Phosphorus in acidified lakes: The example of Lake Gårdsjön,Sweden

Supply and turnover of phosphorus was studied in an acidified lake ecosystem, Lake Gårdsjön, located in southwestern Sweden. This study included transport and budget calculations combined with field and laboratory experimental work on abiotic phosphorus chemistry and biological utilization of phosphorus. The main conclusions presented in this paper are:

- The acidification process in inland waters resulting from acid atmospheric deposition is accompanied by ‘oligotrophication’ because of reduced input of phosphorus from the drainage area, possibly due to efficient fixation of phosphorus to aluminium complexes in the B-horizon of podzol soils

- Primary productivity in acidified lakes is limited mainly by low phosphorus supply

- Algal utilization of phosphorus in acidified lakes is impaired, yielding lower biomass than could be expected from ambient phosphorus concentrations. One possible reason for this could be that enzymatic recycling of organic phosphates is prevented by high levels of aluminium in lake water.

     

Origin and production of phosphatases in the acid Lake Gårdsjön

The activity of acid phosphatases was followed for one year in Lake Gårdsjön as well as in the inlet and the outlet of the lake. A budget of the phosphatases was calculated, including an estimation of the production of phosphatases. The phosphatase activity was also measured in two basins upstream of L. Gårdsjön: the north basin and the south basin of L. Stora Hästevatten.The acid phosphatase activity was very high compared with reported alkaline phosphatase activities in other lakes. About 95% of the phosphatases in L. Gårdsjön was produced in the lake, and the production was highest in early summer.Small Chrysophyceae (< 10 µm) probably produced the majority of the acid phosphatases in the investigated lakes, and accordingly could be favoured in environments with low phosphorus supply due to their ability to produce large amounts of phosphatases.     

Long-term Patterns of Shifts between Clear and Turbid States in Lake Krankesjön and Lake Tåkern

During the past century, Lake Tåkern and Lake Krankesjön, southern Sweden, have shifted repeatedly between a state of clear water and abundant submerged vegetation, and a state of turbid water and sparse vegetation. Long-term empirical data on such apparently alternative stable state dynamics are valuable as complements to modeling and experiments, although the causal mechanisms behind shifts are often difficult to identify in hindsight. Here, we summarize previous studies and discuss possible mechanisms behind the shifts. The most detailed information comes from monitoring of two recent shifts, one in each lake. In the 1980s, L. Krankesjön shifted to clear water following an expansion of sago pondweed, Potamogeton pectinatus. Water clarity increased when the pondweed was replaced by characeans. Zooplankton biomass in summer declined and the concentration of total phosphorus (TP) was reduced to half the previous level. The fish community changed over several years, including an increasing recruitment of piscivorous perch (Perca fluviatilis). An opposite directed shift to turbid water occurred in Lake Tåkern in 1995, when biomass of phytoplankton increased in spring, at the expense of submerged vegetation. Consistent with the findings in L. Krankesjön, phyto- and zooplankton biomass increased and the average concentration of TP doubled. After the shift to clear water in L. Krankesjön, TP concentration has increased during the latest decade, supporting the idea that accumulation of nutrients may lead to a long-term destabilization of the clear water state. In L. Tåkern, data on TP are inconclusive, but organic nitrogen concentrations oscillated during a 25-year period of clear water. These observations indicate that intrinsic processes cause gradual or periodic changes in system stability, although we cannot exclude the possibility that external forces are also involved. During such phases of destabilization of the clear water state, even small disturbances could possibly trigger a shift, which may explain why causes behind shifts are hard to identify even when they occur during periods of extensive monitoring.     

Temporal changes and fluxes of sulphur and calcium in wet and dry deposition, internal circulation as well as in run-off and soil in a forest at Gårdsjön, Sweden

Sulphur dioxide in air as well as dry deposition of sulphur dioxide to a forest has decreased by a factor of 20 during the last two decades. It was earlier found that the internal circulation of calcium in Norway spruce follows the dry deposition of sulphur dioxide. The sulphur and calcium fluxes from 1992 were calculated from wet deposition, throughfall and a surrogate surface. Earlier fluxes from 1981 to 1991 were calculated using assumptions of the dry deposition of non-marine sulphate and calcium. The new estimates confirm the earlier studies that the internal circulation of calcium in a coniferous forest is directly related to the dry deposition of sulphur dioxide to the canopies and that the internal circulation of calcium decreases at the same rate as the deposition of sulphur decreased during the last two decades. The deposition fluxes were also compared to run-off and uptake of calcium in the forest as well as on modelled weathering rates from severely acidified forested catchments near the coast and inland and the soil pool. A reconstruction of changes in the soil pool of calcium over the last 100 years indicate that the soil pool has decreased by ca. 70% in catchments with complete harvest of the forest and ca. 40% if branches and needles are left on the ground. In a natural forest without acid deposition the soil pool of calcium would have increased by 6%. Estimates for the 21st century show that harvesting of stems+branches and needles may almost empty the soil pool of calcium in the next 100 years. Increased nitrogen deposition has increased forest growth, which indirectly increased uptake of calcium by the trees and indirectly caused a further decrease of the soil pool of calcium.     

