Proximate Composition and Nutrient Elements in the “Unusual” Algal “Jellies” of Lake Oguta in Southern Nigeria

The proximate composition, nutrient and trace elements of the planktonic algal “jellies” of Lake Oguta in Southern Nigeria, are provided as guides to their utilization and control, using flood (rainy) and dry season samples. These “jellies” are an unusual, macroscopic planktonic algal community in the lake, made up mostly of blue-green algae (Microcystis, Anabaena, Chroococcus) with some green algae (e. g. Spirogyra) and pennate diatoms (e.g. Navicula) rather epiphytic on the mucous jellies of the blue-green algae. Water content was high (98.2% mean, range 97.5-99.5%). Ash, protein and fat had values of 41.7 (39.0-46.2%), 16.9 (15.6-19.4%), and 2.0 (1.7-2.1%) respectively. Crude fibre and carbohydrates were high (25.8% and 12.4%). The levels of phosphorus and nitrogen were rather high, so were the major cations whose order of dominance (Ca > K > Mg > Na) differed from that of the lake water. Macronutrients increased in their concentrations during the rainy flood season while the reverse was the case with the micronutrients. Diagenesis of the endogenic minerals rather than anthropogenic factors are thought to be the reason for the seasonal changes in the ionic concentrations. Possible uses of the algal jellies are discussed as well as their control options.     

“How” and “what” matters: Sampling method affects biodiversity estimates of reef fishes

Understanding changes in biodiversity requires the implementation of monitoring programs encompassing different dimensions of biodiversity through varying sampling techniques. In this work, fish assemblages associated with the “outer” and “inner” sides of four marinas, two at the Canary Islands and two at southern Portugal, were investigated using three complementary sampling techniques: underwater visual censuses (UVCs), baited cameras (BCs), and fish traps (FTs). We firstly investigated the complementarity of these sampling methods to describe species composition. Then, we investigated differences in taxonomic (TD), phylogenetic (PD) and functional diversity (FD) between sides of the marinas according to each sampling method. Finally, we explored the applicability/reproducibility of each sampling technique to characterize fish assemblages according to these metrics of diversity. UVCs and BCs provided complementary information, in terms of the number and abundances of species, while FTs sampled a particular assemblage. Patterns of TD, PD, and FD between sides of the marinas varied depending on the sampling method. UVC was the most cost‐efficient technique, in terms of personnel hours, and it is recommended for local studies. However, for large‐scale studies, BCs are recommended, as it covers greater spatio‐temporal scales by a lower cost. Our study highlights the need to implement complementary sampling techniques to monitor ecological change, at various dimensions of biodiversity. The results presented here will be useful for optimizing future monitoring programs.     

Preliminary Observations on the Nature,Taxonomic Composition,Distribution, Behaviour and Nutrient Requirements of the “Unusual” Algal “Jellies” of Oguta Lake in Southeastern Nigeria

Preliminary observations were made between October 1982 and May 1983 on the nature, taxonomic composition, spatial distribution, buoyancy behaviour and nutrient requirements of some unusual planktonic algal “jellies” in Oguta Lake in Southeastern Nigeria. These “jellies” are macroscopic, blue-green algal masses whose excessive mucilage of high consistency acts as substrata for other epiphytic components viz. diatoms and green algae. They are more abundant in the lentic areas of the lake, undergo diurnal vertical movements and have their growth enhanced by spikes of nitrogen and phosphorus salts into their aquatic medium. The effects of these “jellies” on the ecology and general water use of the lake are discussed. Speculations on the reasons for their occurrence are given and possible control measures outlined.     

