B43A-0122 1340h
Controls on Leaf Level Isoprene Emission Rates in a Tropical Rainforest
Previous studies have found dramatic seasonal changes in both leaf level and whole system isoprene emission rates from tropical rainforests. Modeling these variations is crucial since the isoprene produced by tropical ecosystems accounts for a large fraction of the global budget. These studies found that basal isoprene emission rates increased by a factor of 2 from the wet to the dry season. Research in mid latitudes has shown that the temperature of the previous 48 hours influences isoprene emission rates. The current study investigates whether the algorithms developed for mid latitude forests can explain observed variations in leaf level isoprene emission rates during the transition from the dry to the wet season. Information on leaf level and whole system isoprene emission rates is compared to meteorological information and leaf level photosynthetic performance. Additional constraints are obtained from level water potential measurements.
B43A-0123 1340h
Soil-Atmosphere Exchange of Nitrous Oxide, Nitric Oxide, Methane, and Carbon Dioxide in Logged and Undisturbed Forest in the Tapajos National Forest, Brazil
Selective logging is an extensive land use in the Brazilian Amazon region. We studied the soil-atmosphere fluxes of nitrous oxide (N$_{2}$O), nitric oxide (NO), methane (CH$_{4}$), and carbon dioxide (CO$_{2}$) on two soil types (clay Oxisol and sandy loam Ultisol) over two years (2000-2001) in both undisturbed forest and forest recently logged using reduced impact forest management in the Tapajos National Forest, near Santarem, Para, Brazil. In undisturbed forest, annual soil-atmosphere fluxes of N$_{2}$O (mean +/- standard error) were 7.9 +/- 0.7 and 7.0 +/- 0.6 ng N cm$^{-2}$ h$^{-1}$ for the Oxisol and 1.7 +/- 0.1 and 1.6 +/- 0.3 ng N cm$^{-2}$ h$^{-1}$ for the Ultisol for 2000 and 2001 respectively. The annual fluxes of NO from undisturbed forest soil in 2001 was 9.0 +/- 2.8 ng N cm$^{-2}$ h$^{-1}$ for the Oxisol and 8.8 +/- 5.0 ng N cm$^{-2}$ h$^{-1}$ for the Ultisol. Consumption of CH$_{4}$ from the atmosphere dominated over production on undisturbed forest soils. Fluxes averaged -0.3 +/- 0.2 and -0.1 +/- 0.9 mg CH$_{4}$ m$^{-2}$ d$^{-1}$ on the Oxisol and -1.0 +/- 0.2 and -0.9 +/- 0.3 mg CH$_{4}$ m$^{-2}$ d$^{-1}$ on the Ultisol for years 2000 and 2001. For CO$_{2}$ in 2001, the annual fluxes averaged 3.6 +/- 0.4 $\mu$mol m$^{-2}$ d$^{-1}$ on the Oxisol and 4.9 +/- 1.1 $\mu$mol m$^{-2}$ d$^{-1}$ on the Ultisol. We measured fluxes over one year each from two recently logged forests on the Oxisol in 2000 and on the Ultisol in 2001. Sampling in logged areas was stratified from greatest to least ground disturbance covering log decks, skid trails, tree-fall gaps, and forest matrix. Areas of strong soil compaction, especially the skid trails and logging decks were prone to significantly greater emissions of N$_{2}$O, NO, and especially CH$_{4}$. In the case of CH$_{4}$, estimated annual emissions from decks reached extremely high rates of 531 +/- 419 and 98 +/- 41 mg CH$_{4}$ m$^{-2}$ d$^{-1}$, for Oxisol and Ultisol respectively, comparable to wetland emissions in the region. We calculated excess fluxes from logged areas by subtraction of a background forest flux and adjusted these fluxes for the proportional area of ground disturbance. Our calculations suggest that selective logging increases emissions of N$_{2}$O and NO from 30$%$ to 350$%$ depending upon conditions. While undisturbed forest was a CH$_{4}$ sink, logged forest tended to emit methane at moderate rates. Soil-atmosphere CO$_{2}$ fluxes were only slightly affected by logging. The regional effects of logging cannot be simply extrapolated based upon one site. We studied sites where reduced impact harvest management was used while in typical conventional logging ground damage is twice as great. Our results indicate that for N$_{2}$O, NO, and CH$_{4}$, logging disturbance may be as important for regional budgets of these gases as other extensive land use changes in the Amazon such as the conversion of forest to cattle pasture.
