Cladoceran (Crustacea: Branchiopoda) subfossils are widely used as indicators of environmental change, yet taxonomic resolution of bosminid (Anomopoda: Bosminidae) subfossils often remains limited in paleoecological studies. Identification guides currently recognize a single species, Bosmina (Eubosmina) coregoni, and two species groups (Bosmina (Bosmina) longirostris and Bosmina (Eubosmina) cf. longispina ‘complexes’) in North America, and rarely include male morphologies, likely leading to an underrepresentation of species diversity and male occurrences in sedimentary records. Here, we refine the taxonomy of subfossil bosminid headshields using diagnostic lateral head pore morphology. We suggest that B. (B.) longirostris in North America can be treated as a single species rather than as a group based on its distinct lateral head pore shape and position, and that a new assemblage should be recognized in paleolimnological contexts – the B. (Bosmina) freyi/liederi group. We also clarify the species composition of the B. (E.) cf. longispina group to facilitate the comparison of subfossil and water column zooplankton data to improve paleoenvironmental inferences. The distribution of male bosminid antennules across Canada is also described, particularly those of members of the B. (E.) cf. longispina group, and we explore their potential use as paleoindicators. Altogether, the improved taxonomic resolution of bosminids, including recognition of an additional species group and male morphologies, should improve paleoecological interpretations and provide new insights into ecological responses to environmental stressors.
We quantified temporal variation in the head capsule (HC) length of subfossil chironomids from two high-elevation subarctic lakes in northern Sweden and explored its potential drivers using chironomid assemblages, sedimentary pigments, and stable isotope analyses. Although establishing a reliable chronology was challenging because of the macrofossil-poor sediment context, radiocarbon dating indicates that the cores span approximately the last 5000 years, corresponding to the long-term cooling trend of the Late Holocene in this area. Temporal changes in the scores of the first principal component axis derived from chironomid assemblage data were strongly correlated with variations in the HC length of Micropsectra insignilobus-type in both lakes, with smaller HC reported when Micropsectra insignilobus-type occurred in high relative abundances. These results suggest that long-term changes in chironomid HC size closely tracked shifts in environmental conditions reflected in chironomid taxonomic composition. The observed increase in HC size over time is also consistent with the niche concept, whereby deviations from species-specific optima can alter fitness and promote size-related responses. Furthermore, no significant relationship was detected between the carbon stable isotope composition of chironomid HC and morphometric characteristics, suggesting that dietary changes were likely not a primary driver of the observed HC size variation. As a result, the observed increase in HC size over time could be driven by Late Holocene cooling favoring larger HC sizes in Micropsectra insignilobus-type. Future studies incorporating more robust chronologies are, however, needed to better resolve the links between climate-driven changes, body size dynamics, and community responses in these ecosystems. Overall, our results demonstrate the potential of paleolimnological records to reveal mechanisms underlying long-term body size variation in aquatic invertebrates.
In the early nineteenth century, Iceland entered the global market, which caused a large expansion and modernisation of agricultural practices, including rising livestock numbers, higher crop density and the introduction of artificial fertilizers and pesticides. However, the impact of these pressures on Icelandic ecosystems over the past two centuries are largely unknown. This study applies paleolimnological analyses to a sediment core taken from Vestra Gíslholtsvatn, a small lake in southern Iceland surrounded by three farms that broadly reflect national agricultural trends, to assess how changes in agricultural practices have influenced lake-ecosystem dynamics over the past 250 years. Geochemical proxies such as total organic carbon and total nitrogen show increasing trends alongside decreasing δ13C values, suggesting increased terrestrial and/or algal organic matter influx, which coincide with the introduction of artificial fertilizers. Additionally, Chironomidae head capsules were analysed to investigate changes in the lake ecosystem. The chironomid community shows no sustained change in the assemblage, with a continuous dominance of Heterotrissocladius grimshawi-type, which favours cold and oligotrophic waters, and Psectrocladius sordidellus-type, which prefers macrophyte-rich littoral habitats. Only Chironomus spp. shows some short term increases possibly in response to artificial fertilizer usage. Despite the relative stability in the chironomid assemblage, statistical analyses of the chironomid record reveal increasing skewness, kurtosis and amplitude of the rate of change towards the top of the core. These results possibly represent early warning signals of ecosystem instability. In spite of these signals, no ecological tipping point was reached within the studied period, indicating that impacts from the agricultural intensification were insufficient to drive regime shifts in the lake ecosystems. Our results highlight the resistance of Icelandic lake ecosystems to the agricultural pressures of the past two centuries, despite growing instability.
Subfossil cladoceran assemblages from a dated sediment core collected from a small, shallow forest lake in northwestern Poland were used to reconstruct changes in water availability and habitat structure over the past ca. 2000 years. To assess the reliability of cladoceran-based paleohydrological record in a dynamic shallow-lake system, we applied both a qualitative planktonic-to-littoral (P/L) ratio and a quantitative modern analog technique (MAT) approach. Both approaches indicate substantial Late Holocene variability in inferred water availability and habitat structure, with relatively high inferred water availability from ca. 70 BC to AD 200, followed by greater variability and an overall tendency toward lower water availability. Some reconstructed phases broadly overlap with commonly recognized regional climatic intervals, including the Roman Warm Period, Dark Ages Cold Period, Medieval Climate Anomaly, and Little Ice Age, although these relationships should not be interpreted as evidence of precise chronological synchrony or direct climatic causation. Water availability is interpreted as the principal external driver of lake development, whereas trophic state, macrophyte structure, oxygen conditions, and possible fish predation acted as interconnected modifiers of the cladoceran signal. These local ecological processes complicate the interpretation of the hydrological signal and should therefore be considered in paleohydrological reconstructions of shallow lakes. The P/L ratio primarily reflects changes in littoral–open-water habitat structure, whereas the MAT model provides semi-quantitative depth estimates that may be sensitive to other changes in species–environment relationships. Agreement between the two approaches supports broad relative trends but does not constitute independent validation because both are derived from the same cladoceran assemblages. Cladoceran-based reconstructions therefore provide a useful record of relative hydrological variability, although absolute water-depth estimates remain uncertain.
Calcite varves are commonly deposited and preserved in the sedimentary record of stratified hardwater lakes. Year-to-year variation in the characteristics of individual calcite varves emphasizes their sensitivity to various environmental controls, mainly lake water temperature and pH. However, knowledge on the relation between environmental variability and calcite-varve characteristics is still limited, and prevents utilizing this year-to-year variation for accurate paleoenvironmental reconstruction. This study uses monthly sediment trap sampling, physical and geochemical characterization of lake water, and environmental monitoring in Tiefer See (NE Germany) to trace the transfer of environmental signals into the sediments. Calcite formation in the lake occurs in the epilimnion during the spring–summer and is experiencing substantial year-to-year variations. Between 2013 and 2019, the annual endogenic calcite accumulation during the spring–summer varies by a factor of 3 between 85 and 277 g m−2 within a period of 64–182 days, which comprises 72–97
