Volcanic tremor of the 2010 Eyjafjallajökull eruption

Summary Volcanic eruptions in Iceland generally start with an increase in tremor levels. These signals do not have clear onset, like many earthquakes. As the character of the tremor signal is variable from one volcano to another, locating the source of the tremor signal may require different techniques for different volcanoes. Continuous volcanic tremor varied considerably during the course of the Eyjafjallajökull summit eruption, April 14th to May 22nd 2010, and was clearly associated with changes in eruptive style. The tremor frequencies ranged between 0.5 and 10 Hz, with increased vigour during an effusive and explosive phase, in comparison with purely explosive phases. Higher-frequency tremor bursts early in the eruption were caused by processes at the eruption site. Location of the tremor using a method based on differential phase information extracted from inter-station correlograms showed the tremor to be stable near the eruption vent, through time, for signals between 0.5 Hz and 2 Hz. Analyses of power variations of the vertical component of the tremor with distance from the eruption site are consistent with tremor waveform content being dominated by surface waves in the 0.5-2 Hz frequency range. The tremor source depth was argued to be shallow, less than about 1 km. The attenuation quality factor (Q) was found to be on the order of Q = 10-20 for paths in the area around Eyjafjallajökull and Q = 20-50 for paths outside the volcano. The pattern of radiated wave energy from the tremor source varied with time, defining ten different epochs during the eruption. Thus the tremor-source radiation did not remain isotropic, which needs to be considered when locating tremor based on amplitude, i.e. azimuthally variable source radiation.

A Modified Distributed CN-VSA Method for Mapping of the Seasonally Variable Source Areas

Many watershed models employ the Soil Conservation Service Curve Number (SCS-CN) approach for runoff simulation based on soil and land use information. These models implicitly assume that runoff is generated by the Hortonian process and; therefore, cannot correctly account for the effects of topography, variable source area (VSA) and/or soil moisture distribution in a watershed. This paper presents a new distributed CN-VSA method that is based on the SCS-CN approach to estimate runoff amount and uses the topographic wetness index (TWI) to distribute the runoff-generating areas within the watershed spatially. The size of the saturated-watershed areas and their spatial locations are simulated by assuming an average annual value of potential maximum retention. However, the literature indicates significant seasonal variation in potential maximum retention which can considerably effect water balance and amount of nonpoint source pollution. This paper focuses on developing a modified distributed CN-VSA method that accounts for the seasonal changes in the potential maximum retention. The results indicate that the modified distributed CN-VSA approach is better than distributed CN-VSA to simulate runoff amount and spatial distribution of runoff-generating areas. Overall, the study results are significant for improved understanding of hydrological response of watershed where seasonal factors describe the potential maximum retention, and, thus, saturation excess runoff generation in the watershed.

Employing Legacy Road Salt and Soil Electrical Conductivity as Tracers to Unlock Glyphosate Transport Processes in a Variable Source Area

<p>Glyphosate is the most widely used herbicide active ingredient in the world, with 1.35 Tg used globally in 2017. Despite a strong affinity for binding to soil and rapid microbial degradation, in recent studies glyphosate has been detected in agricultural runoff at significant concentrations. This unexplained phenomenon necessitates further study into the mechanism of glyphosate transport from agricultural fields. This study was an investigation into the internal hydrology at a 4.9 ha agricultural catchment and the hydrological processes driving glyphosate transport at this site. Chloride is introduced to this standalone watershed via a point source of sodium chloride road de-icer salt at the top edge of the catchment. The goal of this project was to employ chloride as a tracer to unlock how water moves in the catchment. Since 2015, we have been undertaking annual extensive field sampling campaigns to monitor runoff for glyphosate at an outlet weir. In this project, we used archived samples from the 2018, 2019 and 2020 field campaigns and analyzed over 700 samples for electrical conductivity, over 400 samples for chloride and over 500 samples for glyphosate. During storms, chloride concentration and electrical conductivity decreased as the baseflow component carrying dissolved ions was diluted by the fast response overland flow. During the peak flow of a storm, chloride makes up a consistent fraction of electrical conductivity as the entire catchment contributes to flow at the outlet. We also found that the ratio of glyphosate concentration to electrical conductivity increased linearly with flow rate. The rate of increase (ie., the slope of glyphosate to conductivity ratio versus flow rate) decreases between sequential storms as glyphosate adsorbs and microbially degrades, and from this we extrapolated an empirical degradation half-life of less than 10 days. Cumulatively, the observations of chloride and electrical conductivity suggest that the catchment behaves as a series of connected reservoirs, each with a slow-moving subsurface component and a fast-response overland component. By exploiting the existence of a road salt chloride tracer and soil electrical conductivity in a variable source area, we were able to unlock the hydrological processes at play in areas where surface runoff is generated.</p>

