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Author: Nicholas Reed de Sieyes
Publisher: Stanford University
ISBN:
Category :
Languages : en
Pages : 186
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Book Description
is a numerical investigation of groundwater flow at the land-sea interface forced by precipitation and evapotranspiration typical of the Mediterranean climate of coastal California. A numerical groundwater model was developed using the variable density groundwater flow code SEAWAT-2000 to examine the influence of seasonally variable recharge conditions typical of coastal California on the magnitude and timing of fresh submarine groundwater discharge from a generic coastal aquifer with a constant head (non-tidal) ocean boundary. Model dimensions and hydrogeologic characteristics were chosen based on a combination of observations from field studies at Stinson Beach, California, and published numerical investigations of coastal groundwater flow. Average monthly recharge was calculated from historical precipitation records and potential evapotranspiration rates calculated from climatological observations made near the field site. Calculated recharge was approximately sinusoidal across the year, with positive recharge rates dominated by precipitation during the rainy winter and negative recharge rates dominated by evapotranspiration during the hot, precipitation-free summer. Rates of fresh discharge from the model aquifer to the ocean exhibited similar temporal characteristics for two modeled scenarios, a first including a constant head fresh landward boundary condition and a second including a constant flux fresh landward boundary condition. Discharge in both models peaked in January during the period of maximum precipitation and recharge, and declined until reaching a minimum in September, two months after the minimum recharge period in July. Minimum simulated discharge rates for two simulated scenarios were 17% and 18% lower in September than the maximum simulated discharges in winter. Monthly mean discharge from Lagunitas Creek, a creek near Stinson Beach, reached maximum and minimum values in February and September, respectively. The exponential decline in creek discharge was fast compared to the decline in modeled SGD, however, suggesting that fresh SGD and associated nutrient fluxes may play a particularly important role in coastal ecosystems in early summer when surface water discharge has nearly reached a minimum but discharge of substantial quantities of fresh groundwater is still substantial. The final research chapter "Nitrogen, fecal indicator bacteria, and coliphage attenuation and flux from a septic leach field to the coastal ocean" describes a two-year field study to measure the flux and attenuation of nitrogen, fecal indicator bacteria, and bacteriophage in groundwater adjacent to a large coastal septic system in Central California. The study was carried out at Stinson Beach Park, Golden Gate National Recreation Area, sixteen kilometers northwest of the San Francisco Golden Gate Bridge. Long-term measurements of septic effluent quality and volumetric discharge to the leach field, synoptic DC resistivity profiling of the saltwater/freshwater interface, continuous measurements of hydraulic head in the coastal aquifer, and the installation and subsequent monitoring of a dense array of multi-level monitoring wells adjacent to the leach field for chemical and microbiological constituents were carried out. Our results indicate a nitrogen- and inorganic carbon-rich plume of septic effluent flowing from the leach field through the beach to the subterranean estuary, or the mixing zone of fresh and saline groundwaters. Attenuation of E. coli and coliphage was complete within the vadose zone and the first few meters of transport. Enterococci were detected throughout the well network during one sampling event during which no attenuation was observed, and no attenuation of total nitrogen was observed along the flowpath during the experiment. Median estimates of total nitrogen fluxing toward the ocean downgradient from the leach field ranged from 1.6 to 70.6 moles day-1, depending on season and transect location. Except for
Author: Nicholas Reed de Sieyes
Publisher: Stanford University
ISBN:
Category :
Languages : en
Pages : 186
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Book Description
