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  1. Coastal marine heatwaves have destructive and lasting impacts on foundational species 13 and are increasing in frequency, duration, and magnitude. High atmospheric temperatures are 14 often associated with marine heatwaves (MHW) which are defined as 5-days of water 15 temperatures above a seasonally varying 90th percentile threshold. In this study we consider the 16 prevalence of MHW propagation into surficial sediments to cause sediment heatwaves (SHW). 17 Within a shallow, subtidal seagrass meadow in Virginia, USA, sediment temperature was 18 measured at hourly intervals at a depth of 5 cm between June 2020-October 2022 at the meadow 19 edge and central meadow interior. The observed sediment temperature, along with a 29-year 20 record of water temperature and water level was used to develop a sediment temperature model 21 for each location. Modeled sediment temperatures were used to identify sediment heatwaves that 22 may thermally stress belowground seagrass. At both meadow locations, sediment heatwave 23 frequency increased at a rate twice that of MHWs in the average global open ocean, coinciding 24 with a 172% increase in the annual number of SHW days, from 11 to 30 days year-1 between 25 1994-2022. Sediment heatwaves at both meadow locations co-occurred with a MHW 79-81% of 26 the time, with nearly all SHWs having a zero day lag. The top 10% most extreme MHWs and 27 SHWs occurred between November and April when thermal stress to seagrass was unlikely. In 28 June 2015 a SHW co-occurred with an anomalously long duration MHW that was associated 29 with a 90% decline in seagrass from this system, suggesting that SHWs may have contributed to 30 the observed seagrass loss. These results document heatwave propagation across the pelagic-31 sediment interface which likely occur broadly in shallow systems with impacts to critical coastal 32 ecosystem processes and species dynamics. 
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    Free, publicly-accessible full text available December 15, 2024
  2. Coastal landscapes are naturally shifting mosaics of distinct ecosystems that are rapidly migratingwith sealevel rise. Previous work illustrates that transitions among individual ecosystems have disproportionate impacts on the global carbon cycle, but this cannot address nonlinear interactions between multiple ecosystems that potentially cascade across the coastal landscape. Here, we synthesize carbon stocks, accumulation rates, and regional land cover data over 36 years (1984 and 2020) for a variety of ecosystems across a large portion of the rapidly transgressing mid-Atlantic coast. The coastal landscape of the Virginia Eastern Shore consists of temperate forest, salt marsh, seagrass beds, barrier islands, and coastal lagoons. We found that rapid losses and gains within individual ecosystems largely offset each other, which resulted in relatively stable areas for the different ecosystems, and a 4% (196.9 Gg C) reduction in regional carbon storage. However, new metrics of carbon replacement times indicated that it would take only 7 years of carbon accumulation in surviving ecosystems to compensate this loss. Our findings reveal unique compensatory mechanisms at the scale of entire landscapes that quickly absorb losses and facilitate increased regional carbon storage in the face of historical and contemporary sea-level rise. However, the strength of these compensatory mechanisms may diminish as climate change exacerbates the magnitude of carbon losses. 
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    Free, publicly-accessible full text available September 15, 2024
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  4. Abstract

    Dissolved organic carbon (DOC) is a key component of aquatic ecosystems with complex effects on ecosystem function. While long‐term increases in DOC termed “brownification” have received considerable attention, directional trends typically account for a minority of variance. DOC concentrations also fluctuate on seasonal to multiannual timescales, but the causes of such variations are less understood. We used a wavelet‐based approach to study timescale‐specific, spatially synchronous fluctuations in DOC across 49 lakes in the Adirondacks, New York, USA. DOC varies synchronously among lakes at within‐season, annual, and interannual timescales, but relationships with external drivers and internal processes indicated by lake chemistry differed across timescales. External drivers explained 78% of spatial DOC synchrony at the annual time scale. Beyond positive trends related to regional recovery from acidification, variability in DOC is a consequence of fluctuations at several timescales that are common among Adirondack lakes in precipitation, solar radiation, and internal chemical concentrations.

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  5. Abstract

    Impacts of invasive species are often context specific due to varying ecological interactions. Physical structure of environments hosting invaders is also potentially important but has received limited attention. An invasive macroalga,Agarophyton vermiculophyllum, has spread across the northern hemisphere with mixed positive, neutral and negative effects on resident species.Agarophytoncolonizes mudflats that vary in topography due to interactions of sediments with hydrodynamic forces. We tested the hypothesis that mudflat geomorphology moderates the effect ofAgarophytonon shorebirds and invertebrates. We surveyed 30 mudflats in the Virginia Coast Reserve quantifying elevation and topography. Invertebrate and bird abundances were also quantified. Mudflat geomorphology ranged from smooth to hummocky and was correlated with invertebrate and shorebird abundance and interactions based on piecewise structural equation models. After accounting for geomorphology,Agarophytonhad little effect on invertebrate abundance. Shorebird numbers were differentially influenced by mudflat topography, with positive correlations to invertebrates (worms) on smooth mudflats, and to macroalgae on hummocky mudflats. These differences are likely to be due to sediment properties in interaction with structural changes induced byAgarophytonmats that affect prey accessibility for birds. Even on apparently simple mudflats, geomorphic structure emerged as important, modifying invasive species impacts and differentially influencing consumers.

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  6. null (Ed.)