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LAND DEGRADATION IN MOUNTAIN AREAS OF
SÃO PAULO STATE PARK, BRAZIL
Antonio Jose Teixeira Guerra 1, Leonardo dos Santos Pereira1; Aline
Muniz Rodrigues1; Maria do Carmo Oliveira Jorge1; Michael Augustine
Fullen2
1) Department of Geography, Federal University of Rio de Janeiro, Rio de Janeiro,
Brazil antoniotguerra@gmail.com
2) Faculty of Science and Engineering, The University of Wolverhampton,
Wolverhampton, UK
Keywords: Soil erosion, mountainous areas, trails. experimental station, quarrying.
This article investigates land degradation in mountain areas in Brazil, monitoring soil
hydrology at an experimental station, and soil sample collection, both on tourist trails and
quarries. The physico-chemical properties of soil samples were analysed. The results
demonstrate that these activities cause high soil bulk density values and low soil organic
matter (SOM) contents. It is concluded that human intervention has intensified
geomorphological processes, causing slope instability and environmental and socio-economic
damage.
Mountain landscapes may attract economic activities, such as tourism and quarrying. Tourism
is associated with natural beauty, which can be formed due to abrupt relief unevenness,
creating, for instance, water-falls and interesting rock outcrops. In order to access these
appealing environments, trails are created. Erosive processes are usually accelerated on trails,
since the bare soils are exposed and may become preferential paths for surface runoff
(Ballantyne and Pickering, 2015; Guerra et al., 2017; Jorge, 2017). Consequently, this
research investigates land degradation in mountain areas within São Paulo State Park,
specifically on two major soil uses (tourist trails and quarries). Maranduba drainage basin is
situated in Ubatuba Municipality, on the northern coast of São Paulo State, Brazil. Some of
the environmental problems are caused by the transit of tourists on the mountain trails to
reach the waterfalls and beaches. There are large areas under quarrying, mainly for clay
extraction, which causes strong visual and environmental impacts within Maranduba drainage
basin, on the edge of the Serra do Mar State Park (Jorge, 2014; Rodrigues, 2016).
On both land uses, Kopec rings were used to collect 100 cm3 volumetric soil samples for
physico-chemical analysis, following EMBRAPA (2011) procedures. Soil porosity, bulk
31st session of EFC/FAO Working Party on the Management of Mountain Watersheds
170
density, texture, SOM and soil pH were analysed, with triplicate analysis of each sample. An
experimental station (UTM: 0474211/7395934) was established near one of the trails, to
analyse soil hydrology.
2.1. Use of the mountain trails by tourists
Two approaches were adopted to study the trails: 1. Measurements at a soil erosion
experimental station to analyse soil saturation on the trail; 2. Detailed studies of two trails,
near the experimental station, where soil samples were collected for physico-chemical
analysis. The experimental station has three erosion 10 m2 (10 x 1 m) plots. An automatic rain
gauge measured precipitation at hourly intervals. In August 2016, Granular Matrix Sensors
(GMS) were installed in each plot, to measure soil moisture. A data-logger monitored the
sensors, with hourly data downloads. The GMS operate in the ~0 to -250 kPa range.
2.2. Trails case study
Two mountain trails were selected, Água Branca (White Water) and Lama Mole (Soft
Clay) Farm. Soil samples were collected at 0-10 cm depth, both on the ground and talus.
There were four investigated sites on Água Branca (UTM: 0474053/7391677) and three sites
on Lama Mole (UTM: 0473468/7396109).
2.3 Quarrying and soil degradation in mountainous relief
Three degraded talus slopes (TA1, TA2 and TA3) were selected for soil sample
collection. Samples were removed from the saprolite horizon in the mid-section of the talus,
as mining activity usually removes the superficial soil. Talus geographic co-ordinates are:
TA1 UTM: 0473718/7396899; TA2 UTM: 0475815/7397652; and TA3 UTM: 0475179/
7398867.
Comparing soil water matrix potential at 15 cm depth amongst the three erosion plots, it
was observed that Plot A (PA) exhibited least variability in potential, indicative of relatively
higher soil moisture content at this depth. At 15 cm depth on Plot B (PB), there was greater
variability in the negative potential, indicative of effective drainage (Fig. 1). PA is closer to
the talus slope and thus receives more water and is thus more prone to saturation. At 90 cm
depth, water movement is more linear, with little matrix potential variability, and Plots B and
C exhibited similar behaviour and may form part of the recharge zone (Pereira & Rodrigues,
2013). However, 90 cm depth may represent the same soil horizon, with similar matrix
potential. In contrast, the shallower depths may be within different horizons and their
hydrological behaviour may be modified by talus, trail construction and trampling.
In the subsoil of the plots (10-20; 20-30 and 80-90 cm depth), soil porosity results were
relatively homogeneous (means of 39.1, 42.8 and 39.9%, respectively). Bulk density results
show high values at all depths (1.6 g/cm3) (Table 1), characterizing a compacted soil. Plot
soils had a sandy-clay loamy texture. The analysed soils have high sand contents (58.0, 59.1
and 62.1%, respectively, at 10-20, 30-40 and 80-90 cm depth), followed by silt (31.5, 30.3
and 26.9%, respectively) and clay (10.5, 10.5 and 11.1%, respectively) (Table 1).
