Analysis of Land Use Changes in the Sado Estuary (Portugal) from the 19th to the 21st Century, Based on Historical Maps, Fieldwork, and Remote Sensing

Abstract

This study analyses land use changes in the Sado Estuary (West-Central Portugal) based on a multi-temporal analysis of 19th century cartographic data and 21st century remote sensing land use maps, updated by fieldwork. A GIS plot of land use evolution is summarized in a quantitative table. The comparison shows the changes in land use, with increasing occupation by human economic activities, including extensive agriculture and forestry, as well as localized urbanization and industrialization. The main elements of the landscape impacted by anthropogenic uses were (i) hydrography—river dams affected the flow dynamics and sedimentary processes in the estuary; (ii) vegetation—increasing agriculture and forestry reduced the area of native vegetation, which is now mostly occupied by vineyards, pine forests and cork oaks; (iii) wetlands—tidal and alluvial plains are being occupied by rice cultivation, aquaculture, industries, and ports; (iv) coastal dunes—new developments are occupying large areas of Holocene coastal dunes; and (v) natural environment—mining and dredging have affected some habitats and biodiversity. This analysis is intended to help the territorial organization of present and future economic activities, as well as to reduce environmental and social problems, thus promoting the long-term sustainability of this rapidly evolving region.

1. Introduction

Human groups have always recognized soil and water as essential natural resources for food, shelter, and the development of economic activities. Environmental studies dealing with the use and occupation of land by human societies include the analysis of the state of biotic and abiotic components of the landscape—vegetation, mineral resources, soils, slopes, hydrographic network, and fauna. As societies succeed one another in occupying a given space, their relationship with nature also changes according to economic and social interests and the space itself undergoes transformations.

Multi-temporal analysis of land use through geoprocessing techniques serves as an auxiliary tool for monitoring and evaluating urban expansion and economic activities in the territory. Remote sensing becomes important for identifying changes in the landscape and the state of its natural resources, while providing cartographic documents that reveal environmental changes on different scales—local, regional, and global. By integrating the information from these analyses, it is possible to understand the consequences of environmental problems affecting the territory—climate change, soil degradation, and water scarcity and contamination, among others.

With such territorial data, local and public agencies can develop plans for land use planning and management, defining actions for the rational and sustainable use of natural resources, to ensure the well-being and preservation of current and future generations.

In different countries, researchers have studied land use and occupation using satellite images and geoprocessing techniques for various purposes: understanding the impacts on natural resources, proposing mitigation measures for environmental problems, monitoring desertification processes in certain regions, identifying areas under anthropogenic pressure, selecting ecological zones for conservation, and supporting sustainable environmental planning and management [1,2,3,4,5,6,7,8].

Anthropogenic pressures resulting from land use and settlement cause changes in systemic relationships between environmental components, with evident impacts on natural resources. In 1987, the World Commission on Environment and Development produced the document “Our Common Future”, an agenda that pointed out the need for adopting actions to reduce the degradation of nature [9]. This gave rise to the concept of sustainable development, understood as the use of natural resources to meet the needs of the present generation, while ensuring the preservation of these resources to meet the needs of future generations. It therefore proposes the adoption of an economic model that harmonizes development and conservation of natural resources.

“Our Common Future” was followed by numerous international conferences in which representatives of nations established protocols and agendas to reduce impacts on environmental resources and biodiversity. The Rio-92 (United Nations Conference on Environment and Development) established Agenda 21 and promoted the concept of sustainable development, which should be incorporated into planning projects of all sectors, emphasizing the conservation of natural resources [10]. Despite these initiatives, serious environmental problems are still observed in different regions of our planet.

Several researchers use a multi-temporal analysis of a given area, based on historical maps that are georeferenced and digitized so that the information can be compared with that contained in modern cartographic products, such as satellite images and others [11,12]. The use of satellite images and cartographic documents in the multi-temporal analysis of a region can guide actions towards environmental planning focused on sustainability, pointing out the need to harmonize economic development and conservation of environmental resources, as the continuity of humanity depends on these resources.

