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At least 739 records · Page 41Linked to original sources

USGS2017

A reevaluation of the timing and causes of high lake phases in the Lake Michigan basin

Radiocarbon age control on the type Glenwood, Calumet, and Toleston shoreline features and on the abandoned Chicago outlet at the south end of the Lake Michigan basin provides a basis for reevaluating the timing and causes of high lake phases in the basin. Radiocarbon dates suggest that Glenwood-level (195 m) shoreline features formed between 14,100 and 12,700 yr B.P. (Glenwood I and II phases), Calumet-level (189 m) between 12,700 and 11,000 yr B.P. (Calumet I and II phases), and Toleston-level (184.5 m) between 5000 and 4000 yr B.P. (Nipissing phase), and that the Chicago outlet was cut to its present level (180 m) on bedrock while the lake was at the Glenwood level. This new chronology is inconsistent with J H. Bretz' hypothesis ((1951) American Journal of Science249, 401-429) that the progressive lowering of lake level resulted from episodic down-cutting of the outlet. Instead, the changes in lake level appear to relate to changes in the amount of glacial meltwater and precipitation entering the basin. We hypothesize that the Glenwood phases correspond with times when discharge from the Huron and Erie basins also entered the Lake Michigan basin (Lake Border and early Port Huron glacial phases), the Calumet phases with times when drainage was from the Lake Michigan basin alone (late Port Huron and Two Rivers glacial phases), and the Nipissing phase with the postglacial middle Holocene transgression caused by differential uplift in the basin. Estimates of relative net inputs to the basin during the Glenwood, Calumet, and Nipissing lake phases are consistent with estimates of relative outputs (i.e., discharge through the Chicago outlet); the magnitude of relative differences in inputs and outputs between phases is sufficient to explain lake-level changes of 4.5 to 6 m. ?? 1988.

Quaternary Research↗

USGS1990

Temporally intensive study of trace metals in sediments and bivalves from a large river-estuarine system: Suisun Bay/delta in San Francisco Bay

Distributions in time and space of Ag, Cd, Cr, Cu, Pb and Zn were determined in fine-grained sediments and in the filter-feeding bivalve Corbicula sp. of Suisun Bay/delta at the mouth of the Sacramento and San Joaquin Rivers in North San Francisco Bay. Samples were collected from seven stations at near-monthly intervals for 3 years. Aggregated data showed little chronic contamination with Ag, Zn and Pb in the river and estuary. Substantial chronic contamination with Cd, Cu and Cr in Suisun Bay/delta occurred, especially in Corbicula, compared with the lower San Joaquin River. Salinity appeared to have secondary effects, if any, on metal concentrations in sediments and metal bioavailability to bivalves. Space/time distributions of Cr were controlled by releases from a local industry. Analyses of time series suggested substantial inputs of Cu might originate from the Sacramento River during high inflows to the Bay, and Cd contamination had both riverine and local sources. Concentrations of metals in sediments correlated with concentrations in Corbicula only in annually or 3-year aggregated data. Condition index for Corbicula was reduced where metal contamination was most severe. The biological availability of Cu and Cd to benthos was greater in Suisun Bay than in many other estuaries. Thus small inputs into this system could have greater impacts than might occur elsewhere; and organisms were generally more sensitive indicators of enrichment than sediments in this system.

California↗

USGS1993

Factors affecting the geochemistry of a thick, subbituminous coal bed in the Powder River Basin: Volcanic, detrital, and peat-forming processes

