Limnological Studies of a Subarctic Lake System

A limnological study was carried out on a pair of lakes within the taiga forest of interior Alaska. These lakes, Ace and Deuce Lakes, are irregular in that one of them (Deuce Lake) is meromictic, never undergoing complete circulation, and the other (Ace Lake) has a spring circulation which is confined to the surface layers and autumnal mixing is attenuated. The ionic composition is similar to lakes in the surrounding area, with somewhat higher levels of dissolved ions. The unique features of the lake system are related to the meromictic tendencies and highly colored water with rather high ionic content. Primary productivity rates are relatively high by interior Alaskan standards, and nutrient levels are high. Primary productivity is confined to the surface meter, but even so annual productivity amounts to more than 70 g C/m²-yr.     

Thermal stratification and annual heat budget of a Florida sinkhole lake

Summary Aerial photographs of the Florida landscape, an area of Karst topography, show the country-side to be pockmarked by small lakes, many of which are nearly circular in surface outline. Lake Mize is quite typical of these sinkhole or doline lakes in its morphometric features, including its morning glory basin shape. The deeper portion of the basin occupies a relatively small fraction of the area and volume of the lake. Lake Mize becomes stably stratified at superficial depths in early spring and remains so until late fall or early winter. Even the violent winds of a hurricane are insufficiently strong to break up the stratification. Stratification disappears by December and the lake circulates through the winter months during which the water temperature drops to the winter low-generally near 11° C. The circulation pattern is typical of subtropical or warm monomictic lakes-a single, extended period of circulation with the minimum temperature always well above 4° C.Lake Mize has an extremely small annual heat budget. Based upon empirical evidence this is due to a number of factors including latitude (ca 30° N latitude), altitude (ca 30 m above sea level), protected location of the lake, small surface area and restricted solar heating. However, the regression equations of GORHAM relating annual heat budgets to various morphometric parameters of larger temperate zone lakes are not useful for predicting the annual heat budget of a lake such as Lake Mize. Year to year variations in the annual heat budget were rather large, ranging from a low of 3767 cal/cm² to a high of 6003 calf cm², so that the highest annual heat budget was roughly 1.6X that for the lowest of the three years. One expects a fair amount of year to year variation in annual heat budgets based upon Hutchinson's discussion (1957). Since we are dealing with an extremely small annual heat budget small changes are magnified when viewed on a percentage basis.     

Paleopigment evidence of competition between phytoplankton and a cyanobacterial algal mat in a meromictic lake near Toronto,Ontario Canada

Crawford Lake, a meromictic lake located near Toronto, Canada, was cored to determine if algal pigments preserved in its sediments would make it possible to infer past changes in lake productivity over the last five hundred years. From 1500 to 1910 A.D. the sediments display extremely high levels of oscillaxanthin and myxoxanthophyll while chlorophyll derivatives and total carotenoids were relatively low. As the lake became increasingly more eutrophic in the latter part of the twentieth century, this relationship reversed itself. Competition for light between the deep dwelling cyanobacteria in the algal mat on the lake's bottom (8–14 m) and phytoplankton in the overlying surface layers of the water column (5–7 m) was attributed to the observed reduction in oscillaxanthin and myxoxanthophyll as Crawford Lake eutrophied. Because the major cyanobacteria in Crawford Lake are benthic mat forming Lyngbya and Oscillatoria, and not phytoplankton, competition for light with the overlying phytoplankton is critical in determining the total quantity of oscillaxanthin and myxoxanthophyll preserved in the lake's profundal sediments. These findings have major implications for the use of cyanobacterial pigments as indicators of lake trophic status in lakes where benthic algal mats are present.     

A LIMNOLOGICAL SYNOPSIS OF BHANGAZI SOUTH,A DYSTROPHIC COASTAL LAKE IN THE GREATER ST LUCIA WETLAND PARK (KWAZULU/NATAL), WITH COMMENTS ON ITS CONSERVATION VALUE.

