Causes of Lake Area Changes in Poland

Transcription

1 June, 2011 J. Resour. Ecol (2) DOI: /j.issn x Journal of Resources and Ecology Vol.2 No.2 Report Causes of Lake Area Changes in Poland Adam CHOIŃSKI 1, Agnieszka ŁAWNICZAK 2, Mariusz PTAK 1 and Leszek SOBKOWIAK 1* 1 Institute of Physical Geography and Environmental Planning, Adam Mickiewicz University, Poznań, Poland; 2 Chair of Ecology and Agricultural Environment Protection, Poznań University of Life Sciences, Poznań, Poland; Abstract: The northern part of Poland is occupied by numerous lakes formed during the last glaciation as a result of the Scandinavian ice sheet. Studies carried out in the lake district areas show progressive reduction of the surface area of the lakes, which leads to their eventual disappearance. The paper discusses the degree of the observed changes and points out main natural and anthropogenic factors influencing changes of lake area in Poland, including climate change, depth of lake basins, biomass growth, deforestation, hydrotechnical works, use of fertilizers and discharge of wastewater. Key words: Northern Poland; lake districts; lake area changes; natural factors; anthropogenic factors 1 Introduction Among the areal hydrographic objects lakes deserve special attention. They play a vital role in the continental part of the hydrological cycle (e.g., precipitation, runoff, retention), they are also important for biodiversity and economy. The growth of many sectors of economy, as energy industry, agriculture, tourism, etc. would not be possible without the proximity of water; for that reason in areas devoid of lakes artificial reservoirs are often created. Also the immeasurable, aesthetic values of lakes diversifying the landscape have to be pointed out. The presence of most lakes in Poland, as in many other parts of Europe, results from the Scandinavian ice sheet activity during the last glaciation (Fig. 1). Lake basins are subject to constant evolution. Its stages can be defined by characteristic morphometric parameters of the individual lake or physico-chemical properties of its water. Every lake, as a concave geomorphological form, is at a certain point of that evolution, leading to the ultimate disappearance of the lake. The pace and direction of these changes may differ, since they depend on a number of factors, including climate, genetic type of lake basin, land use patterns, degree of anthropopression and other. Lakes are relatively short-lived elements of the landscape. Choiński (2007) defined the age of lakes in Poland at years and predicted their lifetime, assuming the current pace of shallowing, for just few hundred years. Fig.1 Percentage of lake cover in Europe (after Kmicikiewiczowa 1965). 1: 0 0.5%, 2: %, 3: %, 4: %, 5: %, 6: > 10%, 7: Ice age maximum glaciation Received: Accepted: * Corresponding author: Leszek SOBKOWIAK. lesob@amu.edu.pl.

2 176 2 Overview of the research The beginnings of limnological studies in Poland can be traced back to , when Polish researcher Stanisław Staszic carried out preliminary studies on lakes in the Tatra Mountains in the southern part of the country. In the 1930s cartographers of the Military Institute of Geography in Warsaw drew their bathymetric plans (Choiński ). Galon (1954) and Kalinowska (1961) first paid attention to the processes of disappearance of lakes in Poland. Tomaszewski (1974) analysed the influence of vegetation and overgrowing processes, while Babiński (1988) of drainage works on shrinkage of lakes in the Great Poland Lowland. Glazik (1988), Superson and Szwajgier (2003), Marszelewski and Adamczyk (2004) as well as Choiński (2009) studied natural and anthropogenic caused leading to changes in the area of lakes and wetlands in selected parts of Northern Poland. In turn, Borowiak (2002) pointed out the role of rock debris in morphometric changes of lakes in the Polish Tatra Mountains. Journal of Resources and Ecology Vol.2 No.2, 2011 that phenomenon in the years is shown in Fig Causes of changes in lake area Causes of the detected changes should be seen both in natural factors and human activity. 3 Changes in lake area in Poland Lakes in Poland cover nearly ha, that is approximately 0.9% of the country s area (Choiński 2006) and they are located mainly (95.9%) in its northern part, forming three geographical regions (lake districts): the Pomeranian Lake District, the Masurian Lake District and the Great Poland-Kuyavian Lake District (Table 1, Fig. 2). Generally, lakes in Poland show the tendency to decrease both in area and number. On the basis of analysed all Polish lakes with an area 1 ha (as of 1975), Choiński (2006) defined the scope of these changes. The data were compared with the Catalogue of lakes in Poland (1954), containing, among others, the area of lakes measured in the 1920s: over that period the total area has shrunk from ha to ha (11.62%), while the number of lakes decreased from 9296 to 7081 (23.82%). Within the separated three lake districts these changes proceed at different rate: between 1920 and 1975 the largest decline in the surface area of lakes was observed in the Great Poland-Kuyavian Lake District (11.62%), then (9.98%) in the Masurian Lake District, while the lowest (9.69%) in the Pomeranian Lake District. The spatial distribution of Fig. 2 Distribution of lakes in Poland per 100 km 2 of area [in %] (after Majdanowski 1954). decrease by 0% 5% decrease by 5% 10% decrease > 10% growth areas water divides of the 1st rank lake district boundary Fig. 3 Changes in lake area in Poland in (after Choiński 2007). A: the Pomeranian Lake District, B: the Masurian Lake District, C: the Great Poland-Kuyavian Lake District Table 1 Basic data on lake districts in Poland. Great Poland- Lake district Pomeranian Masurian -Kuyavian Poland* Area (km 2 ) Lake coverage (%) Number of lakes Total area of lakes (ha) Total capacity of lakes (km 3 ) *: Including area not covered by last glaciation. Source: Choiński 2006.

