Estuary plumes as drivers of inner continental shelf benthic community structure and function

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In the coastal ocean, nutrient-rich river or estuary waters mix with less-enriched marine waters creating plumes, regions that are very productive and important for fisheries and nutrient cycling. The location and size of these estuary plumes are highly dynamic because of seasonal changes in weather, winds, and ocean currents. The amount of nutrients carried by plumes – and thus their impact on the coastal ocean – also changes seasonally. This project is studying how the plume of the nation’s largest estuary, the Chesapeake Bay, changes over the course of the year and what those changes mean for food webs and nutrient cycles in the coastal Atlantic Ocean. A model of water movements is being developed to predict how river flow, winds, and currents converge to cause seasonal changes in plume size, location, and composition. Research cruises spanning the area of the plume within the coastal ocean are collecting material within the plume as well as the animals living under and on top of the sediments. In parallel, experiments conducted on the ship are investigating how the animals and the chemical reactions in the sediment are affected by materials within the plume. By combining this modelling, measurements of bottom animal biomass and biodiversity, and nutrient experiments, this project is determining how estuarine plumes drive coastal food webs and productivity. Broader impacts include benefits to natural resource management through a better understanding of the linkages between plume dynamics, food webs and fisheries. Doctoral students, a postdoctoral scholar and undergraduate students are being trained in modeling, experimental and field research methods. Increasing diversity in STEM fields is occurring through a partnership with a community college (College of Southern Maryland) to recruit summer interns for research experiences. Outreach activities include the development of age-appropriate educational materials for the public and the use of these materials at ‘in person’ or virtual outreach events.The overarching goal is to determine how the magnitude and reactivity of organic matter inputs and environmental conditions associated with spatially and temporally dynamic estuarine plumes affect inner continental shelf benthic communities. The project is analyzing the role of organic matter deposition, both labile and refractory, as a driver of benthic community structure and sediment-water biogeochemical flux rates. An integrative approach that combines hydrodynamic modelling, field observations and shipboard experiments is linking benthic responses to seasonal changes in plume characteristics. Specifically, a calibrated hydrodynamic model is being used to establish the history of plume-driven conditions and to quantify particle transport and deposition on the inner shelf. A survey of water-column conditions, organic matter pools, and benthic and epibenthic community composition at a fixed station grid are generating empirical measurements of benthic taxonomic and functional composition, biodiversity, and biomass. These measurements are being used to estimate secondary production and assess how it varies seasonally. Sediment-water nutrient fluxes and organic matter-specific nutrient assimilation rates (labile, refractory) by benthos are being quantified using experimental core incubations. Hydrodynamic plume reconstructions are coupled with observational and experimental data to test hypotheses regarding the stimulation of benthic biomass, biodiversity, and secondary production by plume particulate organic matter inputs both seasonally and spatially. Statistical models that account for feeding mode, past exposure to plume influence, lability of deposited organic matter, and physical forces (e.g., temperature, salinity, bed stress) are being developed to predict benthic responses to simulated plume conditions and, potentially, inform understanding of plume dynamics more broadly.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.