Spatial-temporal variation in land use in a coastal watershed under pressure of population growth

ABSTRACT Population progress is one of the main factors affecting the environment, modifying the natural dynamics of ecosystems. The Camboriú River Basin is located on the southern coast of Brazil and is strongly affected by population growth. This paper aimed to verify the space-time variation in the land use of the Camboriú River Basin by identifying changes in occupation and land use between 1986 and 2017. The rapid environmental assessment protocol was applied using the following parameters: bottom substrate, habitat complexity, backwaters quality, stability of banks, vegetative protection, vegetative cover, vegetative quality, and riparian vegetation presence. The changes in occupation and land use show rapid urbanization with a rise of 9% in 1986 to 24% in 2017. In riparian forest, higher altitude regions of the watershed show better results when compared to lower course regions, which are, thus, reflected in the environmental integrity of the stretches of stream studied. As for the behavior of urban occupation in space, it was verified that it did not occur continuously in comparison with the population, data during the studied period.


INTRODUCTION
Rivers and tributaries are the aquatic ecosystems most affected by human activity. Those located in coastal regions when associated with disordered industrial and urban growth suffer adverse consequences in their environmental quality (TUNDISI; TUNDISI, 2008). The contamination of water resources by anthropogenic activities not only reduces the economic potential of the waters (FIQUEPRON; GARCIA; STENGER, 2013), but also restricts its use for leisure and recreation by presenting a risk to the health of the population.
A key part in the maintenance of quality water resources is made by the riparian forest, which, as an ecotone between the terrestrial and aquatic environments, provides protection to the watercourses. Riparian zones supply shelter for biota by detritus deposition (branches, trunks, leaves), help stabilize the banks with tree roots, filter sediment in runoff, and store water in the soil in order to refill the water table and the watercourses in periods of lower rainfall (DOSSKEY et al., 2010;ELMORE;BESCHTA, 1987;LACERDA;FIGUEIREDO, 2009;LIMA;ZAKIA, 2000). Despite vast knowledge about the importance of the riparian forest, there has been a reduction with the advancement of population. Land use represented by urban and rural occupation and some types of crops alters the riparian forest which directly and indirectly affects the integrity of the adjacent water resources (BREN, 1993; CAMPOS; RAMIRES; PAULA, https://doi.org/10.1590/S1413-415220190080 Silva, D.D.P. & Schwingel, P.R. 2011;DONADIO;GALBIATTI;PAULA, 2005;EROL;RANDHIR, 2013;FOLEY et al., 2005;SOUZA;GASTALDINI, 2014;MORING;GARMAN;MULLEN, 1985;POLETO;CARVALHO;MATSUMOTO, 2010;SANTOS;HERNANDEZ, 2013;TUCCI, 2002;VANZELA;FRANCO, 2010).
Statewide, the Camboriú River Watershed is part of the hydrographic region RH7, Itajaí Valley, located in the municipalities of Camboriú and Balneário Camboriú, Santa Catarina State (SANTA CATARINA, 2008). According to the Brazilian Institute of Geography and Statistics demographic census, the municipalities which compose this Basin show accelerated population growth (IBGE, 2018). Furthermore, it shows that Balneário Camboriú is the municipality with the highest population density in the state of Santa Catarina (2,337.67 inhabitants/km 2 ), tending to grow through verticalization. However, the expansion to less inhabited regions such as Camboriú is inevitable due to urban mobility and lack of water supply (PIATTO; POLETTE, 2012). The authors further hold that during holiday season the population of Balneário Camboriú increases tenfold, which overloads basic sanitation systems that are unequipped for such large fluctuations of inhabitants.
Agglomerated population growth poses a risk to the environment due to the concentrated exploitation of natural resources through the expansion of cultivated areas (mainly riziculture), mining, and logging for charcoal and cattle pastures. Studies carried out by Urban (2008) and Padilha (2013) in the Camboriú River Basin showed signs of this degradation, mainly in relation to the permanent preservation areas where it was verified that more than half of these limits are represented by uses different from vegetal occupation.
In this context, the present study aims to diagnose and dimension the current conditions and land use evolution in light of the pressure exerted by population growth in the Camboriú River Watershed, verifying whether the spatiotemporal distribution of these uses presents a linear model (continuous) or shows pulses over time.