Summary

Base-line limnological and biological data are given for Lake Bhangazi South, a small lake on the coastal plain of Kwazulu-Natal, South Africa. This shallow (Z_max < 6 m), subtropical lake is a warm and seemingly continuously polymictic system, but experiences severe (continuous?) deoxygenation of its deeper muddy sediments. Nutrient status (of N in particular), light attenuation, phytoplankton productivity and zooplankton biomass are high relative to other regionally comparable coastal lakes investigated. While the ichthyofauna is quite rich, zooplankton and especially zoobenthos communities are species-poor, and lack the relict estuarine components which often dominate these latter assemblages in comparable coastal lakes. The zooplankton is typically freshwater in composition, and contains a new species of copepod (Tropodiaptomus bhangazii Rayner); the lake may be older, or seen longer evolutionary divergence than its proximate counterparts. Benthic species diversity in the lake is especially low amongst the Crustacea and Mollusca, possibly reflecting the effect of relatively acid waters (pH ca 6.5) on the calcium budgets of these groups. Scanty observational data indicative of ecosystem changes over the past 35 years are reported and briefly evaluated from a conservation/management perspective. Along with the endemic copepod, several rare fish species give the lake added conservation status.     

Omnivory,vertical food‐web structure and system productivity: stable isotope analysis of freshwater planktonic food webs

1. The energetic hypothesis proposes that the vertical structure of food webs should increase in height with increasing system productivity. I measured the trophic positions and extent of trophic separation between the invertebrate planktivores Mysis relicta and Chaoborus spp. and their putative zooplankton prey along a gradient of lake productivity with the use of stable nitrogen isotopes. 2. In lakes of low productivity, these planktivores were found to be herbivorous, becoming omnivorous at intermediate lake productivities, and only able to be truly zooplanktivorous as lakes approached mesotrophy. A subsequent secondary analysis of literature data revealed that the strength of top‐down trophic cascades among these organisms increased with lake productivity as reflected by relationships between the abundance of planktivores and that of phytoplankton. 3. Increased omnivory under conditions of low productivity, effectively shortening the vertical structure of food webs as predicted by the energetic hypothesis, may produce increased community stability.     

The zooplankton-phytoplankton interface in lakes of contrasting trophic status: an experimental comparison

We report here the results of an experimental study designed to compare algal responses to short-term manipulations of zooplankton in three California lakes which encompass a broad range of productivity (ultra-oligotrophic Lake Tahoe, mesotrophic Castle Lake, and strongly eutrophic Clear Lake). To assess the potential strength of grazing in each lake, we evaluated algal responses to a 16-fold range of zooplankton biomass. To better compare algal responses among lakes, we determined algal responses to grazing by a common grazer (Daphnia sp.) over a range ofDaphnia densities from 1 to 16 animals per liter. Effects of both ambient grazers andDaphnia were strong in Castle Lake. However, neither ambient zooplankton norDaphnia had much impact on phytoplankton in Clear Lake. In Lake Tahoe, no grazing impacts could be demonstrated for the ambient zooplankton butDaphnia grazing had dramatic effects. These results indicate weak coupling between phytoplankton and zooplankton in Clear Lake and Lake Tahoe, two lakes which lie near opposite extremes of lake trophic status for most lakes. These observations, along with work reported by other researchers, suggest that linkages between zooplankton and phytoplankton may be weak in lakes with either extremely low or high productivity. Biomanipulation approaches to recover hypereutrophic lakes which aim only to alter zooplankton size structure may be less effective if algal communities are dominated by large, inedible phytoplankton taxa.     

Plankton secondary productivity and biomass: Their relation to lake trophic state

The biomass and production of the most important zooplankton species were followed for two years in three lakes of varying trophic status in the Lake Washington watershed. Cladocerans and copepods were of equal importance in the biomass of lakes Findley and Chester Morse (both oligotrophic), whereas, copepods were the main biomass component in Lake Sammamish (mesotrophic). Cladocerans dominated production in lakes Sammamish and Chester Morse, while in Findley Lake their productive role, like that of biomass, was equal to that of the copepods. Rotifers contributed a relatively small biomass and production.Data from this study supported Hillbricht-Ilkowska's postulate that the energy transfer efficiency between the primary and secondary trophic levels decreases with increasing trophic state. Energy transfer efficiencies for the lakes of this study expressed as a two year mean of the ratio-secondary: primary production, were as follows: Findley Lake-0.13; Chester Morse Lake-0.08; and Lake Sammanish-0.04.On the other hand, the hypothesis of Patalas that the secondary productivity: biomass ratio (P/B) tended to increase in proportion to the productivity of a lake, could not be supported. Lake Sammamish, the most productive of the lakes studied, had a P/B ratio of 0.03 while lakes Findley and Chester Morse had P/B ratios of 0.04.     

