Morphometric indices in the Curuá-Una River sub-basin as potential indicators for forest restoration in hydrographic mesoregions in the Central Amazon

: Watersheds are planning units because they are delimited by topographic divisions formed by a main river and its tributaries, in which water drainage is channeled into a course of greater water volume, such as the Amazon basin, which flows into the Atlantic Ocean. The objective of this work was to analyze the morphometry of the hydrographic sub-basin of the Curuá-Una River (SBHRM), that integrates the Curuá-Una hydrographic micro-region in western Pará, Brazil, and its surroundings. Data from abiotic variables integrated in a geographic information system were used to identify the areas that most need restauration using production systems such as agroforestry as part of a forest restoration process, necessary to land degradation in the sub-basin and its surroundings. It was found that the sub-basin of the Curuá-Una River has a more elongated shape, confirmed by the circularity index, compactness coefficient, and shape factor. It is a fifth order sub-basin with a densely branched drainage network with a low probability of flooding due to the predominance of undulating relief. The morphometric characteristics present conditions that can be used in anthropic areas integrated into production systems such as agroforestry. The existence of tree species such as andiroba , copaíba , and the Brazil nut tree in the Tapajós basin, as inventoried by the Project RADAMBRAZIL, must be included in agroforestry arrangements in the recovery of degraded areas in western Pará.


INTRODUCTION
Water has multiple uses, such as for human consumption, irrigation of crops and gardens, livestock raising, industrial production, and energy generation, besides ecosystem maintenance functions. The projected increase in the worldwide population will put greater pressure on the need for potable water and will decrease the stability of water availability to the global population (UCN and WRI 2014). Water is an essential element for the life on planet Earth. For humans, water resources have social, economic, and environmental relevance, being a raw and fundamental material for industrial processes, energy generation, as well as regulating the plant production cycle (Carvalho et al. 2012). In Amazon, water represents an important transport route, mainly for riverside communities.
Certain abiotic factors modulate geomorphological patterns on the earth's surface (Keith et al., 2022). The dynamic processes associated with the type of parent rock, intensity of weathering factors because of physical resistance to endogenous (tectonic) and exogenous (erosion) mechanical and chemical forces that express morphogenesis and their effects as a result https://doi.org/10.1590/1678-4499.20220098

