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.
Dariusz Borowiak, Kamil Nowiński, Jacek Barańczuk, Włodzimierz Marszelewski, Rajmund Skowron and Adam Solarczyk
Relationship between areal hypolimnetic oxygen depletion rate and the trophic state of five lakes in northern Poland
The oxygen content in a lake is a fundamental factor in lake ecology. In stratified lakes, deep waters are isolated from the atmosphere for several months during the summer; therefore, oxygen (substantially consumed by biological and chemical processes at this time) cannot be replaced before the autumnal mixing period. Hypolimnetic oxygen depletion has been considered an indicator of lake productivity since the early twentieth century. Many recent studies have been in opposition to this view by showing that the areal hypolimnetic oxygen depletion rate (AHOD) is poorly correlated with seston biomass and/or phosphorus concentration. The objective of this study is to show relationships between the mean values of total phosphorus (TP), total nitrogen (TN), chlorophyll a, and water transparency (Secchi disk depth, SDD) during the thermal stratification formation period and the AHOD rate. Hypolimnetic oxygen conditions in five dimictic lakes in northern Poland were examined in 2009 and 2010. Two of them were studied in the previous year. Monthly oxygen profiles taken from April to August, midsummer temperature profiles, and morphological data of the lakes were used to determine the AHOD rate. Standard water quality parameters such as concentrations of chlorophyll a, TP, and TN, as well as water transparency measured at the same time were used to calculate the trophic state indices (TSI) according to the Carlson-type formulas. On the basis of the collected data it is shown that AHOD is highly correlated with the TSI value for chlorophyll a, and poorly correlated with the TSI values for water transparency and phosphorus content. The best correlation between AHOD and TSI has been found for chlorophyll a (r2=0.702; p<0.001), as well as for overall TSI, determined by averaging separate component indices (r2=0.826; p<0.000). No correlation was found between AHOD and total nitrogen concentration. The research also confirmed previous observations, which pointed to a significant role of the hypolimnion depth in increasing oxygen deficits.
Katarzyna Grabowska, Dariusz Borowiak and Kamil Nowiński
The article presents the results of experimental research on evapotranspiration and transpiration of a common reed bed. The study was conducted in 2014–2015 on Lake Raduńskie Górne (Kashubian Lakeland) in the summer half-year from 1 May to 31 October. In the experiment two sets of standard evaporimeters GGI-3000 were used. One of the evaporimeters was filled with water, while the second additionally contained common reed. During the experiment medium reed bed density was 240 shoots per square metre. The results of the study showed that during the research period the average daily common reed transpiration was 3.9 mm, and the daily maxima reached 12.1–12.5 mm. Average monthly transpiration totals ranged from 42.8 (October) to 208.5 mm (August). During the growing season, the loss of water to transpiration reached 872–971 mm. The average transpiration rate, determined in the conditions of already well developed reed bed (June-September), was 1.83 dm3 m−2 d−1. The values of the ratios Th/EO and ETh/EO, determined during the experiment, were within the ranges reported in most previous research. The average ratio Th/EO was 1.6, and the ratio ETh/EO was 2.0. These values indicate that during the vegetation period common reed transpiration is higher by 60% from open water evaporation, and the total water losses from the common reed bed to evapotranspiration are twice as high as water loss in open water evaporation.
Dariusz Borowiak, Kamil Nowiński and Katarzyna Grabowska
The results of the latest bathymetric survey of 21 lakes in the Suwałki Landscape Park (SLP) are presented here. Measurements of the underwater lake topography were carried out in the years 2012–2013 using the hydroacoustic method (sonar Lawrence 480M). In the case of four lakes (Błędne, Pogorzałek, Purwin, Wodziłki) this was the first time a bathymetric survey had been performed. Field material was used to prepare bathymetric maps, which were then used for calculating the basic size and shape parameters of the lake basins. The results of the studies are shown against the nearly 90 year history of bathymetric surveying of the SLP lakes. In the light of the current measurements, the total area of the SLP lakes is over 634 hm2 and its limnic ratio is 10%. Lake water resources in the park were estimated at 143 037.1 dam3. This value corresponds to a retention index of 2257 mm. In addition, studies have shown that the previous morphometric data are not very accurate. The relative differences in the lake surface areas ranged from –14.1 to 9.1%, and in the case of volume – from –32.2 to 35.3%. The greatest differences in the volume, expressed in absolute values, were found in the largest SLP lakes: Hańcza (1716.1 dam3), Szurpiły (1282.0 dam3), Jaczno (816.4 dam3), Perty (427.1 dam3), Jegłówek (391.2 dam3) and Kojle (286.2 dam3). The smallest disparities were observed with respect to the data obtained by the IRS (Inland Fisheries Institute in Olsztyn). The IMGW (Institute of Meteorology and Water Management) bathymetric measurements were affected by some significant errors, and morphometric parameters determined on their basis are only approximate.
Dariusz Borowiak, Katarzyna Bociąg, Kamil Nowiński and Magdalena Borowiak
Maximum depth of colonization (zC) and total area covered by a population of Lobelia dortmanna, as well as underwater light regime were studied in 25 soft water lobelia lakes in north-western Poland. Variations in underwater light conditions among the lakes were described by Secchi disc depths (zSD), and by attenuation coefficients of irradiance within photosynthetically active radiation range (Kd,PAR), and euphotic zone depths (zEU) derived from photometric measurements conducted twice a year (in midspring and midsummer) during the period 2014–2015. Maximum depth of colonization of water lobelia ranged from 0.1 to 2.2 m (median zC = 0.8 m; mean zC = 1.0 m). Nine lakes showed the relative coverage of the littoral zone (RCLZ) by L. dortmanna to be greater than the mean value, which was 4.8%. Studies showed that light requirements of water lobelia increase when the maximum depth of colonization also increases. This pattern could be partially related to the greater energy needs of deeper growing individuals due to enlarged seed production and their incubation, and for the creation of much heavier inflorescences. Assessment of the light requirements of L. dortmanna along the depth gradient indicates that relative irradiance (percentage of subsurface irradiance of PAR) should be at the level of: (i) 47–50% (annual total of quantum irradiance 3083–3280 mol m−2 yr−2) for plants growing within a depth range of 2.0–2.5 m; (ii) 44–47% (2886–3083 mol m−2yr−1) for plants growing within a depth range of 1.5–2.0 m; (iii) 41–44% (2690–2886 mol m−2yr−2) for plants growing within a depth range of 1.0–1.5 m; and (iv) 34–41% (2230–2690 mol m−1 yr−1) for those growing in the littoral zone at a depth of between 0.5 and 1.0 m. In average conditions in the Pomeranian lakes, the maximum depth of colonization by L. dortmanna accounts for approximately a third of the Secchi disc depth and a fifth of the depth of the euphotic zone with irradiance of PAR at zC equal to about 43% of subsurface irradiance. It has also been demonstrated that the light factor is a crucial one that limits the absolute maximum depth of lobelia population occurrence in Pomeranian lakes. The cleanest and most transparent lakes of this region have light attenuation coefficients (Kd,PAR) within the range of 0.35–0.42 m−1, which corresponds to the maximum colonization depths of 1.8–2.2 m.