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USGS1996

Time-dependent Data System (TDDS); an interactive program to assemble, manage, and appraise input data and numerical output of flow/transport simulation models

A system of functional utilities and computer routines, collectively identified as the Time-Dependent Data System CI DDS), has been developed and documented by the U.S. Geological Survey. The TDDS is designed for processing time sequences of discrete, fixed-interval, time-varying geophysical data--in particular, hydrologic data. Such data include various, dependent variables and related parameters typically needed as input for execution of one-, two-, and three-dimensional hydrodynamic/transport and associated water-quality simulation models. Such data can also include time sequences of results generated by numerical simulation models. Specifically, TDDS provides the functional capabilities to process, store, retrieve, and compile data in a Time-Dependent Data Base (TDDB) in response to interactive user commands or pre-programmed directives. Thus, the TDDS, in conjunction with a companion TDDB, provides a ready means for processing, preparation, and assembly of time sequences of data for input to models; collection, categorization, and storage of simulation results from models; and intercomparison of field data and simulation results. The TDDS can be used to edit and verify prototype, time-dependent data to affirm that selected sequences of data are accurate, contiguous, and appropriate for numerical simulation modeling. It can be used to prepare time-varying data in a variety of formats, such as tabular lists, sequential files, arrays, graphical displays, as well as line-printer plots of single or multiparameter data sets. The TDDB is organized and maintained as a direct-access data base by the TDDS, thus providing simple, yet efficient, data management and access. A single, easily used, program interface that provides all access to and from a particular TDDB is available for use directly within models, other user-provided programs, and other data systems. This interface, together with each major functional utility of the TDDS, is described and documented in this report.

Water-Resources Investigations Report↗

USGS2000

Hydrogeology and the distribution of salinity in the Floridan Aquifer system, southwestern Florida

A study was conducted to establish a detailed hydrogeologic framework in the complex Floridan aquifer system of southwestern Florida, and to evaluate and relate the distribution of salinity found in this system. The Floridan aquifer system consists of the Upper Floridan aquifer, middle confining unit, and Lower Floridan aquifer. The Upper Floridan aquifer extends into a basal unit of the Hawthorn Group; however, a regional unconformity present at the base of this unit generally marks the top of the Floridan aquifer system, as it does in the rest of southern Florida. The basal Hawthorn unit, which is defined at its top by a correlative marker unit, ranges in thickness from 120 to 460 feet. Paleotopography present prior to deposition of the basal Hawthorn unit, which resulted at least in part from erosion, is believed to have caused some of this variation in thickness. However, in some areas where the basal Hawthorn unit is thick, particularly in Lee County, depositional buildup created paleotopographic highs at the top of the unit. In these areas, permeable limestone zones are present in the unit, giving the unit a high transmissivity. In most of the study area, the Floridan aquifer system can be divided into a brackish-water zone, a salinity transition zone, and a saline-water zone. The brackish-water zone contains water with a dissolved-solids concentration of less than 10,000 milligrams per liter. The saline-water zone has a dissolved-solids concentration of at least 35,000 milligrams per liter and a salinity similar to that of seawater. The salinity transition zone that separates these two zones is usually 150 feet or less in thickness. The altitude of the base of the brackish-water zone was mapped primarily using geophysical logs; it ranges from as shallow as 565 feet below sea level along the coast to almost 2,200 feet below sea level inland. This mapping indicated that the boundary represents a salinity interface, the depth of which is controlled by head in the brackish-water zone. Chloride concentrations in the upper part of the brackish-water zone range from 400 to 4,000 milligrams per liter. A large area of relatively low salinity in north-central Collier County and to the northwest, as defined by a 1,200-milligram-per-liter chloride-concentration line, coincides with a high area on the basal contact of the Hawthorn Group. As this contact dips away from this high area to central Hendry and southwestern Collier Counties, chloride concentration increases to 2,000 milligrams per liter or greater. However, the increase in salinity in these areas occurs only in the basal Hawthorn unit or Suwannee Limestone, but not in deeper units. In central Hendry County, the increase occurs only in the basal Hawthorn unit in an area where the unit is well developed and thick. These areas of higher salinity could have resulted from the influx of seawater from southwestern Collier County into zones of higher permeability in the Upper Floridan aquifer during high sea-level stands. The influx may only have occurred in structurally low areas and may have experienced incomplete flushing subsequently by the modern freshwater flow system. In an area in north-central Collier County, the altitude of the base of the brackish-water zone is anomalously deep given the position of this area relative to the coast. In this area, the base extends as deep as 2,090 feet below sea level, and the salinity transition zone is not present or is poorly defined. The origin of this anomalous area is interpreted to be related to the development of a unit containing thick dolomite and evaporite beds high in the middle confining unit of the Floridan aquifer system. The top of this dolomite-evaporite unit, which probably has very low permeability, occurs at the base of the brackish-water zone in this area. The axis of a high area mapped at the top of the unit trends to the northwest from central Collier County into north-central Lee County. This axis parallels and lies just to the west of the anomalous area, and it could have acted as an impermeable sill, preventing saline water from moving in laterally from the coast to the southwest and up from the Lower Floridan aquifer. Locating a Floridan aquifer system well field in or near this anomalous area could be optimal because of the lack of a salinity interface at depth.