This study aims to contribute to improved environmental planning in support of a sustainable development. This paper presents a multi-temporal analysis of land use and occupation in the municipalities of the Sado Estuary, from the 19th to the 21st century, using historical maps and satellite images. The 19th century analogue map has been composed and georeferenced using the QGis 2.18 software, in order to compare it with the 21st century GIS map. All the digitized features are available in a database, to serve as a basis for further studies.

The importance of this study consists of making it possible to identify the transformations that have taken place in the territory, and thus to correlate them with the environmental problems present in the current landscape and even to create future scenarios for the occupation of the territory and the rational use of resources, in order to avoid its degradation and environmental impacts. This information supports the decision making of public managers in the organization of economic activities in the territory.

2. Materials and Methods

2.1. Regional Characterization

The study area encompasses lands of four municipalities around the estuary of the Sado River, within the boundaries of the hydrographic basin—Setúbal, Palmela, Alcácer do Sal, and Grândola (Figure 1). The choice of this area is justified by its highly dynamic environment, where natural factors and phenomena interact, alongside with growing urban expansion and economic activities.

The downstream boundary of the study area corresponds to the river mouth of the Sado, a line defined by the Portuguese Official Administrative Chart (CAOP), between the Tróia peninsula and the city of Setúbal. The upstream boundary has been considered to be the upper tip of the higher dynamic tides, located about 15 km SE of the city of Alcácer do Sal [13].

The Sado hydrographic basin drains an area of 7692 km², making it the largest entirely Portuguese basin. It is bounded to the north by the Tagus basin, to the east by the Guadiana basin, to the south by the Mira basin, and to the west by a coastal strip that drains directly into the sea [14]. The Sado River originates in Ourique, in the Serra da Vigia (230 m), and flows into the Atlantic Ocean, with a total length of 180 km. The estuary has a submerged area of approximately 200 km², corresponding to the estuarine basin and the submarine ebb delta [14].

The area falls within the Mediterranean temperate climate zone, with hot, dry summers and an average annual precipitation of around 600 mm [15]. Rainfall is concentrated in the autumn–winter period, accounting for 60% of the annual volume, with more than 70 mm/month from October to January.

The geological basement includes different lithologies and ages, predominantly from the Paleozoic to the Quaternary period. The main river and its tributaries drain mostly Cenozoic terrigenous deposits of the Sado Basin [16]. This basin is bounded (i) to the north by the Arrábida Mountain Range consisting of Mesozoic carbonate rocks; (ii) to the east by a morphological rise, marking the contact between the Cenozooic sedimentary rocks and the Paleozoic, mostly metamorphic rocks of the South Portuguese Zone (SPZ) and the Ossa-Morena Zone (OMZ); (iii) to the west by the Atlantic Ocean; and (iv) to the southwest by the Grândola fault [16].

The geomorphology is characterized by a flat and gently undulating landscape, with a low gradient slope and very small elevations, except for the mountain ranges of Arrábida and Grândola. The predominant soils have a sandy texture due to the rocks and deposits that originated them.

Currently, according to the 2021 demographic census, the resident population in the municipalities corresponds to about 217 thousand inhabitants, engaged in rural and urban activities, port operations, industrial activities, agroforestry production, and tourism. Setúbal has the highest population density and both Setúbal and Palmela showed growth rates, while Alcácer do Sal and Grândola experienced a population decline in 2021, compared to the previous census.

2.2. Methodological Approach

This study focuses on the evolution of land use and occupation of the estuarine municipalities of Sado River, in West-Central Portugal. Historical and recent cartographic documents, satellite images, and geoprocessing techniques have been used, with the help of a Geographic Information System (GIS) to identify changes that occurred during the 19th to 21st centuries.

The spatial analysis of an area using GIS tools allows for the observation of landscape transformations resulting from natural phenomena or induced by anthropogenic interventions. This approach helps to define the management of the territory with the aim of reconciling economic development with environmental and social sustainability. These techniques are therefore important tools for sustainable environmental planning, allowing the prevention and monitoring of impacts on ecosystems.

