Submerged aquatic vegetation correlations with depth and light attenuating materials in a shallow subtropical lake

A 3-year study was done to quantify the biomass of submerged aquatic vegetation (SAV) and its relationship with environmental attributes in Lake Okeechobee, the largest lake in the southeastern United States. Plants were sampled on 21 occasions at sites located along 15 fixed transects around the shoreline, giving rise to 721 observations of SAV species (Chara spp., Vallisneria americana, Hydrilla verticillata, Potamogeton illinoinensis) dry weight biomass. Environmental sampling focused on factors that attenuate light, including phytoplankton chlorophyll a (chl a), total suspended solids (TSS), non-volatile suspended solids (NVSS) and color. Depth and Secchi transparency also were measured. Based on regression analysis, NVSS was considerably more important in attenuating light than chl a or color. Total biomass of SAV varied from 0 to 271 g dw m^–2, with a mean of 4.7 g dw m^–2, and strong dominance by Chara. The SAV biomass was lower than average for Florida lakes, and may reflect the influence of suspended solids on underwater irradiance, as well as high water level in the late 1990s. Dense SAV was found only where depth was < 2 m and TSS < 20–30 mg l^–1. At locations where high biomass of SAV occurred, the plants may have influenced water quality, because concentrations of TSS, NVSS, and chl a were 2–3 fold lower than at sites with no plants. The potential effects of SAV also were apparent at a regional scale. The shoreline region of the lake displayed a pattern of rising and falling chl a and NVSS with water depth. This occurred both at sites with and without plants, suggesting that it may be driven by physical processes, such as water circulation patterns, which are influenced by depth. However, the pattern was dampened at sites with SAV, indicating a potential to influence these attributes of water quality.     

Characterization of the light field in laboratory scale enclosures of eutrophic lake water (Lake Loosdrecht,The Netherlands)

Light conditions in laboratory scale enclosures (LSE) of shallow, eutrophic Lake Loosdrecht (The Netherlands), including a method for simulating a natural incident light course, are described. Total PAR (400–700 nm) and spectral irradiance distribution were measured at sestonic chlorophyll a and dry weight concentrations 100 mg m^–3 and 16 g m^–3, respectively. Phytoplankton was dominated by Oscillatoria spp. The euphotic depth (Z _eu) was 0.7–1.0 m. Shortly after filling the LSE with lake water, diffuse attenuation coefficients ranged from 14 m^–1 for blue to 5 m^–1 for red light. Around Z _eu, attenuation in the blue region was markedly lower and irradiance reflectance (R) continued to increase; these anomalies were caused by lateral incident light from the LSE's waterbath. Spectrophotometry indicated that absorption was mainly by particles, but dissolved humic substances (gilvin) were also important. The particles were likely to be dominated by detritus absorbing more blue relative to red light. Subsurface R in lake water in the LSE had a maximum around 705 nm and low values in the blue band, but was lower than that previously reported for measurements in situ. Wash-out of detritus, presumably both dissolved and particulate fractions, by flow-through with synthetic medium, greatly affected the spectral reflectance measured outside the LSE. The maximum value of R decreased from 0.022 to 0.009, and the peak shifted to 550 nm.     

Secchi disk — chlorophyll relationships in a lake with highly variable phytoplankton biomass

In meseutrophic Lake Constance mean euphotic phytoplankton chlorophyll concentrations vary about 100-fold over the year. Concomitant fluctuations in euphotic depth (Z_eu) and Secchi depth (Z_s) are related to each other in a non-linear fashion that as a rough approximation can be expressed by Z_eu 5 Z_s.Secchi depth is to a great extent a function of beam attenuation of light which depends on the inherent optical properties of the water and is highly sensitive to light scattering from particles. Euphotic depth, by contrast, is a function of the vertical light attenuation coefficient which also depends on absorption and scattering, but is less sensitive to the latter than beam attenuation. Algal cells both absorb and scatter light and therefore influence Secchi depth and euphotic depth, however, in different fashions.Whenever the lake is clear due to scarce phytoplankton, scattering is small and beam attenuation only exceeds vertical light attenuation by a relatively small factor. As a consequence, the ratio of euphotic depth to Secchi depth is small (1.5–2.5). When the lake is turbid due to high algal density, enhanced scattering from algal cells and detrital particles causes beam attenuation to rise more than vertical light attenuation, thus leading to high ratios of euphotic depth to Secchi depth (3–5). The relatively close relationships between Secchi depth and chlorophyll in Lake Constance are due to (1) high influence of chlorophyll concentration on water transparency, (2) co-variation of phytoplankton and other suspended particles, and (3) limited variation of cellular chlorophyll contents.     

