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1. Megafire affects stream sediment flux and dissolved organic matter reactivity, but land use dominates nutrient dynamics in semiarid watersheds

   https://doi.org/10.1371/journal.pone.0257733  

   Crandall, Trevor ; Jones, Erin ; Greenhalgh, Mitchell ; Frei, Rebecca J. ; Griffin, Natasha ; Severe, Emilee ; Maxwell, Jordan ; Patch, Leika ; St. Clair, S. Isaac ; Bratsman, Sam ; et al ( September 2021 , PLOS ONE)

   Martínez-Yrízar, Angelina (Ed.)

   Climate change is causing larger wildfires and more extreme precipitation events in many regions. As these ecological disturbances increasingly coincide, they alter lateral fluxes of sediment, organic matter, and nutrients. Here, we report the stream chemistry response of watersheds in a semiarid region of Utah (USA) that were affected by a megafire followed by an extreme precipitation event in October 2018. We analyzed daily to hourly water samples at 10 stream locations from before the storm event until three weeks after its conclusion for suspended sediment, solute and nutrient concentrations, water isotopes, and dissolved organic matter concentration, optical properties, and reactivity. The megafire caused a ~2,000-fold increase in sediment flux and a ~6,000-fold increase in particulate carbon and nitrogen flux over the course of the storm. Unexpectedly, dissolved organic carbon (DOC) concentration was 2.1-fold higher in burned watersheds, despite the decreased organic matter from the fire. DOC from burned watersheds was 1.3-fold more biodegradable and 2.0-fold more photodegradable than in unburned watersheds based on 28-day dark and light incubations. Regardless of burn status, nutrient concentrations were higher in watersheds with greater urban and agricultural land use. Likewise, human land use had a greater effect than megafire on apparent hydrological residence time, with rapid stormwater signals in urban and agricultural areas but a gradual stormwater pulse in areas without direct human influence. These findings highlight how megafires and intense rainfall increase short-term particulate flux and alter organic matter concentration and characteristics. However, in contrast with previous research, which has largely focused on burned-unburned comparisons in pristine watersheds, we found that direct human influence exerted a primary control on nutrient status. Reducing anthropogenic nutrient sources could therefore increase socioecological resilience of surface water networks to changing wildfire regimes. 

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2. Ecological response of nitrification to oil spills and its impact on the nitrogen cycle

   https://doi.org/10.1111/1462-2920.14391  

   Urakawa, Hidetoshi ; Rajan, Suja ; Feeney, Megan E. ; Sobecky, Patricia A. ; Mortazavi, Behzad ( October 2018 , Environmental Microbiology)

   Marine oil spills are catastrophic events that cause massive damage to ecosystems at all trophic levels. While most of the research has focused on carbon‐degrading microorganisms, the potential impacts of hydrocarbons on microbes responsible for nitrification have received far less attention. Nitrifiers are sensitive to hydrocarbon toxicity: ammonia‐oxidizing bacteria and archaea being 100 and 1000 times more sensitive than typical heterotrophs respectively. Field studies have demonstrated the response of nitrifiers to hydrocarbons is highly variable and the loss of nitrification activity in coastal ecosystems can be restored within 1–2 years, which is much shorter than the typical recovery time of whole ecosystems (e.g., up to 20 years). Since the denitrification process is mainly driven by heterotrophs, which are more resistant to hydrocarbon toxicity than nitrifiers, the inhibition of nitrification may slow down the nitrogen turnover and increase ammonia availability, which supports the growth of oil‐degrading heterotrophs and possibly various phototrophs. A better understanding of the ecological response of nitrification is paramount in predicting impacts of oil spills on the nitrogen cycle under oil spill conditions, and in improving current bioremediation practices.

    

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3. Watershed studies at the Hubbard Brook Experimental Forest: Building on a long legacy of research with new approaches and sources of data

   https://doi.org/10.1002/hyp.14016  

   Campbell, John L. ; Rustad, Lindsey E. ; Bailey, Scott W. ; Bernhardt, Emily S. ; Driscoll, Charles T. ; Green, Mark B. ; Groffman, Peter M. ; Lovett, Gary M. ; McDowell, William H. ; McGuire, Kevin J. ; et al ( January 2021 , Hydrological Processes)

   The Hubbard Brook Experimental Forest (HBEF) was established in 1955 by the U.S. Department of Agriculture, Forest Service out of concerns about the effects of logging increasing flooding and erosion. To address this issue, within the HBEF hydrological and micrometeorological monitoring was initiated in small watersheds designated for harvesting experiments. The Hubbard Brook Ecosystem Study (HBES) originated in 1963, with the idea of using the small watershed approach to study element fluxes and cycling and the response of forest ecosystems to disturbances, such as forest management practices and air pollution. Early evidence of acid rain was documented at the HBEF and research by scientists at the site helped shape acid rain mitigation policies. New lines of investigation at the HBEF have built on the long legacy of watershed research resulting in a shift from comparing inputs and outputs and quantifying pools and fluxes to a more mechanistic understanding of ecosystem processes within watersheds. For example, hydropedological studies have shed light on linkages between hydrologic flow paths and soil development that provide valuable perspective for managing forests and understanding stream water quality. New high frequency in situ stream chemistry sensors are providing insights about extreme events and diurnal patterns that were indiscernible with traditional weekly sampling. Additionally, tools are being developed for visual and auditory data exploration and discovery by a broad audience. Given the unprecedented environmental change that is occurring, data from the small watersheds at the HBEF are more relevant now than ever and will continue to serve as a basis for sound environmental decision‐making.