In order to carry out the multi-temporal comparative analysis, land use maps from the 19th and 21st centuries were developed. Old maps are very important documents for the analysis of geographic space. However, for a comparative analysis with digital products of modern cartography, they need to be available in digital format and georeferenced. The 19th century land use was prepared based on 8 Pery agricultural maps, on a 1:50,000 scale, provided by the DGADR [17]. These maps were articulated to form a mosaic that was georeferenced. The polygons were vectorized, and the features were identified by their corresponding type of use. The areas of each feature were then extracted from the prepared map in order to understand the dominant uses in the 19th century. To facilitate comparative analysis between the two final cartographic products, the 19th century “types of use” classes were adapted to those established for the 21st century D-GTerritory map.

The georeferenced historical maps were compared with current Google Earth Pro Landsat/Copernicus satellite images from 2020, allowing us to observe aspects of current use. The common natural elements in the past and current landscape, such as the mouth of the Sado River and some hilltops, served as control points, allowing us to observe the changes occurring in space. The geographic coordinates of Pery’s charts were used as a reference.

In this comparative study of the use and occupation of the Sado Estuary, nine topographic maps on a scale of 1:25,000 were also used to observe the characteristics of the river mouth and estuarine channel of the Sado; six were produced by the Army Geographic Institute (IGeoE) and three by the Army Cartographic Service (SCE), published between 1987 and 1994.

The 21st century map was produced using the COS 2018 maps, georeferenced in the shapefile format, Datum Lisboa, provided by the D-GTerritório website [18]. Both ancient and modern cartographic outputs were generated using Geographic Information System (GIS) techniques and the QGis 2.18 software.

Polygons were created and integrated to highlight the predominant land use types. The two GIS maps were then superimposed to analyze the changes and evolution in land use and which areas were expanded or decreased. The necessary adjustments to the maps resulted from the combination of satellite image interpretation and fieldwork observations. Thus, qualitative information based on the terrain topography characteristics and land use and cover was added to this analysis. Field work in the municipalities of the Sado Estuary also included photographic records and land use checking.

A table was compiled with information on the main types of land use represented in the 19th- and 21st-century maps, indicating the occupied area, both in km² and percentage, to highlight changes occurring over the period. In addition, graphs were also produced, objectively summarizing these changes.

Land use classes were defined and characterized based on the “Technical Specifications of the Land Use and Occupation Chart of Continental Portugal” with 7 classes—artificial surfaces; agriculture and cultivable lands; pasture; agroforestry and forest area; mixed vegetation; coastal environments; and coastal wetlands [19].

3. Results

3.1. Historical Land Use and Occupation

Land use and occupation patterns reveal how societies manage landscape and use its natural resources. Human interventions tend to create imbalances or environmental impacts, proportional to their technological development.

Human presence around the Sado Estuary dates back to the Mesolithic period [20]. Approximately 20 thousand years ago, global warming led to the melting of ice in the Northern Hemisphere, causing sea levels to rise, and marine transgressions resulted in the flooding of lower river sectors, forming estuaries [21].

The mild temperatures of the Holocene favoured the migration of Mesolithic peoples to coastal regions. Due to its ecological–geographical characteristics, the Sado Estuary was occupied by these peoples, who lived in the area and exploited its food resources [22]. Holocene climatic fluctuations in Portuguese territory modified the original land cover, particularly in the coastal region, where the sub-humid climate favoured the expansion of maritime pine forests (Pinus pinaster) and oak forests (Quercus) [23].

Chalcolithic shell middens have been found in the Sado valley and its tributaries on river terraces and at the base of slopes, indicating the occurrence of sea-level rise and occupation of the area between approximately 8400 and 7000 cal BP [18]. These peoples lived mainly by gathering bivalve mollusks, fishing, and hunting, and remained in this territory for about a thousand years.

Over time, other peoples inhabited the lands of the Sado River and estuary, including the Romans, the Moors, the French, and others who were interested in the natural resources and/or its strategic geographical location. Archeological studies have revealed the existence of Roman kilns dating from the 1st century BC to the 5th century AD, which produced amphorae in the sites of Abul and Herdade do Pinheiro—Alcácer do Sal. The amphorae were destined for the industrial fish salting complex, on the Tróia peninsula [23]. Despite ancient occupation and use of natural resources in this area, these peoples did not cause significant environmental changes.

Salt production has been developed in Setúbal and Alcácer do Sal since the Roman times. In the 16th century, salt pans were built in the marsh areas along the banks of the Sado, mainly in Abul, Batalha, Faralhões, and Gâmbia. In the following century, the activity spread to the Mitrena peninsula. Salt production played a prominent role in the Portuguese economy until the end of the 19th century, when it began to decline [24].

