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At least 757 records · Page 42Linked to original sources
USGS2019

An assessment of plant species differences on cellulose oxygen isotopes from two Kenai Peninsula, Alaska peatlands: Implications for hydroclimatic reconstructions

Peat cores are valuable archives of past environmental change because they accumulate plant organic matter over millennia. While studies have primarily focused on physical, ecological, and some biogeochemical proxies, cores from peatlands have increasingly been used to interpret hydroclimatic change using stable isotope analyses of cellulose preserved in plant remains. Previous studies indicate that the stable oxygen isotope compositions (δ 18 O) preserved in alpha cellulose extracted from specific plant macrofossils reflect the δ 18 O values of past peatland water and thereby provide information on long-term changes in hydrology in response to climate. Oxygen isotope analyses of peat cellulose (δ 18 O cellulose ) have been successfully developed from peat cores that accumulate the same species for millennia. However, to fully exploit the potential of this proxy in species-diverse fens, studies are needed that account for the isotopic variations caused by changes in dominant species composition. This study assesses variation in δ 18 O values among peatland plant species and how they relate to environmental waters in two fens informally named Horse Trail and Goldfin, located on the leeward (dry) and windward (wet) side, respectively, of the climatic gradient across the Kenai Peninsula, Alaska. Environmental water δ 18 O values at both fens reflect unmodified δ 18 O values of mean annual precipitation, although at Goldfin standing pools were slightly influenced by evaporation. Modern plant [mosses and Carex spp. (sedges)] δ 18 O cellulose values indicate that all Carex spp. are higher (~2.5‰) than those of mosses, likely driven by their vascular structure and ecophysiological difference from non-vascular mosses. Moss δ 18 O cellulose values within each peatland are similar among the species, and differences appear related to evaporation effects on environmental waters within hummocks and hollows. The plant taxa-environmental water δ 18 O differences are applied to the previously determined Horse Trail Fen untreated bulk δ 18 O record. Results include significant changes to inferred millennial-to-centennial scale hydroclimatic trends where dominant taxa shift from moss to Carex spp., indicating that modern calibration datasets are necessary for interpreting stable isotopes from fens, containing a mix of vascular and nonvascular plants. Accounting for isotopic offsets through macrofossil analysis and modern plant-water isotope measurements opens new opportunities for hydroclimatic reconstructions from fen peatlands.

Alaska↗
USGS2019

Late-Glacial paleoecology of the Middle Susitna Valley, Alaska: Environmental context for human dispersal

We present here the results of multi-proxy analyses (sediment geochemistry, diatoms, and pollen) from sediment cores collected at four lakes in the middle Susitna Valley, Alaska. These lakes form a transect from the tundra to the boreal forest. The retrieved cores span from ~12,000 cal yr BP to the present, with age control provided by radiometric dates and tephra deposits, some of which are newly identified. Results indicate that deglaciation occurred before 12,000 cal yr BP and that by that time, the lakes were deep, productive, and surrounded by shrub tundra. The lake with the highest sampling resolution indicates a brief climatic reversal ~11,500 cal yr BP with decreased diatom-inferred lake level and lowered lake productivity, and reduced shrub presence. During the early to middle Holocene, all of the sedimentary records provide evidence of climatic amelioration with tree expansion and productive lakes. A middle to late Holocene climatic deterioration with reduced trees and a shallower, less productive lake is also indicated. In addition, the prominent Watana tephra at ~4,000 cal yr BP likely reduced lake productivity and affected the vegetation. Even though the region was relatively productive soon after deglaciation, people did not occupy the region until ~11,000 cal yr BP, about 1000 years later, and then only sparsely. By the middle and late Holocene, the region was more densely populated and this shift in human occupancy presumably reflects changes in resource abundance, especially caribou. Whether the Watana ashfall influenced caribou abundance and thus people, is still under investigation, but given the tephra’s effect on vegetation and lake productivity, it seems likely.