The inorganic geochemistry and mineralogy of three cores from the Anderson-Dietz 1 coal bed, a 15.2-m-thick subbituminous coal bed in the Tongue River Member (Paleocene) of the Fort Union Formation, were examined (1) to determine if the cores could be correlated by geochemical composition alone over a total distance of 2 km and (2) to identify the major factors that influenced the geochemistry of the coal bed. Chemical data (46 elements on a coal-ash basis) for 81 coal samples and 4 carbonaceous rock samples, with most samples representing a 0.6-m-thick (2-ft) interval of core, were grouped into compositional clusters by means of cluster analysis. Seven major clusters were produced; two of these clusters can be used to correlate the coal bed throughout the study area. Data from scanning electron and optical microscope analyses indicate that several factors influenced the geochemistry of the Anderson-Dietz 1 coal bed. The majority of mineral grains in the coal bed are interpreted to be detrital (water borne); evidence includes the presence of rounded to subrounded quartz grains having two-phase, aqueous fluid inclusions characteristic of hydrothermal or low-to-moderate grade metamorphic quartz. These quartz grains are found throughout the coal bed but are most abundant in samples from the midpart of the bed, which was influenced by detrital input associated with the deposition of the clastic rocks that form the split between the Anderson and Dietz 1 coal beds 900 m to the east of the study area. In addition to the detrital minerals mentioned above, volcanic ash that was fluvially transported to the sites of peat deposition or possibly deposited as air-fall volcanic ash also affected the geochemistry of the coal bed. For example, crandallite(?), a mineral reported to form as an alteration product of volcanic ash, is found in seven samples from the coal bed. The presence of quartz grains containing silicate-melt inclusions in eight samples from the coal bed.provides further support for a volcanic ash component. Other factors that probably affected the geochemistry of the coal bed include (1) detrital input associated with the deposition of the roof rocks of the coal bed, (2) peat-forming processes and plant material, and (3) epigenetic ground-water flow.

Montana, Wyoming↗

USGS1989

Spatial and temporal variability in South San Francisco Bay (USA). I. Horizontal distributions of salinity, suspended sediments, and phytoplankton biomass and productivity

The horizontal pattern of mesoscale (1–4 km) variability in salinity was a poor predictor of mesoscale patterns in chlorophyll a , suspended particulate matter, and daily primary productivity in the South San Francisco Bay estuary during spring 1987. The tidally-averaged salinity distribution varied over weekly time scales, reflecting inputs of freshwater as well as transport processes. Spatial distributions of the other quantities also varied weekly, but not in concert with the salt field. Spatial patterns of phytoplankton biomass (chlorophyll a ) deviated from the salinity patterns, largely reflecting in situ production of phytoplankton biomass during the spring bloom. The tidally-averaged distribution of suspended particulate matter (SPM) was highly dynamic and responded to (1) the riverine input of suspended sediment during a freshet, (2) neap-spring variations in tidally-driven resuspension, and (3) resuspension in shallows following a period of wind mixing. Two-dimensional distributions of primary productivity P ′, derived from maps of biomass and turbidity (SPM), also varied weekly, but the spatial variability of P ′ was only about half that of SPM and chlorophyll. Since the magnitude and patterns of spatial variability differ among nonconservative quantities, at least in part because of local sources and sinks, we conclude that the spatial distributions of nonconservative quantities cannot be predicted from distributions of conservative tracers, such as salinity.

California↗

USGS1990

Radium and radon in Charlotte Harbor Estuary, Florida

Radium-226 and 222 Rn activities are greater in the estuarine waters of northern Charlotte Harbor and the lower tidal Peace and Myakka Rivers, Florida, than in either the freshwater reaches of the rivers or waters of the lower estuary and the Gulf of Mexico. The activity of 226 Ra in the tidal rivers increases with decreasing river inflow, with a maximum value of 548 dpm 1001 −1 measured in the tidal Myakka River. The source of the high activity of 226 Ra and 222 Rn is predominantly ground water inflow. Because of the large ground water input, the contribution of 226 Ra from suspended and bottom sediments is a smaller fraction of the total 226 Ra input than in many other estuaries. Although ground water 226 Ra activity in the area varies widely, we estimate that artesian ground water inflow to the tidal rivers is similar in magnitude to the flow of the rivers above the tidal reach during the dry season.

