Implications of river salinization on biogeochemical cycles

Introduction: Freshwater Salinization: Many watersheds in the US and around the world are experiencing episodic salinization due to the application of road salts, and long-term salinization due to land use change, stormwater infrastructure, flooding, and accelerated weathering rates. The magnitude and frequency of anthropogenic salt inputs may be amplified in the near future due to the interactive effect of climate change and urban development growth –which can further elevate the dissolved salt load in rivers in both acute (pulse) and chronic (baseflow) terms.

New Insights:Previous research suggests that changes in freshwater salinization have to the potential to mobilize trace metals into the water column, to exacerbate nutrient pollution by perturbing microbial biogeochemical cycles, to decrease biodiversity by creating toxic conditions for freshwater species, to degrade built infrastructure, and to impact drinking water quality.

Dissolved salts are potentially linked to nitrogen and metals, however their relationship is not well resolved. Dissolved salts can increase pH, and pH is a controlling variable for key microbial nitrogen-transformation processes.  Salts are ionic compounds, and through the process of cation-exchange on soil and sediment surfaces throughout the watershed, they can potentially increase nitrates and trace metals delivery to rivers.  Other studies suggest that there may be a specific threshold salinity level between which salts stabilize colloids or mobilize colloids (i.e. move nitrate, metals, DOC).

This study can mechanistic insights on the potential relationship between salinization, nutrients, and metals –a geochemical coupling that could be incorporated into management practices, stream restoration, or the design and functioning of tomorrow’s engineered green infrastructure. Furthermore, characterizing this geochemical relationship can help constrain river solute fate and transport models, and ultimately enable us to predict water quality.  

Objective and Hypothesis: I propose to investigate the effect of salinization on nutrients and metals in urban streams in the Baltimore-Washington metropolitan area by conducting laboratory simulations, field experiments, and analyzing high frequency sensor data. I hypothesize that there will be an appreciable leaching and transport of nutrients and metals from adsorbed surfaces due to the sequential mechanisms of cation bridging and exchange, followed by DOC dispersal from the sediment. This study seeks to answer two questions:

(1)  What is the magnitude of salinity-induced mobilization of carbon, nitrogen, phosphorus, and trace metals from sediments to streams? What is the mechanism and controlling factors?

(2)  Can the empirical relationship between salinity and nitrogen in the high-frequency sensor record be classified and explained in terms of a chemical coupling?

From Findlay, S.E.G. and V.R. Kelly, 2011, Annals of the NYAS

From Daley, M.L. et al., 2009, JNABS

Data From USGS NWIS-RTWQ

Data From USGS NWIS-RTWQ

Classifying the controls on differential movement of subduction interface blocks: a comparative study

General Background:

Deciphering how materials move and interact within subduction zones is crucial for understanding resultant processes, such as volcanoes and earthquakes, which we observe at Earth’s surface. As oceanic lithosphere subducts beneath a continent, it brings with it crustal material, which forms the interface between the subducting slab and the overlying mantle wedge. At this subduction interface, important devolitization reactions and processes occur that recycle volatiles into the mantle, including both carbon dioxide and water. The net flux of volatiles into the mantle wedge both generates magma and earthquakes, and sequesters CO₂ and H₂O in the deep mantle, playing a significant role in both water and carbon cycles.

Cartoon depiction of the upper ~100km of a subduction zone. The shaded region beneath the continental arc is the subduction interface.

            Exhumed subduction-interface terranes (mélange) typically consist of meter to kilometer-scale blocks of metamorphosed oceanic crust and mangle wedge surrounded by a fine-grained matrix dominated by chain and sheet silicates. Geodynamic modeling suggests that blocks can move at varying rates within the matrix, and has shown that this differential movement can result from several mechanisms: matrix viscosity, plate velocity, duration of subduction, and degree of hydration of the mantle wedge (Gerya et al, 2002).

Within the subduction interface, blocks are disaggregated from both the subducting slab and the overlying mantle wedge. Once these blocks are disaggregated, can they move within the fine-grained matrix? From Bebout and Penniston-Dorland (2016).

Modeling suggests that factors such as matrix viscosity, plate velocity, duration of subduction, and degree of mantle hydration all effect the size of the subduction interface and the degree of differential movement of material within the interface. From Gerya et al (2002).

            This goal of this study is to identify the dominant control on differential movement of material by comparing two exhumed terrains: the Kampos Mélange (Syros, Greece) and the Catalina Schist (Santa Catalina Island, California). These terranes appear to be similar in the degree of differential movement that they experienced; however, the Kampos Mélange experienced high-pressure/low-temperature metamorphism while the Catalina Schist experienced moderate-pressure/moderate-temperature metamorphism. 