Alaska↗
USGS2019

Holocene thermokarst lake dynamics in northern Interior Alaska: The interplay of climate, fire, and subsurface hydrology

The current state of permafrost in Alaska and meaningful expectations for its future evolution are informed by long-term perspectives of previous permafrost degradation. Thermokarst processes in permafrost landscapes often lead to widespread lake formation and the spatial and temporal evolution of thermokarst lake landscapes reflects the combined effects of climate, ground conditions, vegetation, and fire. This study provides detailed analyses of thermokarst lake sediments of Holocene age from the southern loess uplands of the Yukon Flats; including bathymetry and sediment core analyses across a water depth transect. The sediment core results, dated by radiocarbon and 210Pb, indicate the onset of finely laminated lacustrine sedimentation between ~10,000 and 9,000 cal yr BP following basin development through inferred thermokarst processes. Thermokarst expansion to modern shoreline configurations continued until ~5000 cal yr BP, which may have been influenced by increased fire. Between ~5000 and 2000 cal yr BP, the preservation of fine laminations at intermediate and deep-water depths indicate higher lake levels than present. At that time, the lake likely overflowed into an over-deepened gully system that is no longer occupied by perennial streams. By ~2000 cal yr BP, massive sedimentation at intermediate water depths indicates that lake levels lowered, which is interpreted to reflect a response to drier conditions based on correspondence with Yukon Flats regional fire and local paleoclimate reconstructions. Consideration of additional contributing mechanisms include the possible influence of catastrophic lake drainages on downgradient base flow levels that may have enhanced subsurface water loss, although this mechanism is untested. The overall consistency between the millennial lake level trends documented here with regional paleoclimate trends indicates that after lakes formed, their size and depth has likely been affected directly by North Pacific atmospheric circulation changes and indirectly through evolution of permafrost, ground ice and sub-surface hydrology. As the first detailed study of Holocene thermokarst basin expansion, stabilization and subsequent climate-driven lake level variations in a loess upland, results provide a framework for future investigations of paleoclimatic signals from similar lake systems that characterize large regions of Alaska and Siberia.

Alaska↗
USGS2019

A stratigraphic approach to inferring depositional ages from detrital geochronology data

With the increasing use of detrital geochronology data for provenance analyses, we have also developed new constraints on the age of otherwise undateable sedimentary deposits. Because a deposit can be no older than its youngest mineral constituent, the youngest defensible detrital mineral age defines the maximum depositional age of the sampled bed. Defining the youngest `defensible' age in the face of uncertainty (e.g., analytical and geological uncertainty, or sample contamination) is challenging. The current standard practice of finding multiple detrital minerals with indistinguishable ages provides confidence that a given age is not an artifact; however, we show how requiring this overlap reduces the probability of identifying the true youngest component age. Barring unusual complications, the principle of superposition dictates that sedimentary deposits must get younger upsection. This fundamental constraint can be incoporated into the analysis of depositional ages in sedimentary sections through the use of Bayesian statistics, allowing for the inference of bounded estimates of true depositional ages and uncertainties from detrital geochronology so long as some minimum age constraints are present. We present two approaches for constructing a Bayesian model of deposit ages, first solving directly for the ages of deposits with the prior constraint that the ages of units must obey stratigraphic ordering, and second describing the evolution of ages with a curve that represents the sediment accumulation rate. Using synthetic examples we highlight how this method preforms in less-than-ideal circumstances. In an example from the Magallanes Basin of Patagonia, we demonstrate how introducing other age information from the stratigraphic section (e.g., fossil assemblages or radiometric dates) and formalizing the stratigraphic context of samples provides additional constraints on and information regarding depositional ages or derived quantities (e.g., sediment accumulation rates) compared to isolated analysis of individual samples.

