Milla Rautio

Cladocera and Other Branchiopod Crustaceans

Lake sediments contain a variety of organic and inorganic remains that may be used to track the history of a lake or its catchment. Shells, head-shields, post-abdomens and claws of Cladocera are among the most frequently found animal remains in sedimentary deposits. They have played an important role in providing information on various environmental events and disturbances affecting lake status, such as climatic changes, trophic oscillations, acidification, and water-level changes. Yet, one major problem has been to relate sediment core findings to animal ecology. As in the case of other organism groups, many contradictory records and opinions have been presented concerning their paleoecology and indicator value of cladocerans.

Seasonal ecosystem variability in remote mountain lakes: implications for detecting climatic signals in sediment records.

Weather variation and climate fluctuations are the main sources of ecosystem variability in remote mountain lakes. Here we describe the main patterns of seasonal variability in the ecosystems of nine lakes in Europe, and discuss the implications for recording climatic features in their sediments. Despite the diversity in latitude and size, the lakes showed a number of common features. They were ice-covered between 5–9 months, and all but one were dimictic. This particular lake was long and shallow, and wind action episodically mixed the water column throughout the ice-free period. All lakes showed characteristic oxygen depletion during the ice-covered-period, which was greater in the most productive lakes. Two types of lakes were distinguished according to the number of production peaks during the ice-free season. Lakes with longer summer stratification tended to have two productive periods: one at the onset of stratification, and the other during the autumn overturn. Lakes with shorter stratification had a single peak during the ice-free period. All lakes presented deep chlorophyll maxima during summer stratification, and subsurface chlorophyll maxima beneath the ice. Phosphorus limitation was common to all lakes, since nitrogen compounds were significantly more abundant than the requirements for the primary production observed. The major chemical components present in the lakes showed a short but extreme dilution during thawing. Certain lake features may favour the recording of particular climatic fluctuations, for instance: lakes with two distinct productive periods, climatic fluctuations in spring or autumn (e.g., through chrysophycean cysts); lakes with higher oxygen consumption, climatic factors affecting the duration of the ice-cover (e.g., through low-oxygen tolerant chironomids); lakes with higher water retention time; changes in atmospheric deposition (e.g., through carbon or pigment burial); lakes with longer stratification, air temperature changes during summer and autumn (e.g., through all epilimnetic species).

Shallow Freshwater Ecosystems of the Circumpolar Arctic

Abstract: This review provides a synthesis of limnological data and conclusions from studies on ponds and small lakes at our research sites in Subarctic and Arctic Canada, Alaska, northern Scandinavia, and Greenland. Many of these water bodies contain large standing stocks of benthic microbial mats that grow in relatively nutrient-rich conditions, while the overlying water column is nutrient-poor and supports only low concentrations of phytoplankton. Zooplankton biomass can, however, be substantial and is supported by grazing on the microbial mats as well as detrital inputs, algae, and other plankton. In addition to large annual temperature fluctuations, a short growing season, and freeze-up and desiccation stress in winter, these ecosystems are strongly regulated by the supply of organic matter and its optical and biogeochemical properties. Dissolved organic carbon affects bacterial diversity and production, the ratio between pelagic and benthic primary productivity via light attenuation, and the exposure and photoprotection responses of organisms to solar ultraviolet radiation. Climate warming is likely to result in reduced duration of ice-cover, warmer water temperatures, and increased nutrient supplies from the more biogeochemically active catchments, which in turn may cause greater planktonic production. Predicted changes in the amount and origin of dissolved organic matter may favour increased microbial activity in the water column and decreased light availability for the phytobenthos, with effects on biodiversity at all trophic levels, and increased channelling of terrestrial carbon to the atmosphere in the form of greenhouse gases.

