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  • 1.
    Jonsson, Micael
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Hedström, Per
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Stenroth, Karolina
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Hotchkiss, Erin R
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Vasconcelos, Francisco Rivera
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Climate change modifies the size structure of assemblages of emerging aquatic insects2015In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 60, no 1, p. 78-88Article in journal (Refereed)
    Abstract [en]

    Climate change is expected to not only raise water temperatures, but also to cause brownification of aquatic ecosystems via increased inputs of terrestrial dissolved organic matter. While efforts have been made to understand how increased temperature and brownification separately influence aquatic food webs, their interactive effects have been less investigated. Further, although climate change effects on aquatic ecosystems likely will propagate to terrestrial consumers via changes in aquatic insect emergence, this has rarely been studied. We investigated the effect of climate change on aquatic insect emergence, in a large-scale outdoor pond facility where 16 sections - each containing natural food webs including a fish top-consumer population - were subjected to warming (3 degrees C above ambient temperatures) and/or brownification (by adding naturally humic stream water). Aquatic insect emergence was measured biweekly over 18weeks. We found no effect of warming or brownification on total emergent insect dry mass. However, warming significantly reduced the number of emergent Chironomidae, while numbers of larger taxa, Trichoptera and Ephemeroptera, remained unchanged. On average, 57% and 58% fewer Chironomidae emerged from the warmed clear and humic pond sections, respectively. This substantial decrease in emergent Chironomidae resulted in a changed community structure and on average larger individuals emerging from warm sections as well as from humic sections under ambient conditions. There was also a weak influence of fish biomass on the size structure of emergent aquatic insects, with a positive relationship between individual insect size and total fish biomass, but effects of fish were clearly subordinate to those of warming. Climate change impacts on aquatic systems can have widespread consequences also for terrestrial systems, as aquatic insects are ubiquitous and their emergence represents an important resource flow from aquatic to terrestrial environments. While we found that neither warming nor brownification quantitatively changed total aquatic insect emergence biomass, the warming-induced decrease in number of emergent Chironomidae and the subsequent increase in average body size will likely impact terrestrial consumers relying on emergent aquatic insect as prey.

  • 2.
    Jonsson, Micael
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Polvi, Lina E.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Sponseller, Ryan A.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Stenroth, Karolina
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Catchment properties predict autochthony in stream filter feeders2018In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 815, no 1, p. 83-95Article in journal (Refereed)
    Abstract [en]

    Stream ecological theory predicts that the use of allochthonous resources declines with increasing channel width, while at the same time primary production and autochthonous carbon use by consumers increase. Although these expectations have found support in several studies, it is not well known how terrestrial runoff and/or inputs of primary production from lakes alter these longitudinal patterns. To investigate this, we analyzed the diet of filter-feeding black fly and caddisfly larvae from 23 boreal streams, encompassing gradients in drainage area, land cover and land use, and distance to nearest upstream lake outlet. In five of these streams, we also sampled repeatedly during autumn to test if allochthony of filter feeders increases over time as new litter inputs are processed. Across sites, filter-feeder autochthony was 21.1-75.1%, did not differ between black fly and caddisfly larvae, was not positively related to drainage area, and did not decrease with distance from lakes. Instead, lake and wetland cover promoted filter-feeder autochthony independently of stream size, whereas catchment-scale forest cover and forestry reduced autochthony. Further, we found no seasonal increase in allochthony, indicating low assimilation of particles derived from autumn litter fall. Hence, catchment properties, rather than local conditions, can influence levels of autochthony in boreal streams.

  • 3.
    Jonsson, Micael
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Stenroth, Karolina
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    True autochthony and allochthony in aquatic-terrestrial resource fluxes along a landuse gradient2016In: Freshwater Science, ISSN 2161-9549, E-ISSN 2161-9565, Vol. 35, no 3, p. 882-894Article in journal (Refereed)
    Abstract [en]

    Freshwater and terrestrial ecosystems are connected via reciprocal cross-boundary resource fluxes, where terrestrially derived (allochthonous) organic matter is a critical energy source to freshwater food webs. Therefore, some proportion of aquatic-to-terrestrial resource fluxes, which consist primarily of emergent aquatic insects, are of allochthonous origin (i.e., recycled terrestrial matter). Landuse activities modify basal resources and consumer community composition in aquatic systems and, thereby, aquatic resource fluxes to terrestrial systems. The origin of aquatic terrestrial resource fluxes and alterations to them caused by land use should be considered to understand these fluxes better. Resource fluxes at the aquatic terrestrial interface were measured at 10 streams along a forest-to-agriculture gradient. Autochthony in emergent aquatic insects ranged from 10 to 97%. Hence, aquatic fluxes to terrestrial systems drive the flux of matter of aquatic origin (true aquatic flux) and the recycling of terrestrial matter to the terrestrial environment. Land use indirectly affected autochthony of emergent aquatic insects via changes in water chemistry, high-quality resource availability, and in-stream consumer composition. Chironomidae diet shifts along the landuse gradient strengthened the aquatic flux to the land. For every 10% increase in agricultural land cover, aquatically derived matter deposited on land via emergent Chironomidae increased 0.005 g dry mass m(-2) d(-1). Plecoptera strengthened the aquatic flux and the recycling of terrestrial matter via changes in abundance across the landuse gradient. Aquatically derived matter deposited on land via emergent Plecoptera increased 0.002 g dry mass m(-2) d(-1) for every 10% increase in coniferous forest cover. Qualitative changes in resource fluxes across the aquatic terrestrial interface may be driven indirectly by the influences of land use on diets and composition of emergent aquatic insects.

  • 4.
    Stenroth, Karolina
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Polvi, Lina E
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Fältström, Emma
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jonsson, Micael
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Land-use effects on terrestrial consumers through changed size structure of aquatic insects2015In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 60, no 1, p. 136-149Article in journal (Refereed)
    Abstract [en]

    We assessed the influence of agricultural land use on aquatic-terrestrial linkages along streams arising from changes in the emergence of aquatic insects. We expected that terrestrial predators would respond to a change in the abundance and/or the size structure of the emerging aquatic insects by an increase or decrease in population size. We measured the flux of emergent aquatic insects and the abundance of terrestrial invertebrate predators and birds along 10 streams across a forest-to-agriculture land-use gradient. We also performed stable isotope analyses (hydrogen, carbon and nitrogen) of terrestrial invertebrate predators. Small aquatic insects (Nematocera) were most abundant under agricultural land use, whereas larger bodied aquatic insects (Plecoptera and Trichoptera) were more associated with forest land use. Carabid beetles and linyphiid spiders were associated with agricultural streams (where there was a high abundance of small aquatic insects), whereas lycosid spiders and birds were associated with forest streams and a high abundance of large-sized aquatic insects. The contribution of aquatic insects to the diets of riparian Lycosidae, Linyphiidae and Carabidae was estimated to be 44%, 60% and 43%, respectively, indicating the importance of aquatic subsidies to the terrestrial system. Our results show that agricultural land use in an overall forested landscape can have significant effects on the abundance and diet of terrestrial consumers through its impact on the size structure of the assemblage of emerging insects, rather than the overall magnitude (numbers) of the aquatic subsidy. Hence, our results suggest that the composition, not just quantity, of a cross-habitat resource may influence the recipient system.

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