Showing papers in "Aquatic Sciences in 2001"

Approaches for determining phytoplankton nutrient limitation

Abstract: Aquatic primary productivity is frequently limited by the availability of nutrients. The ability to identify factors limiting algal growth is of considerable importance to our understanding of the ecology of aquatic plants and to water management practices. Methods used to identify limiting resources in the past have included a) analysis of nutrient availability, b) elemental composition and cell quotas for various nutrients, c) bio-assays monitoring growth of test species or of natural populations following nutrient enrichment and d) measurements of various physiological parameters, such as enhancement of respiration and dark carbon fixation rates and perturbation of photosynthetic rate following re-supply of nutrients.¶In this paper we briefly review the merits and methodological limitations of these approaches for the assessment of the nutrient status of algal populations. We discuss how an understanding of biochemical and metabolic changes induced by nutrient limitation has led to the development of rapid and simple tools to monitor the nutrient status of aquatic plants and algae. In particular, we describe the use of transient changes in chlorophyll a fluorescence as a potential tool for rapid assessment of algal nutrient status and the development of molecular probes specific to nutrient limited cells, such as flavodoxin as a diagnostic tool for Fe-limitation.

Size- and depth-dependent variation in habitat and diet of the common carp (Cyprinus carpio)

Abstract: The habitat and diet variation of the common carp (Cyprinus carpio) were studied in Lake Banyoles (Catalonia, Spain). Carp was the second most abundant species offshore and used more the littoral in spring and deep bottoms in winter. The diet of carp was based on detritus, amphipods (Echinogammarus sp.), phantom midge larvae (Chaoborus flavicans), diatom mucilages, and plant debris. Amphipods and phantom midge larvae were much more important in diet than previous studies found, because of their greater availability in this lake. Among the carp inhabiting deep waters, there was size-dependent variation in diet, with smaller carp selecting more meiobenthos (cladocerans, ostracods, and small chironomids) and larger carp preying on profundal macrobenthos (phantom midge larvae and large chironomids). Roach (Rutilus rutilus) and carp dominated in abundance the non-littoral zone of the lake and showed resource partitioning, with roach being a more efficient zooplanktivore and carp being more able to prey on hard material (plant seeds, mollusks, and ostracods).

Uncoupling primary production from population growth in photosynthesizing organisms in aquatic ecosystems

Abstract: Whenever actively photosynthesizing cells are exposed to conditions where carbon fluxes exceed intakes of other essential-nutrients required for formation of new biomass, cell division is arrested, and the excess carbon is stored, excreted or directed to secondary functions. The extent of this uncoupling and its’ implications in aquatic systems are discussed. We focus on three examples: the cellular level of free living phytoplankton, the ecosystem level in the microbial food web, and the highly specialized level of species interactions in the symbiotic association between zooxanthellae and corals. These examples highlight the adaptive significance of uncoupling between photosynthesis and growth in aquatic systems. Moreover, we underscore the fact that in many real-world situations, net primary productivity cannot be equated to population growth. Roles of the “excess” carbon include photoprotective pigments and buoyancy regulating ballast. The excreted carbon compounds may protect cells or cell masses from desiccation, and fuel the microbial loop. The microbial loop increases overall nutrient extraction efficiency compared to that of which phytoplankton alone are capable. The zooxanthellae-coelenterate symbiosis drives the nutrient and energy fluxes supporting coral reef life in the nutrient-poor tropical seas. In those mutualistic associations, since photosynthesis is normally uncoupled from cell growth, the algae excrete most of their photosynthate and that supports the metabolic activities of the host.

A comparison of methods for detection of phosphate limitation in microalgae

Abstract: This paper presents the results of studies into the use of the emerging techniques of nutrient induced fluorescence transients (NIFTs) and Fourier Transform InfraRed (FTIR) spectroscopy to determine the nutrient status of microalgae. Four species of microalgae were grown under conditions where growth rate was P-limited or P-replete, and NIFT responses and FTIR spectra in response to the re-supply of P (as $ {\rm PO}^{3-}_4 $ ) measured. These responses were compared to more conventional measures of algal nutrient status such as P-uptake rates, P quotas and transient effects of $ {\rm PO}^{3-}_4 $ on oxygen exchange. The NIFT technique and FTIR spectroscopy gave results that were consistent with those obtained by the other techniques. Furthermore, we were able to demonstrate NIFT responses in phytoplankton samples taken from Lake Lucerne (total ambient P $ \le $ 0.13 μM) but not from Lake Zurich (total P 0.55 μM). The potential and limitations of the various techniques are discussed.