Frontiers in Earth Science↗
USGS2019

Stratigraphic occurrences of sub-polar planktic foraminifera in pleistocene sediments on the Lomonosov Ridge, Arctic Ocean

Turborotalita quinqueloba is a species of planktic foraminifera commonly found in the sub-polar North Atlantic along the pathway of Atlantic waters in the Nordic seas and sometimes even in the Arctic Ocean, although its occurrence there remains poorly understood. Existing data show that T. quinqueloba is scarce in Holocene sediments from the central Arctic but abundance levels increase in sediments from the last interglacial period [Marine isotope stage (MIS) 5, 71–120 ka] in cores off the northern coast of Greenland and the southern Mendeleev Ridge. Turborotalita also occurs in earlier Pleistocene interglacials in these regions, with a unique and widespread occurrence of the less known Turborotalita egelida morphotype, proposed as a biostratigraphic marker for MIS 11 (474–374 ka). Here we present results from six new sediment cores, extending from the central to western Lomonosov Ridge, that show a consistent Pleistocene stratigraphy over 575 km. Preliminary semi-quantitative assessments of planktic foraminifer abundance and assemblage composition in two of these records (LOMROG12-7PC and AO16-5PC) reveal two distinct stratigraphic horizons containing Turborotalita in MIS 5. Earlier occurrences in Pleistocene interglacials are recognized, but contain significantly fewer specimens and do not appear to be stratigraphically coeval in the studied sequences. In all instances, the Turborotalita specimens resemble the typical T. quinqueloba morphotype but are smaller (63–125 μm), smooth-walled and lack the final thickened calcite layer common to adults of the species. These results extend the geographical range for T. quinqueloba in MIS 5 sediments of the Arctic Ocean and provide compelling evidence for recurrent invasions during Pleistocene interglacials.

Frontiers in Earth Science↗
USGS2019

Late Quaternary vegetation development following deglaciation of northwestern Alexander Archipelago, Alaska

The Cordilleran Ice sheet covered most of southeastern Alaska during the Last Glacial Interval (LGI: Marine Isotope Stage 2). Ice began to recede from western Alexander Archipelago ~17,000 + 700 yr BP. In this study pollen analysis and radiocarbon dating of three sediment cores were used to reconstruct, for the first time, the postglacial development of vegetation of the northwestern Alexander Archipelago during the past ~15,240 cal yr. Hummingbird Lake (HL), on southwestern Baranof Island, yielded a sediment core with one of the longest dated records from southeastern Alaska. The earliest part of the HL pollen record (~15,240-14,040 yr BP) indicates that the earliest vegetation was pine (Pinus contorta subsp. contorta) parkland with willows (Salix), heaths (Ericaceae), sedges (Cyperaceae), grasses (Poaceae), herbs and ferns. Starting at ~14,040 yr BP, alder (Alnus) rapidly colonized the area as pine populations declined. By 11,400 yr BP, Sitka spruce (Picea sitchensis) colonized the area, and soon became the dominant conifer. Mountain hemlock (Tsuga mertensiana) also colonized the area by ~11,400 yr BP, followed by western hemlock (Tsuga heterophylla) at ~10,200 yr BP. By ~9200 yr BP, western hemlock had become the dominant species in the area. During the late Holocene yellow cedar (Chamaecyparis nootkatensis) became established. Two marine sediment cores were also analyzed for pollen, with the oldest core from Lower Sitka Sound, between Kruzof and Baranof Islands. The lower part of the core consists of interlayered tephras and freshwater lake muds that are estimated to be ~13,150 to 14,000 yr BP. Pollen evidence indicates that the early postglacial vegetation around Sitka Sound was pine parkland with alders and abundant ferns. Damage to vegetation around Sitka Sound by volcanic eruptions is suggested by abrupt, large shifts in alder and pine pollen, and fern spores in samples adjacent to tephra layers. A marine sediment core from Slocum Arm, a fjord on the western coast of Chichagof Island, has a basal age of ~10,000 yr BP. The pollen record is similar to the Holocene pollen record at Hummingbird Lake. The sequence of vegetation changes interpreted from the three northwestern Alexander Archipelago pollen records are similar to those from other well-dated sites in southeastern Alaska, although chronologies differ between sites.