The 19th-century map (Figure 2) shows the main types of land cover and land use. At that time, most of the territory was occupied by heaths and scrublands—typical xerophytic vegetation covering extensive plains. These protected the low-fertility sandy soils from erosive processes, by adding organic matter to it.

Historical documents record the replacement of extensive areas of pine forests and heaths by vineyards in the 18th century [24]. The property of José Maria dos Santos was by then one of the largest vineyard in the world, covering the territories of Palmela, Setúbal, Alcácer do Sal, and Grândola. Rice cultivation has been established in the district of Setúbal, particularly in Alcácer do Sal, since the 18th century. In the 19th century, the paddy fields covered approximately 55 km² of the area, concentrated in Alcácer. Rice cultivation occupied the alluvial plains of the Sado and its tributaries. Viticulture then covered an area of around 30 km², spread particularly to the north (Palmela) and in Alcácer do Sal, with a small occurrence in Serra de Grândola.

By the end of the 19th century, rice and wheat were the main crops grown along the riverbanks. On the hilltops, historical documents also record the replacement of extensive areas of pine forest and heaths by extensive vineyards. The agroforestry use consisted mainly of extensive “montados” of cork oak (Quercus suber) and holm oak (Quercus ilex), and to a lesser extent stone pine (Pinus pinea). This occupation occurred at the beginning of the Liberal Regime, at the end of the 18th century and the beginning of the 19th century [25]. At that time, large private landholdings, cheap wage labour, and state support for the removal of native vegetation favoured its establishment.

In the 19th century, cork oak “montados” dominated the territory of Grândola, Águas de Moura-Palmela, and Alcácer do Sal. Pine trees covered the central sector of the study area, and holm oaks predominated in areas with drier climatic conditions (Figure 2). Due to the difficulty in visually identifying the shades of these forests in Pery’s maps, these types of cover were grouped into the classes of oak forest and pine forest, corresponding to an area of 184 km² (Figure 2).

Saltpans dominated the plains affected by the ocean tides, while rice cultivation developed on large plains flooded by river waters. In the northwest sector, in Palmela and Setúbal, horticultural crops and vineyards stood out, while in Alcácer do Sal, vineyards were interspersed with olive groves. At the mouth of Sado, the salt marshes and intertidal zones covered about 49 km², predominating the salt flats, concentrated on the right bank, in the parishes of Faralhão and Gâmbia—Setúbal.

3.2. 21st Century Land Use and Occupation

Between the 19th century and the present day, the landscape of the Sado territory has undergone significant changes, with the emergence of new activities and the retraction of others. In this analysis, seven main classes of land use and cover were identified: (1) artificial areas—urban areas, industry, and commerce; (2) agriculture and arable lands—viticulture, olives, rice cultivation, and mixed farming; (3) pasture—native and planted forage; (4) agroforestry—cork oak “montados”, holm oak, and pine trees; (5) mixed vegetation—agroforestry lands with different oak species and shrubs; (6) coastal environments—beaches and dune fields; and (7) coastal wetlands—salt marshes, seagrass meadows, and intertidal zones (Figure 3).

The expansion of the urbanization process in Setúbal is striking in this century, clearly influenced by its proximity to Lisbon, the country’s capital. Setúbal and Palmela form part of the Lisbon Metropolitan Area (LMA). Setúbal is experiencing solid economic development due to the port activity on the Mitrena peninsula, which has also contributed to urban growth (Figure 4g). The urban and industrial built-up areas represent 58.51 km² of the territory, representing 2.3% of the total area.

In all municipalities, the areas of the alluvial plains and part of the tidal plains are cultivated with different varieties of rice (Figure 4b). Portugal is one of the five largest producers (and also per capita consumers) of rice in Europe, with the municipalities of Alcácer do Sal and Grândola standing out at the national scale. Rice fields occupy 78.2 km², about 3% of the study area. Salt production has experienced a sharp decline, and it is now confined to small areas of the tidal plain in the parishes of Faralhão and Gâmbia (Figure 4a). Vineyards are increasing in the northwest region, in the municipalities of Setúbal and Palmela, part of the Arrábida Chain, producing renowned wine for the national and international markets. They occupy almost 50 km², almost 2% of the total area.