B43A-0124 1340h
Major Ions Fluxes and DOC in Rainfall and Throughfall at the Tapajos National Forest - Belterra, Para, Brazil
The Tapajos National Forest -(FLONA Tapajos), an area of 600,000 ha of protected forest, is located 50km south Santarem (Para, Brasil). The FLONA receives approximately 2000 mm.y-1 of rainfall and the forest is evergreen. The tropical forest nutrient cycle depends upon inputs from the atmosphere and from rock weathering. Internally, throughfall and stemflow transfer nutrients from the vegetation to the ground. We collected rainfall and throughfall from [starting date] through [ending date]. Concentrations of the ions Cl-, NO3-, PO4-3, SO4-2, Na+, NH4+, K+, Mg+2 and Ca+2 were analyzed using a Dionex DX-120 ion chromatograph. Total carbon and dissolved organic carbon were analyzed by a Shimadzu TOC V - CSN. Ionic fluxes were calculated from volume-weighted concentrations. The fluxes in precipitation followed the sequence: NH4+ (7.1 kg.ha-1.y-1) < Ca+2 (6.31 kg.ha-1.y-1) < Na+ (6.11 kg.ha-1.y-1) < K+ (4.41 kg.ha-1.y-1) < Cl- (3.61 kg.ha-1.y-1) < SO4-2 (3.11 kg.ha-1.y-1) < NO3- (1.31 kg.ha-1.y-1) < PO4-3 (1.11 kg.ha-1.y-1) < Mg+2 (1.01 kg.ha-1.y-1). In the throughfall, the fluxes were in the sequence: NO3- (31.8 kg.ha-1.y-1) < K+ (27.6 kg.ha-1.y-1) < NH4+ (25.5 kg.ha-1.y-1) < Na+ (17.4 kg.ha-1.y-1) < SO4-2 (15.6 kg.ha-1.y-1) < Cl- (14.5 kg.ha-1.y-1) < Ca+2 (12.7 kg.ha-1.y-1) < Mg+2 (11.1 kg.ha-1.y-1) < PO4-3 (10.8 kg.ha-1.y-1). The seasonality of cation and anion inputs suggests that intensive fertilized grain agricultural activity upwind of the site is contributing a substantial nutrient input to the forest. The fluxes of the total organic carbon for April 2003, May 2003 and February 2004 reached amounts of the 23, 18 and 34 kg.ha-1.y-1, respectively.
B43A-0125 1340h
Controls on stream DOC flux and composition in the Amazon region, Tapajos national forest
To improve predictive capabilities of water, carbon and nitrogen gas fluxes in the Amazon region, we are examining the influence of land cover, topography and soil on stream dissolved organic carbon (DOC) flux and composition. Using 90-m SRTM digtal elevation (DEM) data and land cover/land use maps derived from Landsat-TM we have selected several catchments in the Tapajos national forest drainage area with contrasting land use, topography, and soils. Field sampling of throughfall, lysimeter and stream water components will provide insight into flow path dynamics and a better understanding of the chemical nature of DOC under contrasting land use patterns. DOC samples will be characterized and compared using Nuclear Magnetic Resonance (NMR). In addition to parameterizing model simulations of carbon and nitrogen dynamics, monitoring of DOC flux across select streams will be used for model validation.
B43A-0126 1340h
Profiles of Trace Gas Concentrations in Undisturbed Forest in the Brazilian Amazon
Globally, upland tropical forests are the largest natural source of nitrous oxide (N$_{2}$O). Soils of upland tropical forests generally consume methane (CH$_{4}$) although this process has only a minor effect on the atmospheric CH$_{4}$ budget. In this study, we investigate the concentrations of N$_{2}$O, CH$_{4}$, and carbon dioxide (CO$_{2}$) measured in profiles on towers in undisturbed forest at three Amazon forest sites located in the municipalities of Manaus, Amazonas, Melga?o, Para (Caxiuana), and Sinop, Mato Grosso. We measured gas concentration profiles at six heights above the ground on during both wet and dry seasons in 2003 and 2004. Nylon tubes (0.95 cm OD) were installed on towers used for meteorological and flux measurements in LBA. Gas samples were drawn through teflon filters (1$\mu$m pore size) to a manifold and directed either to an infra-red gas analyzer (LiCor IRGA Model 6262), to sampling canisters, or to exhaust. During sampling periods, we maintained a continuous flow of at least 1 L min$^{-1}$ through all sampling tubes. CO$_{2}$ concentration data from the IRGA were recorded continuously using a Datastick analog to digital converter and a palm top computer. We removed air samples in electro-polished stainless steel canisters for off-site analysis of N$_{2}$O and CH$_{4}$ by ECD and FID gas chromatography respectively. Sampling times were selected based upon real-time measurements of CO$_{2}$ concentration. Relatively stable meteorological conditions at night led to consistent increases in CO$_{2}$ concentrations. At times we also observed increases in the concentrations of CH$_{4}$ and N$_{2}$O concentrations correlated with increasing CO$_{2}$. The source of the increasing CO$_{2}$ is most likely respiration by soil and above-ground organisms. Correlated increases in CH$_{4}$ and N$_{2}$O concentrations also likely result from biological activity in the soil and the canopy layer of the studied forests. Concentrations of these gases increase at night because the rate of gas emission in the canopy layer exceeds the rates of consumption, transport, and dilution. Fluxes of CH$_{4}$ and N$_{2}$O will be estimated as: Fx = ($\Delta$ [X] / $\Delta$ [CO$_{2}$]) * FCO$_{2}$. Where Fx is the ecosystem flux of the gas of interest, FCO$_{2}$ is the ecosystem flux of CO$_{2}$ and the ratio ($\Delta$ [X] / $\Delta$ [CO$_{2}$]) is determined from integrated profile concentrations. Micrometeorological and ecosystem studies in progress will be used to estimate ecosystem CO$_{2}$ flux. The preliminary results indicate that, as expected, the undisturbed forest ecosystem is a source of N$_{2}$O and that the ecosystem N$_{2}$O emissions are lower in the dry season than in the wet season. We found that the upland forest ecosystem appears to be producing CH$_{4}$ independently of season. The source of the CH$_{4}$ is unknown. Upland forest soils generally consume CH$_{4}$ throughout the year.