Water-Resources Investigations Report↗

USGS1972

Determination of mass balance and entrainment in the stratified Duwamish River Estuary, King County, Washington

During a study of the effects of waste-water input on the stratified Duwamish River estuary, intensive water-velocity and salinity measurements were made in both the lower salt wedge and the upper fresher water layer for tidal-cycle periods. The net movement of water and salt mass past a cross section during a tidal cycle was determined from integration of the measured rates of movement of water and salt past the section. The net volume of water that moved downstream past the section during the cycle agreed with the volume of fresh-water inflow at the head of the estuary within (1) 3.8 and 7.2 percent, respectively, for two studies made during periods of maximum and minimum tidal-prism thickness and identical inflow rates .of 312 cfs (cubic feet per second), and (2) 15 percent for one study made during a period of average tidal-prism thickness and an inflow rate of 1,280 cfs. For the three studies, the difference between salt mass transported upstream and downstream during the cycles ranged from 0.8 to 19 percent of the respective mean salt-mass transport. Water was entrained from the .salt-water wedge into the overlying layer of mixed fresh and salt water at tidal-cycle-average rates of 30 and 69 cfs per million square feet of interface for the inflow rates of 312 cfs, and 99 cfs per million square feet of interface for an inflow rate of 1,280 cfs. At a constant inflow rate, the rate of entrainment of salt-wedge water in the Duwamish River estuary more than doubled for a doubling of tidal-prism thickness. It also doubled for a quadrupling of inflow rate at about constant tidal-prism thickness.

Water Supply Paper↗

USGS1982

Geohydrologic appraisal of water resources of the South Fork, Long Island, New York