Determining critical light and hydrologic conditions for macrophyte presence in a large shallow lake: The ratio of euphotic depth to water depth

Light determines macrophyte distribution, community composition and biomass in shallow lakes. Therefore, it is vital to determine the critical underwater light climate thresholds for macrophyte degradation and recovery. In this study, we first proposed a novel index, defined as the ratio of euphotic depth (Z_eu) to water depth (WD), as a measure of the underwater light supply for macrophytes. The underwater light environment in Lake Taihu (a large, shallow, eutrophic lake) was then characterized based on this index (Z_eu/WD) using field measurements collected from 2006 to 2013 (8 years × 4 seasons × 32 sites). The distribution of the macrophyte presence frequency (MPF, the number of investigations that identified macrophytes divided by the total number of investigations) was greater than 0.70 in Xukou Bay and East Lake Taihu over the 32 investigations, followed by the other sites distributed in East Lake Taihu. The proportion of macrophyte coverage increased with the increase in Z_eu/WD. A significant relationship was observed between Z_eu/WD and MPF for the 19 sites with macrophytes (r² = 0.48, p < 0.001, n = 19). In the region with high nutrient concentrations and serious water pollution, better underwater light conditions are required for the growth of macrophytes. A Z_eu/WD value of 0.80 can be regarded as the critical underwater light threshold for the growth of macrophytes in Lake Taihu. The region with Z_eu/WD ranging between 0.57 and 0.80 was usually covered by sparse macrophytes; this region should be vital for macrophyte recovery and environmental management in Lake Taihu. The distribution of Z_eu/WD was further obtained using MODIS satellite-derived Z_eu from June to October in 2003 and 2013. Xukou Bay and Guangfu Bay in the southern part of Lake Taihu could be regarded as potentially crucial regions for the recovery of macrophytes from the perspective of underwater light and nutrient levels.     

Effects of food and silt on filtration,respiration and condition of the freshwater mussel Hyridella menziesi (Unionacea: Hyriidae): implications for bioaccumulation

The effect of exposure to different concentrations of food and suspended silt on filtration, respiration and condition were studied in the freshwater mussel Hyridella menziesi. Using a milk solids-based food and kaolin to simulate silt, mussels were maintained at different combinations of food and silt concentrations for 3 weeks. Between treatments mean filtration rates ranged from 0.97–1.66 l g^–1 h^–1, and respiration from 0.50–1.35 mg O₂ g^–1 h^–1. Silt (non-volatile suspended solids up to 35 mg l^–1) failed to have a significant effect on filtration rate or condition, but with increasing food levels (volatile suspended solids up to 35 mg l^–1) filtration rate was reduced, and condition was reduced at the lowest food concentration (<5 mg l^–1). Respiration showed a food × silt interaction between treatment blocks. When food was low respiration increased with increasing silt concentrations, and when silt was low (<5 mg l^–1) respiration increased with increasing food concentrations. The observed effects of food and silt on filtration, respiration and condition are discussed in terms of their potential for affecting contaminant bioaccumulation. In low-food situations (i.e., <5 mg l^–1), if mussels are pumping large volumes of water, contaminant uptake rates could be enhanced, whereas abundant food would result in lower pumping rates and lower uptake rates. Changes in metabolism with food concentration have implications for contaminant elimination, and changes in biochemical composition associated with changing condition could affect the tissue distribution and retention of contaminants.     