METHODS
This study used the Multi-scale Ottocoded Hydrographic Base (ANA 2017), which has hydrographic details at larger scales for specific areas in the national territory, in addition to the review of the basins previously prepared up to 2017. A cutout was made using four hydrographic mesoregions located in the Central Amazon based on the National Hydrographic Division (DHN250), on a scale of 1:250,000 (IBGE 2019). A cutout was made using four hydrographic macro-regions located in the Central Amazon.
These mesoregions include information generated by the National Water Resources Council (CNRH), where the Orthorectified Hydrographic Base (ANA 2017) includes two more hierarchical levels, including spatial limits, names, and codes. The hydrographic mesoregion approach was adopted because on this basis it is possible to assess the process of use and occupation, fragilities, and water availability aimed at water planning and management in different sectors.
An analysis of natural regeneration can be used to aid in diagnosing the state of conservation of a population and its response to natural or human disturbance since individuals can be recruited to compose posterior successional stages (Silva et al. 2008). Small fragments associated with productive use of soil slowly degrade when native vegetation is removed in areas used for mechanized agriculture. This occurs because of the reduction in ecosystem services that native areas provide such as microclimate regulation, and control of hydrological flux and biogeochemical cycles. Therefore, the relationship between vegetation cover and hydrological cycles can be used as an aid in planning for soil use and occupation.
The Project RADAMBRAZIL was a pioneering effort in the survey of information on Brazilian natural resources, including the Amazon biome, through aerial surveys conducted in the 1970's and 80's. Recently, the Brazilian Institute of Geography and Statistics (IBGE) released an online database called the "Environmental Information Database" (BDiA), including the data from RADAMBRAZIL on forest inventories (IBGE 2019).
Therefore, considering the potential of this database to generate new information, an integrated analysis of databases was carried out plotting the native Amazonian species inventoried by the Project RADAMBRAZIL to stratify those species that were impacted by the anthropogenic processes, focusing only the Central Amazon, delimited by four hydrographic mesoregions. Climatic typology databases were used for the Legal Amazon, using the methodology adapted by Martorano et al. (1993), which was applied to the entire Amazon region by Martorano et al. (2017), evaluating the total species in every typological range with the goal of identifying the most impacted species.
The soils are, in general, well drained, porous, deep, of variable texture, and with low or average fertility. The only exceptions are the soils of basic origin, calcareous soils and the so-called terra preta do índio, with above average natural fertility. Latosols, usually resulting from Tertiary sedimentation processes, have good agricultural potential when rationally used (Falesi 1974, Guimarães et al. 2013. Also, the fragilities database was used regarding the erosive potential of rains in the Amazon to analyze the occurrences of species inventoried in RADAMBRAZIL that would be in the classes of very high and high fragility, as an indicator of use of these species in restoration actions (Engel andParotta 2001, Brienza Júnior et al. 2008) in the hydrographic mesoregion. A Landsat 8 satellite image from 2020 was also used, with a spatial resolution of 30 × 30 m of the Curuá-Una River sub-basin.
Considering that there is a need to implement demonstrative units in restoration actions, in accordance with Federal Law No. 12,651 (Brasil 2012), which provides protection of native vegetation, a morphometric analysis of the hydrographic sub-basin was carried out in SBHRM belonging to the Curuá-Una River basin, located in the surroundings of the Tapajós National Forest (FNT), in the west of the state of Pará, in the municipality of Mojuí dos Campos. Thus, the study area is located in the Santarém microregion, delimited between the parallels 03º 00' 56.23'' and 03º 11' 48.96'' of south latitude and the meridians of 54º 35' 26.31'' and 54º 30' 59.05'' west longitude.
In the area of the municipality of Mojuí dos Campos, there is a total of 4,988.236 km2 (02º 10' 17" south latitude and 56º 44' 42" west longitude), and there are surrounding municipalities of Santarém, Prainha, Alenquer, Belterra, and Uruará. The basins of the Moju and Mojuí rivers are tributaries of the Curuá-Una River basin and together they form the entire existing water network in the so-called Planalto Region. The numerous small streams and rivers converge towards the central one, which is the Curuá-Una. Together, they make up the total of 9,986 km2, or 37.65% of the entire municipality, occupying the eastern portion of the region. In Fig. 1 it is possible to identify the area that can be used for restoration actions. For this study, a georeferenced database was built, with information plans, on a scale of 1:100,000. In this step, the geographic information system (GIS) ArcGIS 10.6 was used. In the second stage, an image of the SRTM S04W055 project was downloaded, which comprises the study area, made available free of charge by the North American government through the United States Geological Survey (USGS), with a spatial resolution of 30 m. In the third stage, using the MDE, the sub-basin was extracted, as well as its drainage network. The extension "Hydrology" was used, according to the diagram shown in Fig. 2. The morphometric study was divided into two categories (Christofoletti 1981), including linear aspects (river hierarchy identification, bifurcation relationship, relationship between the average length of the channels by hierarchy), and areal aspects (shape and determination of drainage density, hydrographic density, maintenance coefficient, relief, and declivity ratio), similar to the work developed by Kanhaiya et al. (2019), using different morphometric parameters.
Subsequently, the data were compared with those from the Project RADAMBRASIL to determine the species that could be used to recuperate areas that are considered as being highly fragile in terms of erosivity as a function of topography and based on regional climatic data.