The ground-water resources of the South Fork of Long Island, N.Y., were investigated from April 1974 to September 1977. The study area encompasses 137 square miles and includes the eastern part of the Town of Southampton and the entire Town of East Hampton. The South Fork consists of a Paleozoic basement complex that is overlain by Cretaceous and Pleistocene sediments. The surficial material is composed of Late Wisconsinan glacial and glaciofluvial deposits in association with beach and marsh deposits of Recent age. Till underlies most of the eastern part of the South Fork. Precipitation is the sole source of fresh ground water on the South Fork. Average annual precipitation recorded at Bridgehampton from 1931-76 is 45 inches; about half this amount reaches the ground-water reservoir. It is estimated that overland runoff amounts to 0.5 inches per year, and evapotranspiration is 23 inches per year. Thus, recharge equals approximately 22 inches per year. Hydraulic conductivity and transmissivity of the Magothy (Cretaceous) and upper glacial (Pleistocene) aquifers on the South Fork were estimated from aquifer tests and specific-capacity data. The average horizontal hydraulic conductivity of the Magothy aquifer is 70 feet per day, and of the upper glacial aquifer 350 feet per day. Transmissivity of the Magothy aquifer on the South Fork ranges from 600 to 24,100 feet squared per day; transmissivity of the upper glacial aquifer ranges from 5,400 feet to 22,700 feet squared per day. No potable water is available from the underlying Lloyd aquifer. The position of the freshwater to saline-water interface is depicted in maps. In the southern part of the area, the freshwater reservoir follows the Ghyben-Herzberg principle, but in the northern part, the depth to interface is less than expected owing to a greater degree of anisotropy of the geologic units. Total public-supply pumpage on the South Fork is estimated to be about 3 Mgal/day, (million gallons per day). Public-supply withdrawals in 1976 averaged 2.75 Mgal/day; of this amount, 2.55 Mgal/day was withdrawn from the upper glacial aquifer, and 0.17 Mgal/day from the Magothy aquifer. Ground water and fresh surface water on the South Fork are generally of suitable quality for drinking and most other uses. However, some substances, for example, iron, chloride, and nitrate, may occur locally in objectionable concentrations.

Water Supply Paper↗

USGS2020

Assessment of burrowing behavior of freshwater juvenile mussels in sediment

Standard laboratory sediment toxicity methods have been adapted for conducting toxicity tests with juvenile freshwater mussels. However, studies looking at juvenile mussel burrowing behavior at the water-sediment interface are limited. Juvenile mussels burrow in sediment for the first 0 to 4 yr of life but also may inhabit the sediment-water interface. The objective of this study was to evaluate burrowing behavior of various species and ages of juvenile freshwater mussels in three control sediments: West Bearskin Lake, Spring River, and coarse commercial sand. Species tested included (1) Fatmucket ( Lampsilis siliquoidea ), (2) Notched Rainbow ( Villosa constricta ), (3) Washboard ( Megalonaias nervosa ), (4) Rainbow ( Villosa iris) , (5) Arkansas Fatmucket ( Lampsilis powellii ), and (6) Oregon Floater ( Anodonta oregonensis ). Greater than 95% of the mussels burrowed into test sediment within 15 min. Across species, life stage, and substrate type, most mussels were recovered from the upper layers of sediment (91% at a sediment depth of 3.4 mm or less), and only 2% of the mussels were recovered at a depth >5.1 mm. No mussels were recovered from a depth >6.8 mm. There was no difference in mussel burrowing depth at 4 h versus 24 h across species, age, and sediment type. Two ages of Fatmucket burrowed to a significantly greater depth in the West Bearskin Lake sediment compared to the Spring River sediment or Coarse Sand. However, there was no significant difference in mean depth across sediment type with the other five species of mussels tested. Based on species and age of mussels tested, juvenile mussels up to an age of at least 20 wk and a length of at least 5 mm readily burrow into sediment and likely would be exposed to contaminants in whole sediment and associated pore water throughout a laboratory sediment toxicity test.

Freshwater Mollusk Biology and Conservation↗

USGS2014

Aragonite saturation states and nutrient fluxes in coral reef sediments in Biscayne National Park, FL, USA