Pine forests have spread widely across the territory on the left bank of the Sado to meet the demands of the timber, furniture, pulp, and paper industries. Both maritime pine and stone pine have adapted to sandy and infertile soils. The increase in areas with maritime pine forests is justified for reducing wind erosion of the sandy soils and also of coastal dunes. Additionally, these pines produce pine nuts, an edible seed highly used in local gastronomy, especially in Alcácer do Sal.

The landscape is characterized by agro-silvo-pastoral systems represented by “montados”, which combine cork oak or holm oak forests, agricultural crops, forage plants, and livestock farming—cattle or sheep (Figure 4f). The cork oak provides raw material for the cork industry, ensuring Portugal’s position as the world’s largest cork producer (Figure 4c,d). These systems are complex to manage, as they are known to benefit landscape conservation/maintenance, soil nutrients, biodiversity, and water resources, as well as being a cultural trait of the vast Alentejo region, the extensive dry plains of southern Portugal.

Agroforestry covers only 4.2% of the territory, encompassing native vegetation. This category has experienced a significant decline due to other economic activities, sometimes supported by public policies and urbanization. Polyculture and water bodies cover 198.31 km² and 158.43 km² of the total area, which is 8% and 6%, respectively. Olive cultivation occupies 20.47 km², about 0.8% of the total area, but demonstrates an increasing trend in the southeast sector of Alcácer do Sal, especially towards the eastern and drier part of the region, near the village of Torrão.

Among the activities identified in the area, limestone extraction for cement production has the greatest visual impact on the landscape. This activity is concentrated in the Arrábida mountain range, which presents highly degraded areas, although it corresponds to a protected environmental unit—the Arrábida Natural Park.

Visual and noise impacts are high, affecting the resident population in the surrounding areas, and plans to enlarge the extraction area have recently been refused by local authorities (CCDR-LVT). The environmental impacts of this activity include the degradation of biotic and abiotic elements of the landscape—relief, soils, vegetation, river channels, habitat destruction, and loss of biodiversity—affecting the interrelationships between components of the environmental system. Although the companies have approved and ongoing plans for environmental restoration, mainly through reforestation, the imbalances disrupt the dynamics of the natural system, which, once disrupted, does not return to its original characteristics.

The Grândola mountain range also shows landscape scars resulting from historical underground mining. For many years, the Caveira and Lousal mines were in operation, extracting ores from the Iberian Pyrite Belt rocks. Studies indicate that besides inheriting landscape degradation, there was also soil and water contamination by heavy metal residues [26]. In Alcácer do Sal, the exploitation of geological resources (kaolin and quartz) occurs in the Casal Ventoso sandpit formed by dunes and deposits of Holocene aeolian sands [27] and in Lagoa Salgada (Figure 4e).

In the river channels of the Sado basin hydrographic network, the most frequent anthropogenic interventions are dams, affecting the flow dynamics of rivers and the volume of transported sediments. Thus, sedimentary processes in the estuary are also altered, with erosion points in the tidal plains, colonized by salt marshes.

In the current spatial organization of the area, the Sado Estuary Natural Reserve (RNES) stands out, an area created by law in 1980 to ensure the conservation of the estuary and the development of activities compatible with this ecosystem [28]. To achieve this, in 2008, the Reserve’s Management Plan (PORNES) established the types of use for the National Ecological Reserve (REN)—areas that are of biological interest or not heavily urbanized—and for the National Agricultural Reserve (RAN): lands with fertile soils or suitable for agricultural use [25,28]. The Directorate-General for Agriculture and Rural Development considers RAN a land management tool, recognizing their suitability for agriculture due to agroclimatic, geomorphological, and pedological characteristics. However, there is an overlap of RAN in some REN areas, as well as the use of parts of the tidal plain for rice and salt production (Figure 3).

Tourism is developing on the coastal beaches of Grândola and in the Sado Estuary itself, where the only community of bottlenose dolphins lives. The historic Roman ruins at Tróia, the palafitic pier at Carvalhal, and the religious and military monuments of the Arrábida mountain range are also important local attractions.

