Volume 537, 15 December 2015, Pages 421–440
Controls and forecasts of nitrate yields in forested watersheds: A view over mainland Portugal
Highlights
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- A framework model describing nitrate yields in forested watersheds is conceived.
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- The framework model is tested using Partial Least Squares (PLS) regression.
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- Validated PLS regression coefficients are used to predict future nitrate yields.
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- Predictions are based on forest management scenarios set up by Portuguese regulations.
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- Implementation of a sustainable forest management may reduce nitrate yields.
Abstract
A
study on nitrate yields was conducted in forested watersheds of
mainland Portugal. The prime goal was to rank parameters in descending
order of their contribution to the export of nitrate towards streams and
lakes. To attain the goal, variables like soil loss, rainfall
intensity, topography, soil type, forest composition and environmental
disturbances such as hardwood harvesting or wildfires were organized in a
conceptual yield model. Because some parameters were potentially
collinear, a robust multivariate statistical technique was selected to
execute the conceptual model and perform the aforementioned ranking,
namely Partial Least Squares (PLS) regression. This technique was tested
with a sample of 60 forested watersheds (> 70% of forest
occupation), being subject to a double-validation process to ensure
prediction capability. According to final regression coefficients, soil
erosion seems to regulate nitrate distribution across the basins,
because soil loss and type, rainfall intensity and topography explained
around 60% of nitrate yield variance. The major importance of erosion is
followed by a moderate role of biochemical processes such as
nitrification or nutrient uptake, which accounted for approximately 15%
of nitrate yield variance. In this case, deciduous forests and scrubland
seem to behave as net sinks of nitrate while coniferous and mixed
forests seem to act dually, as net sources or sinks. The least important
parameters are the environmental disturbances, explaining no more than
5% of nitrate yield variance. The results of PLS regression were coupled
in a scenario analysis with measures designed to protect soil from
erosion and surface water from eutrophication. These interventions are
to be implemented until 2045, according to regional plans of forest
management. Considering the key role of erosion in explaining nitrate
dynamics across the catchments, it was not surprising to verify that
soil protection measures may reduce nitrate yields by some 35% of their
current values.
Graphical abstract
Keywords
- Forested watershed;
- Anthropogenic pressure;
- Soil erosion;
- Nitrate yield;
- Partial Least Squares regression;
- Sustainability scenario
Copyright © 2015 Elsevier B.V. All rights reserved.
