Biogeosciences General Contributions Posters
Presiding: T Bullen, U.S. Geological Survey; A Packman, Northwestern University
B33D-01 1330h
Regional Scaling of Cropland Net Primary Production for Nebraska using Satellite Remote Sensing from MODIS and the Ecosystem Process Model BIOME-BGC
Crops dominate the Midwestern U.S., and this has major implications for the domestic carbon balance. This research is designed to test and improve the ability of satellite remote sensing (MODIS) to estimate cropland productivity through the use of field measurements and ecosystem modeling. The Biome-BGC ecosystem process model (V4.1.2) has been modified for use in agricultural systems, and tested at the field level for both C3 (soybean) and C4 (maize) crops under different irrigation regimes. Biome-BGC results are verified using local AmeriFlux network site measurements of the net CO2 flux and cropland biomass. These results are spatially aggregated within a 7x7km window centered over an intensive study area and compared with satellite-derived GPP and NPP estimates from MODIS. Model results are further extrapolated statewide using available estimates of crop coverage and irrigation to assess regional patterns and seasonal variability in productivity captured from both `bottom-up' ecosystem model simulations and `top-down' satellite remote sensing approaches. Finally, we evaluate regional productivity differences based on model assumptions of both natural (grasslands) and agricultural land cover types, and assess the potential for improving MODIS GPP and NPP algorithms for agricultural regions. Initial results indicate that the model works well in estimating productivity of both maize and soybean using different management techniques. The MODIS algorithm does well when site-specific data are used, but the standard outputs from the MODIS sensor differ from tower estimates of productivity, most likely a result of the scale mismatch between the two methods. We verify spatial MODIS products over a heterogeneous landscape by using Biome-BGC to scale tower-specific measurements to MODIS cutout sizes. These results will be used to provide estimates of the regional carbon balance for the larger 20,000 km2 area within the National Institute for Global Environmental Change (NIGEC) Great Plains and Midwestern study regions.
B33D-02 1330h
Determinants of distribution and abundance of two shrub species, Guiera senegalensis and Piliostigma reticulatum, in Peanut Basin, Senegal
The ability to predict and manage the course of landscape-level ecological change and its longer-term consequences on ecosystem functions (e.g. carbon stabilization and soil degradation mitigation) depends on the ability to understand how a particular ecosystem functions and the mechanisms that control the distribution, configuration and abundance of key species. Guiera senegalensis and Piliostigma reticulatum are two native shrub species that are widely found in Sub-Saharan Africa but unrecognized in their potential role in regulating hydrological and carbon cycles in both natural and agro-ecosystems. Our objective was to conduct a study on the determinants of landscape-level distribution and abundance of these shrub species as a basis for ecological modeling and management of this fragile semiarid environment. Formal Recursive Inference Modeling was used to adduce determinants of species presence while logistic regression and geostatistical approaches were used to estimate shrub abundance within their communities. The results showed that distribution of the shrubs is controlled by four factors: geological substrate, mean annual temperature, mean annual rainfall and landform (profile convexity). Relative abundance within the shrub communities is under the influence of mean annual rainfall, maximum annual temperature and elevation (for G. senegalensis) and mean annual rainfall, mean annual temperature, elevation and landform (profile convexity) (for P. reticulatum). Predictive models for shrub distribution and abundance were generally poor, probably highlighting the weakness of statistical models in analysis and quantification of the spatial structure of ecosystems.
B33D-03 1330h
An Investigation Of The Use Of Song And Territory Defense In Paternity Guarding Behavior Of The Carolina Wren
A banded population of Carolina Wrens (Thryothorus ludovicianus) was observed at Sam Houston State University's Center for Biological Field Studies in Walker Co., Texas to determine if males use paternity guarding behavior. Paternity guards are used by males to prevent the loss of paternity due to copulations that occur outside of the pair bond i.e. extra-pair copulations (EPC's). Song behavior and territory size were quantified over the breeding cycle for 5 males. Males sang at higher rates when their mates were fertile (nest building and egg laying stages) than when their mates were nonfertile (incubation and nestling stages). Males also defended larger territories during their mates' fertile stages. The results are suggestive of a paternity guard function for song and territory defense in the Carolina Wren.