is a numerical investigation of groundwater flow at the land-sea interface forced by precipitation and evapotranspiration typical of the Mediterranean climate of coastal California. A numerical groundwater model was developed using the variable density groundwater flow code SEAWAT-2000 to examine the influence of seasonally variable recharge conditions typical of coastal California on the magnitude and timing of fresh submarine groundwater discharge from a generic coastal aquifer with a constant head (non-tidal) ocean boundary. Model dimensions and hydrogeologic characteristics were chosen based on a combination of observations from field studies at Stinson Beach, California, and published numerical investigations of coastal groundwater flow. Average monthly recharge was calculated from historical precipitation records and potential evapotranspiration rates calculated from climatological observations made near the field site. Calculated recharge was approximately sinusoidal across the year, with positive recharge rates dominated by precipitation during the rainy winter and negative recharge rates dominated by evapotranspiration during the hot, precipitation-free summer. Rates of fresh discharge from the model aquifer to the ocean exhibited similar temporal characteristics for two modeled scenarios, a first including a constant head fresh landward boundary condition and a second including a constant flux fresh landward boundary condition. Discharge in both models peaked in January during the period of maximum precipitation and recharge, and declined until reaching a minimum in September, two months after the minimum recharge period in July. Minimum simulated discharge rates for two simulated scenarios were 17% and 18% lower in September than the maximum simulated discharges in winter. Monthly mean discharge from Lagunitas Creek, a creek near Stinson Beach, reached maximum and minimum values in February and September, respectively. The exponential decline in creek discharge was fast compared to the decline in modeled SGD, however, suggesting that fresh SGD and associated nutrient fluxes may play a particularly important role in coastal ecosystems in early summer when surface water discharge has nearly reached a minimum but discharge of substantial quantities of fresh groundwater is still substantial. The final research chapter "Nitrogen, fecal indicator bacteria, and coliphage attenuation and flux from a septic leach field to the coastal ocean" describes a two-year field study to measure the flux and attenuation of nitrogen, fecal indicator bacteria, and bacteriophage in groundwater adjacent to a large coastal septic system in Central California. The study was carried out at Stinson Beach Park, Golden Gate National Recreation Area, sixteen kilometers northwest of the San Francisco Golden Gate Bridge. Long-term measurements of septic effluent quality and volumetric discharge to the leach field, synoptic DC resistivity profiling of the saltwater/freshwater interface, continuous measurements of hydraulic head in the coastal aquifer, and the installation and subsequent monitoring of a dense array of multi-level monitoring wells adjacent to the leach field for chemical and microbiological constituents were carried out. Our results indicate a nitrogen- and inorganic carbon-rich plume of septic effluent flowing from the leach field through the beach to the subterranean estuary, or the mixing zone of fresh and saline groundwaters. Attenuation of E. coli and coliphage was complete within the vadose zone and the first few meters of transport. Enterococci were detected throughout the well network during one sampling event during which no attenuation was observed, and no attenuation of total nitrogen was observed along the flowpath during the experiment. Median estimates of total nitrogen fluxing toward the ocean downgradient from the leach field ranged from 1.6 to 70.6 moles day-1, depending on season and transect location. Except for
Author: Nicholas Reed De Sieyes
Publisher:
ISBN:
Category :
Languages : en
Pages :
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The focus of this dissertation is submarine groundwater discharge (SGD), the direct flow of groundwater from the seabed to the sea, and onsite wastewater treatment systems in coastal California. The research focuses primarily on a single coastal community in central California, Stinson Beach, where conventional onsite treatment systems, or septic systems, are used exclusively for wastewater disposal. The overarching goal of the work has been to quantify the magnitude and timing of SGD at the site and to provide insight into how onsite wastewater treatment at Stinson Beach affects local groundwater quality and, via SGD, surface water quality, all with the broader goal of informing and guiding future development along the California coast. The dissertation includes four research chapters, each focused on one or more important aspects of the issue of SGD and coastal septic systems at Stinson Beach. The first research chapter entitled "Submarine discharge of nutrient-enriched fresh groundwater at Stinson Beach, California is enhanced during neap tides" describes a 14-day study investigating the influence of fortnightly spring-neap tidal variability on submarine discharge of fresh and saline groundwaters at the site. Fresh, shallow groundwater at the site was observed to contain high concentrations of nutrients including dissolved inorganic nitrogen, soluble reactive phosphate, and silicate, as well as human fecal bacteria. A groundwater-derived freshening and nutrification of the surf zone was observed at neap tide, and was followed by a 4-day increase in chlorophyll a concentrations in the surf zone. Analytical models and a fresh water budget in the surf zone were used to estimate the saline and fresh SGD at