Jennifer J. Guerard

Lignin is a promising renewable feedstock to produce chemicals, fuels, and materials, yet a major challenge for lignocellulosic biorefineries is the significant variation in lignin content and structure. Traditional lignin characterization approaches require time-intensive, wet laboratory procedures, highlighting the need for rapid and reliable characterization methods to quantify lignin content and deconstruction products. This study presents a noninvasive, preharvest approach to determine lignin content, total phenolic monomer yield, and syringyl/guaiacyl (S/G) unit ratios in tree biomass from reductive catalytic fractionation (RCF) utilizing the optical properties of stemflow dissolved organic matter (DOM) as a proxy. A significant relationship between fluorescent signatures in stemflow DOM and constituent-specific composition (bark, twigs/branchlets, foliage) is identified, and stepwise multiple linear regression models showcase stemflow DOM component utilization to estimate lignin content, total phenolic monomer yield, and S/G ratio. Unlike traditional approaches, stemflow fluorescence can be quantified preharvest and pretransportation, enabling early lignin screening and prediction of deconstruction performance and product distribution. This stemflow fluorescence approach, harnessing the characterization of DOM in natural processes, is a higher-throughput, lower-cost screening method that could be a critical solution for biorefineries to overcome challenges due to biomass variability and facilitate feedstock screening, process optimization, and output product prediction.

Yedoma permafrost soils are especially susceptible to abrupt thaw due to their exceptional thickness and high ice content. Compared to other mineral soils, yedoma has a high organic carbon content, which has shown to be particularly biolabile. The organic carbon in these deposits needs to be characterised to provide an identification toolkit for detecting and monitoring the thaw, mobilisation and mineralisation of yedoma permafrost. This study characterised organic carbon isolates from thermokarst lakes (either receiving inputs from thaw of original yedoma or refrozen-thermokarst deposits, or lacking recent thaw) during winter and summer seasons within the Goldstream Creek watershed, a discontinuous permafrost watershed in interior Alaska, to identify the extent to which thermokarst-lake environments are impacted by degradation of yedoma permafrost. Waters from lakes of varied age and thermokarst activity, as well as active layer and undisturbed yedoma permafrost soils were isolated and characterised by functional group abundance (multiCP-MAS ¹³C and SPR-W5-WATERGATE ¹H NMR), absorbance and fluorescence, and photobleaching ability. DOM isolated from winter and summer seasons revealed differing composition and photoreactivity, suggesting varied active layer and permafrost influence under differing ground water flow regimes. Water extractable organic matter isolates from permafrost leachates revealed variation in terms of photoreactivity and photolability, with the youngest sampled permafrost isolate being the most photoreactive and photolabile. As temperatures increase, release of permafrost organic matter is inevitable. Obtaining a holistic understanding of DOM composition and photoreactivity will allow for a better prediction of permafrost thaw impacts in the coming decades.

Nutrient availability and molecular composition of dissolved organic matter (DOM) determine whether the carbon (C) associated with DOM is respired during decomposition or exported from stream networks. High‐latitude ecosystems are changing rapidly due to permafrost thaw, shifts in vegetation, and increasing runoff, which alter sources of DOM and nutrients to rivers. To address how changes in the composition of riverine DOM and nutrients may influence C cycling, we quantified biolability of DOM across a latitudinal gradient in Alaska and assessed temporal patterns associated with intra‐annual variation in hydrology. We measured biolability under ambient and fertilized conditions and characterized optical and chemical properties of DOM to determine the relative influence of nutrients and molecular composition of DOM on its fate in rivers. Biolability was low, comprising 4% of the DOM pool on average and 0–42% across all sites and seasons. Optical indicators of the molecular composition of the DOM pool were more constant in space and time than bulk concentrations of dissolved C and nutrients, and described a DOM pool dominated by humic‐like functional groups. Phosphorus limited biolability at freshet, but biolability was not linked to DOM composition. Strong hydrologic connection of high‐latitude rivers to a large pool of soil organic matter likely results in export of recalcitrant DOM to receiving rivers and coasts in this region, contributing to stability of the high‐latitude C cycle. However, increased inputs of phosphorus or DOM of greater biolability will likely cause increased respiration of riverine DOM and flux of CO₂ to the atmosphere.

In this chapter, we present a model for an entry-level lab-based undergraduate environmental chemistry course delivered simultaneously by face-to-face and distance modalities. This course frames conceptual chemistry using the theme of Alaskan Arctic environmental issues in order to increase engagement and perceived relevance of chemical principles. Synchronously delivered lectures and guided discussions along with the incorporation of peer-mentored research projects encourage the development of a learning community among students in the course. Distance students participate in the same virtual and “kitchen” lab experiments as on-campus students, thus providing an educationally equivalent curriculum to all. In mixed teams of on-campus and distance students, all students participate in research projects to allow entry-level students to explore their interests in STEM fields. Students thereby begin to build an identity as a scientist and hopefully this course will serve as a mechanism to improve recruitment and retention of students, especially from traditionally underrepresented groups, in the chemical sciences and other STEM fields of study. Responses from the first course offering communicated positive attitudes toward the course content and methods.