Seasonal effects of zebra mussels on littoral nitrogen transformation rates in Gull Lake, Michigan, U.S.A.

• 1 Zebra mussels (Dreissena polymorpha) are successful colonisers of lake littoral habitats and they interact strongly with littoral benthos. Previous research suggests that localised areas colonised by zebra mussels may be hotspots of nitrogen (N) cycling.
• 2 The effects of zebra mussels on nitrification and denitrification rates were examined approximately every other month for 1 year in Gull Lake, Michigan, U.S.A. Littoral sediment was collected from an area free of zebra mussels and distributed into shallow trays; rocks colonised with zebra mussels were placed in half of the trays, while uncolonised rocks were placed in the remaining trays. After an incubation period of 6–8 weeks in the lake, sediment and zebra mussels were collected from the trays, replaced with new sediment and zebra mussels, and placed in the lake for the next interval. In the laboratory, sediment nitrification and denitrification rates were measured for each tray.
• 3 Sediment nitrification rates did not increase in the presence of zebra mussels; instead nitrification rates were sensitive to changes in water temperature and increased with increasing exchangeable sediment ammonium. In contrast, denitrification rates increased in sediment trays with zebra mussels in the winter when nitrate (NO₃⁻) availability was high and when Chara did not grow in the trays.
• 4 Sediment denitrification was NO₃⁻‐limited in all seasons, regardless of zebra mussel treatment. However, sediment in the presence of zebra mussels responded less to NO₃⁻ addition, suggesting that NO₃⁻ limitation of denitrification can be reduced by zebra mussel activity. Zebra mussels have a seasonally variable impact on sediment denitrification rates, and this may translate into altered seasonal patterns of N cycling in localised areas of lakes where they are particularly abundant.

     

A dissolved oxygen budget model for Lake Erie in summer

SUMMARY.

• 1 In this paper we extend a vertical mixing model of Lake Erie with an oxygen budget model. The model was tested against data gathered in the summers of 1979 and 1980 with good results, showing that it is capable of simulating vertical distributions of temperature and dissolved oxygen over relatively short time periods.
• 2 The results underline the importance of turbulent mixing in distributing oxygen throughout the water column in the Central Basin of the lake. In addition, the results indicate that production and respiration processes dominate the budget under the influence of low wind speeds, while surface fluxes dominate during periods of high wind.
• 3 Bottom mixing delays the onset of anoxic conditions at the sediment/water interface by distributing the sediment demand over the 5–6 m depth of the bottom mixed layer.

     

High resistance of oligotrophic isoetid plants to oxic and anoxic dark exposure

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Patterns of temporal variation in Lake Titicaca. A high altitude tropical lake. I. Background,physical and chemical processes,and primary production

A statistical analysis is presented of patterns of variation in some physical, chemical, and biological variables for a 6 year series of data from the tropical, high altitude Lake Titicaca (Peru-Bolivia). ANOVA techniques and autocorrelation analyses were used to partition the variance in Titicaca, and in some comparison tropical and temperate series, into components with repeatable annual cycles and components attributable to other kinds of patterns.In Titicaca, insolation and stratification are highly seasonal in pattern of variation, although the amount of variance relative to means is small compared to temperate lakes. However, the seasonal pattern of physical variation is only weakly imposed on chemical and biological processes, to judge from analyses of silicate, oxygen, and primary production series. Comparable temperate series of primary production and chlorophyll a are much more seasonal.     

Microbiological and isotopic geochemical investigation of Lake Kislo-Sladkoe,a meromictic water body at the Kandalaksha Bay shore (White Sea)

