Andrew W. Schroth's research while affiliated with University of Vermont and other places
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Publications (77)
Oxygen (O2) regulates soil reduction‐oxidation processes and therefore modulates biogeochemical cycles. The difficulties associated with accurately characterizing soil O2 variability have prompted the use of soil moisture as a proxy for O2, as O2 diffusion into soil water is much slower than in soil air. The use of soil moisture alone as a proxy me...
In this paper, we examine the interactions, decisions, and evaluations of an interdisciplinary team of researchers tasked with developing an intelligent (AI-based) agricultural decision support system (DSS) that can provide farmers site-specific information about managing nutrients on their land. By doing so, we answer the following research questi...
The supply of aluminum (Al) and manganese (Mn) to the Gulf of Alaska from coastal sources is poorly constrained. Here, we investigate the seasonality of sources to better constrain Al and Mn cycling in the coastal Gulf of Alaska region and add to our understanding of seasonal and interannual inputs. We examine Mn and Al behavior over the shelf to d...
Winters in snow-covered regions have warmed, likely shifting the timing and magnitude of nutrient export, leading to unquantified changes in water quality. Intermittent, seasonal, and permanent snow covers more than half of the global land surface. Warming has reduced the cold conditions that limit winter runoff and nutrient transport, while cold s...
Missisquoi Bay is a shallow eutrophic segment of Lake Champlain that can experience persistent and severe cyanobacteria blooms in summer and fall. High external nutrient loads have driven long-term eutrophication and resulted in accumulation of sediment legacy phosphorus (P). However, P release from sediment to the water column (internal P loading)...
With mounting scientific evidence demonstrating adverse global climate change (GCC) impacts to water quality, water quality policies, such as the Total Maximum Daily Loads (TMDLs) under the U.S. Clean Water Act, have begun accounting for GCC effects in setting nutrient load-reduction policy targets. These targets generally require nutrient reductio...
The frequency and duration of lake ice cover is rapidly declining in the Northern Hemisphere. Limited research in oligotrophic and mesotrophic lakes suggests that extended periods of ice cover influence nitrogen (N) cycling by promoting nitrate (NO3−) accumulation. However, ice cover impacts on N cycling in shallow, high-nutrient, eutrophic lakes r...
Oxygen (O 2 ) is a key regulator of soil reduction-oxidation processes and therefore modulates biogeochemical cycles. The difficulties associated with accurately characterizing soil O 2 variability have prompted the use of soil moisture as a proxy for soil O 2 , based on the low solubility of O 2 in water. Due to seasonal shifts in soil O 2 depleti...
Many recent studies have attributed the observed variability of cyanobacteria blooms to meteorological drivers and have projected blooms with worsening societal and ecological impacts under future climate scenarios. Nonetheless, few studies have jointly examined their sensitivity to projected changes in both precipitation and temperature variabilit...
Synoptic typing is a method of classifying atmospheric conditions (i.e., pressure, temperature, wind direction) and can be used to relate those conditions to terrestrial processes. In this study, a daily synoptic calendar was developed for the northeastern United States to assess the atmospheric controls on variations in stream chemistry across thr...
Using synoptic classification techniques, synoptic-scale weather types associated with large exports of dissolved organic carbon and nitrate-nitrogen in three forested watersheds in the northeastern United States are analyzed. In contrast to Siegert et al. (2021, https://doi.org/10.1029/2020jd033413; Part 1), which details the general synoptic cond...
Redox-driven internal phosphorus (P) loading from lake sediments is a key process for propagating and sustaining cyanobacterial blooms in freshwater lakes. Missisquoi Bay in Lake Champlain, VT regularly experiences cyanobacterial blooms driven by internal P loading as well as from seasonal transitions, but the response of dissolved organic matter (...
Catchment nutrient export, especially during high flow events, can influence ecological processes in receiving waters by altering nitrogen (N) and phosphorus (P) concentrations and relative amounts (stoichiometry). Event‐scale N and P export dynamics may be significantly altered by land use/land cover (LULC) and season. Consequently, to manage wate...
Lake sediment organic matter (OM) is composed of a variety of organic compounds differing in their biolability and origin. Sources of sediment OM can include terrestrial input from the watershed and algal/microbial metabolic byproducts residing in the water column or sediment. Dissolved organic phosphorus (DOP) is a critical component of OM in fres...
Fluorescence spectroscopy is a common tool to assess optical dissolved organic matter (DOM) and a number of characteristics, including DOM biodegradability, have been inferred from these analyses. However, recent findings on soil and DOM dynamics emphasize the importance of ecosystem-scale factors, such as physical separation of substrate from soil...