Port and industrial activities on the Mitrena peninsula require frequent dredging in the estuary to allow for the passage of deep-draft vessels, posing a constant threat to estuarine biotopes. Increased water turbidity and pollution affect the seagrass meadows that support the estuarine food chain, including the bottlenose dolphin community, while salt marshes and mudflat areas are also modified. The Institute for Nature Conservation and Forests recognizes that dredging can cause environmental problems and reduce salt marshes but understands that it is carried out downstream of RNES, i.e., outside the area included in PORNES.

4. Discussion

To facilitate comparison of the evolution of types of use and occupation in the estuarine municipalities of Sado between the 19th and 21st centuries, Figure 5a,b present the areas represented in Figure 2 and Figure 3. These maps are complemented by

Table 1. Quantitative comparison between the 19th century and 21st century land use and occupation (see also Figure 5a,b). (1) With no specific representation at Pery’s maps; (2) Accounted together with “cork oak”, due to the difficulty in distinguishing its shades in Pery’s maps.

Land Use	Types of Use (Dominant)	19th Century Area in km² and (%) of Total	21st Century Area in km² and (%) of Total	% Change (19th to 21st)
Artificial surface	Urban area	2.4 (0.09%)	58.51 (2.3%)	+2.437%
Agriculture and cropland	Paddy fields	54.84 (2.26%)	78.20 (3.11)	+42%
	Vine	29.69 (1.22%)	49.16 (1.95%)	+65.57%
	Olive	(1)	20.47 (0.81%)
	Polyculture	82.89 (3.42%)	198.31 (7.90%)	+139.24%
Agroforests and Forests	Cork Oak	395.44 (16.34%)	899.05 (35.83%)	+127.35%
	Pine	(2)	692.36 (27.60%)
	Holm Oak	(2)	122.21 (4.87%)
Mixed vegetation	Agroforest surfaces	1493.13 (61.70%) (Natural vegetation)	104.69 (4.17%)	−92.98%
Pasture	Pasture and native grasses	(1)	74.46 (2.96%)
Coastal wetlands	Salt marshes/intertidal	49.11 (2.02%)	48.27 (1.72%)	−1.71%
Coastal environments	Beaches, dunes, sand	(1)	4.66 (0.18%)
Other	Water bodies	95.62 (3.95%)	158.43 (6.31%)	+ 65.68%

and Figure 6, to analyze the percentages of activities that had a reduced or increased area.

The total areas obtained for the 19th and 21st centuries have a slight difference of less than 5 km² (around 0.2%), which is quite acceptable for the accuracy of the historical maps. It should be noted that in the 19th century map, there are areas without available cartographic information, which are not accounted for. The values were calculated using geotechnologies, but when compared with the data and textual information compiled from the consulted publications, it is understood that they are consistent, as they generally usually attribute values of around 2500 km².

It is worth highlighting that the public policies implemented in Portugal during the first three decades of the 20th century strongly influenced the use and occupation of land, which explains some of the changes identified and quantified in this region [29]. These policies resulted in new economic guidelines such as the Wheat Campaign, the Irrigation Plan, and the Forestry Plan. The former emphasized the importance of wheat production in the country, and this crop expanded in low fertility soils, previously occupied by heaths and bushes, with the introduction of agrochemicals and mechanization. The Irrigation Plan highlighted the need for dams and agriculture irrigation projects, thus contributing to changes in the dynamics in the network of river channels in the drainage basin. In turn, the Forestry Plan encouraged the expansion of forestry to meet the growing needs of the cellulose industry.

Table 1 and Figure 6 present some gaps due to the lack of all agricultural maps from the 19th century, but they provide a snapshot of the past and present situations.

In the 19th century, almost two thirds (61.70%) of the study area was covered by natural vegetation—heaths, shrubs, and other spontaneous species (Table 1 and Figure 6). The exceptions were about 16% of scattered oak areas and less than 5% of the polyculture along the Sado riverbank. In the current century, the natural vegetation has been strongly replaced by pine forests, which are now planted to control erosion of the sandy soils and dunes in this area. There has also been a marked expansion of cork oak “montados”, often intermingling with pine forests, increasing by around 127%, from less than 400 km² to almost 900 km² (Table 1 and Figure 6).

