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 agricultural, urban, and forested land use/land cover. We examined intrastorm hysteresis and the influences of seasonality, storm size, and dominant land use/land cover on storm DOC and nitrate loads. DOC hysteresis was generally anticlockwise at all sites, indicating distal and plentiful sources for all three streams despite varied DOC character and sources. Nitrate hysteresis was generally clockwise for urban and forested sites, but anticlockwise for the agricultural site, indicating an exhaustible, proximal source of nitrate in the urban and forested sites, and more distal and plentiful sources of nitrate in the agricultural site. The agricultural site had significantly higher storm nitrate yield per water yield and higher storm DOC yield per water yield than the urban or forested sites. Seasonal effects were important for storm nitrate yield in all three watersheds and farm management practices likely caused complex interactions with seasonality at the agricultural site. Hysteresis indices did not improve predictions of storm nitrate yields at any site. We discuss key lessons from using high‐frequency in situ optical sensors.
Key Points
An improved hysteresis index revealed remarkable variation in storm dynamics for 126 storms in watersheds with varied land use/land cover
Seasonality influenced storm nitrate loading; interactions between farm practices and seasonal dynamics were captured by sensors
Sites had generally anticlockwise storm hysteresis for DOC, though storm nitrate hysteresis direction varied by land use/land cover
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 freshwater eutrophic lakes, often acting as a source for bioavailable phosphorus that fuels harmful algal and/or cyanobacterial blooms. Parallel extractions of lake sediment collected from Missisquoi Bay, a eutrophic bay in Lake Champlain, were conducted with the goal of identifying OM and organic P sediment constituents using ultrahigh-resolution mass spectrometry from various extractants. Extractants converged into two groups based on the characteristics of their extracted OM; “stronger extractants” were composed of highly acidic and alkali media, while “milder extractants” represented weaker acids and bases. Sediment treated with the strong extractants afforded highly oxygenated and unsaturated OM thought to be stable with mostly lower heteroatomic content. In contrast, milder extractants yielded highly aliphatic and saturated compounds with lower masses and greater heteroatom functionally, sharing characteristics with labile molecules. Extracted organic P molecules mirrored the bulk OM in terms of lability, mass, and oxygenation within their corresponding extractants. Milder extractants resulted in greater organic P formulae assignments than the stronger extractants, with NaHCO3 resulting in the most aliphatic organic P formulae. We recommend the use of acetic acid to probe lake sediment for overall molecular characterization, spanning the greatest ranges of O/C and H/C ratios and representing both labile and mineral-associated OM. Other extractants should be implemented for a more targeted analysis. For instance, the use of NaHCO3 for organic P characterization, while using NaOH when interested in sediment geochemistry; both of which are critical for understanding the factors contributing to internal P loading.
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•Aqueous and organic solvents fractionate extractable lake sediment organic matter.•Lake sediment organic P compositions investigated using FT-ICR MS.•Labile organic P is primarily extracted with mild reagents.•Stronger acidic and basic reagents extract highly aromatic compounds.•Dissolution of organic extracts with aqueous media further partition organic matter.
Shining light on the storm Vaughan, M. C. H.; Bowden, W. B.; Shanley, J. B. ...
Biogeochemistry,
05/2019, Volume:
143, Issue:
3
Journal Article
Peer reviewed
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 organic carbon (DOC) concentration and spectral slope ratio, a proxy for DOM molecular weight. Measurements were made at 15-minute intervals over three years in three streams draining primarily agricultural, urban, and forested watersheds. We describe storm event dynamics by calculating hysteresis indices for DOC concentration and spectral slope ratio for 220 storms and present a novel analytical framework that can be used to interpret these metrics together. DOC concentration and spectral slope ratio differed significantly among sites, and individual storm DOM dynamics were remarkably variable at each site and among the three sites. Distinct patterns emerged for storm DOM dynamics depending on land use/land cover (LULC) of each watershed. In agricultural and forested streams, DOC concentration increased after the time of peak discharge, and spectral slope ratio dynamics indicate that this delayed flux was of relatively higher molecular weight material compared to the beginning of each storm. In contrast, DOM character during storms at the urban stream generally shifted to lower molecular weight while DOC concentration increased on the falling limb, indicating either the introduction of lower molecular weight DOM, the exhaustion of a higher molecular weight DOM sources, or a combination of these factors. We show that the combination of high-frequency DOM character and quantity metrics have the potential to provide new insight into short-timescale DOM dynamics and can reveal previously unknown effects of LULC on the chemical nature, source, and timing of DOM export during storms.