Overturn in a hypertrophic,warm, monomictic impoundment (Hartbeespoort Dam,South Africa)

A major decrease in air temperature with an increase in wind stress created thermal instability resulting in overturn. Surface oxygen values decreased from 12.6 (170% saturation) prior to overturn to 0.4 mg · l^–1 (5.7%) after overturn. Recovery of surface oxygen concentrations to supersaturation took approximately three months. Changes in the nitrogen balance after overturn indicated that extremely high rates of nitrification occurred. Little change in phosphorus concentration was observed. Surface chlorophyll concentrations decreased from 235 to approximately 2 mg · m^–3, resulting in very low primary production values (A_max = 12.4 mg C m^–3 h^–1). Reduced rates of primary production were maintained for several months after overturn, mainly owing to the low ratio of Z_eu/Z_m (0.17). No significant changes occurred in the total bacterial population other than a redistribution within the water column. Significant changes occurred in the distribution and density of the zooplankton population. No fish kills were observed although fish populations were oxygen-stressed.     

Light limitation of phytoplankton development in an oligotrophic lake - Loch Ness, Scotland

• 1 The underwater light climate in Loch Ness is described in terms of mixing depth (Z_m) and depth of the euphoric zone (Z_eu). During periods of complete mixing, Z_m equates with the mean depth of the loch (132 m), but even during summer stratification the morphometry of the loch and the strong prevailing winds produce a deep thermocline and an epilimnetic mixed layer of about 30 m or greater. Hence, throughout the year the quotient Z_m/Z_eu is exceptionally high and the underwater light climate particularly unfavourable for phytoplankton production and growth.
• 2 Phytoplankton biomass expressed as chlorophyll a is very low in Loch Ness, with a late summer maximum of less than 1.5 mg chlorophyll a m^-3 in the upper 30 m of the water column. This low biomass and the resulting very low photosynthetic carbon fixation within the water column are evidence that a severe restraint is imposed on the rate at which phytoplankton can grow in the loch.
• 3 The chlorophyll a content per unit of phytoplankton biovolume and the maximum, light-saturated specific rate of photosynthesis are both parameters which might be influenced by the light climate under which the phytoplankton have grown. However, values obtained from Loch Ness for both chlorophyll a content (mean 0.0045 mg mm^-3) and maximum photosynthetic rate (1–4 mg C mg Chla^-1 h^-1) are within the range reported from other lakes.
• 4 Laboratory bioassays with the natural phytoplankton community from Loch Ness on two occasions in late summer when the light climate in the loch is at its most favourable, suggest that even then limitation of phytoplankton growth is finely balanced between light and phosphorus limitation. Hence, for most of the year, when the light climate is less favourable, phytoplankton growth will be light limited.
• 5 Quotients relating mean annual algal biomass as chlorophyll a (c. 0.5 mg Chla m^-3) and the probable annual specific areal loading of total phosphorus (0.4–1.7 g TP m^-2 yr^-1) suggest that the efficiency with which phytoplankton is produced in Loch Ness per unit of TP loading is extremely low when compared with values from other Scottish lochs for which such an index has been calculated. This apparent inefficiency can be attributed to suppression of photosynthetic productivity in the water column due to the unfavourable underwater light climate.
• 6 These several independent sources of evidence lead to the conclusion that phytoplankton development in Loch Ness is constrained by light rather than by nutrients. Loch Ness thus appears to provide an exception to the generally accepted paradigm that phytoplankton development in lakes of an oligotrophic character is constrained by nutrient availability.