RESULTS AND DISCUSSION
For the morphometric characteristics, it was found that the sub-basin of the Curuá-Una River has an area of 382.48 km 2 , with perimeter of 117 km, and therefore it is classified as a microbasin. According to Christofoletti (1981), 233 first order channels were identified, corresponding to 50.34% of the channels. As for second order channels, 113 were accounted for, representing 24.4% of the drainage network, followed by 52 third order channels (11.23%), 44 fourth order channels (9.5%) and 21 fifth order channels (4.53%), identified automatically by the hydrology tool, resulting in the total of 463 channels for the drainage system. Therefore, the number of channels in the Curuá-Una River micro basin decreases as the order increases, corresponding to an inverse relationship between the numbers and the orders of the channels. The first order channels had the total length of 192.40 km, the second order 97.104 km, the third order 38.81 km, the fourth order 36.07 km and the fifth order 17.68 km.
According to the channel hierarchy, it was identified that the sub-basin hydrography of the Curuá-Una River (SBHCUR) is of fifth order, evidencing its high ramification, since the lower the order (< 5, for example), the less branched channels are the sub-basins (Ferreira et al. 2012, Campos et al. 2015, Oliveira and Antônio 2015. The values of the main axis length (Lp) and total length of the drainage network (Lt) presented values of 32 and 382.06 km, respectively. Table 1 presents other morphometric characteristics of the sub-basin. For the four hydrographic mesoregions Trombetas/Uatumã, Paru/Jari, Xingu, and Tapajós, 48.1% of the inventoried individuals concentrated in the climate typology Am3, followed by 27.8% in the Aw3 typology, and 16% in the Af3 for the species inventoried by the Project RADAMBRAZIL, indicating that these species occur in areas with total annual rainfall ranging from 2,500 to 2,000 mm. The Curuá-Una sub-basin has typical climate characteristics of the Am3. The monthly rainfall events, in this climatic typology, present values lower than 60 mm in the least rainy month. In the typologies Am2, Am4 and Aw4 (Fig. 2), the percentage of occurrence of native species was 1.3, 2.4, and 4.4%, respectively (Fig. 3). When analyzing the degree of suppression by anthropogenic processes on the vegetation inventoried by Project RADAMBRAZIL, it is noticed that, in the classes of very high fragility, 22.3% of the mapped species were suppressed, and, under conditions of high fragility, the values totaled 18% of loss of species by anthropogenic processes (Fig. 4). It is noteworthy to observe that the Curuá-Una sub-basin is located in a very high fragility area, reinforcing the need for strategic restoration actions.  Figure 5 shows points with occurrence of native species such as Brazil nut (Bertholletia excelsa), copaíba (Copaifera sp.) and andiroba (Carapa guianensis Aubl.), demonstrating the potential for inclusion of these species in agroforestry systems in the process of forest restoration in degraded areas in the hydrographic basin and the subbasin of the Curuá-Una River.
Forest cover in hydrographic basins is very important to the fishing sector in Amazon. Arantes et al. (2018) related that in areas with greater forest cover there was greater total fish biomass, mainly of species that are important commercially speaking. Areas that are exposed without vegetation due to human activities lead to soil erosion (Araújo et al. 2020). These erosive processes are intensified as a larger area loses vegetation cover (Santos et al. 2018, Bramorski andCrestana 2020).
Among the tree species that are most used in agroforestry is the Brazil nut tree (Bertholletia excelsa H. B. K.), due to the high commercial value of its fruits, which are sold nationally and internationally (Silva et al. 2008). This species was found in 26 of a total of 108 agroforestry systems researched in this study, which demonstrates its economic and silvicultural importance to forest restoration. The species Carapa guianensis Aubl. (andiroba) and Copaifera sp.
(copaíba) are Amazonian species with high aggregated value, principally in the cosmetic and pharmaceutical industries (Amorim et al. 2020).

CONCLUSION
The sub-basin of the Curuá-Una River is a basin with an elongated shape, according to circularity indices, the compactness coefficient, and shape factor. The sub-basin falls into the fifth order category with a densely branched drainage network with a low probability of flooding, due to the predominance of undulating relief.
The methodology allows for evaluation of the morphometric characteristics of the basin, as a strategy to support planning based on land use and occupation, as well as of hydrogeological and topoclimatic studies, to point out the most recommended sites for restoration actions. The inclusion of species such as copaíba, Brazil nut and andiroba, which have been highly impacted by anthropogenic processes, may be key species for the restoration of Tapajós basin areas.

DATA AVAILABILITY STATEMENT
The datasets generated and analyzed during the current study are not publicly available because they are easily generated from the bases cited in the methodology. Recently, IBGE released an online database called BDiA, including the data from RADAMBRAZIL Project on forest inventories (IBGE 2019). The datasets used and/or analyzed during the current study will be available upon request.