Regional Variability and Drivers of Below Ice CO2 in Boreal and Subarctic Lakes

Northern lakes are ice-covered for considerable portions of the year, where carbon dioxide (CO2) can accumulate below ice, subsequently leading to high CO2 emissions at ice-melt. Current knowledge on the regional control and variability of below ice partial pressure of carbon dioxide (pCO(2)) is lacking, creating a gap in our understanding of how ice cover dynamics affect the CO2 accumulation below ice and therefore CO2 emissions from inland waters during the ice-melt period. To narrow this gap, we identified the drivers of below ice pCO(2) variation across 506 Swedish and Finnish lakes using water chemistry, lake morphometry, catchment characteristics, lake position, and climate variables. We found that lake depth and trophic status were the most important variables explaining variations in below ice pCO(2) across the 506 lakes(.) Together, lake morphometry and water chemistry explained 53% of the site-to-site variation in below ice pCO(2). Regional climate (including ice cover duration) and latitude only explained 7% of the variation in below ice pCO(2). Thus, our results suggest that on a regional scale a shortening of the ice cover period on lakes may not directly affect the accumulation of CO2 below ice but rather indirectly through increased mobility of nutrients and carbon loading to lakes. Thus, given that climate-induced changes are most evident in northern ecosystems, adequately predicting the consequences of a changing climate on future CO2 emission estimates from northern lakes involves monitoring changes not only to ice cover but also to changes in the trophic status of lakes.Peer reviewe

Influence motor aktivity on physical development of students

The character of organic carbon (OC) in lake waters is strongly dependent on the time water has spent in the landscape as well as in the lake itself due to continuous biogeochemical OC transformation processes. A common view is that upstream lakes might prolong the water retention in the landscape, resulting in an altered OC character downstream. We calculated the number of lakes upstream for 24,742 Swedish lakes in seven river basins spanning from 56º to 68º N. For each of these lakes, we used a lake volume to discharge comparison on a landscape scale to account for upstream water retention by lakes (Tn tot). We found a surprisingly weak relationship between the number of lakes upstream and Tn tot. Accordingly, we found that the coloured fraction of organic carbon was not related to lake landscape position but significantly related to Tn tot when we analysed lake water chemical data from 1,559 lakes in the studied river basins. Thus, we conclude that water renewal along the aquatic continuum by lateral water inputs offsets cumulative retention by lakes. Based on our findings, we suggest integrating Tn tot in studies that address lake landscape position in the boreal zone to better understand variations in the character of organic carbon across lake districts

Increasing dissimilarity of water chemical compositions in a warmer climate

Understanding variability patterns of biogeochemical conditions in water is a key issue for water management strategies. Here a unique homogeneous data set of 1041 Swedish boreal lakes, sampled during three lake inventories along an 8 degrees latitudinal temperature gradient, revealed a systematic increase in the variability of the water chemical composition between lakes with increasing temperatures. The variability pattern was consistent on a spatial and temporal scale and became especially apparent for water chemical variables showing an in-lake biological process-driven seasonality, such as nitrogen, pH, silica, and organic carbon. The degree of dissimilarity in the chemical composition between lakes was well related to the duration of the main growing and runoff season (D-T > 0), both on a spatial scale (R-2 = 0.57-0.79, P < 0.05) and a temporal scale (R-2 = 0.99, P < 0.05). It is suggested that D-T > 0 is a very suitable proxy to explain biogeochemical variability patterns between lakes. According to this study, a further temperature increase will result in an increased biogeochemical dissimilarity between lakes

Temporal and spatial carbon dioxide concentration patterns in a small boreal lake in relation to ice-cover dynamics

Global carbon dioxide (CO2) emission estimates from inland waters commonly neglect the ice-cover season. To account for CO2 accumulation below ice and consequent emissions into the atmosphere at ice-melt we combined automatically-monitored and manually- sampled spatially-distributed CO2 concentration measurements from a small boreal ice-covered lake in Sweden. In early winter, CO2 accumulated continuously below ice, whereas, in late winter, CO2 concentrations remained rather constant. At ice-melt, two CO2 concentration peaks were recorded, the first one reflecting lateral CO2 transport within the upper water column, and the second one reflecting vertical CO2 transport from bottom waters. We estimated that 66%–85% of the total CO2 accumulated in the water below ice left the lake at ice-melt, while the remainder was stored in bottom waters. Our results imply that CO2 accumulation under ice and emissions at ice-melt are more dynamic than previously reported, and thus need to be more accurately integrated into annual CO2 emission estimates from inland waters

Substantial increase in minimum lake surface temperatures under climate change

The annual minimum of lake surface water temperature influences ecological and biogeochemical processes, but variability and change in this extreme has not been investigated. Here, we analysed observational data from eight European lakes and investigated the changes in annual minimum surface water temperature. We found that, between 1973 and 2014, the annual minimum lake surface temperature has increased at an average rate of +0.35°C decade-1; comparable to the rate of summer average lake surface temperature change during the same period (+0.32°C decade-1). Coherent responses to climatic warming are observed between the increase in annual minimum lake surface temperature and the increase in winter air temperature variations. As a result of the rapid warming of annual minimum lake surface temperatures, some of the studied lakes no longer reach important minimum surface temperature thresholds that occur in winter, with complex and significant potential implications for lakes and the ecosystem services that they provide

