmental Protection Inspectorate reports (GIOŚ) on the quality of water, air, and soil in the Boruta landfills from 2018 and 2021 [52,53,54,55,56,57,58,59];
• Analysis of environmental effects after landfill fire in Zgierz based on studies carried out by the Central Center for Contamination Analysis of WIOŚ in Łódź [60];
• Evaluation of the occupation of landfills in the former Boruta plant in Zgierz on the life and health of the inhabitants of Zgierz and the surrounding area, as well as for the environment [6];
• Regulations on landfill waste management in Europe, including Poland, and those on landfill waste in Zgierz [7,41,61,62,63,64,65,66,67,68,69];
• Literature query on the history of the Boruta landfill in Zgierz and soil reclamation [70,71,72];
• Literature query on the microbiological analysis of Boruta landfills [73,74,75,76];
• Statistical data from the Central Statistical Office on deaths and diseases [77] and a survey on the possibilities of revitalizing degraded areas conducted among residents of Zgierz in the period 2022–2024 [78,79].

2.3. Methods

The multi-mixed method was used in the work [77,78], combining different disciplines from landscape architecture, urban ecology, geography, and social research. The case study framework is presented in Figure 2.

First, a literature review was conducted on the development of degraded landfill areas in Europe and Poland, along with a review of satellite image analyses of the vegetation cover of the Boruta landfill in Zgierz from 2004 to 2021.

The second stage of the work included field observations and coverage analyses. During a site visit in July 2022, we examined the development and selected flora, including herbaceous plants, understory plants, trees, and shrubs. This initial visit confirmed the species identified by two remote sensing flights (Airborne Laser Scanning) methods conducted in June and December 2022. The flight method (ALS) included the analysis of the cover of the landfill area along with the surroundings up to 500 m in spring–summer (vegetation period of trees) and winter seasons (no cover by leaves). An analysis of slope stability and the causes of their destruction was also carried out, supporting the remote sensing data with on-site by using LiDAR (Light Detection and Ranging). The analysis of the accuracy of the species classification model is presented in the graphs in Figure 3. High results for the overall accuracy measures and F1 scores for individual classes were achieved. The accuracy assessment was made by repeating the modeling five times on randomly selected training and validation sets in a 50:50 ratio. The graphs show the spread of the obtained accuracy values. The median overall accuracy was 0.87. The median kappa coefficient was 0.82. For the individual classes, the median F1 score coefficients were as follows: ash-leafed maple (A. negundo) = 0.86; silver birch (B. pendula) = 0.93; goat willow (Salix caprea) = 0.73; and other species = 0.91 [49,50,51]. The third stage of the work was to assess the landfill vegetation and its condition (Class 4—very good condition, Class 3—good condition, Class 2—deteriorated condition, Class 1—bad condition), based on NDVI for the landfill area together with its 150 m buffer zone to examine the impact of old deposited landfill pollutants on the external environment. These activities aimed to evaluate the vegetation’s usefulness in terms of its condition, natural value, and future recreational potential. The intensity of the individual effects of landfill impact and their total sum were presented on maps in five classes, showing the number of cases in the grid mesh. The division into classes was made using the Jenks natural breaks method. This method divides values to minimize the variance within classes and maximize the variance between them. Class 1 was assigned to areas where none of the effects of landfill impact were found, and Class 5 was assigned to grid meshes with the highest intensity of landfill impact effects on plant cover. This methodology of remote sensing is thoroughly illustrated in the original source of the Boruta landfill site report, summarizing this task in technical and analytical detail [50].

The next stage of the work was to conduct a questionnaire survey among residents of Zgierz city regarding the possibilities of developing the area for recreational purposes. Data was collected in 2022–2024, and 108 responses were obtained by using the Google Forms tool [77]. We placed the information about the survey (online with QR code) on trees near the site and in the surrounding area (multiple- and single-family housing estates). Respondents interested in the survey could scan a QR code and participate in an anonymous, voluntary survey. The data were then processed in the StatSoft Statistica 13.0 statistical program [78]. Statistical significance (p, 0.05) and correlation were sought in the answers depending on the age, gender, education, and economic–social status of the respondents. The survey provided gives us answers to the following questions: (Q1) Do you see a need to revitalize the landfill area beyond the Bzura River? (Q2) What do you think the direction of the actions taken should be? (Q3) What functions should this area serve in the future? (Q4) In what direction would you steer future revitalization? We used the chi-square test to show differences in answers and the significance of given factors.

