The research has foundations on the General System Theory proposed by the German biologist Ludwig von Bertalanffy in 1930, based on the Pacoti River Watershed. In this perspective, when making a geographic study, it is necessary to use the concept of system to understand the complex issues as they are interdependent, that is, the variable natural units inserted in the study area.

Thus, in a systemic approach, watersheds integrate a joint vision of the behavior of natural conditions and human activities developed in them, since significant changes in any of these units can generate changes, effects, and negative or positive impacts. As a rule, it establishes the relief as a possible unit to map more expressively without losing the sense that they are related [2] , Figure 2.

To the author, the structural elements (rock, climate, and water) that make up the scenario of natural landscapes comprise in this study the exploitation potential constituted by the elements (soil, vegetation, and water) that make up the system. They unfold in the relief and results in the interaction of social actions originating the derived landscapes.

The area in the Pacoti River Watershed is a coastal zone, represented by Eusébio and Aquiraz. The climate is the sub-humid tropical warm (Figure 3), which goes from the coastal region to half of the Great Watershed area.

From data collected by the rainfall stations, the choice for Aquiraz was because it generally represents the coastal zone and a large amount of rainfall data among the collection stations of the nearby municipalities.

In the coastal zone, the rainfall levels are relatively higher than in other towns in Ceará because of the proximity to the ocean. Therefore, the evaporation rate is higher, contributing decisively to higher precipitation levels (Figure 4).

In Figure 5, it is possible to make a monthly analysis regarding the rainfall averages distributed throughout the year. The rainy season in the state of Ceará is in the first half of the year, more precisely in the first four months.

The figure below proves that the highest averages over the year are in March, April, and May, whose values are even higher than other regions in Ceará.

The coastal tablelands represent ancient depositional surfaces presenting extremely smooth gradients towards the coastline. These relief forms are dissected by a network of channels of low drainage density and dendritic pattern, forming shallow u-shaped valleys with, at most, 20 meters of unevenness.

Towards the countryside, the tablelands are fragments amidst the crystalline outback surface because of the partial removal of this sedimentary capping. It indicates a significantly broader and more continuous original coverage of the Barrier Group, which extended for several tens of kilometers into Ceará and may have reached the foot of the Baturité massif [11] .

Using the cartographic bases used to make the maps (Figure 6), one can identify a range of geological units. Six kinds—Holocene Alluvium, Barrier Formation, Holocene Aeolian Cover, Canindé and Independência Units, Marsh Deposits, and Holocene mangroves—were identified in the coastal zone of the Pacoti Watershed.

The Barriers Formation is near the main course of the Pacoti riverbed, while the Holocene swamp deposits are at the mouth. The region has characteristics, such as salinity and amount of nutrients, for the development of mangroves.

Several phenomena of planetary magnitude influence the morphology of coastal zones. The most important are plate tectonics, climate, and relative sea-level variations. The movements between the continental and oceanic plates determine the type of coast and its orientation concerning exposure to waves and

currents. The climate controls continental erosion, is responsible for sea-level oscillations, and influences the coastal plain evolution [12] .

About 120 million years ago, the Ceará coastline did not exist, Africa was still joined to South America, forming Oceania, and India and Antarctica formed the supercontinent Gondwana. The complete rupture of the South American and African plates occurred between 100 and 99 million years ago, during the Cretaceous period of the Mesozoic Era. This process originated the equatorial segment of the South Atlantic and the continental margins of Northeast and West-Central Africa, which slid relative to each other [12] .

It is possible to identify, according to Figure 7, that the main geomorphological features in the coastal zone are mobile and fixed dunes and pre-coastal tablelands.

The pre-coastal tablelands go laterally along the coastal zone, mainly in the area after the beach, and often do not reach long distances towards the continent. There are lots of summer houses, and property speculation is prevalent in such a region. Besides, the area suffers from other forms of environmental degradation. The fixed and mobile dunes, which are tourist attractions, are close to the sea bed.

The coastal plain of Ceará extends over a long stretch of land between the coastline and the coastal tablelands, although it is narrow, covering almost all the Ceará coastal zone. Directly linked to the river mouths, the fluviomarine plains are developed, standing out the mangroves that occur on the margins of the estuaries or river mouths that flow into different regions of the coast [11] .

According to the author [11] states that predominantly, the fluviomarine plains are developed on soils with quartz characteristics, deep, with little adhesion and cohesion between its particles, and low retention capacity of moisture and nutrients, constituting Quartz Neosol in most of the land.

Based on cartographical bases and under the graphic scale adopted in the produced maps—scale 1:100,000—that aim at a macro view of the region, the type of soil found in the coastal zone of the watershed is the Red-Yellow Acrisol, as seen in Figure 8.

According to the authors [13] , the Red-Yellow Soils serve the cultivation of sugar cane, fruits (jackfruit, mango, banana, sapota, citrus, coconut, acerola), pasture (brachiaria, pangola-grass, and elephant grass), cassava, passion fruit, and yam. For rational use, they need fertilization and liming because they are soils of low natural fertility. In the areas where crystalline rock and sub-deciduous forest prevails, the Red-Yellow Soils serve the cultivation of mango, coconut, pastures, among other uses.

