Microwave and Soft X-ray Study of Solar Active Region Evolution

We have studied the properties and evolution of several active regions observed at multiple wavelengths over a period of about 10 days. We have used simultaneous microwave (1.5 and 17 GHz) and soft X-ray measurements made with the Very Large Array (VLA), the Nobeyama Radio Heliograph (NRH) and the Soft X-ray Telescope (SXT) on board the Yohkoh spacecraft, as well as photospheric magnetograms from KPNO. This is the first detailed comparison between observations at radio wavelengths differing by one order of magnitude. We have performed morphological and quantitative studies of active region properties by making inter-comparison between observations at different wavelengths and tracking the day-to-day variations. We have found good general agreement between the 1.5 and 17 GHz radio maps and the soft X-rays images. The 17 GHz emission is consistent with thermal bremsstrahlung (free-free) emission from electrons at coronal temperatures plus a small component coming from plasma at lower temperatures. We did not find any systematic limb darkening of the microwave emission from active regions. We discuss the difference between the observed microwave brightness temperature and the one expected from X-ray data and in terms of emission of a low temperature plasma at the transition region level. We found a coronal optical thickness of 10^-3 and 1 for radiation at 17 and 1.5 GHz, respectively. We have also estimated the typical coronal values of emission measure ( 5 × 10²⁸ cm^-5), electron temperature ( 4.5 × 10⁶6 K) and density ( 1.2 × 10⁹ cm₃). Assuming that the emission mechanism at 17 GHz is due to thermal free-free emission, we calculated the magnetic field in the source region using the observed degree of polarization. From the degree of polarization, we infer that the 17 GHz radiation is confined to the low-lying inner loop system of the active region. We also extrapolated the photospheric magnetic field distribution to the coronal level and found it to be in good agreement with the coronal magnetic field distribution obtained from microwave observations.     

Long term spectral variability in the soft gamma-ray repeater SGR 1900+14

We present a systematic analysis of all the BeppoSAX data of SGR1900+14. The observations spanning five years show that the source was brighter than usual on two occasions: ～20 days after the August 1998 giant flare and during the 10⁵?s long X-ray afterglow following the April 2001 intermediate flare. In the latter case, we explore the possibility of describing the observed short term spectral evolution only with a change of the temperature of the blackbody component. In the only BeppoSAX observation performed before the giant flare, the spectrum of the SGR1900+14 persistent emission was significantly harder and detected also above 10 keV with the PDS instrument. In the last BeppoSAX observation (April 2002) the flux was at least a factor 1.2 below the historical level, suggesting that the source was entering a quiescent period.     

A World-Wide Net of Solar Radio Spectrometers: e-CALLISTO

Radio spectrometers of the CALLISTO type to observe solar flares have been distributed to nine locations around the globe. The instruments observe automatically, their data is collected every day via internet and stored in a central data base. A public web-interface exists through which data can be browsed and retrieved. The nine instruments form a network called e-CALLISTO. It is still growing in the number of stations, as redundancy is desirable for full 24 h coverage of the solar radio emission in the meter and low decimeter band. The e-CALLISTO system has already proven to be a valuable new tool for monitoring solar activity and for space weather research.     

Susceptibility to gravitational processes due to land cover change in the Río Chiquito-Barranca del Muerto subbasin(Pico De Orizaba Volcano,México)

Land cover change can lead to slope instability by accelerating erosive processes associated with agriculture, forestry, and infrastructure. The Rio Chiquito-Barranca del Muerto subbasin has experienced an increase in land cover change due to government programs and the establishment of agricultural and urban areas. The aim of this study was to provide a model to map the susceptibility to gravitational processes along sites where anthropogenic land cover change has occurred. The method was based on the stratification of the subbasin according to landforms and cartographic variables. These variables were used in a multi-criteria assessment to assign weights according to their contribution to the onset of new gravitational processes. Those weights were used to create a susceptibility map based on a weighted linear sum. The accuracy of the resulting map was validated in an error matrix with a random stratified design based on susceptibility classes per landform. The results produced a map of areas with susceptibility to gravitational processes due to land cover change; this susceptibility is very high in the undifferentiated pyroclastic slope and limestone mountain, where it derives not only from anthropogenic effects on natural vegetation cover, but also from steep slopes, weathered materials, low apparent density, high erosivity, and previous gravitational processes. The results support other studies that concluded that loss of vegetation is a triggering factor in the formation of gravitational processes, but also show that excessive reforestation can increase gravitational processes.     

