189 research outputs found
Synchrony in relationships between the North Atlantic Oscillation and water chemistry among Sweden's largest lakes
The North Atlantic Oscillation (NAO) is commonly presented as an easy and reliable index that can be used to study climatic effects on aquatic ecosystems. Here, the NAO winter index (NAO(w)) was applied to determine effects of winter climate changes on 13 water chemical variables measured monthly at 16 sites in Sweden's three largest lakes (Vanern, Vattern, and Malaren). The NAO(w) strongly affected meteorological, physical, and consequently also chemical conditions. Significant relationships were numerous in Sweden's three largest lakes, but they exhibited little agreement among lakes and even across a lake. Synchronous relationships between the NAO(w) and water chemistry among lake sites were restricted to variables closely linked to surface-water temperature (i.e., reactive silica and pH in May). The weaker the association of a lake variable with water temperature, the weaker the mean NAO(w) signal on the variable over the 16 lake sites. The results of this study might facilitate the prediction of lake ecosystem responses to future changes in the weather over a large region
Nonlinear temperature response of lake ice breakup
A uniquely comprehensive set of four decades of ice breakup data from 196 Swedish lakes covering 13degrees of latitude (55.7degrees N to 68.4degrees N) shows the relationship between the timing of lake ice breakup and air temperature to be an arc cosine function. The nonlinearity inherent in this relationship results in marked differences in the response of the timing of lake ice breakup to changes in air temperature between colder and warmer geographical regions, and between colder and warmer time periods. The spatial and temporal patterns are mutually consistent, suggesting that climate change impacts on the timing of lake ice breakup will vary along a temperature gradient. This has potentially important ramifications for the employment of lake ice phenologies as climate indicators and for the future behavior of lacustrine ecosystem
Geographic and tourist position of Ternopil region as a factor of tourism development
The quantity of carbon dioxide (CO2) emissions from inland waters into the atmosphere varies, depending on spatial and temporal variations in the partial pressure of CO2 (pCO2) in waters. Using 22,664 water samples from 851 boreal lakes and 64 boreal streams, taken from different water depths and during different months we found large spatial and temporal variations in pCO2, ranging from below atmospheric equilibrium to values greater than 20,000 μatm with a median value of 1048 μatm for lakes (n = 11,538 samples) and 1176 μatm for streams (n = 11,126). During the spring water mixing period in April/May, distributions of pCO2 were not significantly different between stream and lake ecosystems (P > 0.05), suggesting that pCO2 in spring is determined by processes that are common to lakes and streams. During other seasons of the year, however, pCO2 differed significantly between lake and stream ecosystems (P < 0.0001). The variable that best explained the differences in seasonal pCO2 variations between lakes and streams was the temperature difference between bottom and surface waters. Even small temperature differences resulted in a decline of pCO2 in lake surface waters. Minimum pCO2 values in lake surface waters were reached in July. Towards autumn pCO2 strongly increased again in lake surface waters reaching values close to the ones found in stream surface waters. Although pCO2 strongly increased in the upper water column towards autumn, pCO2 in lake bottom waters still exceeded the pCO2 in surface waters of lakes and streams. We conclude that throughout the year CO2 is concentrated in bottom waters of boreal lakes, although these lakes are typically shallow with short water retention times. Highly varying amounts of this CO2 reaches surface waters and evades to the atmosphere. Our findings have important implications for up-scaling CO2 fluxes from single lake and stream measurements to regional and global annual fluxes
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
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
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
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
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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
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