Experimental simulation of the effects of extreme climatic events on major ions, acidity and dissolved organic carbon leaching from a forested catchment, Gårdsjön, Sweden

Climate change is predicted to lead to an increase in extreme rainfall and, in coastal areas, sea-salt deposition events. The impacts of these two climatic extremes on stream hydrochemistry were separately evaluated via a novel watering manipulation at the Gårdsjön experimental catchment, SW Sweden. In summer 2004, a 2000 m² hillslope draining to a defined stream reach was brought to a high-flow hydrological steady state for a 9 day period by sustained addition of ‘clean’ water using a distributed sprinkler system. Marine ions were then added, to generate a realistic ‘sea salt’ episode. A remarkably well constrained hydrological response was observed, such that a simple two-compartment mixing model could reasonably well reproduce observed conservative tracer (chloride, Cl) measurements, and 78% of added water was recovered in runoff. Stream base cation concentrations and acidity responded predictably to clean water and sea-salt addition, with the former leading to an increase in pH and acid neutralising capacity, and the latter to episodic acidification through hydrogen ion and aluminium displacement from soil exchange sites by marine base cations. Anion responses were less predictable: water addition caused a flush of nitrate, but this was apparently independent of rainfall composition. Sulphate remained near-constant during clean water addition but declined sharply during sea-salt addition, indicative of a strong, pH-dependent solubility control on leaching, presumably adsorption/desorption in the mineral soil. Most strikingly, dissolved organic carbon (DOC) concentrations were stable during clean water addition but varied dramatically in response to sea-salt addition, exhibiting a strong negative correlation with Cl concentrations in water draining the organic soil. These observations provide a robust experimental verification of the hypothesis that deposition chemistry, through its influence on acidity and/or ionic strength, has a major influence on DOC leaching to surface waters.     

Electrocardiographic monitoring in the Göttingen minipig

The purpose of the study reported here was to determine conditions for electrocardiographic monitoring in the G?ttingen minipig in view of its use as a second non-rodent species in toxicology studies. Electrocardiograms were recorded from conscious minipigs (6/sex) maintained in a sling. The three standard bipolar limb leads (I, II, III), the three augmented unipolar limb leads (aVR, aVL, aVF), the triangular Nehb-Sp?ri leads (dorsal, axial, ventral) and their corresponding unipolar leads were recorded, and automated analysis of amplitudes and intervals was made. Major QRS patterns were not observed for any of the bipolar and unipolar leads. For triangular leads, the amplitude of waves was higher than that for limb leads, and the rS pattern dominated for dorsal, axial ventral and aV(F)-Ventral leads. The qR pattern dominated in the aV(R)-dorsal lead, whereas consistency and dominant patterns were not observed for the aV(L)-axial lead. For limb leads, the position of the electrode affected the ECG. Electrodes placed on the cubital and stifle joints were the preferred positions since the P- and R-waves were clearly identifiable with amplitudes > 0.2 mV. Also, the T-wave amplitude was (positive or negative) > 0.2 mV in at least two leads, making the determination of the QT-interval accurate. For the triangular leads, the position of the electrode had less influence on the amplitude of deflections. However, if the axial lead is to be used for calculation of intervals and amplitudes, the xyphoid process is the preferred position. In conclusion, the triangular lead system is recommended for recording ECGs in minipigs. Limb leads could be used in connection. The cubital and stifle joints for standard limb leads and the neck, sacrum, and xyphoid process for triangular leads are the preferred positions for electrodes.     