UV radiation and freshwater zooplankton: damage, protection and recovery

Abstract While many laboratory and field studies show that zooplankton are negatively affected when exposed to high intensities of ultraviolet radiation (UVR), most studies also indicate that zooplankton are well adapted to cope with large variations in their UVR exposure in the pelagic zone of lakes. The response mechanisms of zooplankton are diverse and efficient and may explain the success and richness of freshwater zooplankton in optically variable waters. While no single behavioural or physiological protection mechanism seems to be superior, and while several unexplained and contradictory patterns exist in zooplankton UVR ecology, recent increases in our understanding are consistent with UVR playing an important role for zooplankton. This review examines the variability in freshwater zooplankton responses to UVR, with a focus on crustacean zooplankton (Cladocera and Copepoda). We present an overview of UVR-induced damages, and the protection and recovery mechanisms freshwater zooplankton use when exposed to UVR. We review the current knowledge of UVR impact on freshwater zooplankton at species and community levels, and discuss briefly how global change over the last three decades has influenced the UVR milieu in lakes.

Vertical distribution of Daphnia longispina in a shallow subarctic pond: Does the interaction of ultraviolet radiation and Chaoborus predation explain the pattern?

The adaptive significance of vertical migration by planktonic organisms is often explained in terms of reducing the risk of predation. Observational evidence, however, indicates that migratory patterns may also be triggered by solar ultraviolet (UV) radiation. Such a strategy would allow animals to escape from UV-induced damage into deeper water layers. In this study, we examine the relation of several biotic (invertebrate predators, algae) and abiotic (temperature, radiation) factors to the vertical distribution of Daphnia longispina in a 50-cm-deep, fishless pond in subarctic Finnish Lapland. Samples were taken from three depths, on both sunny and overcast days, and at different hours of day. Our results show that, on sunny days, the vertical distribution of Daphnia responds to ultraviolet radiation, whereas on overcast days, predator avoidance (phantom midge, Chaoborus obscuripes) is a better predictor of Daphnia distribution. Juvenile and adult Daphnia showed a similar distribution pattern.

Zooplankton Assemblages Related to Environmental Characteristics in Treeline Ponds in Finnish Lapland

Zooplankton communities of 17 subarctic ponds with differing catchment areas and habitat types in northern Finland were surveyed during the open water season from June to August. Ponds were located along a gradient that changes from a mountain birch woodland to a treeless tundra. In all sites, cladoceran abundance dominated that of copepods although there was a consistent pattern of increasing relative abundance of copepods toward the most barren ponds. Species richness declined with increasing altitude but diversity remained constant. Zooplankton communities within the same habitat type were similar. Temporal variation in species abundance showed a coherent temperature driven pattern along the whole altitudinal transect.

Sources and controls of organic carbon in lakes across the subarctic treeline

Abundant northern lakes have an intrinsic role in the transport, sequestration, and mineralization of terrestrial organic carbon. The quantity and quality of this carbon control vital aquatic biogeochemical processes, and influence the metabolic balance of lakes with subsequent impact on the global carbon cycle. We measured concentrations and type of dissolved organic matter and elemental and stable isotopic composition of carbon and nitrogen in 31 subarctic lakes with varying catchment types across the treeline in northern Finland, integrating both the pelagic (lake water) and the benthic (surface sediments) carbon pools for a comprehensive understanding of landscape influence on aquatic carbon dynamics. Wetland cover was identified as the primary catchment control over the aquatic carbon pools, reflected particularly in the bio-optical properties of lake water. Landscape influence on sediment carbon content and composition, mirroring largely the structure and productivity of the aquatic communities, was primarily connected to allochthonous nutrient inputs fueling autotrophic production. Basin depth and benthic production were identified as important internal controls on the surface sediment geochemistry. Overall, our results suggest that shallow subarctic lakes will be particularly susceptible to climate-mediated changes in the export of terrestrial organic matter from wetlands. Whether the landscape influence will promote the channeling of terrestrial carbon into the atmosphere via aquatic ecosystems will strongly depend on the interplay between the biogeochemical characteristic of the allochthonous carbon inputs, terrestrial nutrient fluxes, and the depth of the recipient ecosystems.

