Effects of water hardness and alkalinity on the toxicity of uranium to a tropical freshwater hydra (Hydra viridissima)

In tropical Australian freshwaters, uranium (U) is of potential ecotoxicological concern, largely as a consequence of mining activities. Although the toxicity of uranium to Australian freshwater biota is comprehensive, by world standards, few data are available on the effects of physicochemical variables, such as hardness, alkalinity, pH and organic matter, on uranium speciation and bioavailability. This study determined the individual effects of water hardness (6.6, 165 and 330 mg l^-1 as CaCO₃) and alkalinity (4.0 and 102 mg l^-1 as CaCO₃), at a constant pH (6.0), on the toxicity (96 h population growth) of uranium to Hydra viridissima (green hydra). A 50-fold increase in hardness (Ca and Mg concentration) resulted in a 92% (two-fold) decrease in the toxicity of uranium to H. viridissima [i.e. an increase in the EC₅₀ value and 95% confidence interval from 114 (107-121) to 219 (192-246) µg l^-1]. Conversely, at a constant hardness (165 mg l-1 as CaCO₃), the toxicity of uranium to H. viridissima was not significantly (P > 0.05) affected by a 25-fold increase in alkalinity (carbonate concentration) [i.e. EC₅₀ values of 177 (166-188) and 171 (150-192) µg l^-1 at 4.0 and 102 mg l^-1 as CaCO₃, respectively]. A knowledge of the relationship between water chemistry variables, including hardness and alkalinity, and uranium toxicity is useful for predicting the potential ecological detriment in aquatic systems, and can be used to relax national water quality guidelines on a site-specific basis.     

Thermal, mixing, and oxygen regimes of the Salton Sea, California, 1997–1999

The Salton Sea is a shallow (mean depth = 8 m; maximum depth = 15 m), saline (41–45 g l^–1), intermittently mixing, 57 km long, 980 km² lake located in the arid southwestern United States. The Sea is a wind driven system, with predominant winds paralleling the long axis of the lake, being strongest in spring and weakest in summer and fall. The Sea mixed daily or nearly daily between September and January. During this cooling period, moderate to high levels of dissolved oxygen (3–11 mg l^–1) were found throughout the water column. Mean water column temperature ranged from a minimum of 13–14 °C in early January to a maximum of 30–34 °C in July–September. During most of this warming period, the Sea was thermally stratified but subject to periodic wind driven mixing events. Winds were stronger in spring 1998 than in 1997 or 1999, causing more rapid heating of the lake that year and also delaying onset of anoxic conditions in bottom waters. During summer months, mid-lake surface waters were sometimes supersatured with oxygen, and bottom waters were hypoxic or anoxic with sulfide concentrations > 5 mg l^–1. Oxic conditions (> 1 mg O₂ l^–1) often extended a few meters deeper nearshore than they did well offshore as a consequence of greater mixing nearshore. Mixing events in late summer deoxygenated the entire water column for a period of days. Consumption of oxygen by sulfide oxidation likely was the principal mechanism for these deoxygenation events. Sulfide concentrations in surface waters were 0.5–1 mg l^–1 approximately 3 days after one mixing event in mid-August 1999. These mixing events were associated with population crashes of phytoplankters and zooplankters and with large fish kills. In the southern basin, freshwater inflows tended to move out over the surface of the Sea mixing with saline lake water as a function of wind conditions. Salinity gradients often contributed more to water column stability than did thermal gradients in the southeasternmost portion of the lake.     

