Development of water protection of Lake Onega

Lake Onega is the second largest lake in Europe after Lake Ladoga. The lake is located in the Karelian Republic, in the Leningradskaya and Vologodskaya regions of the Russian Federation. The area of the lake is 9800 km2, its max depth is 127 m and the average depth about 30 m. The main cities situated on the shore of the lake are Petrozavodsk and Kondopoga. The lake is connected to the Baltic Sea via the River Svir, Lake Ladoga and the Neva River. Russia is not joining the European Union (EU) in the near future. However, there is tendency to adopt the central principles of many EU directives also in Russia. Water Framework Directive (WFD) is a useful directive giving the main guidelines about how to organize water management. The aim of the project was to make an investigation of the status of Lake Onega, to assess pressures and risks into the lake and make a general plan for water protection to guarantee a good chemical and ecological status of the lake, as expressed on the WFD. One purpose of this project was to transfer Finnish knowledge and results of Finnish investigations concerning the WFD to the area of Lake Onega. In this study, many different steady-state and dynamic catchment and water quality models were used in assessing the effects of different loading scenarios. While Lake Onega preserves a good status of water as a whole, the problems with pollution and eutrophication exist in Petrozavodsk and Kondopoga Bays where anthropogenic loading is more pronounced. The excessive phosphorus loading with Petrozavodsk wastewaters should be reduced considerably to prevent further eutrophication of Lake Onega. The existing treatment removes about 55-60% of total phosphorus from Petrozavodsk wastewaters. Modern technology permits to increase this figure up to 95%. In Kondopoga Bay anthropogenic impact is most severe, the pollution is heaviest at the head of the bay throughout the year, where Kondopoga PPM withdraws wastewaters for nearly 80 years (40 years without treatment). To improve environmental conditions in Kondopoga Bay the effectiveness of wastewater treatment process at Kondopoga PPM has to be enhanced and phosphorus loading has to be reduced

Under-ice convection dynamics in a boreal lake

We investigated radiatively driven under-ice convection in Lake Onego (Russia) during 3 consecutive late winters. In ice-covered lakes, where the temperature of water is below the temperature of maximum density, radiatively driven heating in the upper water column induces unstable density distributions leading to gravitational convection. In this work, we quantified the key parameters to characterise the radiatively driven under-ice convection: (1) the effective buoyancy flux, B∗ (driver), and its vertical distribution; (2) the convective mixed-layer thickness, hCML (depth scale); and (3) the convective velocity,w∗(kinematic scale). We compared analytical w∗ scaling estimates to in situ observations from high-resolution acoustic Doppler current profilers. The results show a robust correlation between w∗and the direct observations, except during the onset and decay of the solar radiation. Our results highlight the importance of accurately defining the upper limit of hCML in highly turbid water and the need for spectrally resolving solar radiation measurements and their attenuation for accurate B∗ estimates. Uncertainties in the different parameters were also investigated. We finally examined the implications of under-ice convection for the growth rate of nonmotile phytoplankton and provide a simple heuristic model as a function of easily measurable parameters

Dissolved oxygen dynamics under ice: three winters of high-frequency data from Lake Tovel, Italy

Under-ice dissolved oxygen (DO) metabolism and DO depletion are poorly understood, limiting our ability to predict how changing winter conditions will affect lake ecosystems. We analyzed under-ice DO dynamics based on high-frequency (HF) data at two depths (5 and 25 m) for three winters (January-March 2014, 2015, and 2016) in oligotrophic Lake Tovel (1178 m above sea level; maximum depth 39 m). Specifically, we assessed diel metabolic rates based on HF data of DO, temperature, and light for winter 2016 and seasonal DO depletion rates based on HF data of DO for all three winters. For 2016, calculations of metabolic rates were possible only for 34% and 3% of days at 5 and 25 m, respectively; these metabolic rates generally indicated net heterotrophy at both depths. Low success in modeling metabolic rates was attributed to low diel DO variability and anomalous diel DO patterns, probably linked to under-ice physical processes. Seasonal DO patterns for the three winters showed increasing, decreasing, or stable DO trends at 5 m while at 25 m patterns always showed decreasing DO trends but with different rates. Our multiyear study permitted us to hypothesize that the observed intraannual and interannual differences in DO depletion can be attributed to variable snow cover determining the penetration of radiation and thus photosynthesis. This study brings new insights to DO dynamics in ice-covered systems, highlights the challenges linked to under-ice lake metabolism, and advocates for a modeling approach that includes physical processes

