scholarly journals A new data set for estimating organic carbon storage to 3 m depth in soils of the northern circumpolar permafrost region

2013 ◽  
Vol 5 (2) ◽  
pp. 393-402 ◽  
Author(s):  
G. Hugelius ◽  
J. G. Bockheim ◽  
P. Camill ◽  
B. Elberling ◽  
G. Grosse ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Mineral Soil ◽  
Geographical Information ◽  
Gis Mapping ◽  
Permafrost Region ◽  
Data Sets ◽  
Depth Range ◽  
Data Set ◽  
Spatial Coverage ◽  
Gis Data

Abstract. High-latitude terrestrial ecosystems are key components in the global carbon cycle. The Northern Circumpolar Soil Carbon Database (NCSCD) was developed to quantify stocks of soil organic carbon (SOC) in the northern circumpolar permafrost region (a total area of 18.7 × 106 km2). The NCSCD is a geographical information system (GIS) data set that has been constructed using harmonized regional soil classification maps together with pedon data from the northern permafrost region. Previously, the NCSCD has been used to calculate SOC storage to the reference depths 0–30 cm and 0–100 cm (based on 1778 pedons). It has been shown that soils of the northern circumpolar permafrost region also contain significant quantities of SOC in the 100–300 cm depth range, but there has been no circumpolar compilation of pedon data to quantify this deeper SOC pool and there are no spatially distributed estimates of SOC storage below 100 cm depth in this region. Here we describe the synthesis of an updated pedon data set for SOC storage (kg C m−2) in deep soils of the northern circumpolar permafrost regions, with separate data sets for the 100–200 cm (524 pedons) and 200–300 cm (356 pedons) depth ranges. These pedons have been grouped into the North American and Eurasian sectors and the mean SOC storage for different soil taxa (subdivided into Gelisols including the sub-orders Histels, Turbels, Orthels, permafrost-free Histosols, and permafrost-free mineral soil orders) has been added to the updated NCSCDv2. The updated version of the data set is freely available online in different file formats and spatial resolutions that enable spatially explicit applications in GIS mapping and terrestrial ecosystem models. While this newly compiled data set adds to our knowledge of SOC in the 100–300 cm depth range, it also reveals that large uncertainties remain. Identified data gaps include spatial coverage of deep (> 100 cm) pedons in many regions as well as the spatial extent of areas with thin soils overlying bedrock and the quantity and distribution of massive ground ice. An open access data-portal for the pedon data set and the GIS-data sets is available online at http://bolin.su.se/data/ncscd/. The NCSCDv2 data set has a digital object identifier (doi:10.5879/ECDS/00000002).

scholarly journals Short communication: a new dataset for estimating organic carbon storage to 3 m depth in soils of the northern circumpolar permafrost region

2013 ◽  
Vol 6 (1) ◽  
pp. 73-93 ◽  
Author(s):  
G. Hugelius ◽  
C. Tarnocai ◽  
J. G. Bockheim ◽  
P. Camill ◽  
B. Elberling ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Geographical Information Systems ◽  
Mineral Soil ◽  
Terrestrial Ecosystem ◽  
Terrestrial Ecosystems ◽  
Geographical Information ◽  
Permafrost Region ◽  
Depth Range ◽  
C Cycle ◽  
Permafrost Regions

Abstract. High latitude terrestrial ecosystems are key components in the global carbon (C) cycle. The Northern Circumpolar Soil Carbon Database (NCSCD) was developed to quantify stocks of soil organic carbon (SOC) in the northern circumpolar permafrost region (18.7 × 106 km2). The NCSCD is a digital Geographical Information systems (GIS) database compiled from harmonized regional soil classification maps, in which data on soil coverage has been linked to pedon data from the northern permafrost regions. Previously, the NCSCD has been used to calculate SOC content (SOCC) and mass (SOCM) to the reference depths 0–30 cm and 0–100 cm (based on 1778 pedons). It has been shown that soils of the northern circumpolar permafrost region also contain significant quantities of SOC in the 100–300 cm depth range, but there has been no circumpolar compilation of pedon data to quantify this SOC pool and there are no spatially distributed estimates of SOC storage below 100 cm depth in this region. Here we describe the synthesis of an updated pedon dataset for SOCC in deep soils of the northern circumpolar permafrost regions, with separate datasets for the 100–200 cm (524 pedons) and 200–300 cm (356 pedons) depth ranges. These pedons have been grouped into the American and Eurasian sectors and the mean SOCC for different soil taxa (subdivided into Histels, Turbels, Orthels, Histosols, and permafrost-free mineral soil taxa) has been added to the updated NCSCDv2. The updated version of the database is freely available online in several different file formats and spatial resolutions that enable spatially explicit usage in e.g. GIS and/or terrestrial ecosystem models. The potential applications and limitations of the NCSCDv2 in spatial analyses are briefly discussed. An open access data-portal for all the described GIS-datasets is available online at: http://dev1.geo.su.se/bbcc/dev/v3/ncscd/download.php. The NCSCDv2 database has the doi:10.5879/ECDS/00000002.