Some coral reefs, such as patch reefs along the Florida Keys reef tract, are not showing significant reductions in calcification rates in response to ocean acidification. It has been hypothesized that this recalcitrance is due to local buffering effects from biogeochemical processes driven by seagrasses. We investigated the influence that pore water nutrients, dissolved inorganic carbon (DIC) and total alkalinity (TA) have on aragonite saturation states (Ω aragonite ) in the sediments and waters overlying the sediment surfaces of sand halos and seagrass beds that encircle Alinas and Anniversary reefs in Biscayne National Park. Throughout the sampling period, sediment pore waters from both bottom types had lower oxidation/reduction potentials (ORP), with lower pH relative to the sediment surface waters. The majority (86.5%) of flux rates (n = 96) for ΣNO x – , PO 4 3– , NH 4 + , SiO 2 , DIC and TA were positive, sometimes contributing significant concentrations of the respective constituents to the sediment surface waters. The Ω aragonite values in the pore waters (range: 0.18 to 4.78) were always lower than those in the overlying waters (2.40 to 4.46), and 52% (n = 48) of the values were <2.0. The DIC and TA fluxes at the sediment–water interface reduced Ω aragonite in 75% (n = 16) of the samples, but increased it in the remainder. The elevated fluxes of nutrients, DIC and TA into the sediment–water interface layer negatively alters the suitability of this zone for the settlement and development of calcifying larvae, while enhancing the establishment of algal communities.

Florida↗

USGS2000

Dynamics of nutrient cycling and related benthic nutrient and oxygen fluxes during a spring phytoplankton bloom in South San Francisco Bay (USA)

Benthic oxygen uptake and nutrient releases of N, P and Si were measured weekly at 2 sites in South San Francisco Bay around the 1996 spring bloom. Exchanges across the sediment-water interface were estimated from whole core incubations performed in the laboratory at in situ temperature and in dark. Fluxes changed significantly on a weekly time scale. Over a period of 15 wk the fluxes of dissolved inorganic N, P and Si ranged from -40 to +200, 0 to 13 and from 30 to 400 µmol m -2 h -1 respectively. Sediment oxygen demand increased from 10 before to 64 mg O 2 m -2 h -1 just after the bloom period. During the bloom, nutrient fluxes represented about 20, 16 and 9% of the Si, P and N requirements for primary production. Before and after the bloom period, Si fluxes contributed up to 30 and >100% of this requirement and P and N fluxes up to 15 and 50% respectively. Simple empirical models explain most of the spatial-temporal variability of benthic fluxes of Si, P and NH 4 (but not NO 3 ) from 3 predictor variables: sediment porosity, nutrient concentration in bottom waters and chlorophyll content of surficial sediments. These models show that algal blooms influence benthic-pelagic nutrient exchange through 2 processes: (1) depletion of nutrients from the water column (which enhances gradient-driven transports across the sediment-water interface) and (2) sedimentation of labile phytodetritus (which promotes remineralization in or on the surficial sediments). Rates and patterns of nutrient cycling were very different at the shallow and deep study sites, illustrating the challenge of extrapolating measurements of coupled algae-nutrient dynamics to whole ecosystems.

Marine Ecology Progress Series↗

USGS2007

Characteristics of vesicomyid clams and their environment at the Blake Ridge cold seep, South Carolina, USA

Spatial distributions and patchiness of dominant megafaunal invertebrates in deep-sea seep environments may indicate heterogeneities in the flux of reduced chemical compounds. At the Blake Ridge seep off South Carolina, USA, the invertebrate assemblage includes dense populations of live vesicomyid clams (an undescribed species) as well as extensive clam shell beds (i.e. dead clams). In the present study, we characterized clam parameters (density, size-frequency distribution, reproductive condition) in relation to sulfur chemistry (sulfide and sulfate concentrations and isotopic compositions, pyrite and elemental sulfur concentrations) and other sedimentary metrics (grain size, organic content). For clams >5 mm, clam density was highest where the total dissolved sulfide concentration at 10 cm depth (ΣH 2 S 10cm ) was 0.4 to 1.1 mmol l –1 ; juvenile clams (<5 mm) were most dense where ΣH 2 S 10cm was lowest. Clams were reproductively capable across a broad range of ΣH 2 S 10cm (0.1 to 6.4 mmol l –1 ), and females in the sampled populations displayed asynchronous gametogenesis. Sulfide concentrations in porewaters at the shell–sediment interface of cores from shell beds were high, 3.3 to 12.1 mmol l –1 , compared to <1 mmol l –1 sulfide concentrations at the clam–sediment interface in live clam beds. Concentration profiles for sulfide and sulfate in shell beds were typical of those expected where there is active microbial sulfate reduction. In clam beds, profiles of sulfide and sulfate concentrations were also consistent with rapid uptake of sulfide by the clams. Sulfate in shell beds was systematically enriched in 34 S relative to that in clam beds due to microbial fractionation during sulfate reduction, but in clam beds, sulfate δ 34 S matched that of seawater (~20‰). Residual sulfide values in clam and shell beds were correspondingly depleted in 34 S. Based on porewater sulfide concentrations in shell beds at the time of sampling, we suggest that clam mortality may have been due to an abrupt increase in sulfide concentration and sulfide toxicity, but other alternatives cannot be eliminated.