Thermal stratification and the stability of meromixis in the Pretoria Salt Pan,South Africa

The Pretoria Salt Pan, South Africa, a small (0.076 km²), shallow (Z_max = 2.85 m), hypersaline, maar lake, lies within a clearly-defined crater and is fed by a perennial, slightly saline (3 g l^-1) artesian spring. The lake has two distinct solar-heated peaks in its temperature profile, each of these peaks located in a highly turbid (>80 JTU) layer below a steep chemocline. The upper thermal peak, located at a depth of 10 cm, was transient, with a distinct diel pattern of diurnal heating and nocturnal cooling. The lower thermal peak, located below a steep chemocline and centred at approximately 60 cm, was stable and showed a seasonal pattern of winter heating (maximum: 38.5°C) and summer cooling (minimum: 27.4°C). The unusual bathymetry of the lake, combined with the sheltering effect of the crater rim and steep salinity gradient between the surface (30–80 g l^-1) and bottom water (280–310 g l^-1) prevented windmixing of surface waters beyond a depth of approximately 50 cm. During a 28 month study all water deeper than 55 cm remained anaerobic, and the lake appeared to be meromictic.     

Phytoplankton ecology of Loch Achray (Scotland)

Loch Achray is a warm monomictic lake in the Scottish highlands with water temperature ranging from 4 °C to 18.7 °C. The oxygen distribution is mainly clinograde with saturation values ranging from 76 to 112%. The general pattern of nutrient variation is irregular particularly for phosphate. Dissolved silica (measured as silicate) showed a range of 24 μg at. Si l⁻¹; phosphate varied from 0.24 to 0.03 μg at. P l⁻¹ while nitrate ranged from 3.5 to 15.2 μg at. N l⁻¹. The pH remained below 7 for the entire year and the alkalinity was very low, ranging from 2.5 to 6 mg CaCO₃ 1⁻¹. The examination of net samples showed Loch Achray to possess a poor phytoplankton population, consisting mainly of desmids and a few diatoms. The quantitative investigation showed a different picture of variation. There was no clear phytoplankton increase till May when a simultaneous increase occurred involving Melosira, Asterionella, Tabellaria fenestrata and Cyclotella. In July the population was dominated by Anabaena, while Cyclotella and Staurastrum became dominant in August.     

Phytoplankton ecology of the Lake of Menteith,Scotland

The results discussed in this paper represent the first seasonal ecological study carried out on the phytoplankton of the Lake of Menteith. All measured nutrients reached maximum levels during the winter, with silicate showing particularly high concentrations (up to 85 µg at Si l^–1). During the summer period phosphate, nitrate and silicate showed almost complete exhaustion in surface waters. The lake water was consistently alkaline, never falling below pH 7, while the alkalinity ranged from 20 to 24 mg CaCO₃ l^–1. Generally, the nutrient status of the main inflow had a rapid effect on the water quality of the lake.The region of the lake under investigation showed no thermal stratification at any period of the year, although continuous thermal gradients were recorded in the winter. The continual circulation of the water mass probably prevented oxygen saturation from falling below 77% even following a large phytoplankton bloom and subsequent decomposition.From an examination of net phytoplankton samples the Lake of Menteith could be described as blue-green or blue-green/diatom in nature. From the quantitative study, large pulses of Melosira, Asterionella and Fragilaria were recorded in the spring. The disappearance of the species appears to be related to silicate limitation. The summer growth of Asterionella may have been promoted by a nitrogen source other than nitrate and nitrite, both of which were reduced to critical levels. This alternative source of combined nitrogen may have been contributed by nitrogen-fixing algae in the lake. Three species of Anabaena were recorded, all of which produced large populations during the year.Department of Botany, The University of GlasgowPresent Address: Department of Biology, College of Science, University of Sulaimaniyah, Sulaimaniyah, Iraq     

Hardness does not affect the physiological responses of wild and domestic strains of diploid and triploid rainbow trout Oncorhynchus mykiss to short‐term exposure to pH 9.5

This study examined the effects of water hardness on the physiological responses associated with high pH exposure in multiple strains of diploid and triploid rainbow trout Oncorhynchus mykiss. To accomplish this, three wild strains and one domesticated strain of diploid and triploid O. mykiss were abruptly transferred from control soft water (City of Vancouver dechlorinated tap water; pH 6·7; [CaCO₃] < 17·9 mg l^?1) to control soft water (handling control), high pH soft water (pH 9·5; [CaCO₃] < 17·9 mg l^?1), or high pH hard water (pH 9·5; [CaCO₃] = 320 mg l^?1) followed by sampling at 24 h for physiological measurements. There was a significant effect of ploidy on loss of equilibrium (LOE) over the 24 h exposure, with only triploid O. mykiss losing equilibrium at high pH in both soft and hard water. Furthermore, exposure to pH 9·5 resulted in significant decreases in plasma sodium and chloride, and increases in plasma and brain ammonia with no differences between soft and hard water. There was no significant effect of strain on LOE, but there were significant differences between strains in brain ammonia and plasma cortisol. Overall, there were no clear protective effects of hardness on high pH exposure in these strains of O. mykiss.     

