Crooked Lake Research Articles

The annual patterns of photosynthesis in two large, freshwater, ultra-oligotrophic Antarctic lakes

The phytoplankton productivity and biomass of two large, freshwater Antarctic lakes (Vestfold Hills, eastern Antarctica) were investigated over a 12-month period. Crooked Lake was sampled at one site, while Lake Druzhby, a complex lake with two shallow and one deep basin, was subject to a more detailed investigation. Concentrations of chlorophyll a were usually below 1 µg l–1, indicating ultra-oligotrophic conditions. Despite periodic low nutrient levels, low temperatures (range 0.4–2.8°C) and periodic poor light climate, some degree of photosynthesis was measurable throughout the year, including the dark winter phase. Snow cover had a pronounced impact on the light climate of the water column and inhibited photosynthesis. Mean rates of carbon fixation in the 0- to 15-m water column varied between 0 and 38.47 µg C l–1 day–1 in Crooked Lake and 0.24 and 37.68 µg C l–1 day–1 in Lake Druzhby. There were significant differences in the seasonal patterns of primary production between the basins of Lake Druzhby. The shallow basins had highest productivity in August, whereas the deep basin had highest rates in summer. Chlorophyll specific rates of photosynthesis or assimilation numbers [µg C (chl. a)–1 h–1] varied between 0.05 and 44.9, and photosynthetic efficiency [µg C (chl. a)–1 h–1 µmol m–2 s–1] between 0.02 and 5.19. The data suggest that the phytoplankton of these lakes is adapted to low irradiance levels, low temperatures and nutrient limitation.

A diatom-inferred water depth reconstruction for an Upper Peninsula, Michigan, lake

Transects of surface sediment samples were taken in 4 lakes from the Sylvania Wilderness Area, Upper Peninsula of Michigan. These surface samples were compared with diatom samples from a core taken in the Northwest basin of Crooked Lake, also from the Sylvania Wilderness Area. Weighted Averaging calibration was used to reconstruct lake depths in Crooked Lake using the diatom microfossils from the core and the surface samples to infer past lake depth. During the early Holocene the lake was dominated by planktonic species and diatom-inferred water depth was large – approx. 13 m. At about 6700 BP inferred water depth was 2 m and samples were dominated by Fragilaria construens var. venter – a species characteristic of shallow parts of the surface sample transects. From 6700 to 5000 BP reconstructed water level was at its shallowest. From 5000 to 3000 BP it increased. This rise in water level was marked by increasing abundances of Aulacoseira ambigua and occurred at the same time increasing percentages of hemlock pollen indicate increasing available moisture. Modern water depth was reached about 3000 BP. The water level changes at Crooked Lake are consistent with regional climate changes in the Upper Midwest during the Holocene. The lake was shallowest during the mid-Holocene warm period documented by other investigators. It deepened as the Midwestern climate became cooler and wetter during the late Holocene.

Holocene Vegetation History in the Sylvania Wilderness Area of the Western Upper Peninsula of Michigan

-Sediment cores spanning the last 10,000 yr from two lakes in the Sylvania Wilderness Area of the Upper Peninsula of Michigan were analyzed for pollen, and the pollen data were compared with the National Geophysical Data Center (NGDC) data set of modern pollen samples. The best modern analogue for the spruce pollen zone (>9000 BP) at the bottom of Glimmerglass Lake was a sample located near Hudson's Bay in Quebec. This zone was not present at Crooked Lake. Modern samples matched the samples from the diploxylon pollen zone (9000 to 8000 BP) poorly. Samples analogous to those from the haploxylon pollen zone (8000 to 3000 BP) come from eastern Minnesota and western Wisconsin. Samples dating from after the arrival of Tsuga (at 3000 BP) are similar to modern surface samples from Sylvania. The surface sample analogues suggest that the arrival of Tsuga at 3000 BP marks the establishment of the modern lake effects climatic regime in the Upper Peninsula.

