Physical and Anthropogenic Controls of the Biogeochemistry of the Ji-Paraná River Basin (Western Amazônia)

Transcription

1 CD-06, ND-03 and ND-09 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

2 Land surface Hydrology and Water Biogeochemistry specific questions 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 i to represent these small scale processes? What are the spatial and temporal patterns of surface and sub-surface surface water storage and flux in the soils and river corridors of the Amazon Basin, and how h 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? 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?

3 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

4 River biogeochemistry drivers Na + Ca 2+ Mg 2+ K + 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 EC Cl - PO 4 3- Ballester et al., 2003 TZ Pasture ECEC

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

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

7 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 Ji-Paraná

8 Land use/cover (1999) estradas estradas 2000 Legenda Classe Pasto Floresta Água Urbanização habitantes estradas Cerrado Culturas Anuais Rebrota Solos expostos Nuvens Outros In 30 years: the population grew 12x, there is an increase in cattle pastures and a loss of about 24% natural forest

9 Legend Soil unit (area) Alfisol (12.6%) Entisol (16.2%) Eptisol (1.8%) 1999 Oxisol (46.1%) 2000 Ultisol (23.1%) Water (0.3%) Legenda: = cabeças estradas

10 To answer our research on land use change and soil properties as drivers of water chemistry in the Ji-Paraná River Basin, we: 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, Discharge (m3.s-1) Ordem D F A J A O D F A J A

11 Each site represents a different mixture of cover type and soil properties Impact (% of pasture area) Low % Medium 15-30% High 30-50% Very high 50-75% Area % Impact Low Medium High Very high SBases Legend Soil unit (area) Alfisol (12.6%) Entisol (16.2%) Eptisol (1.8%) Oxisol (46.1%) Ultisol (23.1%) Water (0.3%)

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

13 RESULTS

14 Pasture areas are related to more fertile soils (higher ECEC and BS) and this relation is statically significant (p<0.01) 80 Pasture Pasture ECEC ECEC Pasture area (%) y = e x R 2 = Base saturation ~90% of the pasture areas were in eutrophic soils in 1999

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

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

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

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

19 TSS, in turn, were originated in pasture areas.

20 The pasture stream showed higher peaks of DOC fluxes when compared to the forest stream 17 Fevereiro - Pastagem 2500 Fluxo C OD Descarga 140 Pasture: soil is compacted, Fluxo (mg.s -1 ) :41 9:51 10:01 10:11 10:21 10:31 10:41 10:51 11:16 11:56 12:36 13: Descarga (L.s -1) there is less infiltration and higher surface run off promoting the leaching of soil superficial layers caring more DOC to the stream Horas 17 Fevereiro - Floresta 70 Fluxo COD Descarga 4.5 Fluxo (mg.s -1 ) Descarga (L.s -1) Forest: higher infiltration deeper into the soils and canopy interaction 0 0 9:37 9:47 9:57 10:07 10:17 10:38 10:48 Horas 10:58 11:08 11:33 12:13 12:53 13:33 Gouveia Neto et al., CD 36.13

21 DOC during the wet season as a function of land use impact Impact Area % Min DOC MAX DOC Low Medium High Very high

22 Wet x Dry season Mg Electric Conductivity WET DRY 0 Wet Dry 66 K Na WET DRY 50 WET DRY

23 Wet x Dry season DOC WET DRY Ca 2+ WET DRY TSS WET DRY

24 Wet x Dry season and Pasture x Soils Wet season Dry season < < 1

25 R 2 Pasture Soil Base Saturation Na + 0, The percentage of the basin Cl - 0, area covered by pasture was consistently the best predictor for all parameters during the K + Mg 2+ 0,72 0, wet season. Ca 2+ 0, DOC 0, Statistically significant for p < 0.01

26 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