Particulate material comprising the detrital remains of terrestrial plants and macrophytes is a substantial source of organic matter to estuaries and therefore has the potential to support the energy demands of the pelagic aquatic food web. Despite the prevalence of macrophytic or terrestrial particulate organic carbon (tPOC), phytoplankton are nutritionally superior and are thought to be the primary food resource for zooplankton. However, estuarine phytoplankton primary productivity abundances can wax and wane, and often production cannot meet heterotrophic energy needs. In this study, we examined how tPOC (detritus of macrophytes and grasses) may affect survival of a calanoid copepod ( Eurytemora affinis ) common in the San Francisco Estuary (SFE), an estuary with relatively low phytoplankton primary productivity. Using chemical biomarkers and a targeted DNA metagenomic methodology, we show that E. affinis consumed tPOC (dominated by Schoenoplectus sp., or tule) even when phytoplankton were abundant and tPOC was scarce. Furthermore, we found that a mixed diet of phytoplankton and terrestrial material (1:3 carbon ratio) enhanced the survival of E. affinis over a diet of phytoplankton alone. These data show that tPOC can be a vital supplementary food source for zooplankton, perhaps extending survival during low phytoplankton periods, and may help explain elevated zooplankton abundances in tidal wetlands and other detrital-dominated regions.

Substantial changes in vegetation are expected as global climatic patterns shift, altering terrestrial sources of dissolved organic matter (DOM) entering rivers and streams. Since differences in the chemical composition of plant litters are reflected in the DOM that is leached, changes in riparian vegetation can directly influence the bioavailability of DOM to local aquatic microbial communities. We assessed the degradation dynamics and optical compositional changes of DOM from a variety of vascular plant leachates through microbial and coupled photochemical‐microbial degradation pathways. Initial decay rates ranged from 0.029 ± 0.011 day−1 (microbial, mixed wetland) to 0.73 ± 0.62 day−1 (photochemical‐microbial, mixed grasses), and all decay rates decreased to below 0.05 day−1 after 1 week, converging below 0.029 day−1 after 2 weeks. Overall, we found a decrease in leachate optical diversity under microbial and photochemical‐microbial degradations, corresponding to a decrease in degraded leachate sample dispersion using principal component analysis. We show that despite initial variability across DOM leachates, successive degradation promotes kinetic and optical convergence such that, in aquatic environments with long residence times, terrestrial DOM source and composition are much less important on exported DOM composition than historically thought. In these systems, DOM compositional convergence may act as a natural buffer to provide stability of aquatic DOM cycling in the face of future landscape changes.

Wet deposition and dry deposition of legacy per- and polyfluoroalkyl substances (PFAS) and perfluoroalkyl ether carboxylic acids (PFECAs) were assessed on the southeastern coast of the United States, specifically, in Wilmington, NC, which is located 110 km from a fluorochemical manufacturer. Analytes were quantified by liquid chromatography coupled to electrospray ionization with triple-quadrupole mass spectrometry. Total concentrations of six PFAS compounds ranged from below the method quantification limit to 110 ng L–1 by wet deposition, and total fluxes of 0.3–29 ng m–2 day–1 by dry deposition were found. The estimated annual flux of all six PFAS was 30 μg m–2 by wet deposition and 1.4 μg m–2 by dry deposition, indicating that PFAS are more effectively removed from the atmosphere by wet deposition. There was a significant rainout/washout effect observed in our data, but there was no impact of the origin of the air mass on concentration or flux, suggesting that the incorporation of PFAS into rainwater is a relatively local phenomenon. This study shows the first direct evidence of PFECAs in wet and dry deposition. The data suggest that the particle-bound and gas-phase PFAS that may have undergone long-range transport can be incorporated into raindrops and removed rapidly.

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The sedimentary fate of hexafluoropropylene oxide dimer acid (HFPO-DA) was investigated over a 12 week time series in HFPO-DA-amended (600 ng of spike addition) freshwater and estuarine tidal sediments collected in southeastern North Carolina. A 40−59% decrease in the concentration of HFPO-DA was observed within 14 days for freshwater and estuarine sediments. This decrease could not be explained by biological degradation because there were no statistically significant differences in HFPO-DA loss between bioactive and autoclaved sediments and no degradation products were detected via highresolution mass spectrometry. An additional 2−3% of HFPO-DA was recovered when sediments were subjected to a more aggressive extraction (12 h soak with 80:20 1 M NaOH in methanol/water), suggesting that HFPO-DA sorbs strongly to sediments and remains undetected by less aggressive PFAS sediment extraction methods. Results of this study highlight that (1) PFAS sediment extraction methodologies need to be re-evaluated, particularly as alternative compounds continue to be synthesized and discovered, and (2) studies employing less aggressive extraction methodologies significantly underestimate PFAS contamination in aquatic sediments. Given that HFPO-DA is resistant to biological degradation and has a high sorption affinity, aquatic sediments may be a more significant long-term sink for HFPO-DA and other short-chain alternative PFAS than previously thought.