Investigating the Link Between Climate and Leptospirosis in the Caribbean Using Wavelet Analysis.
The Caribbean has shown changes in its climate (temperature and rainfall) as a result of urbanisation, population growth and industrialisation. The climatic changes have implications for the emergence and re- emergence of rodent-borne diseases such as leptospirosis. In this paper wavelet analysis is used to investigate the relationship between the incidence of leptospirosis in the Caribbean and climate variables such as temperature and precipitation. Wavelet analysis takes into account characteristics unique to climate and epidemiological data which other spectral techniques failed to do. The analysis reveals 2-3 year periodic signals in both the wavelet power spectrum and wavelet coherency. There is also a correlation between incidence of leptospirosis and late season Caribbean rainfall.
Impact of Drying and Rewetting on Carbon Cycling in a Northern fen
Peatlands are quantitatively important carbon-storing terrestrial ecosystems where peat develops due to the
rate of C input (organic matter as litter) surpassing that of C output (gas efflux and leaching) during biomass
decomposition. High water contents are an important factor controlling such equilibrium in these soils since
water does not become limiting for plant growth while keeping peat in a highly reduced state and thus lowering
peat degradation rate. A predicted effect of current climate change is the potential alteration in the hydrological
regime due to extreme rain events and extended dry periods. Thus, greater fluctuations in the water table levels
may be expected to influence redox processes and carbon cycling in peatlands.
We investigated respiration and transport processes in peat during manipulation of water table level at
ecosystem scale in a small iron-rich fen located in a forested area of North Bavaria (Germany). The
experimental design consists of three treatment (dry-rewetting) and three control plots where spatially high
resolved peat profiles (2.5, 5, 7.5, 10, 12.5, 15, 17.5, 20, 25, 30, 45 and 55 cm depth) were weekly followed up
for 7 months. An approach combining gas (for CO2, CH4 and O2 analysis) and pore-water
sampling allowed gaining insight into spatio-temporal gradients and linking those to water table fluctuations.
Soil moisture, temperature and CO2 concentrations were also investigated by installing sensors in the
upper peat layer to obtain data series during the investigated period.
A seasonal drying event naturally occurred in the control plots during summer. The drying effect was thus
reinforced in intensity and duration in the treatment plots. The main terminal electron accepting process was
Fe(III)-reduction as suggested by high reduced iron and nearly undetected hydrogen sulphide concentrations.
Water table manipulation affected peat redox processes with progressive suppression of Fe(III)-reduction
during the drying period and recover of reduced iron concentrations following the rewetting event. Spatial
gradients were observed in terms of dissolved gas concentrations along the whole experimental period;
O2 concentration decreased, CH4 concentration increased and CO2 concentration increased
with depth. Drying period effects included cessation of CH4 production in the whole investigated profile
and decrease of CO2 concentration. Water table level rapidly rose during the artificial rewetting event from
-80 cm to about -15 cm (data from only one plot). Concomitant response of dissolved gases concentrations
occurred with a sudden drop of O2 in upper peat layers and a steep increase of CO2 in the middle
layers. CH4 concentrations only recovered in the deepest peat layer showing a lag for more than 100
days after the rewetting event. Although the water table level dropped to -80 cm, anoxic conditions were kept in
peat at -50 cm suggesting that the water content was high enough to reduce permeability for O2 which
likely was rapidly consumed. Such a difference becomes relevant when considering carbon fluxes as air-filled
porosity physically controls gas transport across peat profile.
