On the ecology of Thelypteris limbosperma — a synecological investigation of T. limbosperma-dominated stands in W Norway

The investigation is based on phytosociological and ecological analyses of T. limbosperma-dominated stands from different parts of W Norway. The distribution and floristical composition of the stands are related to different environmental parameters, such as climate, soil and topography. The data are analysed by numerical methods, of which two-way indicator species analysis (TWINSPAN), canonical correspondence analysis (CCA), and simple discriminant functions (DISCRIM) are the most useful. The broad-scale distribution of T. limbosperma stands is determined by climatic factors. Within its distribution area soil factors and human influence govern the floristic composition and development of different types of such stands. Based on the TWINSPAN classification 9 different stand types are distinguished.
The first major division of the TWINSPAN classification is mainly correlated with soil factors. Most of the stands growing on the richest soils are interpreted as representing regeneration stages after intensive human influence. Divisions at lower levels are well correlated with altitude and temperature conditions.
The stands are all characterized by low pH and base saturation. Some types are concentrated to certain geographical regions, indicating that both altitudinal and west-east-gradients are important in influencing the floristic composition of the different types. The investigations indicate that T. limbosperma has a rather narrow realised phytosociological niche. It is mainly concentrated to stands that are floristically most related to the poorest part of Vaccinio-Piceion communities. Occasionally it is also dominant in Alno-Padion and Lactucion alpinae communities.     

Pre– and subalpine tall herb and fern vegetation in Røldal, W Norway

Six tall herb and fern vegetation types in Røldal have been investigated. They are referred to the alliances Lactucion alpinae and Alno–Ulmion. Lactucion alpinae is divided into two suballiances, one oligotrophic to mesotrophic (Dryoptero–Calamagrostenion purpureae) to which are referred Athyrium distentifolium– Salix scrub, and Athyrium distentifolium meadow, and one eutrophic (Lactucenion alpinae) to which belongs Geranium sylvatkum meadow and Lactuca alpina meadow. Alnus incana forest, herb/fern and Matteuccia struthiopteris types belong to Alno–Ulmion. Lactucion alpinae is considered subalpine, whilst Alno Uimion is prealpine.
The pre– and subalpine zones are considered oceanic sections of middle– and upper oroboreal vegetation zones.     

A limnological reconnaissance of Lake Tebenquiche,Salar de Atacama,Chile

A number of expeditions to the area of Salar de Atacama, Chile, 68° 15'W, 20° 30'S, have involved studies of the biological and chemical features of Lake Tebenquiche, situated in the interior of the salar. Chemically, Tebenquiche is hypersaline, with practically anoxic waters dominated by sodium and chloride ions but with high concentrations of sulphate also. The lake is surrounded and invaded by macrophytes, dominated by Scirpus olmeyi and Juncus, which provide organic material for the formation of bacterial mats. The fauna of limnetic crustaceans is almost exclusively of Artemia salina. The most important genera of bacteria are: Marinomonas, Halobacterium, Acinetobacter and the sulphur reductors Vibrio and Bacillus. The Cyanobacteria are represented exclusively by Oscillatoria.     

A synecological investigation of Athyrium distentifolium-dominated stands in Western Norway

This paper presents results of a study on the synecology of Athyrium distentifolium. The investigation is based on phytosociological and ecological analyses of stands dominated by A. distentifolium within its whole distributional area in Western Norway. The distribution and floristic composition of the stands are related to different environmental parameters such as climate, soil and topography. The data are analysed by numerical methods, of which two-way indicator species analysis (TWINSPAN), canonical correspondence analysis (CCA), and simple discriminant functions (DISCRIM) are the most useful. Based on a TWINSPAN classification of the 211 investigated stands, 9 different groups (types) are distinguished. These belong mainly to three phytosociological alliances: Cryptogrammo-Athyrion alpestris (1 group), Lactucion alpinae (5 groups) and Vaccinio-Piceion (3 groups). The quadrats are in most cases very poor in species, even in edaphically rich areas. Soil richness in the stands is very variable. A. distentifolium may be dominant in edaphically rich areas and it is not a calciphobe species in W. Norway. Most stands show no signs of human influence. Length of snow-lie is assumed to be of major importance for the development and distribution of A. distentifolium stands.     

