Limnological data of an isolated Dutch broad

Summary Water quality research was started in the province of Friesland, The Netherlands, in order to set the ecological water quality standards. One of the waters under study is the broad of the Boornbergumer Petten. This water, as well as the supplying ditch, was investigated with regard to physico-chemical factors, macro-invertebrates and macrophyte vegetation. Supplementary the broad was sampled on phytoplankton. Preliminary results as well as older limnological data are presented. Macrophytes are the dominating primary producers. Worth mentioning is the extensive vegetation ofScirpus lacustris ssp.lacustris f.fluitans and of someChara species. The Boornbergumer Petten can be regarded as a usable and appropriate reference water for peatdiggings and broads. By means of limnological data of also other waters regional water quality standards will be postulated in the near future. Prepurification of the inflowing water by a marsh vegetation is considered necessary to prevent eutrophication of the broad and may act as a precursor of the appearance of theChara vegetation. Ceasing the inflow of polderwater would lead to drying up of the broad, because of deep draining the surrounding grassland areas.     

Virulence in malaria: an evolutionary viewpoint

Malaria parasites cause much morbidity and mortality to their human hosts. From our evolutionary perspective, this is because virulence is positively associated with parasite transmission rate. Natural selection therefore drives virulence upwards, but only to the point where the cost to transmission caused by host death begins to outweigh the transmission benefits. In this review, we summarize data from the laboratory rodent malaria model, Plasmodium chabaudi, and field data on the human malaria parasite, P. falciparum, in relation to this virulence trade-off hypothesis. The data from both species show strong positive correlations between asexual multiplication, transmission rate, infection length, morbidity and mortality, and therefore support the underlying assumptions of the hypothesis. Moreover, the P. falciparum data show that expected total lifetime transmission of the parasite is maximized in young children in whom the fitness cost of host mortality balances the fitness benefits of higher transmission rates and slower clearance rates, thus exhibiting the hypothesized virulence trade-off. This evolutionary explanation of virulence appears to accord well with the clinical and molecular explanations of pathogenesis that involve cytoadherence, red cell invasion and immune evasion, although direct evidence of the fitness advantages of these mechanisms is scarce. One implication of this evolutionary view of virulence is that parasite populations are expected to evolve new levels of virulence in response to medical interventions such as vaccines and drugs.     

Limnological observations of an intermittent tropical dry forest stream

This study examines aspects of the seasonal limnology of an intermittent stream in the dry forest region of northwest Costa Rica. It focuses on annual water level fluctuations and both seasonal and among pool variation in dissolved oxygen concentration and water temperature. Dry season pools differed in morphometry and the rate of decline in water levels subsequent to the seasonal floods. Rate of water level decline was related both to pool depth and to the exposure of the pool to the sun. Oxygen concentration was generally low in the dry season, but increased during the rainy season in association with rain events and seasonal flooding. A repeated-measures analysis of variance indicated that seasonal effects accounted for 40% of the variance in oxygen concentration for residual pools. Differences among pools were also significant. However, there was strong evidence for a significant interaction between seasonal and spatial influences on oxygen values in the system. Variation in water temperature was small, but differences among pools, sampling dates, and their interaction were all significant. Periphyton production increased significantly between the late wet season sample in November and the dry season sample in February. Incident light intensity explained 76% of the variation among pools in net periphyton production in the dry season.     

Reproductive strategies and disease susceptibility: an evolutionary viewpoint

Arguments about which constitutes the 'weaker sex' notwithstanding, sex differences in mortality and disease susceptibility have been noted in many species of animals, including humans. In this article, Marlene Zuk examines the possible reasons for these differences, relating them to reproductive strategies, and suggests how they may have resulted from selective pressures.     

Pathological hormone imbalances

Plant hormones play important roles in regulating developmental processes and signalling networks involved in plant responses to a wide range of biotic and abiotic stresses. Salicylic acid (SA), jasmonates (JA) and ethylene (ET) are well known to play crucial roles in plant disease and pest resistance. However, the roles of other hormones such as abscisic acid (ABA), auxin, gibberellin (GA), cytokinin (CK) and brassinosteroid (BL) in plant defence are less well known. Much progress has been made in understanding plant hormone signalling and plant disease resistance. However, these studies have mostly proceeded independently of each other, and there is limited knowledge regarding interactions between plant hormone-mediated signalling and responses to various pathogens. Here, we review the roles of hormones other than SA, JA and ET in plant defence and the interactions between hormone-mediated signalling, plant defence and pathogen virulence. We propose that these hormones may influence disease outcomes through their effect on SA or JA signalling.     