Influence of Antecedent Soil Moisture Conditions and Substrate Quality on the Magnitude and Timing of N2O Emissions From Riparian Soil
Nitrous oxide (N2O) is a greenhouse gas with a large global warming potential. Consequently there is concern over increased concentrations of atmospheric N2O. Denitrification and nitrification are the primary sources of N2O emissions from agricultural soils and riparian wetlands within these systems. These processes are regulated by soil moisture, oxygen levels in soil pores, soil substrate/nutrient supply (e.g. carbon (C) and nitrogen (N)), pH, and temperature. Soil moisture history may also be a key determinant of N2O flux timing and magnitude through its influence on soil turnover processes and therefore available nutrient pools. However, the linkages between these controls as well as their relative influence on N2O fluxes are poorly understood. This research uses an experimental approach to examine the combined influences of soil moisture and nutrient availability (as affected by soil antecedent moisture history) on N2O fluxes from riparian soil. Soil cores were collected from both an upland (loam soil) location and a lowland (organic soil) location in an agricultural riparian wetland in Southern Ontario for this experiment. In the laboratory, intact soil cores were subject to moisture cycles (wet-dry-wet; dry-wet-dry) over a six-week period to examine how N2O fluxes and soil available nutrient pools changed throughout different types of moisture cycles. Preliminary results indicate that antecedent soil moisture influences the timing and magnitude of N2O flux due to its influence on both soil available nutrient content and likely O2 availability; however, these relationships differ for the two soil types. Larger N2O fluxes were observed from upland soils on a drying trend as opposed to a wetting trend. In contrast, larger N2O fluxes were observed from soils on a wetting trend rather than a drying trend from lowland soil. In addition, the timing of the onset and cessation of N2O fluxes differed both with soil type and the direction of the moisture cycle (i.e. wet-dry-wet; dry-wet-dry). This research helps to identify critical periods for enhanced N2O fluxes in riparian soil and thus helps to refine field sampling strategies. This work will also improve our understanding of nitrogen dynamics in riparian landscapes by demonstrating the impact of antecedent moisture history on N2O fluxes.
Fractal Vegetative Landscapes and Resilience: Empirical Evidence from Fire-Prone Systems
Background/Question/Methods: Mechanisms for resilience must exist for ecosystems to persist across space and time, often in the face of substantial disturbance, climatic, and environmental fluctuation. Furthermore, resilience mechanisms must occur at spatio-temporal scales that can reinforce the patterns, processes, and interactions that operate in ecosystems. Here, we examine the power law behavior of multi-scale vegetation features, topographies, and fire severity patches of eastern Cascade Mountain forest landscapes. Our objectives were to: (1) use maximum likelihood estimation (MLE) techniques to fit statistical distributions to vegetation, topography, and fire severity patch-size distributions (PSDs) of pre-settlement era landscapes of four ecoregions, (2) evaluate concordance between vegetation, topography, and fire severity PSDs, (3) evaluate scale-invariance and power-law behavior of the best fitting distributions using MLE, broken-stick regression, left truncation, and neutral-modeling techniques, and (4) evaluate the quantitative evidence for exogenous and endogenous controls on the distribution of vegetation (physiognomies, land cover types, structural classes, canopy cover classes) and fire severity patch sizes. Results/Conclusions: From physiognomies to canopy cover classes of all ecoregions, heavy-tailed PSDs were evident. Out of 25 statistical distributions tested, the Pareto and Generalized Beta II (GBII) distributions consistently fit the empirical inverse cumulative distribution functions (CDFs) of vegetation, topography, and fire severity patches. Top-down controls--When PSDs of any vegetation, topography, or fire severity class were pooled across ecoregions, all tested statistical distributions failed to fit the resultant empirical CDFs. However, K-S boot strap and log-likelihood ratio tests revealed that models fit to individual subregions provided good fits. Bottom-up controls--The frequency-size distribution of N and S aspect patches followed a nearly pure power-law distribution for all ecoregions but one. Other topographic features such as slope, curvature, slope*aspect, slope*curvature also followed a power-law relation for some ecoregions, but inconsistencies were pronounced. Neutral models developed for vegetation, topography, and fire severity classes showed conclusive evidence that PSDs were not the result of random influences. We conclude that (1) vegetation and aspect PSDs partially drove fire severity PSDs via mosaics of structural and compositional "fences and corridors" that either resisted or allowed penetration of otherwise contagious fires; (2) topography partially drove vegetation and fire severity PSDs of all ecoregions; (3) ecoregions partially drove vegetation and fire severity PSDs from above; and (4) fine-, meso, and broad-scale process domains may be quantified for vegetation, topography, and fire severity PSDs. This information should be useful to creating more resilient forest landscapes in an uncertain climatic future.