     

Evidence for coupled transport of bicarbonate and sodium in cultured bovine corneal endothelial cells

Summary Usin gintracellular microelectrode technique, the response of the voltageV across the plasma membrane of cultured bovine corneal endothelial cells to changes in sodium and bicarbonate concentrations was investigated. (1) The electrical response to changes in [HCO ₃ ^– ] _o (depolarization upon lowering and hyperpolarization upon raising [HCO ₃ ^– ] _o ) was dependent on sodium. Lithium could fairly well be substituted for sodium, whereas potassium or choline were much less effective. (2) Removal of external sodium caused a depolarization, while a readdition led to a hyperpolarization, which increased with time of preincubation in the sodium-depleted medium. (3) The response to changes in [Na⁺] _o was dependent on bicarbonate. In a nominally bicarbonate-free medium, its amplitude was decreased or even reversed in sign. (4) Application of SITS or DIDS (10^–3 m) had a similar effect on the response to sodium as bicarbonate-depleted medium. (5) At [Na⁺] _o =151mm and [HCO ₃ ^– ] _o =46mm, the transients ofV depended, with 39.0±9.0 (sd) mV/decade, on bicarbonate and, with 15.3±5.8 (sd) mV/decade, on sodium. (6) After the preincubation of cells with lithium, replacement of Li by choline led to similar effects as the replacement of sodium by choline, though the response ofV was smaller with Li. This response could be reduced or reversed by the removal of bicarbonate or by the application of SITS. (7) Amiloride (10^–3 m) caused a reversible hyperpolarization of the steady-state potential by 8.5±2.6 mV (sd). It did not affect the immediate response to changes in [Na⁺] _o or [HCO ₃ ^– ] _o , but reduced the speed of regaining the steady-state potential after a change in [HCO ₃ ^– ] _o . (8) Ouabain (10^–4 m) caused a fast depolarization of –6.8±1.1 (sd) mV, which was followed by a continuing slower depolarization. The effect was almost identical at 10^–5 m. (9) It is suggested, that corneal endothelial cells possess a cotransport for sodium and bicarbonate, which transports net negative charage with these ions. It is inhibitable by stilbenes, but not directly affected by amiloride or ouabain. Lithium is a good substitute for sodium with respect to bicarbonate transport and is transported itself. In addition, the effect of amiloride provides indirect evidence for the existence of a Na⁺/H⁺-antiport. A model for the transepithelial transport of bicarbonate across the corneal endothelium is proposed.     

The 1994 experimental opening of the Bonnet Carre Spillway to divert Mississippi River water into Lake Pontchartrain, Louisiana

A diversion of Mississippi River water into Lake Pontchartrain, Louisiana, USA by way of the Bonnet Carre Spillway has been proposed as a restoration technique to help offset regional wetland loss. An experimental diversion of Mississippi River water into Lake Pontchartrain was carried out in April 1994 to monitor the fate of nutrients and sediments in the spillway and Lake Pontchartrain. Approximately 6.4×10⁸ m³ of Mississippi River water was diverted into Lake Pontchartrain over 42 days. As water passed through the Bonnet Carre Spillway, there were reductions in total suspended sediment concentrations of 82–83%, nitrite+nitrate (NO_x) of 28–42%, in total nitrogen (TN) of 26–30%, and in total phosphorus (TP) of 50–59%. 3.9±1.1 cm of accretion was measured in the spillway. Nutrient concentrations at the freshwater plume edge in Lake Pontchartrain compared to the Mississippi River were lower for NO_x (44–81%), TN (37–57%), and TP (40–70%), and generally higher for organic nitrogen (−7–57%). The Si:N ratio generally increased and the N:P ratio decreased from the river to the plume edge. Nutrient stoichiometric ratios indicate water at the plume edge was not silicate limited, suggesting conditions favoring diatomic phytoplankton.     

