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Nutrient dynamics in nested catchments at nested time scales: trends in hydrologic exports from 1st and 2nd order watersheds in the seasonally dry Southern Amazon

Mark S Johnson, Cornell University, (Presenting)
Eduardo Guimar„es Couto, Universidade Federal de Mato Grosso,
Johannes Lehmann, Cornell University,
Susan J Riha, Cornell University,

Water quality data can present difficulties for assessing trends and patterns among parameters and between study units due to sheer volumes of data and nested time scales. Here we present analysis of three years of data from baseflow and stormflow samples collected from four 1st order streams and one 2nd order stream near Juruena, Mato Grosso in the seasonally dry southern Amazon. Data was grouped by catchment, coded by season (wet, dry, and transition seasons), and analyzed by CHAID (Chi-squared Automatic Interaction Detection). Since more than 90% of annual stream discharge occurs as baseflow after interacting with the soil profile, hydrologic exports would be expected to reflect variability in soil properties. For baseflow conditions, stream water concentrations of base cations derived primarily from mineral weathering (Ca2+, Mg2+, Na+) were found to vary by location, thereby reflecting soil variability between catchments. However, elemental cycles with significant biogenic components (DOC, K+, Si) were found to be more strongly dependent upon season than location. Of this latter group, both DOC and K+ were found to increase with discharge during storms, while Si, Ca2+, Mg2+, Na+ decreased with discharge during storms. Nevertheless, concentrations of both groups were inversely related to discharge at a seasonal scale for both 1st and 2nd order streams.

Science Theme:  ND (Nutrient Dynamics)

Session:  1B: Nutrient Cycling in Terrestrial and Aquatic Systems

Presentation Type:  Oral

Abstract ID: 91

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