Geologic map of Santa Catalina Island basement rock. Modified from Platt (1976).

Simplified geologic map of Syros, Greece showing the location of the Kampos Melange. From Kennedy et al (2003).

Methods

            In order to determine the peak metamorphic conditions for exotic blocks relative to non-exotic blocks in both exhumed terranes, a combination of field mapping, trace element thermometry (Tomkins et al, 2007; Hayden et al, 2008), inclusion barometry (Kohn, 2014b), and U/Pb geochronology (Zack et al, 2011) will be used. These methods have already been successfully applied to blocks from the Catalina Schist (both exotic and non-exotic) (Penniston-Dorland et al, in press; Harvey, unpublished data); therefore, this study relies on new samples and data to be collected for only the Kampos Mélange. The use of the same methods for each terrane allows their characteristics to be directly compared.

Sample data collected from the Catalina Schist showing comparison in peak P-T between exotic and non-exotic blocks of the same metamorphic grade. Temperature determined by Zirconium-in-rutile thermometry, and pressure determined by Raman Spectrometry. Data from Harvey et al (unpublished data) and Penniston-Dorland et al (in press). 

Funds Required

          This project will require funding for 1-2 graduate students, as well as funds for one field excursion to Syros, Greece, conference presentations, the creation of 40-50 thin (30μm) and corresponding thick (75μm) sections, and analysis time on the following instruments:

• Electron Microprobe Analyzer at the University of Maryland
• Laser Ablation Inductively Coupled Plasma Mass Spectrometer at the University of Maryland
• Raman Spectrometer at Boise State University (and associated travel costs)

Selected Literature Cited

Bebout, G.E., Penniston-Dorland, S.E. (20016) Fluid and mass transfer at subduction interfaces -the field metamorphic record. Lithos, 240, 228-258

Gerya, T.V., Stöchert, B., and Perchuk, A.L. (2002) Exhumation of high-pressure metamorphic rocks in a subduction channel: A numerical simulation. Tectonics, 21, doi:10.1029/2002TC001406

Hayden, L.A., Watson, E.B., and Wark, D.A. (2008) A thermobarometer for sphene (titanite). CMP 155, 529-540 (5) Kohn, M.J. (2014b) “Thermoba-Raman-try”: Calibrations of spectroscopic barometers and thermometers for mineral inclusions. EPSL, 388, 187-196 

Kennedy, A., Lagos, M., Ballhaus, C. (2003) Zirconz from Syros, Cyclades, Greece -Recrystallization and mobilization of zircon during high-pressure metamorphism. Journal of Petrology, 44(11), 1977-2002

Kohn, M.J., and Corrie, S.L. (2011) Preserved Zr-temperatures and U-Pb ages in high-grade metamorphic titanite: evidence for a static hot channel in the Himalayan orogen. EPSL, 311, 136-143 

Penniston-Dorland, S.P., Kohn, M.J., Piccoli, P.M., (in press) A mélange of subduction temperatures: Zr-in-rutile thermometry of the Catalina Schist, CA and its tectonic implications. 

Platt, J.P. (1975) Metamorphic and deformational processes in the Franciscan Complex, California: Some insights from the Catalina Schist terrain. GSA Bulletin, 6, 1337-1347. 

Tomkins, H.S., Powell, R., and Ellis, D.J. (2007) The pressure dependence of the zirconium-in-rutile thermometer. JMG, 25, 703-713 

Seismo-Acoustic Energy Produced by Rivers

Project Aim: 

With this study, I intend to advance our understanding of how flowing water in rivers produces seismic noise. I will focus on current knowledge gaps in this field and evaluate the underlying assumptions behind a priori models of seismic noise generation. This study will also monitor bedrock channeled river, which is unrepresented in the literature.

Why would NSF Care?

According to the Geomorphology and Land Use Dynamics solicitation, NSF is interested in the relationship between humans and geomorphology.

With remote seismic methods to evaluate flow velocity, we can improve river monitoring, erosion modeling, and data quality in fluvial geomorphology, which will lead to safer river management. Geomorphologists who study floods and erosion are limited in their ability to monitor rivers in flood, due to physically hazardous conditions. Even under normal flow conditions, direct in-channel measurements of flow velocity are time-consuming and difficult. 

The study area is in an urbanized environment along the Atlantic Fall Zone. Urbanization leads to more intense flooding via increased runoff. The Oroville Dam crisis is a recent and interesting natural laboratory.

