Haviland
Katherine Ann
Haviland
Katherine Ann
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ArticleVariation in sediment and seagrass characteristics reflect multiple stressors along a nitrogen-enrichment gradient in a New England lagoon(Association for the Sciences of Limnology and Oceanography, 2022-01-28) Haviland, Katherine Ann ; Howarth, Robert W. ; Marino, Roxanne ; Hayn, MelanieWe examined concentrations of organic carbon, dissolved sulfides, total sediment sulfur, and stable sulfur isotope ratios in seagrass leaf tissues across a nitrogen-enrichment gradient in a coastal marine ecosystem (Cape Cod, Massachusetts) in 2007–2010 and 2017–2019. We also measured seagrass aboveground and belowground biomass, epibiota biomass, and leaf chlorophyll content. Seagrasses were present at all sites in the former period but were lost at our most nitrogen-impacted site (Snug Harbor) by 2011. In 2007–2010, sediment organic carbon and dissolved sulfides were highest in Snug Harbor and decreased along the gradient; leaf tissues depleted in 34S also indicated higher sulfide intrusion into seagrass tissues in more eutrophic areas. By 2017–2019, sediment organic carbon and pore-water soluble sulfides had decreased in Snug Harbor, but had increased at the intermediate site, to levels found at the most impacted site prior to the seagrass die-off. Again, leaf tissue 34S depletion reflected this pattern, indicating seagrasses were exposed to the highest sulfides at the intermediate site. The decreases in sediment organic carbon and soluble sulfides in Snug Harbor years after the loss of the seagrasses illustrate a feedback between high organic matter in seagrass beds and increasing stressors like elevated soluble sulfides in nutrient-enriched systems. We found significant relationships between sediment conditions and seagrass responses, including greater aboveground to belowground biomass ratios, epibiota biomass, and 34S-depleted leaves at sites with high pore-water sulfide and highly organic sediments. Our research suggests that the reduction of anthropogenic nitrogen entering the harbor is necessary for improving sediment quality and preventing seagrass mortality.
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ArticleCharacterizing spatial and temporal trends in net sediment accumulation in seagrass meadows(Springer, 2024-05-18) Haviland, Katherine Ann ; Howarth, Robert W. ; Hayn, Melanie ; Giblin, Anne E.Seagrass meadows are known as hot spots for carbon accumulation, but there is limited field data on the variability of sediment accumulation across time and space. We developed a method to assess spatial and temporal heterogeneity in net sediment accumulation in seagrass meadows using small, inexpensive samplers, allowing for over 200 unique measurements across multiple transects within our study site. Using this method, we assessed sediment accumulation across seagrass meadow edges, and in varying weather conditions. We found the greatest accumulation of sediment 5 m outside of seagrass meadow edges, with sediment accumulation rates averaging just under 100 g m−2 day−1, though rates were highly variable. Carbon accumulation from settled sediment was generally greater outside of seagrass meadow edges than within the bed, especially at sites undergoing recent expansion. Measurements made during tropical storms showed both scouring of sediment away from sites, and increased accumulation, depending on site properties as well as individual tropical storm characteristics. In the storm that had a measurable storm surge, scouring of sediment was a more dominant mechanism, whereas deposition dominated in the storm that had high winds but no associated storm surge. Our data demonstrate the necessity of including measurements that characterize both spatial and meteorological variability to develop a more holistic understanding of the movement of sediment and particulate organic carbon associated with seagrass meadows, especially as meadow area becomes increasingly fragmented with human activity and global change.
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ArticleThe potential role of sediment iron and sulfur speciation in seagrass meadow loss and recovery(American Association for the Advancement of Science, 2024-10-09) Haviland, Katherine Ann ; Howarth, Robert W. ; Giblin, Anne E. ; Marino, RoxanneOxidized iron (Fe) can reduce seagrass dieback when present in sufficient quantities in the sediment to fix sulfide as pyrite (FeS2) or iron monosulfide (FeS). However, the oxidized Fe pool may become depleted over time as Fe is reduced and precipitated with sulfides. In this study, we estimated long-term variations in the speciation of solid forms of reduced and oxidized Fe along a eutrophication gradient in West Falmouth Harbor (WFH) (a temperate lagoon with substantial seagrass meadows) and conducted a 6-week microcosm study to assess the role of oxidized Fe in supporting seagrass recovery. We planted seagrass in sediments obtained from 2 WFH regions with differing Fe speciation. We found depletion of oxidized Fe over a decade following a seagrass dieback, even when the soluble sulfide levels decreased to concentrations unlikely to cause toxicity in seagrass. The continued absence of large concentrations of available oxidized Fe minerals in sediments, where most Fe was bound in FeS2, could impede the recovery of seagrass in formerly vegetated regions. Seagrass grown in sediments with low Fe:S ratios exhibited an increased probability of survival after 4 weeks. Field and laboratory results indicated that even when the soluble sulfide levels decrease after seagrass dieback, sediments may not be able to support seagrass recovery due to the legacy effects of eutrophication on the sediment Fe pool. However, we observed signs of reoxidation in the Fe pool within a few years of seagrass dieback, including a decrease in the total sediment S concentration, which could help spur recolonization.