Factors Affecting the Sensitivity of Permafrost to Climate Change
Permafrost aggradation and degradation are affected by numerous geomorphological and ecological properties of the landscape that confound our ability to accurately predict the response of permafrost to climate change. Permafrost can persist at mean annual air temperatures (MAAT) of +2 °C and can degrade at MAAT of -15 °C with the help of surface water. Permafrost is decoupled from the atmosphere by the active layer, thus, its thermal regime is mediated by numerous factors such as topography, soil texture, organic-matter accumulation, vegetation, snow, surface water, groundwater movement, and disturbance. Topography affects the amount of solar radiation to the soil surface, causing permafrost in the discontinuous zone to occur generally on north-facing slopes that receive less direct radiation and on flat, low- lying areas where vegetation and organic soils have a greater insulating effect and where air temperatures tend to be colder during winter inversions. Soil texture affects soil moisture and thermal properties. For instance, gravelly soils tend to be well-drained with little difference between thermal conductivities when frozen or thawed. In contrast, surface organic soils, as well as clayey and silty soils, in lowland areas tend to be poorly drained and have much higher thermal conductivities when frozen in winter than unfrozen in summer. In well- drained upland sites, however, organic soils typically are well below saturation. Differences in frozen and unfrozen thermal conductivities lead to more rapid heat loss in winter, depending on snow, and slower heat penetration in summer. Vegetation has important effects through interception of solar radiation, growth of mosses, accumulation of organic matter, and interception of snow by trees and shrubs. Snow protects soil from cooling in winter. Thus, the seasonality (e.g., timing of snowfall in early winter) and depth of snow are very important. Surface water provides an important positive feedback that enhances degradation when water is impounded in sinking depressions. Thus, the amount of ground ice and potential thaw settlement greatly affects permafrost sensitivity. Water bodies (lakes, ponds, rivers) have a warming effect on permafrost and often create thawing zones for which their geometry is defined by water depth, sediment texture, and climate. Convective heat transfer associated with groundwater movement can create an unfrozen zone on top or within permafrost. Surface and groundwater flow, and surface impoundment, in turn are affected by topography and soil texture. Because permafrost is greatly affected by these ecological components, permafrost properties evolve along with the successional patterns of ecosystem development, which in turn affects the sensitivity of permafrost to degradation. We explore the relative effects of these factors through modeling and comparison of field measurements. Because there is no single model available that can include all these disparate factors, we evaluate factors separately and use differences in mean annual ground temperatures at the surface and at 2-m depth to compare the magnitude of each effect.
Seasonal Ice and Drainage Controls over Solute Chemistry in a Rich Boreal Fen: a Field Water Table Manipulation Experiment in Interior Alaska
Boreal and arctic regions are experiencing substantial changes in climate that have caused longer, drier
growing seasons and the degradation of permafrost. Recently, water bodies in some wetland regions in
Alaska are drying (Yoshikawa and Hinzman 2003), while other regions are becoming wetter, but few studies
have explored how boreal wetland drainage and its interactive effects on ice depth will affect dissolved organic
carbon (DOC) loading and potential export from these systems. By facilitating drainage with ditches and with
active pumping, we experimentally manipulated the water tables of two plots (both raised and lowered water
table treatments) within a boreal rich fen in interior Alaska, and measured changes in peat porewater
chemistry, seasonal ice dynamics, and thermal properties over a 4 y period. We documented consistently
higher DOC and total dissolved nitrogen (TDN) concentrations in the drained treatment (71.6 ± 6.6 and
3.1 ± 0.5 mg L -1, respectively) than in both the control (55.6 ± 5.2 and 2.3 ± 0.4 mg L -
1, respectively) and raised (49.1 ± 4.7 and 2.0 ± 0.4 mg L -1, respectively) water table
treatments. Across all plots, depths to seasonal ice and water table height were the strongest predictors of
DOC:Cl- and TDN:Cl- concentrations in peat porewater. These data demonstrate that boreal wetland
drainage, and its interaction with changes in seasonal ice and peat thermal properties, will likely increase
DOC and TDN loading and potential export from these systems.
Human amplification of drought-induced biomass burning in Indonesia since 1960
Much of the interannual variability in global atmospheric carbon dioxide concentrations has been attributed to
variability of emissions from biomass burning. Under drought conditions, agricultural burning in Indonesia
escapes control, and is a disproportionate contributor to these emissions, as seen in the 1997/98 haze
disaster. Yet our understanding of the frequency, severity and underlying causes of severe biomass burning in
Indonesia is limited because of the absence of satellite data that are useful for fire monitoring before the mid-
1990s. Here we present a continuous monthly record of severe burning events from 1960 to 2006 using the
visibility reported at airports in the region. We find that these fires cause what are possibly the world's worst air
quality conditions and that they occur only during years when precipitation falls below a well defined threshold.
