Evaluation of atmospheric dry deposition as a source of nutrients and trace metals to Lake Tahoe

Atmospheric deposition can be an important source of nutrients and trace metals to oligotrophic alpine lakes, affecting their biogeochemistry. We measured trace metal concentrations and lead (Pb) isotope ratios in lake water, river water, ground water, and aerosol total suspended particles (TSP), as well as nutrient (NO 3 − , NH 4 + , PO 4 3− ) concentrations in TSP in the Tahoe Basin. The contribution of TSP deposition to the lake trace metal budget was assessed. Our results show seasonality in TSP and associated trace metal concentrations with higher concentrations during Oct – April. However, trace metal solubilities are higher during May – Sept, resulting in a higher contribution of soluble trace metals to the lake water. The source of most of the trace metals in TSP in the Lake Tahoe Basin is mineral dust; however, Zn, Cu, and Cd also have an anthropogenic origin. Among major nutrients, NO 3 − concentrations are slightly higher during Oct – April, while NH 4 + and soluble reactive phosphorus (SRP) are higher during May – Sept. The distributions of trace metal concentrations and Pb isotopic ratios are homogenous throughout the lake water column, suggesting that the residence time of the trace metals in the lake is longer than the lake water mixing time. The contribution of atmospheric TSP deposition to the upper 20 m of lake water trace metal inventory is low, ranging from 0.03% for V to 5.7% for Mn. A triple-isotopes plot of Pb indicates that riverine and groundwater inputs are the major Pb sources, but aerosols still contribute some Pb to the lake. This article is part of a special issue entitled: Conway GEOTRACES - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. González

A global experiment on motivating social distancing during the COVID-19 pandemic

Finding communication strategies that effectively motivate social distancing continues to be a global public health priority during the COVID-19 pandemic. This cross-country, preregistered experiment (n = 25,718 from 89 countries) tested hypotheses concerning generalizable positive and negative outcomes of social distancing messages that promoted personal agency and reflective choices (i.e., an autonomy-supportive message) or were restrictive and shaming (i.e., a controlling message) compared with no message at all. Results partially supported experimental hypotheses in that the controlling message increased controlled motivation (a poorly internalized form of motivation relying on shame, guilt, and fear of social consequences) relative to no message. On the other hand, the autonomy-supportive message lowered feelings of defiance compared with the controlling message, but the controlling message did not differ from receiving no message at all. Unexpectedly, messages did not influence autonomous motivation (a highly internalized form of motivation relying on one’s core values) or behavioral intentions. Results supported hypothesized associations between people’s existing autonomous and controlled motivations and self-reported behavioral intentions to engage in social distancing. Controlled motivation was associated with more defiance and less long-term behavioral intention to engage in social distancing, whereas autonomous motivation was associated with less defiance and more short- and long-term intentions to social distance. Overall, this work highlights the potential harm of using shaming and pressuring language in public health communication, with implications for the current and future global health challenges

Microbial community composition across a coastal hydrological system affected by submarine groundwater discharge (SGD).

Mobile Bay, the fourth largest estuary in the USA located in the northern Gulf of Mexico, is known for extreme hypoxia in the water column during dry season caused by NH4+-rich and anoxic submarine groundwater discharge (SGD). Nutrient dynamics in the coastal ecosystem point to potentially elevated microbial activities; however, little is known about microbial community composition and their functional roles in this area. In this study, we investigated microbial community composition, distribution, and metabolic prediction along the coastal hydrological compartment of Mobile Bay using 16S rRNA gene sequencing. We collected microbial samples from surface (river and bay water) and subsurface water (groundwater and coastal pore water from two SGD sites with peat and sandy lithology, respectively). Salinity was identified as the primary factor affecting the distribution of microbial communities across surface water samples, while DON and PO43- were the major predictor of community shift within subsurface water samples. Higher microbial diversity was found in coastal pore water in comparison to surface water samples. Gammaproteobacteria, Bacteroidia, and Oxyphotobacteria dominated the bacterial community. Among the archaea, methanogens were prevalent in the peat-dominated SGD site, while the sandy SGD site was characterized by a higher proportion of ammonia-oxidizing archaea. Cyanobium PCC-6307 and unclassified Thermodesulfovibrionia were identified as dominant taxa strongly associated with trends in environmental parameters in surface and subsurface samples, respectively. Microbial communities found in the groundwater and peat layer consisted of taxa known for denitrification and dissimilatory nitrate reduction to ammonium (DNRA). This finding suggested that microbial communities might also play a significant role in mediating nitrogen transformation in the SGD flow path and in affecting the chemical composition of SGD discharging to the water column. Given the ecological importance of microorganisms, further studies at higher taxonomic and functional resolution are needed to accurately predict chemical biotransformation processes along the coastal hydrological continuum, which influence water quality and environmental condition in Mobile Bay