Quantifying denudation and sediment–accumulation systems (open and closed lakes): basic concepts and first results

The quantitative aspects of denudation in the drainage areas and sediment accumulation in the corresponding closed or open lakes are approached using two methods: (1) from known mean rates of mechanical and chemical denudation and the ratio of the drainage/lake area, average terrigenous and potential chemical (biogenic and evaporites) sedimentation rates in the lake are determined; or (2) from known sedimentation rates the average denudation rate is found. In closed systems the total mass denuded during a certain unit of time is deposited in the lake as terrigenous, biogenic and evaporitic sediments, whereas open lake systems lose a major part of the dissolved river input derived from chemical denudation. Applying elementary equations describing these relationships and using ratios between mechanical and chemical denudation (weathering ratio) established in other regions, e.g. chemical weathering in the lake drainage can be estimated. Likewise, the knowledge of the ‘bio-index' (ratio of biogenic sediment/total dissolved mass) allows the calculation of the loss of dissolved matter through the outflow from the lake, etc. In a first step, existing data from modern lake systems are evaluated. Later, idealized lake systems in various climatic and morphotectonic zones can be simulated and the results utilized to better understand ancient lake systems. Modern Alpine lakes reflect increased mechanical denudation rates (100 to ≥300 mm/ka) in highly elevated drainage areas of the Central Alps (mainly crystalline rocks) and high chemical denudation (up to ca. 100 mm/ka) in carbonate rocks of the Northern Calcareous Alps. Mechanical denudation is significantly enhanced by glaciation, but transport of the detritus into lakes may be delayed until the time immediately after glacial retreat. Average rates of terrigenous lake sedimentation amount to 5 to ≥15 mm/a (crystalline rocks, high relief), or are ≤5 mm/a (carbonate rocks). Delta outbuilding was a main factor in the filling of many Alpine lakes. Lakes draining low-altitude, semi-arid parts along the eastern margin of the Alps (Lake Balaton in Hungary) have low sedimentation rates and reflect the influence of increased temperature and vegetation. In East Africa, the transition from the Late Pleistocene (arid) to the early Holocene (humid) and again back to somewhat drier conditions caused substantial rises in lake levels and changes from closed to open lake systems. In such cases, the calculation of denudation from accumulation rates is biassed as a result of intermittent sediment storage at the lake margins (low sedimentation rates in the lake centre during lake highstands) or redeposition of sediment during lowstands (lowstand shedding). The modern denudation rates of East African rift lake systems vary by a factor of ≥15 (Lake Tanganyika, crystalline rocks and more dense vegetation cover, total denudation rate ca. 4 mm/ka; Lake Turkana, young volcanic rocks and tephra, sparse vegetation, mechanical denudation rate ca. 60 mm/ka).     

The meticulous phycological investigation of Lake Rudträsket, Central Sweden, 1947–1949, by Heinrichs Skuja

In 1947–1949, studies of water chemistry, aquatic macrophytes, bryophytes and algae were performed in a small lake, L. Rudträsket, near Stockholm, but only a few results concerning water chemistry and macrophytes have so far been published. Heinrichs Skuja (1892–1972) left 62 hand-written pages with the results of his analyses from the lake: a list of taxa, some measurements and several algal sketches. The main part of this material is presented here. Skuja identified about 640 taxa with a majority for desmids, ca. 290, followed by ca. 100 chlorophyceans, 65 euglenophytes and 60 cyanophytes. The species composition gives a fairly reflection of the character of the lake: small, shallow, rich in humus, acid and surrounded by swampy areas with Sphagnum. Dimensions of algae as well as drawings from L. Rudträsket have partly been published in publications by Skuja. In this paper seven plates with about 115 figures have been drawn in Indian ink and printed. Today, the lake has a lower pH value, pH 4.6, than in 1947–1949, pH 5.3–6.1, and would be a stimulating object for comparative studies.     

Determinants of seston C : P-ratio in lakes

1. The ratio of carbon to phosphorus (C : P) in seston is a major determinant of energy transfer in aquatic food webs and may vary more than an order of magnitude owing to various extrinsic and intrinsic factors. In this study, the determinants of C : P‐ratios in lake particulate matter (seston) was assessed in 112 Norwegian lakes, covering a C : P (atomic ratio) from 24 to 1842 (mean 250). 2. No overall effects of lake area, season or latitude on C : P was detected. Particulate P, but not particulate C, correlated with C : P. Multivariate analysis including a range of lake properties revealed total dissolved P, as the major determinant of sestonic C : P, with the fraction of detritus in total seston, chlorophyll or Secchi depth and lake colour as significant contributors. Together these parameters explained 30% of observed variance if using dissolved P and 81% if using total P as input variable to the multivariate model. 3. Chlorophyll and Secchi depth were highly correlated and substitutable in the analysis. Phytoplankton community composition did not affect seston C : P, probably reflecting the fact that live phytoplankton generally contributed <25% of the seston pool. 4. Total P correlated positively with C : P and is the key determinant of phytoplankton biomass and thus Secchi depth; the latter parameters contributed negatively to seston C : P, probably owing to increased light attenuation. These lake data thus support the light : nutrient ratio hypothesis, i.e. that high light and low P cause skewed uptake ratios of C to P. 5. Zooplankton biomass in general and Daphnia biomass in particular, was negatively correlated with C : P, probably reflecting a negative impact of poor seston quality at high C : P. Zooplankton grazing and nutrient recycling may also have contributed to a negative correlation between zooplankton biomass and sestonic C : P.     