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.     

Limnological Features of a Tropical Meromictic Lake

Summary Studies of a man-made tropical lake bordering the Pacific Ocean revealed a case of thermal inversion caused by the superposition of brackish water upon more saline water. An interesting biological community was observed characterized by sparse plankton and abundant organisms attached to vertical basaltic walls. This unique environment supported a thriving population of mangrove oysters.

---

Zusammenfassung Die Untersuchungen eines menschengeschaffenen tropischen Sees, der an den Stillen Ozean grenzt, haben einen Zustand von thermalischer Umkehrung enthüllt; diese Umkehrungen werden durch die Überlagerung von Brackwasser auf salzbaltigerem Wasser bewirkt. Eine interessante biologische Gemeinschaft wurde beobachtet, die durch spärliche Plankton gekennzeichnet wurde, und reichliche Organismen wurden bereits an senkrechten basaltischen Zellwände befestigt. Diese einzigartige Umgebung hat eine blühende Einwohnerzahl von Mangrove Austern unterstützt.

---

Résumé Les études d'un lac tropical artificiel longeant l'Océan Pacifique ont révélées un cas d'inversion thermale causé par la superposition d'eau saumâtre sur de l'eau plus salée. Une communauté intéréssante biologique a été observée caractérisée par de rares planctons et d'abondant organismes attachés aux murs verticaux basaltiques. Cet unique environnement a soutenu une population florissante d'huîtres mangroves.

     

Limnological studies on freshwater ponds of hyderabad-India

Summary The paper is based on a two-year study of the distribution of phytoplankton in three freshwater, polluted and unpolluted ponds of Hyderabad, India. The distribution of several groups of algae likeVolvocales, Chlorococcales, Desmids, Diatoms, Dinoflagellates, blue-greens andEuglenineae exhibited interesting relationships to the physioo-chemical complexes of the ponds, and throws much light on the algal distribution in Indian waters. The discussion revolves around the yearly and overall averages of the ecological factors and the various groups of algae. Dissolved oxygen, oxidizable organic matter, free carbon dioxide, nitrates, phosphates, calcium and sulfides have been found to play a significant role. The fluctuations of certain ratios such as N : P : K, C/N, percent sodium, percent Cl + NO₃ and Pearsall's basic ratio suggest distinctly important clues in the distribution of various groups of algae.Part of the thesis approved by Osmania University, Hyderabad, India, for the award of the degree of Ph. D.     

A Limnological Survey of Lake Mainit,Philippines

Morphology, bathymetry and climate are described for Lake Mainit, one of the principal lakes of Southeast Asia. Thermal and water chemistry data show that the lake is not meromictic, despite its great depth, and that the water is dilute. Primary production is high but standing crop and diversity of phytoplankton and zooplankton range from moderate to low. The species composition of plankton and other biota is discussed.     

Pyrrolizidine alkaloids in the antipodean genus Brachyglottis (Asteraceae)

The phylogeny of the genus Brachyglottis suggests that its constituent species should contain pyrrolizidine alkaloids. Consistent with this hypothesis, and the established occurrence of such alkaloids in Brachyglottis repanda, Brachyglottis kirkii, and Brachyglottis hectori, an investigation of Brachyglottis adamsii revealed the presence of senecionine and retrorsine; Brachyglottis huntii was found to contain senkirkine and retrorsine; 7-O-angelylheliotridine was the predominant alkaloid in Brachyglottis perdicioides, and the same alkaloid together with senecionine, senkirkine and intergerrimine was present in the Brachyglottis hectori × B. perdicioides “Alfred Atkinson” horticultural hybrid; Brachyglottis sciadophila contained clivorine and neopetasitenine (acetylfukinotoxin); the latter alkaloid was also present in B. kirkii together with the previously reported senkirkine and senkirkine 12-acetate.     

An antipodean perception of the mode of action of glycoprotein hormones.

