Significance of reference observation in the evaluation of Secchi disk visibility on the example of lakes in the vicinity of Ełk
The method of measuring transparency of water environments using the Secchi disc is still applied, despite a certain level of subjectivity of obtained results. At present, it should be used as a supplement to more reliable methods of measuring the thickness of the euphotic zone. A serious drawback is the low informative value of isolated measurements of the transparency of water environments, representing different stages of cyclic annual variability. This is also confirmed by the summer visibility measurements in the waters of lakes near Ełk of 2003 and 2005. Reservoirs investigated twice were sometimes characterised by a significant diversity of the observed absolute values of the Secchi disc visibility in particular years. However, treating them as benchmark reservoirs makes it possible to determine relative relationships of optical properties among water environments of all the 21 lakes analysed then. They can be expressed in the form of an ordered sequence of reservoirs with increasingly better optical properties of water environments. The ordered sequence was verified on the basis of the research results of 2006. The observed stability of the position of the benchmark reservoirs with respect to each other makes it possible to abandon treating the observed isolated values of the Secchi disc visibility in other reservoirs as, out of necessity, representative ones of the investigated lakes. The knowledge of the values of scopes of the disc visibility in the waters of the benchmark lakes makes it possible to precisely estimate, against them, this value in less frequently investigated lakes.
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.
Jerzy Jańczak, Wojciech Maślanka and Kamil Nowiński
Causes of polytrophism of three lakes in the Wdzydze Landscape Park
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.