California↗

USGS2021

Grassification and fast-evolving fire connectivity and risk in the Sonoran Desert, United States

In the southwestern United States, non-native grass invasions have increased wildfire occurrence in deserts and the likelihood of fire spread to and from other biomes with disparate fire regimes. The elevational transition between desertscrub and montane grasslands, woodlands, and forests generally occurs at ∼1,200 masl and has experienced fast suburbanization and an expanding wildland-urban interface (WUI). In summer 2020, the Bighorn Fire in the Santa Catalina Mountains burned 486 km 2 and prompted alerts and evacuations along a 40-km stretch of WUI below 1,200 masl on the outskirts of Tucson, Arizona, a metropolitan area of >1M people. To better understand the changing nature of the WUI here and elsewhere in the region, we took a multidimensional and timely approach to assess fire dynamics along the Desertscrub-Semi-desert Grassland ecotone in the Catalina foothills, which is in various stages of non-native grass invasion. The Bighorn Fire was principally a forest fire driven by a long-history of fire suppression, accumulation of fine fuels following a wet winter and spring, and two decades of hotter droughts, culminating in the hottest and second driest summer in the 125-yr Tucson weather record. Saguaro ( Carnegia gigantea ), a giant columnar cactus, experienced high mortality. Resprouting by several desert shrub species may confer some post-fire resiliency in desertscrub. Buffelgrass and other non-native species played a minor role in carrying the fire due to the patchiness of infestation at the upper edge of the Desertscrub biome. Coupled state-and-transition fire-spread simulation models suggest a marked increase in both burned area and fire frequency if buffelgrass patches continue to expand and coalesce at the Desertscrub/Semi-desert Grassland interface. A survey of area residents six months after the fire showed awareness of buffelgrass was significantly higher among residents that were evacuated or lost recreation access, with higher awareness of fire risk, saguaro loss and declining property values, in that order. Sustained and timely efforts to document and assess fast-evolving fire connectivity due to grass invasions, and social awareness and perceptions, are needed to understand and motivate mitigation of an increasingly fire-prone future in the region.

Arizona↗

USGS2017

Could changes in the agricultural landscape of northeastern China have influenced the long-distance transmission of highly pathogenic avian influenza H5Nx viruses?

In the last few years, several reassortant subtypes of highly pathogenic avian influenza viruses (HPAI H5Nx) have emerged in East Asia. These new viruses, mostly of subtype H5N1, H5N2, H5N6, and H5N8 belonging to clade 2.3.4.4, have been found in several Asian countries and have caused outbreaks in poultry in China, South Korea, and Vietnam. HPAI H5Nx also have spread over considerable distances with the introduction of viruses belonging to the same 2.3.4.4 clade in the U.S. (2014–2015) and in Europe (2014–2015 and 2016–2017). In this paper, we examine the emergence and spread of these new viruses in Asia in relation to published datasets on HPAI H5Nx distribution, movement of migratory waterfowl, avian influenza risk models, and land-use change analyses. More specifically, we show that between 2000 and 2015, vast areas of northeast China have been newly planted with rice paddy fields (3.21 million ha in Heilongjiang, Jilin, and Liaoning) in areas connected to other parts of Asia through migratory pathways of wild waterfowl. We hypothesize that recent land use changes in northeast China have affected the spatial distribution of wild waterfowl, their stopover areas, and the wild-domestic interface, thereby altering transmission dynamics of avian influenza viruses across flyways. Detailed studies of the habitat use by wild migratory birds, of the extent of the wild–domestic interface, and of the circulation of avian influenza viruses in those new planted areas may help to shed more light on this hypothesis, and on the possible impact of those changes on the long-distance patterns of avian influenza transmission.