Phosphatases; origin,characteristics and function in lakes

Phosphatases catalyze the liberation of orthophosphate from organic phosphorus compounds. The total phosphatase activity in lake water results from a mixture of phosphatases localized on the cell surfaces of algae and bacteria and from dissolved enzymes supplied by autolysis or excretion from algae, bacteria and zooplankton. External lake water phosphatases usually have pH optima in the alkaline region. Acid phosphatases generally seem to be active in the internal cell metabolism. The synthesis of external alkaline phosphatases is often repressed at high phosphate concentrations and derepressed at low phosphate concentrations. Phosphatase activity has therefore been used as a phosphorus deficiency indicator in algae and in natural plankton populations. The possibilities for this interpretation of phosphatase activity in lake water are limited, however, and this is discussed. The in situ hydrolysis capacity, i.e. the rate by which orthophosphate is released from natural substrates, is unknown. However, we advocate that this process is important and that the rate of substrate supply, rather than phosphatase activity, limits the enzymatic phosphate regeneration.     

Scaling of Pelagic Metabolism to Size,Trophy and Forest Cover in Small Danish Lakes

ABSTRACT We tested whether pelagic light and nutrient availability, metabolism, organic pools and CO₂-supersaturation were related to lake size and surrounding forest cover in late summer–autumn measurements among 64 small (0.02–20 ha), shallow seepage lakes located in nutrient-rich, calcareous moraine soils in North Zealand, Denmark. We found a strong implicit scaling to lake size as light availability increased significantly with lake size while nutrient availability, phytoplankton biomass and dissolved organic matter declined. Forest lakes had significantly stronger net heterotrophic traits than open lakes as higher values were observed for light attenuation above and in the water, dissolved organic matter, pelagic community respiration (R) relative to maximum gross primary production (R/GPP) and CO₂-supersaturation. Total-phosphorus was the main predictor of phytoplankton biomass (Chl) despite a much weaker relationship than observed in previous studies of larger lakes. Maximum gross primary production increased with algal biomass and decreased with dissolved organic matter, whereas community respiration increased with dissolved organic matter and particularly with gross primary production. These results suggest that exogenous organic matter supplements primary production as an energy source to heterotrophs in these small lakes, and particularly so in forest lakes experiencing substantial shading from the forest and dissolved humic material. This suggestion is supported by 20–30-fold CO₂ supersaturation in the surface water of the smallest forest lakes and more than sixfold supersaturation in 75% of all measurements making these lakes among the most supersaturated temperate lakes examined so far.     

Light and nutrient control phytoplankton biomass responses to global change in northern lakes

Global change affects terrestrial loadings of colored dissolved organic carbon (DOC) and nutrients to northern lakes. Still, little is known about how phytoplankton respond to changes in light and nutrient availability across gradients in lake DOC. In this study, we used results from whole‐lake studies in northern Sweden to show that annual mean phytoplankton biomass expressed unimodal curved relationships across lake DOC gradients, peaking at threshold DOC levels of around 11 mg/L. Whole‐lake single nutrient enrichment in selected lakes caused elevated biomass, with most pronounced effect at the threshold DOC level. These patterns give support to the suggested dual control by DOC on phytoplankton via nutrient (positively) and light (negatively) availability and imply that the lakes' location along the DOC axis is critical in determining to what extent phytoplankton respond to changes in DOC and/or nutrient loadings. By using data from the large Swedish Lake Monitoring Survey, we further estimated that 80% of northern Swedish lakes are below the DOC threshold, potentially experiencing increased phytoplankton biomass with browning alone, and/or combined with nutrient enrichment. The results support the previous model results on effects of browning and eutrophication on lake phytoplankton, and provide important understanding of how northern lakes may respond to future global changes.     

