Publications by authors named "J P Holmquist"

Tidal marshes are threatened coastal ecosystems known for their capacity to store large amounts of carbon in their water-logged soils. Accurate quantification and mapping of global tidal marshes soil organic carbon (SOC) stocks is of considerable value to conservation efforts. Here, we used training data from 3710 unique locations, landscape-level environmental drivers and a global tidal marsh extent map to produce a global, spatially explicit map of SOC storage in tidal marshes at 30 m resolution.

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Article Synopsis
  • Tidal wetlands can absorb greenhouse gases, but methane emissions can vary due to environmental factors and human activities.
  • Land managers require detailed maps of methane properties in these wetlands for effective restoration and greenhouse gas inventories, yet current sampling methods don't align well with broader mapping products.
  • Research involved sampling 27 tidal wetlands, revealing that sulfate concentration is the strongest predictor of methane levels, while salinity also plays a significant role; future studies should focus on understanding local environmental influences on methane variation.
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Article Synopsis
  • * Annual CH fluxes averaged around 26g CH/m²/year; the highest emissions were linked with certain temperature and salinity conditions, particularly in fresh-oligohaline marshes.
  • * The research found that salinity was the main factor affecting annual CH fluxes, while temperature, gross primary productivity, and tidal height influenced shorter-term variability, providing crucial data for better estimating methane emissions in these ecosystems.
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Coastal terrestrial-aquatic interfaces (TAIs) are crucial contributors to global biogeochemical cycles and carbon exchange. The soil carbon dioxide (CO) efflux in these transition zones is however poorly understood due to the high spatiotemporal dynamics of TAIs, as various sub-ecosystems in this region are compressed and expanded by complex influences of tides, changes in river levels, climate, and land use. We focus on the Chesapeake Bay region to (i) investigate the spatial heterogeneity of the coastal ecosystem and identify spatial zones with similar environmental characteristics based on the spatial data layers, including vegetation phenology, climate, landcover, diversity, topography, soil property, and relative tidal elevation; (ii) understand the primary driving factors affecting soil respiration within sub-ecosystems of the coastal ecosystem.

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