    

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4. Assessing Forest Level Response to the Death of a Dominant Tree within a Premontane Tropical Rainforest

   https://doi.org/10.3390/f12081041  

   Flores III, Manuel R. ; Aparecido, Luiza Maria ; Miller, Gretchen R. ; Moore, Georgianne W. ( August 2021 , Forests)

   null (Ed.)

   Small-scale treefall gaps are among the most important forms of forest disturbance in tropical forests. These gaps expose surrounding trees to more light, promoting rapid growth of understory plants. However, the effects of such small-scale disturbances on the distribution of plant water use across tree canopy levels are less known. To address this, we explored plant transpiration response to the death of a large emergent tree, Mortoniodendron anisophyllum Standl. & Steyerm (DBH > 220 cm; height ~40 m). Three suppressed, four mid-story, and two subdominant trees were selected within a 50 × 44 m premontane tropical forest plot at the Texas A&M Soltis Center for Research and Education located in Costa Rica. We compared water use rates of the selected trees before (2015) and after (2019) the tree gap using thermal dissipation sap flow sensors. Hemispherical photography indicated a 40% increase in gap fraction as a result of changes in canopy structure after the treefall gap. Micrometeorological differences (e.g., air temperature, relative humidity, and vapor pressure deficit (VPD)) could not explain the observed trends. Rather, light penetration, as measured by sensors within the canopy, increased significantly in 2019. One year after the tree fell, the water usage of trees across all canopy levels increased modestly (15%). Moreover, average water usage by understory trees increased by 36%, possibly as a result of the treefall gap, exceeding even that of overstory trees. These observations suggest the possible reallocation of water use between overstory and understory trees in response to the emergent tree death. With increasing global temperatures and shifting rainfall patterns increasing the likelihood of tree mortality in tropical forests, there is a greater need to enhance our understanding of treefall disturbances that have the potential to redistribute resources within forests. 

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5. A framework tool for conceptualizing integrated water resources for sustainable water management

   https://doi.org/10.1002/rvr2.14  

   Borden, Carter ; Goodwin, Peter ( September 2022 , River)

   As the pressures on water resources are ever increasing, the organization of complex disparate data and scientific information to inform the actions to protect and enhance the resilience of freshwater resources is key for sustainable development and implementation of integrated water resource management (IWRM). Methodologies supporting IWRM implementation have largely focused on water management and governance, with less attention to evaluation methods of ecologic, economic, and social conditions. To assist in assessing water resource sustainability, the Integrated Hydro‐Environment Assessment Tool (IHEAT) has been developed to create a framework for different disciplines and interests to engage in structured dialogue. The IHEAT builds on the considerable body of knowledge developed around IWRM and seeks to place this information into a single framework that facilitates the cogeneration of knowledge between managers, stakeholders, and the communities affected by management decisions with the understanding that there is a need to merge expert analysis with traditional knowledge and the lived experience of communities. IHEAT merges the driver‐pressure‐state‐impact‐response (DPSIR) framework, the Millennium Ecosystem Assessment's ecosystem services and human well‐being (HWB) framework, sustainability criteria for water resource systems, and water resources indexes and sets of indicators to better understand spatiotemporal interactions between hydrologic, socioeconomic, and ecologic systems and evaluate impacts of disturbances on ecological goods and services and HWB. IHEAT consists of a Conceptual Template (IHEAT‐CT) which provides a systematic framework for assessing basin conditions and guiding indicator selection as well as an Assessment Interface (IHEAT‐AI) for organizing, processing, and assessing analytical results. The IHEAT‐CT, presented herein, is a rapid screening tool that connects water use directly, or through ecosystem goods and services (EGS), to constituents of HWB. Disturbance Templates for eight pressure types, such as land‐use change, climate change, and population growth, are provided to guide practitioners regarding potential changes to landscape elements in the hydrological cycle, impacts on EGS, and societal implications on HWB. The basin screening results in a summary report card illuminating key freshwater ecosystems, the EGS they provide, and potential responses to drivers and pressures acting on the hydrologic system. This screening provides a common understanding by technical and nontechnical parties and provides the foundation for more complex conceptual models should they be required. An indicator list guides the selection of hydrologic, ecologic, economic, and social analytical methods to support IWRM technical input.

    

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