Dr. Johan Liebens

Stream restoration practitioners often rely upon empirical models to quantify annual streambank erosion rates and identify streambank erosion hotspots. Such models are designed to be widely applicable by incorporating readily available field measurements, but they must be calibrated to each hydrophysiographic region and may not reflect the dominant streambank erosion processes in a given region. Here, we present statistical models for streambank erosion using physical and environmental data collected at 53 locations throughout the northern
Gulf of Mexico coastal plain. The data include channel geometry, bank characteristics, precipitation, aboveground biomass density, and root density, the latter two surveyed using techniques introduced here. We developed a statistical model selection process using Akaike's Information Criterion (AIC) and repeated crossvalidation (CV). Models derived from the literature that were applied a priori were only weak predictors of erosion rate, but AIC-CV model selection identified 3 strong statistical models. The best model according to AIC showed a significant correlation to lateral streambank erosion rates (R²=0.54) and included the five strongest covariates of our dataset (bank slope, biomass density, curvature index, BEHI, and understory cover). When volumetric erosion rate (m²/year) was predicted, the fit of this model increased (R²=0.65). CV-based selection resulted in a more conservative model with the four strongest covariates and a lower fit (R²=0.47). The similarity of the AIC and CV models indicates the stability of the two-tier model selection approach, and suggests it has utility for modeling phenomena with many potential variables. Our models also showcase the ability of our biomass survey to quantify root reinforcement of streambanks. Our approach incorporates measurements familiar to the stream restoration community and can be applied throughout the northern Gulf of Mexico coastal plain, a region characterized by low relief fluvial valleys, unconsolidated alluvium and meandering single thread sand bed channels. The approach, which is based on field observations and robust statistical modeling, offers an alternative for stream restoration practitioners to more traditional streambank erosion prediction methods that underperform in the region, and may have applicability elsewhere.

The Bank Assessment of Nonpoint source Consequences of Sediment (BANCS) framework allows river scientists to predict annual sediment yield from eroding streambanks within a hydrophysiographic region. BANCS involves field data collection and the calibration of an empirical model incorporating a bank erodibility hazard index (BEHI) and near-bank shear stress (NBS) estimate. Here we evaluate the applicability of BANCS to the northern Gulf of Mexico coastal plain, a region that has not been previously studied in this context. Erosion
rates averaged over two years expressed the highest variability of any existing BANCS study. As a result, four standard BANCS models did not yield statistically significant correlations to measured erosion rates. Modifications to two widely used NBS estimates improved their correlations (r² = 0.31 and r² = 0.33), but further grouping of the data by BEHI weakened these correlations. The high variability in measured erosion rates is partly due to the regional hydrologic and climatic characteristics of the Gulf coastal plains, which include large, infrequent precipitation events. Other sources of variability include variations in bank vegetation and the complex hydro- and morphodynamics of meandering, sand bed channels. We discuss directions for future research in developing a streambank erosion model for this and similar regions.

This study assessed current profiles of organochlorine pollutants in sediment of Escambia Bay and River in northwest Florida, United States (US), which experienced catastrophic environmental collapse in the 1970s as a result of unregulated industrial and domestic sewage releases. Fifty-seven compositesediment samples were collected with a ponar grab sampler. Organochlorines were extracted with United States Environmental Protection Agency (USEPA) Method 3550 and concentrations were determined with USEPA Method 1668A for
polychlorinated biphenyls (PCBs), USEPA Method1613B for polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/ Fs), and USEPA Method 8081A for 4,4'-dichlorodiphenyltrichloroethane (DDT), 4,4'-Dichlorodiphenyldichloroethane (DDD), and 4,4'-Dichlorodiphenyldichloroethylene (DDE). For PCBs, 12 (21%) out of the 57 samples exceed the Florida threshold effects level (TEL) of 21.6 μg/kg and no sample exceeds the Florida probable effects level (PEL) of 189 μg/kg. The 17 PCDD/F congeners that are considered to have significant toxicity have a mean of 1.9 μg/kg and a range of 0.022–11 μg/kg. The mean total toxic equivalence value (TEQ) of PCDD/Fs and dioxin-like PCBs for the sediments is 2.6 ng/kg. About 56% of the samples exceed the US National Oceanic and Atmospheric Administration (NOAA) TEL for total TEQ, 23% of which also exceed the NOAA TEL, implying that these total TEQ toxicities can impact sediments adversely. DDT was detected in 25% of the samples. All but one of the detections were in the river and adjacent wetlands. The detected DDT concentrations exceed the Florida PEL (4.77 μg/kg) except for one sample that only exceeds the TEL (1.19 μg/kg).

