SUMMARY: Charophytes constitute a group of macrophytes that usually inhabit soft bottoms with shallow water. They occur mostly in fresh-water environments but can also be found in brackish waters. Due to their requirement for clear water they are considered sensitive to eutrophication and therefore often used as an indicator for good water quality. The diverse structure of the Estonian coastline with its numerous sheltered bays and shallow, soft-bottom archipelago areas coupled with low salinity conditions provides an excellent habitat for charophytes. To date, seven species have been described in Estonian coastal waters, NE Baltic Sea. Last systematic investigations on charophyte distribution date back 20-30 years. During the summer of 2001 the locations where charophytes have previously been found were revisited and new sites sampled, to describe the present distribution of quantitative and qualitative parameters of charophyte species. Sampling was performed mainly by SCUBA diving; occurrence, abundance and wet weight biomass were estimated for each location. Six species of charophytes were identified. Compared to previously recorded material, no significant changes in the distribution pattern of charophytes were found. The dependence of charophyte distribution on environmental settings was tested, with depth and substrate quality explaining most of the variability in distribution. Salinity within observed range had minor influence on charophytes.Key words: Charophytes, Baltic Sea, depth distribution, salinity. RESUMEN: DISTRIBUCIÓN DE LAS ESPECIES DE CARÓFITOS EN AGUAS COSTERAS DE ESTONIA (MAR BÁLTICO NE). -Los Caró-fitos son un grupo de macrófitos que por lo general viven en fondos blandos con aguas someras. Se encuentran sobre todo en ambientes de agua continental, pero pueden hallarse asimismo en aguas salobres. Debido a su necesidad de aguas transparentes con frecuencia se les considera sensibles a la eutrofización y, por ello, suelen ser utilizados como indicadores de buena calidad del agua. La estructura variada del litoral de Estonia, con sus numerosas bahías resguardadas y áreas de archipiélagos con fondos blandos y someros, junto a condiciones de baja salinidad, proporciona un hábitat excelente para los carófitos. Hasta la fecha se han descrito siete especies de carófitos en las aguas costeras de Estonia, en el NE del mar Bál-tico. Las últimas investigaciones sistemáticas sobre la distribución de los carófitos se remontan a hace 20-30 años. Durante el verano de 2001 se volvieron a visitar las localidades en las que previamente se habían encontrado carófitos y se muestrearon nuevos emplazamientos, para describir la distribución actual de parámetros cuantitativos y cualitativos relativos a las especies de carófitos. El muestreo se realizó principalmente mediante buceo con escafandra autónoma; para cada localidad se estimaron la presencia, abundancia y biomasa en peso húmedo. Se identificaron seis especies de carófitos. Comparado con el material registrado previamente, no se descubrieron cambios importa...

Optical and biological measurements were performed in Lake Ülemiste in the summer of 1997 (four measurement days), and from May to October in 1998 (12 measurement days). This kind of data, describing the type and amount of optically active substances in the water, phytoplankton characteristics, the underwater light field, and temperature–oxygen situation in the lake are necessary when estimating the ecological state of the lake. Lake Ülemiste is the main drinking water reservoir of Tallinn, the capital of Estonia. Phytoplankton abundance and biomass, chlorophyll a and suspended matter were determined from collected Lake Ülemiste water samples in the laboratory. Spectrophotometrical processing of the filtered and unfiltered water was carried out to describe the beam attenuation coefficient spectra and optical influence of yellow substance in the water. Vertical profiles of downwelling irradiance of the PAR (400–700 m) region of the spectrum (and from these data the averaged over depth diffuse attenuation coefficient) were determined. The relative transparency of the water was estimated by using a Secchi disk. Passive optical remote measurements were episodically made from aboard a boat. Results obtained confirmed that Lake Ülemiste is turbid (almost hypertrophic), comparable with most turbid lakes in Estonia (e.g. Lake Võrtsjärv) and Finland (Lake Tuusulanjärvi). Its chlorophyll a content varied within the range 13–121 mg m–3, phytoplankton biomass 3–107 mg L–1, phytoplankton abundance 65 000–999 000 mL–1, suspended matter 8–34 mg L–1, effective concentration of the yellow substance 6–30 mg L–1, diffuse attenuation coefficient of light in the PAR region 1.0–3.3 m–1 and a Secchi disk depth of 0.5–1.75 m. The temporal variation of the spatial averages of these parameters during 1998 was analysed. Almost all characteristics showed an increase from May to midsummer with a maximum in late July or in August (correspondingly the Secchi depth values were minimal in late summer). The amount of yellow substance was an exception, which was nearly constant during the observation period. The maximum level of chlorophyll a content in July and August 1998 markedly exceeded that in 1997, despite the fact that the summer of 1997 was sunny, but the summer of 1998 was cold and rainy. The correlative relationships between the different parameters were investigated together with the respective data for other lakes. They show that the data of Lake Ülemiste supplemented the correlation graph in the region of turbid lakes, whereby in all cases the correlation coefficient increased following the addition of Lake Ülemiste data. The highest correlation coefficient was obtained when light attenuation coefficient values were correlated with a sum of weighted concentrations of chlorophyll a, yellow substance and suspended matter (multiple regression analysis).

Underwater light climate in strongly eutrophic Lake Ülemiste was studied by applying in situ measurements and model calculations. The attenuation of light in the waters of Lake Ülemiste is rather high, with a diffuse attenuation coefficient of photosynthetically active radiation, spectral region 400–700 nm (PAR) being 1.0–3.3 m–1. From the subsurface irradiance, only 3–13% reaches the depth of 1 m. However, in most cases, 1% from the irradiance just under the surface of water is available at the average depth (2.5 m) of the lake. A simple model is used for an approximate description of the temporal variation of underwater PAR at different depths. The initial data are the episodically determined values of the diffuse attenuation coefficient of PAR, Kd,PAR and the values of continuously recorded incident irradiance. Light is limiting phytoplankton growth in Lake Ülemiste only for a very short time each year: in early spring and late summer. The study should be continued to investigate the effect of artificially regulated influx and outflow of water and nutrients to toxic cyanobacteria blooms in this lake.

Information on the structure of microalgal assemblages in the epiphyton and epilithon is necessary to understand the origin of phytoplankton in lowland rivers. To this end, we carried out concurrent investigations on phytoplankton, epiphyton and epilithon in 18 reaches of three Estonian rivers during the midsummers of 2002 and 2003. A total of 251 taxa was recorded, of which 192 were epiphyton species, 158 were epilithon species and 150 were phytoplankton species. Canonical correspondence analysis (CCA), based on the 31 most abundant taxa, indicated differences in the structure of the algal assemblages between the different biotopes (phytoplankton, epiphyton and epilithon) as well as between the studied rivers. The composition of the phytoplankton clearly differed from that of the other biotopes, with prevailing small flagellates, a chrysophyte (Synura uvella) and cryptophytes (Rhodomonas lacustris and Cryptomonas erosa). The epiphyton was characterized by a large number of diatoms, while the epilithic community contained filamentous cyanobacteria (Phormidium tergestinum and Planktolyngya sp.) and a green alga (Stigeoclonium tenue) in addition to diatoms. Based on redundancy analysis (RDA), phosphorous was the most relevant parameter determining the distribution of species in the phytoplankton assemblages. Shading by trees on the river bank, dissolved oxygen concentration and water temperature as well as river width determined the distribution of species in the epiphyton. The data set on the epilithon did not reveal any significant relationships between species distribution and the measured environmental parameters.

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