Spatio-temporal variations in water quality of a river-lake system during restoration treatments.

To fill the knowledge gap about the functioning of the lake-river system subjected to restoration treatments, two tributaries, a shallow, restored lake and its outflow, were examined. The quality of water inflows, lake and outflow was compared before (BR), during sustainable (SR, deep water aeration, phosphorus inactivation and biomanipulation for 3 years) and limited lake restoration (LR, only aeration for 2 years). Physico-chemical parameters were analysed monthly at five stations. The nutrient concentrations at the inflows decreased over the years due to the improvement of water and sewage management in the catchment (in Mielcuch from 18.0 to 8.0 mgN L-1 and 1.0 to 0.6 mgP L-1). The decline at the outflow was the result of a better quality of water at the tributaries and SR in the lake. During LR, decrease of phosphorus concentration still occurred (0.11 mgP L-1), but nitrogen concentration slightly increased (3.9 mgN L-1). Although the outflowing waters still transported a high content of chlorophyll a and suspended solids during SR, their amount was lower (34.5 µg L-1 and 17 mg L-1, respectively) than that during BR and LR. During restoration, it is significant to monitor the water quality not only in the lake but also at the outflow. The slow deterioration of water quality at the outflow indicated that introducing changes in the applied restoration methods must be done carefully because the previously achieved effect may be lost. Hence, restoration of the upstream lake and good quality of its tributaries are of great importance for water bodies located downstream.

The influence of land use in the catchment area of small waterbodies on the quality of water and plant species composition.

Land use significantly affects the function of waterbodies in landscape. Although there have been numerous studies on the influence of the catchment area on the trophic and ecological status of waterbodies, still is not reached an agreement on the width of the buffer zone that is necessary for effective protection of waterbodies. The aim of the study was to show whether small waterbodies are predominantly influenced by land use in the entire catchment area or only in the zone extending 100 or 200 m away from the shoreline. For two years the waters in six small waterbodies located in the Wielkopolska region (Poland) were analysed. The canonical correspondence analysis (CCA) showed that the influence of land use, especially agricultural land, was much greater within the zone extending 100 m from the shore line of the waterbodies than in the total catchment area. Therefore, it would be advisable to move the border of intensive farming areas beyond the entire 100-m-wide buffer zone, or at least to reduce the intensity of agriculture and to introduce diversified and perennial vegetation creating effective biogeochemical barriers.

Verifying the usefulness of macrophytes as an indicator of the status of small waterbodies.

Small waterbodies are characterised by a high variability of physicochemical parameters. This has an impact on aquatic macrophytes, which are functional components of aquatic ecosystems that also exert a strong influence on other components of these ecosystems. Therefore, their importance in the classification of reservoirs is unquestionable. Unfortunately, the hydromacrophytes found in nutrient-rich small waterbodies in rural areas have a fairly wide ecological scale and are not suitable for a more accurate assessment of these reservoirs. In addition, indicators derived from the classification of lakes, such as phosphorus, nitrogen, chlorophyll-a, organic matter and trophic state indices, have turned out to be of little use in the assessment of small waterbodies. Only a canonical analysis taking into account both environmental variables and the occurring plant species allows satisfactory results to be obtained. Six small waterbodies located in the rural landscape of the Greater Poland Region were studied over three years. 115 plant taxa, 15 of which are hydromacrophytes, were found in the reservoirs and in their immediate vicinity. Three types of small waterbodies were identified in the CCA assessment: (i) those with high TOC, COD and ammonium nitrogen contents, dominated by pleustophytes, and in a saprotrophic state, (ii) those with high nutrient concentrations, dominated by phytoplankton, with a lack of macrophytes or with nymphaeids present, and in a hypereutrophic state, and (iii) those dominated by submerged macrophytes with low chlorophyll-a content, and in a eutrophic state. Thus, macrophytes turn out to be good indicators which support other variables in the classification of small waterbodies.

Zooplankton changes during bottom-up and top-down control due to sustainable restoration in a shallow urban lake.