Polychlorinated biphenyls (PCBs) are anthropogenic substances that have been detected in many parts of the environment and can have major negative impacts on ecosystem and human health. A documented release of PCBs from a nylon plant occurred in 1969 on the Escambia River just upstream of the Escambia Bay estuary along the north coast of the Gulf of Mexico. Other unreported releases of PCBs also likely occurred in the river and bay. The present study sampled sediments in the river and bay and assessed the predominant parent Aroclor of PCBs, and the changes in congener profile and toxic equivalents (TEQ) since the release. United States Environmental Protection Agency (US EPA) method 1668A, which provides quantitative data for 168 elutions, was employed for the analysis according to National Environmental Laboratory Accreditation Program procedures. Correlation analysis and principal component analysis of the PCB congener profiles for the sediments and Aroclors showed that the sedimentary PCB congeners are most similar to that of early production Aroclor 1254 made prior to 1971. Chronologically the use of the early production Aroclor 1254 corresponds to the time of the release. Since the release, overall chlorination of the sedimentary PCBs has decreased by 3% as a result of a shift in chlorination homolog profile to lesser-chlorinated congeners that presumably originated from dechlorination of Aroclor PCBs and from non-Aroclor source(s) of PCB 11, a dichlorobiphenyl. Despite a likely overall decrease in the quantity of dioxin-like PCBs, the TEQ/mole of sediment PCBs, did not substantially change because of a highly toxic congener (PCB 126) that was present at trace amounts in the sediments. There was a modest increase in lesser-chlorinated O,P-congeners that are suspected to have some toxicity to mammals. These findings have relevance for the evolution of environmental PCBs, which has not been studied in this system.

This study assesses the origin and pollution of trace metals in surface soils in a region with contrasting land uses (urban vs. rural). Principal component analysis (PCA) reveals that Cr and Ni are predominantly of geogenic origin. These two trace metals are also the only ones
with statistically significant correlations with soil particle size and organic matter content. Copper, Pb and Zn, and possibly Hg, are of anthropogenic origin, but their concentrations rarely reach levels described as strongly polluted by pollution indexes. The concentrations of these anthropogenic trace metals are statistically not different in urban and rural areas, except for Pb that is higher in the urban area. This general lack of a difference between the two land uses indicates that the influence of this small urban area on trace metal concentrations in soils is minor. Lead and Zn have the most, but still a modest number, of strongly polluted sites, mainly in an industrial part of the city. GIS analysis shows that, based on the pollution load index (PLI), overall concentrations of trace metals also reach their highest levels in that industrial area. These observations indicate that the influence of industry on trace metal pollution in soil exceeds that of other urban activities in the region. Local background concentrations were found to be very different from general crustal background concentrations. This demonstrates the importance of the careful selection of a background type in studies like this.

