Search

Tropical peatlands store copious amounts of carbon (C) and play a critical role in the global C cycle. However, this C store is vulnerable to natural and anthropogenic disturbances, leading these ecosystems to become weaker C sinks or even net C sources. Variabilities in water table (WT) greatly influence the magnitude of greenhouse gas flux in these biomes. Despite its importance in C cycling, observations of the spatiotemporal dynamics of tropical peatland WT are limited in spatial extent and length. Here, we use in situ WT measurements from tropical peatlands in Indonesia, Malaysia, and Peru to evaluate the satellite‐based Optical Trapezoid Model (OPTRAM). The model uses the pixel distribution in the shortwave infrared transformed reflectance and normalized difference vegetation index (NDVI) space to calculate indices that are then compared against in situ WT data. 30‐m resolution Landsat 7 and Landsat 8 images were utilized for model parameterization. We found OPTRAM to best capture tropical peatland WT dynamics in minimally forested and non‐forested areas (low to intermediate NDVI) (0.7 < R < 1) using the "best pixel" approach (the pixel with the highest Pearson‐R correlation value). In areas with relatively higher NDVI, OPTRAM index did not correlate with WT (average R of −0.04 to 0.24), likely due to trees being less sensitive to WT fluctuations. OPTRAM shows potential for reliably estimating tropical peatland WT without the need for direct measurements, which is challenging due to site remoteness and harsh conditions. Plain Language Summary: Tropical peatlands store copious amounts of carbon in their soil and biomass. The position of the water table (WT) relative to the soil surface plays a large role in how much greenhouse gases (GHGs) (i.e., carbon dioxide, methane, and nitrous oxide) is emitted or taken up and may also give insight into areas most vulnerable to fire. Therefore, estimating tropical peatland WT fluctuations over space and time is essential for understanding the global carbon and GHG budgets. Due to harsh environmental conditions and site remoteness, direct measurements of tropical peatland WT are limited in spatial extent and length. As a result, other methods must be developed to estimate the spatiotemporal variability of this parameter. Through manipulation of satellite surface reflectance, we demonstrate the feasibility of estimating fluctuations in tropical peatland WT from space. This method is tested on sites spanning Peru, Indonesia, and Malaysia. We find that WT fluctuations are accurately quantified over areas that are minimally forested or non‐forested. Our findings provide a pathway to map tropical peatland WT from space leading to improved understanding of WT‐dependent processes such as GHG emissions and fire risk, both of which contribute greatly to global climate change. Key Points: OPTRAM is capable of accurately capturing the temporal variability of tropical peatland water tableOPTRAM performs optimally over minimally forested and non‐forested areas [ABSTRACT FROM AUTHOR]

Wetlands are integral to the global carbon cycle, serving as both a source and a sink for organic carbon. Their potential for carbon storage will likely change in the coming decades in response to higher temperatures and variable precipitation patterns. We characterized the dissolved organic carbon (DOC) and dissolved organic matter (DOM) composition from 12 different wetland sites across the USA spanning gradients in climate, landcover, sampling depth, and hydroperiod for comparison to DOM in other inland waters. Using absorption spectroscopy, parallel factor analysis modeling, and ultra‐high resolution mass spectroscopy, we identified differences in DOM sourcing and processing by geographic site. Wetland DOM composition was driven primarily by differences in landcover where forested sites contained greater aromatic and oxygenated DOM content compared to grassland/herbaceous sites which were more aliphatic and enriched in N and S molecular formulae. Furthermore, surface and porewater DOM was also influenced by properties such as soil type, organic matter content, and precipitation. Surface water DOM was relatively enriched in oxygenated higher molecular weight formulae representing HUPHigh O/C compounds than porewaters, whose DOM composition suggests abiotic sulfurization from dissolved inorganic sulfide. Finally, we identified a group of persistent molecular formulae (3,489) present across all sites and sampling depths (i.e., the signature of wetland DOM) that are likely important for riverine‐to‐coastal DOM transport. As anthropogenic disturbances continue to impact temperate wetlands, this study highlights drivers of DOM composition fundamental for understanding how wetland organic carbon will change, and thus its role in biogeochemical cycling. Plain Language Summary: Dissolved organic matter (DOM) is often the most reactive form of organic carbon in wetlands, but its molecular characteristics and distribution are not well defined across different wetland types. We characterized DOM and analyzed dissolved organic carbon (DOC) concentrations across 12 temperate USA wetlands during wet and dry seasons from both surface‐ and porewaters. Wetland DOM primarily originates from the landscapes with greater DOC concentrations than similar inland waters such as lakes and rivers. DOM composition differs mostly by geographic site, suggesting that forested wetlands contain more aromatic DOM compounds from vegetation and soil than grassland/herbaceous wetlands, which contain DOM that is more processed. DOM composition between surface and porewaters is influenced by local ecological properties such as soil content and precipitation, with porewater compositions heavily impacted by mineral interactions. Finally, we identified common molecular signatures across all wetlands that have also been found in the largest arctic rivers, highlighting the role of wetlands as potential organic carbon sources to rivers and coastal systems. As precipitation and temperature patterns continue to change across temperate regions, the balance between different carbon pools will likely respond, particularly between the distribution and composition of wetland surface and porewater organic matter. Key Points: Wetlands contain higher dissolved organic carbon (DOC) concentrations and greater aromatic dissolved organic matter (DOM) composition than other inland waters across the USAWetland DOM composition differs spatially between forested and grassland/herbaceous landcover as well as between surface and porewatersPersistent molecular formulae are observed across all wetlands that may be important for riverine‐to‐coastal DOM cycling [ABSTRACT FROM AUTHOR]