Regional high affinity synaptosomal transport of choline in mouse brain — Influence of oxotremorine treatment

Kinetic parameters for high affinity [HA] uptake $\text{in vitro}$ in synaptosomes from different mouse brain regions were investigated. V_max was highest in the striatum [200 pmol.· mg protein^?1 · 4 min^?1], followed by the cortex [111 pmol · mg protein^?1 · 4 min^?1], hippocampus [63 pmol · mg protein^?1 · 4 min^?1], midbrain [21 pmol · mg protein^?1 · 4 min^?1] and, lowest, medulla oblongata [5 pmol · mg protein^?1 · 4 min^?1]. K_m was about the same in all brain regions [0.9–1.4 μM]. No sign of HA uptake was detected in synaptosomes from the cerebellum. A clear relationship between V_max for synaptosomal HA uptake of Ch $\text{in vitro}$ and apparent turnover of ACh $\text{in vivo}$ was found between the brain regions. Administration of oxotremorine [1 mg·kg^?1 i.p.] decreased V_max for HA uptake of Ch by 60% in the cortex and hippocampus, by 50% in the striatum and by 20% in the midbrain. This effect is in accordance with the previously observed marked decrease in turnover of ACh in these brain regions following oxotremorine treatment.     

Short term toxicity of iron (Fe) and lead (Pb) to the mayfly Leptophlebia marginata (L.) (Insecta) in relation to freshwater acidification

The mayfly Leptophlebia marginata was exposed to different concentrations of Fe²⁺ or Pb²⁺ at pH 4.5 and pH 7.0. The effects of the metals on escape behavior and survival of the mayflies were investigated during an exposure of 120 hours.

1. Whole-body metal loads (Fe; Pb) of the mayflies increased in a dose-dependent way at both pH levels. A significant effect of pH on metal concentration in the mayflies was only found for Pb (p < 0.001).
2. In terms of mortality, both metals were more toxic at pH 4.5 than at pH 7. The 96 h-LC₅₀ values for Fe were 106.3 mg Fe l^-1 at pH 7 and 89.5 mg Fe l^-1 at pH 4.5. Those for Pb were > 5 mg Pb l^-1 at pH 7 and 1.09 mg Pb l^-1 at pH 4.5.
3. The mayflies lost their escape behavior, when exposed to the metals, the effects being more pronounced at low than at circumneutral pH for both metals (p < 0.05). The 96 h-EC₅₀ values for Fe were 70.0 mg Fe l^-1 at pH 7 and 63.9 mg Fe l^-1 at pH 4.5.

     

Study of the acyl transfer activity of a recombinant amidase overproduced in an Escherichia coli strain. Application for short-chain hydroxamic acid and acid hydrazide synthesis

The study of acyl transfer activity of a wide spectrum amidase from Rhodococcus sp. R312, overproduced in an Escherichia coli strain, revealed that the ‘bi-bi-ping-pong’ type reaction was efficient with only four very-short chain (C₂–C₃) aliphatic amides as substrates. The optimum working pH was 7.0 for all neutral amides. Very short-chain aliphatic carboxylic acids were 10–1000-fold less efficient and the corresponding optimum working pH values depended on the acid used. Very polar molecules, such as water, hydroxylamine and hydrazine, were good acyl acceptors. An [acyl donor]/[acyl acceptor] ratio lower than 0.3-0.5 had to be maintained to avoid enzyme inhibition by excess acyl donor. The different acyl-enzyme complexes generally exhibited high affinity for hydroxylamine or hydrazine (except the propionyl-enzyme complex), so that the residual hydrolysis activities were almost totally inhibited at appropriate acyl acceptor concentrations. Molar conversion yields were higher with hydrazine as acyl acceptor (e.g., 97% with acetamide as acyl donor) because of the higher V_max values, but in all cases, interesting quantities of short-chain hydroxamic acids (2.9-6.5 g l⁻¹) and acid hydrazides (6.4–7.8 g l⁻¹) could be quickly obtained (10–60 min) with small amounts of enzyme (0.04-0.20 g l⁻¹).     