3 Adam Choiński, et al.: Causes of Lake Area Changes in Poland 177 Among natural factors the most important role play: climate fluctuations, water inflow and the associated sedimentation of clastic debris, depth of lake basins, biomass growth, chemical precipitation, deforestation caused by pests, and also local factors influencing the incorporation of lakes into the hydrographic network. In turn, the most important anthropogenic factors are: deforestation, hydrotechnical works (including drainage), intensity of agriculture and wastewater discharges within the lake catchment that affect the lake eutrophy. Some regularities of climate change have been observed over centuries. They are determined by astrophysical processes occurring in cycles; it can be concluded that those changes take the form of sine, as for example the sunspots with the 11-year cycles, which affect the distribution of rainfall and temperature. Water inflow plays one of the most important roles in the process of changes in lake area. Main sources of water input include: precipitation onto the lake surface, runoff carried by rivers, surface and groundwater flows. Precipitation is the primary factor. The average annual precipitation in Poland is about 600 mm per year, however, its spatial distribution is not uniform: the lowest values for the analysed lake districts are recorded in their southern part (500 mm per year), which is the area of the largest water deficit in Poland. In the Great Poland-Kuyavian Lake District, where the fastest decrease of lake area is observed, the average amount of precipitation is 530 mm per year (Table 2). Unfavorable water balance in the Great Poland-Kuyavian Lake District is additionally enhanced by high evaporation from the water surface. According to Jurak (1987), who determined its average values for Poland, the most intense evaporation ( mm) is in the central part of the country, including a large part of the above-mentioned lake district. Consequently, the volume of the direct precipitation onto the lake is there much lower than the losses caused by evaporation from the lake surface. In other parts of Poland the vertical water exchange is at least balanced or there is a surplus on the revenue side: for example, in the coastal regions the annual average rainfall is about 650 mm, while the annual average evaporation is around 550 mm. Moreover, studies on climate change carried out by Boryczka (1998) show that in the first half of the 21st century the annual average precipitation in Poland will remain at similar level, yet, it will be accompanied by increasing average temperatures, that in turn will accelerate evaporation. An increasing trend of air temperature has been already recorded for instance at Poznań station (1.1 per 100 years), Kraków station ( ) (0.8 per 100 years) and Warsaw station ( ) (0.66 per 100 years). Lange (1993) states that the longevity of a lake basin is proportional to the share of parts relatively isolated from the lake surface. As a result, the slowest pace of changes is typical for deep lakes with high share of hypolimnion. That relationship can be described by the average depth of the lake, which determines, among others, how quickly the plant succession may proceed. This means that the lake is shallower, the sooner the succession proceeds, leading to shrinkage of the lake basin. Consequently, the biomass growth is also accelerated. Among the investigated lake districts, the lowest value of the average depth, observed in the Great Poland-Kuyavian Lake District, is the result of the long-lasting levelling processes, since that area was at the earliest revealed by the Scandinavian ice sheet. Ptak (2010) defined statistical relationship between the disappearance of the lakes and their average depth. According to his calculations, the correlation coefficient for 562 lakes in Poland in the many years period is 0.22; the minus sign indicates that the degree of lake area reduction is inversely proportional to their average depth. The rate of changes of the lake area is also determined by lake openness. That parameter has a threefold significance: it influences the degree of water level oscillations, the supply of debris and the volume of primary production responsible for the deposition of nutrients. Open lakes in Poland have relatively small Table 2 Selected natural and anthropogenic factors influencing changes of lake area in Poland. Lake District Great Poland Factor Pomeranian Masurian -Kuyavian Precipitation 1) (mm) Average lake depth (m) Percentage of open lakes (%) Forests (%) Consumption of fertilizers 2) (kg ha -1 ) Discharge of fertilizers into surface water 2) (10 6 m 3 ) 1) Average values for ; 2) Average values for , based on: the Statistica Yearbook of Voivodeships Source: Own calculations.