In the past, polycultures extended over an area of 83 km² and were more concentrated around Setúbal, which already had a consolidated urban area in the 19th century. This type of land use included orchards and mainly cereal crops such as wheat. In the current century, its area has decreased due to the growing process of urbanization, but in other municipalities, it has increased, occupying almost 200 km² (Table 1 and Figure 6), representing an increase of almost 140%.

Vineyards have been cultivated since the 19th century, covering almost 30 km², and are a cultural feature of the Palmela region. At that time, there were vineyard properties in Alcácer, but they were not very important. Today, different grape varieties continue to be produced in Palmela and Setúbal, mainly in extensive plains and also in parts of the Arrábida mountain ranges, marking a territorial expansion of 65% (Table 1 and Figure 6).

The changes in coastal wetlands over the analyzed time period are remarkable. These areas, corresponding to high and low marshes at the interface between the continent and the sea, contribute to protecting important and vulnerable coastal biomes, being highly dependent on tidal fluctuations. In the past, these areas covered an area of 49.11 km² compared to 48.27 km² today. This slight reduction may be related to erosive processes due to anthropogenic actions such as (i) damming of river channels, which retains part of the sediments and modifies the deposition processes in the estuary; (ii) degradation of riparian forests, deforestation, etc.; or (iii) natural causes—climate change and sea-level rise.

The surface occupied by water bodies has increased significantly in the 21st century, by almost 66%, or 158.43 km². This increase is likely related to the liquid surfaces of the reservoirs of dams existing in the tributaries of the Sado River, in Alcácer do Sal—Pego do Altar and Vale do Gaio or Trigo de Morais, in operation since 1949. In addition to the dams, there are also weirs scattered around the local farms. The land use that showed a contrasting increase in the analyzed period, with more than 2.40% in the current century, was urban and built-up areas. The demographic growth in Setúbal contributed significantly to these data, and there seems to be a tendency for this population concentration to continue due to important economic activities in this municipality and in Palmela.

Touristic activities are associated with beaches, due to the scenic beauty of the coastal landscapes and the presence of the resident common bottlenose dolphin community in the waters of the estuary, between Setúbal and the Tróia peninsula.

5. Conclusions

The current socio-environmental crisis faced by modern urban–industrial societies is a legacy of a time when the planet’s natural resources were believed to be infinite. Until the end of the 20th century, the management, governance, and appropriation of natural resources were not planned with sustainability in mind, aiming to ensure the maintenance of future generations.

Today, there is a need to establish new relationships between society and nature, based on rationality, as natural or induced environmental problems—climate change, rising sea levels, desertification, water and air pollution, soil erosion, etc.—repeatedly manifest themselves and point to an unsustainable future for humanity.

The multi-temporal analysis showed that the territory of the Sado Estuary municipalities presents a mosaic of different economic activities. Some are quite traditional and date back to the Mesolithic period, such as fishing and shellfish gathering, while others have been gradually introduced in response to market demands or by economic interest groups, such as oak and pine forestry, rice and wheat crops, or more recently mining and industrial port activities. Some recent land uses have been particularly aggressive to more environmentally sensitive areas. There has been a lack of analysis of the “carrying capacity” of the environment, or an assessment of the potential for its resilience. Environmental pressures and impacts are clearly increasing in this region, threatening the preservation of its natural resources for future generations.

The application of geoprocessing techniques using Geographic Information Systems (GISs) allows large areas of the territory to be observed and analyzed at any scale—macro or micro. The cartographic products thus generated make it possible to develop environmental planning based on sustainability, to propose the reorganization of land use based on new management practises, to define the protection of areas with fragile ecosystems, and to monitor deforestation and the degradation of natural resources, in order to achieve better environmental and social quality.

It is necessary to foster debates about the sustainable use of natural resources and to move closer to effective actions that can make it feasible. To this end, governments must propose and adopt socio-economic models that avoid the degradation and waste of these resources, defining the environment as a priority over strictly economic goals. The consumption patterns of modern societies need to be rethought in order to reconcile development with environmental, economic, social, political, and cultural sustainability. It is necessary to recognize that the physical environment is the crucial support of life and human activities. With increased knowledge and awareness, it will be possible to plan for the well-being and preservation of present and future generations.