Occurrence of Cryptophyceae and katablepharids in boreal lakes

One of the most important algal groups in Finnish lakes are the Cryptophyceae. Changes in the community structure of Cryptophyceae in a total of 22 lakes belonging to the Vuoksi river basin in eastern Finland were studied. The existence of lakes with water qualities varying from oligotrophic to eutrophic, often loaded by human activities, provides a good opportunity to study the effects of environmental variables on the occurrence and size variation of Cryptophyceae. In the Vuoksi river basin, the main soil type is moraine. Twelve of the lakes were large or moderately large and with clear, i.e. oligo-humic water, and one lake could be described as a small clear water lake. Eight large or moderately large lakes were humic, with a water colour number of 40–70 mg l^?1 Pt, including three lakes impacted by nutrient loads. One lake was naturally eutrophic, with a high water colour number of 100 mg l^?1 Pt, and was also impacted by municipal and pulping effluents. CCA-ordination analysis grouped the studied lakes into: (1) clear water lakes, (2) humic lakes and (3) the naturally eutrophic brown water lake. In the CCA-ordination analysis based on cell numbers small Cryptophyceae (Cryptomonadales), Rhodomonas lacustris and the katablepharid Katablepharis ovalis were grouped into the first axis, which was positively correlated with Secchi depth (r=0.58) and NO₃N - nitrogen (r=0.24) and negatively with Ptot (r=-0.69), PO₄P (r=-0.69) and water colour number (r=-0.66). In humic lakes, medium-sized Cryptophyceae were abundant. The naturally eutrophic lake was grouped into first axis, which is positively correlated with Ptot (r=0.69), PO₄P (r=0.69) and water colour number (r=0.66). The lake formed a distinct group with large Cryptophyceae. Only in this lake was the heterotrophic Katablepharis ovalis rather abundant. However, large-sized taxa dominated the biomass of the Cryptophyceae assemblage in all lake types excluding large clear water lakes, where Rhodomonas lacustris dominated and large Cryptophyceae co-dominated.     

Diel, episodic and seasonal changes in pH and concentrations of inorganic carbon in a productive lake

