Seasonal dynamics,typhoons and the regulation of lake metabolism in a subtropical humic lake

1. We used high‐frequency in situ dissolved oxygen measurements to investigate the seasonal variability and factors regulating metabolism in a subtropical alpine lake in Taiwan between May 2004 and October 2005, specifically exploring how the typhoon season (from June or July to October) affects lake metabolism. 2. Gross primary production (GPP) and ecosystem respiration (R) both peaked in early summer and mid‐autumn but dropped during the typhoon season and winter. Yuan‐Yang Lake is a net heterotrophic ecosystem (annual mean net ecosystem production ?39.6 μmole O₂ m^?3). 3. Compared to the summer peaks, seasonal averages of GPP and R decreased by approximately 50% and 25%, respectively, during the typhoon season. Ecosystem respiration was more resistant to external disturbances than GPP and showed strong daily variation during typhoon seasons. 4. Changes in the quality and quantity of dissolved organic carbon controlled the temporal dynamics and metabolic regulation. External disturbances (typhoons) caused increased allochthony, increasing DOC and water colour and influencing lake metabolism. 5. Seasonal winter mixing and typhoon‐induced water mixing in summer and autumn play a key role in determining the extent to which the lake is a seasonal carbon sink or source to the atmosphere.     

Effect of pH on the growth cycle of HeLa cells in batch suspension culture without oxygen control

HeLa cells have been cultured at different controlled pH levels in batch suspension culture with open gas phase. Continuous monitoring of the dissolved oxygen tension throughout the culture cycle reveals a characteristic pattern of variation which correlates with various aspects of growth and carbohydrate metabolism. The effect of pH, size, and physiological state of the inoculum on this pattern have been determined, and the results are discussed in terms of a theoretical respiratory rate equation.     

Effects of thermal stratification and mixing on reservoir water quality

In this study, the effect of thermal stratification on water quality in a reservoir has been investigated by field observations and statistical analysis. During the summer period, when stratification is evident, field observations indicate that the observed dissolved oxygen concentrations drop well below the standard limit of 5 mg l⁻¹ at the thermocline, leading to the development of anoxia. The reasons for variations in the dissolved oxygen concentrations were investigated. Variations of air temperature and other meteorological factors and lateral flows from side arms of the lake were found to be responsible for the increase of dissolved oxygen concentrations. It was also observed that turbidity peaked mostly in the thermocline region, closely related to the location of the maximum density gradient and thus low turbulence stabilizing the sediments in the vertical water column. Relatively cold sediment-laden water flowing into the lake after rain events also resulted in increased turbidity at the bottom of the lake. Nondimensional analysis widely used in the literature was used to identify the strength of the stratification, but this analysis alone was found insufficient to describe the evolution of dissolved oxygen and turbidity in the water column. Thus correlation of these parameters was investigated by multivariate analysis. Fall (partial mixing), summer (no mixing), and winter (well mixed) models describe the correlation structures between the independent variables (meteorological parameters) and the dependent variables (water-quality parameters). Statistical analysis results indicate that air temperature, one day lagged wind speed, and low humidity affected variation of water-quality parameters.     

Epilimnetic nutrient loading by metalimnetic erosion and resultant algal responses in Lake Waramaug,Connecticut