Can Simple Empirical Equations Describe the Seasonal Dynamics of Bacterioplankton in Lakes: An Eight-Year Study in Shallow Hypertrophic and Biologically Highly Dynamic Lake Søbygård,Denmark

Abstract Seasonal variation in bacterioplankton abundance, biomass, and bacterioplankton production was studied over eight years in hypertrophic Lake S?byg?rd. Biologically, the lake is highly variable; this is due mainly to large interannual variation in fish recruitment. Bacterioplankton production was low during winter, typically 1–3 × 10⁷ cells l⁻¹ h⁻¹, and high during summer, albeit greatly fluctuating with maximum rates typically ranging from 60 to 90 × 10⁷ cells l⁻¹ h⁻¹ (or 0.4 to 0.6 mg C l⁻¹ day⁻¹). Less pronounced variations were found in bacterioplankton abundance, which typically ranged from 3–8 × 10⁹ cells l⁻¹ in winter to 15–30 × 10⁹ cells l⁻¹ during summer. The specific growth rate of bacterioplankton varied from 0.02–0.2 d⁻¹ in winter to 0.5–2.3 day⁻¹ during summer. Interpolated mean bacterioplankton production, in terms of carbon, ranged from 0.08 to 0.16 mg C l⁻¹ day⁻¹, corresponding to 1.6–5.5% of the phytoplankton production, while biomass ranged from 0.28 to 0.36 mg C l⁻¹, corresponding to 1.9–4.6% of the phytoplankton biomass. We conducted regression analysis, relating the bacterioplankton variables to a number of environmental variables, and evaluated the interannual parameter variability. Chlorophyll a and phytoplankton production contributed less to the variation in the bacterioplankton variables than in most previous analyses using data from less eutrophic systems. We suggest that the proportion of phytoplankton production that is channelized through bacterioplankton in lakes decreases with increasing trophic state and decreasing mean depth. This probably reflects a concurrent increase in fish predation on macrozooplankton and loss by sedimentation. An important part of the residual variation in the equations hitherto proposed in the literature could be explained by variation in macrozooplankton biomass and pH > 10.2. A negative effect of high pH on bacterioplankton production was confirmed by laboratory experiments. The impact of different zooplankton varies considerably, with Daphnia seeming to have a negative impact on bacterioplankton abundance and, thereby, indirectly on bacterioplankton production, while Bosmina, rotifers, and cyclopoid copepods seem to stimulate both abundance and production. Bosmina apparently also stimulate the bacterioplankton specific growth rate. Received: 8 February 1996; Accepted: 16 July 1996     

Ecology and Phenology of Freshwater Ostracods in Lake Gölköy (Bolu,Turkey)

Seventeen ostracod species were recorded from Lake Gölköy (Bolu, Turkey) between January 2000 and December 2001. Limnocythere inopinata is a new record for the Bolu region. Canonical Correspondence Analysis (CCA) explained 73% of the correlation between species and environmental variables, suggesting that the occurrence of many species is temporally variable, and is related to seasonal changes in physico-chemical conditions. The four most frequently occurring cosmopolitan ostracod species (Candona neglecta, Darwinula stevensoni, Physocypria kraepelini, and Cypridopsis vidua) accounted for more than 70% of the species recorded. Water temperature, dissolved oxygen (DO), and redox potential were the most affective variables on the species occurrence. Two species (C. vidua, I. bradyi) were positively correlated to redox potential, while such a correlation was negative for P. kraepelini. The most frequently occurring species C. neglecta was most closely related to the changes in redox potential, whereas C. vidua and D. stevensoni showed a positive correlation to water temperature. Negative strong correlation (p<0.01) was found between pH and I. bradyi, but correlation was positive and weak for C. vidua. Some species (e.g. L. inopinata) showed no clear relationship with any of those environmental variables. UPGMA clustering of species based on their occurrence in different ecological conditions revealed three main species assemblages. Analysis of species phenology using the ‘Ostracod Watch Model’ showed that temporal patterns of occurrence could be similar among species with similar ecological preferences. The current status of the lake is discussed based on the present study.     

Biomass and element pools of understory vegetation in the catchments of Čertovo Lake and Plešné Lake in the Bohemian Forest

This paper presents data on species composition, biomass, and element pools (C, N, P, Ca, Mg, Na, K, Al, Fe, Mn) of the understory vegetation of spruce forests in the catchments of lakes ?ertovo jezero (CT) and Ple?né jezero (PL) in the Bohemian Forest (?umava, Czech Republic). Calamagrostis villosa was the most abundant species in the CT catchment, while Vaccinium myrtillus was the most abundant species in the PL catchment. The catchments weighted mean (CWM) of above-ground biomass of the understory vegetation was 288 and 723 g m^?2 in the CT and PL catchments, respectively. The significant difference in the biomass between the catchments was caused by the much higher abundance of V. myrtillus in the PL catchment. The CWM of below-ground biomass of the fine roots was 491 and 483 g m^?2 in the CT and PL catchments, respectively. The respective CWM element pools of biomass in the CT and PL catchments were: C (33 and 51 mol m^?2), N (0.8 and 1.0 mol m^?2), P (24 and 34 mmol m^?2), Ca (53 and 113 mmol m^?2), Mg (24 and 41mmol m^?2), Na (3.7 and 6.5 mmol m^?2), K (83 and 109 mmol m^?2), Al (50 and 42 mmol m^?2), Fe (13.3 and 7.3 mmol m^?2), and Mn (4.2 and 8.8 mmol m^?2).     