Background:

As rivers flow, they produce ground vibrations from a variety of sources. To date most research has focused on quantifying bedload transport events during floods (1), the monsoon season (2), dam removals (3), and physical dumping of bedload into flowing rivers (4). Far fewer researchers have studied how flowing water generates surface seismic vibrations. Gimbert et al developed an a priori model to predict the total seismic power in the 1 - 100 Hz frequency band, but simplifying model assumptions limit its applicability to bedrock channels (5). 

Unanswered Questions Raised by Previous Work:

1) What is the practical observation window of a seismometer along a river?

Methods to Evaluate: We will investigate the coherence of signals in an along-channel seismic array. If signals are highly coherent, they will not be fully independent measures. 

 2) What are the surface wave characteristics of turbulently flowing water? Do different conditions lead to a change in the surface wave form?

Methods to Evaluate: Deploy 3-component seismometers capable of 30-day continuous recording. Investigate the relationships between up-down, north-south, and east-west motions. Use data collected near Oroville Dam as a natural experiment. 

3) What is the source of seismic energy released from flowing water? Is it related primarily boundary roughness resistance, or internal distortion resistance?

Methods to evaluate: Investigate relationships between roughness (grain size or bedrock roughness metric), turbulence (via Reynold's number), and 3-component response within observation reaches. Use flume scale models for preliminary evaluation.

4) Is seismic energy released appreciably different between similarly sized bedrock and alluvial systems?

Methods to evaluate: Simultaneous deployment 3-component nodes within of bedrock and alluvial reaches of the same river. Conduct active source characterization of along-channel material. 

5) Is cavitation a significant contribution to the acoustic and seismic outputs of rivers under the conditions predicted by Barnes (1956) and Whipple et al. (2000) (7,8)?

Methods to evaluate: Remote deployment of in-stream hydrophone and seismometer under conditions when cavitation is predicted. A the non-linear onset of high frequency (~20 kHz) acoustic noise matching laboratory cavitation will indicate the presence of cavitation.

Sources:

1-  Burtin, A., L. Bollinger, J. Vergne, R. Cattin, and J. L. Nábělek (2008), Spectral analysis of seismic noise induced by rivers: A new tool to monitor spatiotemporal changes in stream hydrodynamics, J. Geophys. Res., 113, B05301, doi:10.1029/2007JB005034.

2-  Chao, W.A., Wu, Y.M., Zhao, L., Tsai, V.C., and Chen, C.H., 2015, Seismologically determined bedload flux during the typhoon season: Scientific Reports, v. 5, 8261, doi: 10 .1038 /srep08261.

3-  Schmandt, B., Aster, R.C., Scherler, D., Tsai, V.C., and Karlstrom, K., 2013, Multiple fluvial processes detected by riverside seismic and infrasound monitoring of a controlled flood in the Grand Canyon: Geology, p. 4858–4863, doi: 10 .1002 /grl .50953.

3- Schmandt, B., Gaeuman, R.C., Stewart, R., Tsai, V.C., and Smith, J., 2017, Seismic array constraints on reach-scale bedload transport: Geophysical Research Letters, v. 40, p. 4858–4863, doi: 10 .1002 /grl .50953. doi: 10.1130/G38639.1

5- Gimbert, F., Tsai, V.C., Lamb, M.P., 2014, A physical model for seismic noise generation by turbulent flow in rivers, JGR-Earth Surface

7- Barnes, H.L., 1956, Cavitation as a Geological Agent: American Journal of Science, v. 254, p. 493-505. 

8- Whipple, K. X., Hancock, G.S., and Anderson, R.S., 2000, River Incision into Bedrock: Mechanics and Relative Efficacy of Plucking, Abrasion, and Cavitation: GSA Bulletin, v. 112(3),

Flux of Extraterrestrial Dust through the Late Holocene and Anthropocene

A cryptocrystalline micrometeorite (~0.25 mm) found in Norway. It still preserves its original mineralogy.
Photo Credit: Jon Larsen and Jan Braly Kihle.

Micrometeorites can come from several types of sources. Fully-melted micrometeorites may be sources from ablation (friction and heat-induced eroding) of infalling meteors as they pass through the atmosphere. These particulates do not preserve any textural characteristics of the original source, but another subgroup, called cryptocrystalline micrometeorites do preserve some of their original mineralogy.

Some studies estimate that the Earth gains as much as 40 kilotons of mass from extraterrestrial dust every year, and it is assumed that the variability in the composition of that mass changes over time as Earth passes through different "clouds" of dust in its orbital path.

The micrometeorite collector at McMurdo Station, water well in Antarctica. Image Credit: Cosmic Dust Research Group.