Hydrographic and climatic changes influencing the proglacial Druzhby drainage system, Vestfold Hills, Antarctica

Freshwater drainage systems, fed by melting of nearby inland ice and perennial snowdrifts, exist in the south-eastern part of arid, ice-free, coastal Vestfold Hills. Most important is the complex Druzhby system. Intriguing questions arise about the conditions controlling its seasonal development and about the consequences of possible changes of those conditions. A water-balance was calculated for 1990–91. The system went through four seasonal phases of which only one displayed a fully developed external drainage. Evidently, the relative duration of those phases can vary considerably from one year to another. The system depends critically on the water supply from ice-dammed Chelnok Lake, which could readily be drained by a minor retreat of Sørsdal Glacier. Exposed to excessive evaporation, the large Crooked Lake would then become internally drained and reach a new equilibrium in ∼830 years. A Crooked Lake sediment core can be interpreted as suggesting this occurred during the Holocene. The idea, inferred from striae, of a late Holocene Chelnok Glaciation reaching the northern shores of Crooked Lake is questioned. Instead, it is suggested that the Chelnok striae originate from local basal melting of the ice sheet draining southward into a deglaciated Sørsdal trough. At present, runoff is determined by opposing short and long-term climatic influences.

Glacial Crooked Lake, Vestfold Hills, East Antarctica

AbstractGlacial Crooked Lake was an ice-dammed impoundment in Vestfold Hills, East Antarctica, that had a volume of (250 ± 45) × 10 m. The impoundment is inferred to have existed during deglaciation following the Late Holocene Chelnok Advance of Sørsdal Glacier. The dam released water incrementally, allowing the formation of four major series of shorelines with a maximum height of 24 m above the current lake level of 22 m asl. Water from Glacial Crooked Lake overflowed into Watts Lake downstream, allowing saltwater there to mix, dilute, and be transported to the sea via Ellis Rapids. In this way water in Watts Lake became fresh, and alluvial fans consisting of cobbles and boulders formed below Crooked Lake and Ellis Rapids.

High-Resolution Seismic Expression of Karst Evolution within the Upper Floridan Aquifer System: Crooked Lake, Polk County, Florida

ABSTRACT We collected 43 km of high resolution seismic reflection profiles from a 14.5-hectare lake in the central Florida sinkhole district and data from three adjacent boreholes to determine the relationship between falling lake levels and the underlying karst stratigraphy. The lake is separated from karstified Paleogene to early Neogene carbonates by 65-80 m of siliciclastic sands and clays. The carbonate and clastic strata include three aquifer systems separated by clay-confining units: a surficial aquifer system (fine to medium quartz sand in the upper 20-30 m), the 25-35 m thick intermediate aquifer system (in Neogene siliciclastics), and the highly permeable upper Floridan aquifer system in Paleogene to early Neogene limestones. Hydraulic connection between these aquifer systems is indicated by superjacent karst structures throughout the section. Collapse zones of up to 1000 m in diameter and > 50 m depth extend downward from a prominent Middle Miocene unconformity into Oligocene and Upper Eocene limestones. Smaller sinkholes (30-100 m diameter, 10-25 m depth) are present in Middle to Late Neogene clays, sands, and carbonates and extend downward to or below the Middle Miocene unconformity. Filled and open shafts (30-40 m diameter; 10-25 m depth) ring the lake margin and overlie subsurface karst features. The large collapse zones are localized along a northeast-southwest line in the northern ponds and disrupt or deform Neogene to Quaternary strata and at least 50 m of the underlying Paleogene carbonate rock . The timing and vertical distribution of karst structures are used to formulate a four-stage model that emphasizes stratigraphic and hydrogeologic co-evolution. (1) Fracture-selective shallow karst features formed on Paleogene/early Neogene carbonates. (2) Widespread karstification was limited by deposition of Middle Miocene clays, but vertical karst propagation continued and was focused because of the topographic effects of antecedent karst. (3) Groundwater heads increase with the deposition of thick sequences of clastics over the semipermeable clays during Middle and Late Neogene time. The higher water table and groundwater heads allowed the accumulation of acidic, organic-rich soils and chemically aggressive waters that percolated down to Paleogene carbonates via localized karst fea ures. (4) After sufficient subsurface dissolution, the Paleogene carbonates collapsed, causing disruption and deformation of overlying strata. The seismic profiles document an episodic, vertically progressive karst that allows localized vertical leakage through the clay-confining units. The spatial and temporal karst distribution is a result of deposition of sediments with different permeabilities during high sea levels and enhanced karst dissolution during low sea levels. Recent decreases in the potentiometric elevation of the Floridan Aquifer System simulates a sea-level lowstand, suggesting that karst dissolution will increase in frequency and magnitude.