A limnological study of the Afram arm of volta lake

A two year's limnological study of the Afram arm of the Volta Lake is reported. This arm of the lake is shallow; it receives frequent winds, which together with the floods of June-September create near isothermal conditions. The upper io m is well oxygenated with some oxygen, about 2 mg/l, reaching the bottom for most part of the year. It is poor in nutrients, values of total dissolved solids lying between 40–60 mg/l. But frequent algal blooms of Oscillatoria curviceps, O. princeps and Mycrocystis aeruginosa occur and the net primary production rate in some areas range between 8.4 and 142.5 mg C/m³/hr. It is suggested that the high tropical temperatures encourage quick recycling leading to relatively high organic production, thus making this arm non-oligotrophic.     

Some limnological characteristics of the Nozha hydrodrome,near Alexandria,Egypt

Some physical and chemical investigations of Nozha Hydrodrome, an Egyptian artificial lake, were studied and discussed. Variations of water level, Secchi disc readings, pH, chlorosity, and total residue are correlated with the introduction of a large amount of fresh Nile water into the lake, to replace that lost mainly by evaporation. Comparison with previous data, obtained from the Hydrodrome prior to the construction of the high dam, gave considerable changes.     

A limnological comparison of two small Idaho reservoirs

Summary Some limnological aspects of two small, widely fluctuating reservoirs were studied for one year. A well defined thermocline did not form in either reservoir. Annual heat budgets were about 15,000 cal/cm² for both waters. Dissolved oxygen concentrations were low on the bottom during the summer months. Both reservoirs were alkaline with the pH ranging from 7.5 to 8.9.The mean primary production summer rates of nannoplankton were 9.9 mg C/m³/hr for Crowthers Reservoir and 6.7 mg C/m³/hr for Deep Creek Reservoir. Standing crop of zooplankton was highest in Deep Creek Reservoir. Biomass of detrital heterotrophs was highest in Crowthers.

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Resumen Algunos aspectos limnológicos de dos reservorios pequeños con extensa fluctuación se estudiaron por un año. Termocline (thermocline)bien definido no se formó en uno u otro reservorio. Las acumulaciones anuales de calor fueron más o menos 15,000 cal/cm² (calorías por centímetros cuadrados) por ambas aguas. La concentración de oxígeno disuelto fué bajo en el fondo durante los meses del verano. Ambos reservorios fueron alcalinos con el pH fluctuando desde 7.5 hasta 8.9.Les clasificaciones del pequeño plankton (nannoplankton) durante la producción en el verano fueron 9.9 mg (miligramos) C/m³/hr (carbóno por metro cúbico por hora) para el Reservorio Crowthers y 6.7 mg C/m³/hr para el Reservorio Deep Creek. La cosecha fija de zooplancton fué más fuerte en el Reservorior Deep Creek. La biomasa de heterótrofo detríticos fué más fuerte en Crowthers.

     

An ecological approach to the investigation of a beech forest in Vestfold, SE Norway

The vegetation in a beech forest, Fritzøehusparken, is analysed using one hundred sample plots, each 25 m², distributed by a restricted random procedure. Percentage cover and frequency in subplots are used for quantification of species amounts, and their relative performance are evaluated. Advantages of choosing frequency in subplots are discussed. Thirteen environmental variables are measured from each of the sample plots. The vegetation is divided into four topographical/ecological types. This classification served as a reference in the further treatment. Ecological gradients corresponding to the most important vegetational gradients in the beech forest are identified by means of DCA ordination followed by statistical interpretation. Two main complex gradients were recognized; (1) the gradient in nutrient conditions, and (2), the gradient inlitter-wind conditions. The advantages of using DCA and statistical interpretation with integration of ecological measurements are emphasized.     

A review: limnological management and biomanipulation in the London reservoirs

Low algal biomasses and high water transparencies are a feature of the storage reservoirs that supply most of London's treated water. This is a result of knowledgeable limnological management and biomanipulation and despite the eutrophic nature of the River Thames with its high nutrients (7 gN m⁻³; 1 gP m⁻³) and particulate organic carbon (2 gC m⁻³). Built-in possibilities of jetting input water are managed to prevent stratification, to ensure isothermy, to mix chemicals and plankton vertically and horizontally and to manipulate the mixed-depth of the algal populations such that their potential for biomass growth is reduced by light-energy limitation. Spring algal growth is delayed and the spring peak is reduced and curtailed by the grazing impact of considerable biomasses of large-bodied daphnid populations (Daphnia magna, pulicaria & hyalina) whose development is also supported by the continuous input of high riverine algal crops. The existence of a large-bodied daphnid zooplankton in the reservoirs is associated with low levels of fish predation since the late 1960s. Variations in the intensity and nature of this vertebrate predation during the subsequent twenty years (1968–88) are illustrated by the changes that have occurred in the relationship between the phytoplankton and zooplankton biomasses of the April-May-June quarter of the year. This example of the London reservoirs serves to illustrate biomanipulation in deep water bodies by bottom-up as well as top-down effects.     

