Assessing the potential for the Surface Water and Ocean Topography (SWOT) mission for constituent flux estimations

The recently launched Surface Water and Ocean Topography (SWOT) satellite will simultaneously measure river surface water widths, elevations, and slopes. These novel observations combined with assumptions for unobserved bathymetry and roughness enable the derivation of river discharge. Derived discharge data will not be available until the fall of 2023, despite the satellite having completed approximately 6 months of observations for validation and calibration and transitioning into the nominal orbit phase. SWOT has an irregular flyover frequency, ranging from roughly 1 to 10 times per 21 days. Here, we present how best to use SWOT data when it becomes live, including consideration of how best to accommodate or utilize the irregular flyover frequency of SWOT as it intersects with river reaches. We investigate the predicted capabilities of SWOT for several major rivers using synthetic/theoretical SWOT time series data and evaluate how the characteristics of river discharge dynamics and SWOT sampling frequency impact discharge estimates. This analysis indicates the irregular frequency of SWOT best captures the hydrology of larger, more stable, rivers but presents challenges in smaller, flashier rivers, particularly when sampling frequency decreases (i.e., falls to once per 21 days). Further, the use of SWOT discharge for quantifying constituent fluxes is considered. We provide recommendations concerning how to best use SWOT data for applications related to hydrology and biogeochemistry, including how to design studies to accommodate its irregular orbit cycle

Dissolved black carbon in aquatic ecosystems

The incomplete combustion of organic molecules produces a chemically diverse suite of pyrogenic residues termed black carbon (BC). The significance of BC cycling on land has long been recognized, and the recognition of dissolved BC (DBC) as a major component of the aquatic carbon cycle is developing rapidly. As we seek a greater understanding of DBC cycling, our interpretation of environmental DBC concentrations and molecular composition should take into account both the formation conditions of charred residues, and the physico‐chemical transformation of DBC that occurs during transit within aquatic systems. We present the current state of knowledge concerning sources, processing, and sinks of DBC in inland, coastal/estuarine, and ocean waters. We feature studies and new methodologies which focus specifically on the aquatic cycling of DBC, explore the relationship between particulate and dissolved BC, and highlight research gaps which should be targeted to advance our current knowledge of DBC biogeochemistry

A Mini-Electrodialysis System for Desalting Small Volume Saline Samples for Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

An affordable, commercially available mini-electrodialysis (mini-ED) system has been evaluated for the efficient desalting of small volume samples of seawater before analysis by electrospray Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). Mini-ED FT-ICR mass spectra were compared with spectra for samples that were treated by C18 solid phase extraction, a commonly used method for rapid sample preparation for this type of analysis. In this comparison, it is clear that mini-ED provides more representative molecular information, compared with C18 isolation, and recovers the overwhelming majority of peaks from salt-free samples, indicating that it adequately represents the DOM that can be ionized and analyzed by ESI FT-ICR MS. The ED system produces a significant carbon blank. However, the substances contributing to this blank are not detectable by ESI FT-ICR MS. Based on these findings mini-ED is recommended as a promising method for the desalting of aqueous environmental samples before analysis by ESI FT-ICR MS. © 2011, by the American Society of Limnology and Oceanography, Inc

Open ocean carbon monoxide photo-production

Sunlight-initiated photolysis of chromophoric dissolved organic matter (CDOM) is the dominant source of carbon monoxide (CO) in the open-ocean. A modelling study was conducted to constrain this source. Spectral solar irradiance was obtained from two models (GCSOLAR and SMARTS2). Water-column CDOM and total light absorption were modelled using spectra collected along a Meridional transect of the Atlantic ocean using a 200-cm pathlength liquid waveguide UV-visible spectrophotometer. Apparent quantum yields for the production of CO (AQYCO) from CDOM were obtained from a parameterisation describing the relationship between CDOM light absorption coefficient and AQYCO and the CDOM spectra collected. The sensitivity of predicted rates to variations in model parameters (solar irradiance, cloud cover, surface-water reflectance, CDOM and whole water light absorbance, and AQYCO was assessed. The model\u27s best estimate of open-ocean CO photoproduction was 47 +/- 7 Tg CO-C yr-1, with lower and upper limits of 38 and 84 Tg CO-C yr-1, as indicated by sensitivity analysis considering variations in AQYs, CDOM absorbance, and spectral irradiance. These results represent significant constraint of open-ocean CO photoproduction at the lower limit of previous estimates. Based on these results, and their extrapolation to total photochemical organic carbon mineralisation, we recommend a downsizing of the role of photochemistry in the open-ocean carbon cycle. (c) 2006 Elsevier Ltd. All rights reserved

Associations Between the Molecular and Optical Properties of Dissolved Organic Matter in the Florida Everglades, a Model Coastal Wetland System

Optical properties are easy-to-measure proxies for dissolved organic matter (DOM) composition, source, and reactivity. However, the molecular signature of DOM associated with such optical parameters remains poorly defined. The Florida coastal Everglades is a subtropical wetland with diverse vegetation (e.g., sawgrass prairies, mangrove forests, seagrass meadows) and DOM sources (e.g., terrestrial, microbial, and marine). As such, the Everglades is an excellent model system from which to draw samples of diverse origin and composition to allow classically-defined optical properties to be linked to molecular properties of the DOM pool. We characterized a suite of seasonally- and spatially-collected DOM samples using optical measurements (EEM-PARAFAC, SUVA254, S275−295, S350−400, SR, FI, freshness index, and HIX) and ultrahigh resolution mass spectrometry (FTICR-MS). Spearman\u27s rank correlations between FTICR-MS signal intensities of individual molecular formulae and optical properties determined which molecular formulae were associated with each PARAFAC component and optical index. The molecular families that tracked with the optical indices were generally in agreement with conventional biogeochemical interpretations. Therefore, although they represent only a small portion of the bulk DOM pool, absorbance, and fluorescence measurements appear to be appropriate proxies for the aquatic cycling of both optically-active and associated optically-inactive DOM in coastal wetlands

