EQUATIONS
EQUATIONS
14393/SN-v32-2020-44054
                                                               Received: 17 August 2018 | Accepted: 13 February 2020
Papers
    Keywords:                      Abstract
    Greenhouse gases               Anthropogenic interference has always impacted the Earth's surface,
    Environmental impacts          with greater intensity in recent times due to land use changes, which
    Transition matrix              contribute to the emission of greenhouse gases, especially carbon dioxide.
                                   In this sense, this study analyzes land use transitions and CO 2 emissions
                                   resulting from these actions in a watershed. For this, land use mappings
                                   were made in 2007, 2010, 2013, and 2016, along with estimates of the
                                   emissions from transitions. The calculation of net CO 2 emissions included
                                   data from the transitions that occurred, from past vegetation, and
                                   pedological information. All procedures were performed with the aid of
                                   geoprocessing and remote sensing techniques, resulting in matrices of
                                   transitions and CO2 emissions, in addition to spatialized information.
                                   The forest category showed the highest conversion to other types of land
                                   use, with a loss of 208.86 ha between 2010 and 2013. In the observed
                                   period of nine years, carbon emissions were higher than its sequestration
                                   from the atmosphere, which shows the need for management and
                                   planning to mitigate the impacts caused by intense land use changes in
                                   the studied watershed.
1  Universidade Estadual Paulista (UNESP), Instituto de Ciência e Tecnologia, Sorocaba, SP, Brazil.
jocy.sousa@unesp.br
2 Universidade Federal do Sul da Bahia. Centro de Formação em Ciências Ambientais, Porto Seguro, BA, Brazil.
elfany@csc.ufsb.edu
3 Universidade Estadual de Goiás. Campus Cora Coralina. Cidade de Goiás, GO, Brazil. jose.souza@ueg.br
4 Universidade Estadual Paulista (UNESP), Instituto de Ciência e Tecnologia, Sorocaba, SP, Brazil.
roberto.lourenco@unesp.br
Figure 1. Location of the Una river watershed, Ibiúna, São Paulo, Brazil.
      To obtain land use transitions and                        for 2016. The images used correspond to
estimates of net CO2 emissions, we used a                       November, except for the image from Landsat
sequence of methodological steps, as described                  5, acquired for September.
below.                                                                  The images were classified using visual
                                                                interpretation           and        multitemporal
Land use mapping                                                retroanalysis.     The     method     of   visual
                                                                interpretation consists of the vectorization of
Land use maps were made using satellite                         the categories or classes identified in the study
images from Landsat 5 for the year 2007, Spot                   area through the identification of features by
5 for 2010, RapidEye for 2013, and Sentinel 2A                  their shape, tone, and texture (PANIZZA;
FONSECA; 2011).                                                 Soil map and soil carbon map under soil-
      The land use categories adopted for the                   vegetation association
legends of the maps were adapted from the
guidelines of the Guide of Good Practices for                   A vector file of the pedological map of São Paulo
Land Use, Changes in Land Use, and Forest                       State (ROSSI, 2017) was clipped to the study
(“Guia de Boas Práticas para Uso da Terra,                      area, seeking to obtain the pedological classes
Mudanças no Uso da Terra e Floresta”) (IPCC,                    in the area. Due to low cartographic quality, the
2003) and the Technical Manual of Land Use                      soil texture was analyzed to detail the
(“Manual Técnico de Uso da Terra”) (IBGE,                       pedological characteristics and to identify more
2013). These categories are: Forest (Fo),                       specifically the soil carbon stock.
Reforestation (R), Field (F), Agriculture (A),                          Soil particle size was analyzed after the
Urban area (Ua), Flooded area (Fa), and                         collection    of   soil   samples   in   35   points
Pasture (P).                                                    irregularly distributed in the different land use
                                                                types. The collection was carried out using a
Past vegetation map                                             soil auger at a depth of 0-20 cm, removing 500
                                                                grams of soil. All samples were packaged and
The past vegetation map was obtained by                         taken to the Water and Soil Laboratory of
clipping the vector file of the past vegetation                 Universidade Estadual Paulista (UNESP),
map of Brazil (IBGE, 2004) to the study area                    Institute of Science and Technology, Sorocaba
and by the construction of a Digital Elevation                  city.
