Audrey Thellman

Bio: Audrey Thellman is an academic researcher from Duke University. The author has contributed to research in topics: Watershed & Streamflow. The author has an hindex of 1, co-authored 1 publications receiving 4 citations.

MacroSheds: A synthesis of long‐term biogeochemical, hydroclimatic, and geospatial data from small watershed ecosystem studies

Abstract: The US Federal Government supports hundreds of watershed monitoring efforts from which solute fluxes can be calculated. Although instrumentation and methods vary between studies, the data collected and their motivating questions are remarkably similar. Nevertheless, little effort toward their compilation has previously been made. The MacroSheds project has developed a future‐friendly system for harmonizing daily time series of streamflow, precipitation, and solute chemistry from 169+ watersheds, and supplementing each with watershed attributes. Here, we describe the breadth of MacroSheds data, and detail the steps involved in rendering each data product. We provide recommendations for usage and discuss when other datasets might be more suitable. The MacroSheds dataset is an unprecedented resource for watershed science, and for hydrology, as a small‐watershed supplement to existing collections of streamflow predictors, like CAMELS and GAGES‐II. The MacroSheds platform includes a web dashboard for visualization and an R package for data access and analysis.

Better Together: Early Career Aquatic Scientists Forge New Connections at Eco‐DAS XV

Abstract: A sense of kuleana (personal responsibility) in caring for the land and sea. An appreciation for laulima (many hands cooperating). An understanding of aloha 'āina (love of the land). The University of Hawai'i at Manoa hosted the 2023 Ecological Dissertations in Aquatic Sciences (Eco-DAS) program, which fostered each of these intentions by bringing together a team of early career aquatic ecologists for a week of networking and collaborative, interdisciplinary project development (Fig. 1). The Association for the Sciences of Limnology and Oceanography (ASLO) sponsors Eco-DAS, which is now in its 30th year. The program aims to unite aquatic scientists, develop diverse collaborations, and provide professional development training opportunities with guests from federal agencies, nonprofits, academia, tribal groups, and other workplaces (a previous iteration is summarized in Ghosh et al. 2022). Eco-DAS XV was one of the largest and most nationally diverse cohorts, including 37 early career aquatic scientists, 15 of whom were originally from 9 different countries outside the United States (Fig. 2). As the first cohort to meet in-person since the COVID-19 pandemic, Eco-DAS participants convened from 5 to 11 March 2023 to expand professional networks, create shared projects, and discuss areas of priority for the aquatic sciences. During the weeklong meeting, participants developed 46 proposal ideas, 16 of which will be further developed into projects and peer-reviewed manuscripts. Bridging divides Global and local perspectives Mentorship and collaboration New tools for aquatic monitoring Impacts of environmental stressors Big data management, equity, and access Precise, shared language Although many of these themes are not novel, they reiterate the challenges and opportunities that emerging aquatic scientists face. Importantly, these themes prevail in the global field of aquatic ecology and highlight the need to continue collaboratively exploring the way forward. Participants were highly enthusiastic to continue to develop ideas collaboratively and there is no doubt that novel contributions to science will be made in the coming years as a result of this symposium. However, Eco-DAS XV was more than just science, networking, and proposals; it was a constructive experience and marked the beginning of a big ohana (family). Our cohort was not only a group of like-minded researchers at similar career stages, but also a group that quickly connected with one another on different levels beyond “science and careers.” It was a group of amazing people who will have a brilliant future in aquatic sciences together—because the connections created during the week will last a year (Kelly et al. 2017), decades, or even a lifetime! All of the 2023 Eco-DAS participants extend a sincere mahalo nui loa (thank you very much) to the program coordinator, Dr. Paul Kemp, the University of Hawai'i at Manoa, the 15 invited speakers and mentors, the Association for the Sciences of Limnology and Oceanography, and the National Science Foundation (Award #OCE-1925796) for generously supporting the program.

Water transport pathways influence the propagation of field‐scale NO3−‐N reductions to the watershed scale

Abstract: Diffuse nutrient runoff from agricultural fields can result in the eutrophication of downstream water bodies, highlighting a need for conservation efforts to reduce dissolved nitrogen (N) and phosphorus (P) loading to adjacent waterways. However, few studies explore how the impacts of field‐scale conservation manifest at the watershed scale. We explored how sources of streamflow and nutrients may influence the magnitude of the impact of conservation practices at a field versus watershed scale at the Shatto ditch watershed (SDW), where the planting of winter cover crops reduced field‐scale nitrate‐N (NO3−‐N) losses from subsurface tile drains by 69%–90%; yet watershed NO3−‐N export only decreased by 13%. To resolve this discrepancy, we used a water budget approach paired with water stable isotope (18O and 2H) analysis to determine the composition of streamflow across seasons, sampling five times from November 2018 to September 2019. While we hypothesized that watershed‐scale patterns in nutrient export were driven by direct groundwater upwelling, we found that this pathway only accounted for 43% of streamflow on average. We also developed a NO3−‐N mass balance for the watershed during our November 2018 sampling; results indicated groundwater upwelling contributed only ~1% of NO3−‐N export at the watershed outlet, while subsurface tile drains contributed the remaining 99%. Specifically, three large county tile drains (with an unknown drainage area and extent of conservation practice implementation) contributed ~69% of the watershed NO3−‐N export, obscuring the impacts of field‐scale conservation in SDW. Our study highlights the importance of cross‐scale analyses to accurately evaluate the effect of conservation given the interactions between sources of streamflow and nutrient loss at the watershed scale.