Integrating Daily CO2 Concentrations in SWAT-VSA to Examine Climate Change Impacts on Hydrology in a Karst Watershed

HighlightsWe used SWAT-VSA to assess the effects of climate change with rising CO2 on the water balance of a karst basin.For future climate, SWAT-VSA with rising CO2 yielded 7.1% less ET and 6.3% more runoff than standard SWAT-VSA.Rising CO2 also affected variable source areas, with greater ET declines and runoff increases in the wettest soils.Findings suggest CO2 effects on water balance should be included in future climate change studies with SWAT-VSA.Abstract. Characterizing the effects of climate change on hydrology is important to watershed management. In this study, we used SWAT-VSA to examine the effects of climate change and increasing atmospheric CO2 (CO2) on the water balance of Spring Creek watershed, a mixed land-use karst basin in the Upper Chesapeake Bay watershed. First, we modified the stomatal conductance and leaf area index (LAI) routines of SWAT-VSA’s Penman-Monteith evapotranspiration (ET) procedure and enabled the model to accept daily CO2 data. Using downscaled climate projections from nine global climate models (GCMs), we then compared water balance estimations from baseline SWAT-VSA against two modified versions of SWAT-VSA. One SWAT-VSA version integrated daily CO2 levels (SWAT-VSA_CO2), while another version added flexible stomatal conductance and LAI routines (SWAT-VSA_CO2+Plant) to the dynamic CO2 capacity. Under current climate (1985-2015), the three SWAT-VSA models produced generally similar water balance estimations, with 51% of precipitation lost to ET and the remainder converted to runoff (10%), lateral flow (9%), and percolate (30%). For future climate (2020-2065), water balance simulations diverged between baseline SWAT-VSA and the two modified SWAT-VSA models with CO2. Notably, variable stomatal conductance and LAI routines produced no detectable effects beyond that of CO2. For the 2020-2065 period, baseline SWAT-VSA projected ET increases of 0.7 mm year-1, while SWAT-VSA models with CO2 suggested that annual ET could decline by approximately -0.4 mm year-1 over the same period. As a result, the two CO2-based SWAT-VSA models predicted streamflow increases of almost 1.6 mm year-1 over the 2020-2065 period, which were roughly double the streamflow increases projected by baseline SWAT-VSA. In general, SWAT-VSA models with CO2 effects produced 22.4% more streamflow in 2045-2065 than the SWAT-VSA model without CO2. Results also showed that adding daily CO2 to SWAT-VSA reduced ET in wetter parts of Spring Creek watershed, leading to greater runoff losses from variable source areas compared to baseline SWAT-VSA. Findings from the study highlight the importance of considering increasing atmospheric CO2 concentrations in water balance simulations with SWAT-VSA in order to gain a fuller appreciation of the hydrologic uncertainties with climate change. Keywords: Carbon dioxide, Climate change, Hydrologic model, Water balance, Watershed.

Local Food as a Tool of Tourism Development in Regions

This study aims to identify the importance of local food for both the demand and supply sides and to show how local food can be bounded with tourism development in the region. The data presented are based on secondary and primary research. Secondary research includes the literature review and content analysis of documents. The qualitative research included a questionnaire survey among guests of the gastronomic establishments and entrepreneurs. Partial least squares variant of linear discriminant analysis (PLS-LDA) and partial least squares (PLS) as an alternative to standard multivariate methods were used to show the gastronomic establishments guests' and entrepreneurs' opinions on local seasonal food and beverages. The opinions are moreover related to the economically driven interest of guests and entrepreneurs. Based on the typical random variable source, data were gathered from three Czech regions covering the scope of this study. The significant disputes between opinions on local food and beverages are directly applicable in practice, including individual items.