Effects of weather-related episodic events in lakes: an analysis based on high-frequency data

1. Weather-related episodic events are typically unpredictable, and their duration is often short. Abiotic and biological responses are often missed in routine monitoring. These responses are, however, now of particular relevance given projected changes in extreme weather conditions. 2. We present data from high-frequency monitoring stations from lakes in Europe, North America and Asia that illustrate two classes of abiotic effects of weather events: (i) generally short-lived effects of storms on lake thermal structure and (ii) the more prolonged effects of high rainfall events on dissolved organic matter levels and water clarity. We further relate these abiotic effects to changes in dissolved oxygen or in chlorophyll a levels. 3. Three differing causes for weather-related decreases in surface dissolved oxygen levels were observed: (i) entrainment of anoxic water from depth, (ii) reduction in primary productivity and (iii) increased mineralisation of organic carbon delivered from the catchment. 4. The duration of in-lake effects tended to be longer for events driven by weather conditions with a longer return period, that is, conditions that were relatively more severe and less frequent at a site. While the susceptibility of lakes to change was related in part to the severity of the meteorological drivers, the impacts also depended on site-specific factors in some cases. 5. The availability of high-frequency data at these sites provided insight into the capacity of the lakes to absorb current and future pressures. Several of the changes we observed, including increases in carbon availability, decreases in photosynthetically active radiation and increased disturbance, have the capacity to shift lakes towards an increased degree of heterotrophy. The magnitude and direction of any such change will, however, also depend on the magnitude and direction of climate change for a given location and on lake and catchment characteristics

Матеріали міжнародної науково-практичної конференції „Маркетинговий інструментарій управління попитом на товари та послуги“

Матеріали міжнародної науково-практичної конференції є результатом наукових досліджень авторів з проблем розроблення концептуальних засад маркетингового інструментарію управління попитом на товари і послуги України

Increased winter drownings in ice-covered regions with warmer winters

Winter activities on ice are culturally important for many countries, yet they constitute a high safety risk depending upon the stability of the ice. Because consistently cold periods are required to form stable and thick ice, warmer winters could degrade ice conditions and increase the likelihood of falling through the ice. This study provides the first large-scale assessment of winter drowning from 10 Northern Hemisphere countries. We documented over 4000 winter drowning events. Winter drownings increased exponentially in regions with warmer winters when air temperatures neared 0 ̊C. The largest number of drownings occurred when winter air temperatures were between -5 ̊C and 0 ̊C, when ice is less stable, and also in regions where indigenous traditions and livelihood require extended time on ice. Rates of drowning were greatest late in the winter season when ice stability declines. Children and adults up to the age of 39 were at the highest risk of winter drownings. Beyond temperature, differences in cultures, regulations, and human behaviours can be important additional risk factors. Our findings indicate the potential for increased human mortality with warmer winter air temperatures. Incorporating drowning prevention plans would improve adaptation strategies to a changing climate.Funding was provided to SS by the Ontario Ministry of Research, Innovation and Science Early Researcher Award and York University Research Chair programme. Funding support for BAD was provided by Kempestiftelserna. AL was supported by Estonian Research Council Grant PSG 32. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Funding was provided to SS by the Ontario Ministry of Research, Innovation and Science Early Researcher Award and York University Research Chair programme. Funding support for BAD was provided by Kempestiftelserna. AL was supported by Estonian Research Council Grant PSG 32. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Citizen science shows systematic changes in the temperature difference between air and inland waters with global warming

Citizen science projects have a long history in ecological studies. The research usefulness of such projects is dependent on applying simple and standardized methods. Here, we conducted a citizen science project that involved more than 3500 Swedish high school students to examine the temperature difference between surface water and the overlying air (Tw-Ta) as a proxy for sensible heat flux (QH). If QH is directed upward, corresponding to positive Tw-Ta, it can enhance CO2 and CH4 emissions from inland waters, thereby contributing to increased greenhouse gas concentrations in the atmosphere. The students found mostly negative Tw-Ta across small ponds, lakes, streams/rivers and the sea shore (i.e. downward QH), with Tw-Ta becoming increasingly negative with increasing Ta. Further examination of Tw-Ta using high-frequency temperature data from inland waters across the globe confirmed that Tw-Ta is linearly related to Ta. Using the longest available high-frequency temperature time series from Lake Erken, Sweden, we found a rapid increase in the occasions of negative Tw-Ta with increasing annual mean Ta since 1989. From these results, we can expect that ongoing and projected global warming will result in increasingly negative Tw-Ta, thereby reducing CO2 and CH4 transfer velocities from inland waters into the atmosphere