Phosphorus regeneration from lake sediments, and subsequent migration to trophogenic surface water, significantly contributes to the lake nutrient budgets and algal bloom conditions in some lake types. Decomposition of organic matter in deep water and sediments results in the accumulation of regenerated nutrients, alternate electron acceptors (reduced products of anaerobic respiration = COD), carbon dioxide, and depletion of dissolved oxygen (electron acceptor in aerobic respiration). Thermal stratification creates spatial segregation of trophogenic and tropholytic environments in the lake, resulting in gradients between sediments, hypolimnion, and the epilimnion. Exchange of oxygen, nutrients, and reduced alternate electron acceptors between the hypolimnion and epilimnion affects the productivity of a lake. Secchi depth, temperature, and dissolved oxygen profiles were determined twice each week from May 1980 to October 1980 at each of five lake stations. Nutrient concentration profiles, including total soluble and total phosphorus, ammonium-N, nitrate, soluble Kjeldahl, and total Kjeldahl nitrogen were determined twice each month. Epilimnetic algal samples were collected twice each week using Kemmerer and water column ‘straw’ amplers. Cell counts of total, green, bluegreen, and diatom algae groups were made. Three methods were used to describe hypolimnetic-epilimnetic exchange, including coefficients of eddy diffusion (based on lake heat budget), a graphical method of defining thermocline location, and relative thermal resistance to mixing (RTRM, based on density differences). All three methods yeilded comparable estimates of net seasonal transport. The graphical and RTRM methods described events occurring at shorter intervals (greater resolution). We find general agreement between the three methods of describing hypolimnetic-epilimnetic transport. The frequency of sampling resulted in increased resolution of thermal profiles (in time), allowing accurate estimation of short-term nutrient flux into epilimnetic waters. An algal bloom event occurred 5 to 12 days following erosion of the top of the metalimnion to below the aerobic-anaerobic interface. The lag time to peak algal concentration, following such events, decreased through the summer (June = 12 days, September = 5 days)     

Some features of the thermal and dissolved oxygen structure in boreal,shallow ice-covered Lake Vendyurskoe,Russia

The 5-year-long (2001–2005) studies of the winter thermal structure and the dissolved oxygen (DO) dynamics in Lake Vendyurskoe, Russia, a typical boreal shallow mesotrophic lake of glacial origin, revealed still poorly studied features of lake-wide dynamics, such as net lateral heat flux towards deeper parts of a lake and development of the anaerobic zone over the deepest points of the lake basin. We estimated magnitude of the heat transport along the bottom slope based on scaling analysis. The seasonal changes in DO concentration appear to be controlled mostly by biochemical consumption. We identify four factors controlling the extent of anoxic zones in shallow ice-covered lakes: (1) the amount of organic matter stored in the bottom layers, including the sediments surface during the autumnal bloom; (2) the length of the ice-covered period; (3) heat content of bottom sediments; and (4) the initial water temperatures at the time of the ice cover formation.     

Structure and dynamics of phytoplankton in an Amazon lake, Brazil

Natural lake systems represent important reservoirs for residential water supply, fish production, recreational activities and enjoyment of their natural beauty. Nevertheless, human impacts may affect their health status resulting in degradation and loss of biodiversity. The aim of the present study was to obtain data on the health status of a natural lake located in an indigenous reservation in the Brazilian Amazon, using the phytoplankton community changes along the rainy (June) and dry (November) seasons of 2006. We collected water (temperature, pH, Secchi depth and conductivity) and phytoplankton samples from the subsurface, middle of the water column, and approximately 30 cm above the bottom, over 24-hour sampling periods, from a central station in the lake. Samples taken from biotic and abiotic variables were correlated using canonical correspondence analysis (CCA). Results showed that the lake exhibited high temperatures in both seasons, and showed thermal stratification only during the rainy season. Dissolved oxygen exhibited a clinograde pattern in the rainy season and high oxygen in the hypolimnion in the dry season. In the rainy season, the water near the bottom was acidic, turbid and had a greater concentration of phosphorus. Dissolved oxygen, conductivity, pH, nitrite, total phosphorus and total dissolved phosphorus exhibited diel variations in the rainy season, whereas water temperature, dissolved oxygen, total nitrogen and total dissolved phosphorus exhibited significant differences between hours of the day in the dry season. The phytoplankton was represented by 39 taxa, and Chlorophyta showed the greatest species richness, totaling 25 taxa. Among Chlorophyta, desmids were the most diverse, accounting 52%. Bacillariophyta (nine species) was the second most diverse group. Cyanophyta was represented by three species, including Merismopedia tenuissima, the most abundant taxon. Despite the occurrence of taxa that indicate organic pollution, their biomass and frequency indicate that the system is not currently threatened. Lake Caracaran? is an oligotrophic system, with low algal density and isolated blooming episodes due to its shallow depth.     