Zooplankton Community Structure in Hardwater Hypertrophic Lakes of Alberta

Excessive concentrations of phosphorus are a common feature of hardwater eutrophic lakes in western Canada. Preliminary experimental lime treatment showed that this approach had a great potential to reduce phosphorus content and algal biomass. Therefore, two pairs of experimental and reference lakes were selected for a whole lake lime treatment and monitored for a full year prior to manipulation. This study presents the composition and size structure of the Zooplankton community of the lakes before treatment in order to assess the natural summer and inter-lake variations. Before lime treatment, seasonal means of total Zooplankton abundance and biomass ranged from 17 ± 8 to 127 ± 84 ind. L−1 and from 4 ± 2 to 138 ± 236 mg m−3, respectively. The two experimental lakes (Halftnoon and Lofty) were the richest in Zooplankton while the references lakes (Crooked and Jenkins) were the poorest. A total of 30 Zooplankton species (17 rotifers, 2 calanoids, 4 cyclopoids and 7 cladocerans) were recorded as well as 3 chaoborid species. The composition and size structure of Zooplankton varied between lakes and dates. Rotifers accounted for the majority of Zooplankton abundances (59-91%) while Cladocera (78-99%) or Copepoda (74%) in Crooked lake formed most of the Zooplankton biomass. Summer variations of the Zooplankton groups were described along with changes in size spectra. The temporal variation and the inter-lake differences in Zooplankton structure were discussed in relation to trophy, fish and invertebrate predation, and cyanophyte interactions.

Seasonal cycle of the microbial plankton in Crooked Lake, Antarctica

Changes in the abundance of the components of the microbial plankton between July 1990 and March 1991 in Crooked Lake, one of the largest and deepest freshwater lakes in Antarctica, are described. Chlorophyll a concentration is low (0.2–0.4μg·1−1) and there is no discernable spring increase. The phytoplankton is largely dominated by flagellates. Bacterioplankton exhibits a seasonal pattern of abundance ranging from 1.0 × 108·1−1 in July to 3.25 × 108·1−1 in September. Changes in bacterial abundance probably relate to temperature and grazing by heterotrophic and mixotrophic flagellates. Total flagellated protozoan concentrations ranged between 25–136 × 102·l−1. Autotrophic and heterotrophic flagellate abundances were coupled and peaks in their abundance oscillated with peaks in bacterioplankton concentration. Four species of ciliated protozoa, dominated by oligotrichs, particularly the plastidic Strombidium, inhabit the lake. The plankton is characterised by the presence of floes which act as loci for bacteria, flagellates and amoebae and feeding sites for the ciliates and the two sparce metazoan components of the plankton. Crooked Lake is extremely oligotrophic but nonetheless supports a plankton community with a low species diversity and simple trophodynamics.

Rapid production and evolution of late Archaean felsic crust in the Vestfold Block of East Antarctica

The aim of this study is to present a definitive chronostratigraphy, based for the first time on Ub zircon ages, for the Vestfold Block of East Antarctica. This region consists of four principal rock units, three of which are composed of felsic orthogneisses, and form the subject of this article. These orthogneiss units comprise the previously defined Crooked Lake and Mossel gneisses, and a newly proposed felsic unit, the Grace Lake granodiorite. The entire gamut of significant felsic igneous activity, the two intense tectonothermal events which preceded the cratonisation of the Vestfold Block, and significant post-tectonic uplift were all accomplished during an approximately 50 Ma interval at the end of the Archaean. This conclusion is in marked contrast to a previously proposed model that such activity had occurred episodically over several hundred million years. The Mossel gneiss (predominantly tonalitic orthogneiss) has the oldest igneous precursors, with a significant age spread, from 2526±6 Ma (in the type area) to 2501±4 Ma. Precursors of the compositionally varied Crooked Lake gneiss (predominantly dioritic, monzodioritic and monzonitic rocks) also show a distinct range of crystallisation ages, from 2501±4 Ma in the type area, through 2493±5 Ma to 2484±6 Ma. Both units appear to show a general northwards migration of igneous activity. The Grade Lake granodiorite, which is defined here on field and isotopic criteria, yields a pooled mean age (from two rocks) of 2487±6 Ma. An undeformed, post-granulite-facies quartz diorite dyke was emplaced at 2477±5 Ma. The new isotopic data constrain the age of the first major granulite-facies deformation (D 1) to have affected the Vestfold Block to lie between 2501±4 Ma and 2487±6 Ma, and that of the second granulite-facies deformation (D 2) to 2487±6 Ma. There is evidence of older precursors for some of the late Archaean gneisses. Zircon cores and xenocrysts together with SmNd model ages indicate that the Grace Lake granodiorite was derived from crustal sources at least 2800 Ma old. The presence of inherited zircon in one of two analysed samples of the Mossel gneiss, and a spread of SmNd model ages, implies derivation by the melting of at least two source components, one at least 2700 Ma old. In contrast, the apparent lack of inherited zircon in the Crooked Lake gneiss samples is consistent with derivation of their precursors either exclusively from the mantle, or by a brief two-stage melting process. The Vestfold Block chronology is completely different from that of the adjacent Rauer Islands region, indicating that they were not juxtaposed during Archaean times. Neither do any nearby Archaean terranes appear to have comparable chronostratigraphy with the Vestfold Block. At our present state of knowledge, only the Napier Complex of Enderby Land, and possibly the southern Prince Charles Mountains of MacRobertson Land contain any rocks of similar age. This makes the Vestfold Block a potentially useful element for theoretical reconstruction of Gondwanaland.