Model (DEM), both used to determine the forest                          The samples were analyzed in the
formation that existed in the watershed.                        laboratory using the pipette method in thin air-
      The DEM was generated by interpolating                    dried soil (TADS), according to the methodology
the contour lines and the rated points using the                of the Agronomic Institute of Campinas (IAC,
Triangulated Irregular Network (TIN) method.                    2009). After obtaining the percentages of silt,
The TIN consists of a vector structure with a                   sand, and clay, the texture was classified
node-arc topology, where for each of the three                  according to the Brazilian Soil Classification
vertices of each element of the triangle there                  System (EMBRAPA, 2006).
are   coordinates      and     altitude    information                  Soil and soil texture information tables
(SOUSA JUNIOR; DEMATTÊ, 2008).                                  were combined using ArcGIS 10.3 (ESRI, 2014)
      Subsequently, past forest physiognomies                   to define the soil groups in the watershed,
were classified in the vegetation categories                    according to Bernuox et al. (2002). The mapping
established by Bernuox et al. (2002).                           of the soil carbon stock under soil-vegetation
                                                                association was carried out based on the past
                                                                vegetation map and the soil groups identified.
                                                                        The carbon values adopted were the same
used by CETESB (2012), which refer to carbon                    area demanded the knowledge of which
median data resulting from the soil-vegetation                  equation would be used.
association, as mentioned in the Reference                              Estimates of CO2 emissions and removals
Report - Carbon Dioxide Emissions and                           from soil carbon stock changes were performed
Removals by Soils due to Land Use Changes                       using Equation 1, as proposed by IPCC (2003).
and Liming (BRASIL, 2006).                                                                                 𝑇
                                                                                                          2
                                                                𝐸𝑆𝑖 = 𝐴𝑖 ∗ 𝐶𝑠𝑜𝑖𝑙 ∗ (𝑓𝑐(𝑡𝑜) − 𝑓𝑐(𝑡𝑓)) ∗ ( 20 )        [1]
      For carbon determination, Brazil (2006)
used data from soils 0-30 cm deep. Then, carbon
                                                                Where:
estimates were made for each profile, obtained
                                                                ESi: net CO2 emission in the area in a given
by multiplying the apparent soil density with
                                                                period (tc);
the concentration and thickness of the horizon.
                                                                Ai: land use category area (ha);
Finally, carbon data were added to obtain
                                                                Csoil: soil carbon content resulting from the
carbon estimates in each location.
                                                                soil-vegetation association [tc.ha-1];
                                                                fc(to): factor of soil carbon change in the
Land use transition
                                                                previous year (dimensionless), referring to the
                                                                previous land use category;
Based on the land use maps obtained, analyses
                                                                fc(tf): factor of soil carbon change in the
of transitions between three periods (2007 to
                                                                following year (dimensionless), referring to the
2010, 2010 to 2013, and 2013 to 2016) were
                                                                following land use category;
performed using the Tabulate Area tool in
                                                                T: time interval (year).
ArcGIS 10.3. Transition matrices consist of
comparing the previous year with the following
                                                                        Equation 2 was used to define the fc
year to detect changes in each category.
                                                                factor.
    Figure 2. Land use map for the year 2007 (A), 2010 (B), 2013 (C) and 2016 (D) for the Una river
                                             watershed.
      There was an increase in the categories of                vegetation and reduction of agricultural areas
agriculture, urban area, and pasture over nine                  due to rural exodus. In this regard, the
years (Table 2). The forest category was the one                difficulty of using mechanized tools in areas
with the greatest loss of area. In a study in the               with     high    declivity    contributes    to   the
Atlantic forest area, Weckmuller et al. (2012)                  abandonment of these areas and consequent
also found an increase in the urban area,                       recovery of the Atlantic forest.
agriculture, and pasture, due to the reduction                          The decrease in natural vegetation shows
of forest areas.                                                the level of anthropogenic exposure to which
      In turn, Eckhardt et al. (2013) identified                the watershed is subject, and the percentage of
opposite results, with the increase of natural                  vegetation      loss   over   nine   years   (4.30%)
reinforces the need to preserve natural areas.                  information made it possible to classify soils
This    preservation      allows     gene     flow,   the       into five groups proposed by Bernuox et al.
formation      of   ecological    corridors, natural            (2002), as shown in Table 4.
regeneration, and the conservation of water                             As for the soil types, the watershed
resources.                                                      presents Oxisols, Ultisol, and Gleisols (Figure
       The Una river watershed comprises the                    3B) and the results of the carbon stock mapping
following       plant      physiognomies:          dense        for the soil-vegetation association are shown in
ombrophilous        montane         forest,    seasonal         Table 5.