Then, the landfill terrain was analyzed to examine the area’s suitability for developing recreational needs. Available hyperspectral images indicating height differences were used for this purpose, thanks to which it was possible to determine the profile of the landfill and create its 3D model (DMT) [49,50].

Afterwards, we discussed the research results and indicated recommendations for the natural and recreational development of the landfill area. New species were selected for planting in degraded areas, mainly on the escarpment near the Bzura River.

The last stages of the work included synthesis, conclusions, and final comments aimed at the directions for the pro-ecological development of the degraded area for recreational purposes (walking park).

3. Results

3.1. Characteristics of the State of the Area for Recreation in Terms of the Vegetation Cover

The landfill’s contents are not fully understood. According to the current literature and reports, it is assumed that the area was closed in 1995 and was primarily used to store paints and dyes from textile production, due to the activities of the industrial plant (ZPB Boruta) in the 19th and 20th centuries [52,53,54,55,56,57,58,59,60,70,71,72,73,74,75,76]. These substances are contained in barrels, while some solid materials, such as fabrics, are covered with soil mounds, that are now overgrown with lush vegetation. This creates a barrier against the larger-scale spread of pollution. The lack of proper land management, along with changes in ownership and regulatory provisions, has postponed the development of a recreational area through subsequent decisions and delays. However, this issue should be viewed as beneficial, considering the tree succession discussed in this paper. The potential of nature may therefore be an alternative to costly landfill reclamation upon closure and ongoing monitoring.

The surface of the landfill and the slopes are covered with grass, shrubs, and trees. These are mainly ruderal and expansive plants, naturally occurring in the landscape of central Poland. The predominant species include ash-leafed maple (A. negundo L.), American bird cherry (Prunus serotina L.), and goldenrod (Solidago hybrida L.), as well as common domestic species such as silver birch (B. pendula Roth), goat willow (S. caprea L.), and saplings of these species [49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82]. The woody species mentioned above were identified as dominant during the remote sensing survey in 2022 and were confirmed by their presence during several on-site environmental inspections [49,50].

The analysis of satellite images from 2005 to 2021 and the remote sensing flight in 2022 indicated an increase in the landfill area covered by woody species of the genera B. pendula (Roth), A. negundo (L.), and S. caprea (L.) (Figure 4), now covering nearly 50% of the site (4.3 ha) within 30–40 years of the cessation of exploitation in 1995 (Figure 3,

Table 1. Number of trees of individual species in the analyzed case study area [50].

Tree Species	Number of Trees [%]	Area: Ha [%]
Betula pendula (Roth)	944 [48.07]	1.9984 [45.4]
Acer negundo (L.)	256 [13.03]	0.5417 [12.3]
Salix caprea (L.)	109 [5.55]	0.1656 [3.8]
Other species	655 [33.35]	1.6934 [38.5]
Total	1964 [100]	4.3991 [100]

) [19]. The field inspection also revealed a dense undergrowth, mainly forming groups of shrubs. In the lower layers, apart from seedlings of the species mentioned, other plants such as ground elder and nettle were observed, indicating soils with high nitrogen content and pollutants, mainly of inorganic origin. Based on the closure date of the landfill, satellite image analysis, and Majdecki tables [80], the age of the trees is estimated at 30–40 years; the youngest trees are between 10 and 20 years old (Figure 3C).

The results of the analysis are presented in raster layers showing the predicted distribution of species, divided into the following classes: ash-leafed maple, silver birch, goat willow, and other tree species. Table 1 and

Table 2. Health condition of landfill trees [50].

	Class 1 (Bad Condition)	Class 2 (Deteriorated Condition)	Class 3 (Good Condition)	Class 4 (Very Good Condition)
Case study area	0 ha [0%]	0 ha [0%]	0.0047 ha [7.86%]	0.0551 ha [92.14%]
Buffer zone	0.0483 ha [0.9%]	0.0115 ha [0.21%]	2.8718 ha [53.36%]	2.4503 ha [45.53%]

present the number of trees of individual species, the total area they occupy, and their percentage share across the analyzed areas.

