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

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

Submarine Groundwater Discharge: A Source of Nutrients, Metals, and Pollutants to the Coastal Ocean

This chapter reviews the current knowledge on submarine groundwater discharge (SGD) and the associated fluxes of nutrients, trace metals, microbes, pharmaceuticals, and other terrestrial constituents to coastal waters. We review methods of estimating SGD, present flux estimates from different locations worldwide, and discuss how various hydrogeologic features such as topography, aquifer substrate, climate, waves, and tides affect SGD. We discuss the range of material concentrations and fluxes, their relationship to land use, and the chemical changes that nutrients and metals undergo during their seaward journey through the aquifer. Climate change is likely to affect both the quantity and the quality of SGD, and we review these effects. The chapter concludes with a discussion of active areas of SGD research, including expanding the geographic scope of SGD studies; characterizing and reducing the uncertainty associated with SGD measurements; understanding the behavior of nutrients, metals, and other pollutants in the subterranean estuary; and modeling SGD on a global scale

High resolution molecular characterization of photochemical and microbial transformation of dissolved organic matter in temperate streams of different watershed land use

The objective of the present study was to provide better understanding of the effects of watershed land use on molecular composition of streamwater DOM and molecular transformations associated with photochemical and microbial processing of DOM. We compared DOM from headwater streams draining forest-dominated watersheds (FW) and pasture-dominated watersheds (PW) in the lower Chesapeake Bay region (Virginia, USA). Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry analysis was conducted on streamwater DOM prior to and after laboratory incubations: 1) bacteria-only incubations; 2) light-only incubations; and 3) combined light+bacterial incubations. Results showed that DOM in FW streams and PW streams differed in molecular characteristics--the former was characterized by greater structural complexity and aromaticity, higher proportions of condensed aromatic molecules and black carbon-like components, while the latter was higher in the proportions of lipid-like components, protein-like components and aliphatic compounds. Relative to DOM from FW streams, DOM from PW streams was more reactive to bacterial transformation. Protein-like components, lipid-like components and unsaturated hydrocarbon-like components are primarily responsible for the changes associated with bacterial transformation of DOM. However, similar behavior was also observed for DOM in FW streams and PW streams under the influence of bacterial and photochemical processes. Bacterial transformation reduced the proportions of lipid-like components but increased the proportions of lignin-like components and carboxyl-rich alicyclic molecule-like components, indicating that lipid-like components was a bioreactive class while lignin-like components and carboxyl-rich alicyclic were resistant to bacterial processing. Photochemical processes, alone or combined with microbial alterations, increased the proportions of protein-like components, which may be due to the light stimulation of autochthonous production of protein-like components, and increased the relative abundance of carboxyl-rich alicyclic molecule-like components, which indicates the refractory nature of these molecules. Photochemical processes also significantly reduced the amount of dissolved black carbon-like components, which suggests dissolved black carbon was a photoreactive class, countering the conventional view that black carbon was an inter group in carbon cycle. Collectively, these findings suggest that human land use in upstream watersheds may lead to alterations to the molecular composition of streamwater DOM as well as to its behavior to photochemical and microbial processing. (Published By University of Alabama Libraries

&#948;<super>15</super>n in mollusk shells as a potential paleoenvironmental proxy for nitrogen loading in chesapeake bay

