Study Notes on Deforestation and Water Biogeochemistry in the Amazon

Timing Since Deforestation for Pastures Implementation in the Western Amazon: Impacts on Stream Water Biogeochemistry

Authors and Institutions

• Felipe Rossetti de Paula - Division of Tropical Ecosystems Functioning, Center for Nuclear Energy in Agriculture, University of São Paulo, Brazil

• Gabriel Lourenço Brejao - Department of Biodiversity, São Paulo State University, Brazil

• María Angelica Pérez-Mayorga - Department of Biological Sciences, São Paulo State University, Brazil

• Lilian Casatti - Department of Biological Sciences, São Paulo State University, Brazil

• Silvio Frosini de Barros Ferraz - Department of Forest Sciences, “Luiz de Queiroz” College of Agriculture, University of São Paulo, Brazil

• Alexandra Montebelo Krusche - Division of Tropical Ecosystems Functioning, Center for Nuclear Energy in Agriculture, University of São Paulo, Brazil

• Alex Vladimir Krusche - Division of Tropical Ecosystems Functioning, Center for Nuclear Energy in Agriculture, University of São Paulo, Brazil

Highlights

• Deforestation is largely associated with pasturelands, causing soil and water degradation.

• Soil nutrients deplete as pasture ages; similar impacts are expected on adjacent streams.

• Pasture aging increases the following concentrations: Magnesium ($Mg^{2+}$), Calcium ($Ca^{2+}$), Dissolved Inorganic Carbon (DIC), Conductivity (COND). Reduces Sulfate ($SO<em>{4}^{2-}$), Nitrate ($NO</em>{3}^{-}$), Ammonium ($NH_{4}^{+}$), Total Nitrogen (TN), Dissolved Organic Carbon (DOC), Dissolved Oxygen (DOX), Temperature (TEM).

• Catchment soil types are significant in explaining water biogeochemistry.

• Long-term sustainability of Amazon pastures is crucial to mitigate soil and water degradation.

Article Information

• Editor: Jay Gan

• Keywords: Stream ecology, water degradation, land use changes, tropics, environmental management, nature conservation

• Abstract: Water quality degradation is a global issue, significantly driven by land use changes. In the Brazilian Amazon, large-scale deforestation primarily occurs due to pasture establishment, seriously affecting soil and stream biogeochemistry. Studies demonstrate a consistent depletion of nutrients in degraded pastures. Our study, focusing on Rondonia State, Brazil, investigates how the timing since deforestation impacts stream water biogeochemistry by analyzing 41 headwater catchments under differing land use intensities. Results indicate significant changes in water chemistry due to pasture age and land use intensity, necessitating urgent reclamation and sustainable management practices.

Introduction

• Increasing demand for clean water is a global challenge driven by economic activities and population growth (Boretti and Rosa, 2019).

• The degradation in water quantity and quality is attributed to environmental degradation, including land use alterations, lack of proper sanitation, droughts, and climate change (Mishra et al., 2021; United Nations, 2023).

• The UN has prioritized clean water and sanitation as a goal for sustainable development.

Deforestation and Land Use

• Anthropogenic land use, particularly tropical deforestation for agriculture, causes significant diffuse water pollution (Mello et al., 2020).

• Large-scale agriculture leads to increased pollution through fertilizers and pesticides, affecting water quality and aquatic ecosystems (Mori et al., 2015).

• Forest cover is vital for reducing agriculture’s ecological impact and preserving water clarity (Taniwaki et al., 2017).

• Functions of forests at various scales include:

  • Intercepting rainwater, enhancing infiltration, and controlling erosion.

  • Maintaining low water temperature and high dissolved oxygen levels.

  • Preventing nutrient and sediment export into waterways.

Methods

Study Area

• The research was located in the Machado River Basin, Rondonia State, Brazil, characterized by tropical humid climate with yearly rainfall averaging 2500 mm.

• Deforestation in Rondonia began in the early 1970s following the construction of the BR-364 highway, leading to rapid land-use changes.

Analysis of Deforestation Dynamics

• Land Use Monitoring: Utilized Landsat 5TM images (30x30 m resolution) for mapping and observing land-use changes from 1984 to 2011.

• Categorization of maps included mature forests, degraded forests, and non-forest areas.

• Introduced Land-Use Change Analysis Tool (LUCAT) for quantifying land use metrics, including:

  • Forest Change Curve Profile (FCCP): Indicates temporal patterns of deforestation.

  • Land Use Intensity (LUI): Reflects deforestation duration, with values ranging from 0 (no deforestation) to 100% (full deforestation).

Water Sampling

• Conducted in June-July 2012, collecting water samples from 41 shallow streams.

• Samples analyzed for major ions, dissolved organic carbon, conductivity, total nitrogen, and other chemical attributes.

Results

Deforestation Timing Effects

• Significant differences observed between primary forests and pastures, indicating changes in ion concentrations and nutrient availability across different pasture ages.

• Statistical Findings:

  • Differences in water quality attributes, notably $SO_{4}^{2-}$ and $TN$, between primary forests (PRI) and newly (NEW) or old (OLD) pastures.

  • LUI relates positively to ion concentrations, emphasizing the connection between land use intensity and water quality degradation.

Effects of Land Use Intensity

• Analysis indicated a direct correlation between increased land use intensity and altered water chemistry (higher around Ca, Mg, DIC, COND, and lower NO3, DOX, TEM).

• Changes observed corroborated earlier studies, emphasizing the necessity of sustainable management practices to mitigate degradation.

Discussion

Deforestation Dynamics and Water Quality

• Deforestation alters ion transport from terrestrial to aquatic ecosystems, leading to altered nutrient dynamics—decreased $NO_{3}^{-}$ and increased $Mg^{2+}$ and $Ca^{2+}$ in older pasture waters.

• Hypothesized that repository processes balance primary production and respiration- dynamics under pasture conditions.

Biogeochemistry Impacts

• Older pastures exhibit reduced nutrient transport to streams due to soil degradation and increased plant nutrient uptake during initial peak growth periods post-deforestation.

• Deterioration of water quality reflects broader ecological implications, particularly for aquatic biodiversity and stream health.

Limitations and Future Directions

• Acknowledgment of study constraints such as non-measured stream metabolism.

• Emphasizing the importance of controlled sampling in future studies to substantiate findings and provide clearer management strategies.

Ecological and Management Implications

• Water quality degradation poses risks for aquatic ecosystems, impacting the physiological processes of organisms, particularly fishes (e.g., reductions in body size due to higher temperatures).

• Importance of implementing Best Management Practices (BMP) such as riparian buffers to protect waters and stream health.

Conclusion

• The study highlights the significant relationship between pasture age, land use intensity, and impacts on stream water biogeochemistry, underscoring the need for sustainable agricultural practices in the Amazon to balance productivity and ecological integrity.

Credits

Author Contributions

• Felipe Rossetti de Paula: Writing, methodology, analysis.

• Gabriel Lourenço Brejao: Review, software application.

• María Angelica Pérez-Mayorga: Review, methodology.

• Lilian Casatti: Project administration.

• Silvio Frosini de Barros Ferraz: Review, investigation.

• Alexandra Montebelo Krusche: Review, data curation.

• Alex Vladimir Krusche: Review, supervision.

Funding

• Research supported by the São Paulo Research Foundation (FAPESP) grant number 2010/17494-8.

Acknowledgments

• Thanks to collaborators and institutions supporting fieldwork and research permissions.