both neap and spring tides. Fresh SGD at the site was estimated at between 1.2 and 4.7 L min-1 m-1 shoreline during neap tides compared to 0.1 and 0.5 L min-1 m-1 during spring tides. This compares to saline SGD estimates of 15.9 and 22.0 L min-1 m-1 during neap and spring tides, respectively. Despite the smaller total discharge of groundwater during neap compared to spring tides, the larger fresh discharge component during neap tides raised surf zone silicate, DIN, and SRP by 14%, 35%, and 27%, respectively, relative to spring tides. The observed fortnightly 'pulse' of fresh groundwater-derived nutrients into the surf zone was consistent with seaward hydraulic gradients across the fresh part of the beach aquifer, which varied due to aquifer overheight, or the mounding of groundwater due to variable infiltration of salt water during tides, adjacent the beach face. Darcy-Dupuit estimates of seaward fresh groundwater flow in this area agreed well with the fresh discharge results of the mass balance.vvThe second research chapter of the dissertation entitled "Submarine groundwater discharge to a high-energy surf zone at Stinson Beach, California, estimated using radium isotopes" describes and compares results from a pair of two-week long experiments conducted in the dry season (July 2006) and wet season (March 2007) to examine tidal, wave-driven and seasonal variability of SGD at the site using natural radium tracers. Tide stage, tide range, breaker height and season each explained a significant degree of radium variability in the surf zone. A mass balance of excess radium in the surf zone was used to estimate SGD and associated nutrient fluxes during each season, confirming larger discharge rates during the wet season. Our results indicate median groundwater discharge rates of 6 to 8 L min-1 m-1 in July 2006 and 38 to 43 L min-1 m-1 in March 2007. SGD from 200 m of Stinson Beach in March 2007 was shown to contribute a flux of phosphate and dissolved inorganic nitrogen approximately equal to that associated with all local creeks and streams within 6 km of the study site at that time. The third research chapter "Fresh submarine groundwater discharge from a coastal aquifer forced by the Mediterranean climate of central California" is a numerical investigation of groundwater flow at the land-sea interface forced by precipitation and evapotranspiration typical of the Mediterranean climate of coastal California. A numerical groundwater model was developed using the variable density groundwater flow code SEAWAT-2000 to examine the influence of seasonally variable recharge conditions typical of coastal California on the magnitude and timing of fresh submarine groundwater discharge from a generic coastal aquifer with a constant head (non-tidal) ocean boundary. Model dimensions and hydrogeologic characteristics were chosen based on a combination of observations from field studies at Stinson Beach, California, and published numerical investigations of coastal groundwater flow. Average monthly recharge was calculated from historical precipitation records and potential evapotranspiration rates calculated from climatological observations made near the field site. Calculated recharge was approximately sinusoidal across the year, with positive recharge rates dominated by precipitation during the rainy winter and negative recharge rates dominated by evapotranspiration during the hot, precipitation-free summer. Rates of fresh discharge from the model aquifer to the ocean exhibited similar temporal characteristics for two modeled scenarios, a first including a constant head fresh landward boundary condition and a second including a constant flux fresh landward boundary condition. Discharge in both models peaked in January during the period of maximum precipitation and recharge, and declined until reaching a minimum in September, two months after the minimum recharge period in July. Minimum simulated discharge rates for two simulated scenarios were 17% and 18% lower in September than the maximum simulated discharges in winter. Monthly mean discharge from Lagunitas Creek, a creek near Stinson Beach, reached maximum and minimum values in February and September, respectively. The exponential decline in creek discharge was fast compared to the decline in modeled SGD, however, suggesting that fresh SGD and associated nutrient fluxes may play a particularly important role in coastal ecosystems in early summer when surface water discharge has nearly reached a minimum but discharge of substantial quantities of fresh groundwater is still substantial. The final research chapter "Nitrogen, fecal indicator bacteria, and coliphage attenuation and flux from a septic leach field to the coastal ocean" describes a two-year field study to measure the flux and attenuation of nitrogen, fecal indicator bacteria, and bacteriophage in groundwater adjacent to a large coastal septic system in Central California. The study was carried out at Stinson Beach Park, Golden Gate National Recreation Area, sixteen kilometers northwest of the San Francisco Golden Gate Bridge. Long-term measurements