Temperature change as a driver of spatial patterns and long-term trends in chironomid (Insecta: Diptera) diversity.

Anthropogenic activities have led to a global decline in biodiversity, and monitoring studies indicate that both insect communities and wetland ecosystems are particularly affected. However, there is a need for long-term data (over centennial or millennial timescales) to better understand natural community dynamics and the processes that govern the observed trends. Chironomids (Insecta: Diptera: Chironomidae) are often the most abundant insects in lake ecosystems, sensitive to environmental change, and, because their larval exoskeleton head capsules preserve well in lake sediments, they provide a unique record of insect community dynamics through time. Here, we provide the results of a metadata analysis of chironomid diversity across a range of spatial and temporal scales. First, we analyse spatial trends in chironomid diversity using Northern Hemispheric data sets overall consisting of 837 lakes. Our results indicate that in most of our data sets, summer temperature (Tjul ) is strongly associated with spatial trends in modern-day chironomid diversity. We observe a strong increase in chironomid alpha diversity with increasing Tjul in regions with present-day Tjul between 2.5 and 14°C. In some areas with Tjul  > 14°C, chironomid diversity stabilizes or declines. Second, we demonstrate that the direction and amplitude of change in alpha diversity in a compilation of subfossil chironomid records spanning the last glacial-interglacial transition (~15,000-11,000 years ago) are similar to those observed in our modern data. A compilation of Holocene records shows that during phases when the amplitude of temperature change was small, site-specific factors had a greater influence on the chironomid fauna obscuring the chironomid diversity-temperature relationship. Our results imply expected overall chironomid diversity increases in colder regions such as the Arctic under sustained global warming, but with complex and not necessarily predictable responses for individual sites.

A database of chlorophyll and water chemistry in freshwater lakes.

Measures of chlorophyll represent the algal biomass in freshwater lakes that is often used by managers as a proxy for water quality and lake productivity. However, chlorophyll concentrations in lakes are dependent on many interacting factors, including nutrient inputs, mixing regime, lake depth, climate, and anthropogenic activities within the watershed. Therefore, integrating a broad scale dataset of lake physical, chemical, and biological characteristics can help elucidate the response of freshwater ecosystems to global change. We synthesized a database of measured chlorophyll a (chla) values, associated water chemistry variables, and lake morphometric characteristics for 11,959 freshwater lakes distributed across 72 countries. Data were collected based on a systematic review examining 3322 published manuscripts that measured lake chla, and we supplemented these data with online repositories such as The Knowledge Network for Biocomplexity, Dryad, and Pangaea. This publicly available database can be used to improve our understanding of how chlorophyll levels respond to global environmental change and provide baseline comparisons for environmental managers responsible for maintaining water quality in lakes.

Characterization of perfluoroalkyl substances in sediment cores from High and Low Arctic lakes in Canada.

Perfluoroalkyl substances (PFASs) are synthetic environmentally-persistent pollutants that are amenable to long-range transport and accumulation in remote Arctic ecosystems. In this study, historical inventories of twenty-three PFASs (i.e. C4-C14, C16 perfluoroalkane carboxylic acids (PFCAs); C4, C6-C8, C10 perfluoroalkane sulfonic acids (PFSAs); perfluoro-4-ethyl-cyclohexane sulfonic acid (PFECHS); dodecafluoro-3H-4,8-dioxanonanoic acid (ADONA); 8-chloro-perfluoro-1-octane sulfonic acid (8-Cl-PFOS); chlorinated polyfluorinated ether sulfonic acids (Cl-PFESAs) including 9-chlorohexadecafluoro-3-oxanonane-1-sulfonic acid (6:2 Cl-PFESA) and 11-chloroeicosafluoro-3-oxaundecane-1-sulfonic acid (8:2 Cl-PFESA); as well as perfluorooctane sulfonamide (FOSA)) are determined in two intact sediment cores collected from Lake Hazen, located in northern Ellesmere Island at 82° N in 2012 and Lake B35, located in central Nunavut at 64° N in 2009. In Lake Hazen, fluxes of perfluorooctanoic acid (PFOA), perfluorodecanoic acid (PFDA), perfluorobutane sulfonic acid (PFBS), and perfluorooctane sulfonic acid (PFOS) increased during 1963-2011. In Lake B35, fluxes of perfluoroheptanoic acid (PFHpA), PFOA, perfluorononanoic acid (PFNA), and perfluoroundecanoic acid (PFUnDA) increased during 1952-2009. The temporal trends for PFASs in Lake Hazen and Lake B35 sediments are consistent with the continuous annual delivery of PFASs to the Arctic of Canada. Temporal trends in sediment cores appear to follow historical market changes in PFAS manufacturing inventory. The doubling time of PFAS fluxes are faster in Lake Hazen sediments than Lake B35 sediments. In Lake Hazen, this may be attributed to the enhanced delivery of sediment and historically-archived PFASs promoted by climate-induced glacier melting in the Lake Hazen watershed post-2005. Exponentially increasing PFAS temporal trends in High and Low Arctic lakes in Canada stress the importance of developing effective global regulatory policies for PFAS manufacturing and highlights the potential for climate change-induced contaminant release from melting glaciers in the Arctic.

Climate-driven regime shifts in the biological communities of arctic lakes.

Fifty-five paleolimnological records from lakes in the circumpolar Arctic reveal widespread species changes and ecological reorganizations in algae and invertebrate communities since approximately anno Domini 1850. The remoteness of these sites, coupled with the ecological characteristics of taxa involved, indicate that changes are primarily driven by climate warming through lengthening of the summer growing season and related limnological changes. The widespread distribution and similar character of these changes indicate that the opportunity to study arctic ecosystems unaffected by human influences may have disappeared.