Florida↗

USGS1991

The interaction between biology and the management of aquatic macrophytes

‘Management’ refers to controlling nuisance aquatic species and to restoring or restructing aquatic plant communities. Producing stable, diverse, aquatic plant communities containing a high percentage of desirable species is a primary management goal. There are a variety of techniques including harvesting, herbicides, water-level fluctuation, sediment alteration, nutrient limitation, light alteration, and biological controls which can be used for managing macrophytes. These techniques are briefly reviewed along with discussions of biological considerations important to the efficacy of the technique and the environmental impacts of the technique. There is a growing interest in restoring and restructing aquatic plant communities. Techniques for community restoration are discussed as are emerging management technologies using growth regulators and bioengineering. New management technologies will probably be limited by costs and environmental impacts. In the near future, better macrophyte management will come through better planning and more effective use of present technology. The challenge is to make current planning and management techniques more effective through increased biological inputs. The potential for biological input ranges from subcellular biology to species biology, to community and ecosystem biology. Some information needs are identified.

Aquatic Botany↗

USGS1990

Estimates of ion sources in deciduous and coniferous throughfall

Estimates of external and internal sources of ions in net througfall deposition were derived for a deciduous and coniferous canopy by use of multiple regression. The external source component appears to be dominated by dry deposition of Ca 2+ , SO 2 and NO 3 − during dormant and growing seasons for the two canopy types. Increases in the leaching rates of K + and Mg 2+ during the growing season reflect the presence of leaves in the deciduous canopy and increased physiological activity in both canopies. Internal leaching rates for SO 4 2− doubled during the growing season presumably caused by increased physiological activity and uptake of SO 2 through stomates. Net deposition of SO 4 2− in throughfall during the growing season appears highly dependent on stomatal uptake of SO 2 . Estimates of SO 2 deposition velocities were 0.06 cm s −1 and 0.13 cm s −1 for the deciduous and coniferous canopies, respectively, during the dormant seasons, and 0.30 cm s −1 and 0.43 cm s −1 for the deciduous and coniferous canopies, respectively, during the growing season. For the ions of major interest with respect to ecosystem effects, namely H + , NO 3 − and SO 4 2− , precipitation inputs generally outweighed estimates of dry deposition input. However, net throughfall deposition of NO 3 − and SO 4 2− accounted for 20–47 and 34–50 per cent, respectively, of total deposition of those ions. Error estimates of ion sources were at least 50–100 per cent and the method is subject to several assumptions and limitations.

Virginia↗

USGS1994

Particulate carbonate matter in snow from selected sites in the south-central Rocky Mountains

Trends in snow acidity reflect the balance between strong acid inputs and reactions with neutralizing materials. Carbonate dust can be an important contributor of buffering capacity to snow however, its concentration in snow is difficult to quantify because it dissolves rapidly in snowmelt. In snow with neutral or acidic pH, most calcite would dissolve during sample melting if snow samples were processed using standard techniques. Here a method is described for separating particulate carbonate matter from snow. Snow samples were melted in solutions close to saturation with calcite, decreasing the dissolution rate by a factor of 100-200 compared with natural melting of snow. Particulate matter larger than 0.45 ??m in diameter was then filtered from solution and analysed for carbonate content. Particulate carbonate matter concentrations are reported for 25 sites in the south-central Rocky Mountains. Results are compared with Ca2+ and H+ concentrations and regional trends are evaluated. In Colorado, mean particulate carbonate in snow was 43 ??g kg-1 at sampling sites in the southern mountains and only 4 ??g kg-1 at sites in the northern mountains. The higher calcite concentrations in the south probably are related to the proximity of sampling sites to major outcrops of limestone. Particulate carbonate at sampling sites in Utah and Wyoming ranged from 3-35 ??g kg-1. The levels of particulate calcite measured in snow samples are sufficient to neutralize an average of 0.4 ??eq H+ kg-1 snow. Strong acid anion concentrations in samples from east of Craig, Colorado, were 30-50% higher than in samples from the Colorado Front Range, but H+ concentrations were 400-600% higher east of Craig. Relatively low Ca2+ concentrations in the samples from east of Craig indicate that the difference in snow acidity was due mostly to lower concentrations of neutralizing materials.Trends in snow acidity reflect the balance between strong acid inputs and reactions with neutralizing materials. Carbonate dust can be an important contributor of buffering capacity to snow; however, its concentration in snow is difficult to quantify because it dissolves rapidly in snowmelt. In snow with neutral or acidic pH, most calcite would dissolve during sample melting if snow samples were processed using standard techniques. Here a method is described for separating particulate carbonate matter from snow. Snow samples were melted in solutions close to saturation with calcite, decreasing the dissolution rate by a factor of 100-200 compared with natural melting of snow. Particulate matter larger than .45 micrometers in diameter was then filtered from solution and analyzed for carbonate content.