scholarly journals Biodegradability of dissolved organic carbon in permafrost soils and aquatic systems: a meta-analysis

2015 ◽  
Vol 12 (23) ◽  
pp. 6915-6930 ◽  
Author(s):  
J. E. Vonk ◽  
S. E. Tank ◽  
P. J. Mann ◽  
R. G. M. Spencer ◽  
C. C. Treat ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Aquatic Systems ◽  
The Arctic ◽  
Permafrost Region ◽  
Soil Leachate ◽  
Discontinuous Permafrost ◽  
Spatial Coverage ◽  
Continuous Permafrost ◽  
Permafrost Regions

Abstract. As Arctic regions warm and frozen soils thaw, the large organic carbon pool stored in permafrost becomes increasingly vulnerable to decomposition or transport. The transfer of newly mobilized carbon to the atmosphere and its potential influence upon climate change will largely depend on the degradability of carbon delivered to aquatic ecosystems. Dissolved organic carbon (DOC) is a key regulator of aquatic metabolism, yet knowledge of the mechanistic controls on DOC biodegradability is currently poor due to a scarcity of long-term data sets, limited spatial coverage of available data, and methodological diversity. Here, we performed parallel biodegradable DOC (BDOC) experiments at six Arctic sites (16 experiments) using a standardized incubation protocol to examine the effect of methodological differences commonly used in the literature. We also synthesized results from 14 aquatic and soil leachate BDOC studies from across the circum-arctic permafrost region to examine pan-arctic trends in BDOC. An increasing extent of permafrost across the landscape resulted in higher DOC losses in both soil and aquatic systems. We hypothesize that the unique composition of (yedoma) permafrost-derived DOC combined with limited prior microbial processing due to low soil temperature and relatively short flow path lengths and transport times, contributed to a higher overall terrestrial and freshwater DOC loss. Additionally, we found that the fraction of BDOC decreased moving down the fluvial network in continuous permafrost regions, i.e. from streams to large rivers, suggesting that highly biodegradable DOC is lost in headwater streams. We also observed a seasonal (January–December) decrease in BDOC in large streams and rivers, but saw no apparent change in smaller streams or soil leachates. We attribute this seasonal change to a combination of factors including shifts in carbon source, changing DOC residence time related to increasing thaw-depth, increasing water temperatures later in the summer, as well as decreasing hydrologic connectivity between soils and surface water as the thaw season progresses. Our results suggest that future climate warming-induced shifts of continuous permafrost into discontinuous permafrost regions could affect the degradation potential of thaw-released DOC, the amount of BDOC, as well as its variability throughout the Arctic summer. We lastly recommend a standardized BDOC protocol to facilitate the comparison of future work and improve our knowledge of processing and transport of DOC in a changing Arctic.

Land Map Image Dataset: Ground-Truth And Classification Using Visual And Textural Features

2014 ◽  
Vol 19 (4) ◽  
pp. 37-55 ◽  
Author(s):  
Sayan Mandal ◽  
Samit Biswas ◽  
Amit Kumar Das ◽  
Bhabatosh Chanda
Keyword(s):  
Ground Truth ◽  
Document Image ◽  
Geographical Information ◽  
Data Sets ◽  
Data Set ◽  
Handwritten Documents ◽  
Form Processing ◽  
Public Data ◽  
Active Research ◽  
The Right