• 1 Two pH electrodes and a thermistor were used to record conditions in the surface of Esthwaite Water every 15 min over a 12-month period. Combined with approximately weekly measurements of alkalinity they allowed inorganic carbon speciation to be calculated.
• 2 Large changes in pH from 7.1 to nearly 10.3, and hence in concentrations of inorganic carbon species, were measured over a year. Carbon speciation and pH varied on a diel, episodic and seasonal basis. Diel variation of up to pH 1.8 was recorded, although typical daily variation was between 0.03 and 1.06 (5 and 95 percentiles). Daily change in concentration of inorganic carbon varied between 4 and 63 mmol m^-3 (5 and 95 percentiles).
• 3 During lake stratification, episodes of high pH, typically of 1–2 weeks' duration were interspersed with episodes of lower pH. These changes appeared to relate to the weather: e.g. low wind velocity, high pressure, low rainfall and high sunshine hours correlated with periods of high pH.
• 4 Seasonal progression of carbon depletion generally followed stratification and the development of high phytoplankton biomass. When the lake was isothermal, the phytoplankton biomass caused relatively small amounts of carbon depletion.
• 5 During autumn, winter and spring, the lake had concentrations of CO₂* (free CO₂) up to 0.12 mol m^-3 which is nearly seven times the calculated atmospheric equilibrium concentration so the lake will accordingly be losing carbon to the atmosphere. In contrast, during periods of elevated pH the concentration of CO₂* was reduced close to zero and the lake will take up atmospheric CO₂. The rates of transfer between water and the atmosphere were estimated using a chemical equilibrium model with three boundary layer thicknesses. The calculations show that over a year the lake loses CO₂ to the atmosphere with the current mean atmospheric level of 360 μmol mol^-1, at between 0.28 and 2.80 mol m^-2 yr^-1. During elevated pH, rates of CO₂-influx increased up to nearly tenfold as a result of chemical-enhancement by parallel flux of HCO^-₃. Input of CO₂* to the lake from the catchment is suggested to be the main source of the carbon lost to the atmosphere.
• 6 The turnover time for CO₂ between the air and water was calculated to be 1 year for the gross influx and 3.3 years for the net flux. These values are less than the average water residence time of 0.25 years, which indicates that over a year inflow from streams is a more important source of inorganic carbon than the atmosphere.
• 7 Influx of CO₂ from the atmosphere was calculated to be roughly equivalent to between 1 and 4% of the rates of production in the water during mid-summer indicating that this source of inorganic carbon is not a major one in this lake.
• 8 Influx of CO₂ from the hypolimnion was estimated on one occasion to be 6.9 10^-9 mol m^-2 s^-1 using transfer values based on mass eddy-diffusion. These rates are equivalent to 23% of the rate of influx of CO₂ from the atmosphere on this occasion which suggests that the hypolimnion is probably a small source of inorganic carbon to the epilimnion. The exception appears to be during windy episodes when pH is depressed. Calculations based on depth-profiles of CO₂* and HCO^-₃ suggest that the measured changes in pH can be accounted for by entrainment of hypolimnetic water into the epilimnion.
• 9 The solubility product for calcite was exceeded by up to about sixfold which, although insufficient to allow homogeneous precipitation, may have allowed heterogeneous precipitation around algal particles.

     

New distribution record for the Asian tapeworm Bothriocephalus acheilognathi Yamaguti, 1934 in the Eastern Cape province,South Africa

Assuming that the inshore and offshore waters of Lake Victoria are impacted differently by human activities in its catchment, this study investigated the water quality dynamics of the lake. A total of 29 stations were sampled in 2005–2008 for dissolved oxygen (DO), pH, Secchi transparencies, temperature, turbidity, chlorophyll a, NO₃, SRSi, TN and TP. There was a decreasing trend of the measured parameters towards offshore sites, except for Secchi transparency and NO₃, which increased towards the offshore waters. DO concentrations (mean ± SD) varied between 6.97 ± 0.57 mg O₂ l^–1 and 5.80 ± 0.72 mg O₂ l^–1 in the inshore and offshore waters, respectively. Turbidity values were comparatively higher in the inshore (3.73 ± 2.21 NTU) than the offshore waters (2.19 ± 1.81 NTU). Chlorophyll a concentrations varied between 17.36 ± 6.13 µg l^–1 and 8.09 ± 4.38 µg l^–1 in the inshore and offshore waters, respectively. Increases of unsustainable human activities in the lake and its catchments, plus increased degradation of wetlands, are among the causes of the observed water quality changes. In order to be fruitful and sustainable, the management of Lake Victoria and its catchment needs to take an ecosystem approach, and to involve all key stakeholders.     

Physiological responses of carbon-sequestering microalgae to elevated carbon regimes