B33D-04 1330h
Estimating Shrub Abundance in Desert Grasslands Using Geometric-Optical Models
This work examines the application of a geometric-optical model of canopy reflectance to provide measures of the physical structure of desert grasslands and shrublands which can provide the metrics required to expand the geographic extent over which ecological process models are able to operate. The work is aimed at estimating the structural attributes of desert grasslands and shrublands by providing a means of explaining the moderate resolution remotely-sensed signal in terms of empirically-derived background spectral directional reflectance and shrub number density. These structural attributes are important in surface hydrology and meteorology as well as for differentiating plant communities. The approach is through inversion of the non-linear simple geometric model (SGM) against red wavelength multiangle reflectance data from the Multiangle Imaging SpectroRadiometer (MISR) flown on the NASA Earth Observing System Terra satellite. These MISR data were corrected for atmospheric scattering and absorption, including estimates of aerosol optical depth and ozone. Observations from all nine cameras were used. The SGM has previously been tested against ground-based canopy maps and measurements but at the landscape scale it is necessary to account for the varying anisotropy of the soil-understory complex. While geometric-optical models often assume a Lambertian background for forest applications, the large fractional cover of exposed soil in arid regions means that this assumption cannot be made. In this study separation of background and upper canopy contributions was effected using a linear scaling of the parameters of the Walthall BRDF model with near-nadir brightness, using an optimization algorithm to adjust its parameters against MISR data for relatively dark and bright locations for which the number density and radius of the shrubs is known from high-resolution imagery. This approach makes the assumption that the understory contributes diproportionately to surface albedo than large shrubs in this environment. Shrub canopy statistics were compiled for each mapped 250 x 250 m observation using high resolution IKONOS panchromatic imagery using background subtraction and thresholding techniques. Shrubs were considered to have a minimum radius of 1 m. Inversion experiments were carried out for an area of 21 x 21 MISR multiangle observations mapped onto a 250 m grid using a direct search optimization algorithm to minimize the absolute root mean square error (RMSE) between observed and modeled bidirectional reflectance values. Constraints were imposed on the parameter space such that the retrieved canopy height is > zero and < 4 m and shrub number density is > zero. Model fits to observations generally provided a low RMSE with a mean of 0.005 (n=441). The results show that with some assumptions and constraints a reasonable relationship between retrieved and measured shrub density and fractional cover can be achieved. However the strongest relationship between modeled and observed density provided a coefficient of determination of only 0.2; more work is needed to determine whether the assumptions and approximations made are valid or too severe.
B33D-05 1330h
Assessment of Ecosystem Change Using Benthic Foraminiferal Data From Three Nearshore Cores, Biscayne Bay, Florida
The benthic foraminifer record from mid-bay cores indicates a relative increase in salinity over the past 150 years has impacted the marine ecosystems of Biscayne Bay. However, the magnitude and rates at which this has occurred remains unresolved. Benthic foraminifer data from three nearshore cores in Biscayne Bay document the transition from terrestrial to marine environments. The variability and magnitude of changes between brackish and marine conditions determined from these data are important for differentiating natural (sea-level) from anthropogenic (water management) influences on the nearshore ecosystem. Three cores were collected from nearshore localities in Biscayne Bay: Chicken Key, Black Point North and Middle Key. The cores were sampled continuously every 2cm. Each sample was processed and a database compiled of foraminiferal assemblage data. Non-metric multidimensional scaling (MDS) based upon these data is used to describe changes to the coastal ecosystems. The MDS plots represent the relative differences between foraminiferal assemblages at each depth in the core and may indicate long-term ecosystem change. Middle Key and Chicken Key are essentially barren of foraminifera below 30cm, which suggests that the sediments in the lower section of each core were not deposited in a marine environment. The transition at each location begins with a brackish assemblage dominated by Ammonia and Elphidium. Each site becomes increasingly marine up to the modern samples at the top of the cores. Black Point North includes foraminifera throughout its 86.5cm depth. The site has been dominantly brackish with increases in Miliolinella, Quinqueloculina and Triloculina indicative of strong shifts toward marine conditions near the base and at the top of the core.
