Water quality of a small headwater lake reflects long-term variations in deposition, climate and in-lake processes (original) (raw)
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Potential impacts of climatic changes on water quality in lakes
Human activities have caused the C0" concentration to increase steadily in the atmosphere of the Globe, the resulting "greenhouse" effect influencing potentially the future climate on global and regional scales alike. Advances have been registered in research into the meteorological and hydrological impacts of the greenhouse effect, whereas studies on water quality have barely started. Water quality can be influenced on many different ways. Higher water temperatures may result primarily in accelerated biological metabolic processes, but also changing the stratification, sediment nutrient release and ice conditions of lakes. The changes in the amount and distribution of precipitation will modify runoff conditions: in the Carpathian Basin a reduction is expected. Due to alterations in runoff, nutrient loads of non-point source origin and residence time of lakes will be modified, too. All the above factors may significantly influence eutrophication of standing waters. Higher C0" concentrations in the atmosphere may have also direct impacts on the chemical equilibrium processes of the inorganic carbon system of waters. It may entail increases in the salt content, especially for waters of typically Ca(HC0,),, character, which is the case for most of the shallow water bodies of Hungary, including Lake Balaton. The latter potential impact on the chemical composition of hard waters have been demonstrated on the basis of classical equilibrium equations, by assuming a twofold increase in the CO. level.
Recovery from acidification of lakes in Finland, Norway and Sweden 1990–1999
Hydrology and Earth System Sciences, 2001
Sulphate deposition has decreased by about 60% in the Nordic countries since the early 1980s. Nitrogen deposition has been roughly constant during the past 20 years, with only a minor decrease in the late 1990s. The resulting changes in the chemistry of small lakes have been followed by national monitoring programmes initiated in the 1980s in Finland (163 lakes), Norway (100 lakes) and Sweden (81 lakes). These lakes are partly a subset from the survey of 5690 lakes in the Northern European lake survey of 1995. Trend analyses on data for the period 1990-1999 show that the non-marine sulphate concentrations in lakes have decreased significantly in 69% of the monitored lakes. Changes were largest in lakes with the highest mean concentrations. Nitrate concentrations, on the other hand, were generally low and showed no systematic changes. Concentrations of non-marine base cations decreased in 26% of the lakes, most probably an ionic-strength effect due to the lower concentrations of mobile strong-acid anions. Acid neutralising capacity increased in 32% of the lakes. Trends in recovery were in part masked by large year-to-year variations in sea-salt inputs and by increases in total organic carbon concentrations. These changes were most probably the result of climatic variations. Nordic lakes, therefore, show clear signs of recovery from acidification. Recovery began in the 1980s and accelerated in the 1990s. Reductions in sulphur deposition are the major "driving force" in the process of recovery from acidification. Further recovery can be expected in the next 10 years if the Gothenburg protocol on emissions of acidifying pollutants is implemented.
The Holocene, 2019
During the Holocene, multiple thermal changes commonly occurred in the northern hemisphere. They are well-recorded in lakes with minimum human impact from the Arctic Circle area. The development of these lakes reflects ecological and climatic changes occurring from the formation of the lakes until present-day times. All environmental fluctuations affect biodiversity and are reflected in the number and composition of species. The goals of this study were to detect the ecological changes in a small Finnish lake using pollen, Cladocera and geochemical analyses. The research area is located within the northern zone of boreal coniferous forest and is the most sparsely populated region of Finland. The lake is located in Kuusamo uplands, E Finland, near the polar circle and over 20 km from the Russian border. Indicators of cold water were found only during the initial stage, after the 8.2 ka event and then the temperature was higher. Trophy was high at the beginning of the lake development...
Oceanological and Hydrobiological Studies, 2000
The national monitoring network of benchmark lakes consists of ten lakes situated in different Polish lakelands. They do not receive wastewater from point sources of pollution and their catchment areas are predominantly forested. Changes in their water quality should be natural or almost natural due to very low anthropogenic pressure. In the majority of the benchmark lakes the values of eutrophication parameters during the 1999-2004 period did not exceed 0.060 mg dm -3 P for total phosphorus or 10 μg dm -3 for chlorophyll a, and Secchi disc readings generally exceeded 2.5 m. Trend analyses in the majority of cases did not reveal significant changes in eutrophication parameters over time.
