FOREST COVER AND WATER
QUALITY IN TROPICAL
AGRICULTURAL WATERSHEDS
Kaline de Mello, Roberta A. Valente, Carlos A. Vettorazzi, and
Timothy Randhir
University of São Paulo, Brazil
University of Massachusetts, Amherst, USA

Introductio
n
Replacing forest with other land uses can have severe impacts on
river water quality, altering its physical, chemical and biological
characteristics.
FOREST OTHER LAND USE

Introduction
Tropical forests are under continual
threat due to deforestation and forest
fragmentation processes
Brazil - the highest rate of annual
deforestation in the world – agricultural
and pasture expansion
Tropical Forest Deforestation

To evaluate the relationship between forest cover and water
quality of tropical agricultural watershed in different scales.
• Ecosystem services
• Landscape planning
• Forest conservation and restoration
• Watershed management
Objectives

• Sarapuí River Basin – São Paulo St,
Brazil
• 6 experimental small watersheds with
different percentage of forest cover
3 forested (≥55%) – S1, S2,and S5
3 degraded (≤35%) – S3, S4, and S6
• Atlantic Forest
• Agriculture, Eucapyptus, Pasture and
Urbanization
Mostly annual crops
Study Area

24 samples October 2013 to October 2014
Temperature (°C)
pH
Dissolved oxygen (mg.L-1)
Streamflow
Water samples
Water quality and streamflow during a year
Turbidity (NTU)
IN-SITU
WATER
QUALITY
DETECTOR
TURBIDIMETER
CURRENT-
METER

Water quality analysis
Total Nitrogen (mg.L-1) – Kjeldahl digestion
Total Phosphorus (µg.L-1) – Spectrophotometric
Total Coliforms (NMP)
Fecal Coliforms (NMP)
Total suspended solids (mg.L-1)
Inorganic suspended solids
Organic suspended solids
GRAVIMETRIC
MULTIPLE-TUBE

Analysis
Comparing Forested and Degraded Watersheds
Statistical analysis
• Spatial variation of water quality
• Pearson correlation between water quality variables
• Linear regression between water quality and stream
flow
• MANOVA – Hotelling-Lawley
• PCA

• Forested watersheds – better water
quality
(Hotelling-Lawley´s λ = 0.47; F = 5; P = 0.0003)
• S4 – High values and temporal
variation agricultural area
• S5 – good water quality forest
• S3 – lowest DO urbanization
Forested vs Degraded
Results
Water quality
Streamflow
Solids
(NTU and SS)
Nutrients
(TP)

Riparian Analysis
Comparing Watershed and Riparian Zone

Water quality variable
T
Land
Use
Q
• Watershed
• Month
Mixed
models
Land use
watershed
Riparian
Zone
RDA
Global
influence on
Water quality
Watershed vs Riparian Zone

• Forest – good water quality in all models
• Pasture – different impacts, in general do not impact water quality negatively
• Agriculture and urbanization water quality degradation
DO Solids
Nutrients
Coliforms
Forest Urbanization and Pasture
DO
Urbanization & Agriculture
Sólids
Nutrients
Coliforms
Temperature and
organic material
Drainage of
agricultural areas
and sewage
Watershed vs Riparian Zone
Results

Variable Escale R2 Int. Q T Agriculture Pasture Urban
DO Watershed 0,72 8,64** 2,46* -0,13** 1,24* -2,41*
TSS Watershed 0,60 0,79** 15.21** 1,69** 6,42**
OSS Riparian Zone 0,51 0,55** 9,69** 1,75** 2,46*
TN Riparian Zone 0,49 4,43** -0,06* -0,09** 5,67**
TP Watershed 0,67 3,03** 5,67** 1,64** 4,86**
FC Watershed 0,65 2,26** 4,91** 5,04*
Mixed models.
Watershed vs Riparian Zone
Results

Watershed Riparian Zone
82% 75%
Pollution gradient
Riparian Zone =
30m: Brazilian law...
Is that enouth?
Watershed vs Riparian Zone
Results
RDA

Third Analysis
Modelling impacts of riparian restoration on water quality
SWAT model
Sarapuí River Basin

Soil
Slope
Land use
River network
Temperature
Preciptation
Humidity
Solar radiation
Wind speed
Streamflow, sediment and
nutrients
2 gates + experimental
watersheds
Source: Projet, IBGE, CPLA, INMET e ANA
Modelling water quality
SWAT model

Modelling water quality
Model calibration – SWAT-CUP
• Streamflow: Daily, Monthly and Yearly - 33 years, 3
warming up
• Performance criteria: R², NS, & PBIAS
• R², NS, & PBIAS
Sensitivity analysis
Validation
Streamfl
ow
Sedim
ent
Nutrien
ts

• Better results for monthly streamflow
• Performance criteria: R², NS, & PBIAS
- good and acceptable values
Modelling water quality
Results
Calibration

Great values of sediment and nutrients at the headwaters
Greater slopes and agricultural areas
Exception for forested watersheds
Figura 9: Distribuição espacial da qualidade da água.
Agriculture and urban
Rainy season
Florest and Pasture
Dry season
P SS
Modelling water quality
Results
Land use and water quality

Modeling water quality
Results
Riparian restoration
• forest 14%
• agriculture 8% and pasture 10%
• SS 9,26%
• N 22,6%
• P 7,89%
30m of Permanent Protected Area

Conclusions
• Importance of forest cover in agricultural watersheds;
• Agriculture and Urbanization generate more pollutants;
• Exposed soil - erosion and runoff - sediments carry pollutants;
• Residential areas, even small ones, generate pollution (without sewage
collection);
• grasslands contribute to water quality;
• Water quality parameters respond differently to scales;
• Watershed management more important than just riparian conservation;
• Riparian restoration as a priority action.

Conclusions
• Landscape planning;
• Best agricultural practices;
• Sewage collection, septic tank;
• Forest conservation and restoration;
• Holistic view of the watershed and ecosystems in decision making.
What to do?

Thank you!
• Contact:
• Randhir@umass.edu
• (413)5453969
• https://eco.umass.edu/people/faculty/randhir-timothy-o/