Microbiological, biogeochemical, and isotopic geochemical investigation of Lake Kislo-Sladkoe (Polusolenoe in early publications) at the Kandalaksha Bay shore (White Sea) was carried out in September 2010. Lake Kislo-Sladkoe was formed in the mid-1900s out of a sea gulf due to a coastal heave. At the time of investigation, the surface layer was saturated with oxygen, while near-bottom water contained sulfide (up to 32 mg/L). Total number of microorganisms was high (12.3 × 10⁶ cells/mL on average). Light CO₂ fixation exhibited two pronounced peaks. In the oxic zone, the highest rates of photosynthesis were detected at 1.0 and 2.0 m. The second, more pronounced peak of light CO₂ fixation was associated with activity of anoxygenic phototrophic bacteria in the anoxic layer at the depth of 2.9 m (413 μg C L^?1 day^?1). Green-colored green sulfur bacteria (GSB) predominated in the upper anoxic layer (2.7–2.9 m), their numbers being as high as 1.12 × 10⁴ cells/mL, while brown-colored GSB predominated in the lower horizons. The rates of both sulfate reduction and methanogenesis peaked in the 2.9 m horizon (1690 μg S L^?1 day^?1 and 2.9 μL CH₄ L^?1 day^-1). The isotopic composition of dissolved methane from the near-bottom water layer (δ¹³C (CH₄) = ?87.76‰) was significantly lighter than in the upper horizons (δ¹³C (CH₄) = ?77.95‰). The most isotopically heavy methane (δ¹³C (CH₄) = ?72.61‰) was retrieved from the depth of 2.9 m. The rate of methane oxidation peaked in the same horizon. As a result of these reactions, organic matter (OM) carbon of the 2.9 m horizon became lighter (?36.36‰), while carbonate carbon became heavier (?7.56‰). Thus, our results demonstrated that Lake Kislo-Sladkoe is a stratified meromictic lake with active microbial cycles of carbon and sulfur. Suspended matter in the water column was mostly of autochthonous origin. Anoxygenic photo-synthesis coupled to utilization of reduced sulfur compounds contributed significantly to OM production.     

The limnology of Lac ďIfni (High Atlas Mountains, Morocco), an unusually productive mountain lake

• 1 Lac ?Ifni (surface area 30 ha, z_max 60 m, altitude 2300 m) lies in a catchment comprised of Precambrian igneous rocks in the High Atlas Mountains of Morocco. Previously described as a typical ohgotrophic lake, it was also reported to have a warm layer at the base of the hypolimnion which was ascribed to phreatic water supply and drainage.
• 2 Visits to the lake made in May/June and September 1990 showed strong thermal stratification but no hypolimnial warm layer. Drainage from the lake is subterranean, through a natural rubble dam, and the water level dropped by at least 7m through the summer. The flushing rate is about 0.6 year^?1.
• 3 The upper part of the metalimnion and the lower epilimnion were strongly supersaturated with oxygen in June, and there was a pH gradient from 7 to 10.5 between the hypolimnion and the epilimnion. These features were less marked in September when planktonic gross primary productivity was estimated to be about 145mgCm^?2 h^?1. In September the hypolimnion was 38% saturated with oxygen; the areal hypolimnetic oxygen deficit between June and September was 0.073mg O₂ cm^?2 day^?1. Total dissolved phosphate concentrations were 7–14 μgl^?1.
• 4 The open water faunal assemblage consisted of Brachionus calyciflorus and Filinia lotigiseta (Rotifera), Cyclops abyssorum (Copepoda), and stunted Salmo trutta (Pisces). Trout diets were comprised principally of adult copepods and copepodites, which showed diurnal vertical migration, and of algal material apparently scraped from rock surfaces. The dry biomass density of Cyclops was at least 2gm^?2 in June and at least 4.1 gm ^?2 in September.
• 5 Tubifex tubifex (Oligochaeta) dominated the benthos below depths of 40m. Mean dry biomass density was 2.8gm^?2, but ranged from 0.6–8.1 gm^?2 between samples. About 50% of the lake bottom is below 40m depth.
• 6 The persistent oxygen supersaruration of the euphoric zone, the field estimate of primary productivity, the hypolimnetic oxygen deficit, the biomass of zooplankton and the benthic biomass together indicate that Lac ?Ifni is an unusually productive mountain lake. This high level of productivity may be sustained by nutrient addition through contamination by dust originating outside the catchment, aided by efficient nutrient recycling in the euphoric zone.

