Diverging life cycle patterns of two Diamesa species (Diptera, Chironomidae) in High Arctic streams, Svalbard

The fauna of streams in the High Arctic, dominated by chironomids, is shaped by extreme environmental conditions that represent the physiological limits for benthic invertebrates. Despite their ecological importance, little is known of chironomid life histories, development strategies and the key abiotic drivers limiting larval growth in High Arctic streams. We investigated the larval development and growth in three High Arctic rivers with contrasting water sources, thermal regimes and nutrient characteristics. Populations of the larvae of Diamesa bohemani (Goetghebuer 1932) and Diamesa aberrata (Lundbeck 1898) from two sampling occasions in July and August 2016 were morphometrically analysed to determine life history patterns and instream productivity. Water temperature differences lead to diverging development patterns on local spatial scales. The lowest larval growth was in a groundwater/snowmelt fed stream with low food concentration and quality, suggesting that stream productivity is not primarily water source dependant, but is dependent on the nutrient supply. Glacially influenced streams are clearly more productive than previously assumed, resulting in comparable secondary production to groundwater/snowmelt-fed streams.

Wavelet Analysis Identifies Carbon Processes in a Subarctic Stream During Snowmelt Spring Flood

<p>Snowmelt spring floods dominate the annual carbon flux in Arctic streams. However, climate change is altering their timing and magnitude due to changes in snow conditions, further altering the processes controlling the carbon cycle at the catchment scale. Current knowledge is limited by a lack of high-resolution data from Arctic areas. In this study we combine high-resolution biogeochemical-hydro-climatological variables with spectral wavelet analysis for new insights into carbon processes.</p><p>This study was conducted during the snowmelt spring flood period in a sub-arctic headwater catchment in Pallas-Ylläs national park, Finland (68°02′N, 24°16′W). We collected in-stream dissolved organic carbon (DOC), carbon dioxide (C0<sub>2</sub>), and terrestrial C0<sub>2 </sub>flux alongside a suite of hydro-climatological variables measured at 30-minute intervals. Continuous wavelet transformations and wavelet coherence were produced to assess the relationship between hydro-climatological variables and carbon variables at different periodicities.</p><p>Wavelet transforms indicated that the onset of snowmelt caused the development of significant diel periodicity for in-stream DOC, CO<sub>2</sub> and terrestrial CO<sub>2 </sub>flux, while substantial periods of significant periodicity were observed at multiple day periodicities. Wavelet coherence analysis identified that DOC was consistently lead by flow and conductivity across daily and multiple daily scales suggesting that transport of carbon from the surface and shallow sub-surface pathways to the stream were the predominant processes controlling in-stream DOC. Interestingly for in-stream CO<sub>2</sub>, groundwater level showed periodic rather than consistent spectral coherence suggesting it is not a consistent control on CO<sub>2</sub> in the spring flood. The strongest coherence for in-stream CO<sub>2</sub> was with in-stream O<sub>2</sub>, which may suggest the importance of in-stream metabolism as a control on in-stream CO<sub>2</sub> dynamics. Terrestrial CO<sub>2 </sub>fluxwas controlled by notably different processes than in-stream Carbon and linked strongest to climatological variables. Photosynthetically active radiation (PAR) showed the strongest relationship with CO<sub>2</sub> terrestrial flux dynamics. </p><p>Our study highlights the unique processes controlling different parts of the carbon cycle in a headwater arctic catchment during the snowmelt spring flood. We highlight in-stream DOC as particularly vulnerable to changes in spring flood magnitude and timing given the importance of snowmelt dominated transport processes to DOC flux. To identify future changes in the Arctic carbon cycle, wavelet analysis shows potential as tool to analyse changes in processes in high-resolution datasets.</p>

Stream diatom assemblages in an Arctic catchment: diversity and relationship to ecosystem-scale primary production