B43A-0127 1340h
Spatial and temporal variation on isotopic composition of CH4 in Eastern Amazon streams
The isotopic composition of methane varied seasonally and spatially among wetland environments as a result of changes in microbial production and oxidation mechanisms. We measured the variation in isotopic composition of CH4 (delta13C-CH4) trapped in bubbles formed in the streams sediment during the period of August 2000 and August 2003. The samples were analyzed in a Finnigan Delta Plus mass spectrometer. The study sites were the Maica, A?u, and Jamaraqua Stream; three different streams in the Eastern Amazonia. The mean isotopic values found during this period were in a range of -78% to -46%. At the Acu Stream, the delta13C-CH4 varied from -66.0 to -47% and at Maica Stream varied from -69 to -40%. The Jamaraqua Stream showed the larger variation with values in a range of -89 to -54%. For helping us to explain the differences between the sites we analyzed the isotopic composition of the sediment at most different sites (Maica and Jamaraqua). Cores sediments (~30cm) and samples of leaves were taken at each site and analyzed by mass spectrometry for delta13C, C/N ratio, and %C. There was a strong evidence of difference between the streams on all of these parameters. The sediment of Maica stream showed heavier values of delta13C (p<0,05), which resulted from the decomposition of grass enriched in 13C. As for the amount of carbon stored in sediment, the Jamaraqua Stream had much more carbon than Maica Stream (p<0,05), and its C/N ratio is two folds bigger than in Maica.
B43A-0128 1340h
The impact of the selective logging in the energy-water and carbon exchange processes using optimization algorithms on the SiB2 model over a tropical forest.
Several studies have demonstrated that the deforestation in the Amazonian rainforest could lead to a significant impact in the regional and even global climate. For instance, it could change the energy, water, and CO2 cycles. In this study, we evaluate the impacts of the selective logging over an undisturbed forest using the second generation Simple Biosphere Model (SiB2). Parameter estimation and calibration plays an important role in model performance and recent studies have shown that even manually calibration can result in a better performance of the model. Therefore, automatic procedures have been applied widely within the scientific community to calibrate land surface models (LSS) such as SiB2, BATS2, etc. The MultiObjective Generalized Sensitivity Analysis (MOGSA - University of Arizona) and the MultiObjective Shuffled Complex Evolution Metropolis (MOSCEM - University of Amsterdam and University of Arizona) have been used to evaluate the differences in the sensitive parameters before and after the selective logging. Understanding this difference can provide background information on changes in some of the (physiological, soil physical, morphological) properties of the ecosystem. We have used observations from meteorological towers in the Brazilian Amazonia to constrain the model and establish preferred parameter sets that improve the model ability to simulate the water, energy, and carbon fluxes. We perform an extensive sensitivity analysis (MOGSA) and optimization (MOSCEM) of the model using multi-criteria techniques to evaluate and improve the model performance and test the transferability of the preferred parameters to different hydrological conditions (such as logging). The data used was from the site named km 83, located in Santarem (Para), one of the sites where data where collected during to the Large-scale Biosphere Atmosphere (LBA) Experiment in the Amazonia, lead by Brazil.
