Peripheral communities of the Eastern Lau Spreading Center and Valu Fa Ridge: community composition,temporal change and comparison to near‐vent communities

Western Pacific hydrothermal vents will soon be subjected to deep‐sea mining and peripheral sites are considered the most practical targets. The limited information on community dynamics and temporal change in these communities makes it difficult to anticipate the impact of mining activities and recovery trajectories. We studied community composition of peripheral communities along a cline in hydrothermal chemistry on the Eastern Lau Spreading Center and Valu Fa Ridge (ELSC‐VFR) and also studied patterns of temporal change. Peripheral communities located in the northern vent fields of the ELSC‐VFR are significantly different from those in the southern vent fields. Higher abundances of zoanthids and anemones were found in northern peripheral sites and the symbiont‐containing mussel Bathymodiolus brevior, brisingid seastars and polynoids were only present in the northern peripheral sites. By contrast, certain faunal groups were seen only in the southern peripheral sites, such as lollipop sponges, pycnogonids and ophiuroids. Taxonomic richness of the peripheral communities was similar to that of active vent communities, due to the presence of non‐vent endemic species that balanced the absence of species found in areas of active venting. The communities present at waning active sites resemble those of peripheral sites, indicating that peripheral species can colonize previously active vent sites in addition to settling in the periphery of areas of venting. Growth and mortality were observed in a number of the normally slow‐growing cladorhizid stick sponges, indicating that these animals may exhibit life history strategies in the vicinity of vents that differ from those previously recorded. A novel facultative association between polynoids and anemones is proposed based on their correlated distributions.     

Stratal composition and stratigraphic organization of stratal elements in an ancient deep‐marine basin‐floor succession,Neoproterozoic Windermere Supergroup,British Columbia,Canada

Despite a globally growing seismic and outcrop analogue data set, the detailed (centimetre to decametre) internal stratal make up of deep‐marine basin‐floor ‘channelized‐lobe’ strata remain poorly known. An ancient analogue for modern, mixed‐sediment, passive margin, deep‐marine basin‐floor fans is the well‐preserved Neoproterozoic Upper and Middle Kaza groups in the southern Canadian Cordillera. This succession is a few kilometres thick and comprises six sedimentary facies representing deposition from different kinds of sediment‐gravity flows. Representative lateral and vertical assemblages of one or more of these facies comprise six stratal elements, including: isolated scours, avulsion splays, feeder channels, distributary channels, terminal splays, and distal and off‐axis fine‐grained turbidite units. The internal characteristics of the various stratal elements do not differ from more distal to more proximal settings, but the relative abundance of the various stratal elements does. The difference in relative abundance of stratal elements in the kilometre‐scale stratigraphy of the Kaza Group results in a systematic upward change in architecture. The systematic arrangement of the stratal elements within the interpreted larger bodies, or lobes, and then lobes within the basin‐floor fan, suggests a hierarchical organization. In this article a hierarchy is proposed that is based on avulsion but, also importantly, the location of avulsion. The proposed avulsion‐based hierarchical scheme will be a useful tool to bridge the scalar gap between outcrop and seismic studies by providing a single stratigraphic framework and terminology for basin‐floor stratal elements.     

The role of porous matrix in water flow regulation within a karst unsaturated zone: an integrated hydrogeophysical approach

Some portions of the porous rock matrix in the karst unsaturated zone (UZ) can contain large volumes of water and play a major role in water flow regulation. The essential results are presented of a local-scale study conducted in 2011 and 2012 above the Low Noise Underground Laboratory (LSBB – Laboratoire Souterrain à Bas Bruit) at Rustrel, southeastern France. Previous research revealed the geological structure and water-related features of the study site and illustrated the feasibility of specific hydrogeophysical measurements. In this study, the focus is on hydrodynamics at the seasonal and event timescales. Magnetic resonance sounding (MRS) measured a high water content (more than 10 %) in a large volume of rock. This large volume of water cannot be stored in fractures and conduits within the UZ. MRS was also used to measure the seasonal variation of water stored in the karst UZ. A process-based model was developed to simulate the effect of vegetation on groundwater recharge dynamics. In addition, electrical resistivity tomography (ERT) monitoring was used to assess preferential water pathways during a rain event. This study demonstrates the major influence of water flow within the porous rock matrix on the UZ hydrogeological functioning at both the local (LSBB) and regional (Fontaine de Vaucluse) scales. By taking into account the role of the porous matrix in water flow regulation, these findings may significantly improve karst groundwater hydrodynamic modelling, exploitation, and sustainable management.     

Antimony deposits in the Variscan Armorican belt,a link with mafic intrusives?