Characterization and Photodegradation of Dissolved Organic Matter (DOM) From a Tropical Lake and Its Dominant Primary Producer, the cyanobacteria Microcystis aeruginosa

This study investigates optical and high-resolution molecular signatures and photochemical degradation of DOM from the Barra Bonita Reservoir (BB-DOM), a tropical eutrophic lake, as well as from its dominant phytoplankton species, the cyanobacteria Microcystis aeruginosa (Microcystis-DOM). Consistent with a predominantly autotrophic source, BB-DOM and Microcystis-DOM exhibited high protein-like fluorescence and contained a large number of aliphatics. Microcystis-DOM was enriched in peptide-like formulae, while BB-DOM had higher chromophoric and fluorescent DOM(CDOM and FDOM) and was enriched in moderately unsaturated formulae, indicating additions of terrigenous DOM and/or in situ processing of autochthonous material in the lake. Consistent with its higher CDOM content, BB-DOM was more photoreactive than Microcystis-DOM. For both types of DOM, photodegradation resulted in loss of CDOM, FDOM, moderately unsaturated structures, high O/C and low H/C formulae, and preservation of aliphatics. The majority of photoproducts of 0.5 d irradiation were subsequently removed by day 7, and photoproducts represented a minor fraction of the photo-irradiated DOM. For BB-DOM, molecular formula photolability increased with increasing aromaticity index values, while for Microcystis-DOM, molecular formula photolability increased with molecular mass. Photodegradation increased the proportion of molecular formulae containing N (CHO + N) in BB-DOM, while the molecular mass and the proportion of CHO + N formulae decreased upon photo-irradiation of Microcystis-DOM. In concert, these molecular shifts due to photodegradation decreased the diversity of and increased the similarity between BB-DOM and Microcystis-DOM, suggesting the selective pressure exerted by photochemistry selects for the survival of similar compounds in both samples

Molecular and Optical Properties of Tree-derived Dissolved Organic Matter in Throughfall and Stemflow From Live Oaks and Eastern Red Cedar

Studies of dissolved organic matter (DOM) transport through terrestrial aquatic systems usually start at the stream. However, the interception of rainwater by vegetation marks the beginning of the terrestrial hydrological cycle making trees the headwaters of aquatic carbon cycling. Rainwater interacts with trees picking up tree-DOM, which is then exported from the tree in stemflow and throughfall. Stemflow denotes water flowing down the tree trunk, while throughfall is the water that drips through the leaves of the canopy. We report the concentrations, optical properties (light absorbance) and molecular signatures (ultrahigh resolution mass spectrometry) of tree-DOM in throughfall and stemflow from two tree species (live oak and eastern red cedar) with varying epiphyte cover on Skidaway Island, Savannah, Georgia, USA. Both stemflow and throughfall were enriched in DOM compared to rainwater, indicating trees were a significant source of DOM. The optical and molecular properties of tree-DOM were broadly consistent with those of DOM in other aquatic ecosystems. Stemflow was enriched in highly colored DOM compared to throughfall. Elemental formulas identified clustered the samples into three groups: oak stemflow, oak throughfall and cedar. The molecular properties of each cluster are consistent with an autochthonous aromatic-rich source associated with the trees, their epiphytes and the microhabitats they support. Elemental formulas enriched in oak stemflow were more diverse, enriched in aromatic formulas, and of higher molecular mass than for other tree-DOM classes, suggesting greater contributions from fresh and partially modified plant-derived organics. Oak throughfall was enriched in lower molecular weight, aliphatic and sugar formulas, suggesting greater contributions from foliar surfaces. While the optical properties and the majority of the elemental formulas within tree-DOM were consistent with vascular plant-derived organics, condensed aromatic formulas were also identified. As condensed aromatics are generally interpreted as deriving from partially combusted organics, some of the tree-DOM may have derived from the atmospheric deposition of thermogenic and other windblown organics. These initial findings should prove useful as future studies seek to track tree-DOM across the aquatic gradient from canopy roof, through soils and into fluvial networks

A Vision for Cleaner Rivers: Harnessing Snapshot Hyperspectral Imaging to Detect Macro-Plastic Litter

Plastic waste entering the riverine harms local ecosystems leading to negative ecological and economic impacts. Large parcels of plastic waste are transported from inland to oceans leading to a global scale problem of floating debris fields. In this context, efficient and automatized monitoring of mismanaged plastic waste is paramount. To address this problem, we analyze the feasibility of macro-plastic litter detection using computational imaging approaches in river-like scenarios. We enable near-real-time tracking of partially submerged plastics by using snapshot Visible-Shortwave Infrared hyperspectral imaging. Our experiments indicate that imaging strategies associated with machine learning classification approaches can lead to high detection accuracy even in challenging scenarios, especially when leveraging hyperspectral data and nonlinear classifiers. All code, data, and models are available online: https://github.com/RIVeR-Lab/hyperspectral_macro_plastic_detection