of septic effluent quality and volumetric discharge to the leach field, synoptic DC resistivity profiling of the saltwater/freshwater interface, continuous measurements of hydraulic head in the coastal aquifer, and the installation and subsequent monitoring of a dense array of multi-level monitoring wells adjacent to the leach field for chemical and microbiological constituents were carried out. Our results indicate a nitrogen- and inorganic carbon-rich plume of septic effluent flowing from the leach field through the beach to the subterranean estuary, or the mixing zone of fresh and saline groundwaters. Attenuation of E. coli and coliphage was complete within the vadose zone and the first few meters of transport. Enterococci were detected throughout the well network during one sampling event during which no attenuation was observed, and no attenuation of total nitrogen was observed along the flowpath during the experiment. Median estimates of total nitrogen fluxing toward the ocean downgradient from the leach field ranged from 1.6 to 70.6 moles day-1, depending on season and transect location. Except for enterococcus, the behavior of nitrogen and microbial pollutants in the field was consistent with results from laboratory experiments, which demonstrated low denitrification potential in slurry tests, but fast fecal indicator bacteria and virus attenuation rates in saturated column experiments. Comparisons of total nitrogen flux to the subterranean estuary in this study agree well with SGD-associated nutrient flux estimates from prior studies at the site, suggesting that septic systems at the site are a persistent source of nitrogen to the subterranean estuary and may at times also be a source of enterococci. Denitrification potentials measured at the site suggest a possible role for in-situ remediation strategies to optimize nutrient removal in the beach aquifer.
Author: Makoto Taniguchi
Publisher: Frontiers Media SA
ISBN: 2889665356
Category : Science
Languages : en
Pages : 158
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Author: Michael A. Mallin
Publisher: Elsevier Inc. Chapters
ISBN: 0128082836
Category : Science
Languages : en
Pages : 35
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Author:
Publisher:
ISBN: 9781339160320
Category :
Languages : en
Pages : 140
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Submarine groundwater discharge to oceans is an ever-increasing topic of study in the earth sciences due to the dynamic geochemical and biological effects it imposes on aquatic systems both by the chemical reactions it induces and the constituents it transports. Studies indicate groundwater discharge can represent a major source of nutrients, fecal indicator bacteria, caffeine, trace metals, and mercury to aquatic systems. In some systems, groundwater discharge can rival rivers and upwelling, as a source of nutrients. The implications of groundwater discharge include harmful algal blooms caused by nutrient loading and poor water quality caused by pollutants transported through groundwater discharge. Much research has been directed at quantifying the flux of groundwater and associated constituents through groundwater discharge using radium isotopes as geochemical tracers. Radium isotopes represent some of the most common geochemical proxies used to calculate groundwater discharge rates to lakes, oceans, and other water bodies. However well-established these tracers are in the scientific community, they are often used as a single proxy for groundwater discharge resulting in large errors due to natural variability and dependence on residence time, and these errors compound through the calculations. Large errors in the estimates of the volume flux of groundwater discharge lead to large errors in constituent fluxes through groundwater discharge, which diminishes the usefulness of such efforts. Additionally most SGD-focused studies stop at calculating the SGD and associated constituent fluxes, and pondering the impacts of the constituents on the marine ecosystem, with out directly measuring the impact on the system through other methods. The focus of my thesis is to integrate methods of calculating SGD fluxes based on multi-radium isotope measurements with mixing models, bioassay incubation experiments, and water isotopes to better understand the impacts of SGD on marine systems. First (Chapter 1) I will integrate a multi-radium isotope method to calculate SGD fluxes with water isotopes to better understand the hydrology of the systems to understand the governing processes and importance of SGD as a conduit of methane to the North Pacific and Artic Oceans. Then (Chapter 2) I will combine a single radium isotope SGD flux model with a bioassay incubation experiment to determine the ability of SGD to impact phytoplankton ecology in Monterey Bay, California. Last (Chapter 3) I will combine a multi-radium isotope and nutrient flux mixing model with a multi-radium isotope SGD flux model to determine the importance of SGD as a nutrient source compared to sub-thermocline water and river water in Monterey Bay, California.
