Geology topics

Sandrine J. Matiasek

Publications and source records attributed to Sandrine J. Matiasek.

3 recordsLinked to original sources

USGS2023

Water-soluble organic carbon release from mineral soils and sediments in an irrigated agricultural system

Water interactions with soil and vegetation are greatly altered in agricultural watersheds compared to natural landscapes, which impacts sources and fates of organic carbon (OC). While mineral soil horizons in natural ecosystems primarily act as filters for dissolved organic carbon (DOC) leached from organic surface horizons, tilled soils largely lack an organic horizon and their mineral horizons therefore act as a source for both DOC and sediment to surface waters. Irrigated watersheds highlight this difference, as DOC and total suspended sediment (TSS) concentrations simultaneously increase during the low-discharge irrigation season, suggesting that sediment-associated OC may constitute a significant source of DOC. While water-soluble OC (WSOC) from sediments and soils has been found to be compositionally similar to stream DOC, these contributions remain poorly quantified in agricultural streams. To address this, we conducted abiotic solubilization experiments using sediments (suspended and bed) and soils from an irrigated agricultural watershed in northern California, USA. Sediments (R 2 > 0.99) and soils (0.74 < R 2 < 0.89) displayed linear solubilization behaviors over the range of concentrations tested. Suspended sediment from the irrigation season exhibited the largest solubilization efficiency (10.9 ± 1.6% TOC sediment solubilized) and potential (1.79 ± 0.26 mg WSOC g −1 dry sediment), followed by suspended sediment from a winter storm, then bed sediment and soils. Successive solubilization experiments increased the total release of WSOC by ∼50%, but most (88–97%) of the solid-phase OC remained insoluble in water. Using these solubilization potential estimates and measured TSS concentrations, we estimated that WSOC from suspended sediment in streams represented 4–7% of the annual DOC export from the watershed. However, field sediment export is much higher than what is represented by suspended sediment in the water column, therefore field-scale contributions from sediments could be much higher than estimated.

California↗

USGS2022

Discovery and potential ramifications of reduced iron-bearing nanoparticles — Magnetite, wüstite, and zero-valent iron — In wildland–urban interface fire ashes

The increase in fires at the wildland–urban interface has raised concerns about the potential environmental impact of ash remaining after burning. Here, we examined the concentrations and speciation of iron-bearing nanoparticles in wildland–urban interface ash. Total iron concentrations in ash varied between 4 and 66 mg g −1 . Synchrotron X-ray absorption near-edge structure (XANES) spectroscopy of bulk ash samples was used to quantify the relative abundance of major Fe phases, which were corroborated by transmission electron microscopy measurements. Maghemite (γ-(Fe 3+ ) 2 O 3 ) and magnetite (γ-Fe 2+ (Fe 3+ ) 2 O 4 ) were detected in most ashes and accounted for 0–90 and 0–81% of the spectral weight, respectively. Ferrihydrite (amorphous Fe( III )–hydroxide, (Fe 3+ ) 5 HO 8 ·4H 2 O), goethite (α-Fe 3+ OOH), and hematite (α-Fe 3+ 2 O 3 ) were identified less frequently in ashes than maghemite and magnetite and accounted for 0–65, 0–54, and 0–50% of spectral weight, respectively. Other iron phases identified in ashes include wüstite (Fe 2+ O), zerovalent iron, FeS, FeCl 2 , FeCl 3 , FeSO 4 , Fe 2 (SO 4 ) 3 , and Fe(NO 3 ) 3 . Our findings demonstrate the impact of fires at the wildland–urban interface on iron speciation; that is, fires can convert iron oxides ( e.g. , maghemite, hematite, and goethite) to reduced iron phases such as magnetite, wüstite, and zerovalent iron. Magnetite concentrations ( e.g. , up to 25 mg g −1 ) decreased from black to gray to white ashes. Based on transmission electron microscopy (TEM) analyses, most of the magnetite nanoparticles were less than 500 nm in size, although larger particles were identified. Magnetite nanoparticles have been linked to neurodegenerative diseases as well as climate change. This study provides important information for understanding the potential environmental impacts of fires at the wildland–urban interface, which are currently poorly understood.

Environmental Science Nano↗

USGS2017

Irrigation as a fuel pump to freshwater ecosystems

We generated a detailed time series of total dissolved hydrolyzable amino acids (DHAA) in a watershed dominated by irrigated agriculture in northern California, USA to investigate the roles of hydrologic and seasonal changes on the composition of dissolved organic matter (DOM). DHAA are sensitive indicators of the degradation state and reactivity of DOM. DHAA concentrations ranged from 0.55 to 9.96 μM (median 3.51 ± 1.80 μM), with expected peaks during high-discharge storms and unexpected high values throughout the low-discharge irrigation season. Overall, summer irrigation was a critical hydrologic regime for DOM cycling since it mobilized DOM similar in concentration and reactivity to DOM released during storms. Together, irrigation and storm flows exported DOM with (1) the largest DHAA contributions to the dissolved organic carbon and the dissolved organic nitrogen pools, (2) the largest proportion of basic amino acids, and (3) the lowest degradation extent based on multiple indices. In this highly disturbed terrestrial system, UV–vis absorbance did not correlate with DHAA concentrations, while classic interpretations of common amino acid indicators (e.g., proportion of basic amino acids, degradation index, percent of non-protein amino acids) were prone to conflicting characterizations of DOM reactivity. Therefore, a new parameter (processing ratio, PR) derived from individual amino acid concentrations was developed that demonstrated a strong potential for mechanistic-driven characterization of the extent of DOM diagenesis in freshwaters. Irrigated agriculture altered stream biogeochemistry by releasing a continuous supply of reactive DOM (lowest PR values), thereby providing an additional energy source to downstream ecosystems.

California↗