Polish rivers, which make up 20% of the Baltic Sea's catchment area, transport a load of nitrogen and phosphorus compounds into the sea. Theoretically, this load should be strongly correlated with the amount of water flowing in those rivers. However, this is not the case, especially in terms of the phosphorus compounds, since most of them come from point source pollution. The outflow load is also significantly influenced by nonpoint source pollution from farmland, which is very difficult to quantify. About 50% of nitrogen and 30% of phosphorus appear to come from nonpoint source pollution. It is important to realize that the load from nonpoint source pollution also includes the load of phosphorus and nitrogen transformed by lakes. Only recently, however, has this issue been mentioned in the specialist literature. In Polish studies on lake balance this remains a marginal issue. A limited number of observations indicate that lakes are capable of both limiting and increasing the load (mainly from the bottom sediments). This article presents some data on this issue which suggest that the roles of lakes in the transformation of the load of biogenic substances may be significant, but diverse.
Circulation of biogenic substances in the Kamionka river-lake system Reservoirs in river-lake systems play a dominant role in the circulation of biogenic substances. Their evolutional transformations, consisting in accumulation of substances, results it their ultimate disappearance. However, at a given moment, the roles played by reservoirs are far more diverse - they accumulate, perform a transit role or supply the system with biogenic substances. The assignment of roles played in the system to reservoirs performed on the basis of data of 2006 was verified in 2007 with respect to the durability of their roles. Some of the lakes consistently accumulated biogenic substances. Their performing of this function in the system was facilitated by favourable morphometric conditions accompanied by strong pressure, exceeding the value determined for critical load. A tendency of supplying the system by other lakes was visible when they were charged with a lower load than the critical values for phosphorus load. The reservoirs then utilised the opportunity to discharge a part of biogenic substance present in them, partially of internal origin.
Water-level fluctuations are among the primary factors determining the functioning of lakes. The volume to which lake basins are filled with water is of major importance to the courses of many processes and phenomena. A particular amount of water in a lake, and water-table stability, are also important from the point of view of human activity, as these elements help determine the quantity and accessibility of the water resources lakes have to offer, and therefore the possibilities for them to be used by different branches of the economy, e.g. industry, agriculture or tourism. The work detailed here is thus a presentation of trends as regards water-level fluctuations in 16 lakes in Poland, over the period 1956–2015. The study results, obtained for the first time in relation to such a long time scale and extending to around a dozen lakes, aim to point to the scale and direction of water-level fluctuations in times of the intensive transformation of the natural environment. They were obtained by reference to water-level observations made by the Institute of Meteorology and Water Management – National Research Institute (IMiGW-PIB). Specifically, data referring to the (November-October) hydrological year were analysed for trends as regards mean annual water levels using the Mann-Kendall test. Results point to major variability in the courses noted for these levels over the analysed multiannual period. Nevertheless, three overall situations could be designated from within the group of cases analysed, i.e. increase, decrease or lack of a trend. The first group includes Lakes Sławskie, Jamno, Łebsko, Nidzkie, and Studzieniczne (where increases were statistically significant at p=0.05); the second, Lakes Ostrzyckie and Ełckie (decreases significant at p=0.05); and the last group all remaining lakes, i.e. Charzykowskie, Jeziorak and Rajgrodzkie, Biskupińskie, Drwęckie and Białe, Gopło, Roś, and Wigry. It was, however, noted that in many cases analysed periods of alternating increase and decrease in water level were to be observed. The causes of such fluctuations were complex, but inter alia reflected droughts of several years’ duration, periods featuring higher-than-average precipitation, and local conditions. In general, water-level fluctuations in lakes result from natural and anthropogenic factors determining the hydrological conditions in catchments. And in the context of the lakes considered here, the courses of water-level fluctuations were mostly a reflection of local, rather than wider climatic conditions – a fact i.a. illustrated by the lack of cohesive regional designations. The situation is different from that of, for example, the thermal or ice regimes of Polish lakes, in relation to which observed similarities in properties are seen to be determined mainly by climatic factors. Information of this kind may be of key importance to the (quantitative and qualitative) management of water resources in the context of the climate change being observed currently.
Abstract:In the lakes Cheb and Słupino, located in the Wdzydze Landscape Park the quality of waters has been deteriorating in recent years. In the hydrologic year 2009 the quality of water was examined three times. Monthly measurements on the lake inflows and outflows were carried out 12 times to determine biogenic loads. In 2010 the supplementary measurements of biogenic loads were taken in the streams five times. According to Vollenweider's criterion, the loads of nitrogen and phosphorus compounds are too big, the heaviest to Lake Cheb. The discharge from the new sewage treatment plant is directed by the inflows into this lake. A similar situation takes place in the inflow to Lake Schodno. Paradoxically, in some catchments the construction of the sewage treatment plant may result in the deterioration of lake water quality.
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