Search Results (7)

Eutrophication process and phytoplankton primary productivity have intensified in continental aquatic ecosystems because of climate change. As a consequence, the proliferation of potentially toxic cyanobacteria is increasing in frequency, magnitude, and duration. For water sources used in public supply, this growth represents an ecological risk to ecosystems and human health. From October 2021 to February 2022, integrated samples of surface water were obtained from 11 reservoirs in São Paulo State, Brazil (Jaguari, Jacarei, Atibainha, Paiva Castro, Rio Grande, Guarapiranga, Barra Bonita, Bariri, Broa, Salto Grande, and Itupararanga). Limnological variables were obtained using the Troll 500 probe, in addition to depth, turbidity (Tur), chlorophyll a (Chla), and phycocyanin (Phy) concentrations (Turner C3 probe). In the laboratory, chlorophyll-a concentrations (ChlaABS) were analyzed. Phytoplankton biovolume (Utermöhl method) was estimated. The concentrations of microcystins (MCs) and saxitoxins (STXs) were analyzed with Beacon kits, in ELISA microplate reader. For the studied reservoirs, the Secchi disc water transparency ranged from 0.6 to 2.3 m. The average values of water temperature, electrical conductivity, pH, and dissolved oxygen were, respectively, 24.8 °C, 162.9 µS/cm, and 8.4 and 9.5 mg/L. For Tur, Chla, Phy, and ChlaABS, ranged from 1.86 to 24.6 NTU, 3.3 to 105.1 µg/L, 12.4 to 445.2 µg/L, and 4.2 to 84.9 µg/L, respectively. Cyanobacteria was the more representative phytoplankton class in biovolume, from 0.07 to 51.7 mm³/L. STXs and MCs were found in most sampled stations. For STXs it ranged from 0.016 µg/L to 0.308 µg/L, and for MCs in some stations it was higher than 200 µg/L. According to the World Health Organization and Brazilian legislation, in the 11 studied reservoirs, the concentrations of saxitoxins are within the maximum allowed limits (3 µg/L), while for microcystins the concentrations are for most reservoirs above the maximum allowed value (1 µg/L). Considering the analyzed information in relation to water quality and the cyanobacterial community, we verify that most of these environments present a worrying water quality, which can represent a risk for public health. Full article

Phytoplankton size structure has profound consequences on food-web organization and energy transfer. Presently, picocyanobacteria (size < 2 µm) represent a major fraction of the autotrophic plankton of Pampean lakes. Glyphosate is known to stimulate the development of picocyanobacteria capable of degrading the herbicide. Due to the worldwide adoption of glyphosate-resistant crops, herbicide usage has increased sharply since the mid-1990s. Unfortunately, there are very few studies (none for the Pampa region) reporting picocyanobacteria abundance before 2000. The proliferation of µm sized particles should decrease Secchi disc depth (ZSD). Therefore ZSD, conditional to chlorophyll-a, may serve as an indicator of picocyanobacteria abundance. We use generalized additive models (GAMs) to analyze a “validation” dataset consisting of 82 records of ZSD, chlorophyll-a, and picocyanobacteria abundance from two Pampean lakes surveys (2009 and 2015). In support of the hypothesis, ZSD was negatively related to picocyanobacteria after accounting for the effect of chlorophyll-a. We then fitted a “historical” dataset using hierarchical GAMs to compare ZSD conditional to chlorophyll-a, before and after 2000. We estimated that ZSD levels during 2000–2021 were, on average, only about half as deep as those during 1980–1999. We conclude that the adoption of glyphosate-resistant crops has stimulated outbreaks of picocyanobacteria populations, resulting in lower water transparency. Full article

Maximum depth of colonization (z_C) 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 (z_SD), and by attenuation coefficients of irradiance within photosynthetically active radiation range (K_d,PAR), and euphotic zone depths (z_EU) 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 z_C = 0.8 m; mean z_C = 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 z_C 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 (K_d,PAR) within the range of 0.35–0.42 m⁻¹, which corresponds to the maximum colonization depths of 1.8–2.2 m. Full article

Secchi disc transparency and optical properties of water, based on measurements for downward irradiance using an underwater radiometer PER-700, were studied in 23 lakes of the Suwałki Landscape Park (SLP) in 2013. Measurements of optically significant constituents of water were also performed (YSI EXO-2) and analysed. Data on water transparency from published studies were used to assess long-term changes in the optical conditions in the deepest water body in Poland—Lake Hańcza. In terms of the optical characteristics of the water, the analysed SLP lakes can essentially be divided into two distinct groups representing different optical lake types. These are optical categories of lakes most common in Poland, namely types II and IIIb. Regional equations describing the relationships between the attenuation coefficient for downward irradiance as well as optically significant constituents of water were developed. The optical properties of the SLP lakes are mainly affected by suspended solids, mostly phytoplankton. Interannual fluctuations in Sechi disc transparency, as well as the attenuation coefficient for downward irradiance and other apparent optical properties of mid-summer water calculated from it, are determined by the spring thermal conditions and intensity of phytoplankton blooms during this period. Application of the attenuation coefficient for downward irradiance as a criterion for the assessment of the trophic status of the SLP lakes indicates that these are generally eutrophic lakes. The largest and deepest lakes of the park, however, are mesotrophic. Lake Hańcza is currently in the stage of α-mesotrophy. Full article

The spatial variation of water transparency of the largest Polish lakes was presented on the basis of documentary material collected by the Voivodeship Inspectorates for Environment Protection as well as university geography departments in the period of 1991–2013. Seasonal results of the Secchi disc measurements (spring, summer) for 706 lakes were gathered. This is more than 68% of the total number of Polish lakes with a surface area larger than 50 ha. The mean water transparency of these lakes was 1.87 m, while the median was 1.58 m. Distinct inter-regional differences of the Secchi disc transparency were found, and it was also possible to distinguish three relatively homogeneous groups of macroregions where lakes have different optical characteristics. They can be divided into areas with lakes with high (3.05 m), medium (1.99–2.11 m) and low (1.22–1.52 m) water transparency. The Secchi disc transparency of these lakes was also analysed in relation to concentration values of the main forms of the optically significant constituents of water (coloured dissolved organic matter, suspended matter). The mean transparency of turbid, stained and clear lakes was, respectively, 1.16, 2.02, and 2.92 m. Moreover, regional empirical models to predict Secchi disc transparency from chlorophyll a concentration were also developed. It was assumed that inter-regional differences between models could be due to the probably different time of the ice sheet recession. The influence of the lake morphometry was most fully reflected in the impact of the depth conditions. Full article

The aim of the study was to reveal differences in the productivity of lakes varying distinctively in water mass dynamics, as shown by the examples of Lakes Track, Miodówko and Szeląg Wielki situated in the Olsztyńskie Lake District. The selected lakes are also characteristic for a high content of nutrients. The analysis of the obtained results has revealed that in the peak of the summer stagnation the productivity was the highest in the polymictic Lake Track. The content of chlorophyll a, which is a measure of primary production, in the Track waters reached the value of 123 mg m⁻³ whereas the water transparency measured as the visibility of a Secchi disc was below 0.6 m. The lowest primary production in the summer was observed in the bradymictic Lake Miodówko. The transparency of water in this lake was nearly 3 m while the content of chlorophyll a merely 1.7 mg m⁻³. Lake Szeląg Wielki, featuring the characteristics of a eumictic reservoir, in the peak of the summer period was noted for the average values of the analysed parameters (1.2 m water transparency, 40.3 mg m⁻³ chlorophyll a). Full article

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. Full article