In order to identify a high carbon-sequestering microalgal strain, the physiological effect of different concentrations of carbon sources on microalgae growth was investigated. Five indigenous strains (I-1, I-2, I-3, I-4 and I-5) and a reference strain (I-0: Coccolithus pelagicus 913/3) were subjected to CO₂ concentrations of 0.03–15% and NaHCO₃ of 0.05–2 g CO₂ l^–1. The logistic model was applied for data fitting, as well as for estimation of the maximum growth rate (μ_max) and the biomass carrying capacity (B_max). Amongst the five indigenous strains, I-3 was similar to the reference strain with regards to biomass production values. The B_max of I-3 significantly increased from 214 to 828 mg l^–1 when CO₂ concentration was increased from 0.03 to 15% (r = 0.955, P = 0.012). Additionally, the B_max of I-3 increased with increasing NaHCO₃ (r = 0.885, P = 0.046) and was recorded at 153 mg l^–1 (at 0.05 g CO₂ l^–1) and 774 mg l^–1 at (2 g CO₂ l^–1). Relative electron transport rate (rETR) and maximum quantum yield (F_v/F_m) were also applied to assess the impact of elevated carbon sources on the microalgal cells at the physiological level. Isolate I-3 displayed the highest rETR confirming its tolerance to higher quantities of carbon. Additionally, the decline in F_v/F_m with increasing carbon was similar for strains I-3 and the reference strain. Based on partial 28s ribosomal RNA gene sequencing, strain I-3 was homologous to the ribosomal genes of Chlorella sp.     

Amino acid and monoamine transport in primary astroglial cultures from defined brain regions

The uptake ofl-[³H]glutamate,l-[³H]aspartate, -[³H]aminobutric acid (GABA), [³H]dopamine,dl-[³H]norepinephrine and [³H]5-hydroxytryptamine (5-HT) was studied in astrocytes cultured from the cerebral cortex, striatum and brain stem of newborn rat and grown for 2 weeks in primary cultures. The astrocytes exhibited a high-affinityl-glutamate uptake withK _m values ranging from 11 to 110 M.V _max values were 4.5 in cerebral cortex, 39.1 in striatum, and 0.4 in brain stem, nmol per mg cell protein per min. There was a less prominent high-affinity uptake ofl-aspartate withK _m values from 88 to 187 M.V _max values were 7.4 in cerebral cortex, 37.1 in striatum, and 3.1 in brain stem, nmol per mg cell protein per min. The high-affinity GABA uptake exhibitedK _m values ranging from 5 to 17 M andV _max values were 0.01 for cerebral cortex, 0.04 for striatum, and 0.1 for brain stem, nmol per mg cell protein per min. No high-affinity, high-capacity uptake was found for the monoamines. The results demonstrate a heterogeneity among the astroglial cells cultivated from the different brain regions concerning the uptake capacity of amino acid neurotransmitters. Furthermore, amino acid transmitters and monoamines are taken up by the cells in different ways.     

Glasgow Lake: an early-warning sentinel of lake acidification in Cape Breton Highlands National Park (Nova Scotia,Canada)

In contrast to other lakes studied in Cape Breton Highlands National Park (Nova Scotia, Canada), our paleolimnological results indicated that Glasgow Lake has been impacted by acidic deposition starting in the early 1900s. Based on analysis of diatom assemblages, the lake experienced a decrease in diatom-inferred lakewater pH from a pre-industrial pH of ~5.8 to a current pH of 5.3 (2000–2002 measured mean pH = 5.0) as well as a decrease in diatom-inferred Gran-alkalinity. In this study, diatom-based paleolimnological techniques were used in conjunction with a dynamic biogeochemical model (MAGIC) to assess both the timing and extent of the acidification trend, as well as determine a probable explanation as to why this lake, and none of the other 15 Cape Breton Highlands lakes studied for paleolimnology thus far, acidified under a peak non-marine sulphate deposition load of 43.6 mmol_c m⁻² year⁻¹ in the mid-1970s. Steady-state models estimate that Glasgow Lake had the lowest buffering capacity of six study lakes and estimated critical sulphate loading of <1 mmol_c m⁻² year⁻¹. MAGIC also estimated a loss of charge balance alkalinity from a pre-1850 value of 38 μmol_c l⁻¹ to a low of 12 μmol_c l⁻¹. While no evidence of biological recovery has been recorded, MAGIC estimates an increase in charge balance alkalinity to 27 μmol_c l⁻¹ in 2002 in response to decreased SO₂ emissions. Of the five other lakes that were modelled, all showed trends towards more acidic states and subsequent increases in charge balance alkalinity; however, the empirical paleo-diatom approach applied to these lakes showed no evidence of acidification. Thus, Glasgow Lake has the lowest buffering capacity among the Cape Breton Highland study lakes and serves as a sentinel of potential acidification trends and recovery in this region. Handling editor: J. Saros     