4 178 fluctuations of water level (up to 50 cm). The amplitudes are higher for other types of lakes and may even exceed 100 cm. Open lakes are recipients of both autochthonic and allochthonic matter. There is a relationship: the higher the percentage of open lakes, the faster disappearance of lakes (the Great Poland-Kuyavian Lake District 56.0%, the Pomeranian Lake District 37.1%). Lakes are also producers of biomass within their own basins. The volume of the biomass production depends on the eutrophic type of the individual lake. The accumulation of allochthonic and autochthonic material results in shallowing and the ultimate disappearance of lakes. This can be clearly seen in particular in shallow bays, which in a relatively short time become asylums for new plant species. These parts of the lake basin quickly change into land, significantly reducing the area of the lake. Such a situation has been observed in the Kaliszańskie Lake (Fig. 4) located in the Great Poland-Kuyavian Lake District. The lake is surrounded by fields a typical land use pattern of the lake districts in Poland. Between 1890 and 2000 the shallowing of the bay and the subsequent plant succession in the southern part of that lake resulted in the reduction of its area by 17.4%. Assuming the continuation of that trend, the complete disappearance of the Kaliszańskie Lake may occur within about 500 years. It has to be noted that the pace of the lake basin shallowing may be several times higher than the changes in the lake area (Choiński and Ptak 2009). Besides natural factors, human activity plays an increasing role in changes in lake area in Poland. The beginnings of growing human impact can be associated with the transition from the nomadic-hunting to the agricultural lifestyle and the related changes in the Journal of Resources and Ecology Vol.2 No.2, 2011 environment through deforestation, development of fields, etc. Along with those changes a number of unintended processes, derived from actions initiated earlier took place. Human impact on the environment, originally marginal, with each epoch (bronze, iron, steam engine) began gaining momentum. Also the approach of man himself to those actions changed: they become deliberate and precise (draining of wetlands, damming of rivers and other). Man became a new source of environmental changes, including those in lakes. Two lakes: Włókna and Brzeźno, located in the Great Poland-Kuyavian Lake District may serve as a good example of the result of human interference in water relations. Due to construction of fish breeding ponds on the nearby Mała Wełna River the water level of the lakes between 1888 and 1998 fell by more than 1 m, while their total area decreased by over 20%. This led to the separation of one body of water from another and changes in the course of the coastline (Fig. 5). The most visible through the centuries is the reduction of forest areas. Studies carried out by Gutry-Korycka (1993) show that from the 10th to the mid-20th century the forest area in Poland decreased by about 60%. Yet at the end of the 18th century forests occupied about 38% of the territory of Poland, while now about 28%. Water circulation within the forest is similar to the natural, undisturbed by man. Hence, from the hydrological point of view, it is important that the watershed had possibly the highest percentage of forest area. In the light of these data, the most favourable conditions are in the Pomeranian Lake District (33.2%), where the relatively lowest percentage of disappearing lakes (9.69%) has been recorded. Hydrotechnical works are another very important Fig. 4 Changes in the shoreline of the Kaliszańskie Lake ( N, E) between 1890 and 2000 (black indicates the extent of the water surface reduction). Fig. 5 The division of one reservoir into two separate lakes as a result of reduction of the lake area between 1888 and 1998 ( N, E). Photo: M. Ptak.