Atmospheric Environment↗

USGS1977

Suspended particle transport and circulation in San Francisco Bay - an overview

Differences in the relative magnitude and timing of wind stress and river inflow in the northern and southern reaches of San Francisco Bay create different sedimentary conditions. The northern reach is a partially to well mixed estuary receiving most of the total annual fresh-water input (840 m 3 sec −1 ) and suspended sediment input (4 × 10 6 metric tons) into the bay; more than 80% of the sediment is received during winter. Density-driven nontidal estuarine circulation (~5 cm sec −1 ) maintains a turbidity maximum which changes seasonally in particle concentration (40 to 80 mg litre −1 ). Strong tidal currents (≤225 cm sec −1 ) and wind-generated waves resuspend sediment from the shallow bay floor: some of the riverborne sediment deposited during winter is resuspended during summer and transported landward to the turbidity maximum. Long-term sediment data (extrapolated from bathymetrie charts) indicate that the northern reach is an effective sediment trap. In contrast, long-term sediment data suggest that the southern reach is experiencing net erosion. The southern reach receives little river inflow or riverborne suspended sediment, and the average nontidal circulation is weak (≤2 cm sec −1 ). The principal source of suspended sediment (25 mg litre −1 ) in the southern reach is the shallow bay floor (average depth 6 m).

Book chapter↗

USGS2009

Assessing the impact of land use change on hydrology by ensemble modelling (LUCHEM) II: Ensemble combinations and predictions

This paper reports on a project to compare predictions from a range of catchment models applied to a mesoscale river basin in central Germany and to assess various ensemble predictions of catchment streamflow. The models encompass a large range in inherent complexity and input requirements. In approximate order of decreasing complexity, they are DHSVM, MIKE-SHE, TOPLATS, WASIM-ETH, SWAT, PRMS, SLURP, HBV, LASCAM and IHACRES. The models are calibrated twice using different sets of input data. The two predictions from each model are then combined by simple averaging to produce a single-model ensemble. The 10 resulting single-model ensembles are combined in various ways to produce multi-model ensemble predictions. Both the single-model ensembles and the multi-model ensembles are shown to give predictions that are generally superior to those of their respective constituent models, both during a 7-year calibration period and a 9-year validation period. This occurs despite a considerable disparity in performance of the individual models. Even the weakest of models is shown to contribute useful information to the ensembles they are part of. The best model combination methods are a trimmed mean (constructed using the central four or six predictions each day) and a weighted mean ensemble (with weights calculated from calibration performance) that places relatively large weights on the better performing models. Conditional ensembles, in which separate model weights are used in different system states (e.g. summer and winter, high and low flows) generally yield little improvement over the weighted mean ensemble. However a conditional ensemble that discriminates between rising and receding flows shows moderate improvement. An analysis of ensemble predictions shows that the best ensembles are not necessarily those containing the best individual models. Conversely, it appears that some models that predict well individually do not necessarily combine well with other models in multi-model ensembles. The reasons behind these observations may relate to the effects of the weighting schemes, non-stationarity of the climate series and possible cross-correlations between models. Crown Copyright ?? 2008.

