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1. Trait–environment relationships could alter the spatial and temporal characteristics of aquatic insect subsidies at the macrospatial scale

   https://doi.org/10.1111/ecog.05298  

   Kopp, Darin; Allen, Daniel (December 2020, Ecography)

   null (Ed.)

   Ecological flows across ecosystem boundaries are typically studied at spatial scales that limit our understanding of broad geographical patterns in ecosystem linkages. Aquatic insects that metamorphose into terrestrial adults are important resource subsidies for terrestrial ecosystems. Traits related to their development and dispersal should determine their availability to terrestrial consumers. Here, we synthesize geospatial, aquatic biomonitoring and biological traits data to quantify the relative importance of several environmental gradients on the potential spatial and temporal characteristics of aquatic insect subsidies across the contiguous United States. We found the trait composition of benthic macroinvertebrate communities varies among hydrologic regions and could affect how aquatic insects transport subsidies as adults. Further, several trait–environment relationships were underpinned by hydrology. Large bodied taxa that could disperse further from the stream were associated with hydrologically stable conditions. Alternatively, hydrologically variable conditions were associated with multivoltine taxa that could extend the duration of subsidies with periodic emergence events throughout the year. We also found that anthropogenic impacts decrease the frequency of individuals with adult flight but potentially extend the distance subsidies travel into the terrestrial ecosystem. Collectively, these results suggest that natural and anthropogenic gradients could affect aquatic insect subsidies by changing the trait composition of benthic macroinvertebrate communities. The conceptual framework and trait–environment relationships we present shows promise for understanding broad geographical patterns in linkages between ecosystems. 

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2. Carbon Dioxide (CO ₂ ) Fluxes From Terrestrial and Aquatic Environments in a High‐Altitude Tropical Catchment

   https://doi.org/10.1029/2020JG005844  

   Schneider, Chloe L.; Herrera, Maribel; Raisle, Megan L.; Murray, Andrew R.; Whitmore, Keridwen M.; Encalada, Andrea C.; Suárez, Esteban; Riveros‐Iregui, Diego A. (August 2020, Journal of Geophysical Research: Biogeosciences)

   Abstract High‐altitude tropical grasslands, known as “páramos,” are characterized by high solar radiation, high precipitation, and low temperature. They also exhibit some of the highest ecosystem carbon stocks per unit area on Earth. Recent observations have shown that páramos may be a net source of CO₂to the atmosphere as a result of climate change; however, little is known about the source of this excess CO₂in these mountainous environments or which landscape components contribute the most CO₂. We evaluated the spatial and temporal variability of surface CO₂fluxes to the atmosphere from adjacent terrestrial and aquatic environments in a high‐altitude catchment of Ecuador, based on a suite of field measurements performed during the wet season. Our findings revealed the importance of hydrologic dynamics in regulating the magnitude and likely fate of dissolved carbon in the stream. While headwater catchments are known to contribute disproportionately larger amounts of carbon to the atmosphere than their downstream counterparts, our study highlights the spatial heterogeneity of CO₂fluxes within and between aquatic and terrestrial landscape elements in headwater catchments of complex topography. Our findings revealed that CO₂evasion from stream surfaces was up to an order of magnitude greater than soil CO₂efflux from the adjacent terrestrial environment. Stream carbon flux to the atmosphere appeared to be transport limited (i.e., controlled by flow characteristics, turbulent flow, and water velocity) in the upper reaches of the stream, and source limited (i.e., controlled by CO₂and carbon availability) in the lower reaches of the stream. A 4‐m waterfall along the channel accounted for up to 35% of the total evasion observed along a 250‐m stream reach. These findings represent a first step in understanding ecosystem carbon cycling at the interface of terrestrial and aquatic ecosystems in high‐altitude, tropical, headwater catchments. 