Long-term cyanobacterial blooms and hypereutrophic state have been typical for the shallow, urban Swarzedzkie Lake for many years. Diversion of sewage did not change its trophic status, so restoration began in autumn 2011 using the sustainable approach based on three methods. The aim of the study was to analyse how sustainable restoration affects zooplankton. We hypothesised that bottom-up and top-down methods reconstructed zooplankton composition. Thus, the abundance of large-size cladocerans increased and controlled phytoplankton effectively. The elimination of cyanobacteria bloom, the decrease of rotifer abundance and the twofold increase of filter-feeder effectiveness were observed in summer 2012. However, high phosphorus concentration, lack of regular cyprinid removal and insufficient fish stocking together with high temperature prevented zooplankton from controlling cyanobacteria bloom in summer 2013. Rotifer domination with high trophy species was noted, as before restoration. The number of rotifers decreased in 2014, while crustaceans increased due to the significant decrease of nutrient concentrations and an intensification of biomanipulation treatments. Therefore, summer phytoplankton growth was low, without cyanobacteria dominance. The rebuilding of zooplankton in Swarzedzkie Lake was observed during sustainable restoration. However, the treatments should be intensified when adverse changes were observed to obtain better results for the improvement of water quality.

Water quality and phytoplankton structure changes under the influence of effective microorganisms (EM) and barley straw - Lake restoration case study.

Many lakes worldwide, especially shallow, experience great changes due to eutrophication, manifested in severe, usually toxic water blooms, disqualifying them from recreation. In order to improve water quality, restoration programs are implemented, including numerous methods. Intense nutrient cycling resulting from detrimental role of sediments impede obtaining of clear water state. One of the restoration methods proposed in recent years was Effective Microorganisms (EM), i.e. the set of microorganisms aiming at the inhibition of harmful bacteria through competitive exclusion. This approach was introduced in shallow Konin Lake (Western Poland), suffering from severe cyanobacterial water blooms. Prior to the treatment, protective action was conducted i.e. the elimination of external nutrient loads with backwater from the river. Changes in water chemistry, phytoplankton structure and macrophytes distribution were noted during the 5-year studies (2011-2015), covering the treatment (2013-2015) as well as two previous years. Oscillatoriacean cyanobacteria were most abundant in (2011-2012), while Nostocales in summer 2014-2015, as a result of decreased phosphorus but increased nitrogen concentrations. Slight increase in Cladoceran zooplankton was observed, but none in submerged macrophytes due to low water transparency. EM application initiated positive changes in the ecosystem by means of excessive organic matter decomposition and increased diversity of phytoplankton, nevertheless cyanobacteria blooms were still present due to high nutrient content.

Internal Phosphorus Loading from the Bottom Sediments of a Dimictic Lake During Its Sustainable Restoration.

The ribbon type Lake Durowskie (Western Poland) is currently undergoing a sustainable restoration process due to water quality deterioration, manifested in water blooms, low transparency, and oxygen deficits near the bottom sediments. Three restoration methods were applied: (i) hypolimnion aeration using two wind-driven pulverizing aerators installed at the deepest places, (ii) phosphorus inactivation using small doses of iron sulfate and magnesium chloride several times a year, and (iii) biomanipulation using pike fry stocking. Research on the exchange of phosphorus in the sediment-water interphase was conducted in the years 2009-2016 to determine the multiannual changes of internal phosphorus loading from bottom sediments during the restoration process. The sustainable approach resulted in a decrease of internal phosphorus loading and a gradual increase in the sorption capacity of bottom sediments, particularly noticeable in the last 2 years. The content of phosphorus in the sediment and in the interstitial water fluctuated, showing an increase during the first years of restoration and then a gradual decrease. It was proved that the process of sustainable restoration is cheap and does not interfere strongly with the ecosystem, although it is long-lasting. It should be continued for many years, especially in the case of continuous external loading of the lake with nutrients from the catchment area, i.e., until the water quality in the main tributary improves and the lake ecosystem stabilizes.

Temperature Effects Explain Continental Scale Distribution of Cyanobacterial Toxins.