Assessing submarine groundwater discharge (SGD) and nitrate fluxes in highly heterogeneous coastal karst aquifers: Challenges and solutions

Groundwater discharge in coastal karst aquifers worldwide represents a substantial part of the water budget and is a main pathway for nutrient transport to the sea. Groundwater discharge to the sea manifests under different forms, making its assessment very challenging particularly in highly heterogeneous coastal systems karst systems. In this study, we present a methodology approach to identify and quantify four forms of groundwater discharge in a mixed lithology system in southern Spain (Maro-Cerro Gordo) that includes an ecologically protected coastal area comprised of karstic marble. We found that groundwater discharge to the sea occurs via: (1) groundwater-fed creeks, (2) coastal springs, (3) diffuse groundwater seepage through seabed sediments, and (4) submarine springs. We used a multi-method approach combining tracer techniques (salinity, 224Ra, and 222Rn) and direct measurements (seepage meters and flowmeters) to evaluate the discharge. Groundwater discharge via submarine springs was the most difficult to assess due to their depth (up to 15 m) and extensive development of the springs conduits. We determined that the total groundwater discharge over the 16 km of shoreline of the study area was at least 11 ± 3 × 103 m3 d−1 for the four types of discharge assessed. Groundwater-derived nitrate (NO3−) fluxes to coastal waters over ∼3 km (or 20%) in a highly populated and farmed section of Maro-Cerro Gordo was 641 ± 166 mol d−1, or ∼75% of the total NO3− loading in the study area. We demonstrate in this study that a multi-method approach must be applied to assess all forms of SGD and derived nutrient fluxes to the sea in highly heterogeneous karst aquifer systems

DOM molecular composition of porewater collected after incubations

The subterranean estuary (STE) has been recognised as a reactive biogeochemical zone at the groundwater-seawater interface in coastal areas. In this study, we collected sediments from different seasons (April 2021 [storm season) and September 2021 [dry season]) from Mobile Bay, USA. We analysed DOM molecular composition using FTICRMS and microbial assemblages by employing 16S rRNA gene sequencing approach

Physicochemical data of porewater collected after incubations

The subterranean estuary (STE) has been recognised as a reactive biogeochemical zone at the groundwater–seawater interface in coastal areas. In this study, we collected sediments from different seasons (April 2021 [storm season) and September 2021 [dry season]) from Mobile Bay, USA. Shallow sediment cores (up to 2 m) were recovered using a Geoprobe coring system (Model 5410, Geoprobe Systems, Inc.). We conducted controlled laboratory experiments using these sediments and subjected them to various nitrate inputs, salinity regimes, and incubation times. We measured (1) inorganic nutrients (nitrate, nitrite, ammonium, phosphate), (2) dissolved organic carbon (DOC) and nitrogen (DON), (3) total alkalinity

A comparison of measurement methods for radium-226 on manganese fiber

Acrylic fibers impregnated with MnO2 (Mn-fiber) have become a valuable tool for concentrating dissolved radium for oceanographic applications. With four naturally-occurring radium isotopes (223Ra, 224Ra, 226Ra, and 228Ra) of vastly different half-lives (3.6 days to 1600 years), radium can be a powerful tool for tracing terrestrial water discharges into the ocean and studying coastal mixing processes. Several techniques have been outlined in the literature describing the measurement of 226Ra on Mn-fiber via its gaseous daughter, 222Rn. We present a proven, air-tight cartridge design that allows one to use these measurement techniques. We then review the procedures for three radon-based nondestructive measurement techniques for 226Ra on Mn-fiber (via RAD7, RaDeCC, and Rn emanation line systems) and perform an intercomparison among them, using the standard technique of γ-spectrometry as a reference. We find that all methods statistically agree in terms of measured activity. The Rn emanation line and the RaDeCC systems (both based on Lucas cell counting) provide the lowest measurement uncertainties and minimum detectable activities (MDAs) for a given counting time. The RAD7 technique, on the other hand, offers the advantage of being an automated system, thus requiring minimal user interaction. The standard γ-spectrometry technique, while more time-consuming and sample destructive, has the advantage of providing a simultaneous measurement for 228Ra