Many micrometeorites have been collected from McMurdo Station in Antarctica. The water well there is drilled into glacial ice, which preserves micrometeorites in layers whose ages are well-known. As more water is collected, the walls of the well melt and deposit more micrometeorites, which sink to the bottom and collect as sediment. This allows scientists to collect micrometeorites with well-constrained ages of deposition (~500-1,000 years old, currently).

Closer to home, a new method of collected micrometeorites from urban rooftops has been developed, and can provide micrometeorites that have been present on Earth for only a few decades at most. This technique allows for the establishment of a dataset of modern extraterrestrial dust compositions.

There's still lots of leftover space dust in our dirty, dirty, Solar System-- but how much?

The availability of both of these sets of data would allow researchers to estimate the change in composition of dust in the Solar System, and form a more accurate picture of how the composition of the Earth's surface can change over shorter timescales. The results of the data may hold implications for other Solar System processes that explain the formation of terrestrial planets, as well.

I propose that the next group of annual Antarctic meteorite hunters (ANTMET) collect micrometeorites at the well and send them to me for analysis. At the same time, I can solicit participation from schools around the U.S. to collect micrometeorites from their facilities' rooftops at virtually no cost and send those to me for analysis as well. The research could have an educational outreach component and involve interested students in STEM activities.

Hydrothermal Indium Removal from Volcanic Glass & Indium-Sphalerite Partitioning

My proposal will be a continuum of the current work being done in the Laboratory for Mineral Deposits Research at the University of Maryland College Park. Currently, my research focuses on indium removal from altered basaltic glass into a potential ore-forming fluid. However, much more work needs to be done to properly assess volcanic glass as a source material for indium.

Figure 1. Efficiency of removal scenarios involving recent data collected by LMDR.

Not only are more experiments needed to determine the efficiencies of removal in basalts under various experimental conditions, but more work is required to understand different volcanic rock compositions, such as rhyolites and andesites. Therefore, more financial assistance is required to supply our lab with platinum, gold, and indium which is used in each of our experiments.

Once this work is complete, we will better understand the conditions under which an indium-bearing ore-forming fluid might form. However, this does not describe deposition of the indium being transported in the ore-forming fluid. Indium, is mostly mined as a byproduct in zinc mining of sphalerite. Therefore, I propose work be done to constrain the partitioning of indium in sphalerite (ZnS) under hydrothermal conditions in order to determine the ideal conditions at which a Zn-In deposit might form.

Figure 2. Sphalerite ore with chalcopyrite (https://www.flickr.com/photos/jsjgeology/18844045435).

In order to achieve this, I will place Zn+S within a 3mm diameter Au capsule within a larger 5mm diameter Pt capsule. 1 M HCl with indium concentrations at about 500ppm will be placed within the Pt capsule. Experiments will be run at 500°C and at 50 MPa for 4-8 weeks long. Experiments will be analyzed using EPMA and ICP-MS here at UMD, College Park.

Understanding fluid flow in subduction zones

Subduction zones are the loci for a number of phenomena that impact human well-being. The largest earthquakes on record, as well as some of the most destructive have been generated within subduction zones. The most explosive and destructive volcanoes are also found in volcanic arcs over subduction zones and are fed by melting processes associated with subduction. But subduction does not just generate natural hazards. Some of the richest ore deposits in the world, such as those in Chile, are associated with volcanic arcs as well. What makes subduction so uniquely capable of pushing the extremity of natural phenomena? During subduction, cold, hydrated oceanic crust is carried deep into the lithospheric mantle where fluid is released sparking reactions that are difficult to produce through other tectonic processes.

            However, even though these fluids have been linked to important processes, their behavior is still poorly understood. Exhumed high-pressure/low-temperature (HP/LT) metamorphic rocks that show evidence of seismic activity (pseudotachylytes, brecciation) also record significant fluid movement associated with these events that is focused along planes of failure. However, it has yet to be determined if the fluid release accompanying earthquakes is a cause or a result. Trace element signatures distinct from those generated by partial melting of the mantle have been identified in volcanic arcs and interpreted as evidence of chemical input from the subducting slab. However, the proportion of the various subduction inputs (lithospheric mantle, oceanic crust, oceanic sediments) and the method of transportation: partial melt versus aqueous fluid, have yet to be definitively established.

Fig. 1: Transect across a fluid alteration zone showing changes in mineralogy.