Seasonal succession,standing crop and determinants of primary productivity of the phytoplankton of Ministik Lake,Alberta, Canada

Ministik Lake (longitude 113°01; latitude 53°21), a well-mixed, shallow (mean depth 1.83 m), eutrophic lake is characterized by eutrophic chlorococcalean and cyanophycean phytoplankton associations, and little change in standing crop size with increasing depth. Standing crops and primary productivity are low during the winter but pronounced spring and late summer/early autumn maxima occur. Mean yearly areal standing crop (B) and primary productivity (A) were 199.2 mg m^–2 chlorophyll a and 319.5 mg C hr^–1 m^–2 respectively. Annual productivity was estimated at 1399,6 g C m^–2yr^–1. The mean increase in the extinction coefficient () per unit increase in standing crop (B) was 0.03 In units m^–1. High non-algal light attenuation (q) occurred averaging 46% which prevented the ratio B from attaining more than 74.2% of the theoretical maximum except once when selfshading occurred. Insignificant relationships existed between B (mg m^–3 chlorophyll a) and A_max (mg C hr^–1 m^–3), A and B and A and B. Close correlations existed between A and A_max/ and A and I₀ (W m^–2). The depth of the euphotic zone (Z_eu) varied between 0.6 and 2.0 m; the average relationship between z_eu and was z_eu = 3.78/_te, and the mean standing crop in the euphotic zone represented 58.3% of the theoritical maximum. The high _q values made the model of Talling (1957) inapplicable to this lake. The Q₁₀ value for the lake was 1.20. _max (mg C chlorophyll a ^–1 hr^–1) was closely related to both temperature and irradiance, and depressed by high pH values.Growth of the cyanophycean algae was correlated with temperature, chlorophycean algae with phosphate-phosphorus and temperature and the diatoms with dissolved silica and phosphate-phosphorus, but only in the case of Chaetoceros elmorii did any nutrient appear limiting. Indirect evidence that free CO₂ limited photosynthetic rates is provided by the _max:pH relationship.     

Denitrification kinetics of simulated fish processing wastewater at different ratios of nitrate to biomass

Denitrification was studied in anoxic batch cultures of a simulated fish processing wastewater at 37 r C and pH 7.5, using a denitrifying enrichment culture from fishery wastewater. Different initial nitrate to biomass ratios (So/Xo) were used: nitrate and biomass varied from 7.5 to 94.7 mg NO₃-N l^–1, and from 20 to 4300 mg volatile suspended solids l^–1, respectively. The specific maximum denitrification rate (r _m) and the cell yield (Y _{X / S}) depended on the So/Xo ratio under anoxic conditions: r _m increased from 1.2 to 1584 mg NO₃-N g^–1 VSS h^–1 and Y _{X / S} decreased from 42 to 0.03 mg VSS mg^–1 NO₃-N when So/Xo varied from 5.5 10^{– 3} to 9.3 mg NO₃-N/mg VSS. Nomenclature C_{NO3 – N} nitrate concentration, mg NO₃-N l^–1 K _S saturation constant, mg NO₃-N l^–1 r _m specific maximum denitrification rate, mg NO₃-N g^–1 VSS h^–1 So initial substrate concentration, mg l^–1 t time, h TOC total organic carbon VSS volatile suspended solids x biomass concentration, g VSS l^–1 Xo initial biomass concentration, g VSS l^–1 Y _X/S substrate to biomass cell yield, mg VSS/mg N Greek symbols: _m maximum specific growth rate of the anoxic microbial population, 1 h^–1     

Water quality of Inanam river estuary and the Ko-Nelayan tiger prawn aquaculture ponds in Sabah,Malaysia

Concentrations of selected metals (Cd, Co, Cr, Fe, Mn and Pb), oxidizable organic carbons, sediment acid potentials, dissolved oxygen (DO), dissolved solids, suspended solids, pH, conductivity, salinity and temperature in the Inanam River Estuary and the KO-Nelayan tiger prawn aquaculture ponds were monitored during the period March to August 1989. Dissolved Co and Pb were found to be higher than the recommended values of 0.05 mgl^–1 (Krenkel & Novotny, 1980; Nemerow, 1985), whereas the other metals were comparable to the recommended safe levels. DO concentrations of the river and pond water were in the range 2.6–4.7 mgl^–1 and 3.0–5.3 mgl^–1 respectively, both with an average which was lower than the optimum value for the growth of prawns which is 5 mgl^–1. Ferrous sulfide concentrations were in the range 0.14–1.20%. Suspended solids were higher than the maximum (40 mgl^–1) recommended value by WHO (1978). Other physical parameters were within the recommended range for optimal growth of tiger prawns.     