Crassostrea virginica is one of the most common oyster species in North America and is frequently found in archaeological sites and sub-fossil deposits, especially in the eastern US. Although there have been several sclerochronological studies on &#948;13C and &#948;18O in the shells of this species, little is known about &#948;15N stored within the shells, which could potentially be a useful paleoenvironmental proxy to determine nitrogen loading and the subsequent anthropogenic impacts within an area. In order to potentially serve as paleoenvironmental proxies for N loading, bivalve shells' organic matter needs to remain chemically unaltered. Since ancient peoples cooked most archaeological shells before depositing them in shell middens, it is necessary to determine if prehistoric cooking methods alter either %N or &#948;15N stored within the shells. Twenty C. virginica oysters and twenty-two Mercenaria spp. clams were treated to five different prehistoric cooking methods: direct exposure to hardwood coals, roasting above hardwood coals, roasting in a dry oven, boiling in freshwater, or boiling in seawater. Each shell was bisected through the resilifer with one half treated with one of the five prehistoric cooking methods and the remaining half serving as a control. With the exception of roasting above the hardwood coals, prehistoric cooking methods do not significantly alter either %N or &#948;15N within the shells. Those shells roasted above the coals were typically enriched in both %N and &#948;15N , which is likely an effect of smoke coming from the hardwood coals and infiltrating pore spaces within the outer layers of the shell. Ninety archaeological C. virginica shells ranging in age from ~120 to 3,400 years old and thirty-two modern C. virginica shells were collected in Chesapeake Bay at the Smithsonian Environmental Research Center in Edgewater, Maryland. One valve from each shell was sub-sampled and the calcite powder was analyzed (without acidification pretreatment) using an EA-IRMS system equipped with a CO2 trap to determine the %N and &#948;15N content of the shells. Comparison of %N and &#948;15N in C. virginica shells from the six different time periods studied show relatively constant values from ~3,400 years ago to 1820 AD. Between 1820 and 1890, there are rapid increases in both %N and &#948;15N in the shells, which continue to exponentially increase in value to the modern shells. The increases in %N and &#948;15N are correlated with increased anthropogenic impact due to human population, sewage discharge, and urbanization in Chesapeake Bay at this time. Therefore, it is likely that C. virginica shells can be used as a paleoenvironmental proxy to measure the anthropogenic impact of a specific area over time. However, the constant, relatively low %N and &#948;15N values from ~3,400 years ago to 1820 AD compared to the increased N concentrations and enriched &#948;15N shells from the modern periods could be influenced by diagenetic alteration of the shell after burial in the midden. It is possible that the shells are losing N and preferentially losing 15N over time. More research is necessary to determine if bivalve shells are geochemically stable with regard to N over time or if diagenesis is likely to have occurred in these shells. (Published By University of Alabama Libraries

Effects of the 1982-1983 El Niño mega event on bivalve mollusk biomineralization

Marine bivalve mollusks are valued as climate change recorders due to predictable growth rates and the recording of the ambient seawater environment into their shells (e.g., temperature, dissolved inorganic carbon (DIC)). Bivalves that endure extreme environmental perturbations also exhibit alteration of the shell microstructure in response to the stress. Numerous studies demonstrate correlations between shell isotopic values and environmental parameters, such as δ^18O and temperature, but the possibility of confounding isotopic signatures between shell layers and microstructures in a single organism, induced by environmental stress factors, has not been sufficiently studied. Two bivalve species (Trachycardium procerum and Chione subrugosa), collected from the Peruvian coast after the 1982-1983 El Niño, exhibit microstructural alterations in the shell in correlation with the sea surface temperature (SST) anomaly during the event. Common biomineral alterations include changes in the relative thickness of certain microstructural types and the loss of intercrystalline organic matrix components. δ^18O_shell and δ^13C_shell data show no significant changes in correlation with the El Niño growth scar in any shell layers of T. procerum. C. subrugosa, an intertidal species, shows δ^13C_shell and δ^18O_shell depletion in the affected area. These data indicate that biomineralization changes are not synchronized with isotopic signatures. Furthermore, bivalve biogeochemical proxies may not be sufficiently sensitive to detect rapid fluctuations in SST, but potentially useful in detecting other localized El Niño associated events, such as an increase in rainfall. (Published By University of Alabama Libraries

Evaluation of submarine groundwater discharge and groundwater quality using a novel coupled approach: isotopic tracer techniques and numerical modeling