            Constraining the behavior of fluids released by dehydration reactions in the subducting slab, and their mass transfer potential is key to understanding their role in seismic and volcanic activity. I propose a geochemical and petrological study of identified fluid pathways in exhumed HP/LT rocks to constrain the source, periodicity, duration, spatial distribution, and mass transfer potential of subduction zone fluid events. Samples will be collected in transects across identified fluid pathways (e.g. shear zones, veins, metasomatic alteration zones) to allow analysis on the meter to micron scale. Geochemical analysis will be carried out on whole rock samples on the millimeter to meter scale to constrain the penetration and mass transfer potential of passing fluids. Diffusion modeling across any measured chemical gradients identified in these whole rock transects will be used to constrain the duration of fluid pulses.

Fig. 2: Complex Mn zoning in garnet from the Western Alps showing the importance of intra-mineral analysis 

Fig. 3: Lithium concentration and δ⁷Li traverse showing evidence for fluid interaction in low-δ⁷Li zone. 

In situ analysis of mineral zoning will be used to constrain the periodicity of fluid movement as well as any disequilibrium between mineral phases associated with preferential alteration during fluid interaction. Geochemical analyses will include major and trace elements as well as lithium and oxygen isotopes. Isotopic signatures will be used to differentiate between fluid sources since both oxygen and lithium have well constrained values for reservoirs such as: altered upper and lower oceanic crust, subducted sediments and serpentinite. The use of both Li and O isotopes provides an opportunity to interrogate the isotopic record of fluid on a range of timescales. Oxygen diffuses slowly in common HP/LT minerals and can retain isotopic heterogeneity over hundreds of millions of years. Lithium on the other hand, has been shown in experimental studies to diffuse much faster than other elements. Thus O isotopes would be expected to robustly record long-lived events while Li isotopes would record more ephemeral fluid interaction. The only other application of Li and O isotopes to metamorphic rocks identified an order of magnitude difference (60m versus 4m) in diffusive exchange across the boundary between a layered mafic complex and a sedimentary diapir. This suggests that pairing O and Li can reveal geochemical nuance not available with a single isotopic system. By constraining fluid behavior within subduction zones on a range of scales we can better understand how it relates to generation of earthquakes and arc volcanism, and improve our models for both natural hazards. 

Tidally Induced Ice quakes: Modeling the Seismicity, Background Noise, and Seismic Detectability of Europa

          Europa, an icy moon of Jupiter, has a thick ice shell that likely experiences active faulting (Fig. 1). Seismology is one of the most efficient methods for measuring the seismic activity and determining physical properties of the ice shell. In order to determine the efficacy of a seismometer, the seismicity and background noise of Europa must be determined.  The models can be used together to determine the frequency and magnitudes of tidally induced ice quakes and determine if larger ice quakes or deep Europa-quakes could be used to survey the interior of Europa and determine the properties of its ice shell.

Animation of Resonant Orbital Periods.  Every time Europa completes one orbit, Io completes two, and Ganymede completes 1/2. This alignment caused strong tidal effects resulting in faulting on Europa.

Figure 1. Large scale faulting of Europa created by induced stresses. Image Credit: NASA JPL

         Europa experiences induced stress from its resonant orbit with Io and Ganymede. These induced stresses can be modeled and compared to estimates of ice strength to determine how often and by how much the ice fractures during an orbital period. When the ice fractures it will produce ice quakes with magnitudes proportional to the released stress. The magnitude and frequency of events can be mapped globally or regionally to create seismicity estimates.

            When small events occur concurrently, the waveforms interfere in a constructive/deconstructive manner creating background noise. This background noise will make interpreting seismograms more difficult, and could prevent proper analysis of the interior structure. If the background noise can be modeled, its signal can be removed and allow for proper interpretation to occur. To create background noise models, I can use the seismicity models to create synthetic seismograms of predicted events. These seismograms can be stacked to simulate what a seismometer may experience. Time-series analysis can be done to measure which frequencies and periods are most susceptible to seismic noise (Fig.2).

Figure 2. A) Examples of seismic noise (purple, blue), calibration (pink, yellow) and seismic events( green, red). B) Resulting Power Spectrum Density for periods of previous signals. C) Resulting probability of noise for station HLID.  D) Noise map for 4-8s noise. 

            The last task will be to test large events predicted by the seismicity models against the background noise model. Previously developed algorithms can be implemented to determine how many events would need to occur to recover the interior structure of Europa. The results will indicate if a single-station seismometer is capable of determining the internal structure and properties of the ice shell and subsurface ocean.
           Exploration of Europa remains a top priority for NASA, and a future lander mission may include a seismometer. This research can be used to determine what the seismometer is likely to detect and how many events would be required to accurately survey Europa's interior. If a seismometer is not part of the payload, hazards from ice quakes will need to be considered when selecting a landing site. The regional seismicity maps can be used with the currently planned Europa Clipper Mission to estimate where new faults may be generated, and which areas showed be imaged.