Microbial microstratification, inorganic carbon photoassimilation and dark carbon fixation at the chemocline of the meromictic Lake Cadagno (Switzerland) and its relevance to the food web

Abstract: The microstratification of the microbial community at the chemocline of Lake Cadagno and the associated inorganic carbon fixation activity was studied by fine layer sampling. A deep chlorophyll maximum caused by diatoms overlying Cryptomonas was found at the upper edge of the chemocline. A high population density of phototrophic sulphur bacteria, mainly Amoebobacter cf. purpureus, occurred closely below the oxic-anoxic boundary. Despite the small fraction of total lake volume represented by the chemocline, half of the total carbon photoassimilation of the lake occurred within the chemocline with approximately equal contributions by oxygenic and anoxygenic phototrophs. Rates of dark carbon fixation in the chemocline were even higher than rates of photoassimilation, especially at the depths where oxygen and sulphide coexisted during part of the day. These results indicate a substantial contribution by chemolithotrophic organisms to the carbon cycle in Lake Cadagno. Analysis of stable carbon isotopes suggests that zooplankton may obtain as much as half of its carbon at the chemocline, indicating a strong link between production in anoxic waters and the food web in the oxic part of the lake.

The nutrient cycle through snow and ice, a review

Abstract: This paper reviews the merging of the nutrient cycle with the water cycle in the seasonal alpine snow cover, emphasizing physical processes at the snowpack and snow grain scale. Nutrients are incorporated into snowflakes growing in the atmosphere, they are part of the dry deposition from the atmosphere to the snowpack and they reach the snow as plant litter. The physical processes of the accumulation of nutrients and their redistribution in and on the snow grains and in the pore space of the snow matrix are described.¶The first flush of meltwater that reaches the soil carries a solution of nutrients and acids in a concentration several times higher than bulk values, an effect that increases with the age of the snow and the number of melt/freeze cycles and is more pronounced for sulfate than for chloride. Species that are attached to insoluble particles will be concentrated near the snow surface and will display peak concentrations in the final fraction of meltwater.

The meromictic alpine Lake Cadagno: Orographical and biogeochemical description

Abstract: Lake Cadagno is a 21 m deep alpine meromictic lake situated at an altitude of 1921 m in the Piora valley in the southern part of central Switzerland. The bedrock of the valley containing dolomite and gypsum determines the chemistry of the water. The lake basin was created by glacial erosion and originally dammed by a glacial moraine. The water body is structured in 3 distinct layers, the oxic mixolimnion, the anoxic monimolimnion and a narrow chemocline in between. The water masses of the lake are stabilized by density differences of salt-rich water which is constantly supplied by subaquatic springs to the monimolimnion. In contrast the mixolimnion is fed by electrolyte-poor surface water. Sulfate, hydrogen carbonate, calcium and magnesium are the dominant ionic species. In the monimolimnion sulfide concentrations of more than 1 mM are found. The chemocline at a depth of 10 to 13 m is characterized by steep chemical and physical gradients. It contains dense populations of up to 105 cells/mL of phototrophic sulfur bacteria consisting of predominantly Chromatium okenii, C. minus and Amoebobacter purpureus. The lake has proven to be an excellent model system for studies of the role of planktonic bacteria which dominate the sulfur cycle.

The meromictic Lake La Cruz (Central Spain). Patterns of stratification

Abstract: The main limnological characteristics of the biogenic meromictic Lake La Cruz, a small karstic lake located on a dolomitic substrate, are outlined below. The lake owes its chemical stratification mainly to high concentrations of bicarbonate and calcium in the permanent monimolimnion, located below a depth of 19 m. A massive precipitation of CaCO3 crystals ("whiting"), occurring in the euphotic zone every summer, leads to further sedimentation and redissolution in deep waters with enhanced CO2 concentrations. Other ions, like magnesium, ammonium, reduced iron, silicate, etc. also contribute to the chemically-induced stability of the monimolimnion. The patterns of stratification during two consecutive thermal stagnation periods (1987-1988) were influenced by different climatological conditions. Depending of the year, the location of the pycnoclines varied; the rainier spring of 1988 favoured a much shallower location of the oxic-anoxic boundary and a much higher primary production reflected by larger oxygen peaks. This greater phytoplanktonic development in upper waters occasioned a shadowing effect on purple and green phototrophic bacterial populations growing in anoxic waters poor in sulphide.