Author: Wai-Yan Cherry Chu
Publisher:
ISBN: 9781361243756
Category :
Languages : en
Pages :
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Author: Karen Lisa Knee
Publisher: Stanford University
ISBN:
Category :
Languages : en
Pages : 236
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Submarine groundwater discharge (SGD) is a spatially pervasive phenomenon that adds freshwater, nutrients, dissolved metals, bacteria, and other constituents to the coastal ocean. This dissertation investigated SGD-related inputs of nutrients and fecal indicator bacteria (Escherichia coli and Enterococcus sp.) to coastal waters in two Hawaiian locations, the north shore of Kaua'i and the Kona coast of Hawai'i. Concentrations of caffeine, which has been used previously as a wastewater tracer, were measured in groundwater and surface water on the north shore of Kaua'i. Both study areas have relatively light levels of urban and agricultural development, and maintaining good water quality is essential for their tourism-based economies, coral reefs, fisheries, and traditional way of life. Radium (Ra), an element with naturally elevated concentrations in coastal groundwater, was used as an SGD tracer and a mass-balance approach was used to quantify SGD. On the north shore of Kaua'i, agriculture was associated with higher nitrate + nitrite concentrations in the fresh SGD component, while phosphate and silica appeared to be controlled by geological differences in aquifer substrate. High ammonium concentrations in the fresh SGD component at one site may have been caused by a leaky cesspool. In Kona, no relation between urban development or agriculture and groundwater nutrient concentrations was observed, but bare lava rock was associated with higher nitrate + nitrite and silica concentrations in fresh SGD. Sites closer to golf courses also had higher nitrate + nitrite concentrations. Conservative estimates of total SGD on the north shore of Kaua'i ranged from 1.3 to 7.8 L per meter per minute, or up to 10% of Hanalei River discharge, and SGD contributed significant nitrate + nitrite inputs to Hanalei Bay. Estimates of SGD in Kona ranged from 5 to 1200 L per meter per minute, with between 10 and 100% of the brackish SGD comprised by the fresh SGD component. SGD-related water and nutrient fluxes on the Kona Coast -- where no rivers and streams are present -- were large compared to those reported for other sites worldwide. Caffeine concentrations in environmental waters on the north shore of Kaua'i ranged from 0-88 ng/L, on the low end of what has been reported for other locations. Metribuzin, an herbicide, was also detected at concentrations from 4-11 ng/L in five groundwater and surface water samples. A sensitivity analysis of Ra-based methods of estimating water ages and coastal mixing rates revealed that water ages shorter than 3 d cannot be estimated with confidence using Ra-based methods, even if the only uncertainty considered is analytical error. In conclusion, this dissertation provides new data about SGD and related inputs of nutrients and bacteria to Hawaiian coastal waters, suggests that even low levels of development may influence nutrient concentrations in coastal groundwater, presents the first caffeine concentrations measured in environmental water samples collected in a tropical setting, and explores the limits of applicability of Ra-based methods of estimating water ages and coastal mixing rates, providing guidance for researchers conducting Ra-based SGD studies in the future.
