Dissolved inorganic carbon and pCO₂ in two small streams draining different soil types in Southwestern Amazonia, Brazil

Abstract

The objective of this study was to determine the dissolved inorganic carbon (DIC) and pCO2 concentrations in two third order streams in southwestern Amazonia, Brazil. From May 2004 to June 2005 water dissolved oxygen, pH, electrical conductivity, temperature were measured to stream water chemical and physical description. DIC and pCO2 measurements were made by headspace extraction and gas samples for pCO2 and DIC extractions were run on an infrared gas analyzer (IRGA, LI-COR Instruments model LI-820). Results indicate a relationship between soil type and water chemistry, where sandy soil stream presented lower pH than silty soil stream – consequently DIC and pCO2 concentrations also varied with soil type. Mean DIC concentration for sitly soil stream was 403±130 ?M month-1, while sandy soil stream DIC concentration was 170±59 ?M month-1. Free CO2 was the dominant form of DIC in both streams. Nevertheless, HCO3- contribuition to DIC was greater for the silty soil stream. DIC contentration also varied seasonally with greater values in the drier period. Absolute pCO2 values were greater for silty soil stream, mean 3067±1228 µatm month-1 and 2321±1020 µatm month-1 for sandy soil stream. Seasonality, pCO2 was higher in the dry season in both streams. Our findings have important implications on the role of soil type in water chemistry and carbon dynamics and also are used in other studies on carbon balance at the landscape level.