Abstract Research on document image analysis is actively pursued in the last few decades and services like OCR, vectorization of drawings/graphics and various types of form processing are very common. Handwritten documents, old historical documents and documents captured through camera are now being the subjects of active research. However, another very important type of paper document, namely the map document image processing research suffers due to the inherent complexities of the map document and also for nonavailability of benchmark public data-sets. This paper presents a new data-set, namely, the Land Map Image Database (LMIDb) that consists of a variety of land maps images (446 images at present and growing; scanned at 200/300 dpi in TIF format) and the corresponding ground-truth. Using semiautomatic tools non-text part of the images are deleted and the text-only ground-truth is also kept in the database. This paper also presents a classification strategy for map images using which the maps in the database are automatically classified into Political (Po), Physical (Ph), Resource (R) and Topographic (T) maps. The automatic classification of maps help indexing of the images in LMIDb for archival and easy retrieval of the right maps to get the appropriate geographical information. Classification accuracy is also tested on the proposed data-set and the result is encouraging.

scholarly journals The SPARC water vapour assessment II: comparison of stratospheric and lower mesospheric water vapour time series observed from satellites

2018 ◽  
Vol 11 (7) ◽  
pp. 4435-4463 ◽  
Author(s):  
Farahnaz Khosrawi ◽  
Stefan Lossow ◽  
Gabriele P. Stiller ◽  
Karen H. Rosenlof ◽  
Joachim Urban ◽  
...  
Keyword(s):  
Time Series ◽  
Water Vapour ◽  
Data Sets ◽  
Data Set ◽  
Spatial Coverage ◽  
Modelling Studies ◽  
The Difference ◽  
The Tropics ◽  
The Antarctic ◽  
Satellite Instruments

Abstract. Time series of stratospheric and lower mesospheric water vapour using 33 data sets from 15 different satellite instruments were compared in the framework of the second SPARC (Stratosphere-troposphere Processes And their Role in Climate) water vapour assessment (WAVAS-II). This comparison aimed to provide a comprehensive overview of the typical uncertainties in the observational database that can be considered in the future in observational and modelling studies, e.g addressing stratospheric water vapour trends. The time series comparisons are presented for the three latitude bands, the Antarctic (80∘–70∘ S), the tropics (15∘ S–15∘ N) and the Northern Hemisphere mid-latitudes (50∘–60∘ N) at four different altitudes (0.1, 3, 10 and 80 hPa) covering the stratosphere and lower mesosphere. The combined temporal coverage of observations from the 15 satellite instruments allowed the consideration of the time period 1986–2014. In addition to the qualitative comparison of the time series, the agreement of the data sets is assessed quantitatively in the form of the spread (i.e. the difference between the maximum and minimum volume mixing ratios among the data sets), the (Pearson) correlation coefficient and the drift (i.e. linear changes of the difference between time series over time). Generally, good agreement between the time series was found in the middle stratosphere while larger differences were found in the lower mesosphere and near the tropopause. Concerning the latitude bands, the largest differences were found in the Antarctic while the best agreement was found for the tropics. From our assessment we find that most data sets can be considered in future observational and modelling studies, e.g. addressing stratospheric and lower mesospheric water vapour variability and trends, if data set specific characteristics (e.g. drift) and restrictions (e.g. temporal and spatial coverage) are taken into account.

scholarly journals Total water vapour columns derived from Sentinel 5p using the AMC-DOAS method

2021 ◽  
Author(s):  
Tobias Küchler ◽  
Stefan Noël ◽  
Heinrich Bovensmann ◽  
John Philip Burrows ◽  
Thomas Wagner ◽  
...  
Keyword(s):  
Water Vapour ◽  
Optical Absorption Spectroscopy ◽  
Data Sets ◽  
Independent Data ◽  
Total Water ◽  
Max Planck ◽  
Ozone Monitoring Instrument ◽  
Data Set ◽  
Medium Range Weather Forecast ◽  
Spatial Coverage

