Life, the universe and everything, with GAIA

Great things are expected of the GAIA Observatory, currently expected to launch in 2011. Gerry Gilmore explains how it will provide accurate measurements that will help us understand the formation of the Milky Way and the distribution of dark matter.
The GAIA Observatory, ESA's Cornerstone 6 mission, addresses the origin and evolution of our galaxy, and a host of other scientific challenges. GAIA will provide unprecedented positional and radial velocity measurements with the accuracies needed to produce a stereoscopic and kinematic census of about one billion stars in our galaxy and throughout the Local Group, about 1% of the galactic stellar population. Combined with astrophysical information for each star, provided by on-board multicolour photometry, these data will have the precision and depth necessary to address the three key questions which underlie the GAIA science case: l when did the stars in the Milky Way form? l when and how was the Milky Way assembled? l what is the distribution of dark matter in our galaxy? The accurate stellar data acquired for this purpose will also have an enormous impact on all areas of stellar astrophysics, including luminosity calibrations, structural studies, and the cosmic distance scale. Additional scientific products include detection and orbital classification of tens of thousands of extrasolar planetary systems, a comprehensive survey of objects ranging from huge numbers of minor bodies in our solar system, including near-Earth objects, through galaxies in the nearby universe, to some 500 000 distant quasars. GAIA will also provide several stringent new tests of general relativity and cosmology.     

Sources of organic matter in surface sediments of the Louisiana Continental margin: Effects of major depositional/transport pathways and Hurricane Ivan

Lignin and pigment biomarkers were analyzed in surface sediments of the Louisiana Continental margin (LCM) to distinguish differences in the degradative state of sedimentary organic matter along and between two major depositional pathways (along shore and offshore to the Mississippi Canyon) from Southwest (SW) Pass in July 2003. Barataria Bay, an inter-distributary estuary, was also assessed as a potential source of terrestrial organic matter to the LCM. Sediment signatures taken along the same pathways after Hurricane Ivan (October 2004) were compared with the pre-Ivan signature to elucidate carbon dynamics after major hurricane events. Density fractions were investigated at key stages across the LCM. Mississippi Canyon sediments are a depocenter for labile and refractory organic matter derived from river and previously deposited shelf sediments. Barataria Bay material may be a contributing source of sedimentary organic matter in shallow shelf areas bordering the bay and is thus potentially important in carbon cycling in sediments of these shallow areas; however, our results show that organic matter inputs from the bay were likely rapidly decomposed and/or diluted. Hurricane Ivan mobilized sedimentary organic carbon (SOC) offshore and homogenized terrestrial sediment parameters and gradients. As observed through pigment concentrations sediments tended to equilibrate to a more steady-state condition within months of the disturbance. Insights from density fractions show that selective degradation and aggregation/flocculation processes were also very important processes during cross-shelf transport. Zooplankton grazing, largely on diatoms and other algae, was a shelf wide phenomenon, however, grazing products dominated the marine-derived SOC in margin sediments west of the birdsfoot delta indicated by the abundance of steryl chlorin esters (SCEs).     

Fishery management as a governance network: Examples from the Gulf of Maine and the potential for communication network analysis research in fisheries

It has been suggested that the fisheries management process with multiple, informed stakeholders and socio-economic, political, and scientific complexity can be considered a governance network. This exploratory study applied communication network analysis (CNA) measures and methods to assess two cases of US federal fishery management in the Northwest Atlantic—Atlantic herring and sea scallop. Through questionnaires and interviews, CNA maps were constructed and quantitative measures of network structure and function (density, weighted average path length) and centrality measures for individual network members (degree, betweenness) were derived using InFlow software. The results show that fishery governance networks are horizontally and vertically integrated across levels of government and public–private–nonprofit sectors. The findings validated existing understanding of fisheries management as a contested, competitive management context among stakeholders, and provided new insights about the effectiveness of information sharing across the network and the critical role of bridgers connecting disparate subgroups. Fisheries management can be conceptualized and analyzed as governance networks, and the paper discusses additional research questions, refinements needed for application of the research methods, and ramifications for managers (e.g., can resource managers manage networks).     

Development of an electronic seepage chamber for extended use in a river

Seepage chambers have been used to characterize the flux of water across the water-sediment interface in a variety of settings. In this work, an electronic seepage chamber was developed specifically for long-term use in a large river where hydraulic gradient reversals occur frequently with river-stage variations. A bidirectional electronic flowmeter coupled with a seepage chamber was used to measure temporal changes in the magnitude and direction of water flux across the water-sediment interface over an 8-week period. The specific discharge measured from the seepage chamber compared favorably with measurements of vertical hydraulic gradient and previous specific discharge calculations. This, as well as other supporting data, demonstrates the effectiveness of the electronic seepage chamber to accurately quantify water flux in two directions over a multimonth period in this setting. The ability to conduct multimonth measurements of water flux at a subhourly frequency in a river system is a critical capability for a seepage chamber in a system where hydraulic gradients change on a daily and seasonal basis.     

Extreme precipitation drives groundwater recharge: the Northern High Plains Aquifer,central United States, 1950–2010

Future extreme precipitation (EP, daily rainfall amount over certain thresholds) is projected to increase with global climate change; however, its effect on groundwater recharge has not been fully explored. This study specifically investigates the spatiotemporal dynamics of groundwater recharge and the effects of extreme precipitation (daily rainfall amount over the 95th percentile, which is tagged by ranking the percentiles in each season for a base period) on groundwater recharge from 1950 to 2010 over the Northern High Plains (NHP) Aquifer using the Soil Water Balance Model. The results show that groundwater recharge significantly (p < 0.05) increased in the eastern NHP from 1950 to 2010, where the highest annual average groundwater recharge occurs compared to the central and the western NHP. In the eastern NHP, 45.1% of the annual precipitation fell as EP, which contributed 56.8% of the annual total groundwater recharge. In the western NHP, 30.9% of the annual precipitation fell as extreme precipitation, which contributed 62.5% of the annual total groundwater recharge. In addition, recharge by extreme precipitation mainly occurred in late spring and early summer, before the maximum evapotranspiration rate, which usually occurs in mid‐summer until late fall. A dry site in the western NHP and a wet site in the eastern NHP were analysed to indicate how recharge responds to EP with different precipitation regimes. The maximum daily recharge at the dry site exceeded the wet site when there was EP. When precipitation fell as non‐extreme rainfall, most recharge was less than 5 mm at both the dry and wet sites, and the maximum recharge at the dry site became lower than the wet site. This study shows that extreme precipitation plays a significant role in determining groundwater recharge. © 2016 The Authors Hydrological Processes Published by John Wiley & Sons Ltd.     

A Tube Seepage Meter for In Situ Measurement of Seepage Rate and Groundwater Sampling

We designed and evaluated a “tube seepage meter” for point measurements of vertical seepage rates (q), collecting groundwater samples, and estimating vertical hydraulic conductivity (K) in streambeds. Laboratory testing in artificial streambeds show that seepage rates from the tube seepage meter agreed well with expected values. Results of field testing of the tube seepage meter in a sandy‐bottom stream with a mean seepage rate of about 0.5 m/day agreed well with Darcian estimates (vertical hydraulic conductivity times head gradient) when averaged over multiple measurements. The uncertainties in q and K were evaluated with a Monte Carlo method and are typically 20% and 60%, respectively, for field data, and depend on the magnitude of the hydraulic gradient and the uncertainty in head measurements. The primary advantages of the tube seepage meter are its small footprint, concurrent and colocated assessments of q and K, and that it can also be configured as a self‐purging groundwater‐sampling device.