Limnological description of the Lakes Zürich, Lucerne, and Cadagno

Abstract: This introductory article of the special GAP issue gives an overview on general limnological characteristics of the prealpine Lakes Zurich and Lucerne and the alpine Lake Cadagno and reports on the specific situation of primary production parameters during the international GAP Workshop in mid September 1999. Furthermore, it describes methods used for water analysis and fieldwork in these lakes.¶A comparison of data related to primary production in the three lakes in September 1999 during stratification shows that (i) phytoplankton community structure varied considerably between the lakes. The dominating algae were Planktothrix rubescens in Lake Zurich, various chrysophytes and diatoms in Lake Lucerne, and Echinocoleum elegans in Lake Cadagno, (ii) the euphotic zone in Lake Lucerne was considerably deeper (app. 15m) than in the other two lakes (app. 10 m), (iii) chlorophyll a standing crop was highest in mesotrophic Lake Zurich (August: 121 mg m-2), followed by oligotrophic Lake Lucerne (August: 75, September: 34 mg m-2) and mesotrophic Lake Cadagno (August: 33, September: 25 and 14 mg m-2), and (iv) areal primary production was highest in Lake Zurich (August: 105, September: 124 mg C m-2 h-1), followed by Lake Cadagno (August: 102, September: 52 mg C m-2 h-1) and Lake Lucerne (August: 90, September: 52 mg C m-2 h-1). Physiological parameters, determined in situ from P versus I relationships, showed a lower initial slope α in Lake Lucerne (August: 0.03, September: 0.02 mg C mg-1 chl a h-1μmol-1 m2 s) than in the other two lakes (Lake Zurich in August: 0.05, in September: 0.11; Lake Cadagno in August: 0.05, in September: 0.11 and 0.28 mg C mg-1 chl a h-1μmol-1 m2 s). Lake Zurich showed the lowest AN max (August: 2.6, September: 3.2 mg C mg-1 chl a h-1, as compared to 5.9 - 7.4 mg C mg-1 chl a h-1 in the Lakes Lucerne and Cadagno), while in Lake Cadagno the highest inhibitory effects of C-assimilation were found (highest slopes of inhibition β, 0.007-0.011, as compared to 0.0003-0.0026 in the other two lakes), due to a higher UV-exposure in this alpine lake.

The effects of diel changes in photosynthetic coefficients and depth of Planktothrix rubescens on the daily integral of photosynthesis in Lake Zurich

Abstract: In late summer and autumn, before the vertical circulation reaches the thermocline, the phytoplankton population of Lake Zurich is dominated by the red-coloured filamentous cyanobacterium Planktothrix rubescens, which stratifies in the metalimnion at depths close to the photosynthetic compensation point. The filament volume concentration reached a maximum of 12 cm3 m-3; the depth of the maximum varied from 10.5 to 12.5 m. Changes in the depth distribution were attributed to a combination of (1) seiche movements, which raised or lowered the thermocline by up to 2 m over 36 h, and (2) flotation by the buoyant filaments relative to the isotherms, by up 0.4 m d-1. These changes caused a 2-fold change in insolation at the Planktothrix peak. Estimates were made of the daily integral of photosynthetic O2-production, ΣΣ(NP), by the population of P. rubescens over a period of four cloudless days. The estimates were calculated from measurements of surface irradiance (at 5-min intervals), vertical light attenuation, temperature, filament volume concentration and the photosynthesis/irradiance (P/I) curves of filaments concentrated from the metalimnion. Despite the similar, high insolation on each of the four days, the calculated values of ΣΣ(NP) varied from 9 to 53 mmol m-2 d-1, owing to the changing depth distribution of the filaments. Measurements of P/I curves of lakewater samples incubated at a depth of 11 m showed changes in the photosynthetic coefficients during the day. These also generated large changes in calculated values of ΣΣ(NP). The computer spreadsheet used to calculate ΣΣ(NP) was modified to incorporate time-based changes in the photosynthetic coefficients and vertical distribution of the organism. These refinements provide a more accurate description of photosynthesis by the deep-living P. rubescens, which adjusts its position by buoyancy regulation to exploit the light field in the metalimnion, where it outcompetes other phytoplankton.

Effects of stream acidification and habitat on fish populations of a North American river

Abstract: Water quality, physical habitat, and fisheries at sixteen reaches in the Neversink River Basin were studied during 1991‐95 to identify the effects of acidic precipitation on stream-water chemistry and on selected fish-species populations, and to test the hypothesis that the degree of stream acidification affected the spatial distribution of each fish-species population. Most sites on the East Branch Neversink were strongly to severely acidified, whereas most sites on the West Branch were minimally to moderately acidified. Mean density of fish populations ranged from 0 to 2.15 fish/m 2 ; biomass ranged from 0 to 17.5 g/m2. Where brook trout were present, their population density ranged from 0.04 to 1.09 fish/m 2