Advances in Water Resources↗

USGS2025

The acoustic-Doppler current profiler (ADCP): A comprehensive tool for river-reach hydromorphodynamics

This paper introduces the use of acoustic Doppler current profiler (ADCP) measurements as input for the Acoustic Mapping Velocimetry (AMV) method, a technique for characterizing the dynamics of riverine bedforms. The performance of this new approach, ADCP-AMV, is compared with input from a multibeam echosounder through a field study conducted on the Mississippi River (USA). A virtual ADCP tool has been created to support the ADCP-AMV measurements with optimal data density predictions. To the authors’ knowledge, this is the first time ADCP measurements have been used in conjunction with the AMV dune-tracking method. Subsequently, the paper discusses the coupling of ADCP-AMV measurements with ancillary data extracted from the ADCP. These ancillary data are processed using previously developed protocols to characterize hydrodynamics and the suspended sediment distribution in the water column. This paper emphasizes the capability of ADCPs to characterize open-channel river hydromorphodynamic parameters with high spatiotemporal resolution. Recommendations to accurately and efficiently acquire these multi-variable measurements and derived datasets are discussed.

Tennessee↗

USGS2009

Simulated dynamics of carbon stocks driven by changes in land use, management and climate in a tropical moist ecosystem of Ghana

Sub-Saharan Africa is large and diverse with regions of food insecurity and high vulnerability to climate change. This project quantifies carbon stocks and fluxes in the humid forest zone of Ghana, as a part of an assessment in West Africa. The General Ensemble biogeochemical Modeling System (GEMS) was used to simulate the responses of natural and managed systems to projected scenarios of changes in climate, land use and cover, and nitrogen fertilization in the Assin district of Ghana. Model inputs included historical land use and cover data, historical climate records and projected climate changes, and national management inventories. Our results show that deforestation for crop production led to a loss of soil organic carbon (SOC) by 33% from 1900 to 2000. The results also show that the trend of carbon emissions from cropland in the 20th century will continue through the 21st century and will be increased under the projected warming and drying scenarios. Nitrogen (N) fertilization in agricultural systems could offset SOC loss by 6% with 30 kg N ha −1 year −1 and by 11% with 60 kg N ha −1 year −1 . To increase N fertilizer input would be one of the vital adaptive measures to ensure food security and maintain agricultural sustainability through the 21st century.

Agriculture, Ecosystems and Environment↗

USGS2022

Connecting regional-scale tree distribution models with seed dispersal kernels

Regional scale forest distribution models are important tools for biogeography and understanding the structure of forest communities in space. These models take climate and geographic variables as input and are therefore helpful for long-term decision support and climate adaptation planning. Generally, local processes of tree germination and seedling survival are resolved probabilistically with explanatory variables such as elevation, latitude, exposure, soil type, moisture availability, climate and weather inputs and `trained’ using landscape and regional presence-absence data and machine learning techniques. How seeds are distributed in these models, that is, determining the dispersal kernel, is far more problematic. The challenge is that variables conditioning vertebrate seed dispersal (motility and probability of utilization or caching in response to cover type) are not represented in large scale distribution models, and in fact vary on scales (10-100 meters) that are much smaller than the smallest pixel size for the distribution model (1-10 kilometers). We present a homogenized seed digestion kernel (HSDK) which incorporates this scale separation. Homogenization naturally links highly variable small-scale processes (like seed foraging and caching by birds and rodents) with large scale effects (like dispersal of seeds over tens of kilometers). We develop a homogenization strategy to predict seed dispersal on landscape scales, analytically linking small-scale variables (landscape fraction cover by tree type, gut residence times and cover type utilization by frugivorous birds) with large scale behaviors. Closed form approximations are developed in two dimensions for two limiting cases of seed handling behavior, and the approach is illustrated using landscape data and piñon-pine dispersal in a 630,000 square kilometer region in the southwestern US.