     

Cryptic diversity within the rotifer Polyarthra dolichoptera along an altitudinal gradient

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Reduced oxygen at high altitude limits maximum size

The trend towards large size in marine animals with latitude, and the existence of giant marine species in polar regions have long been recognized, but remained enigmatic until a recent study showed it to be an effect of increased oxygen availability in sea water of a low temperature. The effect was apparent in data from 12 sites worldwide because of variations in water oxygen content controlled by differences in temperature and salinity. Another major physical factor affecting oxygen content in aquatic environments is reduced pressure at high altitude. Suitable data from high-altitude sites are very scarce. However, an exceptionally rich crustacean collection, which remains largely undescribed, was obtained by the British 1937 expedition from Lake Titicaca on the border between Peru and Bolivia in the Andes at an altitude of 3809 m. We show that in Lake Titicaca the maximum length of amphipods is 2-4 times smaller than other low-salinity sites (Caspian Sea and Lake Baikal).     

Oxygen consumption and ammonia accumulation in the hypolimnion of Walker Lake, Nevada

Walker Lake (area = 140 km², Z _mean = 19.3 m) is a large, terminal lake in western Nevada. As a result of anthropogenic desiccation, the lake has decreased in volume by 75% since the 1880s. The hypolimnion of the lake, now too small to meet the oxygen demand exerted by decaying matter, rapidly goes anoxic after thermal stratification. Field and laboratory studies were conducted to examine the feasibility of using oxygenation to avoid hypolimnetic anoxia and subsequent accumulation of ammonia in the hypolimnion, and to estimate the required DO capacity of an oxygenation system for the lake. The accumulation of inorganic nitrogen in water overlaying sediment was measured in laboratory chambers under various DO levels. Rates of ammonia accumulation ranged from 16.8 to 23.5 mg-N m^–2 d^–1 in chambers with 0, 2.5 and 4.8 mg L^–1 DO, and ammonia release was not significantly different between treatments. Beggiatoa sp. on the sediment surface of the moderately aerated chambers (2.5 and 4.8 mg L^–1 DO) indicated that oxygen penetration into sediment was minimal. In contrast, ammonia accumulation was reversed in chambers with 10 mg L^–1 DO, where oxygen penetration into sediment stimulated nitrification and denitrification. Ammonia accumulation in anoxic chambers (18.1 and 20.6 mg-N m^–2 d^–1) was similar to ammonia accumulation in the hypolimnion from July through September of 1998 (16.5 mg-N m^–2 d^–1). Areal hypolimnetic oxygen demand averaged 1.2 g O₂ m^–2 d^–1 for 1994–1996 and 1998. Sediment oxygen demand (SOD) determined in experimental chambers averaged approximately 0.14 g O₂ m^–2 d^–1. Continuous water currents at the sediment-water interface of 5–6 cm s^–1 resulted in a substantial increase in SOD (0.38 g O₂ m^–2 d^–1). The recommended oxygen delivery capacity of an oxygenation system, taking into account increased SOD due to mixing in the hypolimnion after system start-up, is 215 Mg d^–1. Experimental results suggest that the system should maintain high levels of DO at the sediment-water interface (10 mg L^–1) to insure adequate oxygen penetration into the sediments, and a subsequent inhibition of ammonia accumulation in the hypolimnion of the lake.     

Seasonal microbial activity in Antarctic freshwater lake sediments

Summary Seasonal fluctuations in population numbers and activity were monitored in bottom sediments of oligotrophic Moss Lake, mesotrophic Heywood Lake and eutrophic Amos Lake on Signy Island, South Orkney Islands, during 1976–78. Heywood and Amos Lakes became anoxic under winter ice cover (8–10 months) and significant populations of facultatively anaerobic heterotrophs and sulphate-reducing bacteria developed. In contrast, Moss Lake surface sediments never became anoxic and anaerobic bacteria were virtually absent. Direct microscopic counts and viable plate counts fluctuated relatively little in Moss Lake throughout the study period, whereas distinct seasonality was observed in the more enriched lake systems. Similarly, measurements of oxygen consumption and dark ¹⁴CO₂ uptake by mud cores indicated no obvious seasonal fluctuations in Moss Lake data, in contrast to the marked seasonal pattern observed in data from the other lakes. In these latter systems, oxygen uptake rates were highest in summer (c. 400 mg O₂ m^-2 d^-1) and virtually undetectable in winter. Comparison of oxygen uptake with oxygen concentration and temperature revealed differences, between lakes, in uptake response to oxygen concentration, whereas uptake response to temperature did not differ significantly between lakes. Chemosynthetic production in the Signy Island lake sediments was in the range 1.6–35.3 g C m^-2 (mud surface) d^-1 with highest values recorded in Amos Lake under winter ice cover and anoxic conditions. The findings from this and earlier studies of the three lakes have been assembled to indicate the relative importance of green plants and bacteria to the carbon cycle in these permanently cold systems.     

