ZOOPLANKTON EXPORTED FROM RETENTION RESERVOIRS AT THE POST-PRODUCTION WASTE WATER TREATMENT PLANT

Robert Czerniawski
Department of General Zoology, University of Szczecin, Szczecin, Poland

ABSTRACT

In the years 2002 and 2003 the zooplankton from the outflows from two retention reservoirs, characterised by different biological conditions, at the sewage treatment plant in the area of the Chemical Plant Police was studied. One reservoir was in 70% grown with vegetation, mainly submerged species and hosted fish, while the other had no fish and its bottom was covered only in 10% by emerged vegetation. Cyclic appearance of certain zooplankton species was noted; particularly interesting was increasing abundance of Daphnia magna in warm seasons. The outflows from the second reservoir contained a greater number of taxa and greater abundance and biomass of zooplankton, however, the difference was not statistically significant (p < 0.05).

Key words: artificial reservoirs, Daphnia magna, outflows, water plants, zooplankton.

INTRODUCTION

It is known that small water reservoirs undergo eutrophication relatively fast. Their small area and low depth favour this process accompanied by abundant development of zooplankton. Chemical and biological characteristics of small water reservoirs localised far from human habitation sites are comparable to those in larger reservoirs, however, when they are subjected to considerable anthropogenic pressure the chemical composition of their water can be determined by the limiting element. The polluted and strongly eutrophicated environment is particularly favoured by some species of Rotifera whose abundance can reach a few thousand in L [13,17,31]. Often they belong to the ubiquistic species highly tolerant towards environmental factors [29]. High fertility of water is also a factor permitting the occurrence of large forms of plankton crustaceans, on condition of the absence of fish in a given reservoir. The reservoirs showing considerable development of eutrophication and relatively high abundance and biomass of the zooplankton are, among others, the retention ones at the sewage or waste-water treatment plants and small size artificial and natural reservoirs.  Szlauer [23] studied the quantitative and qualitative composition of the zooplankton in the retention reservoir at the waste-water treatment plant at the Chemical Plants in Police, and reported great abundance and biomass of the zooplankton with a particularly significant contribution of large Cladocerans Daphnia magna. Similarly, in the sedimentation tanks of the sewage treatment plant in Drawno (NW Poland), in late spring, high concentrations of zooplankton were reported [4]. Similarly high abundances of zooplankton have been found in small lakes and ponds surrounded by arable fields, the water of these reservoirs contains relatively high amounts of phosphorus and nitrogen. Demetraki-Paleolog [5] reported the occurrence of Rotifers in the abundances up to 7000 individuals per L in shallow and small lakes.

The aim of the study was a comprehensive analysis of the zooplankton in the outflows of the waste-water treatment plant, in particular determination of its species composition, abundance, seasonal changes and the differences in the zooplankton in two reservoirs of different biological conditions.

In view of the established high abundances of plankton crustaceans in artificial reservoirs, it seemed interesting to analyse the zooplankton carried in the outflow from two retention reservoirs at the waste-water treatment plant at the Chemical Plant Police.

MATERIAL AND METHODS

The zooplankton was analysed in the outflows from two retention reservoirs at the waste-water treatment plant at the Chemical Plant Police. The outflows from the reservoirs 1 and 2 were denoted as Outflow 1 (site 1) and Outflow 2 (site 2) discharge into the Jasienicki Canal joining them directly with the Szczecin Bay. Reservoir 1 occupies the area of 40 ha, has a maximum depth of 2 m, and is in about 70% covered with plants, both submerged and emerged. Almost all along the west shore there are 22 pipes discharging the post-production waste-water from the Chemical Plants obtained after the production process of three-component mineral fertilisers, phosphoric and sulphuric acids, fluorine compounds, titanium white, ammonia and urea.  The temperature of the waste-water released from the plant is 40°C and its pH varies from 1 to 2. The post-production waste-water is directed to the chemical and mechanical purification plant at which phosphates are precipitated. At the next stage the waste water is decanted in Dorr sediment tanks and the process is accelerated by addition of flocculants. From the sediment tanks the water is flown to the retention reservoir. Prior to reaching the outflow the water is directed to pass through three dikes, dividing the reservoir into a few basins. The water is discharged from the reservoir through concrete pipes of 120 cm in diameter localised after the diversion weir on the south shore of the reservoir [29]. The location and map of retention reservoir 1 with marked sites of sample collection is shown in Fig. 1.