CYTOPLASMIC MASSES PRESERVED IN EARLY HOLOCENE DIATOMS: A POSSIBLE TAPHONOMIC PROCESS AND ITS PALEO‐ECOLOGICAL IMPLICATIONS1

In Lake Suigetsu, central Japan, greenish/light‐brown granules identified as cytoplasmic masses had been preserved in siliceous cell walls of freshwater diatoms in annual layers of lacustrine muds since the early Holocene. The lacustrine muds consisted of alternating dark‐colored (rich in diatom valves, clay, and organic matter) and light‐colored (mainly diatom valves) laminae. The greenish/light‐brown granules were predominately preserved in frustules of the genus Aulacoseira preserved in the dark‐colored laminae. The dark‐colored laminae were inferred to have formed annually under stratified water caused by surface water warming in summer that caused the formation of an organic‐rich anoxic layer on the lake bottom that favored granule preservation. The good preservation of cytoplasmic masses in dark‐colored laminae suggested a cause for diatom assemblage periodicity, a phenomenon that was commonly noted in temperate lakes: the cells containing these masses could be potential seed stocks for subsequent spring blooms. Frustules of the most abundant granule‐containing species, Aulacoseira nipponica (Skvortzow) Tuji, in the dark‐colored laminae of the Early Holocene muds were abundant in the overlying light‐colored laminae, suggesting that these species reproduced abundantly in springtime yielding a massive diatom bloom.     

Seasonal Dynamics of Periphyton in a Large Tropical Lake

Tropical aquatic systems are generally assumed to have little seasonality in productivity patterns. However, this study indicated that there was substantial seasonal variation in epilithic productivity and biomass in tropical Lake Tanganyika, due primarily to seasonal patterns in lake hydrodynamics that influence nutrient availability. Although they support much of the lake’s biological diversity, epilithic algae made a minor contribution to the total energy budget in Lake Tanganyika. A comparison among large, oligotrophic lakes revealed no significant latitudinal trends in periphyton productivity or biomass. However, Lake Tanganyika has relatively low benthic algal biomass and is therefore more efficient at photosynthesis than the temperate lakes. The influence of wave action and consumer density and diversity may be important in moderating productivity of the epilithic community.     

Interannual and between-site variability in the occurrence of clear water phases in two shallow Mediterranean lakes

It is widely accepted that clear water phases constitute a regular stage in the seasonal succession of plankton in dimictic lakes and reservoirs (i.e. PEG Model). The occurrence of such a phenomenon in Mediterranean shallow lakes is characterised by a marked interannual variability, which makes it difficult to establish reliable predictions on the dynamics and functioning of plankton in these ecosystems. In the present paper we analyse the factors influencing the occurrence of the clear water phases in the two shallow lakes of the Albufera of Adra, a coastal wetland region of south-eastern Spain: Lake Honda and Lake Nueva. Despite their geographical proximity, both lakes depicted large hydrological and limnological differences. Lake Honda is an epigenic and recharge lake that is strongly influenced by the hydrological conditions in its watershed, while Lake Nueva can be classified as a hypogenic and discharge lake and, as such, is less affected by the hydrological regime. In contrast, the morphometry, exposure and fetch of Lake Nueva make this ecosystem especially sensitive to wind forcing. Clear water phases in these shallow lakes were linked with periods of low thermal stability and the dominance of small-edible algae in the phytoplankton community, both of which allowed a Daphnia magna population to grow up and induce the algae collapse by grazing. In Lake Honda, those conditions were met during the spring of 2002 under the influence of intense rainfall-events, while in Lake Nueva the clear water phase was induced in the spring of 2003 by the occurrence of strong and frequent wind events. In both lakes, a relatively high water column thermal stability and the abundance of cyanobacteria early in the spring prevented the development of the Daphnia magna population and the occurrence of the clear water phase.     