Dissolved organic matter concentration, optical parameters and attenuation of solar radiation in high-latitude lakes across three vegetation zones

ABSTRACT High-latitude lakes are usually transparent, due to their low productivity and low concentration of dissolved organic matter (DOM), but large variations in lake optical properties can be found within and between regions. We investigated the light regimes in relation to DOM in 18 oligotrophic, high-latitude lakes across mountain birch woodland, shrub tundra and barren tundra in north-west Finnish Lapland. In 12 lakes >1% of photosynthetically active radiation (PAR) reached the lake bottom, while 1% UV-B depth ranged from 0.1 to >12 m. Lakes located in barren tundra had highest transparency, lowest dissolved organic carbon (DOC) concentration and lowest DOM absorption (a440) (mean values: Kd PAR 0.3m-1, DOC 2.1mg l-1, a440 0.4m-1), while lakes in shrub tundra and mountain birch forest were less transparent (DOC 4.7 mg l-1, a440 1.4 m-1). Solar attenuation and lake transparency was best explained by a440. Our survey emphasizes the importance of catchment type on DOM characteristics and lake optics. We predict that even small changes in DOM quality may largely change the UV radiation exposure of lakes while changes in PAR may have smaller biological effects in these shallow lakes that are already illuminated to the bottom.

Climate Effects on High Latitude Daphnia via Food Quality and Thresholds.

Climate change is proceeding rapidly at high northern latitudes and may have a variety of direct and indirect effects on aquatic food webs. One predicted effect is the potential shift in phytoplankton community structure towards increased cyanobacterial abundance. Given that cyanobacteria are known to be a nutritionally poor food source, we hypothesized that such a shift would reduce the efficiency of feeding and growth of northern zooplankton. To test this hypothesis, we first isolated a clone of Daphnia pulex from a permafrost thaw pond in subarctic Québec, and confirmed that it was triploid but otherwise genetically similar to a diploid, reference clone of the same species isolated from a freshwater pond in southern Québec. We used a controlled flow-through system to investigate the direct effect of temperature and indirect effect of subarctic picocyanobacteria (Synechococcus) on threshold food concentrations and growth rate of the high latitude clone. We also compared the direct effect of temperature on both Daphnia clones feeding on eukaryotic picoplankton (Nannochloropsis). The high latitude clone had a significantly lower food threshold for growth than the temperate clone at both 18 and 26°C, implying adaptation to lower food availability even under warmer conditions. Polyunsaturated fatty acids were present in the picoeukaryote but not the cyanobacterium, confirming the large difference in food quality. The food threshold for growth of the high latitude Daphnia was 3.7 (18°C) to 4.2 (26°C) times higher when fed Synechococcus versus Nannochloropsis, and there was also a significant negative effect of increased temperature and cyanobacterial food on zooplankton fatty acid content and composition. The combined effect of temperature and food quality on the performance of the high latitude Daphnia was greater than their effects added separately, further indicating the potentially strong indirect effects of climate warming on aquatic food web processes.

Developing a circumpolar monitoring framework for Arctic freshwater biodiversity

Arctic freshwater ecosystems are facing unique challenges through the interaction of natural and human-induced stressors such as climate change and industrial development. Much is unknown about the biodiversity of Arctic freshwaters, although it is believed to have already been affected by climate change. A pan-Arctic monitoring strategy is critically needed to improve abilities to detect and understand ongoing and future changes in Arctic freshwater ecosystems. The challenging issues that Arctic freshwater monitoring must address include: the large diversity of Arctic freshwater ecosystems, varying levels of stressor impacts across the Arctic, lack of historical baseline research and monitoring coordination, and poor among-country standardization of sampling protocols. In response, the Arctic Councils Freshwater Expert Monitoring Group of the Circumpolar Biodiversity Monitoring Program (Conservation of Arctic Flora and Fauna) is developing a framework for monitoring Arctic freshwater biodiversity that will lead to regular reviews of the state of freshwater ecosystems across the circumpolar Arctic. The parameters of primary focus for the monitoring framework are classified by focal ecosystem components (FECs), which are biotic or abiotic factors that are ecologically pivotal, charismatic and/or sensitive to changes in biodiversity. FECs are placed in the context of expected ecosystem change through the development of testable impact hypotheses (or predictions) that outline a cause-effect framework regarding how change in environmental and anthropogenic stressors is expected to affect FECs. These prediction statements provide both guidelines for future scientific data collection and a focus for management decision-making. Here we discuss the design of a proposed monitoring framework and the development of impact hypotheses that focus on climate change effects. We emphasise the connectivity between science, monitoring and management necessary to implement the framework across the Arctic.