**Background:** Arctic lowland tundra is dominated by wetlands that support large populations of migratory waterbirds via invertebrate prey. Climate warming is altering wetland extent, type, and hydrology, with potential effects on organic matter (OM) sources and invertebrate food webs. This study investigated the relative importance of four OM sources—periphytic microalgae, cyanobacteria, macrophytes, and peat—to macroinvertebrate diets across six wetland types, and compared invertebrate biomass among wetland types to assess potential impacts on avian consumers.
**Methods:** The study was conducted in a 180 km² area of lowland tundra near Utqiaġvik, Alaska (71.2906° N, 156.7886° W). Six wetland types were sampled: Shallow Arctophila (n=14), Deep Arctophila (n=10), Shallow Carex (n=11), Deep Carex (n=7), Streams (n=6), and Deep Open Lakes (n=4). Macrophyte and invertebrate samples were collected in June and July of 2013, 2017, and 2018 using sweep nets (500-μm mesh) and sediment cores (5.2 cm diameter). Nine macroinvertebrate taxa were analyzed: Acari, Crustacea (mostly Copepoda), Chironomidae, Plecoptera, Trichoptera, Tipulidae, Coleoptera (mainly Dytiscidae), Oligochaeta, and Physidae (snails). Stable isotope ratios (δ¹³C and δ¹⁵N) were measured after lipid extraction. Endmember values were obtained from literature for periphytic microalgae (δ¹³C = –38.0 ± 2.5‰), cyanobacteria (δ¹³C = –22.6 ± 1.5‰), and peat (δ¹³C = –28.2 ± 0.2‰), while macrophyte values were measured in situ (δ¹³C = –29.5 ± 0.1‰). Macrophytes and peat were combined in mixing models due to isotopic similarity. Bayesian mixing models (MixSIAR) were used to estimate OM source contributions using single-isotope (δ¹³C) models. Invertebrate biomass was compared among wetland types using PERMANOVA.
**Key Results:** Across all shallow wetland types (Shallow and Deep Arctophila, Shallow and Deep Carex, Streams), microalgae were the dominant or major OM source for most invertebrate taxa, contributing 39–82% (mean 59%) of ultimate OM sources. Macrophytes and peat contributed 18–61% (mean 41%). In Shallow Arctophila, Shallow Carex, and Deep Arctophila wetlands, microalgae contributed 50–82% (mean 64%) of OM. In Deep Carex wetlands, microalgae contributed 39–64% (mean 46%) and macrophytes-peat contributed 36–61% (mean 54%). In Streams, microalgae contributed 46–70% (mean 58%) and macrophytes-peat contributed 30–54% (mean 43%). In contrast, in Deep Open Lakes, macrophytes-peat were the dominant carbon source (38–80%, mean 69%), with microalgae contributing 20–62% (mean 31%). Physidae snails were unique in consuming substantial amounts of cyanobacteria. Total invertebrate biomass was 2–3 times higher in Shallow Arctophila and Shallow Carex wetlands compared to Deep Arctophila. Shallow Carex had 54% higher biomass than Deep Carex. Carex wetlands had 41–89% higher total biomass than Arctophila wetlands of comparable depth. Chironomidae consistently had the highest biomass across all wetland types. Invertebrate biomass was generally far lower in Deep Open Lakes than in other wetland types.
**Clinical Implications:** This study demonstrates that shallow vegetated tundra wetlands (especially those dominated by Carex and Arctophila) support the highest invertebrate biomass and diversity, making them critical foraging habitats for breeding waterbirds including spectacled eiders, king eiders, and long-tailed ducks. Although OM sources for invertebrates are relatively consistent across wetland types, shallow wetlands (<1 ha) in the study area declined by 30% in area and 17% in number from 1948 to 2013, a trend observed across circumpolar regions. Climate-driven reductions in the number and area of shallow emergent wetlands—rather than shifts in OM sources—are likely to be the primary factor affecting invertebrate prey availability for avian consumers. The authors recommend that documenting trends in Arctic tundra wetland occurrence and types should be a conservation priority.