Applied Mathematics and Computation↗

USGS2004

Composition of water and suspended sediment in streams of urbanized subtropical watersheds in Hawaii

Urbanization on the small subtropical island of Oahu, Hawaii provides an opportunity to examine how anthropogenic activity affects the composition of material transferred from land to ocean by streams. This paper investigates the variability in concentrations of trace elements (Pb, Zn, Cu, Ba, Co, As, Ni, V and Cr) in streams of watersheds on Oahu, Hawaii. The focus is on water and suspended particulate matter collected from the Ala Wai Canal watershed in Honolulu and also the Kaneohe Stream watershed. As predicted, suspended particulate matter controls most trace element transport. Elements such as Pb, Zn, Cu, Ba and Co exhibit increased concentrations within urbanized portions of the watersheds. Particulate concentrations of these elements vary temporally during storms owing to input of road runoff containing elevated concentrations of elements associated with vehicular traffic and other anthropogenic activities. Enrichments of As in samples from predominantly conservation areas are interpreted as reflecting agricultural use of fertilizers at the boundaries of urban and conservation lands. Particulate Ni, V and Cr exhibit distributions during storm events that suggest a mineralogical control. Principal component analysis of particulate trace element concentrations establishes eigenvalues that account for nearly 80% of the total variance and separates trace elements into 3 factors. Factor 1 includes Pb, Zn, Cu, Ba and Co, interpreted to represent metals with an urban anthropogenic enrichment. Factor 2 includes Ni, V and Cr, elements whose concentrations do not appear to derive from anthropogenic activity and is interpreted to reflect mineralogical control. Another, albeit less significant, anthropogenic factor includes As, Cd and U and is thought to represent agricultural inputs. Samples collected during a storm derived from an offshore low-pressure system suggest that downstream transport of upper watershed material during tradewind-derived rains results in a 2-3-fold dilution of the particulate concentrations of Pb, Zn and Cu in the Ala Wai canal watershed. ?? 2004 Elsevier Ltd. All rights reserved.

Conference Paper↗

USGS2005

Historical backcasting of metal concentrations in the Chattahoochee River, Georgia: Population growth and environmental policy

The impact of increasing urbanization on the quality of a river system has been investigated by examining the current concentration of trace metals in the Chattahoochee River south of Atlanta, GA, and comparing these to previously published historical sediment data from reservoirs along the river. The lack of historical data for dissolved metal concentrations prior to ???1980 requires an approach using these historic metal data from sediment cores. Core data are combined with current suspended load and dissolved metal data to "backcast" dissolved metal concentrations in the metro-Atlanta portion of the Chattahoochee River. The data suggest that the per capita input of dissolved trace metals have actually decreased since the 1920s, but anthropogenic inputs of metal are still a substantial water quality issue. ?? 2005 Elsevier Ltd. All rights reserved.

Applied Geochemistry↗

USGS2007

A simulation-based approach for estimating premining water quality: Red Mountain Creek, Colorado

Regulatory agencies are often charged with the task of setting site-specific numeric water quality standards for impaired streams. This task is particularly difficult for streams draining highly mineralized watersheds with past mining activity. Baseline water quality data obtained prior to mining are often non-existent and application of generic water quality standards developed for unmineralized watersheds is suspect given the geology of most watersheds affected by mining. Various approaches have been used to estimate premining conditions, but none of the existing approaches rigorously consider the physical and geochemical processes that ultimately determine instream water quality. An approach based on simulation modeling is therefore proposed herein. The approach utilizes synoptic data that provide spatially-detailed profiles of concentration, streamflow, and constituent load along the study reach. This field data set is used to calibrate a reactive stream transport model that considers the suite of physical and geochemical processes that affect constituent concentrations during instream transport. A key input to the model is the quality and quantity of waters entering the study reach. This input is based on chemical analyses available from synoptic sampling and observed increases in streamflow along the study reach. Given the calibrated model, additional simulations are conducted to estimate premining conditions. In these simulations, the chemistry of mining-affected sources is replaced with the chemistry of waters that are thought to be unaffected by mining (proximal, premining analogues). The resultant simulations provide estimates of premining water quality that reflect both the reduced loads that were present prior to mining and the processes that affect these loads as they are transported downstream. This simulation-based approach is demonstrated using data from Red Mountain Creek, Colorado, a small stream draining a heavily-mined watershed. Model application to the premining problem for Red Mountain Creek is based on limited field reconnaissance and chemical analyses; additional field work and analyses may be needed to develop definitive, quantitative estimates of premining water quality.

