Geochemical and biological consequences of groundwater augmentation in lakes of west-central Florida (USA)

We studied sediment cores from four Florida (USA) lakes that have received groundwater hydrologic supplements (augmentation) for >30 years to maintain lake stage. Top samples (0–4 cm) from sediment cores taken in Lakes Charles, Saddleback, Little Hobbs, and Crystal had ²²⁶Ra activities of 44.9, 17.5, 7.6, and 8.5 dpm g⁻¹, respectively, about an order of magnitude greater than values in deeper, older deposits. The surface sample from Lake Charles yielded the highest ²²⁶Ra activity yet reported from a Florida lake core. Several lines of evidence suggest that groundwater augmentation is responsible for the high ²²⁶Ra activities in recent sediments: (1) ²²⁶Ra activity in cores increased recently, (2) the Charles, Crystal, and Saddleback cores display ²²⁶Ra/²¹⁰Pb disequilibrium at several shallow depths, suggesting ²²⁶Ra entered the lakes in dissolved form, (3) cores show recent increases in Ca, which, like ²²⁶Ra, is abundant in augmentation groundwater, and (4) greater Sr concentrations are associated with higher ²²⁶Ra activities in recent Charles and Saddleback sediments. Sr concentrations in Eocene limestones of the deep Floridan Aquifer are high relative to Sr concentrations in surficial quartz sands around the lakes. Historical water quality inferences for the lakes were based on diatom assemblages in sediments. Recent alkalization in Lakes Charles, Saddleback, Little Hobbs, and Crystal was inferred from weighted-averaging calibration (WACALIB). The lakes also show recent trophic state increases based on WACALIB-derived estimates for limnetic total P. Although residential and agricultural sources might contribute to increased P loading, P in augmentation waters probably has had significant influence on eutrophication. Dystrophic diatoms were abundant in the early history of Lakes Saddleback, Little Hobbs, and Crystal, which suggests that these lakes contained more tannic waters during the past than at present, perhaps as a consequence of greater inflows from surrounding wetlands. Ionic content of lake waters increased, as indicated by diatom autecological analysis. Recent geochemical and biological changes detected in cores from these lakes probably are a result of deliberate groundwater augmentation, although inputs of groundwater pumped for agricultural and residential development in the watersheds also might have contributed to limnological changes.     

A multi-proxy study of Holocene environmental change in the Maya Lowlands of Peten, Guatemala

We used multiple variables in a sediment core from Lake Peten-Itza, Peten, Guatemala, to infer Holocene climate change and human influence on the regional environment. Multiple proxies including pollen, stable isotope geochemistry, elemental composition, and magnetic susceptibility in samples from the same core allow differentiation of natural versus anthropogenic environmental changes. Core chronology is based on AMS ¹⁴C measurement of terrestrial wood and charcoal and thus avoids the vagaries of hard-water-lake error. During the earliest Holocene, prior to 9000 ¹⁴C yr BP, the coring site was not covered by water and all proxies suggest that climatic conditions were relatively dry. Water covered the coring site by 9000 ¹⁴C yr BP, coinciding with filling of other lakes in Peten and farther north on the Yucatan Peninsula. During the early Holocene (9000 to 6800 ¹⁴C yr BP), pollen data suggest moist conditions, but high ¹⁸O values are indicative of relatively high E/P. This apparent discrepancy may be due to a greater fractional loss of the lake's water budget to evaporation during the early stages of lake filling. Nonetheless, conditions were moist enough to support semi-deciduous lowland forest. Decrease in ¹⁸O values and associated change in ostracod species at 6800 ¹⁴C yr BP suggest a transition to even moister conditions. Decline in lowland forest taxa beginning 5780 ¹⁴C yr BP may indicate early human disturbance. By 2800 ¹⁴C yr BP, Maya impact on the environment is documented by accelerated forest clearance and associated soil erosion. Multiple proxies indicate forest recovery and soil stabilization beginning 1100 to 1000 ¹⁴C yr BP, following the collapse of Classic Maya civilization.     

The Zone Definition Problem in Survey Research: An Empirical Example from New York State*

This paper examines problems of zonal definition in the context of a recent empirical project on the geography of inter-firm linkages in New York State. It is argued that the results of a spatially structured survey of private companies can change significantly depending on the manner in which the study regions of the analysis are defined. Variations in the composition of study regions are a result of either changes in spatial scale, or spatial zoning at any one scale. This point is illustrated with data from 472 New York State manufacturing firms aggregated into four different zonal systems. The results of the analysis suggest that misleading interpretations of spatial data can emerge, even when logical boundaries are selected from the outset.     

Electoral Geography of the Sino-Thai in Thailand's National Elections, 1979–1995

Comparison of Thai and Sino-Thai participation and success rates from the seven elections taking place since 1979 show Sino-Thai participation comparable to their proportion in the country's population. Assimilationist government minority policy and electorate acceptance have served to integrate this group into the mainstream political system. There is no pattern of support for a particular political party and there are no indicators of a separate Sino-Thai political element. Their highest success rates, however, occur in regions of the country that have historically had small Sino-Thai populations. This appears to be the result of factional politics and of monetary and organizational resources needed to garner votes at the provincial level.     

