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Hydrological processes in small forest and pasture catchments of Eastern Amazonia. Schuler, Marysol – CENA/ USP, IPAM Moraes, Jorge M. – CENA/ USP Dunne, Tom - UCSB
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Schuler, Marysol – CENA/ USP, IPAM
Moraes, Jorge M. – CENA/ USP
Dunne, Tom - UCSB
Team project (Biogeochemical Transfers Among Terrestrial and aquatic biospheresand the Atmosphere in Forests and Pastures of Eastern Amazonia):
Davidson, Eric- WHRC
Figueiredo, Ricardo – IPAM, EMBRAPA/ CPATU
Markewitz, Daniel – UGA
Victoria, Reynaldo L. – CENA/ USP
I aknowledge every author efforts to create conditions to this study.
This hydrological study was part of a broader project on Biogeochemical transfers in forest and pastures.
These are springs located in a forested catchment and in a pastured one in Paragominas.
Land use change (forest/pasture) effects on hydrological fluxes processes at small catchment scale are:
In order to verify these hypothesis, we selected 2 catchments: one forested and the other pasture covered.
Both catchments are located at Paragominas county, state of Pará, Eastern Amazonia.
60 0 60 meters
contour (0.5 m)
weir in pasture
20 0 20 meters
weir in forest
contour (0.5 m)
IKONOS satellite imagery: Fazenda Vitória, Paragominas, PA.
In two selected catchments we installed equipments to measure flow of their ephemeral streams.
We used wells to observe water table depth and collect samples to water chemistry analysis.
Water table is deep enough to have no influence on the ephemeral streams flow.
TDR and Ksat
6 m-depth soil pits
Igarapé 54 (stream)
Schematic of hillslope and catchments location. The soil has a plynthite layer and its depth
variesfrom8-10 m, on the top of hillslope, to few centimeters or surface, at footslope.
wood boundary (2x2 m)
OVF + SSF
surface runoff collector
subsurface flow collector
Schematic of monitored catchment: met station, hydraulic conductivity transects, outlet weir,
wells, overland flow and subsurface flow collectors. Let’s see each equipment.
We had a met station, pluviometers next to each catchment and throughfall collectors.
Weirs were equipped with pressure transducer water level and Ksat measured using Guelph permeater.
Four overland flow collectors at 2 m x 2 m plots installed in each catchment.
A 2 m-length pit (0.9m-depth) was located downslope a 12 m slope in each catchment,
These pits had a subsurface flow collector at 0.9 m-depth (plynthite layer) and an overland flow collector.
DS = P- I- ET- OVF - DWater Balance Equation Model
A bucket model based on water balance equation, with evapotranspiration estimated by Penman-Monteith formula,
with surface conductance from a Jarvis-type model estimate.
Soil water storage was calculated by water balance and compared to estimates from tensiometers measurements.
Tension was related to soil moisture applying Van Genuchten equation on soil retention curves.
Soil texture and classification showed 4 different types of soil along the hillslope.
Forest and pasture catchmentswere located in different positions in the hillslope.
Forest one is upslope and pasture is on lower mid-slope. Footslope has gleissolo.
Pasture - Plintossolo
Forest site was on Latossolo (Oxyssol), with a plynthite layer around 0.90 m-depth.
Pasture, in a lower position in the hillslope, is on Plintossolo (Ultissol) with pliynthite signs since 0.40 m-depth.
Box-plot results of Ksat as a function of depth, under forest (a) pasture (b) and (c) capoeira. The length of the box represents the sample interquartile range, the cross bar in the box the sample median, the notch its 95% interval and the circles the outlying data points defined as being larger than 1.5 times the interquartile range.
Saturated hydraulic conductivity (Ksat) presents high variability.
In forest, Ksat on surface reached high values (23 mm h-1, median).
In pasture, we observed the lowest values for Ksat.
In capoeira, intermediate values at surface Ksat showed soil physical properties restoration signs only at surface.
Note the different graph scales.
Results of overland flow shows ratio OVF: total precipitation around 0.04 (4%)
while ratio for pasture is 14%. In both land cover, SSF measured was ~1% precipitation.
Tension data set for different depths (0.15, 0.3, 0.6 and 0.9m) during wet season, shows
that most of the days soil is near saturation. This is markedly observed in pasture,
while in the forest tensions reach lower values due to free drainage.
Mean soil water content for wet season in the pasture (blue diamonds) were higher
than water content in the forest soil plots (circles).
This difference is markedly observed near surface (0.15 and 0.30 m).
Plant water uptake
Plant water uptake
RWater Balance Changes
Changes inWater balance components: Interception decreases, while there are increments
in Evapotranspiration, Overland Flow and Soil water Storage increase.
Although we did not measure Recharge,it should increase due to larger soil water Storage.
Land use change (forest/pasture) effects on hydrological fluxes processes at catchment scale are:
Besides soil class, the presence and depth of hydraulic impeding layers is related to the position in landscape (hillslope height).
The presence of an impeding layer (plinthite, e.g.) may increase forest-pasture conversion effects on hydrological processes, as ET reduction or OVF increment.
Could soil hydraulic properties as driving forces on hydrological changes related to forest conversion be modelled from landscape features?
Higher cations and anions concentrations in stream water during wet season are related to Overland Flow, that increases after forest conversion. How much is nutrients exports in these areas?
Forest conversion should have different soil responses according to landscape position and hydraulic properties.
How can we model these influences on nutrient exports?
For example, rivers with large floodplains and others with steeper mid-slope have different hydrological processes driving geochemistry fluxes.
Hortonian OVF- pasture
return flow - forest
Overland flow on saturated areas
Draining impeded plynthite layer
No drainage, saturated area