Phytoplankton primary production in a shallow,well- mixed,hypertrophic South African lake

This paper reports on a two-year analysis of the wind climateand its effect on phytoplankton primary production in ashallow (mean depth = 1.9 m), hypertrophic South Africancoastal lake, Zeekoevlei. The lake is subject to continuousmixing of the euphotic zone (Z _eu = 0.8 m), andcomplete mixing of the water column to the mean depth on adaily basis. Median annual wind speeds, prevailing fromeither the north or the south, were 6.4 m s^–1. There wasan almost total absence of calms, measured as hourly meanwind speeds of <1 m s^–1. Notwithstanding the highfrequency of mixing, the lake supports a dense population ofphytoplankton, dominated by Cyanophyte and Chlorophytespecies. Mean concentrations of chlorophyll-a were240 g l^–1. The attenuation of photosyntheticallyavailable radiation, PAR, was high, with mean K _dvalues of 6.4 m^–1 and water transparencies of <0.5 m.Levels of primary productivity, determined using the lightand dark bottle oxygen method, were very high, comparable toor exceeding that of the most productive systems yet studied.Maximum volumetric productivity ranged from 525 to 1524 mg Cm^–3 h^–1, and was confined to the upper 0.5 m of thewater column. Daily areal productivity, P _d,varied between 1.2 and 4.3 g C m^–2 d^–1, and that ofthe maximum chlorophyll-a specific photosynthetic rate,P _{B max}, between 1.6 and 7.9 mg C (mgChl-a)^–1 h^–1. Primary production was limited bywater temperature and the attenuation of PAR. The highfrequency of wind-induced mixing resulted in regular mixingof the phytoplankton through the euphotic zone, and reducedthe overall importance of P _max at a single layer inthe depth profile. Similarly, the regularity of mixing wasrecognized as a limitation of the incubation of bottle chainsto determine primary production levels.     

Salinity and dissolved substances in the Vaal River at Balkfontein,South Africa

Seasonal variation and interrelationships between environmental variables and salinity in the Vaal River at Balkfontein were investigated between 1985 and 1989. The salinity levels were high (min. 108, max. 1032, average 512 mg 1^-1), and indications are that salinisation of the river water is continuing at a rate of 15 mg 1^t-1 a^-1. The concentration of major ions (mg 1^-1 or meq 1^-1) in the river water occurred in the proportions of cations, i.e. Ca²⁺ Na⁺ > Mg²⁺ > K⁺ and of anions, i.e. SO₄ ^2- > HCO₃ ^- > Cl^-. The high S0₄ concentration (average 212 mg 1^-1) indicated SO₄ pollution at Balkfontein. High Ca concentrations (average 59 mg 1^-1) evidently interfered with the solubility of phosphate (PO₄) which could play an important role in the availability of PO₄ to phytoplankton in the system. Measured electrical conductivity (EC) values can be used to estimate salinity (S, in mg 1^-1) in the Vaal River, i.e. e. S = 7.13 * EC - 27.8 (from regression analysis) or S = 6.72 * EC (from TDS:EC ratio). Salinity in the river tends to be higher during the dry season, i.e. winter months. All the dissolved ions (except Si) showed decreased concentrations with increased run-off. The main importance of the high salinity in the Vaal River is evidently its influence on turbidity and the possible clarification of the water-column, which results in a deeper euphotic zone and thus more favourable conditions for photosynthesis followed by a biomass build-up of phytoplankton.     