Table 2 presents information on the area occupied by individual condition classes of herbaceous vegetation within the analyzed area, including the buffer zone (Figure 1B).

No areas with reduced herbaceous vegetation have been identified within the study area. The entire area is covered by woody vegetation that grew spontaneously without human interference and exhibited good natural value, as noted during the field inspection conducted in the summer. The slightly reduced indicator values observed in the buffer zone are primarily associated with postproduction infrastructure, which limits proper plant development, including plant statics and crown or root ball growth. To sum up, the health condition of the vegetation in the study area is good and should not pose a threat to the development of recreational functions in the case study area in the future.

3.2. Slopes of the Landfill and Their Erosion Characteristic

The slopes of the Bzura River are overgrown, and access to the river is complex (Figure 4). The river resembles a stream, with a low level of groundwater observed during most months of the year. In spring and autumn, the river level periodically rises due to the accumulation of rainwater from neighboring built-up areas and the river’s retention function. Additionally, the poor condition of the slopes and their erosion-related damage are influenced by the activity of beavers (Castor fiber), which, by felling mature trees, destroy the layers of stored waste, leading to land degradation. Based on the analysis of remote sensing images, it can be observed that the destruction of the slopes has occurred over the past 10 years (Figure 5).

Table 3. Percentage of meshes of a given class in the analysis areas—map showing the sum of the intensity of all effects of the impact of landfills [50].

	Mesh Area of a Given Class in the Area [%]
	Class 1: 0 Mesh Pts.	Class 2: 1–3 Mesh Pts.	Class 3: 4–8 Mesh Pts.	Class 4: 9–14 Mesh Pts.	Class 5: 15–25 Mesh Pts.
Case study area	62.45	30.59	3.50	1.05	2.41
Buffer zone	89.54	7.39	1.40	1.64	0.04

Legend: pts.—points.

presents the results of the intensity distribution of the cumulative effects of the Boruta landfill’s impact on vegetation in the study area and its buffer zone. The percentage of the area occupied by the meshes of each class in relation to the total analyzed area was calculated.

The results indicate an uneven intensity of the landfill’s impact on vegetation. Within the study area, the landfill’s negative impact is concentrated in areas located directly adjacent to the Bzura River. The spread of this negative impact along the river and into nearby areas is also visible. Since the area of concentrated negative impact on vegetation spatially overlaps with the location of the erosion cavity found on the landfill slope, it can be assumed that this cavity is the primary point where pollutants—identifiable through ceiling and visibility analyses—are being released into the environment.

3.3. Pilot Studies: Survey Summary

Revitalization is a measure aimed at the social and economic transformation of post-industrial areas. One of the most important elements of this process is public participation, i.e., the active engagement of residents in the decision-making process regarding how such places should look in the future so they can once again serve society. Therefore, it was necessary to survey public opinion to support this thesis and identify further recommendations. The questionnaire survey consisted of 10 questions (Q1–Q10). The study included 108 respondents, primarily residents of Zgierz [79].

A total of 108 respondents participated in the survey, including 47 men and 61 women. The largest group comprised individuals aged between 19 and 29 (45.4%), while the smallest group consisted of respondents aged over 40.

Table 4. Characteristics of respondents by age.

Sex	Age [Years]
	19–29	30–39	40–49	>50
Male	20 [19.5] *	13 [12.0] *	10 [9.3] *	4 [3.7] *
Female	29 [26.8] *	9 [8.3] *	13 [10.0] *	10 [9.3] *
Total	49 [45.4] *	22 [20.4] *	23 [21.3] *	14 [12.9] *

* % values in the groups were estimated per total number of respondents.

shows the breakdown of respondents by gender and age.

For further analysis, the respondents were divided according to age (regardless of gender). This approach allowed us to assess whether there are differences in the perception of the landfill between those who remember it during its operation and those who have always considered it as an abandoned site with limited accessibility. Since the landfill was closed in 1995, the cut-off point was set at 40 years of age.

The results of the analysis are summarized in

Table 5. Needs and directions for revitalization according to respondents.