Frontiers in Veterinary Science↗

USGS2023

Potential effects of habitat change on migratory bird movements and avian influenza transmission in the East Asian-Australasian Flyway

Wild waterbirds, and especially wild waterfowl, are considered to be a reservoir for avian influenza viruses, with transmission likely occurring at the agricultural-wildlife interface. In the past few decades, avian influenza has repeatedly emerged in China along the East Asian-Australasian Flyway (EAAF), where extensive habitat conversion has occurred. Rapid environmental changes in the EAAF, especially distributional changes in rice paddy agriculture, have the potential to affect both the movements of wild migratory birds and the likelihood of spillover at the agricultural-wildlife interface. To begin to understand the potential implications such changes may have on waterfowl and disease transmission risk, we created dynamic Brownian Bridge Movement Models (dBBMM) based on waterfowl telemetry data. We used these dBBMM models to create hypothetical scenarios that would predict likely changes in waterfowl distribution relative to recent changes in rice distribution quantified through remote sensing. Our models examined a range of responses in which increased availability of rice paddies would drive increased use by waterfowl and decreased availability would result in decreased use, predicted from empirical data. Results from our scenarios suggested that in southeast China, relatively small decreases in rice agriculture could lead to dramatic loss of stopover habitat, and in northeast China, increases in rice paddies should provide new areas that can be used by waterfowl. Finally, we explored the implications of how such scenarios of changing waterfowl distribution may affect the potential for avian influenza transmission. Our results provide advance understanding of changing disease transmission threats by incorporating real-world data that predicts differences in habitat utilization by migratory birds over time.

Diversity↗

USGS2022

Advances in the study and understanding of groundwater discharge to surface water

Groundwater discharge is vitally important for maintaining or restoring valuable ecosystems in surface water and at the underlying groundwater-surface-water ecotone . Detecting and quantifying groundwater discharge is challenging because rates of flow can be very small and difficult to measure, exchange is commonly highly heterogeneous both in space and time, and surface-water hydrodynamics can influence the exchange and hinder measurements . Fortunately, a growing number of methods developed during the last several decades has led to advancements in our capabilities to identify and quantify groundwater discharge to surface water, including better use of seepage meters , application of tracers such as heat or isotopes , and improved groundwater-modeling capabilities . This progress has led to coalescence in characterizing the complex mix of hydrological, biological, and chemical processes that occur at the groundwater-surface water interface , along with relevant societal effects . Still, many uncertainties and assumptions show an incomplete knowledge of these processes, including the lack of studies in many regions of the world, insufficient sharing of practical methodologies between scientific disciplines , incomplete understanding of processes and parameters specific to the sediment-water interface , and challenges associated with measuring exchange at multiple scales of time and space.