Vernal microstratification patterns in a meromictic saline lake: their causes and biological significance

Periodic high spring runoff, in addition to lake surface snow and ice melt, is shown to be a major cause of sharp secondary chemocline formation in a small (20 ha) lake arid and south-central British Columbia. Initially detected in 1982 at about 1 m and enhanced by high inflow of low salinity meltwater in spring 1983, the secondary chemocline gradually deepened and broke down over four subsequent years. Associated microstratification layers (major changes within a few cm of depth), exhibited very high temperatures (> 30 °C), and very high dissolved oxygen (> 200% saturation) as well as very low (close to 0% saturation) levels. Oxygen supersaturation resulted from photosynthetic production at the microstratification boundaries. In the springs of 1982 and 1983, formation of an anoxic layer between regions of high oxygen concentration, separated the phytoplankton and zooplankton communities into two layers above the primary chemocline. The several year persistence of the secondary chemoclines and associated interface processes (concentration of particulate organic matter, bacterial decomposition, nutrient regeneration, phytoplanktonic production) attest to their functional importance in this meromictic lake.     

Physiological reactions of aquatic oligochaetes to environmental anoxia

Aquatic oligochaetes are well known for their ability to resist prolonged periods of anoxia. In fact, the observed mortality is more likely to result from laboratory stress (unnatural sediment, starvation, accumulation of toxic substances) than from lack of oxygen per se. Lumbriculus variegatus feeds under anoxia at 6°C at a low rate and survives more than 40 days. A sudden transfer into anoxic water, however, results in a cessation of defaecation before the gut is half emptied, whereas the gut is completely emptied under aerobic conditions within 8–10 hours (11°C).Anoxic heat dissipation as measured by direct calorimetry is reduced by up to 80% relative to aerobic rates. The basal rate of oxygen uptake is independent of PO₂ above 3 kPa (15% air saturation), but the active rate shows a high degree of oxygen conformity. Whereas the theoretical oxycaloric equivalent yields an accurate estimation of aerobic heat dissipation in Lumbriculus, anoxic catabolism of glycogen explains only up to 60% of the directly measured rates of anoxic heat dissipation in Lumbriculus and Tubifex. Since unknown bioenergetic processes may be important under anoxia, direct calorimetry is required to assess total rates of energy expenditure in anoxic oligochaetes.     

Characteristics of fluctuations in salinity and water quality in brackish Lake Obuchi

Fluctuations in the salinity and physicochemical characteristics of water quality were surveyed in brackish Lake Obuchi on the Shimokita Peninsula in Aomori, Japan. The mean salinity in the surface layer in all regions of Lake Obuchi was about 10 psu, whereas in the basin region at depths of greater than 3 m it was 20 psu. Furthermore, all the year round the halocline was formed at depths of 1–4 m. The maximum density gradient along a vertical axis in the center of the lake was observed at depths of 1–2 m in summer and 2–4 m in spring and fall. The depth of the maximum density gradient fluctuated with the seasons. In summer the water in the bottom layer was anoxic, and Fe, Mn, PO₄ ³⁻-P, and NH₄ ⁺-N supplied from the bottom sediment accumulated at high concentrations below the halocline. Thus, it was observed that the transfer of substances between the layers above and below the barrier formed by the halocline is suppressed. Although Lake Obuchi is small and shallow, the inflowing seawater easily resides, and a stable halocline readily forms because of the shape of its basin, which suddenly deepens on the Pacific Ocean side. Received: May 24, 1999 / Accepted: September 25, 1999     

The calanoid copepod Acartia italica Steuer, phenomenon in the small saline Lake Rogoznica (Eastern Adriatic coast)

Lake Rogoznica, near ibenik, Croatia, is a salt coastal lakewith a maximum depth of about 15 m. During most of the year,this small, naturally eutrophied lake is highly stratified,with hypoxia/anoxia occurring in the bottom layer. Total anoxia,with the presence of hydrogen sulphide, was recorded on September27, 1997. At that moment, massive mortality of all planktonicand benthic organisms was observed. After the anoxia, Acartiaitalica, the only planktonic copepod species of the lake, re-establishedquickly. Before anoxia, the population dynamics of the A.italicapopulation depended primarily on predator/prey relationships.However, in the post-anoxic period, nutrient–phytoplankton–copepodrelationships became more important, as there was no longerany predation pressure. From all accounts, it would appear thatonly A.italica is adapted to the extreme conditions which appearfrom time to time in the lake, and that this species has animportant role in the functioning of the lake ecosystem. Acartiaitalica was very important for the gradual normalization oflife in the lake after total anoxia.     