Effect of macrofaunal bioturbation on bacterial distribution in marine sandy sediments, with special reference to sulphur-oxidising bacteria

We have studied the impact of the bioturbating macrofauna, in particular the lugworm Arenicola marina and the bivalve Cerastoderma edule, on abundances and distribution patterns of total bacteria and of bacteria of selected functional groups in sandy intertidal sediments. The selected groups comprised the colourless sulphur-oxidising bacteria and the anoxygenic phototrophic bacteria, which are expected to occupy small zones at the oxygen–sulphide interface in stable (non-bioturbated) sediments. The presence of a wooden wreck buried in the sediment at 10 cm depth within a large area of intertidal sand flat colonised by lugworms provided a unique opportunity to confront field observations with laboratory simulations. The site with the wooden wreck, which was used as control site, was devoid of both A. marina and C. edule, while the composition of the rest of the zoobenthic community was rather similar to that of the surrounding area. In the field, the density of total bacteria was approximately one order of magnitude higher in the control site than in the natural (bioturbated) site. This can be explained by the higher contents of silt and clay particles (higher surface-area/volume ratio) and higher total organic-carbon contents found at the control site. It appears that the presence of macrofauna affects sedimentation processes, which indirectly influence bacterial dynamics. Samples from the control site have been incubated in the laboratory with A. marina and C. edule added (bioturbated core), while an unamended core served as a control. The laboratory experiments contrasted with the field observations, because it was found that total bacteria were actually higher in the deeper layers of the bioturbated core. Moreover, the populations were more homogeneous (less stratified) and colourless sulphur bacteria were on average less numerous in the bioturbated core. In general, laboratory incubations resulted in a decrease of total bacteria with a concomitant increase of colourless and phototrophic sulphur-oxidising bacteria and thus in modifications of the bacterial community structure. Hence, our results demonstrate that care must be taken in extrapolating results from laboratory experiments (e.g. mesocosm research) to field situations.     

Spring distribution of dissolved organic matter in a system encompassing the Northeast Water Polynya: Implications for early-season sources and sinks

This study addresses sources and diagenetic state of early-season dissolved organic matter (DOM) in the Northeast Water Polynya (NEWP) area northeast of Greenland from distributions of humic substance fluorescence (HSfl), dissolved organic carbon (DOC), and dissolved organic nitrogen (DON) in the water column inside and outside the NEWP area. The water masses of the polynya area had acquired their spring/summer temperature–salinity characteristics at the time of sampling, and also had individual, different DOM signatures. DOC concentrations were variable within and among water masses in the polynya area, indicating patchy local sources and sinks of DOC. PySW and polynya intermediate water (PyIW) had higher average DON concentrations and average lower C:N ratios than polynya bottom water (PyBW), indicating a larger fraction of fresh DOM in PySW and PyIW than in PyBW. Ice-covered, polynya area surface waters (PySW) had higher DOC concentrations (113±14 μM, n=68) than surface water (SW) outside the polynya area (96±18 μM, n=6). The DOM C:N ratios in a low-salinity, ice-melt subgroup of PySW samples indicate labile material, and these low-salinity surface waters appeared to have a local DOC and DON source. In contrast, HSfl was significantly lower inside than outside the NEWP area. Despite the lower HSfl values within the NEWP area, the PySW values were high when compared to open-ocean water. There were no local terrestrial sources for HSfl to the NEWP area and the East Greenland Current is therefore proposed as a likely source of allochtonous HSfl. When HSfl was used as a conservative tracer, up to 70% of the water in PySW and PyIW was found to be derived from SW, which contains a high fraction of water from the East Greenland Current. Similarly, a mixing model based on HSfl indicated that 80% of early-season DOC and 90–100% of early-season DON in PySW and PyIW were derived from SW, indicating a potentially high fraction of terrestrially-derived, relatively refractory DOM in the early-season NEWP area.     