Insight into how environmental change determines the production and distribution of cyanobacterial toxins is necessary for risk assessment. Management guidelines currently focus on hepatotoxins (microcystins). Increasing attention is given to other classes, such as neurotoxins (e.g., anatoxin-a) and cytotoxins (e.g., cylindrospermopsin) due to their potency. Most studies examine the relationship between individual toxin variants and environmental factors, such as nutrients, temperature and light. In summer 2015, we collected samples across Europe to investigate the effect of nutrient and temperature gradients on the variability of toxin production at a continental scale. Direct and indirect effects of temperature were the main drivers of the spatial distribution in the toxins produced by the cyanobacterial community, the toxin concentrations and toxin quota. Generalized linear models showed that a Toxin Diversity Index (TDI) increased with latitude, while it decreased with water stability. Increases in TDI were explained through a significant increase in toxin variants such as MC-YR, anatoxin and cylindrospermopsin, accompanied by a decreasing presence of MC-LR. While global warming continues, the direct and indirect effects of increased lake temperatures will drive changes in the distribution of cyanobacterial toxins in Europe, potentially promoting selection of a few highly toxic species or strains.

Influence of stormwater runoff on macroinvertebrates in a small urban river and a reservoir.

The impact of stormwater on benthic macroinvertebrates was studied in two annual cycles. Five small catchments drained by stormwater sewers to a small urban river and a small and shallow reservoir situated in its course were selected. These catchments were located in residential areas with single-family houses or blocks of flats as well as industrial areas, i.e., a car factory, a glassworks and showroom as well as the parking lots of a car dealer and servicing company. In addition to the five stations situated in the vicinity of the stormwater outlets, three stations not directly influenced by stormwater were also established. Macroinvertebrates were sampled in every season, four times per year. Both abundance and biomass were assessed. Stormwater from industrial areas associated with cars, whose catchments showed a high percentage of impervious areas, had the greatest impact on benthic macroinvertebrates. This was due to a large amount of stormwater and its contamination, including heavy metals. Stormwater outflow from residential multi-family houses exerted the least influence. Macroinvertebrates in the water reservoir were found to undergo more extensive changes than those in the river. The cascade of four reservoirs resulted in a marked improvement of water quality in the river, which was confirmed by species composition, abundance and biomass of macroinvertebrates and indicators calculated on their basis for the stations below the cascade in comparison to the stations above and in the first reservoir. These reservoirs replaced constructed wetlands or other measures, which should be undertaken for stormwater management prior to its discharge into urban rivers and other water bodies.

Cyanobacteria blooms before and during the restoration process of a shallow urban lake.

Swarzedzkie Lake (near Poznan) has been heavily polluted. To improve the water quality, the restoration of lake by three methods: aeration, phosphorus inactivation using small doses of iron sulphate and magnesium chloride (FeSO4 and MgCl2) and biomanipulation was initiated at the end of 2011. The aim of the present study was to determine whether sustainable restoration has a significant impact on phytoplankton, especially cyanobacterial blooms in a shallow, urban, degraded lake. Therefore, phytoplankton and the physico-chemical parameters of water at the summer thermal stratification and autumn water mixing before (2011) and during restoration (2012-2014) was studied. Samples were collected at the deepest place of the lake in depth profile, every 1 m. Phytoplankton samples were preserved with Lugol's solution. The phytoplankton was counted using a Sedgewick-Rafter chamber with a volume of 0.46 ml. Measurements of water temperature were made in the field with a YSI multiparameter meter, transparency - using a Secchi disk. Concentrations of nitrogen, phosphorus and chlorophyll a were analysed in the laboratory according to Polish standards. As a result of restoration the water quality of the lake has improved. Cyanobacteria had almost disappeared during the first year of restoration, however, a short bloom was observed (dominated by Pseudanabeana limnetica) in the second year. The main reason for this reappearance was a higher water temperature stimulating cyanobacteria growth, but an increased supply of phosphorus from the bottom sediments also contributed. A decrease in the temperature in the third year of restoration limited the growth of cyanobacteria again. Although the decrease in the phosphorus concentration as a result of restoration proved to be sufficient for average climatic conditions, it is highly likely to be more intense in the case of increased water temperature caused by global warming.

