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A general outline is given of the development and successive phases of the science of inland waters, variously encompassing ‘limnology’, ‘hydrobiology’ and ‘freshwater biology’. Three periods — pre-1930, 1930–1970 and 1970–present — are arbitrarily but conveniently distinguished. In the first, emphasis is given to the original contributions of pioneers; in the second, to the fuller development of fields of enquiry; and in the third to wider environmental-ecological linkages and outlooks. Example-situations and biographical involvements are illustrated by excerpts from the original literature.
Although phosphorus is an abundant element on Earth, its low availability often constrains the growth and/or biomass of aquatic biota. Introducing large quantities of available P into the biosphere, humans have opened up the relatively closed biogeochemical cycle of P, resulting in the eutrophication of many types of aquatic ecosystems worldwide. A thorough understanding of the P cycle is needed, therefore, to both understand the structure and functioning of aquatic ecosystems and to preserve the quality of our aquatic resources.
In this review, we deal first with the often misused concept of ‘nutrient limitation’. The rather general use of P uptake kinetics as an indicator of nutrient deficiency requires a discussion on methodology. Since metabolic rates and nutrient demands scale with the size of organisms, coexistence of aquatic osmotrophs relies on unique adaptations and is controlled by the whole network of ecological interactions. Some of these adaptations and interactions are reviewed, with a focus on P cycling. Finally, a case study demonstrates that the complicated P cycle must be simplified to extremes to predict eutrophication-related changes in a shallow lake.
Freshwater habitats are beset by a combination of anthropogenic stresses, resulting from a wide array of human activities that occur either within the habitat itself or within the catchment of the habitat. This paper describes the difficulties of making management decisions in fresh waters in the face of this complexity, and outlines the approach adopted by Natural England to counter the problem in a way that allows timely management decisions to protect and restore freshwater sites with special designations for wildlife. The management model outlined has relevance to all those engaged in the management of specially protected freshwater sites, or indeed any type of site suffering from multiple stresses. The approach is also relevant to management models under consideration in England and elsewhere in Europe to fulfil obligations under the EC Water Framework Directive.
Riffle beetles in the family Elmidae are frequent members of the invertebrate community of running water. Over 80 species have been recorded in North America and 46 in Europe; this number decreases in the western and northern fringes of Europe with only 12 species in Britain, many rare, four in Ireland and three in Norway. The present review describes their habitat, food and predators, their life cycles, their dispersal, and human threats to their survival. All elmid species have aquatic larvae with five to eight instars, depending on the genus. Adults of a few species are terrestrial, but most are aquatic with plastron respiration. Most elmid species occur in well-aerated streams and rivers, but some also occur on wave-washed lake shores. A few species live in more unusual habitats, such as thermal pools and hot springs, subterranean habitats, and decaying wood. Little is known about the food of adults or larvae, but they appear to be collector-gatherers and scrapers that feed chiefly on algae and detritus. Adults and larvae are rarely taken by invertebrate predators, but are eaten by fish, especially salmonids. However, their proportion in the diet is always lower than that in the benthos, indicating low availability to the fish. To obtain a quantitative description of the life cycle, information is required on the number of larvae in each instar, the timing of oviposition, the number of eggs laid, the timing of pupation, and the number of adults. Few studies meet these criteria. However, three excellent studies from North America and a detailed study of the four commonest British species illustrate the variation in the life cycles of different species. Life tables, identifying critical periods for survival, are provided for the British species, these being the only such tables currently available for riffle beetles. The ability to disperse by flight varies among species and among individuals of the same species. Adults and larvae disperse downstream in the invertebrate drift, especially at night. In one study, drift densities of different life stages were related positively to their monthly losses in the benthos, but not to their benthic densities. Less information is available on their upstream-downstream movements on the substratum. There are ontogenetic shifts in diel drift periodicity and dispersal, and both relate to seasonal changes in drift density and critical periods for survival in the life cycle. Human threats to the survival of elmids include reduced oxygen concentrations, elevation of water temperature, extremes of flow, especially spates, and pollution, especially by soaps and detergents. Therefore, riffle beetles provide excellent indicators of water quality and perhaps also climate change.
The value of a checklist when recording the species composition of freshwater macrophyte communities has been recognised for over 30 years, yet studies are still published that fail to refer to a specific checklist. This review demonstrates how the recording of British freshwater vascular plants has been enabled and enhanced through the application of checklists. Consideration is given to studies of plants in the context of trophy, pollution, classification, conservation, and spatial and temporal change in freshwater habitats. Twenty-four lists, with diverse origins, were compared using Jaccard similarity coefficients. Similarities tended to be low (mean Sj = 0.37) hence there are difficulties in comparing studies that have used different checklists, and a change of checklist should be avoided during long-term studies. It is suggested that long checklists yield comprehensive data but that shorter lists developed for a particular task will produce useful information, perhaps more quickly and with less need for advanced botanical knowledge. It is emphasised that the checklist used should be cited in all new published studies.