deciduous forest, and seasonal semideciduous
forest (Figure 3A), which correspond to three                   Table 3. Vegetation types found for the Una river
                                                                watershed.
vegetation groups proposed by Bernuox et al.                       Vegetation          Plant Physiognomy
(2002) for the Atlantic Forest biome, as shown                       Group
                                                                       V3         Dense ombrophilous montane
in Table 3.                                                                                   forest
       The textures found vary between clayey,                         V4           Seasonal deciduous forest
                                                                       V5            Seasonal semideciduous
clayey-sandy loam, clayey-sandy, and clayey                                                   forest
loam. Together with the soil types, this                        Source: Adapted from Bernuox et al. (2002). Org.:
                                                                by the authors, 2018.
Table 4. Soil groups found in the Una river                                S2) Oxisols with low activity clay, S3) Soils other
watershed.                                                                 than Oxisols with low activity clay, S4) Sandy
  Group                Soil Category                                       soils, S5) Hydromorphic soils. Source: Adapted
    S1             High activity clay soils                                from CETESB, 2012. Org.: by the authors, 2018.
    S2         Oxisols with low activity clay
    S3       Soils other than Oxisols with low
                        activity clay
                                                                                  Tables 6, 7, and 8 show the transitions
    S4                  Sandy soils                                        from 2007 to 2010, 2010 to 2013, and 2013 to
    S5              Hydromorphic soils
Source: Adapted from Bernuox et al. (2002). Org.:                          2016, respectively. In these tables, gray cells
by the authors, 2018.                                                      correspond to the transitions that occurred
Table 5. Soil carbon stock under the soil-                                 from one period to the next; green cells
vegetation association of the Una river                                    correspond to permanent land use; noncolored
watershed.
                   Soil (Kgc/m2)                                           cells refer to lack of transition; and the
 Vegetação
Table 6. Transition matrix for land use categories from 2007 to 2010 (ha).
   Area
   (ha)                                                     Land use in 2010
                                                                                                       Total     Transition
                                   F        Fo         Ua          A         Fa       P        R
                                                                                                       2007      2007-2010
       Land use in 2007
Legend: (Fo) Forest, (R) Reforestation, (F) Field, (A) Agriculture, (Ua) Urban area, (Fa) Flooded area, (P)
Pasture. Org.: by the authors, 2018.
                          Table 6 shows that the category with the         areas, which corresponded to 89 ha.
greatest loss of area was the forest (130.00 ha),                                 When comparing the transitions in Table
and that the largest conversion of natural areas                           8 with previous periods, it is noted that the
for human use was from forest to agriculture                               least amount of transitions occurred in this
(62.57 ha). From 2010 to 2013 (Table 7), the                               period. However, the forest category still
forest category also accounted for the greatest                            accounted for the main changes.
loss of area, being converted mainly to urban
Table 7. Transition matrix for land use categories from 2010 to 2013 (ha).
 Area
  (ha)                                  Land use in 2013
                                                                                                                   Total    Transition
                                 F         Fo            Ua        A         Fa       P            R
                                                                                                                   2007     2010-2013
   Land use in 2010
                                                                                                                             transition
                                                                                                                             469.19 ha
          2013
                                                                                                                               Total
Legend: (Fo) Forest, (R) Reforestation, (F) Field, (A) Agriculture, (Ua) Urban area, (Fa) Flooded area, (P)
Pasture. Org.: by the authors, 2018.
Table 8. Transition matrix for land use categories from 2013 to 2016 (ha).
 Area
  (ha)                                  Land use in 2016
                                                                                                                   Total    Transition
                                 F         Fo            Ua        A         Fa       P                R
                                                                                                                   2013     2013-2016
   Land use in 2013
Legend: (Fo) Forest, (R) Reforestation, (F) Field, (A) Agriculture, (Ua) Urban area, (Fa) Flooded area, (P)
Pasture. Org.: by the authors, 2018.
                      The   comparison     between        transition       factor, especially when considering the amount
matrices indicated that the forest showed                                  of forests that have been suppressed and its
prominence in the conversion to anthropogenic                              consequences          for       the    environment.        This
areas. The highest numbers occurred from 2010                              compromises one of the main ecosystem
to 2013, with 208.86 ha. Transitions have also                             services, which is CO2 sequestration or storage.
shown                   that    urbanization       has    increased,       When in excess in the atmosphere, CO2
although                    agricultural    areas        are   more        contributes      to    the       intensification      of       the
prominent.                                                                 greenhouse effect (RIBEIRO et al., 2009).