Photosynthetic response of pico- and nanoplanktonic algae to UVB, UVA and PAR in a high mountain lake

Abstract: The objective of the present study was to evaluate the influence of UV radiation on photosynthesis rate, in situ and in laboratory incubations, on size fractionated natural algal assemblages (picoplankton: 0.2-2 μm, nanoplankton: >2 μm) and whole water (total organic carbon TOC). Near surface samples from a mesotrophic high mountain lake (LCD: L. Cadagno, Swiss Alps, Switzerland, 1923 m a.s.l.) and from the oligotrophic pre-alpine L. Lucerne (LLU: Swiss Alps, Switzerland, 434 m a.s.l.) were both incubated at a depth of 30 cm (50 % of surface UV at 323 nm ) in L. Cadagno. At the same time, biological weighting functions for UV inhibition of photosynthesis (BWFs) were determined for the autotrophic picoplankton and whole fraction in a spectral incubator. Photosynthetic assimilation of the pico- and nanoplanktonic algal communities as well as the assimilated total organic carbon (TOC) was estimated separately by 14C uptake under three irradiance conditions: PAR (photosynthetically active radiation), PAR + UVA and PAR + UVA + UVB. UV radiation reduced significantly photosynthesis rate in samples from both lakes (LLU: P = 0.0012; LCD: P = 0.0001). It appears that UVA plus UVB significantly affect the algal assemblage in both lakes; however most of the effect is due to UVA (Mann Whitney U test, two tailed: P = 0.0022). The natural assemblages from LLU transplanted to LCD were more inhibited by UV than the autochthonous assemblages of LCD. Photosynthetic rates of picoplankton from LLU and LCD under full UV exposure was reduced by 73 % and 55 % respectively relative to PAR only. A higher sensitivity of autotrophic picoplankton to the UV radiation, with respect to the nanoplankton, was observed in the biological weighting functions. However this difference was not statistically significant for the in situ incubations.

The influence of selenium on photosynthesis and "light-enhanced dark respiration" (LEDR) in the flagellate Euglena gracilis after exposure to ultraviolet radiation

Abstract: Photodamage of photosynthesis arises from oxidative damage. One of the protective mechanisms is to convert excessive absorbed energy into thermal radiation. Another mechanism could be to strengthen the antioxidative capacity of plants and algae. Selenium is important in antioxidation in humans and may play a role in antioxidative mechanisms in plants. The aim of this investigation was to study the role of selenium in "light-enhanced dark respiration" (LEDR) and photosynthesis in the flagellate Euglena gracilis, after exposure to ultraviolet radiation (UV-radiation). Selenium was added into the growth medium at different concentrations of selenite (10-7, 10-8, 10-9 and 10-10 M, Na2SeO3· 5H2O). E. gracilis were given six different light pulses with a photon fluence rate of 59, 163, 600, 1180, 2080 and 3340 μmol m-2 s-1 and periods of darkness between the light pulses. Photosynthetic saturation occurred at irradiances higher than 600 μmol m-2 s-1 and at the highest irradiance the photosynthetic rate decreased due to photoinhibition. Without any exposure to UV-radiation (UV-A, 320-400 nm, of 1.02 W m-2 plus UV-B, 280-320 nm, of 0.73 W m-2) LEDR increased with increasing photon fluence rate. After 40 min exposure to UV-radiation, photosynthetic rate and LEDR as functions of photon fluence rate were reduced. Neither in control (no UV-radiation) or when measured immediately after exposure to UV-radiation selenium had no stimulating effects on photosynthesis and LEDR. However, after UV-treatment and 24 h of recovery the presence of selenium led to an increase in photosynthesis and LEDR at higher irradiances. The results indicates that selenium might play a role in the repair mechanisms in E. gracilis after UV treatments.

Tracer experiment with sulfur hexafluoride to quantify the vertical transport in a meromictic pit lake

Abstract: This paper describes a tracer experiment with sulfurhexafluoride (SF6) in the monimolimnion of the meromictic mining lake Merseburg-Ost 1b. In October 1998, 1.1 mmol ( 160 mg) of the conservative gas SF6 was released at the site of greatest depth 3.5 m above the sediment to observe its vertical spreading. An easy-to-use system to collect ∼0.5 L water samples using evacuated flasks was developed. The headspace technique, gas chromatographic separation and ECD-detection were used to determine SF6. The main objective is the evaluation of mean vertical diffusion coefficients for SF6 and heat from periodically measured SF6 and CTD profiles. During the study period of 11/2 years, the heat transport was estimated to be molecular in the stratified portion. A thermal flux from the sediments of 0.23 W/m2 was found necessary to balance the heat. In the region of high stability (N2∼10-2 s-2) diffusivities for SF6 were ∼ 10-8 m2/s, whereas in the lower part of the monimolimnion both tracers resulted in K∼ 7 · 10-6 m2/s. We found K to be approximately proportional to N-2.4 ± 0.2.