Restoration of zooplankton in a small acidified mountain lake (Plešné Lake,Bohemian Forest) by reintroduction of key species

Atmospheric acidification brought about the extinction of several species of planktonic Crustacea in lakes of the Bohemian Forest (?umava, Böhmerwald). The recent reversal in chemical parameters of lake water towards pre-acidification values raises the question whether the return of missing species is possible. We have designed a bioassay to test water from different lakes for the survival of Daphnia longispina, which inhabited the lakes under study but disappeared from those most affected by acidification. The bioassay showed the best survival in water from Ple?né Lake, one of those where Daphnia and Cyclops became extinct. A large-scale experiment was conducted by transplanting Daphnia longispina (Crustacea, Cladocera) and Cyclops abyssorum (Crustacea, Copepoda) from Prá?ilské Lake, where they have survived until the present, to Ple?né Lake. One year later, a successful reintroduction was confirmed for Cyclops abyssorum.     

Sediment toxicity in lakes along the river Kolbäcksån,central Sweden

The River Kolbäcksån system is located in a historical mining and steel works district of central Sweden. Ten years ago, intensive limnological studies indicated that the sediments in many of the lakes of this system were contaminated with metals and oil (grease). More recently a very high toxicity was found in the sediments from some of these lakes in tests with Daphnia magna and Tubifex tubifex. The objective of this study was to determine the toxicity to Daphnia magna of surficial sediments from representative locations (N = 39) within this system of lakes and to look for possible correlations with concentrations of metals (Cd, Cr, Cu, Hg, Ni, Pb, Zn) and oil (total) analysed in parallel samples. These results were also compared with spiked sediment toxicity data generated for these metals and with the bottom fauna at 8 of the 39 locations. Among the metals analyzed, only Cd, Pb and Zn were correlated with whole sediment toxicity. Only for Zn and Cr did the maximum concentrations approach those that were toxic in the spiked sediments. Correlations using single and combined metal contamination and toxicity (additive models) explained 16% of the sediment toxicity (r ² = 0.16; N = 39). Significant correlations with the bottom fauna in situ (gross abundance, biomass and species richness) were found for whole sediment toxicity, but not for metal contamination (N = 8). The use of the sediment quality triad approach for assessment of sediment quality is exemplified with a numerical normalization procedure for the latter 8 sites.     

Paleolimnology of the Petén Lake district,Guatemala

The long-term impact of Maya culture on a lowland tropical watershed is assessed, using data from a 9.2 m sediment core taken from deep water (28 m) in Lake Quexil. Human population growth, estimated by the 1980 archaeological survey, is associated with a shift in the composition of the sediment to a dominance by inorganic material, the Maya clay formation, beginning ca. 3500 B.P. Increasing settlement densities are correlated with accelerated influxes of phosphorus, carbonates, and siliceous sediment. However, chemical data do not track short-term population fluctuations closely. Because much of the sediment is delivered as colluvium, and not by running water, there is a lag between terrestrial disturbance and impact on the aquatic system. As an indication of this lag, contemporary high sedimentation rates are a residual of Maya activity that virtually ceased some 300–400 years B.P. Comparison of the deep-water core with a shallow-water (7 m) section, based on palynological correlation, reveals only minor differences in proximate chemical composition. Chemical influxes are much higher at the deep-water site, however, as a consequence of sediment focusing in this hyperconical basin. Chemical analyses of soil samples from 21 test pits in the Quexil basin support the principal conclusion that bulk soil movement was the mode of nutrient transfer to the lake, following forest clearance by the Maya.     

Species composition of phytobenthos in the littoral of Lake Xolotlán (Managua)

The species composition of the phytobenthos in the littoral of Lake Xolotlán (Managua) was determined. Sampling was carried out in November 1987 (end of the rainy season) and in July–August 1988 (rainy season). Sixty-eight taxa were identified;viz. 47 Bacillariophyceae, 13 Cyanophyta and 8 Chlorophyta. The presence of diatom species likeNavicula veneta, Nitzschia amphibia andNitzschia palea indicate eutrophic conditions, high ionic concentration, alkaline conditions and intense organic pollution.     