Deformation of the western margin of the Omineca Belt near Crooked Lake, east-central British Columbia

The western margin of the Omineca Belt near Crooked Lake, British Columbia, consists of metasedimentary rocks (Snowshoe Group) and orthogneisses of the Barkerville terrane, structurally overlain by a mafic volcanic – sedimentary package of rocks belonging to the allochthonous Slide Mountain (Crooked Amphibolite) and Quesnel terranes (Triassic phyllite and Nicola Group). At least two episodes of regional deformational (phases 2 and 3) affected this composite package. Deformation and metamorphism (phase 1) in the Snowshow Group predate the formation of this package and are nowhere evident within the allochthonous terranes.Middle Jurassic metamorphism ranging from chlorite zone through sillimanite zone affected all units. Isograds are folded, together with the junction between the terranes, indicating that the metamorphic assemblages developed prior to folding of this boundary. Granitic orthogneiss (Boss Mountain, Quesnel Lake, and Perseus gneisses), having a minimum age of Late Devonian to Early Pennsylvanian, was intruded into and deformed with the Snowshoe Group during the earliest recognizable phase of deformation in the Barkerville terrane (phase 1). Slide Mountain terrane rocks occupy a narrow zone where large eastward displacement occurred during overthrusting of the Intermontane superterrane upon the western margin of North America in Middle Jurassic time.

Metalimnetic cyanobacteria in hard‐water lakes: Buoyancy regulation and physiological state

During summer stratification, Crooked and Little Crooked Lakes, Indiana, contained phytoplankton dominated by populations of Aphanizomenonflos‐aquae that stratified in the metalimnion where photon irradiance was 6% of that at the surface. The gas vacuolate Aphanizomenon filaments from Little Crooked Lake lost buoyancy when exposed to irradiances >100 µmol photons m−2 s−1. If 2 µM KH2PO4 was added to the water samples, however, exposure to irradiances >200 µmol photons m−2 s−1 was necessary to obtain buoyancy losses. Phosphate also affected the recovery of buoyancy by sinking filaments. Filaments that had lost buoyancy due to incubation in the light recovered it when incubated for 5 h in the dark. Addition of phosphate increased the rate of buoyancy recovery by 50%.The metalimnetic populations had stratified in a zone of relatively low irradiance and inorganic nutrient concentration. The physiological state of the populations was evaluated by determining the kinetic characteristics for phosphate, nitrate, and ammonia uptake and the cellular contents of surplus phosphate and chlorophyll a. On the basis of the premise that cells limited by a particular element will express a high uptake potential for that element, the metalimnetic populations showed characteristics of organisms not limited by the availability of light, phosphorus, or nitrogen.

Geometry of a convergent zone, Central British Columbia, Canada

The Canadian Cordillera is separable into two major northerly trending tectonic units—the Pacific Orogen and the Columbian Orogen, with the latter further separated into the Omineca Crystalline Belt and the easterly Rocky Mountain Fold and Thrust Belt. Synkinematic metamorphism of Jurassic age within the Omineca Belt is thought to be associated with accretion of westerly terranes of the Pacific Orogen—more specifically the Quesnellia terrane—that was thrust easterly over the Omineca Belt towards the craton. Mylonitic rocks mark the margin between these two belts and this margin is well-exposed near Crooked Lake, central British Columbia. Structural analysis across the zone of convergence between these two terranes indicates that the cratonic basement and the accreted cover sequences have several phases of deformation and metamorphism in common. The initial common phase of deformation, wherein convergence is accomplished, is characterized by easterly verging folds that are superposed by a second common phase having westerly verging folds that deform the zone of convergence and control the present regional map pattern. A final common phase of deformation produced easterly verging folds. Change in vergence direction is interpreted as resulting from change in direction of transport related to subduction process: first obduction of Quesnellia onto the Omineca craton, followed later by easterly subduction of an oceanic Quesnellia below the craton. All evidence of transport direction(s) points to convergence occurring at very high angles to the zone of convergence. There appears to be no evidence of transport parallel with the strike of the zone. If transport has taken place parallel to the strike of the zone, then this transport occurred before convergence or evidence of this motion has been destroyed during the convergence.

