“Physical and Anthropogenic Controls of the Biogeochemistry of the Ji-Paraná River Basin (Western Amazônia)” 1 Ballester, M.V.R.; 1 Krusche, A.V.; 1 Kavaguishi, N.L.; 2 Gomes, B.M.; 1 Victoria, D. de C.; Montebelo, A.A.; 3 Neill, C.; 3 Deegan, L.; 4 Richey, J.E. and 1 Victoria, R.L. 1 Centro de Energia Nuclear na Aagricultura – Universidade de São Paulo; 2 Universidade Federal de Rondônia; 3 Marine Biological Laboratory; 4 University of Washington CD-06, ND-03 and ND-09

 What are the water stores and fluxes, and the controls on water movement and transport of constituents on and below the surface of small uniform basins?  How does change of land use affect the sustainability of the ecosystem for different soil types and topographies, and how can the larger scale models be improved to represent these small scale processes?  What are the spatial and temporal patterns of surface and sub-surface water storage and flux in the soils and river corridors of the Amazon Basin, and how are they influenced by variations in climate and land use?  What are the characteristics of soil moisture and river flow for mesoscale basins and how can they be predicted? Land surface Hydrology and Water Biogeochemistry specific questions  How do the pathways and fluxes of organic matter, nutrients and associated elements through river corridors (riparian, floodplain, channels and wetlands) change as a function of land cover?

RATIONALE Several LBA studies have shown that forest clearing in the Amazon can alter the transport of sediments, organic matter and associated nutrients to the rivers Our previous results demonstrated that both soil properties and land use are the main drivers of river biogeochemistry and metabolism

Na + Ca 2+ Mg 2+ K + EC Cl - PO 4 3-  The pasture explained 99% (p < 0,01) of the variability observed in most of the ions concentrations  Cattle pasture are statistically correlated with nutrient content Ballester et al., 2003 River biogeochemistry drivers

[Na] (µM) Q (m 3.s -1 ) - Differential effect of geology and soil properties - Human effects Rio Urupá JIP em Cacoal River ions concentrations are control by different mechanism

Spatially integrated analysis of Ji-Paraná basin (RO). OBJECTIVE Evaluate physical and anthropogenic controls on river biogeochemistry at the mesoscale level

Ji-Paraná Study area  Is the 3 rd most deforest State in the Braziliam Amazon (INPE, 2003)  Is responsible for ~10% of the Braziliam Amazon deforestation, around km 2 year -1 are cleaned in RO

Land use/cover (1999) In 30 years: the population grew 12x, there is an increase in cattle pastures and a loss of about 24% natural forest

Field work at 38 sites during both Wet (January) and Dry (June) seasons Spatially oriented (GIS physical template) Drainage area: km 2 Q = 700m 3.s -1, To answer our research on land use change and soil properties as drivers of water chemistry in the Ji-Paraná River Basin, we:

ImpactSBases Low Medium0.39 – 0.52 High0.57 – 0.91 Very high0.76 – 0.96 Each site represents a different mixture of cover type and soil properties Impact (% of pasture area)Area % Low - 0 –15%37 Medium %16 High %16 Very high %32

To quantify the effects of these two drivers, we performed a multiple linear regression analysis, relating basin characteristics and RBGC Data Analysis Independent variables Saturation of bases and percentage of pastures River water: Electrical conductivity (EC) Na +, Ca 2+, Mg 2+, K +, Cl -, DOC, TSS, DIC and PO 4 3- concentrations Dependent variables

RESULTS

~90% of the pasture areas were in eutrophic soils in 1999 Pasture areas are related to more fertile soils (higher ECEC and BS) and this relation is statically significant (p<0.01)

Higher values of all ions were associated with areas dominated by pasture Spatial patterns

Lower reaches, forests dominate the landscape, and the concentrations drop. Highest concentrations found in the central part of the basin, where pasture areas and soil fertility are at a maximum

TZ+ values for the waters of the Ji- Paraná river

Higher DOC concentrations were related to higher values of TSS During the dry season this pattern was not observed.

TSS, in turn, were originated in pasture areas.

Gouveia Neto et al., CD Forest: higher infiltration deeper into the soils and canopy interaction Pasture: soil is compacted, there is less infiltration and higher surface run off promoting the leaching of soil superficial layers caring more DOC to the stream The pasture stream showed higher “peaks ” of DOC fluxes when compared to the forest stream

DOC during the wet season as a function of land use impact ImpactArea %Min DOCMAX DOC Low Medium High Very high

Wet x Dry season

Wet x Dry season and Pasture x Soils

R2R2 PastureSoil Base Saturation Na + 0, Cl - 0, K+K+ 0, Mg 2+ 0, Ca 2+ 0,81480 DOC0, Statistically significant for p < 0.01 The percentage of the basin area covered by pasture was consistently the best predictor for all parameters during the wet season.

Concluding remarks Conversion of forest into pastures is changing river biogeochemical composition However, the degree of effect of each of these end members varies along a wide range and regional (and local) patterns remains still to be investigated