Leslie A. Morrissey

Microwave backscatter and attenuation dependence on leaf area index for flooded rice fields

As part of an effort to determine whether radar is suitable for wetland vegetation monitoring the authors have studied the dependence of microwave backscatter and attenuation on leaf area index (LAI) for flooded rice fields. They find that the radar return from a flooded rice field does show dependence on LAI. In particular, the C-band VV cross section per unit area decreases with increasing LAI. A simple model for scattering from rice fields is derived and fit to the observed HH and VV data. The model fit provides insight into the relation of backscatter to LAI and is also used to calculate the canopy path attenuation as a function of LAI. >

Differentiating methane source areas in Arctic environments with multitemporal ERS-1 SAR data

An assessment using ERS-1 SAR data to differentiate methane source (wetland) and nonsource (nonwetland) areas was undertaken based on radar backscatter modeling and empirical observations of 24 scenes collected over Barrow, AK, in 1991 and 1992. Differences in backscatter between source and nonsource areas were dependent on surface hydrology and air temperature. Differential freezing of surface materials on daily to seasonal time scales greatly enhanced the separability of wetlands and nonwetlands with ERS-1 SAR. Radar return for nonwetlands decreased dramatically whereas backscatter from wetlands decreased little when freezing air temperatures coincided with the SAR overpass. Maximum separability between wetlands and nonwetlands, as determined from observed and modeled radar backscatter, were the result of changes in the dielectric constant of the plant and surface materials with phase change during freezing. This study has indicated the need to consider air temperature at the time of acquisition in selecting ERS-1 SAR scenes for differentiating methane source and nonsource areas.

Ecohealth Interventions Limit Triatomine Reinfestation following Insecticide Spraying in La Brea, Guatemala

In this study, we evaluate the effect of participatory Ecohealth interventions on domestic reinfestation of the Chagas disease vector Triatoma dimidiata after village-wide suppression of the vector population using a residual insecticide. The study was conducted in the rural community of La Brea, Guatemala between 2002 and 2009 where vector infestation was analyzed within a spatial data framework based on entomological and socio-economic surveys of homesteads within the village. Participatory interventions focused on community awareness and low-cost home improvements using local materials to limit areas of refuge and alternative blood meals for the vector within the home, and potential shelter for the vector outside the home. As a result, domestic infestation was maintained at ≤ 3% and peridomestic infestation at ≤ 2% for 5 years beyond the last insecticide spraying, in sharp contrast to the rapid reinfestation experienced in earlier insecticide only interventions.

Influences of Fire and Climate Change on Patterns of Carbon Emissions in Boreal Peatlands

Projected changes in temperature and precipitation over the next several decades (Houghton et al. 1996) are expected to significantly enhance the release of gaseous carbon from northern peatlands. This enhancement is expected in response to increased rates of microbial decomposition acting on the vast carbon stores underlying these ecosystems (Oechel et al. 1993; Goulden et al. 1998) and to an increase in the frequency, extent, and intensity of peatland wildfires (Zoltai et al. 1998). Over much of the past 10,000 years, northern peatlands have collectively functioned as a globally important sink of atmospheric carbon dioxide (CO2) (Mitsch and Gosselink 1986; Gorham 1991), that is, net primary productivity in these ecosystems has exceeded losses. As a result, nearly one-third of all soil organic matter on earth underlies northern peatlands in the form of partially decomposed organic matter (peat) (Gorham 1991). Evidence is building, however, to suggest that rates of carbon loss from these northern ecosystems due both to microbial decomposition (e.g., Livingston and Morrissey 1991; Carroll and Crill 1997) and fire (Levine et al. 1995) have increased dramatically, even exceeding net primary productivity in some areas (Oechel et al. 1993; Goulden et al. 1998). A dramatic shift in the ecological function of northern peatlands from that of a net carbon sink to a net carbon source could potentially enhance climatic change due to the resultant increased atmospheric loading of radiatively important gases such as CO2 and methane (CH4) (Fung et al. 1991).

Sources of blood meals of sylvatic Triatoma guasayana near Zurima, Bolivia, assayed with qPCR and 12S cloning.