Water quality improvements in shallow eutrophic lakes are commonly delayed due to loading from legacy phosphorus (P)‐enriched sediments, even with reduced external nutrient loads. It is critical to ...understand the drivers of internal P loading to suppress or remove this source of P and meet water quality goals. We contrast the drivers of internal P loading in two shallow eutrophic systems (Lake Carmi and Missisquoi Bay). Legacy P dynamics in the unmanipulated systems were compared to Lake Carmi during aeration. In‐situ high frequency water column monitoring along with water and sediment sampling was used to study P dynamics in response to changing lake conditions and aeration. Despite both systems exhibiting P mobility controlled by iron redox cycling, we observed distinct differences in the spatial extent and drivers of internal P loading. Legacy P loading was controlled by seasonal drivers in Lake Carmi, but by spatially variable and highly transient wind driven forcing of hydrodynamics in Missisquoi Bay. Aeration altered the mixing regime of Lake Carmi and shifted loading dynamics to frequent wind‐driven pulses of legacy P to surface waters akin to those of Missisquoi Bay. Mean hypolimnetic dissolved oxygen increased with aeration, but greater oxygen demand rates and periods of anoxia under transient stratification still resulted in internal P loading. Surface P concentrations were higher in summer months with aeration compared to previous years. This research illustrates the dynamic nature of legacy P behavior within and between shallow eutrophic lakes and the challenges in addressing this common water resources threat.
Plain Language Summary
Shallow lakes with high amounts of nutrients like phosphorus often experience worsening water quality and harmful algae blooms. Even if less phosphorus enters the lake from the watershed, phosphorus already in the lake can cycle between the water and sediment for decades. It is important to understand how phosphorus moves within lakes to make management decisions. We studied what causes the release of phosphorus from sediment in Lake Carmi and Missisquoi Bay, Lake Champlain. These observations were compared to Lake Carmi during 4 years of whole‐lake aeration designed to limit phosphorus release. We found that the release of phosphorus at both study sites was tied to chemical reactions of iron. The timing of this release was controlled by seasonal changes in Lake Carmi before aeration, and by frequent wind‐driven mixing in Missisquoi Bay. Aeration changed the timing of mixing in Lake Carmi but did not decrease the amount of phosphorus recycled from the sediment. Aeration also increased the rate of oxygen consumption in Lake Carmi which quickly led to phosphorus release during periods of calm wind. This research shows the highly dynamic nature of phosphorus behavior within shallow lakes which is important to understand when making management decisions.
Key Points
Legacy phosphorus mobility was driven by either episodic wind‐mediated mixing or seasonal turnover in two proximal shallow eutrophic systems
Aeration altered hydrodynamics to change from seasonal to wind‐driven internal loading of legacy phosphorus, but it was not suppressed
Heterogeneous spatiotemporal controls on internal legacy phosphorus loading present challenges to achieving water quality goals
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 (DOM) to these changing conditions has previously not been investigated in this system and seldom in other redox-dynamic freshwaters. In this study, Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) has been employed to explore the seasonal transformation and distribution of DOM, including organic P (DOP), from spring 2017 to winter 2018 along with high-frequency geochemical monitoring. DOM was largely composed of allochthonous compounds with unique molecules from seasonal autochthonous sources and greater proportions of N,S-containing formulae after the early summer bloom season and during the winter. DOM compositions from spring to late summer was more aliphatic during the early bloom season, while DOM between late summer to winter was more aromatic with greater similarities between the two seasons. In contrast, DOP compositions from all seasons were highly dissimilar and suggested a compartmentalized water column, where riverine DOP compounds that were degraded during transport and in surface waters were largely absent in the benthic DOP. Additional sediment core incubation experiments were implemented to study the effects of short-term oxygen limitation on DOM and DOP composition to better constrain potential redox-based drivers of their mobility between sediment and the water column. Short-term incubations suggested an increase in aliphatic DOM and new DOP compounds, with little change in aromatic DOM, suggesting selective mobilization driven by microbial iron(III) and manganese(IV) reduction. Together, these detailed FT-ICRMS data show, for the first time, how DOM and DOP from various sources respond to changing physical and geochemical conditions in redox-dynamic freshwaters, demonstrating how these compounds cycle in freshwater settings and likely impact nutrient bioavailability.