It has been recognized that submarine groundwater discharge (SGD) may be one of the principal pathways for delivering nutrients to surface water bodies, resulting in eutrophication of many nearshore coastal areas throughout the world. A one-year study of the coastal aquifer system (A1, A2, A3-Aquifers) of Gulf Shores, Alabama was conducted to assess SGD fluxes, characterize contaminant and nutrient transport through the aquifer system, and determine the availability of future aquifer resources. A three-dimensional density-dependent groundwater flow and transport model (SEAWAT), based on the coupling of MOFLOW and MT3DMS, was used to simulate the transport of nitrate and sulfate through the groundwater system to the coast. The model was refined and calibrated using independently determined field-based radon (222Rn, t1/2=3.82 d) isotopic tracer time-series surveys across a portion of the model area to enhance estimates of nearshore SGD. Two SGD approaches, integrated with 222Rn-determined seepage rates, were developed to determine (1) localized; and (2) entire-shoreline SGD. Thirty-two groundwater wells within the study area were sampled to constrain the groundwater 222Rn end-member in the model and characterize the extent of nutrient contamination. The ArcGIS database was used to spatially plot and interpret nutrient and 222Rn data, and generate iso-concentration maps detailing groundwater contamination and aquifer piezometric surfaces across the study area. Radon concentrations measured in groundwater from the shallow A1 and deeper A2 Aquifers were statistically identical, an indication that there is direct connection between the two systems. Elevated nitrate and sulfate concentration (up to 30 mg/L and 724 mg/L, respectively) were observed through active monitoring with zones of principal discharge identified in the lower A2 Aquifer. A groundwater seepage rate of 18.3 cm/day, calculated through the radon mass-balance model at a model area lake, was used to calibrate the numerical model surficial aquifer zone. Final shoreline seepage fluxes of 6.41 and 8.62 cm/day were determined from the results of both the multi-cell and shoreface numerical model simulation SGD approaches, respectively. The results of the two numerical SGD methods demonstrate good agreement with the 222Rn-derived methods, and provided an effective approximation technique that can be inexpensively duplicated in other similar shoreline areas. (Published By University of Alabama Libraries

Biomineralization of giant clam shells (tridacna gigas): implications for paleoclimate applications

The giant clam, Tridacna gigas, is an important faunal component of Indo-Pacific reef ecosystems, for which its shell is often used as an environmental archive for modern and past climates. This thesis is a study of the shell microstructure of modern specimens from Palm Island, Great Barrier Reef (GBR), Australia and Huon Peninsula, Papua-New Guinea (PNG), using a combination of petrography, scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and Raman spectroscopy, as well as a microstructural comparison of fossil T. gigas through 200 ka from PNG. Daily growth increments are recognizable in all specimens through ontogeny within the internal layer. For modern T. gigas from PNG, increments are composed of pairs of organized aragonitic needles and compact, oblong crystals, whereas modern specimens from GBR are composed of shield-like crystals. The combination of nutrient availability and rainfall are likely the most significant factors controlling shell growth and it may explain the observed differences in microstructure. The external layers are composed of a dendritic microfabric, significantly enriched in 13C compared to the internal layer, suggesting a different metabolic control on layer secretion. The internal and external layers are likely mineralized independent from each other, associated with the activity of a specific mantle organ. Furthermore, needles similar to those of modern T. gigas from PNG, are observed and the widths are measured in the set of fossil T. gigas. An exception includes two mid-Holocene-aged individuals, composed of elongated crystals, oblique to the outside of the shell. The results show that widths follows a cyclic pattern, similar to those of solar radiation variability, suggesting there is a relationship between solar activity and the width of aragonitic needles. Differences between modern and mid-Holocene T. gigas, are likely associated with fundamental environmental differences. The results of this study, pointing to locality and environmental dependence, layer specific mantle biomineralization, and co-variation between needle width and solar modulation, advance the potential of giant clam shells to assist in the reconstruction of many climate parameters that were previously limited to chemical analyses. Microstructural results are additionally applicable in engineering and medical research fields. (Published By University of Alabama Libraries