Can allelopathically active submerged macrophytes stabilise clear-water states in shallow lakes?

Inhibition of phytoplankton by allelochemicals released by submerged macrophytes is supposed to be one of the mechanisms that contribute to the stabilisation of clear-water states in shallow lakes. The relevance of this process at ecosystem level, however, is debated because in situ evidence is difficult to achieve. Our literature review indicates that allelopathically active species such as Myriophyllum, Ceratophyllum, Elodea and Najas or certain charophytes are among the most frequent submerged macrophytes in temperate shallow lakes. The most common experimental approach for allelopathic interference between macrophytes and phytoplankton has been the use of plant extracts or purified plant compounds. Final evidence, however, requires combination with more realistic in situ experiments. Such investigations have successfully been performed with selected species. In situ allelopathic activity is also influenced by the fact that phytoplankton species exhibit differential sensitivity against allelochemicals both between and within major taxonomic groups such as diatoms, cyanobacteria and chlorophytes. In general, epiphytic species apparently are less sensitive towards allelochemicals than phytoplankton despite living closely attached to the plants and being of key importance for macrophyte growth due to their shading. Light and nutrient availability potentially influence the sensitivity of target algae and cyanobacteria. Whether or not additional stressors such as nutrient limitation enhance or dampen allelopathic interactions still has to be clarified. We strongly propose allelopathy as an important mechanism in the interaction between submerged macrophytes and phytoplankton in shallow lakes based on the frequent occurrence of active species and the knowledge of potential target species. The role of allelopathy interfering with epiphyton development is less well understood. Including further levels of complexity, such as nutrient interference, grazing and climate, will extend this ecosystem-based view of in situ allelopathy.     

Phosphorus in acidified lakes: The example of Lake Gårdsjön,Sweden

Supply and turnover of phosphorus was studied in an acidified lake ecosystem, Lake Gårdsjön, located in southwestern Sweden. This study included transport and budget calculations combined with field and laboratory experimental work on abiotic phosphorus chemistry and biological utilization of phosphorus. The main conclusions presented in this paper are:

- The acidification process in inland waters resulting from acid atmospheric deposition is accompanied by ‘oligotrophication’ because of reduced input of phosphorus from the drainage area, possibly due to efficient fixation of phosphorus to aluminium complexes in the B-horizon of podzol soils

- Primary productivity in acidified lakes is limited mainly by low phosphorus supply

- Algal utilization of phosphorus in acidified lakes is impaired, yielding lower biomass than could be expected from ambient phosphorus concentrations. One possible reason for this could be that enzymatic recycling of organic phosphates is prevented by high levels of aluminium in lake water.

     

Can novel methods be useful for pain assessment of castrated piglets?

Given that surgical castration is a painful practice performed on millions of pigs every year, a need to identify novel reliable pain assessment tools exists in order to test anaesthetic and analgesic protocols that may reduce related pain. Two treatments were considered: handling (H) and surgical castration (C). Physiological (cortisol, lactate, glycaemia, rectal and eye temperature) and behavioural variables (latency to move after treatment and alterations in posture and walking) were analysed. Cortisol showed the greatest level in C piglets within 20 min after the surgical procedure and a positive correlation with glucose concentration. Eye temperature was higher in C piglets, and the same difference was detected for rectal temperature 3 h after castration. Behavioural parameters revealed that C piglets had longer latency to move and a higher percentage of them showed alterations in posture and walking. Results of this study showed that, in castrated piglets behavioural and physiological alterations occur mainly in the first 3 h from treatment. Latency to move, alterations in posture and walking, and eye temperature appear to give additional and useful information in piglet pain assessment. However, differently from the behavioural parameters considered, eye temperature involves several manipulations of the animals and a long process to acquire the data.     

Is reduction of the benthivorous fish an important cause of high transparency following biomanipulation in shallow lakes?