Changes in photosynthetic properties measured by oxygen evolution and variable chlorophyll fluorescence in a simulated entrainment experiment with the cyanobacterium Planktothrix rubescens

Abstract: The metalimnion of lake Zurich is dominated by the red coloured cyanobacterium Planktotrix rubescens, where it lives in an extremely low light environment. Photosynthesis of the organism was studied using oxygen evolution and variable fluorescence. After transfer to 2m depth in the epilimnion, simulating an entrainment event that normally occurs in late summer, photoacclimation was followed.¶ The metalimnetic population had a very high photosynthetic efficiency, and the minimum quantum requirement varied between 7-12 photons (mol O2)-1. Upon transfer to high light the quantum requirement increased, which was interpreted as inactivation of a number of photosystem II (PSII) units. At the first entrainment we observed only inactivation of PSII, causing a decrease in the slope of the photosynthesis light curve (both for oxygen evolution and photosynthetic electron transport by PSII (ETR)), without affecting the maximal rate of oxygen evolution (PBmax), suggesting no effect on CO2-fixation. During the 2nd entrainment experiment we observed both an inactivation of the number of PSII as well as a decrease in PBmax. In both cases the ETR-based estimates of oxygen evolution (PB) overestimated the measured rate of PB, indicating the operation of alternative electron sinks. Especially at high light respiratory processes were seemingly stimulated.

Effects of UV on carbon assimilation of phytoplankton in a mixed water column

Abstract: Carbon assimilation is usually measured at fairly constant light intensities. Under natural conditions, however, planktonic algae are moved through the water column and experience light of fluctuating intensity and spectral composition. They may cope with strong UV for a short residence in the upper water layer. In order to estimate the effects of UV on primary production of phytoplankton under conditions of turbulent mixing, we compared carbon assimilation and exudation of algae incubated in UV-transparent quartz and in UV-absorbing glass bottles which were moved through different water layers. Computer-controlled elevators were used to simulate mixing depths between 2 and 14 meters. Compared to the glass bottles, particulate C assimilation in the quartz bottles was reduced by 20-30 % at mixing depths between 2 and 10 m. There was no significant difference between both types of incubation bottles at a mixing depth of 14 m. Exudation was enhanced by UV near the water surface (mixing depth up to 4 m) but not in the deep-mixed samples. Our results indicate serious damage of planktonic algae by UV even under conditions of vertical mixing if the euphotic zone exceeds the mixing depth. Depression was low for circulation through the whole euphotic zone and may disappear at even deeper mixing. Our results indicate lower photoinhibition per UV dosage at fluctuating than at constant light intensities. A model predicting inhibition as function of weighted irradiance spectra was adapted to describe wavelength dependent photoinhibition occurring at different mixing depths. The model results agreed very well with the inhibition rates measured under fluctuating light. These preliminary results are used to discuss the importance of UV on photosynthesis of planktonic algae in aquatic environments of different mixing depths and stabilities of stratification.

Determining the photosynthetic productivity of a stratified phytoplankton population

Abstract: During the summer, a stratified population of the red-coloured cyanobacterium Planktothrix rubescens dominates the phytoplankton of Lake Zurich. The organism hovers in the metalimnion by regulating its buoyancy, provided by gas vesicles. The daily integral of primary production by the organism has been calculated from its P/I curve and measurements of the vertical distributions of Planktothrix sp., irradiance and temperature in the lake, using numerical integration with Excel spreadsheets. The basic methods are described and the particular problems of analysing production by stratified populations are discussed. Daily integrals of primary production based on measured growth/irradiance (μ/I) curves of P. rubescens produce a closer correspondence to the changes in the natural population than do integrals based on P/I curves.

Will Astacus leptodactylus displace Astacus astacus and Austropotamobius torrentium in Lake Ägeri, Switzerland?