The natural fertility level in this soil ranges from low to medium, being the reliefs in crystalline rock environments a significant limitation. In the study area, there is slightly rugged relief and the presence of crystalline rocks. In coastal tablelands, these soils need correctives and fertilizers to obtain good crop productivity, requiring the use of organic matter in the superficial horizon, especially in soils with sandy texture [13] .

Soils lose a large part of their genetic seed bank because of the erosional process,

which is a factor present in almost all regions of the state of Ceará, even in the coastal zone. Erosion makes the soil lose its surface cover, rendering natural revegetation difficult even in the rainy season. If it happens over the years, desertification starts to a certain degree.

As shown below, three phyto-ecological units are present in the coastal zone of that area, which are cerrado, coastal cerrado, coastal vegetation complex, and mangrove (Figure 9). They have adapted to the local conditions, such as temperature, climate, soil, salinity, and nutrients.

The mangrove presents greater fragility and vulnerability because it is an environment extremely sensitive to environmental changes. Its system is a typical coastal ecosystem of tropical and subtropical regions defined as transitional zones between the marine and terrestrial environments. This environment serves for fish, crustaceans, and mammals to reproduce, being a nursery for them.

By being close to the caatinga and cerrado [14] , the coastal vegetational complex in Ceará is the coexistence of species from such domains and species from the restinga in other formations. Despite the ecological and botanical importance of this ecotone, there are few studies on the regional flora.

To record in which environments the species occur [14] used categories of coastal environments of the phyto-ecological unit system of Ceará [15] with adaptations and identified as constituent units of the coastal vegetational complex: Psammophilous pioneer vegetation I, Psammophilous pioneer vegetation II, fixed dunes forest and dune rear, pre-coastal tablelands vegetation, aquatic and paludose vegetation of lagoons and marshes, and dicotyl-palmaceous forest.

The predominant economic activities in the coastal region of Ceará are extensive livestock farming (goats, sheep, and cattle), cotton, and subsistence agriculture (corn and beans) on the best soils. However, indiscriminate deforestation and overgrazing have led to the loss of biodiversity of the caatinga and the expansion of agricultural activities, and without the use of techniques to protect the soil and water resources, they are making extensive areas of the outback depression vulnerable to desertification [11] .

In the coastal zone, agricultural activities occur because it is the prevailing subsistence activity of local families. Annual, temporary and permanent crops occupy a great area in the coastal zone of the Pacoti River Watershed, Figure 10. Although agriculture prevails, there are areas with the presence of remnant natural vegetation near the Pacoti Riverbed.

According to data from the Superintendência Estadual do Meio Ambiente do Ceará (State Superintendence of the Environment of Ceará, [16] , the Pacoti River has an Area de Proteção Ambiental (Environmental Protection Area, APA). It is a sustainable conservation unit created by Decree No 25.778 on February 15^th, 2000, and approximately 2914.93 hectares of the municipalities of Fortaleza, Eusébio, and Aquiraz. The access to this conservation unit is the Washington Soares avenue and then the CE-025 road.

In the area shown in Figure 11, there are mangroves, mobile and fixed dunes, and tableland forests. Mangroves are in the fluvial-marine plain representing the

estuarine zone from the mouth of the river to the vicinity of Aquiraz. The most notorious vegetation along the margins of the estuary is the mangrove forest, called the maritime perennial paludose forest, which stretches about 15 km from the mouth of the river and occupies around 150 km². According to studies carried out in the Pacoti River estuarine zone, it has 158 hectares of mangroves distributed along the waterways to where the tides have influence. Contiguous to the mangrove area, there is a transitional zone formed by grasses, characterizing the change in vegetation typology. After this narrow zone, the vegetation is typical of the coastal zone, which involves the coastal tableland and dune vegetation [16] .

According to studies [16] , the fauna is diversified because of the variety of ecosystems. The mangrove area is composed of invertebrates belonging to the groups of decapod crustaceans. There are reptiles, birds, and mammals in the dunes and tableland, besides aquatic species in the estuarine zone.

The residents of Fortaleza, Eusébio, and Aquiraz, along with tourists, enjoy the environmental richness of the area through tourism and leisure activities.

Within the limits of the APA, nine communities survive directly from the use of natural resources, basically from subsistence agriculture, fishing and tourism-related activities: the beach communities of Abreulândia, Porto das Dunas, Fazendinha, Tupuiú, Jacundá, Piranha, Mangabeira and Vila Cabral [16] .

The main problems in the APA are the result of human action caused by real estate speculation with the construction of summer houses, gated communities, and hotel developments, disposal of solid waste on the banks of the spring, occupation by residences in the area of permanent preservation of the river, and vehicle traffic on the dunes.

The main prohibited activities are the implantation or expansion of civil construction without environmental licensing; suppression of vegetation; use of fire without authorization from SEMACE; activities that may pollute or degrade the water resources covered by the APA; dumping of effluents, waste, and debris capable of causing damage to the environment; intervention in areas of permanent preservation such as the water resources, dunes, and mangrove ecosystem.