The Aquatic Vegetation of the English Lakes

Abstract

The complete water analyses given were performed by Messrs A. W. Richardson and R. Jaffe, of Bradford, to whom my thanks are due. All of the data given here, are for the vegetative period, June to September, unless otherwise stated. Considerable care was taken to get data representing the normal summer conditions in these lakes. Thus the water samples were taken with the lakes at normal summer level and after a week's fine weather. PHYSICAL FEATURES. The English lakes lie in a small area of hilly country in Cumberland, Westmorland and Lancashire, about 30 miles (48 km.) in diameter, and including eight summits of over 900 m. and about fifty of over 600 m. The hills radiate like the spokes of a wheel from a common centre, and the lakes are situated in the long, narrow valleys between them.

Adaptations for an amphibious life: changes in leaf morphology, growth rate, carbon and nitrogen investment, and reproduction during adjustment to emersion by the freshwater macrophyte Littorella uniflora

“…However, it seems that even these low levels of sexual reproduction and recombination can be sufficient to maintain genetic variation and evolutionary potential (Silander, 1985). That this is the case for L. uniflora is suggested by the wide range of habitats occupied (see Pearsall, 1920 ;Spence, 1964 ;Robe, 1989).…”

“…In lake and tarn habitats, the majority of plants are submersed throughout the year in 0n3-2 m of water and reproduce vegetatively, often covering large areas (e.g. Pearsall, 1920 ;Misra, 1938 ;Spence, 1964 ;Farmer & Spence, 1986).…”

“…Low O # concentrations in anaerobic sediments may inhibit root metabolism, nutrient supply and uptake (SandJensen, Prahl & Stokholm, 1982 ;Christensen, Revsbech & Sand-Jensen, 1994), and nutrient concentrations are generally very low in oligotrophic habitats such as those in which L. uniflora is most common (see Robe & Griffiths, 1994). A wide range of light intensities is encountered (Spence, 1981 ;, while epiphytes and pleustophytes (Roelofs, 1983), wave action and silting (Pearsall, 1920 ;Spence, 1981) are additional hazards. In contrast, in the terrestrial environment, atmospheric CO # is readily available, and nitrate (the form of nitrogen mainly utilized by L. uniflora ; Schuurkes, Kok & Den Hartog, 1986) may increase in concentration as nitrification increases in aerobic sediments.…”

Assembly and response rules: two goals for predictive community ecology

“…To illustrate this, consider the functional group of small evergreen rosette plants in wetlands, termed isoetids (Hutchinson 1975) or stress tolerators (Boston & Adams 1986). These species are characteristic of infertile, wave-washed shorelines, and their presence can be predicted from knowledge of substrate (Pearsall 1920), wave and ice scour (Keddy 1983) or vegetation biomass (Wisheu & Keddy 1989a). However, in some habitats this functional group is represented by the common and widespread species Lobelia dortmanna or Eriocaulon septangulare.…”

Seasonal variation in the ecophysiology of Littorella uniflora (L.) Ascherson in acidic and eutrophic habitats

“…Oa exchange takes place via roots as well as shoots (Sand-Jensen, Prahl & Stokholm, 1982) and nutrient uptake is also thought to take place over both roots and shoots (Christiansen et al, 1985;Schuurkes, Kok & Den Hartog, 1986). L. unifiora is widespread in the UK, being found in a range of sediment t>-pes and water depths (Pearsall, 1920;Misra. 1938;.…”