Historically, large fire events have occurred in Sumatra at least since the 1960s. By contrast, the first large fires
are recorded in Kalimantan (Indonesian Borneo) in the 1980s, despite earlier severe droughts. We attribute
this difference to different patterns of changes in land use and population density. Fires in Indonesia have often
been linked with El Niño, but we find that the Indian Ocean Dipole pattern is as important a contributing factor.
GPR profiles of Saddle Mountain scoria deposits on Walker Lake Crater tuff ring in Arizona help understanding of geomorphological response to wildland fire
Walker Lake tuff ring in the San Francisco Volcanic Field, Arizona, experienced a significant forest fire in 1996. Extensive event scale studies suggested a highly increased (by two orders of magnitude) erosion rate both due to raindrop impact and overland flow. However, the 2.3 million year old cone's materials are partially covered by a 15,000-year-old scoria cone deposit from nearby Saddle Mountain. Although previous studies of the geomorphology of Walker Lake crater provided insight into the Saddle Mountain deposit, new studies have actually shown the extent and depth of the deposit on the cone. We present data obtained with ground penetrating radar (GPR) that gives a clearer data set on the depth (4-7m) of the younger deposit in one of the more extensively studied areas. Data were collected along longitudinal and horizontal profiles along the southwestern part of the cone where the deposit is clearly recognizable on the surface and the wild land fire devastation is enormous. Future analysis will shed quantitative light on the effect that the younger, less cohesive materials has on the increased erosion rates in the event scale to decadal scale erosion rates after wildland fire.
Anomalies of CO Global and Regional Burdens Measured by Satellites: Update to Present Time
CO has several natural and human-induced sources. They are comparable in strength, but biomass burning (BB) is the only one that experiences significant interannual and seasonal variations. The importance of CO global monitoring is connected with predicted long-term increases in global and regional BB. A comparison of global data from different orbital instruments in combination with their validation vs ground-based instruments provides a fast and direct way for prompt and reliable estimation of BB variations. This report presents analyses of Level 3 global CO measurements retrieved from satellite observations by MOPITT and AIRS through April 2009. Global CO burden anomalies are recalculated into anomalies of CO BB emissions assuming stable [OH]. Regional CO burden is a good indicator for regional BB variations, as well.
Charcoal-Based Paleoecological Investigation of the Holocene Fire Regime of St. Lawrence Islands National Park, Southeastern Ontario
Wildfire is an ecological disturbance that plays a role in ecosystem function and is complexly associated with climate and vegetation. The study of long-term fire regimes can provide information about the range of conditions that have existed in an environment and supply context for future shifts in those conditions. There has been little research of paleofire in Southeastern Ontario, Canada, though it is a relevant process. To address the gap, our project is investigating the long-term history of fire during the Holocene within this area using paleolimnological methods. The primary objective is the reconstruction of the fire frequency of a small watershed in this region over approximately the past 10000 years. The results will be applied to the ecological management of St. Lawrence Islands National Park. Analysis of the macroscopic charcoal content in lake sediment is the primary technique. A surface sediment core (0.65m) and a long sediment core (4.15m) were extracted in Summer 2008 from Mud Lake, a small (2ha) lake approximately 20-40km from St. Lawrence Islands National Park territory. Preliminary analysis of the charcoal content indicates no local fires for the past several hundred years. Initial results also indicate a fire return interval on the order of hundreds of years. The findings coordinate with the region's humid, continental climate and mixed forest. AMS radiocarbon and 210Pb dating provide a chronology for the sediment cores, and its magnetic susceptibility has also been analyzed. The study will contribute to the park's fire management and ecological restoration practices. The long-term history of fire is of particular interest as a provincially rare species, Pinus rigida, the pitch pine, has numerous populations in the park boundaries and adjacent to the lake site and has been present in this region for several thousand years. As this species relies on fire for its life cycle, knowledge of the fire patterns that have existed in its range will assist in managing its restoration. Furthermore, the results may aid in addressing future environmental variability and in managing the overall ecological integrity of the region.