B43A-0129 1340h
Development and application of large-scale hydrologic and aquatic carbon models to understand riverine CO$_{2}$ evasion in Amazonia
Many researchers are investigating the topic of CO$_{2}$ efflux to the atmosphere from waters of the Amazon basin at several scales. We are developing a physically based modeling system to simulate this flux throughout the whole basin as a function of time-transient climate, vegetation, and hydrology. This modeling system includes an ecosystem land surface model (IBIS; Foley et al. 1996, Kucharik et al. 2000), a hydrological routing model (HYDRA; Coe 2000, Coe et al. 2002), and a new aquatic carbon processing module that we are incorporating into HYDRA (Howard et al. in prep). HYDRA has been recently modified to better represent river discharge and flood extent and height throughout the Amazon Basin. These modifications include: 1) using empirically derived equations representing stream width and height at flood initiation (Costa et al. 2002) to provide more accurate estimates of the initiation and cessation of flood conditions; and 2) using spatially explicit river sinuosity data (Costa et al. 2002) and a stream velocity function based on the Manning equation to provide more realistic representation of stream flow timing and magnitude. HYDRA has been calibrated and validated with observations of river discharge, water height, and flooded area at numerous locations in the mainstem and headwaters of the basin. Results of this validation show better agreement with observations than the previous version of HYDRA but also indicate the need for improved land surface topography and precipitation datasets. The aquatic carbon processing module prototype is currently implemented as an aspatial STELLA/textregistered model, decoupled from HYDRA, that simulates individual grid cells (at $\sim$ 9 km resolution). We drive the model with IBIS-derived hydrological inputs from the land, and with empirically derived estimates of C inputs (from CAMREX and LBA sources). To allow for seasonal fluctuations in the aquatic-terrestrial transition zone, for each timestep we simulate the volume of water contained in each of four chemically-distinct zones in the grid cell: pelagic (open water), littoral (near-shore), floodable lowland, and terra firme (upland). With this information the model simulates the dynamics among six different pools of aquatic C: autotrophs; coarse (CPOC) and fine (FPOC) particulate organic carbon; dissolved organic carbon (DOC); dissolved inorganic carbon (DIC); and sediment. The amount of CO$_{2}$ efflux from the water surface is calculated for the grid cell in each timestep. We identify 9 environments that are hydrochemically distinct at this coarse scale: the Amazonas mainstem downstream of the Rio Negro; small, medium, and large whitewater rivers; small, medium, and large blackwater rivers; whitewater floodplain/lake environments; and blackwater floodplain/lake environments. We use the aspatial prototype of our aquatic carbon model to determine the CO$_{2}$ efflux from each of these different environments. We use imagery classified by Hess et al. (2003) to determine the area of lowland Amazonia falling into each of these categories. Finally, we use these model results and data to extrapolate the aquatic CO$_{2}$ efflux across the Amazon basin, and then put our exploratory results in the context of previous and on-going studies in this area.
B43A-0130 1340h
Parameterization of Leaf-Level Gas Exchange for Plant Functional Groups From Amazonian Seasonal Tropical Rain Forest
Plant communities exert strong influence over the magnitude of carbon and water cycling through ecosystems by controlling photosynthetic gas exchange and respiratory processes. Leaf-level gas exchange fluxes result from a combination of physiological properties, such as carboxylation capacity, respiration rates and hydraulic conductivity, interacting with environmental drivers such as water and light availability, leaf-to-air vapor pressure deficit, and temperature. Carbon balance models concerned with ecosystem-scale responses have as a common feature the description of eco-physiological properties of vegetation. Here we focus on the parameterization of ecophysiological gas-exchange properties of plant functional groups from a pristine Amazonian seasonally dry tropical rain forest ecosystem (FLONA-Tapaj\'{o}s, Santar\'{e}m, PA, Brazil). The parameters were specific leaf weight, leaf nitrogen content, leaf carbon isotope ratio, maximum photosynthetic assimilation rate, photosynthetic carboxylation capacity, dark respiration rates, and stomatal conductance to water vapor. Our plant functional groupings were lianas at the top of the canopy, trees at the top of the canopy, mid-canopy trees and undestory trees. Within the functional groups, we found no evidence that leaves acclimated to seasonal changes in precipitation. However, there were life-form dependent distinctions when a combination of parameters was included. Top-canopy lianas were statistically different from top-canopy trees for leaf carbon isotope ratio, maximum photosynthetic assimilation rate, and stomatal conductance to water vapor, suggesting that lianas are more conservative in the use of water, causing a stomatal limitation on photosynthetic assimilation. Top-canopy, mid canopy and understory groupings were distinct for specific leaf weight, leaf nitrogen content, leaf carbon isotope ratio, maximum photosynthetic assimilation rate, and photosynthetic carboxylation capacity. The recognition that plant functional groups have distinct impacts on ecosystem-scale gas exchange can increase the accuracy of process-based carbon balance models where structure is known and when logging activities are incorporated into production models.
B43A-0131 1340h
Remotely Sensed Carbon and Water Variations at LBA Site to Amazon Regional Scales With Hyperion and MODIS Data
We investigated the spatial and temporal variations in vegetation biologic activity at various LBA core and field sites with carbon and water indices derived from fine resolution Hyperion data and moderate resolution MODIS observations. Leaf level and canopy level surface moisture indices were computed over a range of climate conditions and land cover conversions with hyperspectral Hyperion data. The moisture indices were combined with carbon measures, such as vegetation indices, to map spatial and temporal patterns of above-ground net productivity and analyze ecosystem sensitivity to water availability. The coupled water and carbon indices were scaled up to MODIS data for spatial and seasonal extension. MODIS water indices, land surface temperature, vegetation indices, and LAI and FPAR products were extracted over both natural and converted areas and over a climatic gradient of Amazon sites. Land surface moisture and carbon patterns behaved in an opposite manner between natural and converted areas and exhibited significant seasonal variations. Our results show that these satellite datasets can track vegetation activity in the Amazon region, including biologic responses to shifts in vegetation type and disturbance. Remotely-sensed land surface water indices combined with the carbon products yield important information useful in the prediction of vegetation health response to climate change and human land cover modifications.
