A field study (Massachusetts, USA) of the factors controlling the depth of groundwater flow systems in crystalline fractured-rock terrain

Groundwater movement and availability in crystalline and metamorphosed rocks is dominated by the secondary porosity generated through fracturing. The distributions of fractures and fracture zones determine permeable pathways and the productivity of these rocks. Controls on how these distributions vary with depth in the shallow subsurface (<300 m) and their resulting influence on groundwater flow is not well understood. The results of a subsurface study in the Nashoba and Avalon terranes of eastern Massachusetts (USA), which is a region experiencing expanded use of the fractured bedrock as a potable-supply aquifer, are presented. The study logged the distribution of fractures in 17 boreholes, identified flowing fractures, and hydraulically characterized the rock mass intersecting the boreholes. Of all fractures encountered, 2.5% are hydraulically active. Boreholes show decreasing fracture frequency up to 300 m depth, with hydraulically active fractures showing a similar trend; this restricts topographically driven flow. Borehole temperature profiles corroborate this, with minimal hydrologically altered flow observed in the profiles below 100 m. Results from this study suggest that active flow systems in these geologic settings are shallow and that fracture permeability outside of the influence of large-scale structures will follow a decreasing trend with depth.     

A Decade of Change in the Skidaway River Estuary. III. Plankton

The Skidaway River estuary, GA (USA), a tidally dominated subtropical system surrounded by extensive Spartina salt marshes, is experiencing steady increases in nutrients, chlorophyll, and particulate matter and decline in dissolved oxygen, associated with cultural eutrophication. A long-term study is documenting changes in these parameters: previous papers Verity (Estuaries 25:944–960, 2002a, Estuaries 25:961–975, b) reported on hydrography, nutrients, chlorophyll, and particulate matter during 1986–1996; plankton community responses are reported here. Phytoplankton, bacteria, heterotrophic nanoplankton and dinoflagellates, ciliates, and copepods exhibited strong seasonal cycles in abundance driven by temperature and resource availability, typically with summer maxima and winter minima. However, cultural eutrophication coincided with altered planktonic food webs as autotrophic and heterotrophic communities responded to increasing concentrations and changing ratios of inorganic and organic nutrients, potential prey, and predators. Small (<8 μm) photosynthetic nanoplankton increased in absolute concentration and also relative to larger cells. In contrast, diatoms did not show consistent increases in abundance, despite significant long-term increases in ambient silicate concentrations. Mean annual bacteria concentrations approximately doubled, and eukaryotic organisms in the microbial food web (heterotrophic and mixotrophic flagellates, dinoflagellates, ciliates, and metazoan zooplankton) also increased. All plankton groups except copepods showed trends of increasing annual amplitudes between seasonal high and low values, with higher peak concentrations each year. These observations suggest that the eutrophication signal was gradually becoming uncoupled from regulatory mechanisms. Theory and evidence from other more impacted waters suggest that, if these patterns continue, changes in the structure and function of higher trophic levels will ensue.     

Can Plant Competition and Diversity Reduce the Growth and Survival of Exotic <Emphasis Type="Italic">Phragmites australis</Emphasis> Invading a Tidal Marsh?

The rapid proliferation of Phragmites australis in North America has challenged resource managers to curb its expansion and reduce the loss of functional tidal marsh. We investigated whether native plant competition could reduce the ability of Phragmites to invade a tidal marsh, and if plant diversity (species richness, evenness, and composition) altered the competitive outcome. Immature Phragmites shoots and four native halophytes were transplanted to small but dense field plots (~1,200 shoots m⁻²) comprising three community structure types (Phragmites alone, Phragmites + 1 native species, and Phragmites + 4 native species). Interspecific competition significantly reduced Phragmites aboveground biomass, shoot length production, density, and survival by approximately 60%. Additionally, plots planted with greater native diversity contained Phragmites with the lowest growth and survival, potentially indicating diversity-enhanced resource competition. Competition consistently reduced the growth of Phragmites even under favorable conditions: lack of strong tidal flooding stresses as well as elevated nutrient pools.     