                      The greater conversion of the forest                        According to Baird and Cann (2011), a
category in the studied periods is a worrying                              large amount of CO2 is emitted into the
atmosphere when forests are cut down, with                                  have values, the first because it corresponds to
deforestation accounting for about a quarter of                             the category in which there were no transitions
CO2                emissions.         Regarding       urbanization,         from one period to the next, and the other
watersheds become vulnerable to rapid changes                               because there was no transition. In the
in natural conditions, influencing landscape                                Emission/Removal column, we have the total
quality                  and        encouraging    environmental            net issue for each category. Lines represent the
degradation                     and       irregular       occupation        previous year and columns the following year
(GUIMARÃES; PENHA, 2009).                                                   (CETESB, 2011; 2012).
          Tables 9, 10, and 11 show the estimates of                               Table 9 shows that CO2 emission was
net CO2 emissions from 2007 to 2010, 2010 to                                greater than its removal, and the change from
2013, and 2013 to 2016, respectively. Gray cells                            forest to field was the one that most contributed
represent CO2 emissions (positive values) or                                to emissions.
removals (negative values) from one period to
the next. Green and noncolored cells do not
Table 9. Matrix of Estimates of net CO2 emissions (GgCO2) from 2007 to 2010.
    GgCO2                                Land use in 2010                                                       Emission/
                                        F          Fo        Ua            A       Fa           P        R      Removal
      Land use in 2007
          Total net emissions were higher from                              to 2013. During this period, the estimated
2010 to 2013 (Table 10) compared to the period                              emissions were approximately twice those of
from 2007 to 2010, which was consistent with                                the 2007-2010 period and those of the 2013-
the number of transitions that occurred, mainly                             2016 period. Although all categories present
of forests. From 2013 to 2016 (Table 11), in                                some type of transition that would emit this
turn, there was a decrease in emissions, but                                gas, forest conversions accounted for the largest
these were still higher than removals.                                      emissions: 2.15, 4.26, and 2.11 for the periods of
          When comparing Tables 9, 10, and 11, it                           2007-2010,       2010-2013,    and     2013-2016,
can be seen that the highest estimate of CO2                                respectively.
emissions (4.1422 GgCO2) occurred from 2010
Table 10. Matrix of Estimates of net CO2 emissions (GgCO2) from 2010 to 2013.
   GgCO2                                Land use in 2013                                                         Emission/
                                     F         Fo         Ua            A       Fa           P            R      Removal
      Land use in 2010
Table 11. Matrix of Estimates of net CO2 emissions (GgCO2) from 2013 to 2016.
  GgCO2                                 Land use in 2016                                                         Emission/
                                    F          Fo         Ua         A          Fa            P           R      Removal
   Land use in 2013
                  This greater conversion of forest to other             conversions from forest to agriculture and from
categories can be justified by the fact that these                       forest to pasture, as well as from pasture to
areas have a high amount of carbon in their                              agriculture.
biomass. Thus, when vegetation is suppressed                                  The estimated values of net emissions are
to meet the demand of other land use                                     generally consistent with the dynamics of land
categories, the amount of CO2 emitted will be                            use in the watershed. Due to the size of the
greater than the capacity to sequester carbon in                         watershed, these emissions could not be
new uses. According to Don et al. (2011) and                             compared to the state or country level, since the
Kim and Kirschbaum (2015), forest suppression                            dynamics would be much greater in these
causes a rapid loss of carbon, especially if the                         locations.     Notwithstanding,        these    results
biomass is burned, increasing atmospheric                                reinforce      the       importance    of      studying
CO2.                                                                     watersheds, since they are conceived as basic
                  Carbon dioxide (CO2) emissions in the                  units of environmental planning and have
three periods indicate consistency with the data                         multiple uses.
reported in the study by Kim and Kirschbaum                                   Looking for a comparison, the CETESB’s
(2015),                  who   identified   emissions    in   the        inventory (2012) for São Paulo State identified
that conversion from agriculture to urban areas                         The Una river was shown to have
between 1994 and 2008 accounted for an                          anthropogenic interferences mainly in the
emission equivalent to 444.26 GgCO2. This                       central and northern portion, where most of the
value is much higher than that obtained in the                  emissions      were       found,       indicating
watershed (0.0142 GgCO2), since they have                       environmental degradation in this location
different scales.                                               (Figure 4).
Figure 4. CO2 flux due to land use change from 2007 to 2016 in the Una river watershed.
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