Long-term (30 years) dynamics of Chironomidae (Diptera) fauna in the Kuibyshev water reservoir associated with eutrophication processes

Benthos investigations were carried out in the channel and flood-plain of the Kuibyshev water reservoir during 1958–1985. Hydrobiological monitoring data obtained at 12–16 stations in all Deeps excluding littoral areas are discussed. In 1987–1900 benthofauna distribution was also studied at the Priplotinny Deep. An increase of the reservoir trophic state is reported. The observed trend was an increase of the total benthos biomass. Changes in both species and trophic structure of the chironomid community due to the eutrophication problem are discussed.     

Seasonal variation in effects of urea and phosphorus on phytoplankton abundance and community composition in a hypereutrophic hardwater lake

1. Urea accounts for half of global agricultural fertiliser applications, yet little is known of its role in eutrophication of freshwater ecosystems, nor how it interacts with phosphorus (P) in regulating phytoplankton composition, especially during spring and autumn.
2. To identify when and how urea and P inputs interact across the ice-free period, we conducted seven monthly fertilisation experiments in 3,240-L mesocosms from ice-off to ice-formation in a hypereutrophic lake. In addition, we ran bioassays with ammonium (NH₄⁺) to compare the effects of urea with those of NH₄⁺, the immediate product of chemical decomposition of urea.
3. Analysis of water-column chlorophyll a and biomarker pigments by high-performance liquid chromatography revealed that addition of inorganic P alone (100 µg P L^–1 week^–1) had no significant impact on either algal abundance or community composition in hypereutrophic Wascana Lake. Instead, fertilisation with urea (4 mg N L⁻¹ week^–1) alone, or in concert with P, significantly (p < 0.05) increased algal abundance in spring and much of summer, but not prior to ice formation in October. In particular, urea amendment enhanced abundance of cryptophytes, chlorophytes, and non-diazotrophic cyanobacteria during April and May, while fertilisation in summer and early autumn (September) increased only chlorophytes and non-diazotrophic cyanobacteria.
4. Comparison of urea mesocosms with NH₄⁺ bioassays demonstrated that urea lacked the inherent toxicity of NH₄⁺ in cool waters, but that both compounds stimulated production during summer experiments.
5. This study showed that urea pollution can degrade water quality in P-rich lakes across a variety of seasonal conditions, including spring, and underscores the importance of quantifying the timing and form of N inputs when managing P-rich freshwaters.

     

The impact of effluents of Pitkäranta pulp mill on the water quality of Lake Ladoga: a model study

The aim of this study is to show the effects of the Pitkäranta pulp mill on the water quality of Northern Ladoga by using water quality models. The effluent loading of the pulp mill with its full production capacity is as follows: Water flow 85 000 m³ d^–1 BOD₅ 2.4 t d^–1 Suspended solids 4.1 t d^–1 tot-N 330 kg d^–1 tot-P 68 kg d^–1 COD(Cr) 14.4 t d^–1 Org. C 6 t d^–1 Lignosulphonates 9.4 t d^–1 Loadings of lignosulphonates and organic C are estimations. Lignosulphonate concentrations of 10.5 mg 1^–1 have been reported in the region of Pitkäranta. The study area of northern Ladoga near the pulp mill was divided into three zones (I, II and III). The mean depth of each of them is considered as 10 m, their respective areas 5, 10 and 50 km², and volumes 50, 100 and 500 million m³. The estimated discharges of the zones are 10, 20 and 50 m³ s^–1, respectively. With the aid of simple water quality models the effects of the pulp mill effluents on the concentrations of oxygen, total phosphorus, lignin, COD(Mn) and Secchi disk depths in each of the zones were estimated. Estimations were made during full production capacity and half production capacity of the pulp mill. The modelling results were compared with the preliminary water analysis results of the Finnish-Russian joint research expedition into Lake Ladoga in August 1993. The results show that near the pulp mill (zone I) phosphorus concentrations are high even with half production capacity. Also lignin and COD(Mn) contents have increased, and oxygen concentrations are low both in the summer and during wintertime. Farther away in the open water (zone III) the pollution effects are low. Eutrophication, indicated by high total phosphorus concentrations, is the main effect of the pulp mill effluents.     