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3. Effect of source habitat spatial heterogeneity and species diversity on the temporal stability of aquatic‐to‐terrestrial subsidy by emerging aquatic insects

   https://doi.org/10.1111/1440-1703.12125  

   Uno, Hiromi; Pneh, Shelley (May 2020, Ecological Research)

   Abstract Duration and temporal stability of resource subsidy largely affect the response of recipient communities. Factors that influence the temporal dynamics of resource subsidy from aquatic‐to‐terrestrial habitats by emerging aquatic insects were examined in this study. By measuring the flux of aquatic insect emergence from six habitats in a river over summer, we found that the timing of emergence varied by habitats for each dominant taxa, and that different species emerged at different times of the summer sequentially. We found that spatial variation in the emergence timing caused by the spatial heterogeneity of the water temperature, and so on in the source habitat can temporally stabilize the subsidy of each species from the whole river. Similarly, we found that the variation in emergence timing between species contributed to the temporal stability of subsidies from each habitat. The contribution of spatial heterogeneity to the temporal stability varied by the focal species and the contribution of species diversity varied by habitats. This study demonstrates how the ecological function of spatial heterogeneity and species diversity crosses the boundary of ecosystems by temporally stabilizing resource subsidies. 

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4. Global patterns of allochthony in stream–riparian meta‐ecosystems

   https://doi.org/10.1111/ele.14401  

   Allen, Daniel C.; Larson, James; Murphy, Christina A.; Garcia, Erica A.; Anderson, Kurt E.; Busch, Michelle H.; Argerich, Alba; Belskis, Alice M.; Higgins, Kierstyn T.; Penaluna, Brooke E.; et al (March 2024, Ecology Letters)

   Abstract Ecosystems that are coupled by reciprocal flows of energy and nutrient subsidies can be viewed as a single “meta‐ecosystem.” Despite these connections, the reciprocal flow of subsidies is greatly asymmetrical and seasonally pulsed. Here, we synthesize existing literature on stream–riparian meta‐ecosystems to quantify global patterns of the amount of subsidy consumption by organisms, known as “allochthony.” These resource flows are important since they can comprise a large portion of consumer diets, but can be disrupted by human modification of streams and riparian zones. Despite asymmetrical subsidy flows, we found stream and riparian consumer allochthony to be equivalent. Although both fish and stream invertebrates rely on seasonally pulsed allochthonous resources, we find allochthony varies seasonally only for fish, being nearly three times greater during the summer and fall than during the winter and spring. We also find that consumer allochthony varies with feeding traits for aquatic invertebrates, fish, and terrestrial arthropods, but not for terrestrial vertebrates. Finally, we find that allochthony varies by climate for aquatic invertebrates, being nearly twice as great in arid climates than in tropical climates, but not for fish. These findings are critical to understanding the consequences of global change, as ecosystem connections are being increasingly disrupted. 

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5. Carbon Emissions From Low‐Order Streams in a Tropical, High‐Elevation, Peatland Ecosystem Are Mediated by Catchment Morphology

   https://doi.org/10.1029/2024WR038036  

   Whitmore, Keridwen_M; DelVecchia, Amanda_G; Farquhar, Elizabeth; Rocher‐Ros, Gerard; Suárez, Esteban; Riveros‐Iregui, Diego_A (April 2025, Water Resources Research)

   Abstract Inland waters emit large amounts of carbon and are key players in the global carbon budget. Particularly high rates of carbon emissions have been reported in streams draining mountains, tropical regions, and peatlands. However, few studies have examined the spatial variability of CO₂concentrations and fluxes occurring within these systems, particularly as a function of catchment morphology. Here we evaluated spatial patterns of CO₂in three tropical, headwater catchments in relation to the river network and stream geomorphology. We measured dissolved carbon dioxide (pCO₂), aquatic CO₂emissions, discharge, and stream depth and width at high spatial resolutions along multiple stream reaches. Confirming previous studies, we found that tropical headwater streams are an important source of CO₂to the atmosphere. More notably, we found marked, predictable spatial organization in aquatic carbon fluxes as a function of landscape position. For example,pCO₂was consistently high (>10,000 ppm) at locations close to groundwater sources and just downstream of hydrologically connected wetlands, but consistently low (<1,000 ppm) in high gradient locations or river segments with larger drainage areas. Taken together, our findings suggest that catchment area and stream slope are important drivers ofpCO₂and gas transfer velocity (k) in mountainous streams, and as such they should be considered in catchment‐scale assessments of CO₂emissions. Furthermore, our work suggests that accurate estimation of CO₂emissions requires understanding of dynamics across the entire stream network, from the smallest seeps to larger streams. 

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