Spring development of a Chlamydomonas population in Lake Nimetön,a small humic forest lake in southern Finland

Biomass development and vertical distribution of a Chlamydomonas population in a small humic forest lake was followed by daily sampling in May-June, 1984. Chlamydomonas dominated the phytoplankton spring bloom, forming 71% of the maximum phytoplankton biomass on 18 May. In early May the outflow rate was high and during the 24 hour period when the maximum rate of surface runoff was recorded (8–9 May), 43% of the Chlamydomonas biomass was flushed out of the lake, which delayed the onset of biomass increase. When surface runoff had slowed down Chlamydomonas biomass started increasing and during wax of the population most cells were < 10 µm in diameter. Population maximum lasted for one day (18 May) and there-after Chlamydomonas biomass decreased towards the end of the study. During wane of the population most cells were > 10 µm in diameter.     

Mercury contamination in Lake Xolotlán (Managua)

Total mercury was measured in different compartments of Lake Xolotlán's (Managua) ecosystemviz., sediments, water, fish and men. Sediments from 18 localities at 5 depths inside the sediment (5, 10, 15, 20 and 25 cm) contained an average concentration of 0.62 g Hg.g^–1±0.46 at the surface, with extreme values of 0.16 and 1.8 g.g^–1. The highest concentration was observed at 25 cm depth in front of the chlor-alkaly factory (ELPESA). This maximum is associated with the period of highest production of this factory. The highest mercury concentrations in water were also measured close to the discharge of ELPESA,viz. 787 g.Hg^–1 in January and 506 g.g^–1 in April. The mean mercury concentrations measured in the muscles of the most consumed fish were 0.63 g.g^–1±0.22 (extreme values 0.22 and 1.45) inCichlasoma managuense, and 0.07 g.g^–1±0.14 (extreme values 0.004 and 0.63) inC. citrinellum. The concentration in the liver was 0.79 g.g^–1±1.29 inC. managuense and 0.62 g.g^–1±0.44 inC. citrinellum. Human hairs (n=98) of fishermen and their families contained 5.03 g.g^–1±6.2 (extreme values 0.02 and 38.22). The mean concentration measured in men was 6.22 g.g^–1±6.34 (n=58), and in women 3.39 g.g^–1±5.7 (n=40). The average mercury concentration of hairs of workers of ELPESA was 91.24 g.g^–1±156.9 (extreme values 0.46 and 724.53; n=32). We conclude that total mercury levels in the various ecosystem compartments are very high and mercury contamination in the lake may be considered as dangerous for human health.     

Excursionen in die nördlichen Kalkalpen

Ohne Zusammenfassung     

Bacterioplankton Production in Humic Lake Örträsket in Relation to Input of Bacterial Cells and Input of Allochthonous Organic Carbon

In order to compare riverine bacteria input with lake water bacterial production and grazing loss with output loss, a bacterial cell budget was constructed for humic Lake ?rtr?sket in northern Sweden. The riverine input of bacterial cells in 1997 represented 29% of the number of bacterial cells produced within the layer of the lake affected by inlet water. A large share of the in situ lake bacterial production was consumed by grazers, mainly flagellates, which stresses the importance of bacteria as energy mobilizers for the pelagic food web in the lake. The bacterial production in Lake ?rtr?sket, which is almost entirely dependent on humic material as an energy source, was clearly stimulated by high flow episodes which brought high amounts of little degraded material into the lake. During base flow condition the bacterial production in the inlet rivers was high, which led to an input of more degraded material to the lake. This material did not stimulate the lake bacterial production. Internal factors that determined the utilization of the allochthonous DOC in the lake were the retention time and the exposure to light and high temperatures. Thus, the potential for in situ production of bacteria in Lake ?rtr?sket was to a large extent a function of how precipitation and runoff conditions affected terrestrial losses and river transport of humic material.     

The management of fisheries in Lake Vörtsjärv

L. Vörtsjärv is a eutrophic lake in Central Estonia. The area of the lake is 270 km², the average depth only 2.8 m. The biological productivity of the lake is rather low. Twelve to fifteen years ago the main fish were ruff and perch (80–90% of catch), while the numbers of valuable fish were small. At the same time the total catch of fish was relatively high — about 300 tons a year. Attempts were made to reduce the numbers of undesirable fish by intense trawl-catch but no marked results were achieved. Subsequently trawl-catch was ended, elvers were regularly introduced into the lake and protection of valuable fish was improved. At the present time the total catch of fish has decreased (184 tons in 1979), but pike-perch and eels are now the main game fish (50–60% of catch) and the value of the catch of fish has risen 2–3 times.