Alaska↗
USGS2019

Variability in shelf sedimentation in response to fluvial sediment supply and coastal erosion over the past 1,000 years in Monterey Bay, CA, United States

Continental shelf environments are uniquely situated to capture some of the most dynamic processes on Earth including climatic variability and anthropogenic modifications to coastal systems. Understanding how these processes have affected sediment delivery and accumulation on the shelf in the past may provide insight into potential changes in the future. To address this, we investigated shelf sedimentation within Monterey Bay, California. Sediment cores were collected from four locations throughout the bay to capture both the modern and late Holocene sedimentological record using grain size analysis, and sediment chronologies determined from 210 Pb, 137 Cs, and 14 C. From the grain size results we focused on the total percent sand, and established a Littoral Sand Fraction (LSF) index to assess sediment contribution from the littoral zone as a result coastal erosion. Grain size results from the multicores consistently showed an increase in sand over the past several decades (post 1970s). For the cores located within the bay proximal to three major rivers, the increase in sand corresponded to a general increase in the LSF over the same period. We attributed these trends to increased sediment contributions to the shelf due to accelerated coastal erosion in the region. This accelerated coastal erosion was likely the combined result of dam construction in the mid-twentieth century that limited fluvial supply to the coast, and a shift in climate toward wetter, stormier period. Applying these sediment characteristics back over the past ∼1,000 years we found that dry climatic periods resulted in deposits that were limited in total sand but enriched in littoral material suggesting elevated coastal erosion. During wet periods deposits were enriched in total sand but limited in littoral sand suggesting elevated fluvial supply and low erosion. Compared to the late Holocene record, the previous several decades represent a shift to a new regime, uncharacteristic of deposits over the past millennia, highlighting the impact humans have had on shelf sedimentation.

California↗
USGS2019

The risk reduction benefits of the Mesoamerican Reef in Mexico

Coastal development and climate change are dramatically increasing the risks of flooding, erosion, and extreme weather events. Coral reefs and other coastal ecosystems act as natural defenses against coastal hazards, but their degradation increases risk to people and property. Environmental degradation, however, has rarely been quantified as a driver of coastal risk. In Quintana Roo, Mexico, a region on the Mexican Caribbean coast with an annual tourism economy of 10 billion USD, coral reefs constitute a natural barrier against flooding from hurricanes. This study spatially quantifies the risk reduction benefits of the Mesoamerican Reef in Quintana Roo for people, buildings, and hotel infrastructure. The risk reduction benefits are substantial. For example, the reefs prevented 43% additional damage during Hurricane Dean in (2007) and provide nowadays hazard risk reduction for 4.3% of the people, 1.9% of the built capital, and 2.4% of the hotel infrastructure, per year. The annual benefits are estimated in 4,600 people, 42 million USD damage prevention for buildings, and 20.8 million USD for hotel infrastructure. The study also compares the risk reduction of coral reefs with (i) the protection offered by dunes and (ii) the increase in coastal risk from sea-level rise (SLR). The risk reduction of dunes is more critical where there are no coral reefs offshore and for small return-periods storms. Sea-level rise, however, will make the more frequent storms more impactful and will drive significant increases in annual expected damages across the region. However, we demonstrate that, in coral reef environments, the contribution of reef degradation to coastal risk is larger than the expected increase in risk from SLR. However, the spatial distribution of the risk reduction benefits from reefs differs for people and infrastructure, and in particular for hotels, which receive the most protection from reefs. Furthermore, many sections present larger benefits than the typical costs of restoration. This valuation makes a compelling case for protecting and maintaining this natural infrastructure for its risk reduction service, but also allows the development of piloting innovative strategies, such as risk finance and insurance strategies, that can align environmental and risk management goals.