Heterotrophic bacterial activity and primary production in a hypertrophic African lake

The relationship between heterotrophic bacteria and phytoplankton in the epilimnion (0–10 m) of hypertrophic Hartbeespoort Dam, South Africa, was examined by statistically analyzing three years of parallel measurements of heterotrophic bacterial activity (glucose uptake) and phytoplankton particulate and dissolved organic carbon production. Algal biomass ranged between 4.0 and 921.1 mg Chl a m^-3 at the surface. Primary production varied between 69.5 and 3010.0 mg C m^-2h^-1 while algal production of dissolved organic carbon (EDOC) ranged from 2.5 to 219.2 mg C m^-2h^-1. Bacterial numbers reached a summer peak of 44.23 × 10⁶ cells ml^-1 in the first year and showed no depth variation. The maximum rate of glucose uptake, V_max, reached a peak of 5.52 g C l^-1h^-1. V_max, maximum glucose concentration (K_t + S_n) and glucose turnover time (T_t) were usually highest at the surface and decreased with depth concomitant with algal production. At the surface, V_max was correlated to EDOC (r = 0.59, n = 67, p < 0.001) and primary production (r = 0.71, n = 70, p < 0.001). At 5 and 10 m, V_max was correlated to integral euphotic zone (~ 4 m) algal production and bacterial numbers. Glucose turnover time was inversely related to integral algal production (r = -0.72, n = 70, p < 0.001) and less strongly to bacterial numbers. The data indicated that although bacterial numbers and biomass were low relative to algal biomass in this hypertrophic lake, the heterotrophic bacteria attained high rates of metabolic activity as a result of enhanced algal production of available organic carbon.     

Performance and ethanol oxidation kinetics of a sulfate-reducing fluidized-bed reactor treating acidic metal-containing wastewater

The treatment of simulated acidic wastewater (pH 2.5–5)containing sulfate (1.0–2.2 g l^-1), zinc (15–340 mg l ^-1) and iron (57 mg l ^-1) was studied in a sulfate-reducing fluidized-bed reactor (FBR) at 35 °C.The original lactate feed for enrichment and maintenance of the FBRculture was replaced stepwise with ethanol over 50 days. The robustnessof the process was studied by increasing stepwise the Zn, sulfate andethanol feed concentrations and decreasing the feed pH. The following precipitation rates were obtained: 360 mg l ^-1 d ^-1 for Zn and 86 mg l ^-1 d ^-1 for Fe, with over 99.8% Zn and Fe removal, with a hydraulic retention time of 16 h. Under these conditions, 77–95% of the electrons were accepted by sulfate reduction. The alkalinity produced from ethanol oxidation increased the wastewater pH from 2.5 to 7.5–8.5. Michaelis–Menten constants (K_m) determined in batch FBR experiments, were 4.3–7.1 mg l ^-1 and 2.7–3.5 mg l ^-1 for ethanol and acetateoxidation, respectively. The maximum oxidation velocities (V_max)were 0.19–0.22 mg gVS ^-1 min ^-1 and0.033–0.035 mg gVS ^-1 min ^-1, for ethanol and acetate, respectively. In summary, the FBR process produced a good quality effluent as indicated by its low organic content and Zn and Fe concentrations below0.1 mg l ^-1.     

A comparison of zooplankton communities in saline lakewater with variable anion composition

