ABSTRACT

1. 10 0.40 Nitrate-N Chloride 8 0.30 ppm 6 ppm 0.20 4 0.10 2 0.00 0 Altamira Santarém Manaus Altamira Santarém Manaus 1.00 0.12 Sulfate Ammonium-N 0.10 0.75 0.08 ppm 0.06 0.50 ppm 0.04 0.25 0.02 0.00 0.00 Altamira Santarém Manaus Altamira Santarém Manaus 0.8 5 Magnesium Potassium 0.6 4 ppm 3 ppm 0.4 2 0.2 1 0.0 0 Altamira Santarém Manaus Altamira Santarém Manaus 8 Calcium 6 ppm 4 2 0 Altamira Santarém Manaus 11.6 Regional patterns in inorganic nutrient lossesacross the central Amazon Basin: preliminary results Megan McGroddy1, Lars Hedin1, Emilio Moran2, and Mateus Batistella3 1 Princeton University, 2 ACT Indiana University, 3 EMBRAPA, Campinas SP  ABSTRACT Nutrient losses have important implications for sustainability, productivity and carbon balance of forest ecosystems. Losses are particularly important in ecosystems where mineral nutrient inputs from weathering processes and atmospheric deposition are limited. The traditional notion that ecosystem losses of biotically available nutrients (e.g., inorganic forms such as NO3- and PO43-) are a consequence of nutrient limitation are being expanded by the new idea that losses of biotically unavailable forms (organically bound forms) can control nutrient-carbon interactions in forests over time. We examined patterns in nutrient loss across geographically broad variations in state factors (e.g., parent material, climate, and soil development as an index of time). Controls over nutrient losses are fundamental to the question of ecosystem sustainability of native forests and how these processes might respond to land use and land cover change. Moving from Altamira in the southeast to study sites north of Manaus in the northwestern end of our transect we characterized hydrologic losses of major anion and cation nutrients from primary forests in both dry and wet seasons (October-November 2002 and April 2003). Chloride (Cl-), potassium (K+) and calcium (Ca2+) all decreased significantly across the transect as we moved inland (Cl: 6.2 to 1.0 ppm, K: 0.7 to 0.1 ppm, and Ca: 4.4 to 1.0 ppm) . In contrast, the highest concentrations of nitrogen as nitrate ( NO3--N) and total phosphorus (Ptot) were found in Manaus the westernmost site (0.2 ppm and 1.4 ppb respectively). Santarém showed the most significant effects of seasonality especially for nitrogen as ammonium (NH4+-N) and sulfate (SO42-). At all three sites significantly higher NO3--N concentrations were measured in the wet season. The higher concentrations of rock nutrients in Altamira may reflect the younger soils found there ( Alfisols as compared to Ultisols and Oxisols at the other two sites). More intensive sampling in the coming year will allow us to better disentangle the importance of state factors that co-vary across the transect. Manaus Santarem Altamira INTRODUCTION Losses of nutrients have important implications for productivity and carbon balance of forest ecosystems. Nitrogen (N) and phosphorus (P) are particularly important as the two most common limiting nutrients in forests worldwide. Our view of how N and P losses are linked to forest carbon sequestration is presently undergoing dramatic change: The traditional notion that ecosystem losses of biotically available nutrients (e.g., inorganic forms NO3- and PO43-) are a consequence of nutrient limitation is being expanded by the new idea that losses of unavailable forms (e.g., dissolved organic complexes of N and P) can control how nutrient-carbon interactions develop over time in forests. For example, we have recently shown that the latter mechanism (organic-bound nutrients) dominates hydrologic losses of nitrogen from unpolluted old-growth forests in broad geographic regions of Chile and Argentina. These results offer a revised view of the link between N and carbon balances in unpolluted temperate forests. It has only recently become clear that models of forest carbon sequestration (e.g., TEM, Century, PnET, MEL, etc.) must incorporate the effects caused by export of nutrients in dissolved organic forms. Such incorporation is prohibited however by our exceedingly poor understanding of how inorganic and organic nutrient losses vary across natural landscapes, as a function of major factors thought to influence ecosystem nutrient cycles (i.e., so-called “state factors”). The problem is especially troubling for tropical regions such as the Amazon Basin, as there exists little to no information on how patterns of nutrient loss depend on geographically broad variations in state factors. Yet, such information is essential for developing temporally and geographically comprehensive models of carbon sequestration We want to characterize the patterns of hydrologic N and P losses across the Amazon