Question 1	Do You See a Need to Revitalize the Landfill Area Beyond the Bzura River?
	Yes n [%]		I Don’t Know/I Haven’t Thought About it n [%]				No n [%]
<40 years (n = 71)	64 [90.1]		5 [7.0]				8 [2.9]
>40 years (n = 37)	34 [91.9]		3 [8.1]				0 [0.0]
p chi square	p = 0.5805 (chi2 = 1.09; df = 2)
Question 2	What do you think the direction of the actions taken should be?
	Liquidation, removal of pollutants	Recognition of an area as a protected object		Resumption or continuation of waste storage		Reconstruction and change of purpose			Other
<40 years (n = 71)	43 [60.6]	8 [11.3]		0 [0.0]		33 [46.5]			9 [12.7]
>40 years (n = 37)	27 [73.0]	8 [21.3]		0 [0.0]		17 [46.0]			4 [10.8]
p chi square	p = 0.1999 (chi2 = 1.64; df = 1)	p = 0.1501 (chi2 = 2.07; df = 1)		p = 1.0000 (chi2 = 0.00; df = 1)		p = 0.9580 (chi2 = 0.00; df = 1)			p = 0.7774 (chi2 = 0.07; df = 1)
Question 3	What functions should this area serve in the future?
	It should not be used for any purpose (due to contamination)	Leisure/ recreational		natural		Service			industrial
<40 years (n = 71)	10 [14.1]	33 [46.5]		36 [50.7]		22 [31.0]			10 [14.1]
>40 years (n = 37)	8 [21.6]	20 [54.0]		22 [59.5]		5 [13.5]			3 [8.1]
p chi square	p = 0.3185 (chi2 = 0.99; df = 1)	p = 0.4549 (chi2 = 0.59; df = 1)		p = 0.3861 (chi2 = 0.75; df = 1)		p = 0.0465 (chi2 = 3.96; df = 1)			p = 0.3650 (chi2 = 0.82; df = 1)
Question 4	In what direction would you steer future revitalisation?
	I wouldn’t change a thing. Let nature take its course.	A park adapted to the needs of people of all ages and needs.			A “nature” park with parking facilities etc., but more of a forest-like character.			A large sports complex with sports fields, playgrounds etc.
<40 years (n = 61)	14 [22.9]	32 [52.5]			18 [29.5]			19 [31.5]
>40 years (n = 29)	10 [34.5]	11 [37.9]			5 [17.2]			6 [20.7]
p chi square	p = 0.2476 (chi2 = 1.34; df = 1)	p = 0.1972 (chi2 = 1.66; df = 1)			p = 0.2124 (chi2 = 1.55; df = 1)			p = 0.5850 (chi2 = 1.07; df = 1)

. Regardless of the age of the respondents, over 90% considered the revitalization of the landfill site necessary. Respondents were then asked what they thought the directions of action should be. For this question, respondents could select more than one proposed answer or indicate their own option. Regardless of age, the most frequently selected answers were liquidation and removal of pollution (60.6% for respondents under 40 and 73.0% for those over 40, respectively).

The next most popular responses were the possibility of rebuilding the site and using it for another purpose (46.5% and 46.0%, respectively). Older respondents were almost twice as likely to suggest that the site should be protected, e.g., as a landscape conservation area. In the “other” category, the most common responses indicated that the landfill site should be left unchanged. Respondents were also asked what roles this area could play in the future, and in this case, they could again select more than one answer. No other responses are included in Table 2 because those given by respondents could be classified under the proposed options. Regardless of age, respondents most often indicated that these areas should serve a natural and recreational purpose. Almost 22% of respondents over the age of 50 believe that these areas should not fulfill any of the above roles in the future and should be made inaccessible to users (in the “other answers” option, they specified this was due to a serious ecological threat and the fact that no one really knows what is inside the piezometers). A similar opinion is held by about 14% of respondents under 40 years of age. At the same time, respondents under 40 are more than twice as likely to view this area as a potential service location, primarily for leisure activities—e.g., an amusement park, sports complexes, etc. This approach to the potential use of the Boruta area is the only issue on which people who remember the landfill’s operation statistically differ in opinion from those who do not remember it.

In the next question, those who did not indicate that the landfill site should be inaccessible were asked how they would approach the reclamation and future development of the area. People over 50 were almost 1.5 times more likely to choose leaving the area unchanged and allowing nature to continue its work (in the “other” options, they specify this would occur after the waste had been removed). One of the most frequently indicated options was to transform the area into a fully organized park, with attractions adapted to users of all ages and with diverse needs.