Experimental reduction of the fish stock in two shallow lakes in The Netherlands shows that such a biomanipulation can lead to a substantial increase in transparency, which is caused not only by a decrease in algal biomass, but also by a decrease in resuspended sediment and detritus. A model was developed to describe transparency in relation to chlorophyll-a and inorganic, suspended solids (resuspended sediment). With the use of this model it is shown that more than 50% of the turbidity in these shallow lakes before biomanipulation was determined by the sediment resuspension, mainly caused by benthivorous fish. Another analysis reveals that the concentration of inorganic suspended solids and the biomass of benthivorous fish are positively correlated, and that even in the absence of algae a benthivorous fish biomass of 600 kg ha⁻¹ can reduce the Secchi depth to 0.4 m in shallow lakes. In addition, it is argued that algal biomass is also indirectly reduced by removal of benthivorous fish. Reduction of benthivorous fish is necessary to get macrophytes and macrophytes seem to be necessary to keep the algal biomass low in nutrient-rich shallow lakes. It is concluded that the impact of benthivorous fish on the turbidity can be large, especially in shallow lakes.     

Can phaeopigments be used as markers for Daphnia grazing in Lake Constance?

The formation of chlorophyll a degradation products was measuredwith natural phytoplankton from Lake Constance and Daphnia magnaand native Daphnia as grazers in grazing experiments duringspring bloom conditions using high-pressure liquid chromatography(HPLC). Chlorophyll a start concentrations were between 1.2and 16.3 µg l^–1; phaeopigment weights constituted5% of chlorophyll a weight. Only phaeophorbide a was a markerfor Daphnia grazing; concentrations of other phaeopigments (phaeophytina, chlorophyllide a and two unidentified phaeopigments) didnot increase during Daphnia grazing. Conversion efficiencies(chlorophyll a to phaeophorbide a) were between 0 and 43% ona weight basis, and between 0 and 65% on a molar basis. Conversionefficiencies were highest at high grazer density (40 Daphnial^–1) and after a 24 h exposure time. Grazing by microzooplanktonprobably led to the formation of the two unidentified phaeopigments.In Lake Constance, Daphnia density was significantly positivelycorrelated with the phaeophorbide a/chlorophyll a ratio whenit was <5000 Daphnia m^–3. However, when higher Daphniadensities were included in calculations, then Daphnia densitywas positively, but insignificantly, correlated with the phaeophorbidea/chlorophyll a ratio. This suggests that when the level offood per Daphnia is low, then grazing is more efficient withless production of phaeophorbide a and a higher production ofcolourless products.     

Horizontal distribution of cladocerans in arctic Greenland lakes – impact of macrophytes and fish

Submerged macrophytes may play an important role as a refuge for zooplankton against predators. However, a recent study suggests that their importance depends on the trophic state of the lake. We studied the impact of fish and macrophytes on the horizontal distribution of pelagic cladocerans in 56 oligotrophic arctic Greenland lakes. In north-east and western Greenland, zooplankton was sampled in the near-shore (littoral) and central (pelagial) part of all lakes and fish were sampled with multiple mesh-sized gill nets. Macrophytes were visually estimated in the littoral. In north-east Greenland, 5 taxa of cladocerans were found, while 14 taxa were recorded in western Greenland. Daphnia pulex occurred only in fishless lakes in both northeast and western Greenland and avoided the near-shore areas in the shallow and deep lakes. Bosmina spp. and Holopedium gibberum were evenly distributed between the littoral and the pelagial in the deep and shallow fishless lakes. However, their near-shore density was lowest in the presence of fish. Macrophyte-related and benthic cladocerans concentrated either in the littoral or were evenly distributed between the littoral and the pelagial, irrespective of depth and fish presence or absence. Macrophytes had no impact on the horizontal distribution of pelagic cladocerans. Thus, it is concluded that horizontal heterogeneity of Bosmina spp. and Holopedium gibberum might be affected by the presence of fish.     

Can macroscopic identification of large ovarian follicles be useful in eliminating follicles with impaired steroid function?