Basin in order to compare these patterns to indices of terrestrial nutrient cycling and stocks across soil types in the Basin itself, as well as to those seen in temperate forest systems in North and South America. This extensive survey approach will cover a larger geographical scale while complementing some of the more intensive site-specific work already underway within the LBA ecology project. Our initial focus is on primary forests, with the goal of deriving a baseline for natural variability in N and P losses from these systems. SITE DESCRIPTION This research was carried out along a transect running from southeast to northwest across the central Amazon Basin. Along this transect a variety of key factors change including: annual precipitation and distribution, soil fertility and land use patterns. Soils in Altamira, the southern and eastern end of the gradient vary between nutrient rich Alfisol patches and highly weathered, less fertile Oxisols (Moran et al. 2000) while the other at the other two sites Oxisols and Ultisols dominate (Silver et al. 2000, Telles et al. 2003). In Santarém, most of the samples were collected streams within the Floresta Nacional Tapajós, a largely intact 560, 000 ha forest. In Manaus samples were also collected from protected forests: the Instituto Nacional de Pesquisas da Amazônia (INPA) reserves north of the city, ZF-2 and the Ducke Reserve. In contrast forest fragments in Altamira were smaller (all greater than 5 ha but less than 100 ha in size) and contained in a landscape of multiple land use. Santarém recieves 2500 mm of rainfall over the course of a year with a significant dry period lasting from July through December most years ( Parrotta et al 1995). In contrast Manaus receives 2200 mm of precipitation with a dry season between June and September (Chambers et al 2000) and in Altamira apprioximately the same amount of rainfall is more evenly distributed across the year. METHODS In each site along the transect 5- 15 streams with sources in protected, intact forest were located in October/November of 2002. All sites were re-sampled in March/April of 2003 and several additional streams were added to the sampling scheme. Samples were collected from each stream as close as possible to the source and were filtered through 0.45 micron filters (Pall Gelman PTFE filters) in the field. Samples were analyzed for anions ( Cl-, NO3-, PO43- and SO42-) and cations ( K+, NH4+, Ca2+ and Mg2+) using a portable Dionex ICS-90 ion chromatograph as soon as possible after collection. LEGEND Mean values for each site are presented in parts per million (ppm) with standard error bars. Each site mean represents the average of at least 4 streams. Data from the dry season collection (October/ November 2002) are presented in yellow and data from the wet season collection ( March/ April 2003) are presented in green. METHODS In each site along the transect 5- 15 streams with sources in protected, intact forest were located in October/November of 2002. All sites were re-sampled in March/April of 2003 and several additional streams were added to the sampling scheme. Samples were collected from each stream as close as possible to the source and were filtered through 0.45 micron filters (Pall Gelman PTFE filters) in the field. Samples were analyzed for anions ( Cl-, NO3-, PO43- and SO42-) and cations ( K+, NH4+, Ca2+ and Mg2+) using a portable Dionex ICS-90 ion chromatograph as soon as possible after collection. REFERENCES   Chambers, J.Q, N. Higuchi, J.P. Schimel, L. V. Ferreira, and J.M. Melack. 2000. Decomposition and carbon cycling of dead trees in tropical forests of the central Amazon. Oecologia 122: 380-388 Moran, E.F., E. S. Brondizio, J.M. Tucker, M. C. da Silva-Fosberg, S. McCraken, and I. Falesi. 2000. Effects of soil fertility an d land-use on forest succession in Amazônia. Forest Ecology and Management 139:93-108. Parrotta, J.A., J.K. Francis and R. Rolo de Almeida. 1995. Trees of the Tapajos: A Photographic Field Guide. GTF IITF-1 USDA/Forest Service. Silver, W. J. Neff, M.McGroddy, E. Veldkamp, M.Keller and R. Cosme. 2000. Effects of soil texture on belowground carbon and nutrient storage in a lowland Amazonian forest ecosystem. Ecosystems 3: 193-209. ACKNOWLEDGEMENTS This work could not have been done without the support and assistance of many people. In particular we would like to thank the LBA-ECO support offices in Manaus and Santarém for unfailingly providing resources and advice, Dr. Niro Higuchi, Dr. Joao Ferraz, Dr. Flavio Luizao, Dr Claudio Carvalho and Raimundo Cosme for access to their research sites and laboratories, Jo Baino in Altamira, and Chico Aves and Kadson Oliveira da Silva in Santarém for all their patience in the field.