An Upwelling Event at Onondaga Lake, NY: Characterization, Impact and Recurrence*

The occurrence, features and impacts on oxygen resources of an upwelling event in culturally eutrophic Onondaga Lake, NY, are documented, and recurrence is investigated, based on data collected as part of long-term, robotic, and event monitoring programs. The upwelling event occurred on September 11, 2002, in response to a wind event of average wind speed of ～10 m s^?1 that extended over an interval of 11 hours along the main axis of the lake. Longitudinal differences in temperature (T) and dissolved oxygen (DO) documented for the lake's surface waters during the upwelling event were 5.7?°C and 10 mg l^?1. DO concentrations <1 mg l^?1 were observed in surface waters at the windward end of the lake. Oxidation of reduced oxygen-demanding by-products of anaerobic metabolism supplied to the upper waters from stratified layers during the event contributed to a loss of DO from the lake. Review of historic lake stratification, water quality related to oxygen resources, and long-term wind data indicate upwelling events with coupled deleterious impacts on DO resources have not been rare; at least 14 such events are estimated to have occurred over the 1990–2002 interval. The documented event probably represents a worst case for oxygen impacts for this period. An underway rehabilitation program, that will reduce anthropogenic phosphorus loading and implement hypolimnetic oxygenation, may ameliorate the impacts of upwelling events on the DO resources of the lake.     

Effects of dissolved oxygen concentration on biodegradation of 2,4-dichlorophenoxyacetic acid.

Batch experiments were conducted to examine the effects of dissolved oxygen concentration on the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) by an enrichment culture of 2,4-D-utilizing bacteria. A modified Monod equation was found to describe the relationship between the specific growth rate and the concentrations of both the organic substrate and dissolved oxygen. Values for the maximum specific growth rate, yield, and Monod coefficient for growth on 2,4-D were 0.09 h-1, 0.14 g/g, and 0.6 mg/liter, respectively. The half-saturation constant for dissolved oxygen was estimated to be 1.2 mg/liter. These results suggest that dissolved oxygen concentrations below 1 mg/liter may be rate limiting for the biodegradation of chlorinated aromatic compounds such as 2,4-D, which have a requirement for molecular oxygen as a cosubstrate for metabolism.     

Effects of dissolved oxygen concentration on biodegradation of 2,4-dichlorophenoxyacetic acid

Batch experiments were conducted to examine the effects of dissolved oxygen concentration on the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) by an enrichment culture of 2,4-D-utilizing bacteria. A modified Monod equation was found to describe the relationship between the specific growth rate and the concentrations of both the organic substrate and dissolved oxygen. Values for the maximum specific growth rate, yield, and Monod coefficient for growth on 2,4-D were 0.09 h-1, 0.14 g/g, and 0.6 mg/liter, respectively. The half-saturation constant for dissolved oxygen was estimated to be 1.2 mg/liter. These results suggest that dissolved oxygen concentrations below 1 mg/liter may be rate limiting for the biodegradation of chlorinated aromatic compounds such as 2,4-D, which have a requirement for molecular oxygen as a cosubstrate for metabolism.     

Nutrient limitation of phytoplankton in a central Arizona reservoir

The influence of added nutrients nitrogen, phosphorus and carbon on the phytoplankton of a small recreational reservoir in central Arizona was investigated during the summer, 1974. Polyethylene bags were used to isolate lake water and the natural populations for the addition of nitrogen, phosphorus and carbon individually and in combination. A large increase in phytoplankton numbers, extractable chlorophyll, pH and dissolved oxygen occurred only in bags to which both nitrogen and phosphorus were added, suggesting that both nitrogen and phosphorus levels were limiting to the primary producers. Little alteration in species composition resulted from the addition of the above nutrients.     