171
Fig. 1 Soil water matrix potentials in each plot at 15, 30 and 90 cm depth.
Lama Mole (Soft Clay) trail: bulk densities on the trail and talus are >1.5 g/cm3, which
are high values (Fullen & Catt, 2004). Concomitantly, soil porosity values are low (Table 1).
These results indicate compacted soils. SOM values accord with local field values (2.4 and
3.0%), due to litter on the trail ground and talus. Most soils are loamy clays and sandy clay
loams. The soils are highly weathered, with pH values ranging between 4.38-4.48.
Água Branca (White Water) trail: The mean bulk densities are much lower than Lama
Mole, ranging between 1.1-1.2 g/cm3, which are medium values (Fullen & Catt, 2004; Guerra
et al., 2017). Consequently, porosity is relatively high (~50%), which facilitates infiltration.
Soil pH values are very low, ranging between 3.7-3.8, indicative of a highly weathered and
leached environment. Most soil samples have high sand content, being sandy loams, which
are highly erodible (Fullen & Catt, 2004; Morgan, 2005; Guerra et al., 2017). Nevertheless,
the vegetation cover and litter along the trail, and the high SOM content, give some protection
from erosion. SOM contents range between 7.3-7.7%, which are the highest measured values.
Table 1. Soil physico-chemical properties on the experimental station, trails and quarries
Soil collecting sites
depth (cm)
Porosity
(%)
Bulk
density
(g/cm3)
Coarse sand
(%) Fine sand (%) Silt (%) Clay (%) SOM pH
SD SD SD SD SD SD SD SD
Experi
mental
station
10-20 39.1
0.3 1.6 0.0 46.2
2.4 11.8 0.5 31.5 1.6 10.5 3.3 0.5 0.1 5.1 0.1
30-40 42.8
0.7 1.6 0.0 45.3
1.4 13.8 1.3 30.3 2.0 10.5 1.2 0.5 0.0 5.1 0.1
80-90 39.9
1.8 1,6 0.1 47.5
1.7 14.6 0.3 26.9 1.6 11.1 0.2 0.4 0.1 5.1 0.1
Água
Branca
TA 55.0
4.0 1.1 0.0 46.3
8.5 14.4 3.5 25.5 9.3 13.8 7.5 7.7 1.2 3.7 0.2
TR 48.8
3.4 1,2 0.1 51.3
9.1 12.6 2.5 26.1 11.7 9.5 1.8 7.3 1.0 3.8 0.1
Lama
Mole
TA 43.9
9.5 1.4 0.2 37.1
7.6 9.8 1.6 21.2 6.0 31.8 3.3 2.4 0.2 4.4 0.1
TR 34.7
2.8 1.6 0.1 44.6
7.0 10.4 1.7 20.9 2.6 23.9 5.6 3.0 0.7 4.4 0.1
Quarryi
ng
TA1 48.1
9.3 1.4 0.3 49.1
7.5 15.8 2.8 17.4 2.7 17.4 7.6 0.3 0.0 5.1 0.3
TA2 50.5
3.8 1.3 0.1 46.0
2.7 12.1 2.8 13.0 0.6 28.7 5.4 1.4 0.2 4.3 0.1
TA3 40.1
0.7 1.6 0.1 53.5
0.7 13.2 0.7 16.2 1.3 16.9 1.5 0.7 0.5 4.7 0.1
n = 3; Standard deviation (SD); Sand = 2000-50 µm, Silt = 50-2 µm, Clay <2 µm (USDA, 2017).
31st session of EFC/FAO Working Party on the Management of Mountain Watersheds
172
On the three cut quarry talus slopes (TA1, TA2 and TA3) mean bulk densities are 1.4,
1.3 and 1.6 g/cm3, respectively, and mean porosity values are 48.1, 50.5 and 40.1%,
respectively (Table 1). These values may be related to the weight exerted by the upper soil
layers, since the samples were collected in the intermediate part of the talus. The texture of
talus soils were sandy loams (TA1 and TA3) and sandy clay loams (TA2), with relatively
high coarse sand contents (Table 1). Much of the coarse sand is derived from saprolite, which
is exploited for building material. SOM values were generally low, with mean values of 0.3,
1.4 and 0.7%, respectively, for TA1, TA2 and TA3 (Table 1). These results can be explained
by the sampling location, that is, in the intermediate section of the talus, where SOM tends to
be naturally lower than in the epipedon. The mean soil pH values for TA1, TA2 and TA3
were 5.1, 4.3 and 4.7, respectively (Table 1).
Quarrying causes land degradation, mainly in the form of soil erosion and landslides.
The construction of roads to access the quarries and houses next to these quarries also
contributes to land degradation. The trails are responsible for erosion, landslides and
contributing sediment, which in turn is causing siltation in the Maranduba drainage basin.
Mountainous areas have specific characteristics. such as steep slopes and abrupt rock-soil
contacts, where human activities, when conducted without adequate management, can
seriously disturb these environmental systems.
Acknowledgement
The authors thank CNPq, CAPES (Brazilian Research Council) and FAPERJ (Rio de Janeiro
State Council) for financial support and for three PhD grants.
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