Shrimps and eutrophication in the waterbodies of a coastal grazing marsh

The influence of shrimps on turbidity was examined in laboratory and field experiments. Palaemonetes varians in the laboratory stimulated populations of both rotifers and Anabaena, which was the main cause of increased turbidity. In field experiments, P. varians increased and Neomysis integer decreased turbidity. In feeding trials P. varians took cladocerans and culicids in preference to copepods. It is considered that shrimps are likely to be important predators of cladocerans in shallow, coastal waterbodies and result in phytoplankton blooms, with reduced water transparency. This revised version was published online in July 2006 with corrections to the Cover Date.     

Restoration of Botshol (The Netherlands) by reduction of external load: Problem analyses and restoration methods

Since 1960 the water quality of the nature reserve Botshol has been deteriorated. An increase in the nutrient load caused an escalation in phytoplankton biomass and turbidity problems. This may have been caused by nutrient-rich water flowing into the reserve from the agricultural areas and from the polder of Nellestein. From 1980 to 1985 much research has been undertaken and participation of different disciplines gave the opportunity to analyse the cause of the changes. An integrated restoration plan has been drawn up to reduce the eutrophication. The plan was implemented in 1989 and in order to reverse the external nutrient load the following measures were taken. 1. Execution of a water management plan with the intention to isolate the agricultural areas from the reserve area. 2. Dephosphorization of the inlet water. These restoration measures resulted in a reduction of the external load from 0.6 to 0.1 g P m^–2 year^–1.     

Fecundity of whitefish (Coregonus lavaretus) during the eu-and oligotrophication of Lake Constance

About 20 ovaries of the whitefish 'Blaufelchen' ( Coregonus lavaretus L.) of Lake Constance (Bodensee) were collected annually from 1964-1991. Absolute and relative fecundity peaked in the early 1980s, lagging about 2 years behind the maximum of total-P in the water (during the circulation period). Out of the biological time-series of Lake Constance, whitefish fecundity is the only one known to follow the phosphorus curve, and this may be the first time-series documented case of parallel trend reversal in the trophic state of a lake and fish biology. It is concluded that fish fecundity serves, at best, as an unspecific monitor of the overall well-being of the fish.     

The ecological history of a mediaeval man-made lake. Hickling Broad,Norfolk, United Kingdom

Changes in Hickling Broad, since its creation in the 14th or 15th centuries by the flooding of peat diggings, have been deduced from dating and analysis of a sediment core, historical information and current limnological studies. Until the 1930's there was little major change. Increased agricultural land fertilization led to markedly increased organic sedimentation from the 1930's onwards, due to increased growth of submerged macrophytes. Inorganic sedimentation increased concurrently as more powerful pumps were installed to help drain the adjacent fens and marshes.There was no evidence of increased plankton populations during this phase, but epiphytic diatom populations increased. In the mid 1960's the current period of hypereutrophication began. Epiphytic diatom numbers increased markedly and in the early 1970's the previous luxuriant macrophytes became sparse and the water became turbid with phytoplankton. These changes are attributable mainly to increases in the size of a roost of migratory black headed gulls (Larus ridibundus L.) on the lake in autumn and winter.     

Non-siliceous algae in a five meter core from Lake Kinneret (Israel)

The composition and succession of non-siliceous algae, studied in a five meter core from Lake Kinneret (Israel), are described. Only Chlorophyta species were recorded, probably due to the standard palynological sample processing which was used. In the lower part of the core, from the bottom to 300 cm (interval 5500–2500 years B.P.), Botryococcus braunii was the only common alga. Relevant changes in algal diversity and abundance occur at 300 cm. Many species of green algae were recorded for the first time (Pediastrum, Scenedesmus, Coelastrum, etc.). These changes may be related to an increase in nutrient concentration as a consequence of cultural disturbance. In the interval 300-0 cm, a succession of Pediastrum species is followed. The recovered green algae are extant in the present plankton of Lake Kinneret. They also constitute an important part of the algae found in the profundal sediments today.