Mesoamerican Reef↗
USGS2019

Hysteretic response of solutes and turbidity at the event scale across forested tropical montane watersheds

Concentration-discharge relationships are a key tool for understanding the sourcing and transport of material from watersheds to fluvial networks. Storm events in particular provide insight into variability in the sources of solutes and sediment within watersheds, and the hydrologic pathways that connect hillslope to stream channel. Here we examine high-frequency sensor-based specific conductance and turbidity data from multiple storm events across two watersheds (Quebrada Sonadora and Rio Icacos) with different lithology in the Luquillo Mountains of Puerto Rico, a forested tropical ecosystem. Our analyses include Hurricane Maria, a category 5 hurricane. To analyze hysteresis, we used a recently developed set of metrics to describe and quantify storm events including the hysteresis index (HI), which describes the directionality of hysteresis loops, and the flushing index (FI), which can be used to infer whether the mobilization of material is source or transport limited. We also examine the role of antecedent discharge to predict hysteretic behavior during storms. Overall, specific conductance and turbidity showed contrasting responses to storms. The hysteretic behavior of specific conductance was very similar across sites, displaying clockwise hysteresis and a negative flushing index indicating proximal sources of solutes and consistent source limitation. In contrast, the directionality of turbidity hysteresis was significantly different between watersheds, although both had strong flushing behavior indicative of transport limitation. Overall, models that included antecedent discharge did not perform any better than models with peak discharge alone, suggesting that the magnitude and trajectory of an individual event was the strongest driver of material flux and hysteretic behavior. Hurricane Maria produced unique hysteresis metrics within both watersheds, indicating a distinctive response to this major hydrological event. The similarity in response of specific conductance to storms suggests that solute sources and pathways are similar in the two watersheds. The divergence in behavior for turbidity suggests that sources and pathways of particulate matter vary between the two watersheds. The use of high-frequency sensor data allows the quantification of storm events while index-based metrics of hysteresis allow for the direct comparison of complex storm events across a heterogeneous landscape and variable flow conditions.

Luquillo Mountains↗
USGS2019

Linking direct measurements of turbidity currents to submarine canyon-floor deposits

Submarine canyons are conduits for episodic and powerful sediment density flows (commonly called turbidity currents) that move globally significant amounts of terrestrial sediment and organic carbon into the deep sea, forming some of the largest sedimentary deposits on Earth. The only record available for most turbidity currents is the deposit they leave behind. Therefore, to understand turbidity current processes, we need to determine the degree to which these flows are represented by their deposits. However, linking flows and deposits is a major long-standing scientific challenge. There are few detailed measurements from submarine turbidity currents in action, and even fewer direct measurements that can be compared to resulting seabed deposits. Recently, an extensive array of moorings along Monterey Canyon, offshore California, took measurements and samples during sediment density flow events, providing the most comprehensive dataset to date of turbidity current flows and their deposits. Here, we use sediment trap samples, velocity measurements, and seafloor cores to document how sand is transported through a submarine canyon, and how the transported sediment is represented in seafloor deposits. Sediment trap samples from events contain primarily fine to medium-grained sand with sharp bases, normal grading, and muddy tops. Sediment captured from the water column during the flow shows normal grading, which is broadly consistent with the initial peak and waning of flow velocities measured at a single height within the flow, and may be enhanced by collapsing flows. Flow events contain coarser sand concentrated toward the seafloor and larger grain sizes on the seafloor or in the dense near-bed layer, possibly representative of stratified flows. Although flow velocity varies, sand grain sizes in sediment traps are similar over distances of 50 km down-canyon, suggesting that grain size is an unfaithful record of down-canyon changes in maximum flow speeds. Sand transported within flow events and sampled in sediment traps is similar to sand sampled from the seafloor shortly after the events, but traps do not contain pebbles and gravel common in seabed deposits. Seabed deposits thus appear to faithfully record the sand component that is transported in the water column during sub-annual turbidity currents.