Study area
The study area comprises the region occupied by the Camboriú River Watershed,

Identification of occupation and land use patterns
The evolution of changes in occupation and land use in the Camboriú Basin in the last three decades was studied based on Landsat 5 and Landsat 8 satellite images provided by the Brazilian National Institute for Space Research (Instituto  , being 1986, 1993, 2004, 2006, 2010, and 2017.

Riparian forest analysis
The methodologies proposed by Minatti-Ferreira and Beaumord (2006), Cionek, Beaumord and Benedito (2011) and Leal (2012) were applied to determine the condition of the riparian forest along the tributaries of the Camboriú River  (BRASIL, 2012). In this way, it was possible to identify the presence of riparian forest within the limits imposed by legislation through the aerophotogrammetry of the watershed and to classify the area according to the methodology of Leal (2012). The state of the riparian forest is determined by the following parameters applied in field visits: the vegetal quality of the margins, the vegetal cover of the banks, the vegetal protection of the ravines, and its stability.

Application of the rapid environmental integrity assessment protocol
The Rapid Assessment Protocol (RAP) of the environment was based on the simplified model of Minatti-Ferreira and Beaumord (2006), which consists of the in situ observation of the environment for analysis of different parameters through a scoring system which will eventually score the environment in a range from optimum to poor. The RAP includes the parameters of: bottom substrate, habitat complexity, and backwater quality. Through field visits and the photogeorreferenced survey provided by the Camboriú Committee, the environmental integrity of the tributaries of the Camboriú River Basin was determined. The RAP was applied only to streams and upstream regions of the basin, resulting in 54 sample points analyzed.

Land use and occupation patterns
The occupation and land use classification enabled visualize the distribution and quantification of urban, agricultural, natural, and pasture/undergrowth areas in the Camboriú River Basin (Figures 2 and 3; Table 1). Although it is still the most representative class in the basin, the natural area suffered the greatest percentage reduction, reaching almost 10% between 1986 and 1993. In 2006, natural areas began to grow again in places formerly occupied by pasture/undergrowth.
The Camboriú River region has the lowest vegetal representation among the studied localities while also seeing the greatest percentage reduction in this class of land use during the period 1986-2017, reaching approximately 12% ( Figure 3A).
Difficult access to some forest areas due to hills helps to maintain a great part of its extension, although urban occupation has also advanced in these regions, mainly from 2004 onwards. A study of the Camboriú River Basin by Dortzbach et al. (2015) shows that areas with declivity above 20% are represented mainly by forest cover, confirming the hypothesis that difficult access helps to preserve vegetation. On the other hand, the increase of natural areas in environments exposed to stressful factors may be associated with the abandonment of cultivated areas and pasture and planting of species for wood exploitation (DORTZBACH et al., 2015;RUDEL et al., 2005;YACKULIC et al., 2011).
The area occupied by pasture/undergrowth increased more than 8% between 1986 and 1993, including in the upper reaches of the basin, regions such as the Braço and Macacos Rivers. The removal of native vegetation for eucalyptus plantations or cattle occupation in these regions was observed during field visits.
This class presents great variation of area in the basin with different land uses over time, a fact also observed in the studies of Yackulic et al. (2011), in Puerto Rico, andDortzbach et al. (2015) in the Camboriú River Basin.
Urban area increased from 9 to 10% in the period of 1986-1993, reaching 24% of the land occupation in 2017, making it the class of highest growth in the watershed. The increase of urban areas was more notable in the Camboriú River and Pequeno River regions, in which a gradual densification of urban areas was observed (Figures 3A and 3B). The Pequeno River and the Macacos River regions contain upper areas where new patches of urban occupation were also registered, including near the water springs. In the Pequeno River region, urban area increased from 11% in 1986 to 35% in 2017, the highest relative growth in the Camboriú River Basin. Conversely, the Braço River and Macacos River regions had the lowest urban occupation, however its extension has doubled in the Macacos region between 2006 and 2010. The urbanization process is strongly related to forest cover loss, a fact pointed out by Campos and Souza (2003) while studying the rate of deforestation and colonization of the island of Puerto Rico, Paraná, Brazil.
In general, the agricultural areas remained stable throughout the period, reaching almost 5% of occupation. Agriculture is located mostly in the region The data also revealed that the Camboriú River region was little occupied by this land use class, representing less than 1% until 2006 and has since been no longer registered.
In the spatial-temporal behavior of urban occupation, comparing the occupied area with the data of the resident population in the Camboriú River Basin obtained through IBGE (2018), it was observed that the occupation did not occur in a linear way (Figure 4)