The plankton community of a young, eutrophic, Antarctic saline lake

A shallow, saline lake (Rookery Lake) close to the sea and surrounded by a penguin rookery was investigated during the austral spring and summer of 1996/1997. The proximity to the sea means that the lake is likely to have been formed recently during isostatic uplift. Inputs of carbon and nutrients from the penguin rookery have rendered Rookery Lake eutrophic compared with other brackish and saline lakes in the Vestfold Hills. Chlorophyll a concentration, bacterioplankton, heterotrophic nanoflagellate and phototrophic nanoflagellate abundances were all significantly higher than in other non-enriched lakes. The high productivity created seasonal anoxia during winter and spring below ice cover. The ciliate community resembled the marine community, and was dissimilar to that seen in older saline lakes within the Vestfold Hills. Thus Rookery Lake provides valuable evidence of the impact of natural eutrophication on an Antarctic lake, as well as of the evolution of the typical microbial community which dominates the older lakes of the Vestfold Hills. Accepted: 2 May 1999     

The effect of long wave ultraviolet radiation (UV-A) on the photosynthetic activity of natural population of freshwater phytoplankton

The effect of ultraviolet radiation on diel changes and depth profiles of phytoplankton photosynthesis was studied in four temperate freshwater lakes. Photosynthetic oxygen production was determined by incubating lake water in light and dark bottles under various weather conditions. Half the light bottles were wrapped with sheets of vinyl chloride film to exclude light with wavelengths shorter than 400 nm. The inhibition of photosynthesis due to UV-A (320–400 nm) was observed during most of the daytime and was very strong around noon on both sunny and cloudy days. On sunny days, when the surface waters of the highly eutrophic Lake Suwa and Senzoku Pond were dominated by denseMicrocystis populations, cumulative daily production at the surface, estimated from the incubation of bottles from which UV-A was excluded by the vinyl film, were about double the rates obtained from glass bottles in which UV-A was present. The UV-A inhibition was detected from the surface toca 20 cm depth in hypereutrophic lakes and at depths greater than 50 cm in mesotrophic lakes. Analysis of the photosynthesis-irradiance (P-I) relationship obtained in the present study shows β, a parameter that describes photo-inhibition, is higher in the presence of UV-A than in its absence. This indicates that UV-A is the major cause of photo-inhibition of phytoplankton photosynthesis.     

Ecology of Dictyosphaerium pulchellum Wood (Chlorophyta, Chlorococcales) in a shallow, acid, forest lake

This study relates to the ecology of Dictyosphaerium pulchellum Wood in Delamere Lake in Cheshire, UK. Dictyosphaerium pulchellum is a cosmopolitan, green colonial phytoplankton species that occasionally forms dense, monospecific populations in lakes. Delamere Lake is a small, shallow, acid lake (mean pH, 4.5) with very high phytoplankton biomass (annual mean chlorophyll a, 290 μg l⁻¹) and devoid of any significant cladoceran population, the efficient grazers of phytoplankton. A predominantly unicellular form of D. pulchellum was the dominant species in Lake Delamere, and it comprised on average ca. 80% (maximum >99%) of the lake phytoplankton biovolume. Laboratory and lake experiments were conducted on this species showed that its pH tolerance varied between 2.4 and 10.7, and its optimum tolerance range between 3.3 and 8.5 depending on other environmental variables. Low pH was not responsible for the unicellular habit of this alga, but a very high nutrient regime could be an important factor. Bioassays revealed that in Delamere Lake this species was limited by nitrogen, but nitrogen did not hamper high growth in the lake. Dictyosphaerium pulchellum can persist at low light levels, tolerate CO₂-deficiency and can grow in polyhumic water with water colour around 300 mg Pt l⁻¹, but probably not in darker waters. The dominance of D. pulchellum in Delamere Lake is apparently due to a combination of several factors: its ability to tolerate both low pH and high turbidity, exploit high nutrient conditions, absence of effective grazing pressure by zooplankton and being a superior competitor.     