Modeling impacts of Yangtze River water transfer on water ages in Lake Taihu, China

To improve water quality and alleviate eutrophication in Lake Taihu, the third largest freshwater lake in China, a Yangtze River water transfer project was initiated in 2002 to bring water from the Yangtze River to Lake Taihu to dilute and divert pollutants out of the lake. We used a three-dimensional numerical model, Environmental Fluid Dynamics Code, to study the impacts of water transfer on the transport of dissolved substances in the lake by using the concept of water age. In particular, the influences of inflow tributaries and wind forcing on water age were investigated. Model results showed that the effect of water transfer on transport processes in the lake is strongly influenced by hydrodynamic conditions induced by wind and inflow/outflow tributaries. During the simulation year (2005), the water ages in Lake Taihu were highly variable both spatially and temporally, with a mean of approximately 130 days in summer and 230 days in the other seasons. Southeasterly winds—dominant in the summer—could improve the quality of water by reducing the water age in the eastern areas of the lake, which are used as a drinking water source, and in Meiliang Bay, the most polluted bay. In terms of dilution, the most efficient flow rate for transferred water was predicted to be approximately 100 m³/s. The spatial distribution of water ages showed that water transfer may preferentially enhance exchanges in some areas of the lake unless nutrient concentrations in the transferred water are reduced to a reasonable level. This study provides useful information for a better understanding of the complex hydrodynamic and mass transport processes in the lake, which is important for developing and implementing effective ecological restoration strategies in the region.     

Intensity of mineralization processes in mountain lakes in NW Slovenia

The potential and actual intensity of mineralization in sediments of fourteen mountain lakes and one subalpine lake in NW Slovenia have been measured. Potential mineralization was measured as the intensity of the electron transport system (ETS) activity of microzoobenthos and microbial communities and the actual mineralization as the oxygen consumption of respiration processes, both measured at a standard temperature of 20°C. The lakes are of different trophic levels and some exhibit seasonal anoxia. All but one are hardwater lakes. Two layers of sediment cores from the deepest point of the lakes were analysed: a surface layer and one below 15 cm. Significant differences among different lakes in their ETS activity and oxygen consumption in the surface and lower layers of sediment were observed. ETS activities and oxygen consumption rates were higher in the surface layers of all the lakes. From the three investigated deterministic factors (temperature, lake depth and total phosphorus in the water column) on sedimentary metabolism ETS activity in the surface layer correlated significantly with total phosphorus and lake depth, but oxygen consumption rate showed a significant correlation only with total phosphorus. The relationship between oxygen consumption and ETS activity was also investigated. ETS activities correlated with oxygen consumption rates according to the equation of logR = 0.421^* logETS + 0.898 (r=0.82; n=30; p<0.001). The R/ETS ratio was lower at the sediment surface than in the layers deeper than 15 cm. It is concluded that ETS activity and oxygen consumption are good indicators of the intensity of the metabolic activity and mineralization in lake sediments. As the characteristics of lakes and some environmental factors influence the ETS activity and the oxygen consumption differently, the same R/ETS ratio should not be used as conversion factor in calculations for different lakes.     

Evaluation of the rate of basal oxygen consumption in the isolated frog skin and toad bladder.

In the study of active transport it is important to distinguish between oxygen consumption sustaining transepithelial transport and that responsible for other tissue functions (basal metabolism). Since amiloride blocks transepithelial active sodium transport and the associated oxygen consumption in the frog skin and toad bladder, we and others have employed this agent to evaluate the rate of basal metabolism. This technique has recently been criticized in a report that amiloride (and ouabain) increased oxygen consumption when no sodium was available for transport. We have been unable to corroborate these observations. With magnesium-Ringer as external bathing solutions, amiloride and ouabain failed to stimulate oxygen consumption. With sodium-Ringer as external bathing solution amiloride reduced oxygen consumption about 30%, to a level indistinguishable from that found on external substitution of magnesium-Ringer for sodium-Ringer. We conclude that the use of amiloride permits evaluation of the rate of basal metabolism with acceptable accuracy; a possible slight depressant effect of ouabain on basal metabolism remains to be investigated.     