In summary, the opinions presented indicate that most city residents perceive the need to revitalize the post-industrial Boruta area.

3.4. Determination of the Suitability of the Landfill for Recreational Purposes

Analysis of the Terrain

The landfill terrain was analyzed based on available hyperspectral images and the Digital Terrain Model (DTM). The landfill profile with two cross-sections and a 3D model of the site is illustrated in Figure 6. Analyzing the DTM from 2011 to 2022, it can be assumed that the terrain relief has remained largely unchanged [49,50,51]. The area is characterized by point changes in terrain relief. The most significant alteration was observed in the escarpment area along the right bank of the Bzura River. Between 2011 and 2022, due to erosion, a localized decrease in terrain elevation exceeding one meter was recorded (Figure 6C).

Based on the observed diversity of the landfill area, it was found that the area is highly suitable for recreational purposes, mainly due to the slope profile (inclination ranging from 45 to 90 degrees) and elevation differences of approximately 22 m (with the lowest point at 170 m above sea level and the highest at 192 m). An additional natural value is the lush vegetation covering the landfill, including native plant species. The survey results also point to the area’s potential for recreational development, provided that remediation and slope stabilization are undertaken to ensure the safety of visitors. This direction is further supported by literature reviews on the development of formerly degraded areas for recreation and tourism in the region.

Based on the terrain analysis, the landfill site exhibits favorable elevation properties that diversify the otherwise flat landscape of the Łódź agglomeration (Figure 1A). This makes it a valuable location with a potential viewpoint within the Łódź Voivodeship and a foundation for developing interesting pedestrian and bicycle paths, as well as skate parks for extreme sports cyclists. Based on the analysis of the terrain, it can be seen that the landfill site has good elevation properties that diversify the flat terrain of the Łódź agglomeration (Figure 1A) and can be a valuable place with a viewpoint on the map of the Łódź Voivodeship, as well as a basis for developing interesting pedestrian and bicycle paths in the area and skate parks for extreme sports cyclists. It is also optional to use the land for the development of sled or ski trails, mainly cross-country, provided that the costs of such investments are covered and there is a demand for this type of recreation preferred by the residents. However, it should be noted that due to the existing succession of plants, the area has good properties for being a peaceful recreation area with minimal external infrastructure influence needed to expand the place into a multifunctional sports facility. The results of these analyses and our research results, as well as a discussion of the problems of the selected site, formed the basis for writing a reflection on the development possibilities, limitations, and difficulties of these studies.

4. Discussion

4.1. Good Practices—Revitalization or Preservation of Large-Scale Landfill Sites in Poland

The most attractive approach, due to the positive social reception, is the transformation of degraded natural environments into new green spaces, even though this requires significant investment in the initial phase. Some degraded areas, converted into amusement parks, botanical gardens, or geological gardens, offer residents many opportunities to spend their free time in contact with nature [18]. The example of cities within Polish post-industrial agglomerations, such as the Łódź and Silesia regions, is also noteworthy. These areas often contain natural and semi-natural habitats that serve as breeding and living grounds for many species of amphibians and birds [15,16,17,18,19,20]. These areas are usually left in a state of rest and are sometimes subjected to a protection process. This is due to legal complexities or a lack of funds to transform these areas, such as recreation or education. In turn, Western European countries, with many good examples of landscape architecture revitalization projects, show many examples of well-conducted restoration and revitalization of the landscape of degraded areas. At the forefront are projects depicting post-industrial areas, such as the Ruhr area in Germany or Charleroi in Belgium, where the whole mining area has been developed for tourist and leisure purposes using the landscape qualities of anthropogenic transformations of old, degraded areas [17,29]. Another example of such development, although rarely mentioned, is found in the post-industrial areas of Weisswasser, Saxony, Germany. Here, sites that were initially devoid of any landscape value have been converted into recreational facilities, while preserving the original character of the degraded areas. A good example is the Rieselfelder field in East Berlin [13,81], where the former sewerage and wastewater areas have been adapted as open areas for active recreation. On the other hand, examples of municipal waste landfill management (e.g., Brownfields in Leipzig) show the active recreation of the city’s inhabitants concerning the value of the property and the use of recreation and maximum use of vegetation to mask the old charms of this degraded area [13]. It is worth emphasizing that these examples, although currently exemplary, were supported by a revitalization and reclamation plan and legally strengthened, and adequate funds from the dedicated budget have been allocated for their implementation. Thus, the method of revitalization successfully applied by Germany should serve as a model for Polish municipalities so that they can now apply for appropriate financial subsidies under the new law in Poland. A good premise for this is the new Act on the Revitalization of Large-Scale Degraded Areas in Poland [64], which also concerns the Zgierz case study. On the other hand, it is doubtful whether municipalities (local authorities), as managers of newly transferred degraded areas from the State (national level) without funds for this purpose, will now effectively apply for EU funds, as such action is not obligatory. At the same time, there is the goodwill of the manager to try to help researchers in interdisciplinary research, which can help to obtain funds to support the implementation of budget projects, e.g., from the financing of state funds or foreign funds within the framework of signed cooperation, e.g., Norway Grants for activities selling revitalization and remediation, which the city is already partly benefiting from by implementing other or, e.g., revitalization of urban space [14].