The transboundary Missisquoi Bay in Lake Champlain, situated between Vermont (USA) and Quebec (Canada), is a shallow eutrophic embayment (depth < 5 m) with a limited water flux and connectivity to the rest of the lake. The bay has experienced persistent toxic cyanobacterial blooms during summer months in recent decades impairing recreational and ot...
Land use/land cover (LULC) change has significant impacts on nutrient loading to aquatic systems and has been linked to deteriorating water quality globally. While many relationships between LULC and nutrient loading have been identified, characterization of the interaction between LULC, climate (specifically variable hydrologic forcing) and solute...
Soluble nutrient flux is increasingly implicated in the degradation of receiving water quality. With high-frequency sensors, river discharge along with nitrate and orthophosphate concentrations were collected over 2 years. We examined how storms (16 events) affected the dissolved nutrient flux in two watersheds with contrasting landcover—urban and...
The quantity and character of dissolved organic matter (DOM) can change rapidly during storm events, affecting key biogeochemical processes, carbon bioavailability, metal pollutant transport, and disinfection byproduct formation during drinking water treatment. We used in situ ultraviolet–visible spectrophotometers to concurrently measure dissolved...
Although many climate predictions suggest that the frequency and intensity of large storm events might increase in the coming decades, few studies document the full impact of such events along their path. Here, we synthesize information on the impact of Hurricane Irene (formed August 21 2011) and Tropical Storm Lee (formed August 30, 2011) on erosi...
In the Anthropocene, watershed chemical transport is increasingly dominated by novel combinations of elements, which are hydrologically linked together as ‘chemical cocktails.’ Chemical cocktails are novel because human activities greatly enhance elemental concentrations and their probability for biogeochemical interactions and shared transport alo...
Accurate riverine phosphorus concentration measurements are often critical to meet watershed management goals. Phosphorus monitoring programs often rely on proxy variables such as turbidity and discharge and have limited ability to accurately estimate concentrations of dissolved phosphorus fractions that are most bioavailable. Optical water quality...
We assessed stream ecosystem-level response to a drought-induced defoliation event by gypsy moth caterpillars (Lymantria dispar) with high-frequency water quality sensors. The defoliation event was compared to the prior year of data. Based on long-term records of precipitation and drought indices, the drought of 2015–2016 in Rhode Island, USA was a...
Studying the hysteretic relationships embedded in high-frequency suspended-sediment concentration and river discharge data over 600⁺ storm events provides insight into the drivers and sources of riverine sediment during storm events. However, the literature to date remains limited to a simple visual classification system (linear, clockwise, counter...
Given the variable biogeochemical, physical, and hydrological processes driving fluvial sediment and nutrient export, the water science and management communities need data-driven methods to identify regions prone to production and transport under variable hydro-meteorological conditions. We use Bayesian analysis to segment concentration-discharge...
It is well established that cyanobacteria populations in shallow lakes exhibit dramatic fluctuations on both interannual and intraannual timescales; however, despite extensive research, disentangling the drivers of interannual variability in bloom severity has proved challenging. Critical thresholds of abiotic drivers such as wind, irradiance, air...
Storm events dominate riverine loads of dissolved organic carbon (DOC) and nitrate and are expected to increase in frequency and intensity in many regions due to climate change. We deployed three high-frequency (15 min) in situ absorbance spectrophotometers to monitor DOC and nitrate concentration for 126 storms in three watersheds with agricultura...
Phytoplankton growth in the Gulf of Alaska (GoA) is limited by iron (Fe), yet Fe sources are poorly constrained. We examine the temporal and spatial distributions of Fe, and its sources in the GoA, based on data from three cruises carried out in 2010 from the Copper River (AK) mouth to beyond the shelf break. April data are the first to describe la...
Our understanding of glacial flour dust storm delivery of iron to the Gulf of Alaska (GoA) is limited. Here we interpret concurrent time-series satellite, meteorological, and aerosol geochemical data from the GoA to examine how inter-annual variability in regional weather patterns impacts offshore aerosol glacial Fe deposition. In 2011, when a nort...
Concentrations of nitrogen (N) and phosphorus (P) in lakes may be differentially impacted by climate-driven changes in nutrient loading and by direct impacts of temperature and wind speed on internal nutrient cycling. Such changes may result in systematic shifts in lake N:P under future climate warming. We used 21 years of monitoring data to compar...
While decreasing occurrence and duration of lake ice cover is well-documented, biogeochemical dynamics in frozen lakes remain poorly understood. Here, we interpret winter physical and biogeochemical time series from eutrophic Missisquoi Bay (MB) and hyper-eutrophic Shelburne Pond (SP) to describe variable drivers of under ice biogeochemistry in sys...
