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1. Microplastics in the Sediments ofShelves and Basins offshore of SouthernCalifornia

   Sarner, R.; Gray, S.C. (February 2020, Ocean Sciences Meeting)

   none. (Ed.)

   Microplastics are abundant in beach and bay sediments near urban areas. However, it is less well known whether they are present in the sediments of the shelves and isolated deep basins offshore of southern California. The objectives of this research were a) to test the best methodologies to extract microplastics from organic-rich sediments (silty sands), and b) to determine how the abundance of microplastics in sediments collected from offshore shelves and deep basins compared to their abundance in sediments of San Diego Bay (< 5m depth). Surface sediment samples were collected using a multicore from shelves (10-14km offshore; 100-300 m deep) and basins (90-130km offshore; 618-997m deep) on two cruises in 2018 on the RV Sally Ride and RV Sproul. For comparison, shallow (2-5m deep) sediments were collected in San Diego Bay. To extract microplastics from the samples, 78-100mL of sediment from the upper 1cm layer of the core was processed by density floatation in Zinc Chloride (1.5 g/cm ³). Floating material was then vacuum filtered and identified by counting under a light microscope. Analytical blanks were processed everythree samples and methods were further modified to minimize the amount of contaminant plastic found on filters. The mean [SD] abundance of microplastics in the sediments of San Diego Bay (2.5 [2.3] pieces/ml)was over 4 times greater than in the shelf (0.42 [.11] pieces/ml) and offshore deep basin sediments(0.57 [0.22] pieces/ml). We found microplastic abundances above analytical blanks at all 10 off shore sites including the deep basins. A better understanding of the microplastic distributions in off shore sediments will help us better predict the impact of plastics on deep-sea marine 

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2. Microplastics affect sedimentary microbial communities and nitrogen cycling

   https://doi.org/10.1038/s41467-020-16235-3  

   Seeley, Meredith E.; Song, Bongkeun; Passie, Renia; Hale, Robert C. (May 2020, Nature Communications)

   Abstract Microplastics are ubiquitous in estuarine, coastal, and deep sea sediments. The impacts of microplastics on sedimentary microbial ecosystems and biogeochemical carbon and nitrogen cycles, however, have not been well reported. To evaluate if microplastics influence the composition and function of sedimentary microbial communities, we conducted a microcosm experiment using salt marsh sediment amended with polyethylene (PE), polyvinyl chloride (PVC), polyurethane foam (PUF) or polylactic acid (PLA) microplastics. We report that the presence of microplastics alters sediment microbial community composition and nitrogen cycling processes. Compared to control sediments without microplastic, PUF- and PLA-amended sediments promote nitrification and denitrification, while PVC amendment inhibits both processes. These results indicate that nitrogen cycling processes in sediments can be significantly affected by different microplastics, which may serve as organic carbon substrates for microbial communities. Considering this evidence and increasing microplastic pollution, the impact of plastics on global ecosystems and biogeochemical cycling merits critical investigation. 

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3. Patterns of sediment-associated fecal indicator bacteria in an urban estuary: Benthic-pelagic coupling and implications for shoreline water quality.

   O'Mullan, G.; Juhl, A.; Reichert, R.; Schneider, E.; and Martinez, N. (January 2019, Science of the total environment)

   Estuarine and coastal waterways are commonly monitored for fecal and sewage contamination to protect recreator health and ecosystem functions. Such monitoring programs commonly rely on cultivation-based counts of fecal indicator bacteria (FIB) in water column samples. Recent studies demonstrate that sediments and beach sands can be heavily colonized by FIB, and that settling and resuspension of colonized particles may significantly influence the distribution of FIB in the water column. However, measurements of sediment FIB are rarely incorporated into monitoring programs, and geographic surveys of sediment FIB are uncommon. In this study, the distribution of FIB and the extent of benthic-pelagic FIB coupling were examined in the urbanized, lower Hudson River Estuary. Using cultivation-based enumeration, two commonly-measured FIB, enterococci and Escherichia coli, were widely distributed in both sediment and water, and were positively correlated with each other. The taxonomic identity of FIB isolates from water and sediment was confirmed by DNA sequencing. The geometric mean of FIB concentration in sediment was correlated with both the geometric mean of FIB in water samples from the same locations and with sediment organic carbon. These two positive associations likely reflect water as the FIB source for underlying sediments, and longer FIB persistence in the sediments compared to the water, respectively. The relative representation of other fecal associated bacterial genera in sediment, determined by 16S rRNA gene sequencing, increased with the sequence representation of the two FIB, supporting the value of these FIB for assessing sediment contamination. Experimental resuspension of sediment increased shoreline water column FIB concentrations, which may explain why shoreline water samples had higher average FIB concentrations than samples collected nearby but further from shore. In combination, these results demonstrate extensive benthic-pelagic coupling of FIB in an urbanized estuary and highlight the importance of sediment FIB distribution and ecology when interpreting water quality monitoring data. 