4.2. Developmental Eco-Recreational Directions of the Landfill Area

Pro-ecological recreational development is possible in post-industrial waste landfill areas [15,16,17]. However, how it shows selected reports and other degraded areas cases in Europe, it requires prior preparation of analyses to limit the impact of substances on the environment and human health [18,26,27]. To assess the current condition of the unreclaimed Boruta waste landfill in Zgierz covered by the study, comprehensive research was conducted using ground measurements (field observation and LiDAR) and remotely acquired data (flight method). The distribution of tree species was identified based on the mentioned aerial data (ALS) and satellite images [49,50,51]. Individual species were identified with high accuracy thanks to field vision and dendrological observation. Among the species analyzed, the largest share in each area was silver birch (B. pendula Roth), and the smallest was goat willow (S. caprea L.). The health condition of trees and herbaceous vegetation were assessed. In the case of trees, individuals assessed in the field as being in good or weakened condition were used as standards. The final product is a tree condition map showing their status and indicating trees in a weakened or poor state. The condition of herbaceous vegetation was presented on a 4-point scale (very good, good, deteriorated, and poor), identifying where poor vegetation condition could be linked to the impact of the landfill (Table 3). An analysis of the landfill’s impact on vegetation was carried out, taking into account the general condition of trees and herbaceous vegetation. The intensity of the landfill’s impact on vegetation is uneven. The effect of the landfill located in the study area is visible primarily along the right bank of the Bzura River, where the condition of the vegetation is significantly worse than in the surrounding area [44].

The analysis of the survey results conducted among city residents indicates the need to reclaim the degraded area and create places with a recreational function [77]. This is important from the perspective of the population’s needs. The creation of such spaces and the scope of recreational functions—for example, appropriately selected equipment—could in the future relieve heavily used parks or urban forests and provide entertainment, especially for local residents, by utilizing the natural potential of this previously unused area. The ecological trend of landfill remediation is beneficial, particularly in the context of sustainable urban development, smart cities, and the limited budgets of local governments financing the revitalization of degraded areas [16,26]. It should be noted that natural succession is the best proof of the potential for plant-based remediation to improve the condition of the natural environment, especially in the selected DMT area of slope near the Bzura River (Figure 6C). The selection of appropriate plants with anti-erosion properties can further help protect landfills from additional degradation. Therefore, specialist construction engineering procedures are unnecessary if a landfill exclusion period of 30 years is assumed, allowing for the development of natural vegetation. It would be sufficient to monitor and care for plants whose root systems can strengthen slopes, thereby preventing waste from escaping and contaminating neighboring areas. Fascine tubers used to reinforce slopes can be obtained from the basket willow (S. viminalis L.) or from seedlings of plants that tolerate partial shade due to tree crowns limiting solar radiation. These include Berberis thunbergii (DC), Cornus mas (L.), Corylus avellana (L.), Forsythia × intermedia (L.), Lonicera xylosteum (L.), Sambucus nigra (L.), Symphoricarpos albus (L.), as well as ground cover plants: Hedera helix, Ajuga reptans (L.), Asarum europaeum (L.), Pachysandra terminalis, and Vinca minor (L.) [49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82].