Oxygen dynamics in permafrost thaw lakes: Anaerobic bioreactors in the Canadian subarctic

Permafrost thaw lakes occur in high abundance across the subarctic landscape but little is known about their limnological dynamics. This study was undertaken to evaluate the hourly, seasonal, and depth variations in oxygen concentration in three thaw lakes in northern Quebec, Canada, across contrasting permafrost regimes (isolated, sporadic, and discontinuous). All lakes were well stratified in summer despite their shallow depths (2.7-4.0m), with hypoxic or anoxic bottom waters. Continuous automated measurements in each of the lakes showed a period of water column oxygenation over several weeks in fall followed by bottom-water anoxia soon after ice-up. Anoxic conditions extended to shallower depths (1m) over the course of winter, beginning 18-137 d after ice formation, depending on the lake. Full water column anoxia extended over 33-75% of the annual record. There was a brief period of incomplete spring mixing with partial or no reoxygenation of the bottom waters in each lake. Conductivity measurements showed the build-up of solutes in the bottom waters, and the resultant density increase contributed to the resistance to full mixing in spring. These observations indicate the prevalence of stratified conditions throughout most of the year and underscore the importance of the fall mixing period for gas exchange with the atmosphere. Given the long duration of anoxia, subarctic thaw lakes represent an ideal environment for anaerobic processes such as methane production. The intermittent oxygenation also favors intense methanotrophy and aerobic bacterial decomposition processes

Pan-Eurasian Experiment (PEEX): Towards a holistic understanding of the feedbacks and interactions in the land-Atmosphere-ocean-society continuum in the northern Eurasian region

The northern Eurasian regions and Arctic Ocean will very likely undergo substantial changes during the next decades. The Arctic-boreal natural environments play a crucial role in the global climate via albedo change, carbon sources and sinks as well as atmospheric aerosol production from biogenic volatile organic compounds. Furthermore, it is expected that global trade activities, demographic movement, and use of natural resources will be increasing in the Arctic regions. There is a need for a novel research approach, which not only identifies and tackles the relevant multi-disciplinary research questions, but also is able to make a holistic system analysis of the expected feedbacks. In this paper, we introduce the research agenda of the Pan-Eurasian Experiment (PEEX), a multi-scale, multi-disciplinary and international program started in 2012 (https://www.atm.helsinki.fi/peex/). PEEX sets a research approach by which large-scale research topics are investigated from a system perspective and which aims to fill the key gaps in our understanding of the feedbacks and interactions between the land-Atmosphere-Aquatic-society continuum in the northern Eurasian region. We introduce here the state of the art for the key topics in the PEEX research agenda and present the future prospects of the research, which we see relevant in this context

Investigation of the spring thermal regime in Lake Ladoga using field and satellite data

We use a combination of field and satellite data to investigate the thermal regime in Lake Ladoga in spring 1992. The analysis concentrates mainly on the temperature structure in the convectively mixed region and the dynamics of a special thermo‐hydrodynamic phenomenon called “thermal bar” (a zone of descending water with the temperature of maximum density equal to ∼4°C). A theoretical model of the temperature distribution in the convectively mixed region (temperatures <4°C) and the thermal bar progression is also applied and compared with satellite data. The study shows that the temperature offshore the 4°C isotherm in the convectively mixed region of the lake is almost depth‐constant because of strong convective mixing and that the horizontal heat flux seems to be of minor importance in this region. The comparison between predictions from the simple theoretical model describing the temperature evolution and movement of the thermal bar with observations showed a fairly good agreement. However, calculations of the change of heat content in water columns along sections indicate heat transport from the nearshore, stably stratified region toward the 4°C isotherm which will affect the movement of the thermal bar. This effect has been incorporated in an improved model of the thermal bar progression. A better agreement between predictions and observations was also obtained with this model