DDTs were sprayed extensively in Belize to combat malaria but widespread use ceased after 1997. To determine if DDTs still persist in Belize’s soils, 23 composite soil samples were collected from each of the two towns of Dangriga and Punta Gorda. Dichlorodiphenyltricholoroethane (DDT) and its breakdown products dichlorodiphenyldichloroethylene (DDE) and dichlorodiphenyldichloroethane (DDD) were the only organochlorine compounds detected in the soils. Results show that DDTs are transferred to the soil environment as a result of spraying houses and that the pesticides still persist in soils in southern Belize after more than 10 years of non-use. Sprayed lots had DDT concentrations up to 240 μg/kg in Dangriga and up to 410 μg/kg in Punta Gorda. All unsprayed lots had below detection limit concentrations, with the exception of two sites in Punta Gorda. Hot spot analysis in GIS indicates that significant spatial variability exists in detected concentrations of DDTs, which has implications for extrapolation of local data. Belize currently has no guidelines for determining risk of DDTs to human health and soil cleanup, but soil cleanup guidelines employed by foreign governmental entities such as the Netherlands and California show that all detected pesticide concentrations in this study are below mandated concentrations of concern for the residential areas of these regions. However, since exposure scenarios may be different in Belize, it is recommended that the Belize Ministry of Health conducts a risk analysis to ascertain if the concentrations of DDTs in sprayed areas pose a risk
to the inhabitants of the two towns.

The objective of the present study was to evaluate the relationships between the quantity, toxicity, and compositional profile of dioxin/furan compounds (PCDD/Fs) and dioxin-like polychlorinated biphenyls (DL-PCBs) in estuarine sediment and in the blue crab (Callinectes sapidus). Sediment and blue crab samples were collected in three small urban estuaries that are in relatively close proximity to each other. Results show that differences between PCDD/F and DL-PCB mass concentrations and total toxic equivalents (TEQ) toxicity in sediments of the three estuaries are reflected in those of the blue crab. TEQs are higher in the hepatopancreas of the crabs than in the sediment, but the concentration factor is inversely proportional to the TEQ in the sediments. Congener profiles in the crabs are systematically different from those in the sediments, and the difference is more pronounced for PCDD/Fs than for DL-PCBs, possibly due to differences in metabolization rates. Compared with sediment profiles, more lesser-chlorinated PCDD/Fs that have higher TEFs accumulate in crab hepatopancreas. This selective bioaccumulation of PCDD/Fs results in a TEQ augmentation in crab hepatopancreas compared with sediments. The bioaccumulation in the blue crab is also selective for PCDD/Fs over DL-PCBs.

Background: Relatively few studies have examined the association between air pollution and stroke mortality. Inconsistent and inclusive results from existing studies on air pollution and stroke justify the need to continue to investigate the linkage between stroke and air pollution. No studies have been done to investigate the association between stroke and greenness. The objective of this study was to examine if there is association of stroke with air pollution, income and greenness in northwest Florida.

Results: Our study used an ecological geographical approach and dasymetric mapping technique. We adopted a Bayesian hierarchical model with a convolution prior considering five census tract specific covariates. A 95% credible set which defines an interval having a 0.95 posterior probability of containing the parameter for each covariate was calculated from Markov Chain Monte Carlo simulations. The 95% credible sets are (-0.286, -0.097) for household income, (0.034, 0.144) for traffic air pollution effect, (0.419, 1.495) for emission density of monitored point source polluters, (0.413, 1.522) for simple point density of point source polluters without emission data, and (-0.289,-0.031) for greenness. Household income and greenness show negative effects (the posterior densities primarily cover negative values). Air pollution covariates have positive effects (the 95% credible sets cover positive values).

Conclusion: High risk of stroke mortality was found in areas with low income level, high air pollution level, and low level of exposure to green space.

Estuaries are among the environmentally most heavily impacted coastal ecosystems (Lewis et al., 2001). Sediment and water quality in estuaries have been found to be greatly influenced by urbanization and industrialization (Feng et al., 2004; Ramessur, 2004; Sarkar et al., 2004; Cave et al., 2005). Because of the ever increasing human activities in coastal areas there is a continued need for a better understanding of pollution in these estuaries. In the Pensacola, FL area the local estuaries have been an integral part of life and have been the focus over the years of mounting concerns as recipients of sewage, stormwater, and industrial releases, particularly from several Superfund sites.