Experimental whole‐lake increase of dissolved organic carbon concentration produces unexpected increase in crustacean zooplankton density

The observed pattern of lake browning, or increased terrestrial dissolved organic carbon (DOC) concentration, across the northern hemisphere has amplified the importance of understanding how consumer productivity varies with DOC concentration. Results from comparative studies suggest these increased DOC concentrations may reduce crustacean zooplankton productivity due to reductions in resource quality and volume of suitable habitat. Although these spatial comparisons provide an expectation for the response of zooplankton productivity as DOC concentration increases, we still have an incomplete understanding of how zooplankton respond to temporal increases in DOC concentration within a single system. As such, we used a whole‐lake manipulation, in which DOC concentration was increased from 8 to 11 mg L^?1 in one basin of a manipulated lake, to test the hypothesis that crustacean zooplankton production should subsequently decrease. In contrast to the spatially derived expectation of sharp DOC‐mediated decline, we observed a small increase in zooplankton densities in response to our experimental increase in DOC concentration of the treatment basin. This was due to significant increases in gross primary production and resource quality (lower seston carbon‐to‐phosphorus ratio; C:P). These results demonstrate that temporal changes in lake characteristics due to increased DOC may impact zooplankton in ways that differ from those observed in spatial surveys. We also identified significant interannual variability across our study region, which highlights potential difficulty in detecting temporal responses of organism abundances to gradual environmental change (e.g., browning).     

Effects of weather‐related episodic events in lakes: an analysis based on high‐frequency data

1. Weather‐related episodic events are typically unpredictable, and their duration is often short. Abiotic and biological responses are often missed in routine monitoring. These responses are, however, now of particular relevance given projected changes in extreme weather conditions. 2. We present data from high‐frequency monitoring stations from lakes in Europe, North America and Asia that illustrate two classes of abiotic effects of weather events: (i) generally short‐lived effects of storms on lake thermal structure and (ii) the more prolonged effects of high rainfall events on dissolved organic matter levels and water clarity. We further relate these abiotic effects to changes in dissolved oxygen or in chlorophyll a levels. 3. Three differing causes for weather‐related decreases in surface dissolved oxygen levels were observed: (i) entrainment of anoxic water from depth, (ii) reduction in primary productivity and (iii) increased mineralisation of organic carbon delivered from the catchment. 4. The duration of in‐lake effects tended to be longer for events driven by weather conditions with a longer return period, that is, conditions that were relatively more severe and less frequent at a site. While the susceptibility of lakes to change was related in part to the severity of the meteorological drivers, the impacts also depended on site‐specific factors in some cases. 5. The availability of high‐frequency data at these sites provided insight into the capacity of the lakes to absorb current and future pressures. Several of the changes we observed, including increases in carbon availability, decreases in photosynthetically active radiation and increased disturbance, have the capacity to shift lakes towards an increased degree of heterotrophy. The magnitude and direction of any such change will, however, also depend on the magnitude and direction of climate change for a given location and on lake and catchment characteristics.     

Limnological study of a Pantanal saline lake.

Limnological studies involving physical, chemical and biological aspects, with emphasis on the zooplankton community, were carried out in a saline lake of the Pantanal floodplain, in the subregion of Nhecolandia (Mato Grosso do Sul, Brazil), during the dry and wet seasons of the local hydrological cycle. The results show that the lake is not directly affected by the flood-pulse through superficial coalescence, probably receiving groundwater instead. Most of the measured variables showed extremely high values, particularly dissolved salts, pH, conductivity, nutrients and chlorophyll a. These values were highest during the dry period due to the system's low water volume. The zooplankton community was basically represented by Metacyclops mendocinus, which displayed high population densities throughout the periods studied. The low diversity recorded is congruent with other studies on continental saline water-bodies.     