Abstract. Water vapour is the most abundant natural greenhouse gas in the Earth's atmosphere and global data sets are required for meteorological applications and climate research. The Tropospheric Ozone Monitoring Instrument (TROPOMI) onboard Sentinel 5 Precursor (S5P) launched on 13 October 2017 has a very high spatial resolution of around 5 km and a daily global coverage. Currently, there is no operational total water vapour product for S5P measurements. Here, we present first results of a new scientific total column water vapour (TCWV) product for S5P using the so-called Air Mass Corrected Differential Optical Absorption Spectroscopy (AMC-DOAS) scheme. This method analyses spectral data between 688 and 700 nm and has already been successfully applied to measurements from the Global Monitoring Experiment (GOME) on ERS-2, the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) on Envisat and GOME-2 on MetOp. The adaptation of the AMC-DOAS method to S5P data especially includes an additional post-processing procedure to correct the influences of surface albedo, cloud height and cloud fraction. The quality of the new S5P AMC-DOAS water vapour product is assessed by comparisons with data from GOME-2 on MetOp-B retrieved also with the AMC-DOAS algorithm and with four completely independent data sets, namely re-analysis data from the European Centre for Medium range Weather Forecast (ECMWF ERA5), data obtained by the Special Sensor Microwave Imager and Sounder (SSMIS) flown on the Defense Meteorological Satellite Program (DMSP) platform 16 and two scientific S5P TCWV products derived from TROPOMI measurements. Both are recently published TCWV products for S5P provided by the Max Planck Institute for Chemistry (MPIC) in Mainz and the Netherlands Institute for Space Research (SRON), Utrecht. The SRON TCWV is limited to clear sky scenes over land. These comparisons reveal a good agreement between the various data sets but also some systematic deviations between all of them. On average, the derived offset between AMC-DOAS S5P TCWV and AMC-DOAS GOME-2B TCWV is negative (around −1.5 kg m−2) over land and positive over ocean surfaces (more than 1.5 kg m−2). In contrast, SSMIS TCWV is on average lower than AMC-DOAS S5P TCWV by about 3 kg m−2. TCWV from ERA5 and S5P AMC-DOAS TCWV comparison shows spatial differences over both land and water surface. Over land there are systematical spatial structures with enhanced discrepancies between S5P AMC-DOAS TCWV and ERA5 TCWV in tropical regions. Over sea, S5P AMC-DOAS TCWV is slightly lower than ERA5 TCWV by around 2 kg m−2. The S5P AMC-DOAS TCWV and S5P TCWV from MPIC agree on average within 1 kg m−2 over both land and ocean. TCWV from SRON shows differences to AMC-DOAS S5P TCWV of around 1.2 kg m−2. All of these deviations are in line with the accuracy of these products and with the typical range of deviations of 5 kg m−2 obtained when comparing different TCWV data sets. The AMC-DOAS TCWV product for S5P provides therefore a valuable new and independent data set for atmospheric applications which also shows a better spatial coverage than the other S5P TCWV products.

scholarly journals Biodegradability of dissolved organic carbon in permafrost soils and waterways: a meta-analysis

2015 ◽  
Vol 12 (11) ◽  
pp. 8353-8393 ◽  
Author(s):  
J. E. Vonk ◽  
S. E. Tank ◽  
P. J. Mann ◽  
R. G. M. Spencer ◽  
C. C. Treat ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Aquatic Ecosystems ◽  
The Arctic ◽  
Permafrost Region ◽  
Soil Leachate ◽  
Discontinuous Permafrost ◽  
Spatial Coverage ◽  
Continuous Permafrost ◽  
Permafrost Regions

Abstract. As Arctic regions warm, the large organic carbon pool stored in permafrost becomes increasingly vulnerable to thaw and decomposition. The transfer of newly mobilized carbon to the atmosphere and its potential influence upon climate change will largely depend on the reactivity and subsequent fate of carbon delivered to aquatic ecosystems. Dissolved organic carbon (DOC) is a key regulator of aquatic metabolism and its biodegradability will determine the extent and rate of carbon release from aquatic ecosystems to the atmosphere. Knowledge of the mechanistic controls on DOC biodegradability is however currently poor due to a scarcity of long-term data sets, limited spatial coverage of available data, and methodological diversity. Here, we performed parallel biodegradable DOC (BDOC) experiments at six Arctic sites (16 experiments) using a standardized incubation protocol to examine the effect of methodological differences used as common practice in the literature. We further synthesized results from 14 aquatic and soil leachate BDOC studies from across the circum–arctic permafrost region to examine pan-Arctic trends in BDOC. An increasing extent of permafrost across the landscape resulted in higher BDOC losses in both soil and aquatic systems. We hypothesize that the unique composition of permafrost-derived DOC combined with limited prior microbial processing due to low soil temperature and relatively shorter flow path lengths and transport times, resulted in higher overall terrestrial and freshwater BDOC loss. Additionally, we found that the fraction of BDOC decreased moving down the fluvial network in continuous permafrost regions, i.e. from streams to large rivers, suggesting that highly biodegradable DOC is lost in headwater streams. We also observed a seasonal (January–December) decrease in BDOC losses in large streams and rivers, but no apparent change in smaller streams and soil leachates. We attribute this seasonal change to a combination of factors including shifts in carbon source, changing DOC residence time related to increasing thaw-depth, increasing water temperatures later in the summer, as well as decreasing hydrologic connectivity between soils and surface water as the seasons progress. Our results suggest that future, climate warming-induced shifts of continuous permafrost into discontinuous permafrost regions could affect the degradation potential of thaw-released DOC as well as its variability throughout the Arctic summer. We lastly present a recommended standardized BDOC protocol to facilitate the comparison of future work and improve our knowledge of processing and transport of DOC in a changing Arctic.