California↗
USGS2019

Hydroacoustic, meteorologic and seismic observations of the 2016 Nansen Ice Shelf calving event and iceberg formation

On 7 April 2016, the Nansen Ice Shelf (NIS) front calved into two icebergs, the first large-scale calving event in >30 years. Three hydrophone moorings were deployed seaward of the NIS in December 2015 and over the following months recorded hundreds of short duration, broadband (10-400 Hz) cryogenic signals, likely caused by fracturing of the ice-shelf. The majority of these icequakes occur between January and early March 2016, several weeks prior to the calving observed by satellite on 7 April. Barometric pressure and wind speed records show the day the icebergs drifted from the NIS coincided with the largest low-pressure storm system recorded in the previous 7 months. A nearby seismic station also shows an increase in low-frequency energy, harmonic tremor, and microseisms on 7 April. Our interpretation is the northern segment of the NIS leading edge broke free during mid-January to February, producing high acoustic energy, but the icebergs remained stationary until the combination of a strong low-pressure system, with high winds freed the icebergs. As the unpinning of Antarctic ice shelves is not a well-documented process, our observations show that storm systems may play an under-appreciated role in Antarctic ice shelf break-up.

Frontiers in Earth Science↗
USGS2019

Editorial: Synthetic Aperture Radar and natural hazards: Applications and outlooks

The ability of Synthetic Aperture Radar (SAR) to image the Earth’s surface, even through dense cloud cover and in night-and-day conditions, can facilitate the evaluation and monitoring of natural hazards and the management of natural disasters. The family of SAR satellite sensors orbits the Earth at an altitude ranging from 500 to 800 km, following sun-synchronous, near-polar orbits, slightly inclined with respect to Earth meridians. The most commonly used bands in SAR applications are the C-band (5–6 GHz, ~5,6 cm wavelength), the X-band (8–12 GHz, ~3,1 cm wavelength) and the L-band (1–2 GHz ~23 cm wavelength) with a temporal resolution depending on the satellite revisiting time. The availability of SAR has made a new spectrum of measurements possible on a global and spatial scale not attainable by ground-based studies, revealing critical insights into remote or poorly understood areas (e.g., Biggs et al., 2014). This Research Topics presents a review of articles on the state-of-art in the application of SAR sensors to study surface deformation in different geologic environments and triggered by a variety of processes. The topics discussed range from the analysis of co-seismic deformation (Marryman Boncori) to studies of volcanic unrest (Dzurisin et al., Garthwaite et al.), monitoring of landslides (Bianchini et al.) and ground subsidence in urban areas (Solari et al.).

Frontiers in Earth Science↗
USGS2019

Commentary: Variability in shelf sedimentation in response to fluvial sediment supply and coastal erosion over the past 1,000 Years in Monterey Bay, CA, United States

A commentary on: Variability in Shelf Sedimentation in Response to Fluvial Sediment Supply and Coastal Erosion Over the Past 1,000 Years in Monterey Bay, CA, United States. by Carlin J., Addison J., Wagner A., Schwartz V., Hayward J., Severin V. (2019) Front. Earth Sci., 7:113. doi: 10.3389/feart.2019.00113

Frontiers in Earth Science↗
USGS2019

Dissolved organic carbon turnover in permafrost-influenced watersheds of interior Alaska: Molecular insights and the priming effect

Increased permafrost thaw due to climate change in northern high-latitudes has prompted concern over impacts on soil and stream biogeochemistry that affect the fate of dissolved organic carbon (DOC). Few studies to-date have examined the link between molecular composition and biolability of dissolved organic matter (DOM) mobilized from different soil horizons despite its importance in understanding carbon turnover in aquatic systems. Additionally, the effect of mixed DOM sources on microbial metabolism (e.g., priming) is not well understood. No studies to-date have addressed potential priming effects in northern high-latitude or permafrost-influenced aquatic ecosystems, yet these ecosystems may be hot spots of priming where biolabile, ancient permafrost DOC mixes with relatively stable, modern stream DOC. To assess biodegradability and priming of DOC in permafrost-influenced streams, we conducted 28 day bioincubation experiments utilizing a suite of stream samples and leachates of fresh vegetation and different soil horizons, including permafrost, from Interior Alaska. The molecular composition of unamended DOM samples at initial and final time points was determined by ultrahigh resolution mass spectrometry. Initial molecular composition was correlated to DOC biodegradability, particularly the contribution of energy-rich aliphatic compounds, and stream microbial communities utilized 50–56% of aliphatics in permafrost-derived DOM within 28 days. Biodegradability of DOC followed a continuum from relatively stable stream DOC to relatively biolabile DOC derived from permafrost, active layer organic soil, and vegetation leachates. Microbial utilization of DOC was ∼3–11% for stream bioincubations and ranged from 9% (active layer mineral soil-derived) to 66% (vegetation-derived) for leachate bioincubations. To investigate the presence or absence of a priming effect, bioincubation experiments included treatments amended with 1% relative carbon concentrations of simple, biolabile organic carbon substrates (i.e., primers). The amount of DOC consumed in primed treatments was not significantly different from the control in any of the bioincubation experiments after 28 days, making it apparent that the addition of biolabile permafrost-derived DOC to aquatic ecosystems will likely not enhance the biodegradation of relatively modern, stable DOC sources. Thus, future projections of carbon turnover in northern high-latitude region streams may not have to account for a priming effect.