The effects of temperature on bacterial production in a dimictic eutrophic lake

The incorporation of [3H](methyl)thymidine into DNA by the planktonic heterotropic bacteria of Little Crooked Lake (Noble Country, IN) was determined at different incubation temperatures. The highest rates of thymidine incorporation generally occurred at temperatures exceeding the in situ temperature of the sample. The optimal temperature for thymidine incorporation ranged from 1.0–3.4 times the in situ temperature. As the summer of 1983 progressed, the optimal temperatures for thymidine incorporation by epilimnetic samples and the in situ temperatures converged. This trend was reversed as fall overturn was approached.

The effects of temperature on bacterial production in a dimictic eutrophic lake

The incorporation of [ 3H](methyl)thymidine into DNA by the planktonic heterotropic bacteria of Little Crooked Lake (Noble Country, IN) was determined at different incubation temperatures. The highest rates of thymidine incorporation generally occurred at temperatures exceeding the in situ temperature of the sample. The optimal temperature for thymidine incorporation ranged from 1.0–3.4 times the in situ temperature. As the summer of 1983 progressed, the optimal temperatures for thymidine incorporation by epilimnetic samples and the in situ temperatures converged. This trend was reversed as fall overturn was approached.

Primary and Bacterial Production in Two Dimictic Indiana Lakes

The relationship between primary and bacterial production in two dimictic Indiana lakes with different primary productivities was examined during the summer stratification period in 1982. Primary production rates were calculated from rates of HCO(3) incorporation by natural samples, and bacterial production was calculated from rates of [H-methyl]thymidine incorporation by natural samples. Both vertical and seasonal distributions of bacterial production in the more productive lake (Little Crooked Lake) were strongly influenced by primary production. A lag of about 2 weeks between a burst in primary production and the subsequent response in bacterial production was observed. The vertical distribution of bacterial production in the water column of the less productive lake (Crooked Lake) was determined by the vertical distribution of primary production, but no clear relationship between seasonal maxima of primary and bacterial production in this lake was observed. High rates of bacterial production in Crooked Lake during May indicate the importance of allochthonous carbon washed in by spring rains. Bacterial production accounted for 30.6 and 31.8% of total (primary plus bacterial) production in Crooked Lake and Little Crooked Lake, respectively, from April through October. High rates of bacterial production during late September and October were observed in both lakes. Calculation of the fraction of bacterial production supported by phytoplankton excretion implies an important role for other mechanisms of supplying carbon, such as phytoplankton autolysis. Several factors affecting the calculation of bacterial production from the thymidine incorporation rates in these lakes were examined.

Seasonal Bacterial Production in a Dimictic Lake as Measured by Increases in Cell Numbers and Thymidine Incorporation

Rates of primary and bacterial production in Little Crooked Lake were calculated from the rates of incorporation of HCO(3) and [methyl-H]thymidine, respectively. Growth rates of bacteria in diluted natural samples were determined for epilimnetic and metalimnetic bacterial populations during the summers of 1982 and 1983. Exponential growth was observed in these diluted samples, with increases in cell numbers of 30 to 250%. No lag was observed in bacterial growth in 14 of 16 experiments. Correlation of bacterial growth rates to corresponding rates of thymidine incorporation by natural samples produced a conversion factor of 2.2 x 10 cells produced per mole of thymidine incorporated. The mass of the average bacterial cell in the lake was 1.40 x 10 +/- 0.05 x 10 g of C cell. Doubling times of natural bacteria calculated from thymidine incorporation rates and in situ cell numbers ranged from 0.35 to 12.00 days (median, 1.50 days). Bacterial production amounted to 66.7 g of C m from April through September, accounting for 29.4% of total (primary plus bacterial) production during this period. The vertical and seasonal distribution of bacterial production in Little Crooked Lake was strongly influenced by the distribution of primary production. From April through September 1983, the depth of maximum bacterial production rates in the water column was related to the depth of high rates of primary production. On a seasonal basis, primary production increased steadily from May through September, and bacterial production increased from May through August and then decreased in September.

