Hydrological processes in small forest and pasture catchments of eastern amazonia
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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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Hydrological processes in small forest and pasture catchments of eastern amazonia

Hydrological processes in small forest and pasture catchments of Eastern Amazonia

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.


How land use change will affect hydrological processes at small catchment scale
How land use change will affect hydrological processes at small catchment scale?

These are springs located in a forested catchment and in a pastured one in Paragominas.


Hypothesis
Hypothesis small catchment scale?

Land use change (forest/pasture) effects on hydrological fluxes processes at small catchment scale are:

  • Root zone soil permeability is reduced.

  • Increment in overland flow and subsurface flow.

  • Decrease of pasture evapotranspiration, and increment of soil water storage.

  • Water balance partitioning among different processes is altered.

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.


Hydrological processes in small forest and pasture catchments of eastern amazonia

Site Location small catchment scale?


Hydrological processes in small forest and pasture catchments of eastern amazonia

Paragominas small catchment scale?

(Fazenda Vitória)

Igarapé 54

60 0 60 meters

contour (0.5 m)

stream

weir in pasture

20 0 20 meters

weir in forest

contour (0.5 m)

wells

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.


Hydrological processes in small forest and pasture catchments of eastern amazonia

Forest small catchment scale?

Forest catchment

TDR and Ksat

6 m-depth soil pits

Capoeira

Fallow Plot

Pasture

8

-

10 m

45 m

Plynthite

layer

Pasture catchment

1

-

2 m

Water

Table

Deep percolation

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.


Hydrological processes in small forest and pasture catchments of eastern amazonia

pluviometer small catchment scale?

wood boundary (2x2 m)

surface runoff

collector

reservoir

Ksat transects

well

meteorological station

water table

OVF + SSF

collectors

OVF collector

weir

surface runoff collector

hillslope

soil

plastic cover

gravel

90cm

plastic plate

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.


Hydrological processes in small forest and pasture catchments of eastern amazonia

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.


Hydrological processes in small forest and pasture catchments of eastern amazonia

Forest and throughfall collectors.

Pasture

  • Subsurface flow

  • Overland Flow

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.


Water balance equation model

P and throughfall collectors.e = P - I

gs

ET

OVF

S

i+1

sat

cc

w

D

DS = P- I- ET- OVF - D

Water Balance Equation Model

  • Evapotranspiration

    • Penman- Monteith

    • Stomatal Conductance - Jarvis-type model(1976)

  • Soil water storage

  • Van Genuchten Equation

  • Water balance equation

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.


Results
Results and throughfall collectors.


Soil texture along the hillslope
Soil texture along the hillslope and throughfall collectors.

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.


Hydrological processes in small forest and pasture catchments of eastern amazonia

Forest – Latossolo with Plynthite signs at 1 m depth and throughfall collectors.

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.


Hydrological processes in small forest and pasture catchments of eastern amazonia

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.


Overland flow and subsurface flow

Overland flow and 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. Subsurface flow

Pasture

Forest

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.


Hydrological processes in small forest and pasture catchments of eastern amazonia

Pastagem 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.

Floresta

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.


Hydrological processes in small forest and pasture catchments of eastern amazonia

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).


Water balance partitioning
Water Balance Partitioning diamonds) were higher


Water balance changes

P diamonds) were higher

P

ET

ET

I

I

Pe

Pe

OVF

OVF

qv

qv

Plant water uptake

Plant water uptake

SSF

SSF

S

S

qv

qv

R

R

Water Balance Changes

Forest

Pasture

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.


Conclusions
Conclusions diamonds) were higher

Land use change (forest/pasture) effects on hydrological fluxes processes at catchment scale are:

  • Root zone soil permeability is reduced.

  • Increment of overland flow and possibly subsurface flow.

  • Decrease of pasture evapotranspiration, and increment of soil water storage.

  • Water balance partitioning is altered within different components.


Observations for future studies
Observations for future studies diamonds) were higher

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?


Relations to biogeochemistry
Relations to Biogeochemistry diamonds) were higher

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.


Hydrological processes in small forest and pasture catchments of eastern amazonia

Vertical and Subsurface Flow diamonds) were higher

Veg: Forest

Overland flow

Hortonian OVF- pasture

return flow - forest

Overland flow on saturated areas

Well Drained

plinthite

Draining impeded plynthite layer

No drainage, saturated area

Water table

Latossolo Amarelo

Plintossolos

Gleissolo