Characteristic seasonal variation in dissolved uranium concentration induced by the change of lake water pH in Lake Biwa,Japan

Epilimnion-dominated profiles of dissolved uranium (U) have been observed during summer in an oxygenated Japanese lake, Lake Biwa, contrary to the commonly accepted view that U shows conservative behavior in oxygenated seas and lakes. Monthly observations were conducted to reveal the mechanism for such characteristic distribution and geochemical behavior of dissolved U in the lake. In the surface water, dissolved U concentration started to increase in spring, peaked in summer, and decreased from autumn to winter. In contrast, the concentration remained almost constant in the middle layer (40 m depth) and decreased slightly in the bottom layer (70 m depth) throughout the stagnation period. Mass balance calculations of U suggest that the major mechanism for seasonal variations in the surface layer is the supply of U, not via water inflow from the watershed, but by internal chemical reactions within the lake. A laboratory experiment using the lake water and sediment demonstrated that U was desorbed from and adsorbed onto sediment in response to variations in lake water pH. From these results, it is inferred that the seasonal variation in the concentration of dissolved U in the epilimnion results mainly from the desorptive/adsorptive processes of U between sediment/water interface in response to variation in water pH, which is affected by biological activity in the lake.     

The importance of transport processes and spatial gradients on in situ estimates of lake metabolism

We measured spatial gradients of dissolved oxygen in a eutrophic reservoir from repeated transects over a 5-day period. The equation typically used to compute lake metabolism was extended to the full advection?Cdiffusion?Creaction equation, which includes transport terms. These transport terms were computed and found to be of similar magnitude to the rate of change of dissolved oxygen. We demonstrate that neglecting transport terms in this reservoir could lead to over-estimates in net ecosystem production calculations in the surface layer of up to 100%. We advocate the calculation of nondimensional Peclet and Damkohler numbers in future studies to assist in determining the importance of transport terms on lake metabolism estimates.     

Measurements of spectral optical properties and their relation to biogeochemical variables and processes in Crater Lake,Crater Lake National Park,OR

Spectral inherent optical properties (IOPs) have been measured at Crater Lake, OR, an extremely clear sub-alpine lake. Indeed Pure water IOPs are major contributors to the total IOPs, and thus to the color of the lake. Variations in the spatial distribution of IOPs were observed in June and September 2001, and reflect biogeochemical processes in the lake. Absorption by colored dissolved organic material increases with depth and between June and September in the upper 300 m. This pattern is consistent with a net release of dissolved organic materials from primary and secondary production through the summer and its photo-oxidation near the surface. Waters fed by a tributary near the lake’s rim exhibited low levels of absorption by dissolved organic materials. Scattering is mostly dominated by organic particulate material, though inorganic material is found to enter the lake from the rim following a rain storm. Several similarities to oceanic oligotrophic regions are observed: (a) The Beam attenuation correlates well with particulate organic material (POM) and the relationship is similar to that observed in the open ocean. (b) The specific absorption of colored dissolved organic material has a value similar to that of open ocean humic material. (c) The distribution of chlorophyll with depth does not follow the distribution of particulate organic material due to photo-acclimation resulting in a subsurface pigment maximum located about 50 m below the POM maximum.     

Responses of king penguin Aptenodytes patagonicus adults and chicks to two food‐related odours

Increasing evidence suggests that penguins are sensitive to dimethyl sulphide (DMS), a scented airborne compound that a variety of marine animals use to find productive areas of the ocean where prey is likely to be found. Here we present data showing that king penguins Aptenodytes patagonicus are also sensitive to DMS. We deployed DMS on a lake near a king penguin colony at Ratmanoff beach in the Kerguelen archipelago. We also presented DMS to ‘sleeping’ adults on the beach. On the lake, penguins responded to the DMS deployments by swimming more, while on the beach, penguins twitched their heads and woke up more for the DMS than for the control presentations. Interestingly, penguins did not respond to cod liver oil deployments on the lake; mirroring at‐sea studies of other penguins. Although at‐sea studies are needed to confirm that king penguins use DMS as a surface cue that informs them of productivity under the water, this study is an important first step in understanding how these birds locate prey over significant distances.     