Riparian forest analysis
Regarding the state and presence of the riparian forest, the results show that 65% of the studied sections are in poor or regular conditions ( Figure 5). In only 13% of the evaluated sections the riparian forest was classified as in an optimal state, while the presence registered 17% of the areas in this category. These data show that the Camboriú River and its tributaries are in misalignment with the Brazilian Forest Code (BRASIL, 2012) considering that the optimal classification refers to the margins 100% covered by vegetation, meaning that the permanent preservation areas (PPA) are being maintained.
The Camboriú River has the worst state of riparian forest, where only 23% of the existing vegetation is in good condition ( Figure 6). The sections that compose this region are predominantly occupied by anthropogenic activities with concretized margins in several spots. This leads to a poor classification of the stability of the ravines in these sections due to the decharacterization of the natural environment. Regarding the presence of the riparian forest, the Camboriú River also shows 69% of its sections classified as poor or without vegetation.
The Pequeno River region shows a better state of riparian forest, with 39% of the areas in good condition and 14% in optimal (Figure 7). There were

Analysis of the environmental integrity
The environmental integrity analysis of the main tributaries of the Camboriú River Basin was carried out exclusively for streams in rhithral areas, thus, the Camboriú River region and low-lying sections were not considered. Of the 171 sections with riparian forest analysis, the environmental integrity was verified in 54 points ( Figure 10) as the description of the parameters applies only to these points. Approximately 60% of the evaluated sections received good or optimal ratings. The results found for riparian zone and environmental integrity were distinct, which may be associated with the location and number of stretches analyzed.
In contrast to what was verified regarding the riparian zone, the Pequeno River region saw the worst conditions related to its environmental integrity.
Of the evaluated sections, 60% were classified in poor or regular conditions. Furthermore, the Macacos River region had similar results to the Pequeno River region, registering 50% of the areas classified as poor or regular ( Figures 10A   and 10C). The Braco River region saw 26% of its areas in poor or regular conditions with a predominance of sections classified as good (30%) and optimal (44%) ( Figure 10B). In general, environmental integrity parameters such as the bottom substrate and the complexity of the habitat present similar characteristics, providing food and refuge for the biota (MINATTI-FERREIRA; BEAUMORD, 2006).
The situation of the riparian zone found in upper course stretches showed that in preserved areas the environmental integrity of the streams was better classified. This proves that the quality of the riparian zone directly reflects on the integrity of the aquatic ecosystems, a theme addressed by several authors (DEBANO; SCHMIDT, 1989;ELMORE;BESCHTA, 1987;LIMA;ZAKIA, 2000;MISERENDINO et al., 2011;SOUZA et al., 2013).
Although the low-course sections have not been evaluated for environmental integrity, the relationship between riparian conditions and watercourses can be indicative of poor quality in these locations where very poor riparian conditions were recorded.

REFERENCES FINAL CONSIDERATIONS
From the results obtained for the Camboriú River Basin (Santa Catarina), in reference to changes in land use and occupation, it was concluded that the urban area of the basin grew by 156% between 1986 and 2017, which led to a reduction of 11% decrease in the natural area during the same period.
Although the expansion of urban area was high, this pattern was verified only from the 2000s, thus not presenting a linear model in relation to the number of inhabitants during the studied period. This model of urban occupation over the watershed area is influenced by different external factors which shapes its pattern of dispersion in space. In the case of the studied coastal basin, one characterized by high touristic potential, the growth of urban occupation occurred vertically. This pattern is associated with periods of elevated population densification, thus reducing the speed of the land occupation process in adjacent areas until the year 2000.