Abstract: Lake Ageri hosts three crayfish species: Austropotamobius torrentium, Astacus astacus and Astacus leptodactylus. To study the interspecific competition and a possible scenario of displacement, we monitored the distribution and relative densities of the different species during the years 1996-1999 by SCUBA diving. We examined the association of the species with different types of substrate and investigated the frequency of limb loss and the life history characteristics of the three species.¶A. leptodactylus was found at more sites than A. astacus and A. torrentium. It was also present in much higher densities than the other two species. A. torrentium preferred areas with hard substrate, whereas A. astacus was more often found at sites with soft substrate and reed vegetation. A. leptodactylus was observed on soft and hard substrate. The frequency of limb loss was highest in A. astacus and more frequent at sites with a high density of A. leptodactylus. Limb loss in A. leptodactylus and A. torrentium was more frequent at sites with high self-densities. Females of the two Astacus species carried more eggs than A. torrentium females. The eggs of A. astacus were larger than the eggs of the other two species. Juveniles of A. leptodactylus grew significantly faster in their first year than juveniles of A. astacus and A. torrentium. During the four years of the study A. leptodactylus expanded its range along the southeastern shore of Lake Ageri. At the northwestern border of its distribution the portion of A. leptodactylus had slightly increased by the end of the study period. In two areas of the lake the population of A. astacus and A. leptodactylus declined between 1997 and 1999.

Quantifying the response of phytoplankton photosynthesis to ultraviolet radiation: Biological weighting functions versus in situ measurements in two Swiss lakes

Abstract: The sensitivity of photosynthesis to ultraviolet radiation (UV) was assessed for phytoplankton assemblages in two Swiss lakes, pre-alpine Lake Lucerne (Vierwaldstattersee) and alpine Lake Cadagno, using both in situ and laboratory incubations. Biological weighting functions for UV inhibition of photosynthesis (BWFs) were determined in the laboratory using polychromatic exposures in a Xe-lamp based incubator. Samples were concurrently incubated in situ under UV exposed and protected bottles (profiles 0‐5 m), while additional spectral treatments were carried out at the 50% UV-B penetration depth: full spectrum, UV-A only (Mylar protected) and UV protected quartz tubes. Both particulate (> 0.2 mm) and total organic carbon incorporation were measured. Measured attenuation coefficients and incident UV spectral irradiance data was used to evaluate a BWF/photosynthesis-irradiance model (BWF/P-I) for in situ exposure conditions and compared with measurements. The BWFs showed sensitivity across the UV spectrum at similar, though somewhat lower, levels than an average BWF for marine assemblages. Relative photosynthesis in situ (UV exposed/UV excluded) was about 40% at the surface and about 60% at the 50% UV-B penetration depth. Similar inhibition was predicted by the BWF/P-I model. Generally, full spectrum (UV-B and UV-A) exposure had little additional effect compared to UV-A only exposure. Reciprocal transfer of samples between lakes showed enhancement of UV effects in L. Cadagno compared to incubation of the same sample in L. Lucerne, consistent with increased UV sensitivity due to the 5°C cooler water temperature in L. Cadagno. Similarly, BWF prediction of in situ response in L. Cadagno was improved by increasing UV sensitivity according to a Q10 of 2.

Incident and in situ irradiance in Lakes Cadagno and Lucerne: A comparison of methods and models

Abstract: Incident surface irradiance of photosynthetically available radiation (PAR), and ultraviolet radiation (UV-A and UV-B) was monitored during the GAP Workshop (8-15 September 1999) at the field stations Kastanienbaum at Lake Lucerne (434 m a.s.l.) and Piora at Lake Cadagno (1923 m a.s.l.), Switzerland, with broad band sensors (LiCOR and Macam) and multifilter spectral radiometers (Smithsonian UV-B radiometer SR18, Satlantic and Biospherical Profilers). Calculations of clear sky spectral irradiance were performed using computer implementations of atmospheric radiative transfer models STAR and FASTRT as well as a simple two-stream model. Clear sky conditions prevailed at Lucerne so that detailed comparisons could be made between measured irradiance and model predictions. Good correspondence was found for the measurements and predictions. The best agreement was with the STAR model. Spectral measurements were consistent with measurements of the broad band UV-A and UV-B sensors after accounting for the manufacturer specified spectral response. The effective center wavelength of the broad band UV-B sensor is 320 nm, despite the fact that the maximum sensitivity of the sensor is at 310 nm. A daily UV index was estimated from the midday SR18 data. An analysis of the UV-A and UV-B data at the two sites of different altitude indicates that the so called altitude effect (AE) is variable during the course of the day and usually higher for UV-B than for UV-A. Lakes Lucerne and Cadagno have moderate transparency to UV and PAR with 50 % of 320 nm irradiance penetrating to 1 m in Lake Lucerne and 0.3 m in Lake Cadagno.