Phytoplankton of shallow lakes: Seasonal succession, standing crop and the chief determinants of primary productivity, 1. Cooking Lake, Alberta, Canada

Cooking Lake (113°02′W, 53°26′N), a well-mixed, shallow (mean depth (1.59 m), eutrophic lake in Alberta, Canada, is characterized by eutrophic chlorococcalean and cyanophycean phytoplankton associations, and little change in standing crop with increasing depth. Standing crop and primary productivity are low during the winter but pronounced spring and summer maxima occur. Mean yearly areal standing crop (ΔB) and primary productivity (ΔA) were 212.4 mg m^?2 chlorophyll a and 301.8 mg C h^?1 m^?2 respectively. Annual productivity was estimated at 1322 g C m^?2. The mean increase in the extinction coefficient (?) per unit increase in standing crop (B) was 0.03 In units m^?1. High non-algal light attenuation (?_q) occurred avenging 41 which prevented the ratio B/? from attaining more than 65% of the theoretical maximum except once when algal self-shading occurred. Close correlations existed between B (mg m^?3 chlorophyll a) and A _max (mg h_?1 m_?3) ΔA and ΔB, ΔA and B, A_max, and A_max/?, and ΔA and I_o′, (W m^?2). The depth of the euphotic zone (Z_eu) varied between 0.5 and 1 25 m; the average relationship between z_eu and E was Z_eu= 3.74/?, and the mean standing Crop found in the euphotic zone represented 55.2% of the theoretical maximum, The high ?_q, values made the model of Tailing (1957) inapplicable to Cooking Lake. The Q₁₀ value for the lake was 2.2. The maximum rate of photosynthesis per unit of population per h. Ø^max, (mg C sag chlorophyll a_?1 h_?1) was more closely related to temperature than irradiance and ma depressed by pH values greater than 9.1. Growth of the phytoplankton was not nutrient limited: instead irradiance and temperature were more important. Indirect evidence that free CO₂ limited photosynthetic rates, is provided by the Ø_max: pH relationship.     

Enzymatic pre-hydrolysis and anaerobic degradation of wastewaters with high fat contents

Dairy wastewaters containing elevated fat and grease levels (868 mg l^–1) were treated in an upflow anaerobic sludge blanket reactor (UASB) and resulted in effluents of high turbidity (757 nephelometric turbidity units), volatile suspended solids up to 944 mg l^–1 and COD removal below 50%. When the same dairy wastewater was pre-treated with 0.1% (w/v) of fermented babassu cake containing Penicillium restrictum lipases, turbidity and volatile suspended solids were decreased by 75% and 90%, respectively, and COD removal was as high as 90%.     

The effect of sewage-enriched river Ganga water on the biomass production of theAzolla-Anabaena complex

The biomass formation ofAzolla was greatly enhanced by water of the River Ganga and by prevailing environmental conditions. It increased gradually from January to April (first maximum 2.409 g.m^–2.day^–1), declined during June (1.185 g.m^–2.day^–1), and reached a second its maximum during September (2.629 g.m^–2.day^–1). The biomass formation was related to the nutrient availability in the medium in a particular season (measured were: nitrate-N, available phosphorus, total suspended solids, and conductivity). The average annual production of 6.73 ton.ha^–1.yr^–1 is equivalent to the average production of 0.025 ton.ha^–1.yr^–1 phosphorus, 0.252 ton.ha^–1.yr^–1 nitrogen, and 1.57 ton.ha^–1.yr^–1 crude protein.     

Photosynthetic bacteria in meromictic lakes and stratified fjords of the Vestfold Hills,Antarctica

Thirteen meromictic lakes and two permanently stratified fjords in the Vestfold Hills, Antarctica, were surveyed in 1983 for photosynthetic bacteria. Burton Lake and Ellis Fjord were sampled throughout the year to determine seasonal variations. Physical and chemical parameters were recorded and related to the species present. The dominant species in waters with salinities of 100.7 g kg^–1 were Chlorobium vibrioforme and Chlorobium limicola with populations at the O₂–H₂S interface in the range 0.3 to 6.7 × 10⁶ ml^–1. Neither of these species was found at higher salinities. Thiocapsa roseopersicina and a Chromatium sp. were found in low numbers (< 10⁵ ml^–1) in most of the same waters as the Chlorobium spp. These bacterial phototrophs developed in a narrow band below the O₂–H₂S interface where both light and H₂S were available. Very low numbers (< 10² ml^–1) of Rhodopseudomonas palustris were found in both oxic and anoxic waters having salinity 148 g kg^–1. The dominance of the Chlorobium spp. is ascribed to their more efficient maintenance metabolism during the darkness, their faster growth at low light intensities (< 1 µE m^–2 s^–1) and the lack of selective filtering of incident light. The Chlorobium spp. grew well at –2 °C, but not –5°C in hypersaline waters. The concentration of H₂S had no apparent effect on the development of the bacterial flora. Viable cells were found to depths of 100 m in Ellis Fjord indicating that viability in total darkness could have been maintained for periods of the order of 1700 days.     