Excretion of photosynthetically fixed organic carbon by metalimnetic phytoplankton

The effects of light intensity, oxygen concentration, and pH on the rates of photosynthesis and net excretion by metalimnetic phytoplankton populations of Little Crooked Lake, Indiana, were studied. Photosynthetic rates increased from 1.42 to 3.14 mg C·mg(-1) chlorophylla·hour(-1) within a range of light intensities from 65 to 150μE·m(-2)·sec(-1), whereas net excretion remained constant at 0.05 mg C·mg(-1) chlorophylla·hour(-1). Bacteria assimilated approximately 50% of the carbon released by the phytoplankton under these conditions. Excreted carbon (organic compounds either assimilated by bacteria or dissolved in the lake water) was produced by phytoplankton at rates of 0.02-0.15 mg C·mg(-1) chlorophylla·hour(-1). These rates were 6%-13% of the photosynthetic rates of the phytoplankton. Both total excretion of carbon and bacterial assimilation of excreted carbon increased at high light intensities whereas net excretion remained fairly constant. Elevated oxygen concentrations in samples incubated at 150μE· m(-2)·sec(-1) decreased rates of both photosynthesis and net excretion. The photosynthetic rate increased from 3.0 to 5.0 mg C·mg(-1) chlorophylla· hour(-1) as the pH was raised from 7.5 to 8.8. Net excretion within this range decreased slightly. Calculation of total primary production using a numerical model showed that whereas 225.8 g C·m(-2) was photosynthetically fixed between 12 May and 24 August 1982, a maximum of about 9.3 g C·m(-2) was released extracellularly.

Geochemical evolution of Archaean granulite-facies gneisses in the Vestfold Block and comparisons with other Archaean gneiss complexes in the East Antarctic Shield

The Vestfold Block, like other Archaean cratons in East Antarctica and elsewhere, consists predominantly of felsic orthogneiss (Mossel and Crooked Lake gneisses), with subordinate mafic granulite (Tryne metavolcanics) and paragneiss (Chelnok supracrustals). Two major periods of continental crust formation are represented. The Mossel gneiss (metamorphosed about 3,000 Ma ago) is mainly of tonalitic composition, and is similar to much of the roughly coeval Napier Complex in Enderby Land. The Crooked Lake gneiss was emplaced under high-grade conditions about 2,450 Ma ago and comprises a high proportion of more potassic rocks (monzodioritic and monzonitic suites), as well as tonalite and minor gabbro and diorite. Both Mossel and Crooked Lake gneisses are depleted in Y and have moderate to high Sr, Ce/Y, and Ti/Y, consistent with melting of a mafic source (?subducted hydrated oceanic crust) leaving major residual hornblende (± garnet). Most Crooked Lake gneisses are more enriched in incompatible elements (P, Sr, La, Ce, and particularly Rb, Ba, and K) than Mossel gneisses, suggesting derivation from a more enriched mafic source. The Vestfold Block contains few orthogneisses derived by melting of older felsic crustal rocks, in marked contrast to the Archaean Napier Complex and, in particular, southern Prince Charles Mountains. Both Mossel and Crooked Lake tonalites are strongly depleted in Rb, K, Th, and U, and have very low Rb/Sr and high K/Rb; more potassic orthogneisses are depleted in Th, U, and, to lesser extents, Rb. Tryne metavolcanics are depleted in Th and Rb, but appear to have been enriched in K (and probably Na), possibly during early low-grade alteration.

Physiological ecology of a metalimnetic Oscillatoria rubescens population1

Measurements of biochemical composition and photosynthetic carbon metabolism were used to determine the physiological state of a metalimnetic population of Oscillatoria rubescens in Crooked Lake, Indiana, during 1979 and 1980. The percentage of photosynthetically fixed CO2 incorporated into protein did not vary diurnally, but the variation observed over 3‐day periods was as large as that found seasonally, which suggested that changes in environmental conditions occurred during these intervals. Several of the biochemical measurements did not change during the year, including the ratios of chlorophyll a or phycoerythrin to protein and protein to dry weight; the ratios of carbohydrate or RNA to protein were more promising indicators of long term changes in the physiological state of the population because there were seasonal changes in these. Alkaline phosphatase activities were measured in the epilimnion and metalimnion as an index of phosphate limitation. In the epilimnion levels were similar to those found in phosphate‐limited algal cultures, whereas in the Oscillatoria layer the activities were sevenfold lower.

Snowy Egret at Crooked Lake

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