Composition and transport of settling particles in Lake Zurich: relative importance of vertical and lateral pathways

Abstract: Time- and space-dependent variations in the composition of settling particles were investigated along a longitudinal transect in Lower Lake Zurich. The study was carried out during summer stratification using a two-dimensional array of sediment traps deployed in the hypolimnion. Samples of the sedimentary material were analysed for total C and total N, P, Ca, Si, Al, Fe, Mn, Mg, Na, K, and the trace elements Zr, Sr, Rb, Ti, Ba, S, Pb and Zn. The elements can be classified according to their preferences in associating with a specific carrier phase. The fluxes and composition of trapped particles were found to vary seasonally with fluctuations in the main components (organic matter, calcium carbonate, biogenic silica, manganese and iron oxides, silicates) and spatially due to the following in-lake processes: 1) increasing vertical particle transport of biomass and mineralic material in the shoreward direction, 2) lateral sediment transport, which caused sediment accumulation rates to increase with depth, leading to sediment focusing, 3) episodic and patchy events of CaCO3 precipitation in the epilimnion followed by sedimentation and lateral dispersion, and 4) formation of a patchy nepheloid layer in the slightly denser bottom waters containing more fine-grained particles in suspension. Sediment focusing by lateral pathways caused by particle transport between the southern and the northern basin of Lower Lake Zurich gave rise to post-depositional in-lake redistribution of particle-bound contaminants.

Lake Lucerne, Switzerland, a Long Term Study of 1961 - 1992

Abstract: Lake Lucerne, Switzerland, "Kreuztrichter"-basin, was investigated between 1961 and 1992. This time period offered a unique opportunity to study an eutrophication event lasting some ten years and the following recovery period as well as the limnological behavior of a deep pre-alpine lake. Results are presented as isopleths and long-term trends. Five year averages show clear patterns in the dynamics of ammonia or nitrite. Lake Lucerne (Kastanienbaum basin) is a monomictic lake, with only one complete overturn every six years. Other basins of Lake Lucerne such as the southernmost basin (Lake Uri), destratify each year, because of its wind-channel orientation.¶Kreuztrichter Basin was physically stabilized for years by trophic-induced processes. As the lake recovered, the density gradient in the bottom water layer decreased and turnover frequency increases. The oxygen peak in summer was usually overridden by temperature effects. Nitrogen concentration increased steadily during the 30 year period. Data for N, P, Si and O2 suggested the concept of compensation depth could be applied. The results were e.g. settling seston had no effect on nitrogen but caused a decrease in soluble phosphorus. In the most productive years silica use was more intense. The abyssal part of the wind-shielded Weggis-Vitznau basin is the most sensitive spot to the effects of nutrients in the lake. This paper is a summary of a more extensive report of the data (Buhrer and Ambuhl 1996).

14C photosynthesis and pigment pattern of phytoplankton as size related adaptation strategies in alpine lakes

Abstract: The hypothesis that both photosynthesis and pigment pattern are more reflective of size related strategies than taxonomic composition of the assemblages was tested under natural conditions in alpine lakes during fall 1999. The small size fraction ( 10 μm) were photosynthetically less efficient but high light adapted having low ratios of chlorophyll-a to \( \beta \)-carotene. In contrast to low light adapted small cells the high light adapted large-cells increased their relative proportion of photo-protective carotenoids above saturating light levels. At light limitation in deeper water layers lipophilic accessory photo-synthetic versus photo-protective pigments increased for all fractions.

Isolation of Sox11a, Sox11b and Sox19 genes from Rice field eel (Monopterus albus) using degenerate primers and nested PCR

Abstract: Sox proteins belong to the HMG box-containing family of DNA-binding proteins and are found in vertebrates. They have diverse functions in the regulation of development. We present here the two kinds of Sox genes, the Sox11, Sox11a and Sox11b, and the Sox19 genes from rice field eel (Monopterus albus) using highly degenerate and nested PCR. All the three Sox genes fall into group C of the Sox gene family.

Nonparametric evaluation of environmental parameters determining the occurrence of stonefly larvae (Plecoptera) in streams

Abstract: This study explored the relationship between the occurrence of stonefly species, stream type and basic environmental conditions Only 13 taxa, out of 115 species occurring in catchments investigated in the Czech Republic (Soldan, Zahradkova, Helessic, Dusek and Landa, 1998), were selected for this study The environmental parameters chosen were those that characterized the hydraulic and physical environments of almost all the streams: slope, current velocity, discharge regime, bottom roughness, current type (Reynolds number and Froude number) Organic water pollution, characterized as BOD5 and saprobity, was intentionally not embodied in the evaluation, because the chosen sampling sites were in streams which proved to have minimal or almost no organic pollution The relationships between the occurrence of stoneflies and the stream types (as set out by Illies and Botosaneanu, 1963) were evaluated on the basis of chi-square tests For two species (Nemurella pictetii - crenal and Perla burmeisteriana - epipotamal) there was strong evidence of affinity to the stream type The following parameters were shown to have a statistically significant influence on stonefly communities: slope, substrate roughness, current velocity and current type (Reynolds number and Froude number) For the most abundant individual species, Perla burmeisteriana, Isoperla grammatica, Leuctra albida, Leuctra nigra and Isoperla sudetica the influence of the investigated factors on occurrence and species abundance was assessed