Psykososialt arbeid med einslege mindreårige flyktningar

International audienceGroundwater discharge in coastal karst aquifers worldwide represents a substantial part of the water budget and is a main pathway for nutrient transport to the sea. Groundwater discharge to the sea manifests under different forths, making its assessment very challenging particularly in highly heterogeneous coastal systems karst systems. In this study, we present a methodology approach to identify and quantify four forms of groundwater discharge in a mixed lithology system in southern Spain (Maro-Cerro Gordo) that includes an ecologically protected coastal area comprised of karstic marble. We found that groundwater discharge to the sea occurs via: (1) groundwater-fed creeks, (2) coastal springs, (3) diffuse groundwater seepage through seabed sediments, and (4) submarine springs. We used a multi-method approach combining tracer techniques (salinity, Ra-224, and Rn-222) and direct measurements (seepage meters and flowmeters) to evaluate the discharge. Groundwater discharge via submarine springs was the most difficult to assess due to their depth (up to 15 m) and extensive development of the springs conduits. We determined that the total groundwater discharge over the 16 km of shoreline of the study area was at least 11 +/- 3 x 10(3) m(3) d(-1) for the four types of discharge assessed. Groundwater-derived nitrate (NO3-) fluxes to coastal waters over similar to 3 km (or 20%) in a highly populated and farmed section of Maro-Cerro Gordo was 641 +/- 166 mol d(-1), or similar to 75% of the total NO3- loading in the study area. We demonstrate in this study that a multi-method approach must be applied to assess all forms of SGD and derived nutrient fluxes to the sea in highly heterogeneous karst aquifer systems

Hydrogeologic controls on chemical transport at Malibu Lagoon, CA : implications for land to sea exchange in coastal lagoon systems

© The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Journal of Hydrology: Regional Studies 11 (2017): 219-233, doi:10.1016/j.ejrh.2016.08.003.Hydrogeologic controls on seasonal land/sea exchange are investigated in Malibu, California, USA. An assessment of regional groundwater/surface water exchange and associated biogeochemical transport in an intermittently open, coastal lagoon in California is developed using naturally occurring U/Th-series tracers. Nearshore lagoons that are seasonally disconnected from the coastal ocean occupy about 10% of coastal areas worldwide. Lagoon systems often are poorly flushed and thus sensitive to nutrient over-enrichment that can lead to eutrophication, oxygen depletion, and/or pervasive algal blooms. This sensitivity is exacerbated in lagoons that are intermittently closed to surface water exchange with the sea and occur in populous coastal areas. Such estuarine systems are disconnected from the sea during most of the year by wave-built barriers, but during the rainy season these berms can breach, enabling direct water exchange. Using naturally-occurring 222Rn as groundwater tracer, we estimate that groundwater discharge to Malibu Lagoon during open berm conditions was one order of magnitude higher (21 ± 17 cm/day) than during closed berm conditions (1.8 ± 1.4 cm/day). The SGD (submarine groundwater discharge) into nearshore coastal waters at the SurferRider and Colony Malibu was 4.2 cm/day on average. The exported total dissolved nitrogen (TDN) through the berm during closed berm was 1.6 × 10−3 mol/day, whereas during open berm (exported by the Creek) was 3.5 × 103 mol/day. Although these evaluations are specific to the collection campaigns the 2009 and 2010 hydro years, these two distinct hydrologic scenarios play an important role in the seasonality and geochemical impact of land/sea exchange, and highlight the sensitivity of such systems to future impacts such as sea level rise and increasing coastal populations.This work was co-funded by the City of Malibu and the U.S. Geological Survey

Extended time series measurements of submarine groundwater discharge tracers (222Rn and CH4) at a coastal site in Florida

We report the results of an experiment in which we measured 222Rn (15,000 observations), CH4 (40,000 observations), and associated variables in seawater nearly continuously at a coastal site in the Gulf of Mexico for almost two years. Significant correlations between 222Rn and CH4 imply that they are derived from a common source, most likely groundwater. However, we were unable to explain the overall tracer variability as a single function of groundwater table height, temperature, tidal range, and wind speed, indicating multiple, overlapping controls on SGD dynamics at this site. Methane and radon concentrations may vary 2-fold in a given well in the subterranean estuary over tidal time scales, demonstrating the complexity of determining SGD endmember concentrations and suggesting that unaccounted for temporal changes in groundwater may explain some of the patterns observed in seawater. Surprisingly, the variability of 222Rn and CH4 in seawater over short (e.g., hourly) time scales was generally comparable to or even more pronounced than fluctuations over much longer (e.g., monthly) scales. While high tracer concentrations usually occurred during low tide and low tracer concentrations during high tide, this pattern was occasionally inverted or absent indicating that no single model can be used to describe the entire data set. We also describe a sequence of events in which SGD tracers were depleted in coastal waters during storms and regenerated afterwards. We found no increase in radon activities immediately after the largest storm (75 mm rainfall) perhaps because of the short residence times of groundwater in contrast to the ingrowth time of radon. Marine controls appeared to be the most important SGD drivers with only minor influence relating to the shallow and deep aquifers. This implies that seasonal investigations of SGD tracers in the coastal ocean may be masked by short-term variability