Some physical and chemical effects of the Cow Green (Upper Teesdale) impoundment

SUMMARY. The paper describes observations on water temperature and dissolved oxygen in Cow Green reservoir and also changes caused by impoundment to temperature, chemistry, dissolved oxygen and the discharge regime of the River Tees immediately downstream of the dam.
Impoundment and river regulation have considerably smoothed-out fluctuations in discharge of the Tees and have ehminated the very low and very high discharges which were characteristic of the natural river.
Reservoir water levels show an annual pattern of draw-down during summer, refilling in autumn and overflow during winter and spring. Tliermal stratification of the reservoir occurs rarely and is generally of short duration. Water temperatures at mid-reservoir correspond closely to those of water discharged from the reservoir. The temperature regime in the river downstream is modified as follows:

• (1)

  reduction in amplitude of annual temperature fluctuations by 1–2°C,
• (2)

  marked reduction of diel fluctuations, (3) delay of the spring rise in water temperature by 20–50 days and of the autumn fall by 0–20 days. These temperature changes could reduce the annual maintenance ration of a 10 g brown trout ( Salmo trutta L.) by about 15% and delay the annual peak of metabolism by about 1 month. The effect upon growth rate of trout would be negligible.

Fluctuations in ionic content at the reservoir inflow are comparatively large and can be related approximately to river discharge. Fluctuations at the outflow are smaller and appear to be largely seasonal. Regulation has not appreciably altered the dissolved oxygen content of the River Tees.     

Can zebra mussels change stratification patterns in a small reservoir?

Colonization and proliferation of zebra mussel (Dreissena polymorpha) population in Hargus lake, a small thermally stratified reservoir in Ohio, U.S.A., caused a significant increase in water clarity and a remarkable decrease in phytoplankton biomass during the period from 1993 to 1995. Increased light penetration and reduced organic matter loading to the meta-and hypolimnion were reflected in the lake stratification patterns, particularly in the temperature and oxygen profiles in the metalimnion. The meta- and hypolimnetic water temperature increased significantly over three years, irrespective of variation in surface water temperature. The epilimnion depth (mixing depth) increased by about the same magnitude as did the average Secchi depth. However, the total heat content of the lake did not show a consistent trend to increasing zebra mussel abundance, as it was largely influenced by the temperature of the large water volumes near the surface, which were in turn affected by weather conditions. Concurrent with the thermal structure change, the dissolved oxygen structure also changed over three years, though to a lesser extent. The changes in oxygen stratification pattern were reflected by increased oxygen concentrations in the metalimnion and a lowered depth of 3 mg l^–1 DO isopleth. These observed changes were likely attributed to increased water mixing depth, metalimnion photosynthesis and reduced oxygen consumption by organic matter. With increased epilimnion thickness and improved oxygen conditions in the metalimnion, the habitable space for aquatic macro-organisms (including fish) expanded substantially. Our results suggest that the indirect impacts of zebra mussels on small lake stratification patterns may have much broader implications than do the direct trophic interactions to the whole ecosystem.     

Biodegradation of Benzene in a Laboratory-Scale Biobarrier at Low Dissolved Oxygen Concentrations

A laboratory-scale permeable biobarrier exhibited high removal efficiencies of benzene at inlet concentrations of 0.4 to 35.1?mg/L and with a limited supply of dissolved oxygen. The supplied oxygen was less than the demand for a complete aerobic oxidation of benzene. Stainless steel pieces or granulated peat moss were used as packing material for microbial support in the biobarrier. Removal efficiencies ranged from 63.9% to 99.9% in the stainless steel-packed biobarrier and from 70.4% to 97.2% in the peat moss-packed biobarrier, while benzene elimination rate changed from 0.2 to 10.4?mg/L-d and from 0.1 to 3.7?mg/L-d in the two biobarriers, respectively. The consumption of sulfate and the presence of sulfate-reducing bacteria suggested the contribution of anaerobic metabolism in the biodegradation of benzene. The biodegradation of benzene under microaerophilic conditions (defined as dissolved oxygen concentrations <2?mg/L) was demonstrated during independent batch experiments. The maximum specific rate of benzene biodegradation with concentrations of 22.0 to 65.9?mg/L under microaero-philic conditions was 2.6 mg/mg biomass-d.     