Seasonal distribution of nitrifying bacteria and rates of nitrification in coastal marine sediments

The distribution of nitrification potential (NP) with depth in sediment and season was investigated in a shallow sandy sediment (0.5 m water) and a deeper muddy sediment (17m water). In both sediments, nitrifying bacteria were present in the anoxic strata (oxygen penetration was 5 mm below the surface). The NP at 6–8 cm depth in the sediment was 50% and 10% of the surface NP at the sandy and muddy sediment, respectively. It is suggested that bioturbation and physical disturbance of the sediment were the most likely reasons for this distribution. The NP increased as sediment temperature decreased. This effect was less marked in the muddy sediment. It is concluded that during the summer, the numbers or specific activity of nitrifying bacteria diminished for the following reasons: There was decreased O₂ penetration into the sediment and increased competition for O₂ by heterotrophs; there was increased competition for NH₄ ⁺ and there was inhibition by H₂S. These effects counteracted the potentially higher growth rates and increased rates of NH₄ ⁺ production at the elevated summer temperatures. The potential nitrification rates in the upper 1 cm, which were measured at 22°C, were converted to calculated rates at the in situ temperature (Q₁₀=2.5) and in situ oxygen penetration. These calculated rates were shown to closely resemble the measured in situ rates of nitrification. The relationship between the in situ rates of nitrification and the nitrification potential is discussed.     

Interannual variability of algal populations and their influence on lake metabolism

• 1 An input-output phosphorus budget is given for Windermere and its two basins based on data available for the late 1980s. The annual areal total phosphorus loading for the whole lake was 1.04 g P m^-2 yr^-1 and for the North and South Basins were 1.08 and 1.70 g P m^-2 yr^-1, respectively. For the whole lake and its South Basin the values were similar to the upper range of critical loads calculated according to the equation of Vollenweider (1976) for the transition between oligotrophy and eutrophy while that for the North Basin (1.08 g P m^-2 yr^-1) was within this range of critical loadings but towards its lower end.
• 2 Changes in the quality of summer phytoplankton are described for Windermere, particularly its South Basin, between 1978 and 1989 in relation to the utilization of nitrate-nitrogen (NO³-N) in the epilimnion, deoxygenarion of the hypolimnion and the ratio of epilimnetic volume to hypolimnetic volume, E_v/H_v The two basins of Windermere with values of E_v/H_v of 0.79 (South Basin) and 0.50 (North Basin) have contrasting conditions of summer deoxygenarion. The shallower South Basin shows marked interannual variability in the development of hypolimnetic anoxia. Years with large hypolimnetic anoxia during autumn are correlated with the production during summer of large populations of the poorly grazed blue-green alga Oscillatoria bourrellyi and exhaustion of NO₃-N in the upper layers. During years when anoxia does not develop the summer phytoplankton consists of small easily grazed algae or larger ones subject to parasitic epidemics. The deeper North Basin never becomes anoxic even though it can contain similar sized populations of O. bourrellyi to the South Basin.
• 3 A possible explanation of the between basin and, for the South Basin, between year variation of utilization of NO₃-N and level of hypolimnetic deoxygenarion is that algal quality can determine lake metabolism dependent upon lake or basin morphology. Poorly grazed large forms such as O. bourrellyi act as sinks for NO₃-N. On sedimentation such populations act as a ‘short circuit’ mechanism descending into deeper layers in sufficient quantities to cause anoxia. Other species subject to crustacean or microbial grazing are mineralized in the epilimnion with little sedimentation to the deeper waters. Subsequent recycling of nitrogen as NH₄-N takes place in the upper layers or thermocline which is more readily taken up by subsequent production. The influence of such ‘short circuit’ mechanisms is reduced in deep lakes and exacerbated in shallow ones.
• 4 The success of species such as O. bourrellyi is dependent upon a sufficient inoculum, an adequate supply of nutrients and the depth of intermittent mixing. The importance of these factors in regulating presence and timing of summer populations is illustrated and discussed.