Spring runoff often comprises the majority of annual discharge and riverine phosphorus (P) export due to sustained high flow, and the magnitude of spring runoff can be a strong predictor of receiving water summer harmful algal bloom severity. Yet the loading of reactive forms of P during this time period remains poorly-characterized in time, space...
The Coupled impacts of climate and land use change across a river–lake continuum: insights from an integrated assessment model of Lake Champlain's Missisquoi Basin, 2000–2040 supplementary data article
Global climate change (GCC) is projected to bring higher-intensity precipitation and higher-variability temperature regimes to the Northeastern United States. The interactive effects of GCC with anthropogenic land use and land cover changes (LULCCs) are unknown for watershed level hydrological dynamics and nutrient fluxes to freshwater lakes. Incre...
The cover image, by Audrey H. Sawyer et al., is based on the Advanced Review From soil to sea: the role of groundwater in coastal critical zone processes, DOI: 10.1002/wat2.1157.
Near coasts, surface water–groundwater interactions control many biogeochemical processes associated with the critical zone, which extends from shallow aquifer to vegetative canopy. For example, submarine groundwater discharge delivers a significant fraction of weathering products such as silica and calcium to the world's oceans. Owing to changing...
The management of external nutrient inputs to eutrophic systems can be confounded due to a persistent pool of phosphorus (P) in lake sediments. The behaviors of P and trace metals depend largely on the reductive dissolution of amorphous iron (Fe) and manganese (Mn) (oxy)hydroxides in sediments; however, a holistic understanding of these dynamics in...
Missisquoi River discharge at Swanton, VT (cubic meters per second, cms) in 2013. Red symbols indicate the study period and vertical dashed lines delineate the bloom periods
Abstract: The behavior of metals and associated nutrients in lakes under ice cover is poorly understood, although wintertime metal nutrient dynamics near the sediment water interface (SWI) could impact water quality and algal ecosystems. To examine the behavior of these biogeochemical constituents under ice, we collected water column and sediment t...
Synthesis of work done during research experience for undergraduates at the University of Vermont examining internal trace metal and nutrient loading in Lake Champlain. This research was focused on a smaller body of water (Shelburne Pond) located near Lake Champlain.
Decreasing duration and occurrence of northern hemisphere ice cover due to recent climate warming is well-documented; however, biogeochemical dynamics underneath the ice are poorly-understood. We couple time-series analyses of water column and sediment water interface (SWI) geochemistry with hydrodynamic data to develop a holistic model of iron (Fe...
The shallow bays of Lake Champlain have experienced increasingly severe algal blooms over recent decades, but the drivers of inter- and intra-annual variability of bloom severity are poorly understood. Disentangling the relative importance of multiple processes driving cyanobacteria blooms is difficult, in part because traditional monitoring progra...
Lake sediments represent a potentially significant source of phosphorus (P) in eutrophic waters. The organic P (Porg) fraction of sediments may become mobilized or hydrolyzed to orthophosphate during periods of high biological productivity or redox cycling; however, few studies have investigated the inter-seasonal or annual variability of these pro...
The input of iron to the Arctic Ocean plays a critical role in the productivity of aquatic ecosystems and is potentially impacted by climate change. We examine Fe isotope systematics of dissolved and colloidal Fe from several Arctic and sub-Arctic rivers in northern Eurasia and Alaska. We demonstrate that the Fe isotopic (δ56Fe) composition of larg...
Although commonly used by those tasked with lake management, the statistical approach of data averaging ( DA ) followed by ordinary least‐squares regression ( OLSR ) to generate nutrient limitation models is outdated and may impede the understanding and successful management of lake eutrophication.
Using a 21‐year data set from Lake Champlain as a...
Over the past 30+ years, researchers and water resource managers have often relied on a set of regression-based equations to describe the relationships between secchi depth (SD), chlorophyll (Chl) and total phosphorous (TP) and quantitatively assess lake trophic status after Carlson (1977). Here, we develop a revised framework for eutrophication as...
Lake sediments are known to be a significant source of phosphorus (P) to plankton populations under certain biogeochemical conditions; however, the contribution of sediment organic P (P) to internal P loads remains poorly understood. We investigated P speciation and bioavailability in sediments collected over multiple months from a shallow, eutroph...
Lake sediments represent a potentially significant internal source of phosphorus (P) in eutrophic freshwater systems during periods of high temperature, biological activity, and oxygen depletion. This work describes the contribution of organic P (P o) to the internal cycling of sediment P during multiple algal bloom stages in Lake Champlain, VT USA...
While recent work demonstrates that glacial meltwater provides a substantial and relatively labile flux of the micronutrient iron to oceans, the role of high-latitude estuary environments as a potential sink of glacial iron is unknown. Here we present the first quantitative description of iron removal in a meltwater-dominated estuary. We find that...