Ulva rigida (Ulvales,Chlorophyta) tank culture as biofilters for dissolved inorganic nitrogen from fishpond effluents

Ulva rigida was cultivated in 7501 tanks at different densities with direct and continuous inflow (at 2, 4, 8 and 12 volumes d^–1) of the effluents from a commercial marine fishpond (40 metric tonnes, Tm, of Sparus aurata, water exchange rate of 16 m³ Tm^–1) in order to assess the maximum and optimum dissolved inorganic nitrogen (DIN) uptake rate and the annual stability of the Ulva tank biofiltering system. Maximum yields (40 g DW m^–2 d^–1) were obtained at a density of 2.5 g FW 1^–1 and at a DIN inflow rate of 1.7 g DIN m^–2 d^–1. Maximum DIN uptake rates were obtained during summer (2.2 g DIN M^–2 d^–1), and minimum in winter (1.1 g DIN m^–2 d^–1) with a yearly average DIN uptake rate of 1.77 g DIN m^–2 d^–1 At yearly average DIN removal efficiency (2.0 g DIN m^–2 d^–1, if winter period is excluded), 153 m² of Ulva tank surface would be needed to recover 100% of the DIN produced by 1 Tm of fish.Abbreviations DIN= dissolved inorganic nitrogen (NH _inf4 ^sup+ + NO _inf3 ^sup– + NO _inf2 ^sup– ); - FW= fresh weight; - DW= dry weight; - PFD= photon flux density; - V= DIN uptake rate     

Performances of constructed wetlands for municipal wastewater treatment in rural mountainous area

A global performance evaluation of an experimental Horizontal SubSurface Flow Constructed Wetlands (HSSF) was made after 6 years of functioning. This wetland is situated in French prealpine mountain, at 720 m elevation. The HSSF process treatment consists in a three-stage system dimensioned for 350 People Equivalent. Different helophytes were planted such as Typha latifolia, Phragmites australis and Scirpus maritimus. The mean hydraulic residence time for sewage was closed to 4–5 days, but in summer the mean pollutant residence time increases to 6 days due to an important evapotranspiration. There is no clogging of the gravel matrix and the hydraulic conductivity was very good and stabilized. Removal pollutant efficiency was determinate at each stages. There was a high removal of total suspended solids (TSS) all year around with an average of 95.6% (±3.6). More than 80% of removal occurred in the first stage. Physical processes (decantation, filtration) associated with biological oxidation were the principal factors of this removal. For COD and BOD₅, removal efficiency in the first stage were close to 60% on average and more than 90% at the outlet of the wetland. These results are similar to those observed with SSFW in many cases. Influence of temperature seems very weak because there were no significant seasonal variations of the process efficiency. Minimum effluent quality standards (30 mg l^–1 TSS; 120 mg l^–1 COD; 40 mg l^–1 BOD₅) were always respected. In cold periods, nutrients uptake was reduced but remained up to 60% in average. Mean bacterial removal efficiency was about two order of magnitude (99%) but can reach up to five order of magnitude in summer. These cyclic variations follow a sinusoidal variation around an annual mean. Pollutants removals were correlated to their respective loadings and no limits has been observed except for nitrogen. These results confirm that SSFW, an ecotechnology, should be considered as an alternative to conventional treatment methods (activated sludge, fixed biofilm) for small communities even in mountainous area.