B33D-06 1330h
Tracer Dynamics in a Lattice-Automaton Model of Bioturbation
Biogenic sediment mixing is commonly described as a diffusive process, quantified by modelling the vertical distribution of particle-bound radioisotopes. The resulting diffusion coefficient (Db) that characterises the intensity of the mixing regime often exhibits a dependence on tracer half-life; short-lived radioisotopes (e.g.234Th) tend to yield notably larger Db values than longer-lived radioisotopes (e.g.210Pb). While it has previously been hypothesized that this dependence is due to differential mixing of tracers by particle selective benthos, modelling work presented here demonstrates that this trend can result from a more fundamental mechanism: violation of the assumptions required for bioturbation to be considered diffusive. The model employed in this study, the Lattice-Automaton Bioturbation Simulator (LABS), is a computational model comprising a two-dimensional sediment-water lattice inhabited by automatous entities. Stochastic and deterministic rules define the behaviour of these "automatons" to mimic real fauna, passing through the sediment-water matrix displacing particles by burrowing, feeding, etc., and thus mixing the sediment. Every particle in the matrix is tagged with the same array of radioisotopes so that all tracers experience exactly the same degree of mixing; tracer profiles are achieved by averaging lateral "slices" of the sediment-water lattice. Fitting a biodiffusion model to such profiles allows mixing coefficients to be determined from the various tracers and compared to a theoretically calculated Db value. The point at which tracer determined Db values deviate from the theoretical mixing coefficient coincides with the violation of the biodiffusion model's spatial criterion, while violation of the frequency criterion manifests itself as an increased temporal variability in Db. The biodiffusion model breakdown is rarely apparent from tracer profiles, emphasizing the need to evaluate the model criteria from biological parameters rather than relying on obvious indications of model breakdown, e.g. subsurface maxima.
B33D-07 1330h
Multidisciplinary Investigations of Submarine Flow to Biscayne Bay, Florida
Biscayne Bay and Biscayne National Park (BNP) are located next to the Miami-Dade urban complex and are adjacent to the Dade County South Dade Landfill Facility and the Miami-Dade Water and Sewer South District Plant. The base of the landfill is lined to separate it from the underlying Miami Limestone, the host rock for the surficial Biscayne Aquifer. The sewage-treatment facility injects treated sewage into the lower Florida Aquifer (750 m) that is overlain by an aquitard termed the Middle Confining Unit (450 m). The Biscayne Aquifer (up to 50 m thick) borders the western margin of BNP, and the Floridan Aquifer underlies the entire park. There is concern about leakage of contaminated aquifer water into BNP and its potential effects on water quality. Groundwater flux to Biscayne Bay is being studied using pressure measurements and geochemical analyses from submarine wells, electromagnetic seepage meters, streaming resistivity profiling, and local and regional model simulations. Both seepage meters and water analyses provide point information that can be placed into the regional context provided by flow models and geochemical and geophysical profiling, which, in turn, constrain the groundwater contribution. Water samples were collected approximately quarterly from August 2002 until March 2004 from submarine wells along a transect through Biscayne Bay and across the reef to the shelf edge. Samples were analyzed for conductivity (salinity), dissolved oxygen, temperature, redox potential, nutrients, metals, strontium isotopes, radon, sulfate, and wastewater compounds. Low-salinity water was identified from nearshore wells and indicates seepage from the Biscayne Aquifer and/or surface-water intrusion into the rocks along western Biscayne Bay. Analyses of water samples (n = 109) collected from wells across the Florida shelf show no consistent evidence of wastewater contaminants occurring in groundwater beneath BNP. No significant leakage from the Floridan Aquifer (characterized by low strontium-isotope ratios) was detected in the wells. The groundwater beneath the shelf can be characterized as reduced seawater, modified by microbial respiration to remove oxygen, and interacting with sediments and minerals in the host limestone. The data from submarine well samples are consistent with groundwater model results that indicate a narrow zone of discharge along the western margin of Biscayne Bay. This zone varies in width from 100 to 1000 m along the coast. A seepage meter placed in this zone during March 2004 recorded an average flow of 23 cm/day. Submarine discharge is estimated to be about 6% of the surface-water flow to Biscayne Bay, and almost all of this is in the northern half of the bay, where shoreline and water-table elevations are greatest. Saltwater intrusion extends farther inland in the southern portion of the bay, where water-table and coastal elevations are low. Shoreline-parallel radon-222 profiles also indicate more seepage in the north than south, but suggest low-salinity water extends between 1 and 2 km offshore. Resistivity profiling provided a fourth technique (along with wells, models, and radon) that documents low-salinity water along the coast, particularly toward the northern bay. Resistivity is the only methodology that indicates presence of brackish water 5 km offshore, an observation that requires verification. Interdisciplinary approaches that estimate submarine flow to this tropical estuary are helping reinforce observations made by complimentary methods, while clearly identifying other observations as worthy of further investigation and verification.
B33D-08 1330h
Soil Development on Maya Structures at Piedras Negras, Guatemala
Ancient Maya structures and the ambient spaces around them are under-used barometers of soil development. The Piedras Negras region in northwestern Guatemala is uniquely suited to such research because unlike many other parts of the Maya Lowlands it was abandoned after about AD 850-900, and never substantially disturbed by humans thereafter. Recently excavated rural sites near Piedras Negras show that upland soils developed over the last 1100-1200 years are quite thin, and raise the issue of how deep the original upland soils were that were encountered by the first farmers.