In the planning documents of the commune (Study of Conditions and Directions of City Development, Environmental Impact Forecast, Environmental Protection Program, and Local Land use plan), this place is designated as a future green area (ZN), as well as a part of the blue–green infrastructure of the city of Zgierz and the Łódź agglomeration [44,83]. It holds significant recreational potential with the possibility of being developed into a park and walking area, while preserving valuable tree species and adapting the space to meet the needs of the local community (e.g., walking paths, bicycle paths, recreational clearings along the river). Example visualizations are presented in Figure 7. Recreational activities (ecosystem services) can be freely conducted in available recreational areas, on slopes, and along pedestrian and bicycle paths. This should take into account the natural conditions and terrain, as well as the preferences of residents gathered from survey results [39]. It is recommended to utilize the natural values of altitude, as in the case of areas similar to construction waste landfills in the immediate vicinity, such as Górka Rogowska or Górka Retkińska in Łódź, at a relatively short distance from our study in Zgierz [21]

It is worth noting that these sites serve as locations for places to locate bicycle routes for free or extreme cycling, viewpoints, and pedestrian paths for active recreation, and some sports facilities rarely observed and developed in the Zgierz urban site. In addition, a playground, skate park, gym, and dog park organized as separate zones within so-called garden interiors and enclosed with vegetation would complement the more open recreation.

4.3. Revitalization of the River at the Landfill

Apart from the landfill area and escarpments, a significant problem is the surrounding environment, particularly the river and its bank reinforcement, which is not only dangerous for locals but also for national and European interests [73,74,75]. The microbiological risk of contamination in storage facilities and the close proximity of the river provide opportunities for the rapid spread of infected compounds from former dye factories [70,71]. Due to the age of the slag heap and the vegetation growing on it, classical methods of reclamation and waste neutralization are not possible [6,11,47]. However, they can help with the environmental problem through ecological methods using appropriate vegetation with remediation properties. Along the Bzura River, it is possible to plan plantings with biofiltration properties (e.g., reed canary grass, reed, calamus, and water palla), using buffer zones to collect and purify water from pollutants. A model for revitalization efforts may be the renaturalization of the area surrounding the ponds along the Bzura River in Łagiewnicki Forest, in Łódź, which borders the city of Zgierz to the south (Figure 1A). Another example includes the valleys of the Sokołówka River in Łódź and the Mleczna River in Radom (in the outskirts of Central Poland, in the eastern districts), where purification techniques and technologies have been applied using natural materials for separation (jute mats, stones, and plants from the biofiltration group) [84,85,86,87,88,89]. Eco-friendly materials such as fascines (S.viminalis L.) and wooden pegs could be implemented to strengthen riverbanks, reduce erosion, and create bypasses to calm river flow [88,89,90,91]. Examples of the renaturalization of small rivers are presented in Figure 8A–D.

The introduction of biofiltration zones constitutes an intervention in the landscape; however, it may reduce the activity of beavers, damaging the landfill area and the slopes near the river. At the same time, it is worth noting that appropriately selected recreational development could encourage wild animals to relocate to the protected forest areas nearby. A developed network of rivers exists in the Łódź agglomeration, including Łagiewnicki Forest with the tributaries of the Bzura River: Sokołówka River (Figure 1A and Figure 8A) and the Wrząca River with two smaller Zgierz’s wooden areas (Okrąglak, and the Krogulec forests) adjacent to the landfill area [84,88,89,90,91]. It should be emphasized that the mere presence of beavers (Castor fiber) may damage valuable trees such as S. caprea (L.) and B.pendula (Roth), which play a key role in remediation and recreation. However, according to Góralczyk-Bieńkowska’s environmental and microbiological research and Boruta landfill state of the knowledge from several WIOŚ and GDOŚ reports, it is crucial that these animals do not pose a threat by destroying ecological “bombs” within the landfills and releasing pollutants into the environment, potentially reaching the Vistula River (main Polish river) and Baltic Sea [5,47,52,53,54,55,56,57,58,59,73,74,75].

