ORCID ID

https://orcid.org/0000-0002-0189-0530

Date Awarded

2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Virginia Institute of Marine Science

Advisor

Amber K Hardison

Committee Member

Bongkeun Song

Committee Member

Mark J Brush

Committee Member

Chris J Hein

Committee Member

Jim W McClelland

Abstract

At the intersection of land, sea, and atmosphere, coastal lagoons act as bioreactors, processing both terrestrial and autochthonous organic matter production before export to the coastal ocean. Approximately half of the Beaufort Sea coast is outlined by barrier island chains that enclose shallow lagoons and sounds. These lagoons are subject to extreme seasonal variations in ice cover, temperature, and salinity, yet are home to a diverse and productive food web. Bound between the arctic tundra and Beaufort Sea, these shallow systems receive and process resources from both sea and particularly land in the form of coastal erosion and riverine export. While we know these terrestrial inputs are driving increasing rates of primary production in the Arctic Ocean, the role of nearshore coastal retention and processing of this material before export remains underexplored. To that end, the overarching goal of this dissertation was to assess seasonal and spatial dynamics of carbon and nutrient cycling in coastal Arctic lagoons as part of the Beaufort Lagoon Ecosystems Long-Term Ecological Research (BLE-LTER) program from 2018-2022. Water column and sediment samples were collected at five lagoons (Elson Lagoon, Simpson Lagoon, Stefansson Sound, Kaktovik Lagoon, Jago Lagoon) during Ice Cover (April), Break Up (June), and Open Water (August) in alignment with the major hydrological phases. In Chapter 2, Abiotic and biotic controls on nutrient cycling in coastal Arctic lagoons, I present seasonally collected water column nutrient data and estimated physical vs. biological controls on their concentrations. During Ice Cover, inorganic nutrient concentrations likely increased in response to brine exclusion and biotic remineralization. In contrast nutrient concentrations rapidly decreased during Break Up and Open Water through freshwater input dilution and autotrophic uptake during Break Up. In Chapter 3, Physical drivers of sediment distribution and organic matter oxidation in coastal Arctic lagoons, I focused on sediment characteristics and the physical conditions that drive organic matter distribution and microbial aerobic oxidation. Sediment grain size, organic matter content, and isotopic composition consistently differed between lagoons and water depths, reflecting the variability in sediment organic matter retention, source, and processing. In Chapter 4, Seasonal cycles of benthic productivity and N cycling in Beaufort Sea lagoons I present results from seasonal batch sediment incubations to quantify benthic metabolism and nitrogen cycling. In general, lagoon sediments shifted from net heterotrophy in Ice Cover, exhibiting net inorganic nutrient production and net denitrification before transitioning into net autotrophy during Break Up and Open Water with increased sediment nutrient consumption and nitrogen fixation. As the coastal Arctic undergoes rapid changes in temperature, duration of sea ice, river discharge, and coastal erosion, our understanding of seasonal nearshore coastal metabolism will help to better constrain future projections of coastal Arctic ecosystem productivity.

DOI

https://dx.doi.org/10.25773/v5-twg5-qx31

Rights

© The Author

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