B43A-0132 1340h
Micrometeorology, CO2 and H2O Exchange of a Tropical Rainforest Before and After Selective Logging
We are using long-term eddy covariance to study the effects of selective logging on the energy and trace gas exchange at km 83 in the Tapajos National Forest, Para, as a component of LBA. In addition to the core flux measurements of carbon dioxide, water vapor, momentum and heat, sensors were installed to measure vertical profiles of CO2, H2O, wind velocity, and temperature within and above the forest. Continuous tower and biometric measurements began a year before logging (June 2000) when the forest was still considered primary. A similar tower in an unlogged area of the same forest (km 67) provides a control for the logged site measurements. Selective logging in fall 2001 was conducted by a local firm using reduced impact procedures, and included ~400-ha of forest that extended ~2-km upwind of the tower. The loggers removed ~6 T C/ha in large tree stem wood, left another ~15 T C/ha of the biomass as slash, and eliminated ~13 percent of the canopy on an area basis. Tower and biometric measurements at both sites continued throughout the 3 month logging period and up to the present. After the logging, a second 65 m tall tower was installed in a large gap created by the logging, and similarly instrumented, in order to address the role of gaps in affecting forest atmosphere exchange. Preliminary analysis of the tower observations indicate that canopy photosynthesis declined following logging, and that ecosystem respiration increased in the subsequent wet season.
B43A-0133 1340h
Drop-size Characteristics and Evolution of Widespread Nocturnal Light Rainfall in Forested Western Amazonia
The Tropical Rainfall Measuring Mission / Large Scale Biosphere - Atmosphere (TRMM-LBA) and the coincident Wet-season Atmospheric Mesoscale Campaign (WETAMC) examined wet-season precipitation in southwestern Amazonia, focusing in part on the relationship between precipitating systems and land-use patterns. One interesting result from the campaign was the observation of nocturnal weak, widespread rainfall often covering much of the forested western portion of Amazonia. Satellite, radar, and sounding observations suggested that the origin of this rainfall was stratiform cloud in the mid-troposphere (6 km - 9km AGL), not associated with deep convection in any part of its lifecycle. The origin of this widespread, mid-level nocturnal cloudiness is an intriguing mystery. The present study places observations of surface raindrop size and number concentration via disdrometer measurements in the context of radar, satellite, and sounding observations of this phenomenon in order to shed light on its origin. A working hypothesis centers on precipitation formation above the freezing level by destabilization of pre-existing cloud by nocturnal cooling. This phenomenon, though likely a small contributor in the water cycle in Amazonia, may have implications for the total radiation budget in western Amazonia.
B43A-0134 1340h
Uncertainties in Satellite Based Fire Emission Inventories in the Amazon
The uncertainties of developing satellite geolocation based fire emissions inventories for air quality models are discussed in this work. Various satellite hot spot detection and burn scar area products are routinely combined with emission factors to develop monthly and daily gridded fire emission inventories for both air quality modeling applications and global models Here, we compare the spatial autocorrelations between fire hot spots detected in the infrared by the Geostationary Operational Environmental Satellites (GOES) Wildfire Automated Biomass Burning Algorithm (WF ABBA), the Moderate Resolution Imaging Spectroradiometer (MODIS) 5 minute L2 thermal anomaly, and the NOAA-14 Advanced Very High Resolution Radiometer (AVHRR), and the Defense Meteorological Satellite Program (DMSP) visible channel for one month from 20 September 2002 to 20 October 2002 for an approximately 1000 km x 1000 km domain in Amazonia. Because of the differing overpass times of the polar orbiting satellites and the differing temporal and spatial resolutions of the sun-synchronous satellites and geosynchronous satellites, there is no discernable spatial autocorrelation between the detected hot spots on a 1 to 2.5 kilometer scale. Once these hot spots are counted and allocated to either 10 km2 or 20 km2 grid cells typically used for regional air quality modeling applications, spatial autocorrelation increases from 0.55 to 0.69, indicating that all the satellites examined here detect fires in the same general geographic locations. Further inventories of hot spots detected as a function of ecosystem type (GLCC version 2.0) in the GOES WF ABBA data are consistent with recent fire spots as a function of ecosystem type in the Global Wildland Fire Emission Model as reported by Hoelzemann et al in 2004. Comparison of the number of hotspots in South America month period, respectively 227,159 for GOES WF ABBA, 28,359 for MODIS L2 and 13,334 for AVHRR indicate that although these satellites observe similar spatial patterns, the number of hot spot detections observed by the different satellites differs substantially and therefore emissions modelers must take this into consideration. Examination of the fire area, maximum fire duration, and the diurnal pattern in the GOES WF ABBA dataset further indicates that no one satellite product, is appropriate for detecting small short duration fires. The uncertainties in emissions inventories can be reduced by using a combination of satellite products.