Background In this study we compared the utility of two molecular biology techniques, cloning of the mitochondrial 12S ribosomal RNA gene and hydrolysis probe-based qPCR, to identify blood meal sources of sylvatic Chagas disease insect vectors collected with live-bait mouse traps (also known as Noireau traps). Fourteen T. guasayana were collected from six georeferenced trap locations in the Andean highlands of the department of Chuquisaca, Bolivia. Methodology/Principal Findings We detected four blood meals sources with the cloning assay: seven samples were positive for human (Homo sapiens), five for chicken (Gallus gallus) and unicolored blackbird (Agelasticus cyanopus), and one for opossum (Monodelphis domestica). Using the qPCR assay we detected chicken (13 vectors), and human (14 vectors) blood meals as well as an additional blood meal source, Canis sp. (4 vectors). Conclusions/Significance We show that cloning of 12S PCR products, which avoids bias associated with developing primers based on a priori knowledge, detected blood meal sources not previously considered and that species-specific qPCR is more sensitive. All samples identified as positive for a specific blood meal source by the cloning assay were also positive by qPCR. However, not all samples positive by qPCR were positive by cloning. We show the power of combining the cloning assay with the highly sensitive hydrolysis probe-based qPCR assay provides a more complete picture of blood meal sources for insect disease vectors.

Remote sensing of high-latitude wetlands using polarized wide-angle imagery

Representing the areal extent of circumpolar wetlands is a critical step to quantifying the emission of methane, an important greenhouse gas. Present estimates of the areal extent of these wetlands differ nearly seven fold, implying large uncertainties exist in the prediction of circumpolar methane emission rates. Our objective is to use multi- directional and polarization measurement provided by the French POLDER sensor to improve this estimate. The results show that wetlands can be detected, classified and their area quantified using the unique, highly polarized angular signature of the sunglint measured over their water surfaces.

Uncovering vector, parasite, blood meal and microbiome patterns from mixed-DNA specimens of the Chagas disease vector Triatoma dimidiata

Chagas disease, considered a neglected disease by the World Health Organization, is caused by the protozoan parasite Trypanosoma cruzi, and transmitted by >140 triatomine species across the Americas. In Central America, the main vector is Triatoma dimidiata, an opportunistic blood meal feeder inhabiting both domestic and sylvatic ecotopes. Given the diversity of interacting biological agents involved in the epidemiology of Chagas disease, having simultaneous information on the dynamics of the parasite, vector, the gut microbiome of the vector, and the blood meal source would facilitate identifying key biotic factors associated with the risk of T. cruzi transmission. In this study, we developed a RADseq-based analysis pipeline to study mixed-species DNA extracted from T. dimidiata abdomens. To evaluate the efficacy of the method across spatial scales, we used a nested spatial sampling design that spanned from individual villages within Guatemala to major biogeographic regions of Central America. Information from each biotic source was distinguished with bioinformatics tools and used to evaluate the prevalence of T. cruzi infection and predominant Discrete Typing Units (DTUs) in the region, the population genetic structure of T. dimidiata, gut microbial diversity, and the blood meal history. An average of 3.25 million reads per specimen were obtained, with approximately 1% assigned to the parasite, 20% to the vector, 11% to bacteria, and 4% to putative blood meals. Using a total of 6,405 T. cruzi SNPs, we detected nine infected vectors harboring two distinct DTUs: TcI and a second unidentified strain, possibly TcIV. Vector specimens were sufficiently variable for population genomic analyses, with a total of 25,710 T. dimidiata SNPs across all samples that were sufficient to detect geographic genetic structure at both local and regional scales. We observed a diverse microbiotic community, with significantly higher bacterial species richness in infected T. dimidiata abdomens than those that were not infected. Unifrac analysis suggests a common assemblage of bacteria associated with infection, which co-occurs with the typical gut microbial community derived from the local environment. We identified vertebrate blood meals from five T. dimidiata abdomens, including chicken, dog, duck and human; however, additional detection methods would be necessary to confidently identify blood meal sources from most specimens. Overall, our study shows this method is effective for simultaneously generating genetic data on vectors and their associated parasites, along with ecological information on feeding patterns and microbial interactions that may be followed up with complementary approaches such as PCR-based parasite detection, 18S eukaryotic and 16S bacterial barcoding.

Mapping Wetlands Cover Types with Directional Polarization Signatures

We present an approach to mapping surface waters at local to global scales. In prior research we demonstrated that wide angle remotely sensed imagery having high radiance values measured near the direction of the sun glint in the principal plane signaled the presence of either open water or inundated plant communities, in contrast to dry upland plant communities. We demonstrated that regional to global scale wetlands issues that do not involve one meter resolution per se may be addressed with acceptable accuracy by applying spectral mixture analysis (SMA) and atmospheric correction techniques to the 6-10 km pixel imagery from POLDER. Here we investigate the influence of wind speed upon the discrimination process, showing that at very low wind speeds and very high wind speeds we are not able to discriminate the three cover types and that when wind speeds are moderate there is potentially an error associated with estimation of the areal extent of open water areas.