scholarly journals Integrating GIS and statistical approaches to enhance allocation of highway patrol resources

2019 ◽  
Vol 22 (1) ◽  
pp. 84-95
Author(s):  
Mahdi Rezapour ◽  
Er Yue ◽  
Khaled Ksaibati
Keyword(s):  
Traffic Safety ◽  
Geographical Information Systems ◽  
Geographical Information ◽  
Gis Mapping ◽  
Crash Data ◽  
Gis Applications ◽  
Spatial Coverage ◽  
The Usa ◽  
Highway Patrol ◽  
The Right

Large truck crashes undermine the contribution of trucks to the U.S. economy due to the economic costs of the crashes. Wyoming has the highest truck crash rate and the lowest budget contribution for traffic enforcement in the USA. Because of the state’s intensive truck corridors, the Wyoming Highway Patrol (WHP) might not be able to use their resources efficiently. Previous studies have indicated that WHP performed better when they allocate their resources efficiently at the right locations and towards the right enforcements. This study used 4-year historical crash and enforcement data along Interstate 80 (I-80), which has the highest truck-related crash rate in Wyoming. Crash data were filtered to include truck crashes only. However, both truck and no-truck enforcements were included in the data because both could be at fault in truck crashes. This study used two approaches to help state policy-makers improve traffic safety on I-80. First, a statistical method was used to identify geometric variables contributing to allocated enforcement and truck crashes. Second, truck crashes and related enforcements were visually assessed using Geographical Information Systems (GIS) mapping. Crash data were disaggregated into the main driver actions of no improper driving, following too closely, improper lane change and driving too fast for the conditions. These driver actions accounted for more than 70% of all truck crashes on I-80. Related enforcements were also identified and disaggregated by driver actions. Disaggregated enforcements and crashes were visualized along the I-80 corridor using GIS maps to see if WHP allocated their resources efficiently. Cluster index, enforcement spatial coverage and mean density are some of the parameters used for the analyses. This study aimed to contribute to research on police effectiveness in reducing truck crashes, police innovation and the use of GIS applications in enforcement. This methodology can be used by other agencies to better allocate resources to improve traffic safety in most efficient ways.

scholarly journals Hydrogeophysical data integration through Bayesian Sequential Simulation with log-linear pooling

2020 ◽  
Vol 221 (3) ◽  
pp. 2184-2200
Author(s):  
Raphaël Nussbaumer ◽  
Grégoire Mariethoz ◽  
Erwan Gloaguen ◽  
Klaus Holliger
Keyword(s):  
Data Sets ◽  
Sequential Simulation ◽  
Data Set ◽  
Resistivity Tomography ◽  
Simulation Process ◽  
Spatial Coverage ◽  
Linear Pooling ◽  
Log Linear ◽  
Primary Variable ◽  
Secondary Variable

SUMMARY Bayesian sequential simulation (BSS) is a geostastistical technique, which uses a secondary variable to guide the stochastic simulation of a primary variable. As such, BSS has proven significant promise for the integration of disparate hydrogeophysical data sets characterized by vastly differing spatial coverage and resolution of the primary and secondary variables. An inherent limitation of BSS is its tendency to underestimate the variance of the simulated fields due to the smooth nature of the secondary variable. Indeed, in its classical form, the method is unable to account for this smoothness because it assumes independence of the secondary variable with regard to neighbouring values of the primary variable. To overcome this limitation, we have modified the Bayesian updating with a log-linear pooling approach, which allows us to account for the inherent interdependence between the primary and the secondary variables by adding exponential weights to the corresponding probabilities. The proposed method is tested on a pertinent synthetic hydrogeophysical data set consisting of surface-based electrical resistivity tomography (ERT) data and local borehole measurements of the hydraulic conductivity. Our results show that, compared to classical BSS, the proposed log-linear pooling method using equal constant weights for the primary and secondary variables enhances the reproduction of the spatial statistics of the stochastic realizations, while maintaining a faithful correspondence with the geophysical data. Significant additional improvements can be achieved by optimizing the choice of these constant weights. We also explore a dynamic adaptation of the weights during the course of the simulation process, which provides valuable insights into the optimal parametrization of the proposed log-linear pooling approach. The results corroborate the strategy of selectively emphasizing the probabilities of the secondary and primary variables at the very beginning and for the remainder of the simulation process, respectively.