Continuance of vertebrate species and maintenance of metabolism have an absolute requirement for the glycoprotein hormones of the anterior pituitary gland. It is now firmly accepted that the N-glycans of these and the related placental hormone, chorionic gonadotropin, have essential if undefined roles in their mechanism of action. However, recent investigations by Weisshaar and his colleagues on the oligosaccharides of human luteinizing hormone and chorionic gonadotropin, do not support the generally accepted view of carbohydrates in hormone-receptor interactions and a further concept is proposed that invokes negative charges and changes in structured water.     

Umbilical metastases: current viewpoint

BACKGROUND: Umbilical metastases from a malignant neoplasm, also termed Sister Mary Joseph's nodule, are not commonly reported in the English literature, and they have usually been considered as a sign of a poor prognosis for the patient. The present article reports on the current view point on umbilical metastasis besides discussing the epidemiology, clinical presentation, pathophysiology and treatment. METHOD: A search of Pubmed was carried out using the term 'umblic*' and 'metastases' or metastasis' revealed no references. Another search was made using the term "Sister Joseph's nodule" or sister Joseph nodule" that revealed 99 references. Of these there were 14 review articles, however when the search was limited to English language it yielded only 20 articles. Articles selected from these form the basis of this report along with cross references. RESULTS: The primary lesions usually arise from gastrointestinal or genitourinary tract malignancies and may be the presenting symptom or sign of a primary tumour in an unknown site. CONCLUSION: A careful evaluation of all umbilical lesions, including an early biopsy if appropriate, is recommended. Recent studies suggest an aggressive surgical approach combined with chemotherapy for such patients may improve survival.     

Limnological studies on some lakes in the Netherlands

Most Dutch lakes are small and shallow, resulting from peat dredging since the late 18th century. However, deep lakes have appeared recently owing to sand digging. Limnological features of one such lake, Wijde Biik (N. Holland), were studied during 1968–70. The lake with an average depth of 11 4 m (maximum depth 31 m) and area of 2·65 × 10⁶m² is one of the deepest and biggest in the Loosdrecht-lakes area. The lake is 125 cm below sea level, and underground water-movements play an important part in the lake's hydrology. The lake exhibits thermal stratification on warm and calm days; since the lake surroundings are open and flat, wind and nocturnal cooling destroy such a stratification. There is continuous circulation from autumn through spring. The O2 saturation (%) in the upper water varies from 70 to 120%. Bottom waters were never anaerobic (lowest values 10% O₂ saturation). CI^? (2·8m-equiv.) and HCO^?₃ (1·9 m-equiv.) were the dominant anions just as Ca⁺⁺ (2·77 m-equiv.) and Na⁺ (2·5 m-equiv.) formed the main cations. Chlorides have increased 2·5-fold in the 40 years as a geochemical consequence of deepening. The surface drainage has minor influence on lake's water chemistry. Part-P (10–140 μg/I) and PO₄-P (2–40 μg/1) recorded maximum and minimum respectively, and NO₃-N (0·05–1·15 mg/1) its minimum, during Microcystis abundance in August 1968. The SiO₂-Si decreased from February 1969 (400 μg/l) to June 1969 as Diatotna elongatum increased. The Si-decrease to <30% of the 1932 values is due to removal of Si-rich clay and silt, due to sand digging. Chlorococcales were the important lake algae. Desmids were poor. Microcystis dominated as a rule from July-September, achieving from 15 to 31 colonies/ml. Poor light transmission rather than nutrients limits plankton growth as also the primary production in the lake. Copepoda were the dominant zooplankton. Bosmina coregoni recorded between 2 and 44 individuaIs/1 in summer 1968 and was the main cladoceran. The average primary production during summers of 1969 and 1970 was 380 and 497 mg C m^?2 day^?1 respectively. Light limited production below 1 m—1 % light in 1969 and 10% in 1970 penetrated down to 4 m. About 70% of the production took place in the upper 2 m. Calculation of production according to theoretical models under-estimated the observed values by 12% because Z_0·5Ik lay much above (0·8–2·8 m) the expected value of 3·5 m. It is suggested that in turbid lakes like Wijde Blik in situ incubations should be done at 0·5 m intervals in the upper 2 or 3 m.     

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.