Synthesis of Nutrient Interactions in Secondary Vegetation in Amazonia
Claudio JosÚ Reis de Carvalho Embrapa Amaz˘nia Oriental (SA-PI)
Agricultural land in the Amazon Basin often goes through cycles of clearing and abandonment, depending on the interacting effects of soil properties, climate, economics, and technology. Secondary forest regrowth contributes to the regional carbon balance and restores hydrological functions. Our previous LBA research has demonstrated an important role of soil nutrients in rates of forest regrowth. Understanding the legacy of previous land uses and the demands of current vegetation for soil nutrients can help identify current and future land management options. The theme of this proposal is nutrient cycling in forests and pastures and the small streams that drain them. The proposal is divided into three sections: (1) A model of plant demand, soil supply, fire loss, and leaching loss of macronutrients in mature forests, cattle pastures, and secondary forests. The model integrates into a common conceptual and numerical framework our research findings on plant growth, soil chemistry, carbon dynamics, soil trace gas emissions, and streamwater chemistry and discharge. The model developed for study sites near Paragominas, Para, will be applied to other LBA datasets from the central and western Amazon regions, thus testing whether our mechanistic understanding of how land use change affects nutrient cycling in the highly weathered deep Oxisols of eastern Amazonian ecosystems, as represented in our model structure, also applies to other regions and soil types; (2) Spectral mixture analysis of Landsat imagery will be used to estimate photosynthetic vegetation (PV) and non-photosynthetic vegetation (NPV), the latter indicating the presence of senescent foliage in degraded pastures. The NPV scalar provides an objective tool for quantifying degrees of pasture degradation as defined by this criterion. Accumulation of NPV is mechanistically linked to our nutrient cycling model, as senescent vegetation sequesters actively cycling nutrients in degraded pastures and young secondary forests. Low rates of gaseous emissions and hydrologic leaching of N can be inferred where nutrients are sequestered in NPV and aggrading woody vegetation of old pastures, thus providing a means of scaling up estimates from the nutrient cycling model to Landsat scenes; (3) Completion of data analysis of phase II projects, including stream chemistry and hillslope and riparian hydrologic processes in three small watersheds of mixed uses. Concentration-discharge relationships will be examined by land-use and watershed size determined from Landsat imagery and will be compared to similar results in other Amazonian regions. Combining these project components, we will demonstrate how landscape-scale changes in land cover resulting from agricultural management affect nutrient cycling processes, thus addressing the LBA objectives of understanding how land use change affects Amazonian carbon dynamics, trace gas emissions, and water quality.
Eric A. Davidson WHRC - Woods Hole Research Center (US-PI)
Ricardo Figueiredo Embrapa Meio Ambiente (SA-PI)
Ima Vieira MPEG - Museu Paraense Emilio Goeldi (SA-PI)