We quantified benthic diatom diversity in streams in the Miellajokka catchment, about 200 km north of the Arctic circle in Sweden. Beta diversity among sites was related to local-scale environmental heterogeneity (occurring on the order of 1 km or less), and its magnitude was equal (Sørensen Index = 0.62) to levels previously reported for rivers on regional environmental gradients across hundreds of kilometres of Arctic Fennoscandia. Species turnover was the dominant (77%) component of beta diversity in the Miellajokka catchment. Small, stress-tolerant taxa dominated the assemblages, and there were no clear patterns of functional class among sites. Site ordinates from non-metric dimensional scaling were most strongly correlated with flood frequency (r = 0.83) and water temperature (r = 0.89), which was higher in harsh tundra sites than below treeline. Additionally, site ordinates were correlated (r = 0.83) with ecosystem-scale gross primary production — indicative of a link between diatom diversity and ecosystem function. Our results advance understanding of patterns diatom diversity in Arctic streams by quantifying local-scale variation that is understudied in this region, and by identifying the consequences of this local-scale diversity for an ecosystem-scale process.

Understanding interacting dynamics of hydrology, carbon cycle, and greenhouse gas fluxes in Arctic watersheds

<p>Carbon -water interactions are critical components of Arctic freshwater ecosystems. Dissolved organic matter (DOM) is the basis for in stream biological processes and is the foundation of biogeochemical linkages between terrestrial and aquatic landscapes, and also between the river bodies and the atmosphere via outgassing. Quantity and quality of DOM is further affecting the biochemical processes of aquatic ecosystems, as it is strongly related to the abundance, activity and composition of microbial communities. Microbes are an important part of the freshwaters biochemical cycle as they convert DOM into nutrients. They also play a vital role in carbon mineralization into carbon dioxide (CO<sub>2</sub>) and methane (CH<sub>4</sub>), which can further be released to the atmosphere resulting substantial greenhouse gas (GHG) emissions. Thus, streams play an important role in global carbon processing, storage and release. However, small Arctic streams and ecologically important interfaces between aquatic and terrestrial ecosystems, in particular, are under-represented in global atmospheric GHG emission estimates owing to a lack of spatial and temporal flux measurements in Arctic conditions.</p><p>The objective of our study was to improve understanding of the connections between hydrology, carbon cycle and GHG flux dynamics in Arctic watersheds. We used combination of multiscale measurements to quantify carbon availability (DOC/DIC concentrations) and quality (water absorbance, SUVA<sub>254</sub> index), water sources (stable H<sub>2</sub>O isotope proxies), microbial community structure (rRNA sequencing), and CO<sub>2</sub> and CH<sub>4</sub> fluxes and stream water concentrations. Our study site is typical groundwater influenced peatland dominated second order watershed located at Pallas-Yllästunturi National Park in northern Finland. Sampling was conducted three times during summer 2019 at 20 locations along the stream gradient.</p><p>Preliminary results indicate this stream to be a significant contributor of CO<sub>2</sub> and CH<sub>4</sub>. GHG fluxes increased from headwaters towards the stream outlet. However, the groundwater hotspots decreased, while runoff from peatland sections increased the fluxes. One particular groundwater hotspot was an exception, as its emission rates of CH<sub>4</sub> were exceptionally high in June, probably due to increased anaerobic microbial activity within the groundwater system. Microbial contribution to carbon dynamics was evident during our study period as increased DOC loads due to late spring snowmelt dominated runoff from surrounding peatland was mineralized and DIC amount increased towards midsummer. This will be further supported by results from microbial community analysis. Same was evident also in spatial scale, as higher DOC values of headwater sites was reduced downstream and DIC values were increasing respectively. SUVA<sub>254 </sub>index, which correlates positively with higher DOC aromaticity and molecular weight, was lower at groundwater hotspots. This indicates that groundwater hotspots were producing better quality C for microbes, as microbes tend to prefer compounds with lower aromaticity and molecular weight.</p><p>Our study addresses the urgent need for catchment level studies on carbon and GHG cycling that focuses on terrestrial-aquatic linkages, and on the mechanistic processes involved, such as microbe-mediated mineralization. Catchment wide studies conducted in Arctic and Boreal regions including interactions between ecosystems are especially needed today as northern areas are experiencing unprecedented extreme warming, precipitation changes and shifting snow depths.</p>