Environmental factors influencing the vertical migration of planktonic rotifers in a hypereutrophic tarn

The diel vertical migration of planktonic rotifers in a small, hypereutrophic tarn was investigated on four occasions in 1983. When the tarn was isothermal the rotifers were distributed throughout the water column. After stratification, the rotifers were confined to the top 1–2 m of oxygenated water. On all four dates the rotifers were aggregated at specific depths in the water column. On some occasions, the pattern of aggregation changed as the animals performed distinct diurnal migrations. Keratella cochlearis, K. quadrata and Polyarthra vulgaris usually followed the reverse migrations of the phytoplankton. In contrast, the movements of Anuraeopsis fissa were less pronounced and were associated with variations in the depth of the oxycline.     

Periglacial tarn on the Rock and Pillar Range crest,south‐central South Island,New Zealand,and its surrounding snowbank community

A small 18 × 1–5 m, distinctive, teardrop‐shaped alpine tarn about 55‐cm deep with a variable schist plate rock‐silty bed, a wetland rim and surrounding snowbank community is described from a shallow depression in the headwaters of a small primary stream at 1400 m on the crest of the Rock and Pillar Range (1450 m), south‐central South Island, New Zealand. Its initiation some 2500–3000 years ago (based on radiocarbon dating of peaty material near the base of the dam front) may have been serendipitous, but the prevailing periglacial environment of the area, involving seasonal freezing of the pond surface, has probably been conducive to its maintenance and slow extension. Despite some floristic similarities, it differs from any known alpine tarns, and a request via a YouTube video has not revealed any similar features.     

A limnological study of some man-made lakes in the province of South Holland

Summary In 1974 an introductory comparative limnological study was made in three deep man-made lakes in the province of South Holland.In all the lakes thermal stratification was followed by chemical stratification. This stratification was not permanent. A difference in location of the metalimnion in the lakes could be demonstrated due to differences in the fetch of the wind.There was little similarity in the composition of the phytoplankton biocoenosis in the three pits. The zooplankton, species in the Ommedijkse and Kinkerberger pits were in some accordance.     

The life history of rock gurnard (Trigloporus lastoviza, Brünn. 1768) in the Saronikos Gulf

Age, growth and reproduction of rock gurnard in the Saronikos Gulf (Greece) were studied. Otoliths from 638 specimens (sex combined) were read for age determination. The body length-otolith radius relationship was found linear (L = -18.0 + 4.99 _xR; where L = fish length in mm, R = otolith radius 20 X). The life span of females seemed to be longer than that of males, indicating a differential mortality with sex. The growth was lower than that in the Catalane Sea. The maximum age of fish collected was VIII and the maximum fork length estimated by von Bertalanffy equation was 356 mm. Weight increased as the 3.054252 power or the length. Reproduction was observed to take place between winter and early spring and occasionally in early winter. Males began to mature after completion of the second year and the females after the third. The exploitation rate was rather high, which suggests that the rock gurnard stock was overfished in Saronikos Gulf. The male to female ratio was usually 1:1.     

Herb-rich spruce forests in W Nordland, N Norway: an ecological and methodological study

The vegetation of herb-rich spruce forests in three localities in Brønnøy municipality, W Nordland, N Norway, has been analysed using 120 sample plots, each 25 m², distributed by a restricted random method. In connection with every sample plot a set of ecological variables have been measured. The most important gradients for the differentiation of the vegetation were identified by DCA ordination and statistical analysis of the vegetational and the ecological data sets. The gradients were: (1) the nutrient gradient, (2) the soil moisture gradient and (3) the microclimate gradient. The importance of choice of ordination technique (DCA or LNMDS) relative to the importance of the choice of some parameters in DCA and LNMDS has been evaluated. Indicating from this evaluation were (1) the choice of weighting function prior to DCA ordination can be as important as the choice of ordination technique when the data set is small; (2) choice of dimensionality in LNMDS is normally not as decisive for the ordination result as the choice of ordination technique and (3) when the data set is larger, the choice of scale range is less decisive for the ordination result than the choice of dimensionality in LNMDS.