The influence of restoration measures on phosphorus internal loading from the sediments of a hypereutrophic lake.

Uzarzewskie Lake was a hypereutrophic, dimictic lake characterized by low water transparency, high chlorophyll-a concentration and intense phytoplankton blooms; thus, restoration treatment was started. A chemical treatment, based on phosphorus inactivation with small doses of iron sulphate, was undertaken in 2006-2007. Nitrate-rich groundwater flowing from seepage springs was directed into the lake hypolimnion to increase redox potential since 2008. Phosphorus internal loading was reduced by more than 80% as a result of restoration treatment. In the profundal zone, where P release from the bottom sediments prevailed throughout the year, it decreased from 13.02 mg P m-2 day-1 in 2010 to 2.81 mg P m-2 day-1 in 2015. Meanwhile, in the littoral zone, P accumulation in bottom sediments predominated; hence, the mean value of internal loading was increasing from 2.61 mg P m-2 day-1 in 2011 to 10.24 mg P m-2 day-1 in 2015. The annual P load from the bottom sediments in the profundal zone was much higher than from the littoral zone as a result of (i) a higher P release in most years and (ii) the greater area of this zone (82% of the lake's area). The fraction of residual phosphorus (Res-P) has the largest share, and in recent years, this has shown a tendency to decrease. The sum of bioavailable fractions was low (average 5.7%) showing a downward trend in recent years. Sustainable restoration of the lake resulted in a slow but steady decreasing trend in internal phosphorus loading.

Chemometric approach to evaluate element distribution in muscle, liver and fish bone of roach (Rutilus rutilus), silver bream (Blicca bjoerkna) and crucian carp (Carassius carassius) from Swarzedzkie Lake (Poland) using ICP-MS and FIAS-CVAAS techniques.

The content of elements in fish tissues and organs from Swarzedzkie Lake was investigated in order to evaluate the possible risk associated with their consumption by animals as well as humans. Samples of muscle, liver and fish bone of three fish species; roach (Rutilus rutilus), silver bream (Blicca bjoerkna) and crucian carp (Carassius carassius) were collected from seine catches undertaken as part of the biomanipulation of Swarzedzkie Lake. Element concentration (Al, As, Cd, Co, Cr, Cu, Hg, Ni, Pb, Zn) was determined by inductively coupled plasma mass spectrometry (ICP-MS), with the exception of Hg where the flow injection analysis system cold vapour atomic absorption spectrometry (FIAS-CVAAS) was applied. The study indicated a large variation in the occurrence of the investigated elements in different parts of the fish body. The highest content of Al and Zn was stated in all fish organs for each fish species. The majority of the applied statistical and chemometric methods (e.g., PCA, CA) refer to roach since we had a large number of data for this species. The obtained results were assessed in terms of their accuracy and precision using certified reference material of Fish Muscle ERM BB422.

Phytoplankton Composition and Abundance in Restored Maltanski Reservoir under the Influence of Physico-Chemical Variables and Zooplankton Grazing Pressure.

In this paper we present the effects of environmental factors and zooplankton food pressure on phytoplankton in the restored man-made Maltanski Reservoir (MR). Two methods of restoration: biomanipulation and phosphorus inactivation have been applied in the reservoir. Nine taxonomical groups of phytoplankton represented in total by 183 taxa were stated there. The richest groups in respect of taxa number were green algae, cyanobacteria and diatoms. The diatoms, cryptophytes, chrysophytes, cyanobacteria, green algae and euglenophytes dominated in terms of abundance and/or biomass. There were significant changes among environmental parameters resulting from restoration measures which influenced the phytoplankton populations in the reservoir. These measures led to a decrease of phosphorus concentration due to its chemical inactivation and enhanced zooplankton grazing as a result of planktivorous fish stocking. The aim of the study is to analyse the reaction of phytoplankton to the restoration measures and, most importantly, to determine the extent to which the qualitative and quantitative composition of phytoplankton depends on variables changing under the influence of restoration in comparison with other environmental variables. We stated that application of restoration methods did cause significant changes in phytoplankton community structure. The abundance of most phytoplankton taxa was negatively correlated with large zooplankton filter feeders, and positively with zooplankton predators and concentrations of ammonium nitrogen and partly of phosphates. However, restoration was insufficient in the case of decreasing phytoplankton abundance. The effects of restoration treatments were of less importance for the abundance of phytoplankton than parameters that were independent of the restoration. This was due to the continuous inflow of large loads of nutrients from the area of the river catchment.