5 Adam Choiński, et al.: Causes of Lake Area Changes in Poland 179 factor influencing changes in lake area in Poland. While the creation of reservoirs has a positive effect on the phenomenon in question, the regulation of rivers significantly accelerates the disappearance of lakes. The most often implemented in Poland hydrotechnical works consisted of straightening of the river channels for shipping, which accelerated the outflow from the watershed. Increase in the longitudinal fall of rivers accelerated the outflow of water from open lakes, which resulted in the decrease of their area (Kaniecki 1997). Agricultural land improvement (amelioration) includes measurements aimed to control water circulation in order to use the area for agriculture. They are: collection of water in reservoirs, drainage, etc. The first works on the drainage of the Great Poland Lowland was started in the late 18th century and ended in the mid-19th century (Kaniecki 1991). As a result, the water level of Lake Gopło was lowered by 2.7 m, while many, mainly smaller lakes completely disappeared. In that way areas were converted into grasslands. At present agriculture plays a fundamental role in the processes of disappearance of lakes in Poland. Intensification of that sector of the economy, aiming at an increase of productivity, enforces the use of synthetic fertilizers, which through surface flow enrich surface water in nutrients (nitrogen and phosphorus compounds). Equally serious are the risks posed by wastewater discharges, both industrial and municipal. As a result, an adverse eutrophic growth (eutrophication) is observed. Eutrophication is a natural process, however, in recent decades it has been greatly intensified by human activity (Fig. 6). The major adverse effects of eutrophication include reduction in water transparency and algal blooms contributing to the extinction of aquatic life and the Fig. 6 The increase in eutrophy of water as a result of growth (on a global scale) of quantity of the total phosphorus loads to water (Σ) (after Kajak 2001). N.a.: natural area sources; A.a.: anthropogenic area sources; A.p.: anthropogenic point sources Table 3 Tolerable and dangerous loads of nitrogen and phosphorus. Average lake Load (g m -1 y -1 ) depth (m) Tolerable Dangerous N P N P Source: Kajak formation of oxygen deficits (including the total lack of oxygen). Kajak (2001) on the basis of research on eutrophication on a global scale defined the approximate amounts of eutrophying substances, which pose no threat to the lake (i.e. lake is able to neutralize them). The data are summarized in Table 3. Release of 1 kg of phosphorus into water increases the weight of the plankton by 1 ton (Kajak 1979). This process initiates a drastic acceleration of the biomass growth in the reservoir, which in turn leads to an accelerated growth of lake deposits and results in shallowing and eventual disappearance (terrestialisation) of the lake basin. Therefore, reduction in the inflow of the nutrients into the lake would have resulted in the slowdown of the abovementioned changes. Churski (1993) concludes that at present human activity poses serious threat to all lakes in Poland, especially shallow and polymictic ones located in the agricultural and built-up zones. It should be noted that despite initiated in Poland in the 1990s economic transition and the associated significant reduction of human influence on the lakes (reflected in decrease in quantity of wastewater discharged into the lakes and used fertilizers), a negative process of disappearance of lakes is still observed, as it has been proved by the results of studies on individual lakes and their groups. The main reason of these changes is a huge amount of nutrients deposited in the sediments. They are a source of internal feeding, which will remain active for the next dozen or even several dozen years. 5 Summary Disappearance of lakes is a very complex process that depends on a number of overlapping factors; these outlined in the paper refer to the separated at the macro scale geographical regions (lake districts) in Poland. Since the response of every lake to the changes in its catchment is different, detailed studies on causes of that phenomenon should be carried out at a scale of individual lake basins and their catchments. However, such studies would be

