Evolution of forest precipitation water storage measurement methods

Precipitation intercepted by forests plays a major role in more than one‐fourth of the global land area's hydrologic cycle. Direct in situ measurement of intercepted precipitation is challenging, and thus, it is typically indirectly estimated through comparing precipitation under forest cover and in the open. We discuss/compare measurement methods for forest precipitation interception beyond classical budgeting and then recommend future directions for improving water storage estimation. Comparison of techniques shows that methods submerging tree components produce the largest water storage capacity values. Whole‐tree lysimeters have been used with great success at quantifying water storage for the integrated system yet are unable to separate trunk versus canopy storage. Remote sensing, particularly signal attenuation, may permit this separation. Mechanical displacement methods show great promise and variety of techniques: pulley/spring system, branch strain sensors, trunk compression sensors and photography. Relating wind sway to water storage also shows great promise with negligible environmental disruption yet is currently at the proof‐of‐concept stage. Suggested future directions focus on development of common features regarding all discussed methods: (i) measurement uncertainties or processes beyond interception influencing the observed signal, (ii) scaling approaches to move from single tree components to the single‐tree and forest scales and (iii) temporal scaling to estimate the relevance of single‐interception components over longer timescales. Through addressing these research needs, we hope the scientific community can develop an ‘integrated’ monitoring plan incorporating multiple measurement techniques to characterize forest‐scale water storage dynamics while simultaneously investigating underlying (smaller‐scale) components driving those dynamics across the spectrum of precipitation and forest conditions. Copyright © 2014 John Wiley & Sons, Ltd.     

Timing and duration of hydrological transitions in Arctic polygonal ground from stable isotopes

Land surface models and Earth system models that include Arctic landscapes must capture the abrupt hydrological transitions that occur during the annual thaw and deepening of the active layer. In this work, stable water isotopes (δ²H and δ¹⁸O) are used to appraise hydrologically significant transitions during annual landscape thaw at the Barrow Environmental Observatory (Utqiaġvik, Alaska). These hydrologically significant periods are then linked to annual shifts in the landscape energy balance, deduced from meteorological data and described by the microclimatic periods: Winter, Pre-Melt, Melt, Post-Melt, Summer, and Freeze-Up. The tight coupling of the microclimatic periods with the hydrological transitions supports the use of microclimatic periods as a means of linking polygonal surface water hydrology to meteorological datasets, which provides a mechanism for improving the representation of polygonal surface water hydrology in process-based models. Rayleigh process reconstruction of the isotopic changes revealed that 19% of winter precipitation was lost to sublimation prior to melting and that 23% of surface water was lost to evaporation during the first 10 days post-melt. This agrees with evaporation rates reported in a separate study using an eddy covariance flux tower located nearby. An additional 17% was lost to evaporation during the next 33 days. Stable water isotopes are also used to identify the dominant sources of surface water to various hydrogeomorphological features prevalent in polygonal terrain (a lake, a low centre polygon centre, troughs within the rims of low centre polygons, flat centre polygon troughs, a high centre polygon trough, and drainages). Hydrogeomorphologies that retained significant old water or acted as snow drifts are isotopically distinct during the Melt Period and therefore are easily distinguished. Biogeochemical changes related to the annual thaw are also reported and coupled to the hydrological transitions, which provides insight into the sources and sinks of these ions to and from the landscape.     

Eustatic control of late Quaternary sea-level change in the Arabian/Persian Gulf

Accurate sea-level reconstruction is critical in understanding the drivers of coastal evolution. Inliers of shallow marine limestone and aeolianite are exposed as zeugen (carbonate-capped erosional remnants) on the southern coast of the Arabian/Persian Gulf. These have generally been accepted as evidence of a eustatically driven, last-interglacial relative sea-level highstand preceded by a penultimate glacial-age lowstand. Instead, recent optically stimulated luminescence (OSL) dating suggests a last glacial age for these deposits, requiring > 100 m of uplift since the last glacial maximum in order to keep pace with eustatic sea-level rise and implying the need for a wholesale revision of tectonic, stratigraphic and sea-level histories of the Gulf. These two hypotheses have radically different implications for regional neotectonics and land–sea distribution histories. Here we test these hypotheses using OSL dating of the zeugen formations. These new ages are remarkably consistent with earlier interpretations of the formations being last interglacial or older in age, showing that tectonic movements are negligible and eustatic sea-level variations are responsible for local sea-level changes in the Gulf. The cause of the large age differences between recent studies is unclear, although it appears related to large differences in the measured accumulated dose in different OSL samples.     