The Development of the Chagas' Online Data Entry System (CODES-GIS)

This article describes a web‐based data entry and GIS‐driven mapping system designed for an ethnographic and entomological survey of Chagas’ disease, an emerging zoonotic disease, and Triatoma dimidiata, a primary vector, in the Los Tuxtlas region of Veracruz, Mexico. To better understand this disease in the region, a collaborative, multi‐disciplinary study was initiated to conduct a spatial investigation of T. dimidiata and a community‐by‐community survey of local perceptions of the disease. In order to facilitate such a collaborative effort the CODES‐GIS was developed. This system allows for (near) real‐time mapping, analyses, disease reporting, and results sharing. CODES‐GIS provides a framework for a research team working in a remote area with limited technology, software, or GIS expertise to benefit from (near) real‐time spatial analyses performed at collaborating institutions. The system is bi‐directional, where field personnel can upload data to the system for field‐based map production. Likewise, laboratory personnel can upload diagnostics data for viewing by field personnel. In this way, the system provides a virtual link between the field and the laboratory to increase the speed at which results are returned to the local community. The CODES‐GIS is described along with a selection of study results.     

Implications of land use change on the national terrestrial carbon budget of Georgia

Background  

Globally, the loss of forests now contributes almost 20% of carbon dioxide emissions to the atmosphere. There is an immediate need to reduce the current rates of forest loss, and the associated release of carbon dioxide, but for many areas of the world these rates are largely unknown. The Soviet Union contained a substantial part of the world's forests and the fate of those forests and their effect on carbon dynamics remain unknown for many areas of the former Eastern Bloc. For Georgia, the political and economic transitions following independence in 1991 have been dramatic. In this paper we quantify rates of land use changes and their effect on the terrestrial carbon budget for Georgia. A carbon book-keeping model traces changes in carbon stocks using historical and current rates of land use change. Landsat satellite images acquired circa 1990 and 2000 were analyzed to detect changes in forest cover since 1990.     

Professional Technologies in Schools: The Role of Pedagogical Knowledge in Teaching With Geospatial Technologies

Preparing learners for the future requires twenty-first-century teaching that integrates professional tools in the classroom. Geospatial technologies (GST), which represent geographical professional technologies, lack robust integration in high school geography. Researchers continue to ask why educators teach about rather than with GST. Understanding teacher decisions is paramount. This mixed methods study examined commonalities among teachers who use GST using Mishra and Koehler’s (2006 Mishra, P., and M. J. Koehler. 2006. Technological pedagogical content knowledge: A framework for teacher knowledge. Teachers College Record 108 (6):1017–54.[Crossref], [Web of Science ®] , [Google Scholar]) Technological, Pedagogical, Content Knowledge (TPCK) framework as a theoretical lens. This investigation examined whether geography teachers who exhibit stronger geospatial TPCK used GST more frequently than other teachers who exhibited a less developed knowledge base.     

Preserving Ground Water Samples With Hydrochloric Acid Does Not Result in the Formation of Chloroform

Water samples collected for the determination of volatile organic compounds (VOCs) are often preserved with hydrochloric acid (HCl) to inhibit the biotransformation of the analytes of interest until the chemical analyses can he performed. However, it is theoretically possible that residual free chlorine in the HCl can react with dissolved organic carbon (DOC) to form chloroform via the haloform reaction. Analyses of 1501 ground water samples preserved with HCl from the U.S. Geological Survey's National Water-Quality Assessment Program indicate that chloroform was the most commonly detected VOC among 60 VOCs monitored. The DOC concentrations were not significantly larger in samples with detectable chloroform than in those with no delectable chloroform, nor was there any correlation between the concentrations of chloroform and DOC. Furthermore, chloroform was detected more frequently in shallow ground water in urban areas (28.5% of the wells sampled) than in agricultural areas (1.6% of the wells sampled), which indicates that its detection was more related to urban land-use activities than to sample acidification. These data provide strong evidence that acidification with HCl does not lead to the production of significant amounts of chloroform in ground water samples. To verify these results, an acidification study was designed to measure the concentrations of all trihalomethanes (THMs) that can form as a result of HCl preservation in ground water samples and to determine if ascorbic acid (C₆H₈O₆) could inhibit this reaction if it did occur. This study showed that no THMs were formed as a result of HCl acidification, and that ascorbic acid had no discernible effect on the concentrations of THMs measured.     

Forecast of Tsunamis from the Japan–Kuril–Kamchatka Source Region

This paper describes an investigation of the subfault distribution along the Japan–Kuril–Kamchatka subduction zone for the implementation of a far-field tsunami forecast algorithm. Analyses of seismic data from 1900 to 2000 define the subduction zone, which in turn is divided into 222 subfaults based on the fault characteristics. For unit slip of the subfaults, a linear long-wave model generates a database of mareograms at water-level stations along the subduction zone and at warning points in the North Pacific. When a tsunami occurs, an inverse algorithm determines the slip distribution from near-source water-level records and predicts the waveforms at the warning points using the pre-computed mareograms. A jackknife resampling scheme uses combinations of input water-level records to provide a series of waveform predictions for the computation of the confidence-interval bounds. The inverse algorithm is applied to hindcast two major tsunamis generated from the Japan–Kuril–Kamchatka source and the computed tsunami heights show good agreement with recorded water-level data.