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4. MICROPLASTIC POLLUTION IN THE TIJUANA ESTUARY BEACHESOF SOUTHERN CALIFORNIA

   Sheppard, Q.; Gray, S.C. (February 2022, Ocean Sciences Meeting)

   no editor. (Ed.)

   The Tijuana River Watershed encompasses 1750 square miles of territory in both Mexico and the United States, culminating at the National EstuarineResearch Reserve. While this area comprises one of the largest undisturbed wetlands in the state, it is one of the most polluted rivers in SouthernCalifornia, draining raw sewage and nonpoint source pollution. Despite extensive research, microplastic pollution along the beaches has not been explored. The objective of this study is to determine how the abundance and morphology of microplastic pollution in beach sediments vary with distance along the littoral cell from the Tijuana River outfall. Twenty samples were collected at 10 sites that span from the Tijuana River outfall to Mission Beach, San Diego. They are characterized as outfall sites, low-visitation beaches near the outfall, and high-visitation beaches further from the outfall. Solutions of 100ml sediment and 400ml hyper-saline solution were mixed and settled for 16 hours before being processed using a vacuum filtration system in a laminar fl ow hood. The microplastics (MP)were counted and classified using light microscopy. Laboratory practices to reduce laboratory contamination were employed and analytical blanks were run for every 3 samples. MPs ranged from 1 to 199/100ml sediment, of which approximately 91% were fibers. The greatest MP abundance occurred at the river outfall sites, but recovery rates were highly variable, and the analytical blanks ranged from 3-63/100ml sediment. The results oft his study suggest that microplastic distribution in sandy beach sediments is patchy but higher near the Tijuana River Outfall, and that future studies should report analytical blanks and employ methods to reduce contamination. Understanding the relationship between watersheds and microplastic distributions may inspire policy change on water quality protections in watersheds. 

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5. A Decade of Time Series Sampling Reveals Thermal Variation and Shifts in Pseudo-nitzschia Species Composition That Contribute to Harmful Algal Blooms in an Eastern US Estuary

   https://doi.org/10.3389/fmars.2022.889840  

   Roche, Katherine M.; Sterling, Alexa R.; Rynearson, Tatiana A.; Bertin, Matthew J.; Jenkins, Bethany D. (July 2022, Frontiers in Marine Science)

   Mulholland, Margaret R (Ed.)

   In 2016-17, shellfish harvesting closed for the first time in Narragansett Bay, Rhode Island, USA, from domoic acid (DA), a neurotoxin produced by diatoms of the Pseudo-nitzschia genus. Pseudo-nitzschia have occurred frequently for over 60 years in Narragansett Bay’s Long-Term Plankton Time Series (NBPTS), therefore it is surprising that the first closure only recently occurred. Pseudo-nitzschia species are known to vary in their toxin production, thus species identification is critical for understanding the underlying ecological causes of these harmful algal blooms (HABs). DNA in plankton biomass can be preserved for many years, so molecular barcoding of archived samples is useful for delineation of taxa over time. This study used amplification of the Pseudo-nitzschia -specific 18S-5.8S rDNA internal transcribed spacer region 1 (ITS1) in plankton samples and high throughput sequencing to characterize Pseudo-nitzschia species composition over a decade in Narragansett Bay, including eight years before the 2016-17 closures and two years following. This metabarcoding method can discriminate nearly all known Pseudo-nitzschia species. Several species recur as year-round residents in Narragansett Bay ( P. pungens var. pungens, P. americana, P. multiseries , and P. calliantha ). Various other species increased in frequency after 2015, and some appeared for the first time during the closure period. Notably, P. australis , a species prevalent in US West Coast HABs and known for high DA production, was not observed in Narragansett Bay until the 2017 closure but has been present in several years after the closures. Annual differences in Pseudo-nitzschia composition were correlated with physical and chemical conditions, predominantly water temperature. The long-term composition trends of Pseudo-nitzschia in Narragansett Bay serve as a baseline for identifying the introduction of new species, understanding shifting assemblages that contributed to the 2016-17 closures, and monitoring species that may be cause for future concern. 

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