During recent decades the amounts of nutrients discharged to Finnish surface waters have markedly decreased. This has been achieved by considerable investments in water protection, which were made mainly to improve municipal and industrial wastewater purification. We investigated whether these water protection measures have decreased phosphorus and nitrogen concentrations in Finnish rivers and lakes. In addition, possible trends in chlorophyll a concentrations in lakes were studied. The data consisted of a total of over 68 000 monitoring results of 22 rivers and 173 lakes (or sub-basins of lakes) with different types of catchment areas. The study period covered the years 1975-2000 and the non-parametric Kendall Tau b and Seasonal Kendall tests were applied for detecting trends. Decreasing nutrient concentration trends were typical in many lakes and rivers earlier polluted by municipal and industrial wastewaters. Increasing nutrient concentration trends were common in smaller rivers and lakes receiving diffuse loading from agriculture. The results show that the investments directed towards wastewater purification have effectively improved the quality of Finnish inland waters. However, no clear effects of decreasing non-point loading were found. Thus, more effective measures should be directed towards decreasing non-point source loading. ᮊ
Long-Term Chemical Changes in Lakes
Advances in Chemistry, 1994
One of the best ways, and often the only way, to obtain long-term data on lake-water chemistry is by inference from stratigraphic remains of aquatic biota preserved in sediment cores. Techniques are available for making accurate inferences of a variety of historical water chemistry characteristics (e.g., pH, aluminum, total phosphorus, and salinity). Many groups of biota can be used, including diatoms, chrysophytes, chironomids, and Cladocera. Inference techniques are based on the strong relationships that exist between the contemporary distributions of taxa and water chemistry characteristics. Recent advances in paleolimnological protocols, taxonomy, interpretations of ecological data, computer technology, and development of new statistical and multivariate techniques allow inferences of ever-increasing accuracy and precision. In our view, canonical correspondence analysis and weighted averaging regression and calibration are currently the best techniques available for exploring relationships between biota and chemistry and for making quantitative inferences of water chemistry, respectively. Computer-intensive techniques, such as bootstrapping, are available to estimate errors of prediction associated with inferred values. M ANY ENVI RONMENTAL PROBLEMS that involve chemical characteristics of lakes could be understood and managed better if we knew background
Science of The Total Environment, 2003
The regional-scale response of Finnish headwater lakes to changes in acidifying deposition loads was studied using data from a national deposition monitoring network (19 stations), acidification monitoring lakes (163 lakes) and results of a statistically based national lake survey (873 lakes). Data from 1990 to 1999 were used for statistical trend analysis. A deposition model was used to assess changes in S and N deposition for the year 2010, assuming emission reductions according to two international agreements. The deposition of sulfate and H showed statistically q significant (Kendall-t, P-0.05) decreasing trends at nearly all deposition stations. For N compounds, nearly all slopes were negative, but rarely statistically significant. Sulfate concentrations have declined in all types of small lakes throughout Finland in the 1990s (significant decline in 64-85% of the lakes in three different lake regions), indicating a clear response to S emission reductions and declined sulfate deposition. Base cation concentrations decreased in both deposition and lake water, especially in southern Finland, but to a lesser extent than sulfate concentrations. The median slope of the trend for Gran alkalinity in lakes ranged between 0.98 and 2.1 meq l a. y1 y1 Some 1400 (27%) of Finnish headwater lakes of size 4-100 ha were estimated to show statistically significant increases in Gran alkalinity (recovery). No large changes were observed in the lake water TOC concentrations. The reduction in S deposition is the main driving factor for the lake acidification recovery process in Finland. Deposition model calculations showed that further large reductions in S deposition beyond the 1999 level are not likely to occur by the year 2010, particularly for southeastern Finland. The mean estimated S deposition change by 2010 for the three lake regions in Finland was only between y0.9 and y6.6% for the two policy scenarios (UNyECE Gothenburg protocol, EU NEC-directive), respectively. A slower acidification recovery of the lake ecosystems is, therefore, anticipated in the future.
Ambio, 2014
Long-term (1987-2012) water quality monitoring in 36 acid-sensitive Swedish lakes shows slow recovery from historic acidification. Overall, strong acid anion concentrations declined, primarily as a result of declines in sulfate. Chloride is now the dominant anion in many acid-sensitive lakes. Base cation concentrations have declined less rapidly than strong acid anion concentrations, leading to an increase in charge balance acid neutralizing capacity. In many lakes, modeled organic acidity is now approximately equal to inorganic acidity. The observed trends in water chemistry suggest lakes may not return to reference conditions. Despite declines in acid deposition, many of these lakes are still acidified. Base cation concentrations continue to decline and alkalinity shows only small increases. A changing climate may further delay recovery by increasing dissolved organic carbon concentrations and sea-salt episodes. More intensive forest harvesting may also hamper recovery by reducing...