scholarly journals Conservation area networks for the Indian region: Systematic methods and future prospects

1970 ◽  
Vol 4 (6) ◽  
pp. 27-40 ◽  
Author(s):  
Sahotra Sarkar ◽  
Michael Mayfield ◽  
Susan Cameron ◽  
Trevon Fuller ◽  
Justin Garson
Keyword(s):  
Geographical Information Systems ◽  
Vascular Plant ◽  
Regional Scale ◽  
Geographical Information ◽  
Data Sets ◽  
Conservation Area ◽  
Data Set ◽  
Entire Study ◽  
Eastern Himalayas ◽  
Entire Study Area

We present a framework for systematic conservation planning for biodiversity with an emphasis on the Indian context. We illustrate the use of this framework by analyzing two data sets consisting of environmental and physical features that serve as surrogates for biodiversity. The aim was to select networks of potential conservation areas (such as reserves and national parks) which include representative fractions of these environmental features or surrogates. The first data set includes the entire subcontinent while the second is limited to the Eastern Himalayas. The environmental surrogates used for the two analyses result in the selection of conservation area networks with different properties. Tentative results indicate that these surrogates are successful in selecting most areas known from fieldwork to have high biodiversity content such as the broadleaf and subalpine conifer forests of the Eastern Himalayas. However, the place-prioritization algorithm also selected areas not known to be high in biodiversity content such as the coast of the Arabian Sea. Areas selected to satisfy a 10% target of representation for the complete surrogate set provide representation for 46.03% of the ecoregions in the entire study area. The algorithm selected a disproportionately small number of cells in the Western Ghats, a hotspot of vascular plant endemism. At the same target level, restricted surrogate sets represent 33.33% of the ecoregions in the entire study area and 46.67% of the ecoregions in the Eastern Himalayas. Finally, any more sophisticated use of such systematic methods will require the assembly of Geographical Information Systems (GIS)-based biogeographical data sets on a regional scale. Key words: Indian biodiversity, Eastern Himalayas, complementarity, area prioritization, reserve selection, surrogacy Himalayan Journal of Sciences Vol.4(6) 2007 p.27-40

Application and evaluation of electromagnetic methods for imaging saltwater intrusion in coastal aquifers: Seaside Groundwater Basin, California

Geophysics ◽  
2013 ◽  
Vol 78 (2) ◽  
pp. B77-B88 ◽  
Author(s):  
Vanessa Nenna ◽  
Daan Herckenrath ◽  
Rosemary Knight ◽  
Nick Odlum ◽  
Darcy McPhee
Keyword(s):  
Coastal Aquifers ◽  
Saltwater Intrusion ◽  
Groundwater Resources ◽  
Management Strategies ◽  
Geophysical Methods ◽  
Unconfined Aquifer ◽  
Data Sets ◽  
Data Set ◽  
Aquifer System ◽  
Spatial Coverage

Developing effective resource management strategies to limit or prevent saltwater intrusion as a result of increasing demands on coastal groundwater resources requires reliable information about the geologic structure and hydrologic state of an aquifer system. A common strategy for acquiring such information is to drill sentinel wells near the coast to monitor changes in water salinity with time. However, installation and operation of sentinel wells is costly and provides limited spatial coverage. We studied the use of noninvasive electromagnetic (EM) geophysical methods as an alternative to installation of monitoring wells for characterizing coastal aquifers. We tested the feasibility of using EM methods at a field site in northern California to identify the potential for and/or presence of hydraulic communication between an unconfined saline aquifer and a confined freshwater aquifer. One-dimensional soundings were acquired using the time-domain electromagnetic (TDEM) and audiomagnetotelluric (AMT) methods. We compared inverted resistivity models of TDEM and AMT data obtained from several inversion algorithms. We found that multiple interpretations of inverted models can be supported by the same data set, but that there were consistencies between all data sets and inversion algorithms. Results from all collected data sets suggested that EM methods are capable of reliably identifying a saltwater-saturated zone in the unconfined aquifer. Geophysical data indicated that the impermeable clay between aquifers may be more continuous than is supported by current models.

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