The past and future of global river ice

Abstract: More than one-third of Earth’s landmass is drained by rivers that seasonally freeze over. Ice transforms the hydrologic1,2, ecologic3,4, climatic5 and socio-economic6–8 functions of river corridors. Although river ice extent has been shown to be declining in many regions of the world1, the seasonality, historical change and predicted future changes in river ice extent and duration have not yet been quantified globally. Previous studies of river ice, which suggested that declines in extent and duration could be attributed to warming temperatures9,10, were based on data from sparse locations. Furthermore, existing projections of future ice extent are based solely on the location of the 0-°C isotherm11. Here, using satellite observations, we show that the global extent of river ice is declining, and we project a mean decrease in seasonal ice duration of 6.10 ± 0.08 days per 1-°C increase in global mean surface air temperature. We tracked the extent of river ice using over 400,000 clear-sky Landsat images spanning 1984–2018 and observed a mean decline of 2.5 percentage points globally in the past three decades. To project future changes in river ice extent, we developed an observationally calibrated and validated model, based on temperature and season, which reduced the mean bias by 87 per cent compared with the 0-degree-Celsius isotherm approach. We applied this model to future climate projections for 2080–2100: compared with 2009–2029, the average river ice duration declines by 16.7 days under Representative Concentration Pathway (RCP) 8.5, whereas under RCP 4.5 it declines on average by 7.3 days. Our results show that, globally, river ice is measurably declining and will continue to decline linearly with projected increases in surface air temperature towards the end of this century. An analysis based on Landsat imagery shows that the extent of river ice has declined extensively over past decades and that this trend will continue under future global warming.

Winter weather whiplash: impacts of extreme meteorological events misaligned with natural and human systems in seasonally snow-covered regions

Abstract: Weather whiplash” is a colloquial phrase for describing an extreme event that includes shifts between two opposing weather conditions. Prior media coverage and research on these types of extremes have largely ignored winter weather events. However, rapid swings in winter weather can result in crossing from frozen to unfrozen conditions, or vice versa; thus, the potential impact of these types of events on coupled human and natural systems may be large. Given rapidly changing winter conditions in seasonally snow‐covered regions, there is a pressing need for a deeper understanding of such events and the extent of their impacts to minimize their risks. Here we introduce the concept of winter weather whiplash, defined as a class of extreme event in which a collision of unexpected conditions produces a forceful, rapid, back‐and‐forth change in winter weather that induces an outsized impact on coupled human and natural systems. Using a series of case studies, we demonstrate that the effects of winter weather whiplash events depend on the natural and human context in which they occur, and discuss how these events may result in the restructuring of social and ecological systems. We use the long‐term hydrometeorological record at the Hubbard Brook Experimental Forest in New Hampshire, USA to demonstrate quantitative methods for delineating winter weather whiplash events and their biophysical impacts. Ultimately, we argue that robust conceptual and quantitative frameworks for understanding winter weather whiplash events will contribute to the ways in which we mitigate and adapt to winter climate change in vulnerable regions. Plain Language Summary Weather whiplash is a term used by researchers and the media to describe wild and rapid shifts in weather conditions. Here we investigate “winter weather whiplash” events, which are characterized by weather conditions swinging from frozen to unfrozen (or vice versa). These events have important consequences for ecosystems and communities, especially when they occur at unusual times of the year. Impacts of these events include tree damage, flooding, electrical outages, and crop damage. We use a series of case studies to explore the impacts of these events and analyze a long‐term data set to demonstrate how they might be detected from weather data. Understanding winter weather whiplash events will help decision makers and planners adapt and mitigate these events in the future.

River ecosystem metabolism and carbon biogeochemistry in a changing world

Abstract: River networks represent the largest biogeochemical nexus between the continents, ocean and atmosphere. Our current understanding of the role of rivers in the global carbon cycle remains limited, which makes it difficult to predict how global change may alter the timing and spatial distribution of riverine carbon sequestration and greenhouse gas emissions. Here we review the state of river ecosystem metabolism research and synthesize the current best available estimates of river ecosystem metabolism. We quantify the organic and inorganic carbon flux from land to global rivers and show that their net ecosystem production and carbon dioxide emissions shift the organic to inorganic carbon balance en route from land to the coastal ocean. Furthermore, we discuss how global change may affect river ecosystem metabolism and related carbon fluxes and identify research directions that can help to develop better predictions of the effects of global change on riverine ecosystem processes. We argue that a global river observing system will play a key role in understanding river networks and their future evolution in the context of the global carbon budget.

Effects of River-Ice Breakup on Sediment Transport and Implications to Stream Environments: A Review

Abstract: During the breakup of river ice covers, a greater potential for erosion occurs due to rising discharge and moving ice and the highly dynamic waves that form upon ice-jam release. Consequently, suspended-sediment concentrations can increase sharply and peak before the arrival of the peak flow. Large spikes in sediment concentrations occasionally occur during the passage of sharp waves resulting from releases of upstream ice jams and the ensuing ice runs. This is important, as river form and function (both geomorphologic and ecological) depend upon sediment erosion and deposition. Yet, sediment monitoring programs often overlook the higher suspended-sediment concentrations and loads that occur during the breakup period owing to data-collection difficulties in the presence of moving ice and ice jams. In this review paper, we introduce basics of river sediment erosion and transport and of relevant phenomena that occur during the breakup of river ice. Datasets of varying volume and detail on measured and inferred suspended-sediment concentrations during the breakup period on different rivers are reviewed and compared. Possible effects of river characteristics on seasonal sediment supply are discussed, and the implications of increased sediment supply are reviewed based on seasonal comparisons. The paper also reviews the environmental significance of increased sediment supply both on water quality and ecosystem functionality.