Recognizing the current development and, consequently, the problems of the revitalization of old dangerous landfills (including, among others, the course of long-term secondary plant succession) may help assess and plan the further implementation of spatial plans adapting these degraded sites to a new recreational and natural function in the future [77,78,79,80,81,82]. Apart from the issue of landfill reclamation, the subject of the article is the relationship of Zgierz with its main river, the Bzura, which is currently underestimated due to long-term neglect of management and care and needs strengthening and revitalization, similar to the old waste landfill in Zgierz. Due to the need to maintain the flow connectivity and stability of river environmental conditions for aquatic organisms, ecological flows are essential when designing new lateral reservoirs, which is especially important in shallow water ecosystems [92,93]. Environmental flows refer to the intra- and inter-annual variability of the natural flow regime, which applies especially to small rivers in Central Poland. This issue describes the quality, quantity, and timing of flow discharge required to preserve the ecosystem and sustain essential services upon which humans interact. Therefore, the conservation of environmental flows should be considered an important factor during new reservoir planning and management [94]. Landfill leachates contain many compounds, some of which can be expected to threaten health and nature if released into the natural environment. The content of the Boruta landfill has not been thoroughly investigated. Still, it is worth a more profound analysis because many studies indicate that a couple of 100 compounds have previously been identified in landfill leachates in Western and Northern Europe [32,33,34,35,36,95,96]. In the future, consideration should be given to relocating the riverbed of the Bzura River a few meters away from the landfill slopes. It could prevent landfill escarpment from being washed away and allow the waste collected and protected by vegetation and soil to escape. As mentioned in this chapter, it requires including ecological revitalizing methods and further consultations with stakeholders and local authorities, which is also an issue for future research.

5. Conclusions

Pro-ecological recreational development can be achieved through the succession of plants that naturally appear and quickly develop on post-industrial landfill sites. In Central Poland, pioneer species such as B. pendula (Roth), S. caprea (L.), and A. negundo (L.) rapidly established and reached maturity within three decades of landfill closure, creating a green area comparable to natural forests. We claim that the primary succession of these trees that reached the mature age of 30–40 years influenced the improvement of the environmental conditions of inactive waste landfills (ecologically slowing down the environmental threat) as a potential place for active recreation.

Remote sensing tools proved valuable for monitoring land development, from the moment the landfill is closed to its transformation into a recreational park, reflecting the growing trend of reclaiming degraded land for ecological and social benefits. This case study illustrates a cost-effective and sustainable model of urban landfill reclamation that can inspire similar initiatives in other cities.

The questionnaire survey highlights the significance of the degraded landfill site in Zgierz and its recreational potential due to its natural values. It is important to incorporate the public opinion into revitalization models for degraded sites within landscape architecture research, as well as into future sociological studies, as a meaningful consideration for future generations. This approach serves as a response to the challenges of sustainable development and landscape architecture in the context of climate change strategies based on ecosystem services and nature-based solutions. This issue should serve as the foundation for future interdisciplinary research integrating urban ecology, landscape architecture, environmental engineering, green microbiology, and urban geography. The survey is an important public opinion research tool and provides insight into the preferred development of degraded spaces.

The study highlights the necessity of interdisciplinary collaboration, integrating several disciplines. Public surveys are a valuable tool for understanding residents’ preferences and should be applied more frequently in planning the transformation of degraded spaces. This is particularly relevant in Poland and other post socialist cities of Europe, where many similar areas exist—including so-called ecological bombs of urban development in Europe. In such cases, the interests of local authorities are too often the only ones considered, while broader community perspectives and ecological functions deserve greater attention.

The presence of the Bzura River along the landfill may significantly limit the revitalization processes, as it is a barrier that facilitates the erosion of the slopes due to the activity of beavers (Castor fiber), as confirmed by our observations. The river itself, by undermining the waste material from the destroyed slopes, intensifies the spread of pollutants into the environment. The revitalization of the Bzura River and the application of slope reinforcement methods through the selection of biofiltration methods and new plant species can significantly improve the environmental quality around the area, reducing the risk of pollutants entering the Vistula River and the Baltic Sea. This action can be linked to recreational development based on new ecological methods.

This research offers guidelines for similar case studies of dangerous landfills in Poland on how to approach the remediation of degraded areas like post-industrial waste landfills. It is essential to address these often under-researched ecological bombs, especially through economic and ecological approaches, and to strengthen the pro-ecological trend toward sustainable, smart cities in Europe and worldwide. As an example of Western European countries (Germany), sports and leisure development should be carried out in the discussed area of the former landfill so that the facility can perform a new recreational function as an important element of the city’s green infrastructure, promoting the city and the region of Zgierz in Łódzkie agglomeration in the central part of Poland.