Intermittent streams are globally ubiquitous and represent a large percentage of stream networks. As climate change in many arid regions increases the frequency and intensity of drying disturbances, it is important to understand how aquatic biota will respond to such disturbances and how it would impact aquatic biodiversity. To address these topics, we sampled 10 stream reaches in the Sycamore Creek basin, an arid‐land stream in central Arizona (USA), with reach‐scale flow regimes ranging from perennial to highly intermittent. We sampled aquatic macroinvertebrates during 4 seasons to explore seasonal variability in community structure through flowing and drying phases. We also collected continuous flow data with remote data loggers to explore the impacts of intermittency and distance to perennial refuges on species richness, taxonomic composition and trait composition. Overall, richness was lower at intermittent reaches than perennial reaches, and richness values increased linearly as flow duration increased. We found no relationship between richness and distance to the nearest perennial refuge. Community assemblages differed significantly by season but were not distinct between perennial and intermittent reaches. Trait composition was also distinct between seasons and flow regimes, with traits such as a lack of diapause, longer life span and predatory feeding behaviours being indicators for perennial reaches. As climate change alters natural flow regimes, understanding the responses of macroinvertebrate community structure to drying disturbances in arid‐land streams can provide insight on aquatic community responses to climate change at larger scales.
Semi‐arid riparian woodlands face threats from increasing extractive water demand and climate change in dryland landscapes worldwide. Improved landscape‐scale understanding of riparian woodland water use (evapotranspiration, ET) and its sensitivity to climate variables is needed to strategically manage water resources, as well as to create successful ecosystem conservation and restoration plans for potential climate futures. In this work, we assess the spatial and temporal variability of Cottonwood (
- NSF-PAR ID:
- 10449702
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Hydrological Processes
- Volume:
- 34
- Issue:
- 25
- ISSN:
- 0885-6087
- Page Range / eLocation ID:
- p. 4884-4903
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Intermittent streams currently constitute >50% of the global river network, and the number of intermittent streams is expected to increase due to changes in land use and climate. Surface flows are known to expand and contract within the headwater channel network due to changes in the water table driven by climate, often changing seasonally. However, the underlying causes of disconnections and reconnections throughout the stream network remain poorly understood and may reflect subsurface flow capacity. We assess how 3D subsurface flowpaths control local surface flows at Gibson Jack Creek in the Rocky Mountains, Idaho, USA. Water table dynamics, hydraulic gradients, and hyporheic exchange were monitored along a 200‐m section of the stream throughout the seasonal recession in WY2018. Shallow lateral hillslope‐riparian‐stream connectivity was more frequent in transects spanning perennially flowing stream reaches than intermittent reaches. During low‐flow periods, larger losing vertical hydraulic gradients were observed in paired piezometers in intermittent reaches than in adjacent perennial reaches. Contrary to dominant conceptual models, longitudinal measurements of hydrologic exchange in both intermittent and perennial reaches were seasonally variable except for one perennial reach that showed consistent significant gains. Observed drying dynamics, as well as subsurface pathways, were highly variable even over short distances (30 m). Flow probability and subsurface flow capacity at upstream locations can be assessed with an outlet hydrograph and upstream flow measurements. Accurate characterization of subsurface storage, discharge, and connection is critical to understanding the drivers of drying cycles in intermittent streams and their likely responses to future change.
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Abstract Non-perennial rivers and streams make up over half the global river network and are becoming more widespread. Transitions from perennial to non-perennial flow are a threshold-type change that can lead to alternative stable states in aquatic ecosystems, but it is unknown whether streamflow itself is stable in either wet (flowing) or dry (no-flow) conditions. Here, we investigated drivers and feedbacks associated with regime shifts between wet and dry conditions in an intermittent reach of the Arkansas River (USA) over the past 23 years. Multiple lines of evidence suggested that these regimes represent alternative stable states, including (a) significant jumps in discharge time series that were not accompanied by jumps in flow drivers such as precipitation and groundwater pumping; (b) a multi-modal state distribution with 92% of months experiencing no-flow conditions for <10% or >90% of days, despite unimodal distributions of precipitation and pumping; and (c) a hysteretic relationship between climate and flow state. Groundwater levels appear to be the primary control over the hydrological regime, as groundwater levels in the alluvial aquifer were higher than the stream stage during wet regimes and lower than the streambed during dry regimes. Groundwater level variation, in turn, was driven by processes occurring at both the regional scale (surface water inflows from upstream, groundwater pumping) and the reach scale (stream–aquifer exchange, diffuse recharge through the soil column). Historical regime shifts were associated with diverse pressures including network disconnection caused by upstream water use, increased flow stability potentially associated with reservoir operations, and anomalous wet and dry climate conditions. In sum, stabilizing feedbacks among upstream inflows, stream–aquifer interactions, climate, vegetation, and pumping appear to create alternative wet and dry stable states at this site. These stabilizing feedbacks suggest that widespread observed shifts from perennial to non-perennial flow will be difficult to reverse.more » « less
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