Water↗

USGS2008

Characterizing submarine ground‐water discharge using fiber‐optic distributed temperature sensing and marine electrical resistivity

Submarine ground‐water discharge (SGD) contributes important solute fluxes to coastal waters. Pollutants are transported to coastal ecosystems by SGD at spatially and temporally variable rates. New approaches are needed to characterize the effects of storm‐event, tidal, and seasonal forcing on SGD. Here, we evaluate the utility of two geophysical methods‐fiber‐optic distributed temperature sensing (FO‐DTS) and marine electrical resistivity (MER)—for observing the spatial and temporal variations in SGD and the configuration of the freshwater/saltwater interface within submarine sediments. FO‐DTS and MER cables were permanently installed into the estuary floor on a transect extending 50 meters offshore under Waquoit Bay, Massachusetts, at the Waquoit Bay National Estuarine Research Reserve, and nearly continuous data were collected for 4 weeks in summer 2007. Initial results indicate that the methods are extremely useful for monitoring changes in the complex estuarine environment. The FO‐DTS produced time‐series data at approximately 1‐meter increments along the length of the fiber at approximately 29‐second intervals. The temperature time‐series data show that the temperature at near‐shore locations appears to be dominated by a semi‐diurnal (tidal) signal, whereas the temperature at off‐shore locations is dominated by a diurnal signal (day/night heating and cooling). Dipole‐dipole MER surveys were completed about every 50 minutes, allowing for production of high‐resolution time‐lapse tomograms, which provide insight into the variations of the subsurface freshwater/saltwater interface. Preliminary results from the MER data show a high‐resistivity zone near the shore at low tide, indicative of SGD, and consistent with the FO‐DTS results.

Conference Paper↗

USGS2016

Effects of salt pond restoration on benthic flux: Sediment as a source of nutrients to the water column

Understanding nutrient flux between the benthos and the overlying water (benthic flux) is critical to restoration of water quality and biological resources because it can represent a major source of nutrients to the water column. Extensive water management commenced in the San Francisco Bay, Beginning around 1850, San Francisco Bay wetlands were converted to salt ponds and mined extensively for more than a century. Long-term (decadal) salt pond restoration efforts began in 2003. A patented device for sampling porewater at varying depths, to calculate the gradient, was employed between 2010 and 2012. Within the former ponds, the benthic flux of soluble reactive phosphorus and that of dissolved ammonia were consistently positive (i.e., moving out of the sediment into the water column). The lack of measurable nitrate or nitrite concentration gradients across the sediment-water interface suggested negligible fluxes for dissolved nitrate and nitrite. The dominance of ammonia in the porewater indicated anoxic sediment conditions, even at only 1 cm depth, which is consistent with the observed, elevated sediment oxygen demand. Nearby openestuary sediments showed much lower benthic flux values for nutrients than the salt ponds under resortation. Allochthonous solute transport provides a nutrient advective flux for comparison to benthic flux. For ammonia, averaged for all sites and dates, benthic flux was about 80,000 kg/year, well above the advective flux range of −50 to 1500 kg/year, with much of the variability depending on the tidal cycle. By contrast, the average benthic flux of soluble reactive phosphorus was about 12,000 kg/year, of significant magnitude, but less than the advective flux range of 21,500 to 30,000 kg/year. These benthic flux estimates, based on solute diffusion across the sediment-water interface, reveal a significant nutrient source to the water column of the pond which stimulates algal blooms (often autotrophic). This benthic source may be augmented further by bioturbation, bioirrigation and episodic sediment resuspension events.

California↗

USGS2003

Transient and steady-state salt transport between sediments and brine in closed lakes

A diffusional transport model for Lake Abert, Oregon, predicts the rates of salt transport from pore fluids into lake waters. In a lake without outflow dissolved salts may migrate across the sediment-water interface in response to a concentration difference between lake and interstitial brine. Transport of salt upward is transient; its direction can be reversed by external input of salt or by depletion of salts stored in the sediments, and a steady-state concentration in lake water is not attainable. Downward transport can be a stationary process if the sedimentation rate is rapid compared with molecular diffusion of salt in interstitial brine, but characteristic rates arc too slow to lead to steady-state concentrations within the lifetime of a closed lake. In Lake Abert, diffusional flux upward was much more important than input of salt from other sources; 45% of the salt of lake brine in 1963–1964 was added from the sediment pore space during the preceding 25 years, only 0.1% from external inflow. The sediment source will dominate input during high water level. Such models permit comparison of salt transport across the sediment-water interface with other input sources at different times of the lake’s history.