Author: Daniel Agustin Montiel Martin
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 271
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Submarine groundwater discharge (SGD) is an important source of natural and anthropogenic nutrients and contaminants in coastal waters. Nutrient inputs from SGD can cause or exacerbate eutrophication, hypoxia, seagrass beds degradation, and harmful algal blooms (HABs), among other ecological impacts. Coastal karst systems and estuaries are among the most complex coastal areas, where the assessment of SGD and derived nutrient fluxes is particularly challenging. Their typically heterogeneous hydrogeology combined with temporal fluctuations of marine and terrestrial forcing result in large variations of SGD in both systems. In this dissertation I evaluated the magnitude and mechanisms driving SGD and its importance as a source of water and nutrients to Maro-Cerro Gordo (a coastal karst system in southern Spain) and Mobile Bay (an estuary of the northern Gulf of Mexico). In Maro-Cerro Gordo I found that SGD accounted for an important part of the water budget of the coastal karst aquifer, the only source of freshwater for nearby population and agricultural activities. Additionally, SGD served as a vector for NO3- fertilizers contamination to the sea, putting at risk the endangered species of the coastal ecosystem. In Mobile Bay I found that 1/4 of the nutrient budget is delivered by SGD during the dry season as NH4+ (56% of the total) and DON (15% of the total), mostly on the east shore, where Jubilees occur. I demonstrated that these SGD-derived nutrient inputs, in contrast to previous hypotheses, are originated naturally from organic matter mineralization in a peat layer found only on the east shore of the bay. In comparison, groundwater discharge in Maro-Cerro Gordo was primarily controlled by the terrestrially driven hydraulic gradient of the karst aquifer, while in Mobile Bay SGD was mainly marine-driven by sea level fluctuations (tidal pumping). Furthermore, the extremely fast groundwater flow of the karst aquifer in Maro-Cerro Gordo always created oxic conditions, allowing the NO3- contamination to reach the sea. In contrast, in the shallow coastal aquifer of Mobile Bay I found that, while the main form of nitrogen in inland fresh groundwater was NO3-, the SGD-derived nitrogen inputs to the bay was almost entirely in the form of NH4+. These large fluxes of NH4+ were produced by two main processes: organic matter mineralization and dissimilatory nitrate reduction to ammonium (DNRA).
Author:
Publisher: DIANE Publishing
ISBN: 9781422325759
Category :
Languages : en
Pages : 130
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Author: Tom Beer
Publisher: Springer Science & Business Media
ISBN: 9401001677
Category : Technology & Engineering
Languages : en
Pages : 245
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1 AUK ISMAIL-ZADEH ,2, TOM BEER3 1 International Institute of Earthquake Prediction Theory and Mathematical Geophysics, Russian Academy of Sciences, Warshavskoye shosse 79-2, Moscow 113556, Russia; e-mail:
[email protected] 2 Geophysikalisches Institut, Universittit Karlsruhe, Hertzstr. 16, Karlsruhe 76187, Germany; e-mail:
[email protected] 3 CSIRO Environmental Risk Network, CSIRO Atmospheric Research, Aspendale, Vic. 3195 Australia; e-mail:
[email protected] The world faces major threats to the sustainability of our planet. These threats are accompanied by the immediate dangers of natural and man-made disasters. Our vulnerability to them is greatly magnified with each passing year undermining our ability to maintain a sustainable and productive world into the 21st Century and beyond. Both history and common sense teach us that science has a tremendous potential to find ways to cope with these threats. 1 The EUROSCIENCE working group "Science and Urgent Problems of Society" 2 and the IUGG Commission on Geophysical Risk and Sustainability were initiators of the EUROSCIENCE - IUGG Advanced Research Workshop "Science for Reduction of Risk and Sustainable Development of Society" sponsored by the NATO Science Program. The Workshop was held on 15-16 June 2002 in Budapest, Hungary. More than 40 participants from 17 countries took part in the Workshop. Talks and discussions addressed mainly the question of how science can help in reduction of risk and sustainable development of society.