Alaska↗
USGS2020

Spatial and temporal variations in SO2 and PM2.5 levels around Kīlauea volcano, Hawai'i during 2007–2018

Among the hazards posed by volcanoes are the emissions of gases and particles that can affect air quality and damage agriculture and infrastructure. A recent intense episode of volcanic degassing associated with severe impacts on air quality accompanied the 2018 lower East Rift Zone (LERZ) eruption of Kīlauea volcano, Hawai'i. This resulted in a major increase in gas emission rates with respect to usual emission values for this volcano, along with a shift in the source of the dominant plume to a populated area on the lower flank of the volcano. This led to reduced air quality in downwind communities. We analyse open-access data from the permanent air quality monitoring networks operated by the Hawai'i Department of Health (HDOH) and National Park Service (NPS), and report on measurements of atmospheric sulfur dioxide (SO 2 ) between 2007 and 2018 and PM 2.5 (aerosol particulate matter with diameter <2.5 μm) between 2010 and 2018. Additional air quality data were collected through a community-operated network of low-cost PM 2.5 sensors during the 2018 LERZ eruption. From 2007 to 2018 the two most significant escalations in Kīlauea's volcanic emissions were: the summit eruption that began in 2008 (Kīlauea emissions averaged 5–6 kt/day SO 2 from 2008 until summit activity decreased in May 2018) and the LERZ eruption in 2018 when SO 2 emission rates reached a monthly average of 200 kt/day during June. In this paper we focus on characterizing the airborne pollutants arising from the 2018 LERZ eruption and the spatial distribution and severity of volcanic air pollution events across the Island of Hawai'i. The LERZ eruption caused the most frequent and severe exceedances of the Environmental Protection Agency (EPA) PM 2.5 air quality threshold (35 μg/m 3 as a daily average) in Hawai'i in the period 2010–2018. In Kona, for example, the maximum 24-h-mean mass concentration of PM 2.5 was recorded as 59 μg/m 3 on the twenty-ninth of May 2018, which was one of eight recorded exceedances of the EPA air quality threshold during the 2018 LERZ eruption, where there had been no exceedances in the previous 8 years as measured by the HDOH and NPS networks. SO 2 air pollution during the LERZ eruption was most severe in communities in the south and west of the island, as measured by selected HDOH and NPS stations in this study, with a maximum 24-h-mean mass concentration of 728 μg/m 3 recorded in Ocean View (100 km west of the LERZ emission source) in May 2018. Data from the low-cost sensor network correlated well with data from the HDOH PM 2.5 instruments, confirming that these low-cost sensors provide a robust means to augment reference-grade instrument networks.

Hawaii↗
USGS2020

Towards reproducible environmental modeling for decision support: A worked example

A fully worked example of decision-support-scale uncertainty quantification (UQ) and parameter estimation (PE) is presented. The analyses are implemented for an existing groundwater flow model of the Edwards aquifer, Texas, USA, and are completed in a script-based workflow that strives to be transparent and reproducible. High-dimensional PE is used to history-match simulated outputs to corresponding state observations of spring flow and groundwater level. Then a hindcast of a historical drought is made. Using available state observations recorded during drought conditions, the combined UQ and PE analyses are shown to yield an ensemble of model results that bracket the observed hydrologic responses. All files and scripts used for the analyses are placed in the public domain to serve as a template for other practitioners who are interested in undertaking these types of analyses.