B43A-0135 1340h
Detection of Interannual Climate Variability in Secondary Forests and Crops Under Traditional and Alternative Shifting Cultivation Using Ikonos Data
Regenerating forests play an important role in long-term carbon sequestration and sustainable landuse as they act as potentially important carbon and nutrient sinks during the shifting agriculture fallow period. The long-term functioning of secondary forests (capoeira) is increasingly threatened by a shortening fallow period during shifting cultivation due to demographic pressures and associated increased vulnerability to severe climatic events. Declining productivity and functioning of fallow forests of shifting cultivation combined with progressive loss of nutrients by successive burning and cropping activities has resulted in declining agricultural productivity. In addition to the effects of intense land use practices, droughts associated with El Nino events are becoming more frequent and severe in moist tropical forests and negative effects on capoeira productivity could be considerable. The principal goal of the research is to determine the extent to which capoeira and agricultural fields are susceptible to extreme climate events (drought) under contrasting landuse/clearing practices. In Igarape-A?u (near Belem, Para), we hypothesize that experimental alternative landuse/clearing practices (mulching) may make capoeira and crops more resilient to the effects of agricultural pressures and drought through increased biomass, soil organic matter and associated increase in soil water storage, and nutrient retention. This experimental practice (mechanized chop-and-mulch) has resulted in increased soil moisture during the cropping phase, reduced loss of nutrients and organic matter, and higher rates of secondary-forest biomass accumulation. This project aims to measure water availability and it's relation to secondary forest and crop productivity in the Brazilian Amazon. We have conducted field efforts during two dry seasons (August-December). Field data on water relations were collected during the dry season of 2001 and 2002 in capoeira and crops for both traditional slash-and-burn and alternative chop-and-mulch practices. These data will be used to compare with IKONOS data (2001 and 2002) products for the detection of moisture status differences. Current research includes comparison of IKONOS vegetation indices (NDVI and EVI) and the Tasseled Cap transformation for detection of water stress in capoeira and crops that were measured in the field.
B43A-0136 1340h
Stable isotope analyses provide evidence of drought stress impacting plant function at the Seca Floresta
Carbon and oxygen isotope ratios have been measured to examine the impacts of a long-term drought treatment at the Seca Floresta in Santarem, Para, Brazil. We measured the carbon isotope ratio values of leaf organic matter and on the carbon dioxide effluxing from soil and litter components in droughted and non-droughted plots. We measured the oxygen isotope ratios of leaf water throughout the day. In addition, we quantified soil carbon dioxide efflux rates in order to partition this flux into its soil and litter components. The observations suggest that a reduction in soil moisture availability resulted in increased carbon isotope ratio values of the leaf organic matter, increased carbon isotope ratio values of the soil carbon dioxide efflux, and increased oxygen isotope ratios of leaf water. Further examination of the data suggest that the carbon isotope ratio values of the soil carbon dioxide efflux can be partitioned into two components: a litter component that changed modestly its carbon isotope ratio value seasonally and a soil component that showed larger interseasonal fluctuations in carbon isotope ratio values. The seasonal fluctuations in both the leaf organic matter and the carbon dioxide efflux of the soil component were consistent with a photosynthetic activity reflecting significant reductions in stomatal conductance.
B43A-0137 1340h
Soil-Atmosphere Carbon Dioxide and Methane Fluxes in Undisturbed Tropical Forest
Measured carbon dioxide (CO$_{2}$) fluxes at soil surfaces are are the result of many biological below ground and surface processes that remineralize organic matter. Methane fluxes are the result of the balance between production and oxidation and transport. Soil temperature and moisture exert strong controls on the soil-atmosphere trace gas fluxes. We measured the soil-atmosphere flux of CO$_{2}$ and CH$_{4}$ with an automated chamber system that was installed in April 2001 in the Tapajos National Forest, Para, Brazil. This is a mature forest on a clay Oxisol. The mean annual temperature is 25$\deg$C with diurnal range often exceeding the variability in the annual daily means. The mean annual precipitation is ca. 2000 mm per year with a distinct dry season from July to December. Eighteen aluminum chambers were installed in a 0.5 ha area close to the flux tower at the km 67 LBA site. Eight of these chambers are sampled about 5 times per day (closed 7$%$ daily) and the other 10 chambers are sampled individually approximately once per day (closed 1.5$%$ daily). For the 8 frequently sampled chambers, dry season fluxes over the 3 year period averaged 2.4 $\mu$mol CO$_{2}$ m$^{-2}$ s$^{-1}$ and the wet season averages were 3.0 $\mu$mol CO$_{2}$ m$^{-2}$ s$^{-1}$ . As expected, the drained upland soils were most often a weak CH4 sink but during wet periods erratic positive fluxes of greater than 20 mg CH$_{4}$ m$^{-2}$ d$^{-1}$ were measured. The soil effluxes do not appear to be consistent with nocturnal accumulations of CH4. Soil CO$_{2}$ flux is positively correlated with both soil temperature and soil moisture content. In tropical forests, soil temperature and soil moisture are often negatively correlated with one another, thereby complicating their combined effect on soil efflux.