Mantle electrical conductivity profile of Niger delta region

The mantle electrical conductivity-depth profile of the Niger delta region in Nigeria has been determined using solar quiet day ionospheric current (Sq). The magnetometer data obtained in 2010 from geomagnetic stations installed in Lagos by magnetic dataset (MAGDAS) in 2008 and data from magnetometers installed in some parts of Niger delta by Center for Basic Space Science, University of Nigeria, Nsukka, were employed in this study. Gauss spherical harmonic analysis (SHA) method was used to separate the internal and external field contributions to Sq current system. The result depicted that the conductivity profile rose steadily from about 0.032 S/m at a depth of 89 km to 0.041 S/m at 100 km and 0.09 S/m at 221 km. This high conductivity region agreed with the global seismic low velocity region, the asthenosphere. The conductivity profile continued increasing downward until it got to 0.157 S/m at a depth of about 373 km (close to the base of upper mantle), 0.201 S/m at 784 km and reached 0.243 S/m at a depth of 1179 km at the lower mantle.     

Effects of the 2004 hurricanes on the fish assemblages in two proximate southwest Florida estuaries: Change in the context of interannual variability

We examined interannual differences in fish assemblage structure in Tampa Bay and Charlotte Harbor, Florida, from 1996 to 2005 to reveal the extent of hurricane-induced changes in relation to multiannual variability for five different assemblages in each estuary: small-bodied fishes (<generally 80-mm standard length) along river shorelines, in river channels, along bay shorelines, and on the bay shelf (<1.5-m water depth); and large-bodied fishes (>generally 100-mm standard length) along bay shorelines. Fish assemblages tended to differ, between estuaries, as did interannual variability in assemblage structure. In the lower portions of tributary rivers to Tampa Bay, the small-bodied shoreline fish assemblage during August 2004 to July 2005, i.e., during and after the multiple hurricanes, was different from assemblages of August to July in previous years. This may have been a result of physical displacement of fish or suboptimal salinities caused by increased freshwater inflow. The small-bodied shoreline fish assemblage in Charlotte Harbor also differed between prehurricane and hurricane periods, possibly because damage to vegetated shorelines affected fish survival through a decrease in feeding and refuge habitats. In the remaining habitats, fish assemblage structure from August 2004 to July 2005 were within the range of variability exhibited over the 9-yr study period. There were several unusual fish assemblages that appeared to be attributable to drought conditions (1996, 1999–2000), suggesting that other major environmental perturbations may be as important as hurricanes in influencing assemblage structure. We conclude that although the 2004 hurricane season affected some of the fish assemblages of Tampa Bay and charlotte Harbor, these assemblages generally appeared quite resilient to natural environmental perturbations from a decadal perspective.     

The cool wake around 4C 34.16 as seen by XMM–Newton

We present XMM–Newton observations of the wake–radio galaxy system 4C 34.16, which shows a cool and dense wake trailing behind the host galaxy of 4C 34.16. A comparison with numerical simulations is enlightening, as they demonstrate that the wake is produced mainly by ram pressure stripping during the galactic motion through the surrounding cluster. The mass of the wake is a substantial fraction of the mass of the X-ray halo of an elliptical galaxy. This observational fact supports a wake formation scenario similar to that recently demonstrated numerically by Acreman et al.: the host galaxy of 4C 34.16 has fallen into its cluster, and is currently crossing its central regions. A substantial fraction of its X-ray halo has been stripped by ram pressure, and remains behind to form the galaxy wake.