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  1. Abstract

    Riverine floodplains exhibit high floral and faunal diversity as a consequence of their biophysical complexity. Extension of such niche partitioning processes to microbial communities is far less resolved or supported. Here, we evaluated the responses of aquatic biofilms diversity to environmental gradients across ten riverine floodplains with differing degrees of flow alteration and habitat diversity to assess whether complex floodplains support biofilm communities with greater biodiversity and species interactions. No significant evidence was found to support a central role for habitat diversity in promoting microbial diversity across 116 samples derived from 62 aquatic habitats, as neither α (H’: 2.8–4.1) nor β (Sørensen: 0.3–0.39) diversity were positively related to floodplain complexity across the ten floodplains. In contrast, our results documented the sensitivity of biofilm communities to regional templates manifested as gradients of carbon, nitrogen, and phosphorous availability. Large-scale conditions reflecting nitrogen limitation increased the relative abundance of N-fixing cyanobacteria (up to 0.34 as fraction of total reads), constrained the total number of interactions among bacterial taxa, and reinforced negative over positive interactions, generating unique microbial communities and networks that reflect large-scale species sorting in response to regional geochemical gradients.

  2. Free, publicly-accessible full text available April 3, 2023
  3. Free, publicly-accessible full text available March 8, 2023
  4. Abstract Nitrogen loss from cultivated soils threatens the economic and environmental sustainability of agriculture. Nitrate (NO 3 − ) derived from nitrification of nitrogen fertilizer and ammonified soil organic nitrogen may be lost from soils via denitrification, producing dinitrogen gas (N 2 ) or the greenhouse gas nitrous oxide (N 2 O). Nitrate that accumulates in soils is also subject to leaching loss, which can degrade water quality and make NO 3 − available for downstream denitrification. Here we use patterns in the isotopic composition of NO 3 − observed from 2012 to 2017 to characterize N loss to denitrification within soils, groundwater, and stream riparian corridors of a non-irrigated agroecosystem in the northern Great Plains (Judith River Watershed, Montana, USA). We find evidence for denitrification across these domains, expressed as a positive linear relationship between δ 15 N and δ 18 O values of NO 3 − , as well as increasing δ 15 N values with decreasing NO 3 − concentration. In soils, isotopic evidence of denitrification was present during fallow periods (no crop growing), despite net accumulation of NO 3 − from the nitrification of ammonified soil organic nitrogen. We combine previous results for soil NO 3more »− mass balance with δ 15 N mass balance to estimate denitrification rates in soil relative to groundwater and streams. Substantial denitrification from soils during fallow periods may be masked by nitrification of ammonified soil organic nitrogen, representing a hidden loss of soil organic nitrogen and an under-quantified flux of N to the atmosphere. Globally, cultivated land spends ca. 50% of time in a fallow condition; denitrification in fallow soils may be an overlooked but globally significant source of agricultural N 2 O emissions, which must be reduced along-side other emissions to meet Paris Agreement goals for slowing global temperature increase.« less
    Free, publicly-accessible full text available March 1, 2023
  5. Mendoza-Lera, Clara (Ed.)
    Hyporheic exchange is now widely acknowledged as a key driver of ecosystem processes in many streams. Yet stream ecologists have been slow to adopt nuanced hydrologic frameworks developed and applied by engineers and hydrologists to describe the relationship between water storage, water age, and water balance in finite hydrosystems such as hyporheic zones. Here, in the context of hyporheic hydrology, we summarize a well-established mathematical framework useful for describing hyporheic hydrology, while also applying the framework heuristically to visualize the relationships between water age, rates of hyporheic exchange, and water volume within hyporheic zones. Building on this heuristic application, we discuss how improved accuracy in the conceptualization of hyporheic exchange can yield a deeper understanding of the role of the hyporheic zone in stream ecosystems. Although the equations presented here have been well-described for decades, our aim is to make the mathematical basis as accessible as possible and to encourage broader understanding among aquatic ecologists of the implications of tailed age distributions commonly observed in water discharged from and stored within hyporheic zones. Our quantitative description of “hyporheic hydraulic geometry,” associated visualizations, and discussion offer a nuanced and realistic understanding of hyporheic hydrology to aid in considering hyporheic exchange inmore »the context of river and stream ecosystem science and management.« less
    Free, publicly-accessible full text available January 14, 2023
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  10. Abstract Even in advanced economies, underperforming infrastructure is a persistent rural development challenge, with the case of non-compliant small drinking water systems (SDWSs) especially concerning because of the importance of safe drinking water to human health. While technical and financial deficits are known contributors to SDWS underperformance in rural settings, the role of local cultural and social context in water governance are less clear. The need for interoperable concepts that help explain how local contextual factors influence rural water governance and operation motivates this study. Drawing on insights from community resilience and critical infrastructure scholarship, this study draws attention to a previously overlooked dimension of local infrastructure governance: social memory. Archival research and 25 semi-structured interviews with experts and local stakeholders inform the paper’s reconstruction of the 100 years history of an SDWS in rural Montana, USA and analysis of the contemporary social memory it has generated. The study finds that social memory acts as a medium through which the lived experience of infrastructure influences priorities and values about its governance, especially in the context of small towns. Three major themes in the dynamics of social memory of infrastructure are described, including longevity, aesthetic and material qualities, and articulation withmore »economic trajectories. In addition to establishing social memory as an effective conceptualization of the generative influence of infrastructure in water governance at the local scale, the paper has implications for policy; specifically, the observation that in addition to financial and technical capacity, historical experience is a powerful driver of infrastructure governance and outcomes such as underperformance.« less
    Free, publicly-accessible full text available November 15, 2022