Oregon↗

USGS2008

Nitrogen biogeochemistry of submarine groundwater discharge

To investigate the role of the seepage zone in transport, chemical speciation, and attenuation of nitrogen loads carried by submarine groundwater discharge, we collected nearshore groundwater samples (n = 328) and examined the distribution and isotopic signature (δ 15 N) of nitrate and ammonium. In addition, we estimated nutrient fluxes from terrestrial and marine groundwater sources. We discuss our results in the context of three aquifer zones: a fresh groundwater zone, a shallow salinity transition zone (STZ), and a deep STZ. Groundwater plumes containing nitrate and ammonium occurred in the freshwater zone, whereas the deep STZ carried almost exclusively ammonium. The distributions of redox-cycled elements were consistent with theoretical thermodynamic stability of chemical species, with sharp interfaces between water masses of distinct oxidation : reduction potential, suggesting that microbial transformations of nitrogen were rapid relative to dispersive mixing. In limited locations in which overlap occurs between distribution of nitrate with that of ammonium and dissolved Fe 2+ , changes in concentration and in δ 15 N suggest loss of all species. Concurrent removal of NO 3 − and NH 4 + , both in freshwater and the deep STZ, might occur through a range of mechanisms, including heterotrophic or autotrophic denitrification, coupled nitrfication : denitrification, anammox, or Mn oxidation of NH 4 + . Loss of nitrogen was not apparent in the shallow STZ, perhaps because of short water residence time. Despite organic Cpoor conditions, the nearshore aquifer and subterranean estuary are biogeochemically active zones, where attenuation of N loads can occur. Extent of attenuation is controlled by the degree of mixing of biogeochemically dissimilar water masses, highlighting the critical role of hydrogeology in N biogeochemistry. Mixing is related in part to thinning of the freshwater lens before discharge and to dispersion at the fresh : saline groundwater interface, features common to all submarine groundwater discharge zones.

Limnology and Oceanography↗

USGS2015

From submarine to lacustrine groundwater discharge

Submarine groundwater discharge (SGD) and its role in marine nutrient cycling are well known since the last decade. The freshwater equivalent, lacustrine groundwater discharge (LGD), is often still disregarded, although first reports of LGD are more than 50 years old. We identify nine different reasons why groundwater has long been disregarded in both freshwater and marine environments such as invisibility of groundwater discharge, the size of the interface and its difficult accessibility. Although there are some fundamental differences in the hydrology of SGD and LGD, caused primarily by seawater recirculation that occurs only in cases of SGD, there are also a lot of similarities such as a focusing of discharge to near-shore areas. Nutrient concentrations in groundwater near the groundwater–surface water interface might be anthropogenically enriched. Due to spatial heterogeneity of aquifer characteristics and biogeochemical processes, the quantification of groundwater-borne nutrient loads is challenging. Both nitrogen and phosphorus might be mobile in near-shore aquifers and in a lot of case studies large groundwater-borne nutrient loads have been reported.

Conference Paper↗

USGS2023

Quantifying salinity in the layered coastal aquifers underlying and adjacent to Delaware Bay USA using AEM-derived resistivity

Airborne electromagnetic (AEM) methods are particularly well suited to coastal aquifer salinity studies, yet the quantitative translation from bulk resistivity to fluid salinity carries uncertainty that can impact mapped salinity distributions and interpretations of the freshwater-saline interface and hydrostratigraphic layers. A recent AEM survey of the region near the Delaware Bay, USA highlights several challenges common to coastal hydrogeologic settings that may influence both qualitative and quantitative interpretation. We use a Bayesian inversion to estimate geophysical parameter uncertainty, and results are integrated with hydrogeologic measurements to develop quantitative interpretations of salinity across the freshwater-saline interface in stacked aquifers.

Delaware, New Jersey↗