Oxygen conditions and trophic state of Lake Głębokie (Szczecin, Poland) in the years 2008-2010

Abstract

Oxygen conditions and trophic state of Lake Głębokie (Szczecin, Poland) in the years 2008-2010The research in Lake Głębokie was conducted in the years 2008-2010. Sampling from three selected sites was designed in such a way that vertical profiles of the characteristics of interest were obtained. Measurements were performed to determine the content of dissolved oxygen, oxygen saturation expressed as a percentage, water temperature, total phosphorus, chlorophyll a, dry seston mass, and Secchi disk depth. During the course of a year, water temperature varied from 0.58°C to 24.72°C. However, a permanent thermal stratification was not observed in the summer season due to complete water mixing. Dissolved oxygen concentrations in the water varied within a range that started at hard-to-measure insignificant values and reached up to 9.63 mg O2 l-1, while oxygen saturation reached a maximum of 116% O2. At the same time, it was observed that oxygen conditions gradually worsened as the depth became greater. The largest oxygen deficits occurred in the winter season of 2009-2010. The oxygen conditions were typical for an eutrophic lake. Its high trophic state was confirmed by an analysis performed using the method proposed by Carlson (1977) as well as by an analysis performed according to the directives of the OECD (1982). The trophic state of this lake is borderline eutrophic and hypertrophic. The oxygen conditions found in this lake ought to be seen as not beneficial to fish.

Glebokie Lake in Szczecin after hydrotechnical regulations

“…Assessing the trophic status of examined waters according to the procedure given by Carlson, based on the concentration of total phosphorus and chlorophyll in surface watersit was determined that the water had the status eutrophic/hypertrophic, regardless of the season [50]. Similar conclusions could be found, based on research results of Glebokie Lake in years 2008-2010 -in paper [13].…”

“…The removal of excess phosphate was supposed to diminish strong phytoplankton blooms occurring in the lake [12]. However, as confirmed by a study conducted in 2010, the applied measures -water aeration and coagulant supplydid not bring any improvement in oxygen situation of the lake water [12,13]. There are stable phytoplankton and zooplankton communities in the lake, with taxonomic structure and abundance resembling those of dam reservoirs in Poland.…”

“…Anoxia formed in the lake in recent years, particularly intensive in summer. The aerator is operating continuously, except when the ice cover appears on the lake [13]. The aerator was also used to discharge a coagulant PIX (acidic solution of FeSO 4 ) into the near bottom water.…”

“…The intake is operating since 1929. The aquifers in this area are located at 20 to 50 m depth below the soil level [12,13].…”

“…The negative water balance in this lake is caused by strong anthropopressure resulting primarily from an excessive exploitation of a water intake in close proximity (water intake station in Pilchowo). In order to stabilize water volume in the lake, a supply pipeline from the Gunica River was constructed since 2004, delivering annually as much as 30% of the lake volume [12,13]. Having the water balance stabilized, the Glebokie Lake became a reservoir replenishing the aquifer in the Pilchowo water intake zone.…”