B43A-0138 1340h
CO$_{2}$ Flux from Coarse Woody Debris from a Tropical Forest at the FLONA Tapajos, Brazil
The release of carbon dioxide (CO$_{2}$) from tropical forests has a strong effect on the global carbon cycle due to fast turnover rates of organic matter than for other biomes. Despite its importance coarse woody debris (CWD) pools have been overlooked for estimates of carbon balance and especially in tropical forests where few studies have been conducted. Measurements were made on CWD in areas of undisturbed tropical forests and areas under selective logging. CO$_{2}$ emissions from CWD averaged 1.95 \pm 1.95 \mu mol CO$_{2}$ m$^{2}$ Wood $_{surf}$^{-1}$$ s$^{-1}$ for undisturbed forests and 2.61 \pm 1.44 \mu mol CO$_{2}$ m$^{2}$ Wood $_{surf}$^{-1}$$ s$^{-1}$ for selective logging areas. For selective logging areas, a chronosequence study was established to follow up the five years of logging. Three wood species were sorted due differences in density to be studied and observe differences in CO$_{2}$ efflux. Andiroba (Carapa guianensis) showed a average flux of 3.15 \pm 3.2 \mu mol CO$_{2}$ m$^{2}$ Wood $_{surf}$^{-1}$$ s$^{-1}$, tauari (Couratari stellata) with 2.88 \pm 2.03 \mu mol CO$_{2}$ m$^{2}$ Wood $_{surf}$^{-1}$$ s$^{-1}$ and macaranduba (Manilkara huberi) with an average flux of 1.69 \pm 1.6 \mu mol CO$_{2}$ m$^{2}$ Wood $_{surf}$^{-1}$$ s$^{-1}$. An area of undisturbed forest was studied to quantify the efflux of CO$_{2}$ in natural conditions. CO$_{2}$ emissions from CWD were of 3.76 Mg C ha$^{-1}$ y${-1}$ in logged areas and 1.43 Mg C ha$^{-1}$ y${-1}$ for undisturbed forests. Wood water content and wood decay classes (year of logging) were some of the factors studied on controlling of CO$_{2}$ efflux from CWD.
B43A-0139 1340h
Estimating Scalar Fluxes in Tropical Forests from Concentration/Temperature Profile Measurements
Eddy Covariance (EC) flux measurements are now widely used for estimating long-term biosphere-atmosphere gas exchange. However, gap-filling and constraining these EC estimates using other techniques that are sensitive to different assumptions remains a high priority. Improved ability to recover fluxes from concentration and temperature profile data could serve as one such constraining and gap-filling method. Furthermore, if successful, concentration profiles permit estimating fluxes of chemical fluxes for which high frequency gas analyzers are not currently available. We investigate the ability of higher order closure models to estimate CO2 fluxes from a 40 m tall tropical forest on the Floresta Nacional do Tapajos, Para, Brazil. Eddy covariance measurements of sensible and latent heat, CO2 and momentum fluxes were collected along with profile measurements of CO2 and water vapor concentrations and temperature as part of the LBA program. To this end, we extended a 2nd order Eulerian approach for CO2 along with the appropriate stability correction regimes. Also, we included in the model transient term in an attempt to improve estimates over periods in which storage and turbulent fluxes may be of comparable magnitude. For comparison, we performed calculations using a 1st order closure model and a "dummy" model where perfect similarity between heat and CO2 transfer is assumed.
B43A-0140 1340h
Estimating Evapotranspiration Over the Amazon Basin Using Multiple Data Sources
Estimates of regional evapotranspiration (ET) over the Amazon basin have been found to be highly dependent on the parameterization of transpiration. The inadequately understood and difficult to model vegetation control over ET under different conditions of energy and water availability leaves us with divergent estimates of the annual ET cycle in the basin. We estimate regional ET over the Amazon basin on a monthly timescale, independently of land surface models, as the residual of the atmospheric water balance. The control volume is defined to be the atmosphere overlying the basin and the variables involved are area-averaged ET, precipitation, vertically integrated moisture convergence, and change in total moisture storage. Other workers have shown that significant differences exist between measures of these water balance components obtained from different data sources, and thus the uncertainties associated with these available measures cannot be neglected. We apply a framework that utilizes multiple datasets to derive a `best' estimate of ET, minimizing its uncertainty. Multiple measures of each water balance component are used in a least squares estimator, where each input value is weighted by its variance. To further reduce the uncertainty in the derived ET estimate, we include a measure of ET and its variance and constrain the optimization with the water balance equation to ensure conservation of mass. This approach is tested over the 5-year period 1997-2001. We evaluate our ability to resolve the seasonal ET cycle with the available data, during regular years and during the 1998 ENSO-related drought that affected the region. The NCEP-NCAR Reanalysis-1, NCEP-DOE Reanalysis-2 and the ECMWF ERA-40 Reanalysis data products are used to derive alternative input estimates of moisture convergence and change in precipitable water. We use the TRMM 3B43 monthly precipitation rate along with its random error estimate, and the GPCP One-Degree Daily Precipitation Data Set that also includes a random error estimate, to obtain alternative estimates of monthly precipitation. Information on the uncertainty associated with each data product is extrapolated from the individual gridpoints to the area-averaged basin scale. An ET estimate computed as the mean over different model results and its corresponding variance are used in the constrained least square optimization.