Observations of near-bottom currents in the Gulf of Riga, Baltic Sea

Abstract: Near-bottom currents and temperature were measured at 2 and 4 m above bottom (m.a.b.) in the Gulf of Riga, a semi-enclosed sub basin of the Baltic Sea. Measurements were taken during three periods of different vertical stratification and weather conditions. Water depth was 54 meters. The studied area comprised the outer region of the bottom boundary layer, as judged by the observed Ekman veering of the current vector.¶Local wind was the primary driving force of near-bottom currents in the deepest area of the Gulf of Riga. Imposed wind stress induced surface-layer flow to the right, while compensating return flow developed in the bottom boundary layer. The response of current field was dominated by low-frequency variability with a clear indication of topographic steering and minor variability due to near-inertial frequency processes. The near-inertial frequency processes were generated also by interaction of low-frequency waves with the topography. The low-frequency and near-inertial frequency processes were of equal value in producing vertical shear of horizontal velocity in the near-bottom layer. The quasi-steady flow in autumn was forced by strong net inflow to the Gulf of Riga through the Irbe Strait. Lateral advection of water is important for the deep-water renewal that is due to dominating low-frequency currents.

Changes in the photosynthetic coefficients α and Pm of Planktothrix rubescens grown on light-dark cycles

Abstract: The relationship between photosynthesis and irradiance was investigated in a strain of the cyanobacterium Planktothrix rubescens isolated from Lake Zurich, using cultures grown on a 12:12-h light-dark cycle. From the photosynthesis-irradiance (P/I) curves, values of the light-affinity coefficient, α, and the maximum rate of photosynthesis, P m, were determined: in different cultures α ranged from 0.02-0.08 μmol mg-1 h-1 (μmol m-2 s-1)-1 and P m from 0.6-2.6 μmol mg-1 h-1 (rates of O2 production related to dry biomass). Comparisons made at different phases of the light-dark cycle in individual cultures showed that in the first hour of the light phase α rose by an average of 21 % and P m by 7 %. In cultures that had been grown in many light-dark cycles, however, the rise occurred only if light was given at the beginning of the notional light phase; cultures kept in darkness showed no rise. It is concluded that the observed increases in α and P m after dawn were in response to the exogenous irradiance rather than due to endogenous rhythms. These findings are discussed in relation to diel variations in the photosynthetic coefficients of natural populations of P. rubescens in Lake Zurich.

Inverse model method for estimating assimilation by aquatic invertebrates

Abstract: Physiological data indicate that a 3-compartment model appropriately represents ingestion, assimilation, and accumulation of somatic and reproductive tissue by an aquatic invertebrate predator. A secondary production model calibrated to growth and respiration data is used to constrain the model equations. Inverse solution methods are used to estimate rate constants for digestion and for net accrual of tissue by growing animals at different temperatures. Predicted time to 50% maximum digestion matches well with the empirical rate of digestion of prey enzymes in the predator gut. Model-derived digestion rates are consistent with the assimilation rate constant obtained by independent radiotracer methods, and with experimental detection time for prey enzymes. The model approach permits parameter estimation within a complex system of equations so that results can be compared with experimental data.

Egg to adult identification of 13 freshwater fishes from Italy: a biochemical-genetic key

Abstract: The family Cyprinidae comprises most of the freshwater fauna of the North Mediterranean region and it is often numerically dominant. Taxonomy based on morphology is problematic, owing to the high intraspecific variation in phenotypic traits, their overlap between species and environmental plasticity of morphometric and meristic characters. A difficult diagnosis, particularly for young developmental stages, can increase resource mismanagement. Here we report on the occurrence of species-specific allozymic patterns, consistent from eggs to adults. These allowed the construction of a biochemical-genetic key for the identification of all stages of 13 freshwater fishes, mainly cyprinids native to the North Mediterranean region (Alburnus alburnus alborella, Barbus plebejus, Chondrostoma genei, Gobio gobio, Leuciscus cephalus, L. lucumonis, L. souffia, Rutilus rubilio, R. erythrophthalmus, Scardinius erythrophthalmus, Tinca tinca, Pseudorasbora parva and Padogobius martensii).