Influence of Sediment Inflow on Phytoplankton Primary Productivity in Lake Tahoe (California-Nevada)

Light, nutrient concentrations and phytoplankton photosynthesis were studied in a Lake Tahoe sediment plume during maximum spring runoff. They were compared with conditions in clear lake waters not influenced by inlets. In the plume, nutrient concentrations increased in proportion to sediment density whereas light transmission of water was reduced with little effect on the spectral composition except for red light. Light inhibition of photosynthesis at the lake surface was less pronounced in the plume than in clear water and light limitation occurred more rapidly in deeper layers. Evidence from both lake experiments and laboratory bioassays suggests that iron had the greatest stimulatory effect on both photosynthetic activity and biomass growth at maximum sediment densities near the stream inlet. Because of less surface inhibition, photosynthetic light energy utilization efficiency was usually higher in the sediment plume which occurred in relatively shallow areas near the shore. In order to estimate overall effects of enhanced turbidity associated with nutrient loading on Lake Tahoe's primary productivity, profiles taken in shallow areas near the lakeshore were extrapolated to the maximum depth of photosynthesis. Light limitation would cause decreasing productivity, but nutrient stimulation would make this effect less pronounced. The overall effect would depend on the extent of sediment loading relative to nutrient loading.     

Primary productivity,phytoplankton and limiting nutrient factors in labrador lakes

The primary productivity of some lakes and reservoirs in western Labrador was measured by the ¹⁴C method in order to determine the range of productivities and the effects of impoundment. No primary productivity data previously existed for this part of Canada. Both the primary productivity and standing crops of phytoplankton were found to be low in a newly impounded lake but later rose to levels greater than in surrounding natural lakes. In nutrient enrichment experiments, carbon was never found to be limiting but phosphorus stimulated primary productivity when added alone or in combination with nitrogen.     

Geothermal heat flux into deep caldera lakes Shikotsu, Kuttara, Tazawa and Towada

Geothermal heat fluxes into the deepest waters of four caldera lakes were measured. Temperature profiles within the stratification period between July and November 2007 allowed a quantification of the acquired heat. Due to their enormous depth, heat input from the lake bed was locally separated from heat fluxes at the surface. In conclusion, a direct measurement of geothermal heat input could be accomplished. Although enhanced geothermal activity could be suspected in all cases, two lakes showed a geothermal heat flux of 0.29 or 0.27 W/m² (Lake Shikotsu and Lake Tazawa), as found in other regions not affected by volcanism, while both other lakes (Lake Kuttara and Lake Towada) showed a greatly enhanced heat input of 1 or 18.6 W/m², respectively. In conclusion, within our investigated set, all lakes acquired more heat from the underground than the continental heat flux average. Hence, the heat flux into the lakes from the ground was not dominated by the temperature gradient implied by the inner heat of the earth. Other effects like the general temperature difference of deep lake water and the groundwater or local sources of heat in the underground deliver more important contributions. Obviously the flow of water in the underground can play a decisive role in the heat transport into the deep waters of lakes.     

Bacterial Growth on Allochthonous Carbon in Humic and Nutrient-enriched Lakes: Results from Whole-Lake 13C Addition Experiments

Organic carbon (C) in lakes originates from two distinct sources—primary production from within the lake itself (autochthonous supply) and importation of organic matter from the terrestrial watershed (allochthonous supply). By manipulating the ¹³C of dissolved inorganic C, thereby labeling within-lake primary production, we examined the relative importance of autochthonous and allochthonous C in supporting bacterial production. For 35 days, NaH¹³CO₃ was added daily to two small, forested lakes. One of the lakes (Peter) was fertilized so that primary production exceeded total respiration in the epilimnion. The other lake (Tuesday), in contrast, was low in productivity and had high levels of colored dissolved organic C (DOC). To obtain bacterial C isotopes, bacteria were regrown in situ in particle-free lake water in dialysis tubes. The contribution of allochthonous C to bacterial biomass was calculated by applying a two-member mixing model. In the absence of a direct measurement, the isotopic signature of the autochthonous end-member was estimated indirectly by three different approaches. Although there was excess primary production in Peter Lake, bacterial biomass consisted of 43–46% allochthonous C. In Tuesday Lake more than 75% of bacterial growth was supported by allochthonous C. Although bacteria used autochthonous C preferentially over allochthonous C, DOC from the watershed contributed significantly to bacterial production. In combination with results from similar experiments in different lakes, our findings suggest that the contribution of allochthonous C to bacterial production can be predicted from ratios of chromophoric dissolved organic matter (a surrogate for allochthonous supply) and chlorophyll a (a surrogate for autochthonous supply).     

