Environmental controls on benthic food web functions and carbon resource use in subarctic lakes

Abstract

Climate warming and consequent greening of subarctic landscapes increase the availability of organic carbon to the detrital food webs in aquatic ecosystems. This may cause important shifts in ecosystem functioning through the functional feeding patterns of benthic organisms that rely differently on climatically altered carbon resources. Twenty‐five subarctic lakes in Finnish Lapland across a tree line ecotone were analysed for limnological and optical variables, carbon (δ13C) and nitrogen (δ15N) stable isotope (SI) composition of surface sediment organic matter (OM) and fossil Chironomidae (Diptera) remains to examine environmental controls behind chironomid functional feeding group (FFG) structure and their isotopic associations for assessing ecosystem functioning and carbon utilisation. We hypothesise that the chironomid SI signatures reflect increased allochthony with increasing allochthonous input, but the resource use may be altered by the functional characteristics of the assemblage. Multivariate analyses indicated that carbon geochemistry in the sediments (δ13C, δ15N, C/N), nutrients, indices of productivity (chlorophyll‐a) and lake water optical properties, related to increasing presence of OM, played a key role in defining the chironomid FFG composition and isotopic signatures. Response modelling was used to examine how individual FFGs respond to environmental gradients. They showed divergent responses for OM quantity, dissolved organic carbon and nutrients between feeding strategies, suggesting that detritivores and filter feeders prefer contrasting carbon and nutrient conditions, and may thus hold paleoecological indicator potential to identify changes between different carbon fluxes. Benthic production was the primary carbon source for the chironomid assemblages according to a three‐source SI mixing model, whereas pelagic and terrestrial components contributed less. Between‐lake variability in source utilisation was high and controlled primarily by allochthonous OM inputs. Combination of biogeochemical modelling and functional classification is useful to widen our understanding of subarctic lake ecosystem functions and responses to climate‐driven changes in limnology and catchment characteristics for long‐term environmental change assessments and functional paleoecology.

Biogeochemical cycling and ecological thresholds in a High Arctic lake (Svalbard)

“…In addition to taxonomic compositions, applications of functional characteristics of aquatic organisms can be valuable for understanding ecosystem processes and dynamics (Jeppesen et al 2001;Nevalainen and Luoto 2017;Kivilä et al 2019). In Revvatnet, the changes in diatom ecological guilds support the environmental evidence derived from taxonomic compositions.…”

Late-Holocene variability in chironomid functional assemblages and carbon utilization in a tundra lake food web

“…Based on the SI measurements from the chironomid remains, a three-source Bayesian mixing model was built with simmr (Parnell & Inger, 2016) in R (R Core Team, 2018) to examine the relative proportions of different nutritional sources incorporated into the chironomid assemblage. The model with the same attributes has been previously applied on a surface sediment data set by Kivilä et al (2019). The endmembers were based on published measurements from close-by region or similar environments (for further details see Kivilä et al, 2019, Appendix 2).…”

“…For secondary producers, habitat attributes (such as oxygen levels, substrate organic matter quantity and quality) and physiological factors (body size, developmental stage) have been noted important in defining the feeding mode and resource utilization (Merritt et al, 2008;Craig et al, 2015). In addition, Kivilä et al (2019) recently showed that occurrence of chironomid functional feeding groups (FFGs) was connected to habitat-related factors, such as DOC and nutrient concentrations. In this study, we use FFGs, which are defined by feeding mode but also have their general preferred type of nutrition (Mandaville, 2002;Merritt et al, 2008), to capture temporal patterns in functional assemblage composition and feeding modes, and assess their connections to environmental changes and macrobenthic resource utilization.…”

“…Resource utilization in contemporary ecology is commonly studied by consumer stable isotope (SI) signatures, which have been increasingly applied to chitinous invertebrate remains for disentangling various paleoecological questions (van Hardenbroek et al, 2018). Paleoecological work on chironomid SI signatures has demonstrated timeand space-sensitive consumption of both autochthonous and allochthonous resources (Belle et al, 2017(Belle et al, , 2018Kivilä et al, 2019), as well as feeding on isotopically distinct methane-oxidizing bacteria (van Hardenbroek et al, 2012(van Hardenbroek et al, , 2013). Yet, questions like what in the end controls the resource utilization, what might be its cascading effects for the food web functions and can we find such insight into aquatic carbon processing from paleolimnology, remain largely unanswered requiring further research.…”

Cladoceran (Crustacea) Niches, Sex, and Sun Bathing—A Long-Term Record of Tundra Lake (Lapland) Functioning and Paleo-Optics

“…RDA was performed with Canoco 5 software [33] and linear regressions with PAST3 software [34]. In addition to OM%, organic matter δ 13 C, and SSN, mean carbon source contributions in the benthic food web (based on fossil Chironomidae δ 13 C), modeled with a three-source (benthic, planktonic, and terrestrial) Bayesian mixing model previously applied in [22], were utilized as paleoenvironmental reference data. Here, the modeled planktonic and benthic carbon contributions (to Chironomidae diet) were used in a planktonic to benthic (P/B) ratio.…”