Texas↗
USGS2020

Organic matter integration, overprinting, and the relative fraction of optically active organic carbon in a human-impacted watershed

Rivers continually integrate terrestrial organic matter (OM) into their waters, in a process that transfers 1.9 Pg C yr –1 as the primary linkage between oceanic and terrestrial carbon cycles. Yet rivers are not simple, conservative OM integrators. Patchy local land uses (wetlands, bogs, agriculture) release OM that can disproportionately alter river biogeochemistry and overprint upstream carbon. These releases are quantifiable at the plot scale but remain unpredictable across river reaches and watersheds, critically inhibiting our ability to scale up terrestrial-aquatic linkages to regional/global carbon cycling models. We evaluated OM overprinting distance along a human-influenced watershed to quantify river integration of terrestrial OM and to bridge the quantification gap between habitats and waterway biogeochemistry. We investigated changes in dissolved organic carbon (DOC) concentration and dissolved organic matter (DOM) composition (lignin phenols, fluorescence excitation-emission spectra using parallel factor analysis [PARAFAC], and the relative fraction of optically active DOM [EEM DOC ]). DOC concentrations increased continually ( p < 0.001) downstream, from median 1.0 mg L –1 at 30 km (headwaters) to 3.3 mg L –1 at the river mouth. This rate of increase corresponded to a DOC overprinting distance—the longitudinal distance over which DOC concentrations double—of 13 km. Mainstem DOC overprinting distance ranged from 8 km (winter, rainy season) to 21 km (summer, dry season with irrigation), highlighting stronger overprinting during increased hydraulic connectivity. Stronger overprinting also correlated to higher EEM DOC ( p < 0.001). Overprinting distance effectively quantifies river integration of DOM along the terrestrial-aquatic interface, helping to refine bottom-up carbon cycle estimates, inform upscaling of site-specific fluxes, and to track land use and climate influence on river biogeochemistry.

California↗
USGS2020

Deglacierization of a marginal basin and implications for outburst floods, Mendenhall Glacier, Alaska

Suicide Basin is a partly glacierized marginal basin of Mendenhall Glacier, Alaska, that has released glacier lake outburst floods (GLOFs) annually since 2011. The floods cause inundation and erosion in the Mendenhall Valley, impacting homes and other infrastructure. Here, we utilize in-situ and remote sensing data to assess the recent evolution and current state of Suicide Basin. We focus on the 2018 and 2019 melt seasons, during which we collected most of our data, partly using unmanned aerial vehicles (UAVs). To provide longer-term context, we analyze DEMs collected since 2006 and model glacier surface mass balance over the 2006–2019 period. During the 2018 and 2019 outburst flood events, Suicide Basin released ~30 × 10 6 m 3 of water within approximately 4–5 days. Since lake drainage was partial in both years, these ~30 × 10 6 m 3 represent only a fraction (~60%) of the basin's total storage capacity. In contrast to previous years, subglacial drainage was preceded by supraglacial outflow over the ice dam, which lasted ~1 day in 2018 and 6 days in 2019. Two large calving events occurred in 2018 and 2019, with submerged ice breaking off the main glacier during lake filling, thereby increasing the basin's storage capacity. In 2018, the floating ice in the basin was 36 m thick on average. In 2019, ice thickness was 29 m, suggesting rapid decay of the ice tongue despite increasing ice inflow from Mendenhall Glacier. The ice dam at the basin entrance thinned by more than 5 m a –1 from 2018 to 2019, which is approximately double the rate of the reference period 2006–2018. While ice-dam thinning reduces water storage capacity in the basin, that capacity is increased by declining ice volume in the basin and longitudinal lake expansion, with the latter process challenging to predict. The potential for premature drainage onset (i.e., drainage before the lake's storage capacity is reached), intermittent drainage decelerations, and early drainage termination further complicates prediction of future GLOF events.

Alaska↗