In vitro studies, commonly using porcine ovarian follicles, may generate inconsistent results when atretic follicles are not eliminated from the pool of experimental follicles. The present experiment was conducted to test the practical value of the macroscopie identification of large porcine follicles, which were assumed to be atretic. Histological observations of hematoxylin-eosin stained follicular sections confirmed the results of the macroscopic classification. The follicles classified as presumably abnormal revealed signs of atresia at the light microscopic level. Such follicles (type 2) showed decreased levels of estradiol and androgens in comparison with the healthy-looking follicles (type 1).Steroid analysis also revaled that practically all estradiol from an ovarian follicle could be detected in the follicular fluid, whereas androgens extracted from follicular fluid represented approximately half of the total amount of follicular androgens.The experimental results indicate that the introduced macroscopic classification could be helpful in eliminating follicles with an impaired steroid function.     

How useful are environmental safety standards in economics? — The example of safe minimum standards for protection of species

The use of environmental safety standards is being increasingly advocated, and economists are being increasingly required to adapt their policy models to take account of such standards, e.g. by the use of transferable environmental damage quotas. The use of these standards may be a consequence of a greater desire to achieve more sustainable development and preserve the natural wealth available to future generations. An important means to this goal is to preserve biodiversity and genetic variability. Safe minimum standards for conservation of wildlife have been suggested as a way to achieve this. Sometimes safe minimum standards for conservation of species are defined in terms of their minimum viable populations and their minimum habitat requirements. However, as a review of recent scientific literature indicates, these safe minimum standards are very uncertain.Environmental safety standards have been integrated into economics in a variety of ways, e.g. via constraints to ensure sustainability at the macro-level, via minimum safety standards necessary to ensure survival of species. Despite the commendable support which safe minimum standards appear to give for nature conservation, they involve conceptual problems and uncertainties as outlined in this paper. In fact, safe minimum standards for the conservation of species do not exist — no standard ensures the continued existence of any species. This is not to deny that an improvement in standards can up to a point increase the probability of survival of a species for a specified period of time. It implies that minimum standards need to be cast in terms of those required to achieve a particular probability of survival of the targeted species for a specified period. It may, however, be impossible to achieve the goal specified, e.g. the probability of survival of a species aimed for, may be greater than can be achieved for any attainable standard. In general, the paper makes it clear that standards suggested by natural scientists and others need to be subjected to careful serutiny before they can be used as a reliable basis for economic policy.     

Can morphogenesis be understood in terms of physical rules?

Because the morphogenesis of biological systems is not fully understood, researches from various points of view are necessary. The present author has recently made computer simulations with his colleagues to construct branching systems of human organs, such as the lung airway and the liver blood vessels. In the simulations certain rules are assumed to govern bifurcating processes of the systems. These rules are expressed in terms of physical and geometrical concepts, such as minimum energy consumption and uniform filling of branches in the space of organs. Results of computer simulation are quite similar to real structures. However, actual mechanisms of morphogenesis, i.e. effects of genes or proteins, are not considered in these studies. In this article, the present work is discussed in relation to the concept of biological pattern formation by Meinhardt and a recent study by Miura and Shiota on lung growth.     

Can submerged macrophytes be effective for controlling waterborne phytopathogens in irrigation ponds? An experimental approach using microcosms

Irrigation ponds may act as a source of phytopathogenic species that might infest crops through the irrigation systems. Many studies have shown that submerged macrophytes can improve water clarity by out-competing phytoplankton by means of various mechanisms: favoured phytoplankton-grazing zooplankton, reduced nutrient and light availability, increased sinking losses and the release of allelopathically active substances. However, less information is available on the effects of submerged macrophytes on heterotrophic aquatic organisms such as pathogenic bacteria, fungi or oomycete species. This paper studies the effects of three submerged macrophytes—Chara fragilis, Potamogeton pectinatus and Najas marina—on the viability in water of propagules of two phytopathogenic isolates of the oomycetes Pythium aphanidermatum and Pythium ultimum. Moreover, we tested general antimicrobial properties (against bacteria and fungi in water) for these macrophytes. The results showed clear inhibitory effects of all three macrophytes on bacterial density in water and of C. fragilis on the viability of Pythium. Thus, preserving aquatic vegetation in irrigation ponds (i.e. charophytes), besides its purely environmental interest, may have important agronomic benefits owing to their role as biological control against some phytopathogenic agents.     