In-Lake Processes Offset Increased Terrestrial Inputs of Dissolved Organic Carbon and Color to Lakes

Increased color in surface waters, or browning, can alter lake ecological function, lake thermal stratification and pose difficulties for drinking water treatment. Mechanisms suggested to cause browning include increased dissolved organic carbon (DOC) and iron concentrations, as well as a shift to more colored DOC. While browning of surface waters is widespread and well documented, little is known about why some lakes resist it. Here, we present a comprehensive study of Mälaren, the third largest lake in Sweden. In Mälaren, the vast majority of water and DOC enters a western lake basin, and after approximately 2.8 years, drains from an eastern basin. Despite 40 years of increased terrestrial inputs of colored substances to western lake basins, the eastern basin has resisted browning over this time period. Here we find the half-life of iron was far shorter (0.6 years) than colored organic matter (A₄₂₀ ; 1.7 years) and DOC as a whole (6.1 years). We found changes in filtered iron concentrations relate strongly to the observed loss of color in the western basins. In addition, we observed a substantial shift from colored DOC of terrestrial origin, to less colored autochthonous sources, with a substantial decrease in aromaticity (-17%) across the lake. We suggest that rapid losses of iron and colored DOC caused the limited browning observed in eastern lake basins. Across a wider dataset of 69 Swedish lakes, we observed greatest browning in acidic lakes with shorter retention times (< 1.5 years). These findings suggest that water residence time, along with iron, pH and colored DOC may be of central importance when modeling and projecting changes in brownification on broader spatial scales.     

Picoplankton photosynthesis and diurnal variations in photosynthesis-irradiance relationship in a eutrophic and meso-oligotrophic lake

The abundance and relative importance of autotrophic picoplankton were investigated in two lakes of different trophic status. In the eutrophic lake, measurements of primary production were performed on water samples in situ and in a light incubator three times during the day whereas for the oligotrophic lake, only one measurement of primary production was performed on water samples in the incubator. Dark-carbon losses of phytoplankton from Lake Loosdrecht were investigated in time series. Cell numbers of autotrophic picoplankton in eutrophic Lake Loosdrecht (3.2 × 10⁴ cells ml^–1) were lower than in meso-oligotrophic Lake Maarsseveen (9.8 and 11.4 × 10⁴ cells ml^–1 at the surface and bottom respectively). In the phytoplankton of both lakes the ratio of picoplankton production increased with decreasing light intensity. In Lake Loosdrecht depth-integrated contribution of picoplankton to total photosynthesis was less than 4%. The P-I-relationship showed diurnal variations in light saturated photosynthesis, while light limited carbon uptake remained constant during the day. Dark carbon losses from short-term labelled phytoplankton during the first 12 hours of the night period accounted for 10–25% of material fixed during the preceeding light period.     

Using Satellite Remote Sensing to Estimate the Colored Dissolved Organic Matter Absorption Coefficient in Lakes

Given the importance of colored dissolved organic matter (CDOM) for the structure and function of lake ecosystems, a method that could estimate the amount of CDOM in lake waters over large geographic areas would be highly desirable. Satellite remote sensing has the potential to resolve this problem. We carried out model simulations to evaluate the suitability of different satellite sensors (Landsat, IKONOS, and the Advanced land Imager [ALI]) to map the amount of CDOM in concentration ranges that occur in boreal lakes of the Nordic countries. The results showed that the 8-bit radiometric resolution of Landsat 7 is not adequate when absorption by CDOM at 420 nm is higher than 3 m⁻¹. On the other hand, the 16-bit radiometric resolution of ALI, a prototype of the next generation of Landsat, is suitable for mapping CDOM in a wider range of concentrations. An ALI image of southern Finland was acquired on 14, July 2002 and in situ measurements were carried out in 15 lakes (18 stations). The results showed that there is a high correlation (R² = 0.84) between the 565 nm/660 nm ALI band ratio and the CDOM absorption coefficient in lakes. Analysis of 245 lakes in the acquired satellite image showed a normal distribution of CDOM concentration among the lakes. However, the size distribution of lakes was highly skewed toward small lakes, resulting in the CDOM concentration per unit lake area being skewed toward high values. We showed that remote sensing enables synoptic monitoring of the CDOM concentration in a large number of lakes and thus enables scaling up to the level of large ecosystems and biomes.