B43A-0141 1340h
The Spatial Pattern of Soil Nutrients in a dry Tropical Forest Following Shifting Culitvation
The role that fallow vegetation plays in the recovery of soil nutrient concentrations is the basis of shifting cultivation, yet its role in structuring spatial patterns in the soil is not well understood. To determine the effect of shifting cultivation on the distribution of soil properties in a dry tropical forest, we intensively sampled three forest stands in El Refugio, an agricultural community in the Southern Yucatan Peninsula Region (SYRP). These sampling sites, which included a mature forest and two 8-year old secondary forests, represented a gradient of cultivation history (0-2 cycles). Using geostatistics, we characterized the degree and extent of spatial variability in P, K, Al, and organic matter content. In the mature forest, P and K were autocorrelated over a distance $<$ 6 m. In the forest fallows, where the density of small stems was greatest, P and K were autocorrelated over 1.3 to 4.8 m. Conversely, Al, which is not required by plants and is potentially toxic, was autocorrelated over similar distances (1.8 to 2.5 m) at all 3 sites. These results suggest that the spatial pattern of biologically important soil properties changes following shifting cultivation, most likely reflecting differences in the size of individual trees in stands with different cultivation histories.
B43A-0142 1340h
Role of "electron shuttles" in the bioreduction of Fe(III) oxides in humid forest tropical soils.
Dissimilatory iron-reducing bacteria (DIRB) can reduce Fe(III) oxides either by direct contact between the organisms and the oxide surface or by indirect mechanisms not involving contact. These latter mechanisms can include (i) "electron shuttling" or (ii) soluble Fe(III) complexation with subsequent reduction. In the presence of humic substances, indirect Fe(III) reduction occurs, particularly by mechanism (i). Important electron-accepting groups in humic substances include quinone moieties, complexed Fe(III) and conjugated aromatic moieties. A model compound frequently used to study mechanism (i) is anthraquinone-2,6-disulfonate (AQDS), which is believed to function as an "electron shuttle" in a manner similar to humic substances. We are currently investigating Fe(III) reduction in humid tropical forest soils as affected by "electron shuttles," using AQDS and humic substances in our experiments. The soil samples were collected at the bottom of a toposequence in the Luquillo Experimental Forest, Puerto Rico. Development of anaerobic conditions in these soils occurs due to high precipitation and runoff water inputs. Fourteen-day anoxic incubations of soil suspensions amended with AQDS showed enhanced production of both soluble and particulate forms of Fe(II) as compared to non-amended soil suspensions. Our data indicated clearly that DIRB in the soil could utilize added "electron shuttles" effectively to reduce Fe(III). To examine factors controlling Fe(III) reduction by humic acid (HA), three IHSS HA samples (soil, peat and Leonardite) were both abiotically reduced by H2 treatment and microbially reduced by incubation with a filtrate from a soil suspension, then titrated with three different oxidants (iodine, cyanoferrate, and ferric citrate) to provide chemical and biological estimates of electron-accepting capacity at pH 5 and 7. The results will be discussed in terms of the three oxidants used, the properties of the HA samples, pH, and the effects of chemical vs. biological reduction.
B43A-0143 1340h
Distribution of Carbon Uptake Capacity of Plant Functional Groups Across the Canopy Gradient in Old-Growth Tropical Wet Forest in Costa Rica
Because of the difficulties of accessing leaves within tree crowns, little is known about the photosynthetic capacity of different functional groups within tropical rain forest canopies. To address this deficiency, we measured photosynthetic capacity (A$_{max}$) {\it in situ} along vertical transects through old-growth forest canopy using a mobile walkup tower at the La Selva Biological Station in Costa Rica. We asked: What groups are responsible for most C-fixation and at what height in the canopy does most C-fixation occur? Photosynthesis (using a LI-COR Li-6400) and total leaf area were measured for all vascular plant species encountered within the tower footprint (4.6 m$^{2}$). Plants were grouped into trees, palms, ferns, lianas, epiphytes, herbs, {\it Pentaclethra macroloba} (the dominant canopy tree), and vines. A$_{max}$ values differed among functional groups. The ranking of A$_{max}$ among the groups was trees $<$ {\it P. macroloba} $<$ palms $<$ lianas $<$ vines $<$ epiphytes $<$ herbs $<$ ferns. Trees and {\it P. macroloba} had the highest photosynthetic rates, but the maximum rates occur at different heights. A$_{max}$ of {\it P. macroloba} increases with canopy height to a maximum 10.3 \mumol m$^{-2}$ s$^{-1}$ at 17.5 m. A$_{max}$ of trees increases with canopy height (r$^{2}$ = 0.77) and attains the highest A$_{max}$ at 32.5 m (10.6 \mumol m$^{-2}$ s$^{-1}$). Palms and lianas presented similar patterns of A$_{max}$. However, lianas reach the canopy top whereas palms are shorter and were not observed above 27.5 m. The maximum photosynthetic rates for both groups were: lianas 9.2 \mumol m$^{-2}$ s$^{-1}$ at 27.5 m and palms 9.6 \mumol m$^{-2}$ s$^{-1}$ at 17.5 m. By scaling the functional group A$_{max}$ values with their leaf area, we estimated that most of the photosynthetic capacity occurs between 17.5 m and 37.5 m and is attributed mainly to trees, followed by {\it P. macroloba} and then lianas.