In discussing issues of landscape change, the complex relationships in the landscape have to be assessed. In participative planning processes, 3D visualisations have a high potential as an aid in ...understanding and communicating characteristics of landscape conditions by integrating visual and non-visual landscape information. Unclear is, which design and how much interactivity is required for an indicator visualisation that would suit stakeholders best in workshop situations. This paper describes the preparation and application of three different types of integrated 3D visualisations in workshops conducted in the Entlebuch UNESCO Biosphere Reserve (CH). The results reveal that simple representations of a complex issue created by draping thematic maps on the 3D model can make problematic developments visible at a glance; that diagrams linked to the spatial context can help draw attention to problematic relationships not considered beforehand; and that the size of species as indicators of conditions of the landscape's production and biotope function seems to provide a common language for stakeholders with different perspectives. Overall, the of the indicators the functions required to assist in information processing. Further research should focus on testing the effectiveness of the integrated visualisation tools in participative processes for the general public.
A 7.1-Mn 0.1-C transformation-induced plasticity steel was intercritically annealed at 600°C and 650°C for 168h. Ultra-fine-grained microstructures with annealing temperature dependent retained ...austenite fractions and tensile properties were produced. in situ neutron diffraction was used to investigate the change in tensile properties via measurement of phase fractions, elastic phase strains, and diffraction peak broadening during deformation. Austenite transformation to martensite controlled initial yielding in the 650°C annealed steel and stress induced transformation was observed. In contrast, yielding after annealing at 600°C was controlled by plastic deformation of ferrite, with austenite transformation initiating only after yield point elongation. The sequence of deformation between constituents was readily apparent in the lattice strain and peak width data. During deformation, compressive lattice strains were always developed in austenite, ferrite plastic deformation initiated around 700MPa in both steels, and tensile stress was preferentially transferred to deformation-induced martensite. The development of compressive strains in austenite was related to constraint of the volume expansion during austenite transformation to martensite.
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 the waste-rock pile with which these solutions come in contact. ASW were sampled in the mineshaft prior to entering the waste-rock pile and upon discharge from the waste-rock pile aquifer near the pile toe. ASW composition changed as solutions flowed through the waste-rock pile due to sulfide and silicate weathering and schwertmannite precipitation.
Schwertmannite and goethite were both sampled in the waste-rock pile where a distinct field relation was observed between the two minerals. Schwertmannite was always in contact with actively flowing ASW, while goethite was never in direct contact with ASW and was generally above the waste-rock water table. Goethite is hypothesized to be re-dissolved/re-precipitated schwertmannite that was deposited under higher flow conditions and subsequently transformed to goethite through exposure to wet/dry cycling associated with seasonal fluctuations in the amount of water moving through the hydrogeologic system. Trace metal concentrations in ammonium oxalate extracts of these minerals provides the first published data on the behavior of multiple trace metals through this phase transformation, which has important ramifications for considering schwertmannite as a long term metal sink due to its known metastability with respect to goethite. A relative retention scale through this phase transformation of Pb
>
Zn, Mn
>
As, Al, Cu is potentially applicable to other ASW systems.
The paper contains the author's personal account of the professional achievements of Professor Friedrich (Fritz) Ackermann based on the author's memories and private documents which demonstrate ...Ackermann's significant influence throughout various professional phases over a period of four decades. The structure of the paper is based on the path of the author's studies, the period as a member of the Institute of Photogrammetry at Stuttgart University, and finally, a professional career in photogrammetry, geoinformation and management. The emphasis is on the character and skills of Friedrich Ackermann. Profession, team spirit and social skills are demonstrated with impressive examples.
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 temperature, and tributary inputs may control the development and collapse of blooms, but these thresholds are difficult to identify in large and complex datasets. In this study, we compared high-frequency estimates of oxygen metabolism in a shallow bay of Lake Champlain to concurrent measurements of physical and chemical parameters over 3 years with very different bloom dynamics. We clustered the data using supervised and unsupervised self-organizing maps to identify the environmental drivers associated with key stages of bloom development. We then used threshold analysis to identify subtle yet important thresholds of thermal stratification that drive transitions between bloom growth and decline. We found that extended periods with near-surface temperature differentials above 0.20 °C were associated with the initial development of bloom conditions, and subsequent frequency and timing of wind mixing events had a strong influence on interannual variability in bloom severity. The methods developed here can be widely applied to other high frequency lake monitoring datasets to identify critical thresholds controlling bloom development.
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