Use of Remote Imagery to Analyse Changes in Morphology and Longitudinal Large Wood Distribution in the Blanco River After the 2008 Chaitén Volcanic Eruption,Southern Chile

The 2008 Chaitén volcanic eruption generated significant changes in the channel morphology and large wood (LW) abundance along the fluvial corridor of the Blanco River, southern Chile. Comparisons of remote sensing images from the pre‐eruption (year 2005) and post‐eruption (years 2009 and 2012) conditions showed that in a 10.2 km long study segment the Blanco River widened 3.5 times from 2005 to 2009, and that the maximum enlargement was nine times the original width. Changes in channel width were lower between the years 2012 and 2009. The sinuosity and braiding indexes also changed between 2005 and 2009. After the eruption the channel sinuosity was higher and specific river reaches developed a braided pattern, but by 2012 the channel was recovering pre‐eruption characteristics. Huge quantities of LW were introduced to the study segment; individual LW per km of channel length were 1.6 and 74.3 in 2005 and 2009, respectively, and more than 30 log jams km^?1 were observed in the year 2009. Between 2009 and 2012 the quantity of LW was very similar. Statistically significant relationships were found between the number of log jams and channel sinuosity and between the number of pieces of large wood with sinuosity and channel width. Wood was highly dynamic between 2009 and 2012: 78% of individual pieces and 48% of log jams identified in the 2009 image had moved by 2012. Finally the supervised classification of imagery associated with ArcMap tools was tested to identify large wood.     

Changes in Coastal Benthic Algae Succession Trajectories and Assemblages Under Contrasting Nutrient and Grazer Loads

Eutrophication plays a crucial role in coastal systems, driving changes in the composition and abundance of flora and fauna with consequent effects for the entire ecosystem. Sensitive to nutrient levels, micro- and macroalgal blooms serve as valuable indicators of eutrophication. The San Antonio Bay (Northern Argentinean Patagonia, 40° 43′ S, 64° 56′ W) provides an appropriate system to study in situ eutrophication processes on coastal communities. In a multi-scale approach, using two different kind of settlement substrates (micro: polyethylene terephthalate, and macro: ceramic), the present study followed benthic algal dynamics over one year, distinguishing changes in natural succession and seasonality. Strong differences were found in the biofilm assemblages after three days, marked by tube dwelling diatoms and Cocconeis spp. under high nutrient-grazer conditions and needle like diatoms (e.g. Nitzschia spp., Tabularia spp.) under lower nutrient-grazer loads. The succession continued by the colonization of macroalgae, with a higher recruitment rate in the nutrient and grazer rich environment with a concomitant higher diversity. Our results show that under higher nutrient-grazer conditions natural benthic succession not only differs in trajectory but in its final taxa composition promoting higher biodiversity and biomass accumulation. In addition, taxa specific substrate preferences interfere with the observed eutrophication pattern, suggesting substrate dependant interrelations between the bloom forming taxa. These findings provide evidence that nutrient enrichment can not only affect an established assemblage but also affect the early succession stages, changing the succession trajectory and thus the final assemblage.     

Conservation and management of ecological systems in a changing California

Climate change in California is altering habitat conditions for many species and exacerbating stress from other factors such as alien invasive species, pollution, and habitat fragmentation. However, the current legal and planning framework for species protection does not explicitly take climate change into account. The regulatory framework is primarily reactive, kicking in only after species’ health is gravely threatened. Neither federal nor state regulations require forward-looking, climate-sensitive species or ecosystem protection plans. Habitat planning is poorly funded and often piecemeal. In this context, the wrong lands may be protected, with development allowed to occur in areas that would be most beneficial for species conservation in the future. A more forward-looking approach to habitat conservation is needed, one based on a statewide strategy to identify and protect critical habitat areas, including corridors to enable species migration. The approach would also require development of assessment indicators and assistance strategies not dependent on current habitat structure, and a governance structure to implement regular, periodic updates of management plans in relation to agreed-upon performance indicators. Such a strategy should integrate habitat conservation planning with other state and regional plans and objectives, such as for transportation infrastructure, urban development, and mitigation of climate change.