Lake Name or Name Lake? The etymology of lake nomenclature in the United States

1. The rationale for the naming of lakes has often puzzled limnologists. This problem is especially apparent in North America because the nomenclature of lakes across the continent appears to be variable, with ‘Name Lake’ occurring frequently, such as in Trout Lake, but also ‘Lake Name’, as in Lake Sunapee.
2. We examined the potential drivers of lake naming patterns using the U.S. EPA National Lakes Assessment database of c. 1000 lakes chosen in a randomised, stratified design. Potential drivers included major limnological characteristics and geographical position relative to European settlement patterns.
3. Of a list of 814 lakes with this binary nomenclature, almost 20% had a Lake Name, with the other 80% being a Name Lake. Across the U.S.A., lakes with larger surface areas were more likely to have a Lake Name, but there was no significant relationship between nomenclature and maximum depth.
4. Examining naming patterns by EPA ecoregion and by state revealed that Lake Names were more common in the southern states and along the eastern seaboard, regardless of their surface area.
5. Analysis of available databases of lake nomenclature in Europe and Canada suggests that these geographical shifts in lake names may be due to the main European colonist source countries that settled these regions, with Lake Name predominating in countries where Gaelic and Romance linguistic influences were strongest.

     

Can ephemeral proliferations of submerged macrophytes influence zoobenthos and water quality in coastal lagoons?

Hydrology is often the main determinant of water chemistry and structure of the aquatic communities in coastal lagoons, driven by the interaction of freshwater load from the catchment and marine intrusions. However, submerged aquatic vegetation (SAV) can have important local effects on both features, even during sporadically and short proliferations. A SAV summer proliferation was observed during 2003 in a coastal lagoon in Uruguay (Laguna de Rocha), increasing macrophyte cover and biomass in the less saline zones. SAV summer proliferations were first observed in summer 2001, with no records prior. The aim of this paper is to describe the ephemeral proliferation of SAV in this shallow brackish lagoon and to analyze its effects on the abiotic environment and on the zoobenthic community. Vegetated and unvegetated zones were sampled in the northern more limnic area (9.1 mS cm⁻¹ ± 4.8) and the southern brackish area (20.9 mS cm⁻¹ ± 5.2). Water and sediment chemistry were analyzed by standard methods and benthos and plants were collected with an Ekman grab. During SAV proliferation, suspended solids were five times lower inside macrophyte patches and water column total phosphorus and nitrogen were three and two times lower, respectively. Zoobenthos abundance and richness were higher in vegetated patches. However, no differences were found between sampling sites in the more brackish southern area and in the North after the SAV proliferation ended. This indicates that SAV can influence water chemistry and benthos structure above a biomass threshold of 100 g DW m⁻². Although hydrology is the driving force regulating communities and water chemistry in these coastal lagoons, our results showed that SAV can also be an important local factor above a certain biomass threshold.     

Can antioxidants be beneficial in the treatment of lead poisoning?

Recent studies have shown that lead causes oxidative stress by inducing the generation of reactive oxygen species, reducing the antioxidant defense system of cells via depleting glutathione, inhibiting sulfhydryl-dependent enzymes, interfering with some essential metals needed for antioxidant enzyme activities, and/or increasing susceptibility of cells to oxidative attack by altering the membrane integrity and fatty acid composition. Consequently, it is plausible that impaired oxidant/antioxidant balance can be partially responsible for the toxic effects of lead. Where enhanced oxidative stress contributes to lead-induced toxicity, restoration of a cell's antioxidant capacity appears to provide a partial remedy. Several studies are underway to determine the effect of antioxidant supplementation following lead exposure. Data suggest that antioxidants may play an important role in abating some hazards of lead. To explain the importance of using antioxidants in treating lead poisoning the following topics are addressed: (i) Oxidative damage caused by lead poisoning; (ii) conventional treatment of lead poisoning and its side effects; and (iii) possible protective effects of antioxidants in lead toxicity.