The next layer: Towards open pedagogy in geospatial education

Open-source software and open data are becoming increasingly popular in the teaching and learning of geographic information science. The cost savings that are derived from using free software over proprietary software are one driving factor, yet the move from “closed” to “open” represents much more than financial austerity—it signifies a broader shift in educational philosophy. This article documents the gradual transition of an introductory undergraduate course in geographic information systems from an entirely closed course to one that has become increasingly open. Having completely adopted the first three layers of open—software, data, and educational resources—the course is now turning toward the next layer: embracing the philosophy of open pedagogy.     

Recent Developments in the Analysis of the Black Mat Layer and Cosmic Impact at 12.8 ka

Recent analyses of sediment samples from “black mat” sites in South America and Europe support previous interpretations of an ET impact event that reversed the Late Glacial demise of LGM ice during the Bølling Allerød warming, resulting in a resurgence of ice termed the Younger Dryas (YD) cooling episode. The breakup or impact of a cosmic vehicle at the YD boundary coincides with the onset of a 1‐kyr long interval of glacial resurgence, one of the most studied events of the Late Pleistocene. New analytical databases reveal a corpus of data indicating that the cosmic impact was a real event, most possibly a cosmic airburst from Earth's encounter with the Taurid Complex comet or unknown asteroid, an event that led to cosmic fragments exploding interhemispherically over widely dispersed areas, including the northern Andes of Venezuela and the Alps on the Italian/French frontier. While the databases in the two areas differ somewhat, the overall interpretation is that microtextural evidence in weathering rinds and in sands of associated paleosols and glaciofluvial deposits carry undeniable attributes of melted glassy carbon and Fe spherules, planar deformation features, shock‐melted and contorted quartz, occasional transition and platinum metals, and brecciated and impacted minerals of diverse lithologies. In concert with other black mat localities in the Western USA, the Netherlands, coastal France, Syria, Central Asia, Peru, Argentina and Mexico, it appears that a widespread cosmic impact by an asteroid or comet is responsible for deposition of the black mat at the onset of the YD glacial event. Whether or not the impact caused a 1‐kyr interval of glacial climate depends upon whether or not the Earth had multiple centuries‐long episodic encounters with the Taurid Complex or asteroid remnants; impact‐related changes in microclimates sustained climatic forcing sufficient to maintain positive mass balances in the reformed ice; and/or inertia in the Atlantic thermohaline circulation system persisted for 1 kyr.     

Mapping Energy: Cartographies of Energy Into The Twenty‐First Century

“Energy” presents a number of complex and interrelated challenges regarding the environment, economy, and politics. In this paper, we argue that cartography should help clarify our understanding of energy issues, but ask whether this has in fact been the case. In a review of over 100 articles pulled from twenty‐three peer‐reviewed geography journals, we qualitatively assess energy maps published since the early 20^th century, examining trends in topic and cartographic technique. Energy maps in geography journals have focused on North America and Western Europe while relying on proportional symbols, grayscale production, and the analysis of energy phenomena at the national scale—tendencies that in many instances have limited our understanding of the ways in which energy is actually consumed. Simultaneously, cartographers are limited to the energy data available to them, frequently precluding small‐scale consumption analysis or consideration of diurnal and seasonal trends. We argue that the future of energy cartography relies on access to consumption data coupled with greater user interactivity.     

Ethnic Place Identity Within A Parisian Neighborhood

The Goutte d'Or neighborhood of Paris has long been seen as an impoverished yet colorful quarter of the city. In recent years, it has also developed a reputation as a center for immigrants. Three populations now share the neighborhood: the European French, the Maghrebi immigrant population and their children, and the newest population of migrants from former Francophone colonies. This paper examines how the Goutte d'Or's social and ethnic identity is revealed in the built environment and in its social and economic activity. This neighborhood demonstrates how different communities and place identities coexist. It also shows how global networks of migration, exchange, and visits infuse local places. The Goutte d'Or distills many aspects of French immigrant identities, providing an example for increasing numbers of immigrant neighborhoods in France and across the world.