Retention reservoir 2 has been founded on the basis of the earlier natural pond supplied by ground water and precipitations. It is the last element of the post-production waste-water treatment plant in the Chemical Plant Police, in which the water subjected earlier to mechanical and chemical cleaning is biologically purified. Reservoir 2 occupies the area of about 40 ha and its depth reaches 3 m at the waste water inflow and 1 m at the discharge to the Jasienicki Canal, and is grown in about 10% with emerged plants. In the reservoir there are three dikes prolonging the flow of water and hence the time of retention. The reservoir hydrology is controlled by the inflow of waste-water and partly by precipitations. The water temperature in reservoir 2 is relatively high and in summer reaches even 31ºC, so it is higher than the temperatures of natural surface water in the same period [22]. The outflow occurs through three metal pipes of 70 cm in diameter. The location and map of retention reservoir 2 with marked site of sample collection is shown in Fig. 2.

The observations were carried out in the years 2002–2003. The samples of zooplankton were collected every month at the sites marked on the maps (except January and December 2002). At each site and each time two samples were collected: for the quantitative study by filtering 100 L of water through the mill gauze of the mesh size 50 µm and for the qualitative study by placing the mill gauze of the mesh size 50 µm in the water current for 10 minutes. Depending on the density of zooplankton the volume of the sample was reduced to 10 – 80 cm³, from which 1 mL was collected to the chamber and analysed. The count was at least three times repeated and performed of the individuals representing particular systematic groups of crustaceans, the species were identified and the individuals of rotatoria were counted. The abundance of zooplankton was expressed per 1 L. In order to find the abundance of species represented by large individuals, occurring often in small numbers, the volumes of the whole samples were analysed. In each sample the lengths of at least 30 individuals from each species represented were measured. The data were used for calculation of the biomass of the zooplankton and the so-called wet mass of the zooplankton carried out with the outflow in kg per day.

The weight of the animals was calculated from their lengths on the basis of the tables proposed by Morduchaj-Bołtovskoj [21] and Starmach [27]. The species were identified with the help of the keys prepared by Wagler [32], Kutikova [17], Kiefer and Fryer [12], Rybak [23,24].

The taxonomic similarity between the sites was calculated according to the formula of  Marczewski and Steinhaus [19]:
S = ^W/_{A + B – W}

Where:
S – is the statistical similarity between the two sites compared,
A – is the number of elements in set,
A, B – is the number of elements in set B,
W – is the number of elements common for sets A and B.

The data on abundances and biomass of the zooplankton were subjected to statistical analysis with the help of the software Excel and Statistica. The hypothesis of the equality of the mean values was verified after prior testing the normalcy of distribution of the feature analysed (Shapiro-Wilk test) and the Levene test of homogeneity of variance.  The significance of differences was determined by the Scheffe test (p<0.05) and variance analysis (W) (for many samples) [26].

RESULTS

The species composition and frequency of zooplankton at the sites of study are presented in Tables 1 and 2. At the outflows from retention reservoirs 1 and 2, at the both sites the number of taxa noted was 30 and 33, with 21 and 26 species, respectively. The most often represented were: nauplius Cyclopoida, kopepodit Cyclopoida, Acanthocyclops robustus, Eucyclops serrulatus, Daphnia magna, Brachionus angularis, Brachionus calyciflorus, Brachionus variabilis, Keratella cochlearis, Keratella quadrata, Polyarthra sp. The occoncurence and abundance of some zooplankton components was definitely seasonal. The most important species with cyclic presence at site ZbR 1 included: A. robustus, E. serrulatus, Cyclops vicinus, D.a magna, Ceriodaphnia quadrangula, Brachionus angularis, B. variabilis, Keratella quadrata, Polyarthra sp., Notholca squamula. At site ZbR2 the most important cyclically appearing species were: A. robustus, D. magna, B. angularis, B. calyciflorus, B.s variabilis, K. quadrata. At both sites K. quadrata appeared only in colds seasons.

As to the frequency of the taxa at site 1 it was found that only representatives of Nauplii Cyclopoida were present in 100% of the qualitative samples throughout the period of the study. The frequency of 80% was established for the three taxa: including Copepoda, Copepodites Cyclopoida (95%) and Rotifera non det. (95%). No taxa were characterised with a frequency from the range 60–80%. Only Polyarthra sp. was characterised with a frequency from the range 40–60% , while seven taxa occurred with frequencies from the range 20–40%, including B. variabilis (36%), Asplanchna sp., K. cochlearis i K. quadrata (32%). Twenty taxa were characterised with a frequency below 20%, of which the highest frequency of 18% was found for A. robustus, E. serrulatus and Brachionus urceus.