Although salinity and aquatic biodiversity are inversely related in lake water, the relationship between types of salts and zooplankton communities is poorly understood. In this study, zooplankton species were related to environmental variables from 12 lakes: three saline lakes with water where the dominant anions were SO₄ and CO₃, four saline lakes with Cl-dominated water, and five dilute, subsaline (0.5–3 gl^?1 total dissolved solids) lakes of variable anion composition. Although this study comprised only 12 lakes, distinct differences in zooplankton communities were observed among the two groups of chemically defined saline lakes. Canonical correspondence analysis identified total alkalinity, sulphate, chloride, calcium, sodium, potassium, and total phosphorus as all contributing to the first two ordination axes (λ₁ = 0.97 and λ₂ = 0.62, P<0.05). The rotifer Brachionus plicatilis and the harpactacoid copepod Cletocamptus sp. prevailed lakes with Cl-dominated water. In contrast, the calanoid copepods Leptodiaptomus sicilis and Diaptomus nevadensis were dominant in the SO₄/CO₃-dominated lake water with elevated potassium (79–128 mg l^?1) and total phosphorus concentrations (1322-2915 μg l^?1). The contrasting zooplankton species distribution among these two saline lake types is likely explained by variable selective pressure on zooplankton and their predators from differing physiological tolerances to salt stress and specific ions. While inland saline lakes with Cl as the dominant anion are relatively rare in Canada and SO₄/CO₃ are the common features, our study provided an opportunity to compare zooplankton communities across the two groups of lakes.     

Seasonal water quality of shallow and eutrophic Lake Pamvotis, Greece: implications for restoration

Lake Pamvotis is a moderately sized (22 km²) shallow (z _avg=4 m) lake with a polymictic stratification regime located in northwest Greece. The lake has undergone cultural eutrophication over the past 40 years and is currently eutrophic (annual averages of FRP=0.07 mg P l^-1, TP=0.11 mg P l^-1, NH₄ ⁺=0.25 mg N l^-1, NO₃ ^–=0.56 mg N l^-1). FRP and NH₄ ⁺ levels are correlated to external loading from streams during the winter and spring, and to internal loading during multi-day periods of summer stratification. Algal blooms occurred in summer (July–August green algae, August–September blue-green algae), autumn (October blue-green algae and diatoms), and winter (February diatoms), but not in the spring (March–June). The phytoplankton underwent brief periods of N- and P-limitation, though persistent low transparency (secchi depth of 60–80 cm) also suggests periods of light limitation. Rotifers counts were highest from mid-summer to early autumn whereas copepods were high in the spring and cladocerans were low in the summer. Removal of industrial and sewage point sources a decade ago resulted in a decrease in FRP. A phosphorus mass balance identified further reductions in external loading from the predominately agricultural catchment will decrease FRP levels further. The commercial fishery and lake hatchery also provides opportunities to control algal biomass through biomanipulation measures.     

Environmental chemistry of rivers and lakes, part v: a comparative study of the chemical and physicochemical characteristics of organic carbon dissolved in river and lake waters

To determine the chemical and physicochemical characteristics of dissolved organic carbon in the Ado River and the Yasu River, the main rivers flowing into Lake Biwa, the adsorption behavior onto hydrous iron oxide (HIO) and the reactivity to KMnO₄ oxidant were investigated in parallel with measurement of the distribution profiles of dissolved organic carbon (DOC) along the rivers. In one year of observation at the mouths of the two rivers, DOC concentrations were found to vary in the Ado over the range 0.28–1.21 mg C l⁻¹ and in the Yasu over the range 1.01–2.68 mg C l⁻¹. Act-DOC, one of the fractions separated from the total DOC by its adsorption-active character onto HIO at pH 4, was thought primarily to control the variation of total DOC, as in Lake Biwa. The int-DOC, another fraction separated by its adsorption-inert or -inactive character onto HIO, remained at almost a steady value around 0.18 ± 0.07 mg C l⁻¹ in the Ado, which was lower than that (0.35 ± 0.05 mg C l⁻¹) in Lake Biwa. The act-DOC in river waters was reactive to KMnO₄ oxidant, showing a linear relation with the amount of permanganate consumed for the reaction (chemical oxygen demand: COD). In river waters, the relation can be approximated by a straight line expressed as COD (mg O₂ l⁻¹) = 0.64 × act-DOC (mg C l⁻¹) − 0.02. In contrast, in the lake water the relation was COD (mg O₂ l⁻¹) = 0.97 × act-DOC (mg C l⁻¹) − 0.50. Received: March 3, 1999 / Accepted: December 2, 1999