6 180 complicated and time-consuming. Consequently, at the initial stage of the research information on the driving forces of the observed changes should be obtained. Finally, in has to be mentioned that over the last few years a number of measures have been taken to slow down the process of disappearance of lakes in Poland. Examples include programs launched by the local authorities, aiming to protect lakeshores and reduce eutrophication through improvement of water quality. Further actions should also focus on the inhabitants in order to raise their awareness of human impact on the lakes. References Babiński Z Influence of melioration on changes of water level and area of Lake Pniewite. In: Churski Z (ed.). Natural and anthropogenic changes of lakes and marshes in Poland. Toruń: UMK. (in Borowiak D Changes in the morphometry of the basin of Lake Czerwony Staw Gąsienicowy Zachodni caused by debris flow. Limnological Review, No. 2. Boryczka J Changes in the Earth s climate. Warsaw: Dialogue Academic Press. (in. Catalogue of lakes in Poland Polish Academy of Sciences, Institute of Geography. Geographical Documentation. Warsaw. (in Choiński A Catalogue of lakes in Poland. Poznań: Wydawnictwo Naukowe UAM. (in Choiński A Ice phenomena on Lake Morskie Oko in the Tatra Mountains. Folia Geographica, Series Geographica-Physica, 37-38: (in Choiński A Physical limnology of Poland. Poznań: Wydawnictwo Naukowe UAM. (in Choiński A Changes in the area of lakes from the Obra River drainage basin taking place from the beginning of the 19th century. Limnological Review, 9 (4): Choiński A, M Ptak Lake Infill as the Main factor Leading to Lake s Disappearance. Polish Journal of Environmental Studies. 18 (3): Churski Z Tendencies of changes of lakes and marshes. In: I. Dynowska (ed.). Changes of water relations in Poland as a result of natural and anthropogenic processes. Kraków. (in Galon R Preliminary information on disappearance of lakes in Poland. Przegląd Geograficzny. 26(2): (in Journal of Resources and Ecology Vol.2 No.2, 2011 Glazik R Natural and anthropogenic changes of area of lakes and marshes in the western part of the Plock Basin. In: Churski Z (ed.). Natural and anthropogenic changes of lakes and marshes in Poland. Toruń: UMK. (in Gutry-Korycka M Influence of different forms of economic activity on the water cycle. In: Dynowska I (ed.). Changes of water relations in Poland as a result of natural and anthropogenic processes. Kraków: Polish Academy of Sciences. (in Jurak D Evaporation from water surface. In: J. Stachy (ed.). Hydrological Atlas of Poland. Vol. I. Warsaw: Institute of Meteorology and Water Management, Geological Publishing House. (in Kajak Z Eutrophication of lakes. Warsaw: PWN. (in Kajak Z Hydrobiology-Limnology. Warsaw: PWN. (in Kalinowska K Disappearance of glacial lakes in Poland. Przegląd Geograficzny, 33 (3): (in Kaniecki A Problems of drainage of the Great Poland Plain in the last 200 years and changes of water relations. In: Protection and rational use of water resources in the agricultural areas of the Great Poland region. Poznań. (in Kaniecki A Influence of the 19th century hydrological land ameliorations on changes of water level. In: Choiński A (ed.). Influence of anthropopression on lakes. Poznań: Homini Publishing House. (in Kmicikiewiczowa S Percentage of lake cover in Europe. Czasopismo Geograficzne, 36 (4): (in Lange W Lakes as objects of geographical study. In: Lange W (ed). Methods of physico-limnological studies. Gdańsk: University of Gdańsk. (in Majdanowski S Lakes in Poland. Przegląd Geograficzny, 26: (in Marszelewski W, A Adamczyk Changes in the Area of the Masurian Lakes in the Light of the Cartographic Materials at the scale 1: Limnological Review, 4: Ptak M Changes of lake density in the lower and middle Warta River basin since the 19th century (manuscript). Adam Mickiewicz University, Institute of Physical Geography and Environmental Planning, Poznań. (in Statistical Yearbook of Voivodeships Warsaw: GUS. (in Superson J, W Szwajgier Natural and anthropogenic conditioning of the changes of the shoreline of Brudno, Brudziec and Płotycze lakes (the Łęczna Włodawa Lake District). Limnological Review, 3: Tomaszewski H Vegetation and overgrowing processes of the Gostynin lakes. Notatki Płockie, 2. (in 波兰湖泊面积变化因素 Adam CHOIŃSKI 1, Agnieszka ŁAWNICZAK 2, Mariusz PTAK 1, Leszek SOBKOWIAK 1 1 亚当密茨凯维奇大学自然地理与环境规划研究所, 波兹南 , 波兰 ; 2 波兹南大学生命科学学院生态学与农业环境保护研究室, 波兹南 , 波兰 ; 摘要 : 波兰北部有众多斯堪的纳维亚冰盖冰期形成的湖泊 通过湖泊区的研究, 发现湖泊面积在逐渐减少, 甚至导致消失 本文对变化的程度进行了观测, 指出影响波兰湖泊面积变化的主要自然与人为因素, 包括气候变化 湖盆深度 生物量增长 森林砍伐 水利工程建修 农药利用和排污等 关键词 : 波兰北部 ; 湖泊地区 ; 湖泊面积变化 ; 自然因素 ; 人为因素