Groundwater nitrogen processing in Northern Gulf of Mexico restored marshes.

Groundwater nitrogen processing was examined in a restored black needlerush (Juncus roemerianus) marsh to assess its potential for removing land-derived nitrogen pollution. Two restoration designs, one initially planted at 50% cover (half density plots) and the other one at 100% cover (full density plots), were compared with non-vegetated controls. The introduction via groundwater of a NO3(-) solution with a conservative tracer (Br(-)) and labeled isotopically ((15)N) allowed calculation of nitrogen removal in the plots following two methods. The first method used changes in the ratio [NOx]:[Br(-)] as the groundwater plume traveled through the plot, and the second method relied on balancing (15)N input with (15)N export. Both methods showed ≈97% of the N from the simulated groundwater plume was removed (i.e. not delivered to the open waters of the adjacent estuary) in vegetated plots and ≈86% was removed in non-vegetated controls. The most dominant routes of N removal from the introduced solution were N2 production and assimilation into macrophyte biomass, which were similar in magnitude for the vegetated plots, whereas N2 production dominated in the unvegetated plots. The majority of N removed from the introduced solution occurred in the first 30 cm the solution traveled in the vegetated treatments. In addition, ambient porewater concentrations of dissolved inorganic nitrogen (DIN) were similar between full and half density plots, but lower than the non-vegetated control (≈8.5× and 7.5×), suggesting full and half density plots removed more DIN than non-vegetated plots. These results suggest that restoring marshes by planting 50% of the area may be a more cost-effective restoration design in terms of mitigating land-derived nutrient pollution than planting 100% of the area since it requires less effort and cost while removing similar quantities of N.

Designing coastal conservation to deliver ecosystem and human well-being benefits.

Conservation scientists increasingly recognize that incorporating human values into conservation planning increases the chances for success by garnering broader project acceptance. However, methods for defining quantitative targets for the spatial representation of human well-being priorities are less developed. In this study we employ an approach for identifying regionally important human values and establishing specific spatial targets for their representation based on stakeholder outreach. Our primary objective was to develop a spatially-explicit conservation plan that identifies the most efficient locations for conservation actions to meet ecological goals while sustaining or enhancing human well-being values within the coastal and nearshore areas of the western Lake Erie basin (WLEB). We conducted an optimization analysis using 26 features representing ecological and human well-being priorities (13 of each), and included seven cost layers. The influence that including human well-being had on project results was tested by running five scenarios and setting targets for human well-being at different levels in each scenario. The most important areas for conservation to achieve multiple goals are clustered along the coast, reflecting a concentration of existing or potentially restorable coastal wetlands, coastal landbird stopover habitat and terrestrial biodiversity, as well as important recreational activities. Inland important areas tended to cluster around trails and high quality inland landbird stopover habitat. Most concentrated areas of importance also are centered on lands that are already conserved, reflecting the lower costs and higher benefits of enlarging these conserved areas rather than conserving isolated, dispersed areas. Including human well-being features in the analysis only influenced the solution at the highest target levels.

A prototype piecewise-linear dynamic attenuator.

The piecewise-linear dynamic attenuator has been proposed as a mechanism in CT scanning for personalizing the x-ray illumination on a patient- and application-specific basis. Previous simulations have shown benefits in image quality, scatter, and dose objectives. We report on the first prototype implementation. This prototype is reduced in scale and speed and is integrated into a tabletop CT system with a smaller field of view (25 cm) and longer scan time (42 s) compared to a clinical system. Stainless steel wedges were machined and affixed to linear actuators, which were in turn held secure by a frame built using rapid prototyping technologies. The actuators were computer-controlled, with characteristic noise of about 100 microns. Simulations suggest that in a clinical setting, the impact of actuator noise could lead to artifacts of only 1 HU. Ring artifacts were minimized by careful design of the wedges. A water beam hardening correction was applied and the scan was collimated to reduce scatter. We scanned a 16 cm water cylinder phantom as well as an anthropomorphic pediatric phantom. The artifacts present in reconstructed images are comparable to artifacts normally seen with this tabletop system. Compared to a flat-field reference scan, increased detectability at reduced dose is shown and streaking is reduced. Artifacts are modest in our images and further refinement is possible. Issues of mechanical speed and stability in the challenging clinical CT environment will be addressed in a future design.

Understanding the Groundwater Hydrology of a Geographically-Isolated Prairie Fen: Implications for Conservation.

The sources of water and corresponding delivery mechanisms to groundwater-fed fens are not well understood due to the multi-scale geo-morphologic variability of the glacial landscape in which they occur. This lack of understanding limits the ability to effectively conserve these systems and the ecosystem services they provide, including biodiversity and water provisioning. While fens tend to occur in clusters around regional groundwater mounds, Ives Road Fen in southern Michigan is an example of a geographically-isolated fen. In this paper, we apply a multi-scale groundwater modeling approach to understand the groundwater sources for Ives Road fen. We apply Transition Probability geo-statistics on more than 3000 well logs from a state-wide water well database to characterize the complex geology using conditional simulations. We subsequently implement a 3-dimensional reverse particle tracking to delineate groundwater contribution areas to the fen. The fen receives water from multiple sources: local recharge, regional recharge from an extensive till plain, a regional groundwater mound, and a nearby pond. The regional sources deliver water through a tortuous, 3-dimensional "pipeline" consisting of a confined aquifer lying beneath an extensive clay layer. Water in this pipeline reaches the fen by upwelling through openings in the clay layer. The pipeline connects the geographically-isolated fen to the same regional mound that provides water to other fen clusters in southern Michigan. The major implication of these findings is that fen conservation efforts must be expanded from focusing on individual fens and their immediate surroundings, to studying the much larger and inter-connected hydrologic network that sustains multiple fens.