     

Dark aerobic sulfide oxidation by anoxygenic phototrophs in anoxic waters

Anoxygenic phototrophic sulfide oxidation by green and purple sulfur bacteria (PSB) plays a key role in sulfide removal from anoxic shallow sediments and stratified waters. Although some PSB can also oxidize sulfide with nitrate and oxygen, little is known about the prevalence of this chemolithotrophic lifestyle in the environment. In this study, we investigated the role of these phototrophs in light-independent sulfide removal in the chemocline of Lake Cadagno. Our temporally resolved, high-resolution chemical profiles indicated that dark sulfide oxidation was coupled to high oxygen consumption rates of ~9 μM O₂·h⁻¹. Single-cell analyses of lake water incubated with ¹³CO₂ in the dark revealed that Chromatium okenii was to a large extent responsible for aerobic sulfide oxidation and it accounted for up to 40% of total dark carbon fixation. The genome of Chr. okenii reconstructed from the Lake Cadagno metagenome confirms its capacity for microaerophilic growth and provides further insights into its metabolic capabilities. Moreover, our genomic and single-cell data indicated that other PSB grow microaerobically in these apparently anoxic waters. Altogether, our observations suggest that aerobic respiration may not only play an underappreciated role in anoxic environments but also that organisms typically considered strict anaerobes may be involved.     

Inhibition of phytoplankton photosynthesis by solar ultraviolet radiation: studies in Lake Titicaca, Bolivia

1. Lake Titicaca is a large, high altitude (3810 m a.s.l.) tropical lake (16°S, 68°W) that lies on the border of Bolivia and Perú, receiving high fluxes of ultraviolet radiation (UVR) throughout the year. Our studies were conducted during September of 1997 with the main objective of studying the impact of solar UVR upon phytoplankton photosynthesis.
2. Water samples were taken daily and incubated in situ (down to 14 m depth) under three radiation treatments to study the relative responses to PAR (Photosynthetic Available Radiation, 400–700 nm), UV-A (320–400 nm), and UV-B (280–320 nm) radiation.
3. Photosynthetic inhibition by UVR in surface waters was about 80%, with UV-A accounting for 60% and UV-B for 20%; the inhibition by high levels of PAR was less than 20%. The inhibition due to UVR decreased with depth so that there were no significant differences between treatments at 8.5 m depth.
4. The amount of inhibition per unit energy received by phytoplankton indicates that even though there was a significant inhibition of photosynthesis due to UVR, species in Lake Titicaca seem to be better adapted than species in high latitude environments.
5. The cellular concentration of UV-absorbing compounds, a possible mechanism of photoadaptation, was low in phytoplanktonic species. However, they were abundant in zooplankton, suggesting a high rate of bioaccumulation through the diet.     

Nitrogen transformations at the sediment–water interface across redox gradients in the Laurentian Great Lakes

The capacity of a lake to remove reactive nitrogen (N) through denitrification has important implications both for the lake and for downstream ecosystems. In large oligotropic lakes such as Lake Superior, where nitrate (NO₃ ^?) concentrations have increased steadily over the past century, deep oxygen penetration into sediments may limit the denitrification rates. We tested the hypothesis that the position of the redox gradient in lake sediments affects denitrification by measuring net N-fluxes across the sediment–water interface for intact sediment cores collected across a range of sediment oxycline values from nearshore and offshore sites in Lake Superior, as well as sites in Lake Huron and Lake Erie. Across this redox gradient, as the thickness of the oxygenated sediment layer increased from Lake Erie to Lake Superior, fluxes of NH₄ ⁺ and N₂ out of the sediment decreased, and sediments shifted from a net sink to a net source of NO₃ ^?. Denitrification of NO₃ ^? from overlying water decreased with thickness of the oxygenated sediment layer. Our results indicate that, unlike sediments from Lake Erie and Lake Huron, Lake Superior sediments do not remove significant amounts of water column NO₃ ^? through denitrification, likely as a result of the thick oxygenated sediment layer.