The Variscan Armorican belt was the World leading producer of antimony at the beginning of the twentieth century. However, geological controls on the deposits remain unconstrained. Here, we illustrate the field setting of mineralisations and perform a statistical analysis using Geographical Information System software, geophysical and geological data. The analysis shows that Sb deposits are spatially correlated with high‐density and magnetic zones. This may reflect the presence of mafic/ultramafic bodies at depth – a suggestion that is further supported by numerous occurrences of doleritic dykes throughout the region. Future antimony prospecting should focus on the high‐density and high‐magnetic zones which comprise about 18% of the Armorican massif. Links between Sb deposits and mafic intrusions are recognised elsewhere in the West European Variscan belt, emphasising that these may be key for antimony prospecting in deformation belts.     

The application of electrical conductivity as a tracer for hydrograph separation in urban catchments

Two‐component hydrograph separation was performed on 19 low‐to‐moderate intensity rainfall events in a 4·1‐km² urban watershed to infer the relative and absolute contribution of surface runoff (e.g. new water) to stormflow generation between 2001 and 2003. The electrical conductivity (EC) of water was used as a continuous and inexpensive tracer, with order of magnitude differences in precipitation (12–46 µS/cm) and pre‐event streamwater EC values (520–1297 µS/cm). While new water accounted for most of the increased discharge during storms (61–117%), the contribution of new water to total discharge during events was typically lower (18–78%) and negatively correlated with antecedent stream discharge (r² = 0·55, p < 0·01). The amount of new water was positively correlated with total rainfall (r² = 0·77), but hydrograph separation results suggest that less than half (9–46%) of the total rainfall on impervious surfaces is rapidly routed to the stream channel as new water. Comparison of hydrograph separation results using non‐conservative tracers (EC and Si) and a conservative isotopic tracer (δD) for two events showed similar results and highlighted the potential application of EC as an inexpensive, high frequency tracer for hydrograph separation studies in urban catchments. The use of a simple tracer‐based approach may help hydrologists and watershed managers to better understand impervious surface runoff, stormflow generation and non‐point‐source pollutant loading to urban streams. Copyright © 2007 John Wiley & Sons, Ltd.     

Investigation of hydraulics transport time scales within the Arvand River estuary,Iran

Transport time scales are key parameters for understanding the hydrodynamic and biochemical processes within estuaries. In this study, the flushing and residence times within the Arvand River estuary have been estimated using a two‐dimensional hydrodynamic model called CE‐QUAL‐W2. The model has been calibrated and verified by two different sets of field data and using the k‐ε vertical eddy diffusivity scheme. Flushing time has been estimated using different methods such as the tidal prism and fraction of freshwater methods. Moreover, residence times have been investigated using pulse residence time, estuarine residence time and remnant function approaches. The results have shown that different methods yield different time scales, and freshwater inflow has the greatest impact upon estimation of residence time, whereas tidal circulation hardly contributes to residence time at all. It has also been shown that the neap‐spring circulation and start phase of simulations have negligible effects on the Arvand's time scales. The investigation of bathymetry showed that two sills of the estuary tend to significantly increase residence time. Understanding the applicability of these time scales and their estimation approaches helps us to evaluate the water quality management of estuaries. Copyright © 2013 John Wiley & Sons, Ltd.     

Surface water and groundwater interactions in an extensively mined watershed,upper Schuylkill River,Pennsylvania, USA

Streams crossing underground coal mines may lose flow, whereas abandoned mine drainage (AMD) restores flow downstream. During 2005–2012, discharge from the Pine Knot Mine Tunnel, the largest AMD source in the upper Schuylkill River Basin, had near‐neutral pH and elevated concentrations of iron, manganese and sulphate. Discharge from the tunnel responded rapidly to recharge but exhibited a prolonged recession compared with nearby streams, consistent with rapid infiltration of surface water and slow release of groundwater from the mine complex. Dissolved iron was attenuated downstream by oxidation and precipitation, whereas dissolved CO₂ degassed and pH increased. During high flow conditions, the AMD and downstream waters exhibited decreased pH, iron and sulphate with increased acidity that were modelled by mixing net‐alkaline AMD with recharge or run‐off having low ionic strength and low pH. Attenuation of dissolved iron within the river was least effective during high flow conditions because of decreased transport time coupled with inhibitory effects of low pH on oxidation kinetics. A numerical model of groundwater flow was calibrated by using groundwater levels in the Pine Knot Mine and discharge data for the Pine Knot Mine Tunnel and West Branch Schuylkill River during a snowmelt event in January 2012. Although the calibrated model indicated substantial recharge to the mine complex took place away from streams, simulation of rapid changes in mine pool level and tunnel discharge during a high flow event in May 2012 required a source of direct recharge to the Pine Knot Mine. Such recharge produced small changes in mine pool level and rapid changes in tunnel flow rate because of extensive unsaturated storage capacity and high transmissivity within the mine complex. Thus, elimination of stream leakage could have a small effect on the annual discharge from the tunnel, but a large effect on peak discharge and associated water quality downstream. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.