Iron is an important micronutrient that limits the growth of
phytoplankton in much of the global ocean. In the Gulf of Alaska (GoA),
we have a limited knowledge of the processes that transport iron, and in
particular, the role eolian dust plays in delivering iron to the ocean
surface. In order to better understand both modern and past mechanisms
of...
Riverine iron (Fe) derived from glacial weathering is a critical micronutrient source to ecosystems of the Gulf of Alaska (GoA). Here we demonstrate that the source and chemical nature of riverine Fe input to the GoA could change dramatically due to the widespread watershed deglaciation that is underway. We examine Fe size partitioning, speciation,...
Riverine iron (Fe) derived from glacial weathering is a critical micronutrient source to ecosystems of the Gulf of Alaska (GoA). Here we demonstrate that the source and chemical nature of riverine Fe input to the GoA could change dramatically due to the widespread watershed deglaciation that is underway. We examine Fe size partitioning, speciation,...
Iron is an essential micronutrient that limits primary productivity in much of the ocean, including the Gulf of Alaska (GoA). However, the processes that transport iron to the ocean surface are poorly quantified. We combine satellite and meteorological data to provide the first description of widespread dust transport from coastal Alaska into the G...
The Copper River is the largest point source of fresh water to the northern Gulf of Alaska, but the hydrography, biogeochemistry, and biology of the region are not well described. Oceanographic surveys were conducted in April, May, June and July 2010, along a transect line stretching from the mouth of the Copper River, across the plume, to well pas...
Iron (Fe) is a micronutrient that is thought to limit phytoplankton productivity in offshore waters of the Gulf of Alaska (GoA). However, it has been proposed that in coastal regions where offshore, Fe-limited, nitrate-rich waters mix with relatively Fe-rich river plumes, productive ecosystems and fisheries result. Indeed, an observed northward inc...
Recent work has suggested that high iron supply may contribute to a northward increase in phytoplankton biomass along the U.S. west coast, consistent with ``bottom-up'' control of these coastal ecosystems. We examine this hypothesis in waters of the Copper River plume and nearby continental shelf in the northern Gulf of Alaska (GoA). These are the...
Although abundant in the Earth's crust, iron is present at trace
concentrations in sea water and is a limiting nutrient for phytoplankton
in approximately 40% of the ocean. Current literature suggests that
aerosols are the primary external source of iron to offshore waters, yet
controls on iron aerosol solubility remain unclear. Here we demonstrate...
A primary source of bioavailable iron (Fe) to the open ocean is terrestrially-derived particulate aerosols, often assumed to be sourced from arid soil-based dust storms. However, portions of Fe-limited regions of the ocean are in the high latitudes, proximal to coasts that are strongly influenced by glacial weathering and associated sediment fluxes...
Serpentine soils derived from the weathering of ultramafic rocks and their metamorphic derivatives (serpentinites) are chemically prohibitive for vegetative growth. Evaluating how serpentine vegetation is able to persist under these chemical conditions is difficult to ascertain due to the numerous factors (climate, relief, time, water availability,...
The turnover of soil organic matter (SOM) maintains a dynamic chemical environment in the forest floor that can impact metal speciation on relatively short timescales. Here we measure the speciation of Pb in controlled and natural organic (O) soil horizons to quantify changes in metal partitioning during SOM decomposition in different forest litter...
Soil organic matter (SOM) is a primary rȩservoir of terrestrial sulfur (S), but its role in the global S cycle remains poorly understood. We examine S speciation by X-ray absorption near-edge structure (XANES) spectroscopy to describe S species behavior during SOM decomposition. Sulfur species in SOM were best represented by organic sulfide, sulfox...
While potentially important in the context of global biogeochemical change, the influence of different forest communities on chemical weathering rates in soils is poorly understood. We investigated the influence of four forest types (northern hardwood vs. three conifer plantations) on base cation depletion and redistribution in soils at Marsh-Billi...
Although legislation in the late 1970s significantly reduced atmospheric lead (Pb) inputs to ecosystems in North America, organic (O) horizons in forests of the northeastern USA still contain up to 30 kg of gasoline-derived Pb ha¹. The residence time, geochemical behavior, and fate of this contaminant Pb in soils is poorly understood. Here we use f...
Several studies have suggested that forest-type plays an important role in the deposition and mobility of atmospherically derived anthropogenic lead within forest soils, but a specific forest-type effect remains elusive because of confounding and complimentary variables associated lead mobility within natural systems. Here we examine the amount and...
Solutions draining the Alta Mine, Jefferson County, MT, were contaminated by acid sulfate waters (ASW) generated from anthropogenic exposure of meteoric waters to sulfidic underground mine workings and a waste-rock pile. In 1999, a remediation effort was initiated in an attempt to improve the quality of water draining the site through removal of th...