Colorado↗

USGS2015

Stable-isotope and solute-chemistry approaches to flow characterization in a forested tropical watershed, Luquillo Mountains, Puerto Rico

The prospect of changing climate has led to uncertainty about the resilience of forested mountain watersheds in the tropics. In watersheds where frequent, high rainfall provides ample runoff, we often lack understanding of how the system will respond under conditions of decreased rainfall or drought. Factors that govern water supply, such as recharge rates and groundwater storage capacity, may be poorly quantified. This paper describes 8-year data sets of water stable isotope composition ( δ 2 H and δ 18 O) of precipitation (4 sites) and a stream (1 site), and four contemporaneous stream sample sets of solute chemistry and isotopes, used to investigate watershed response to precipitation inputs in the 1780-ha Río Mameyes basin in the Luquillo Mountains of northeastern Puerto Rico. Extreme δ 2 H and δ 18 O values from low-pressure storm systems and the deuterium excess ( d -excess) were useful tracers of watershed response in this tropical system. A hydrograph separation experiment performed in June 2011 yielded different but complementary information from stable isotope and solute chemistry data. The hydrograph separation results indicated that 36% of the storm rain that reached the soil surface left the watershed in a very short time as runoff. Weathering-derived solutes indicated near-stream groundwater was displaced into the stream at the beginning of the event, followed by significant dilution. The more biologically active solutes exhibited a net flushing behavior. The d- excess analysis suggested that streamflow typically has a recent rainfall component (∼25%) with transit time less than the sampling resolution of 7 days, and a more well-mixed groundwater component (∼75%). The contemporaneous stream sample sets showed an overall increase in dissolved solute concentrations with decreasing elevation that may be related to groundwater inputs, different geology, and slope position. A considerable amount of water from rain events runs off as quickflow and bypasses subsurface watershed flowpaths, and better understanding of shallow hillslope and deeper groundwater processes in the watershed will require sub-weekly data and detailed transit time modeling. A combined isotopic and solute chemistry approach can guide further studies to a more comprehensive model of the hydrology, and inform decisions for managing water supply with future changes in climate and land use.

Applied Geochemistry↗

USGS2026

Evaluating drivers of environmental change in a lake sediment core: Insights from spectroscopic metrics of water-extractable organic matter and stable carbon isotopes

Freshwater lakes play a critical role in the global carbon cycle by storing and transforming organic matter (OM) from both terrestrial and aquatic sources. Small lakes in northern temperate regions, despite their limited surface area, disproportionately influence regional carbon budgets. Buried sediments integrate OM inputs over time and archive ecosystem responses to natural and anthropogenic disturbances. However, the direction and magnitude of recent environmental changes on sediment carbon (C) dynamics remain poorly understood. A 23-cm core was collected from a small temperate lake in northeastern USA to evaluate sediment OM content and composition over timescales relevant to historical land-use change, damming, and recovery from acid deposition. Patterns in OM burial and source contributions were revealed via elemental and isotopic analyses of bulk OM and ultraviolet-visible spectrophotometry of water-extractable organic matter (WEOM). The optical metrics expanded observations of likely OM sources beyond the information gained from bulk carbon metrics (total carbon, δ 13 C). The aromaticity of WEOM increased downcore, which is consistent with a shift from increased terrestrial inputs during early logging and damming activity (pre ∼1920) to more microbial-derived OM in recent surficial sediments. Future applications of WEOM optical properties as complements to traditional geochemical metrics can enhance interpretations of lake ecosystem responses recorded in lake sediments to environmental perturbations in temperate lakes.

New York↗