The Influence of Hydrologic Residence Time on Lake Carbon Cycling Dynamics Following Extreme Precipitation Events

The frequency and magnitude of extreme events are expected to increase in the future, yet little is known about effects of such events on ecosystem structure and function. We examined how extreme precipitation events affect exports of terrestrial dissolved organic carbon (t-DOC) from watersheds to lakes as well as in-lake heterotrophy in three north-temperate lakes. Extreme precipitation events induced large influxes of t-DOC to our lakes, accounting for 45–58% of the seasonal t-DOC load. These large influxes of t-DOC influenced lake metabolism, resulting in lake net heterotrophy following 67% of the extreme precipitation events across all lakes. Hydrologic residence time (HRT) was negatively related to t-DOC load and heterotrophy; lakes with short HRT had higher t-DOC loads and greater net heterotrophy. The fraction of t-DOC mineralized within each lake following extreme precipitation events generally exhibited a positive relationship with lake HRT, similar to the previous studies of fractions mineralized at annual and supra-annual time scales. Event-associated turnover rate of t-DOC was higher than what is typically reported from laboratory studies and modeling exercises and was also negatively related to lake HRT. This study demonstrates that extreme precipitation events are ‘hot moments’ of carbon load, export, and turnover in lakes and that lake-specific characteristics (for example, HRT) interact with climatic patterns to set rates of important lake carbon fluxes.     

Regularities in Primary Production,Secchi Depth and Fish Yield and a New System to Define Trophic and Humic State Indices for Lake Ecosystems

General relationships between phytoplankton production, chlorophyll, total, dissolved and particulate phosphorus, Secchi depth, humic level, trophic level, fish production and latitude are described by regression equations using an extensive “Soviet” data base covering a wide domain of lake characteristics and a European data base. New systems for defining lake trophic and humic status are presented. The results may be used for more precise estimates of fundamental lake properties and for many practical issues of lake management, e.g., predictions of fish catch. We have used strict chlorophyll‐a concentrations for every trophic class and we have omitted Secchi depth from the trophic classes, since Secchi depth and other variables strongly related to water clarity (like suspended particulate matter and particulate organic carbon) depend on autochthonous production, allochthonous influences and resuspension. We have used the Secchi depth as a simple operational measure of the effective depth of the photic zone. It has also been shown that among these lakes there exist a very strong relationship between primary production and latitude. In fact, 74% of the variability among the lakes in mean summer primary production can be statistically related to variations in latitude. These data also show a strong relationship between primary production and fish yield, which can be used to address many fundamental issues in lake management, like “normal and abnormal fish production”.     

Influence of soil temperature and moisture on the dissolved carbon,nitrogen, and phosphorus in organic matter entering lake ecosystems

Concentrations of terrestrially derived dissolved organic matter (DOM) have been increasing in many north temperate and boreal lakes for over two decades. The concentration of DOM in lakes is influenced by a number of environmental factors, but there is still considerable debate about how the availability of terrestrial DOM, and associated dissolved nitrogen and phosphorus, may be affected by drivers of climatic change. Using experimental and observational methods, we considered how changes in soil temperature and moisture affected the composition of carbon, nitrogen, and phosphorus entering freshwater lakes. In our experiment, organic soil cores were collected from the wetland shoreline of a darkly-stained seepage lake in northern Wisconsin, USA and manipulated in laboratory with temperature and moisture treatments. During the 28-day study, soil leachate was sampled and analyzed for optical properties of DOM via UV/Vis absorbance, as well as concentrations of dissolved organic carbon (DOC), total dissolved nitrogen, and total dissolved phosphorus (TDP). DOM optical properties were particularly sensitive to moisture, with drier scenarios resulting in DOM of lower molecular weight and aromaticity. Warmer temperatures led to lower DOC and TDP concentrations. To consider long-term relationships between climate and lake chemical properties, we analyzed long-term water chemistry data from two additional Wisconsin lakes from the long term ecological research (LTER) project in a cross correlation analysis with Palmer drought severity index data. Analysis of the LTER data supported our experimental results that soil moisture has a significant effect on the quality of DOM entering lakes and that climate may significantly affect lake chemical properties. Although unexpected in terms of DOM loading for climate change scenarios, these results are consistent with patterns of decomposition in organic soils and may be attributed to an increase in soil DOM processing.