Storm water contamination and its effect on the quality of urban surface waters.

We studied the effect of storm water drained by the sewerage system and discharged into a river and a small reservoir, on the example of five catchments located within the boundaries of the city of Poznan (Poland). These catchments differed both in terms of their surface area and land use (single- and multi-family housing, industrial areas). The aim of the analyses was to explain to what extent pollutants found in storm water runoff from the studied catchments affected the quality of surface waters and whether it threatened the aquatic organisms. Only some of the 14 studied variables and 22 chemical elements were important for the water quality of the river, i.e., pH, TSS, rain intensity, temperature, conductivity, dissolved oxygen, organic matter content, Al, Cu, Pb, Zn, Fe, Cd, Ni, Se, and Tl. The most serious threat to biota in the receiver came from the copper contamination of storm water runoff. Of all samples below the sewerage outflow, 74% exceeded the mean acute value for Daphnia species. Some of them exceeded safe concentrations for other aquatic organisms. Only the outlet from the industrial area with the highest impervious surface had a substantial influence on the water quality of the river. A reservoir situated in the river course had an important influence on the elimination of storm water pollution, despite the very short residence time of its water.

Spatial and seasonal variability of pore water phosphorus concentration in shallow Lake Swarzedzkie, Poland.

Pore waters play an important role in phosphorus dynamics in aquatic ecosystems. Phosphorus concentrations in pore waters are much higher than above the bottom. This is confirmed by the results of this study concerning the hypereutrophic lake. Pore water was analyzed at 11 sampling stations in the upper layer of bottom sediments. This water was separated by centrifugation and phosphorus level was measured spectrophotometrically with ascorbic acid as a reducer. Total phosphorus concentration in pore waters ranged from 0.5 to 8.1 mgP l(-1) (mean 3.2 mgP l(-1)). Mean phosphorus concentration in pore water samples of this lake was the highest in summer and the lowest in winter. High concentrations were observed in samples from the pelagial and low from the macrophyte zone.

Environmental applications of ICP-MS for simultaneous determination of trace elements and statistical data analysis.

Water samples collected from two lakes separated from each other by the cascade of four small lowland reservoirs were subjected to analyses in order to compare contamination levels in these ecosystems. Inductively coupled plasma mass spectrometry was used to determine eight elements: Al, As, Cd, Cr, Li, Mn, Sb, and Zn. Statistical methods were applied in order to assess the degree of self-purification of water, during its flow from Swarzedzkie Lake to Malta Lake. Obtained distinctly, lower concentrations of all studied elements in Malta Lake than in Swarzedzkie Lake indicated the role of self-purification processes, which occurred in the distance between these lakes.

Spatial distribution of major and trace elements in the water of Swarzedzkie Lake (Poland).

In order to characterize the contamination of the Swarzedzkie Lake and generate elemental distribution patterns 18 elements have been determined in samples of water, taken just above the bottom sediments. Analyses were carried out using two instrumental techniques - ICP-OES and ICP-MS. Two main sources of contamination were identified - diffuse pollution from agriculture and stormwater from the town. Three separate groups of elements were distinguished using cluster analysis and two groups using principal component analysis. These three groups are characterized as geogenic elements (Ag, As, Mg and Sb), elements supplied by the agricultural catchment (Ca, Mn, Sr, Na, K and Al) and elements originated from the urban contamination (Ni, Cr, Cu, Fe, V, Ba, Zn and Pb). PCA differentiated the above group of urban elements from the rest, originated from diffuse sources, with exception of alluminium, which was situated between two distinguished groups.