Spatial variations in and controls on the calcite saturation index in Acton Lake, Ohio

SUMMARY.

• 1 Acton Lake is a small, hardwater, eutrophic reservoir located in the southwestern corner of Ohio. Over a period of 5 weeks in mid-summer 1979, water samples were collected from the lake and its streams and analyzed for seven major ionic species and for temperature, dissolved O₂, pH and conductivity. Geochemically the waters are characterized by high calcium and bicarbonate concentrations.
• 2 Data obtained on all samples were used to compute calcite saturation indices (SI) and to map the spatial distribution of this function throughout the system. The saturation indices were corrected for activity and ion pairing effects and yet are still to our knowledge among the highest values reported for a natural water.
• 3 The good correlations obtained between the SI and both the pH and dissolved oxygen clearly indicate that biological activity is the dominant control on the degree of saturation in this largely isothermal lake. To account for the extreme departure from chemical equilibrium, it is proposed that dissolved organic matter may be poisoning freshly formed calcite surfaces and preventing them from serving as effective nucleation centers.

     

Ferrous iron transport in Streptococcus mutans.

Radioiron uptake from 59FeCl3 by Streptococcus mutans OMZ176 was increased by anaerobiosis, sodium ascorbate, and phenazine methosulfate (PMS), although there was a 10-min lag before PMS stimulation was evident. The reductant ascorbate may have provided ferrous iron. The PMS was reduced by the cells, and the reduced PMS then may have generated ferrous iron for transport; reduced PMS also may have depleted dissolved oxygen. We conclude that S. mutans transports only ferrous iron, utilizing reductants furnished by glucose metabolism to reduce iron prior to its uptake.     

Evaluation of the rate of basal oxygen consumption in the isolated frog skin and toad bladder

In the study of active transport it is important to distinguish between oxygen consumption sustaining transepithelial transport and that responsible for other tissue functions (basal metabolism). Since amiloride blocks transepithelial active sodium transport and the associated oxygen consumption in the frog skin and toad bladder, we and others have employed this agent to evaluate the rate of basal metabolism. This technique has recently been criticized in a report that amiloride (and ouabain) increased oxygen consumption when no sodium was available for transport. We have been unable to corroborate these observations.With magnesium-Ringer as external bathing solutions, amiloride and ouabain failed to stimulate oxygen consumption. With sodium-Ringer as external bathing solution amiloride reduced oxygen consumption about 30%, to a level indistinguishable from that found on external substitution of magnesium-Ringer for sodium-Ringer. We conclude that the use of amiloride permits evaluation of the rate of basal metabolism with acceptable accuracy; a possible slight depressant effect of ouabain on basal metabolism remains to be investigated.     

The response by microorganisms to steady-state growth in controlled concentrations of oxygen and glucose. II. Saccharomyces carlsbergensis

The growth of Saccharomyces carlsbergensis in continuous culture has been studied when dissolved oxygen and glucose concentrations were held constant at a series of steady-state levels. Both oxygen and glucose controlled the degree of aerobic metabolism and of ethanolic fermentation. When the glucose uptake rate was low (between 1.2 and 2.8 mmoles per hour per gram of yeast) the relative distribution of glucose between ethanolic and aerobic fermentation was sensitive to oxygen: when dissolved oxygen was near to saturation, glucose metabolism was 0.98 aerobic; when dissolved oxygen was 0.01 saturated, 0.8 of intake glucose metabolism was by ethanolic fermentation. On the other hand when glucose intake was high (between 7.6 and 18.2 mmoles) metabolism was predominately by ethanolic fermentation even when dissolved oxygen concentration was at saturation. The extent, to which catabolism proceeded by an anaerobic or aerobic pathway, as judged by ethanol production, was controlled more by the uptake of glucose than of oxygen.