The chalk-stream environment

Abstract

Chalk is a very pure and porous form of limestone. Water percolates down through the rock to form aquifers which overflow as springs forming chalk streams which receive little surface runoff. Passage through the rock is relatively slow and smooths out irregularities in rainfall and stabilises the water temperature. As a result the streams tend to have a regular annual hydrograph with a relatively small difference between winter and summer flows and with no spate conditions; and the temperature range in the streams remains closer to the annual mean than in rivers receiving more surface runoff. The water is calcareous with a pH of 7.4-8.0 and an ample supply of plant nutrients. The streams support diverse and productive communities of plants and animals and the restricted temperature range is particularly suitable for the growth of brown trout.

The response of perennial and temporary headwater stream invertebrate communities to hydrological extremes

“…Most research studies considering other types of 609 temporary stream communities in temperate regions 610 have focussed on chalk streams (Ladle & Bass, 1981;611 Wright et al, 1984). In contrast to limestone streams, 612 temporary chalk streams are characterised by rela-613 tively diverse invertebrate communities, for example 614 75-89 taxa were recorded at intermittent sites on a 615 small 'winterbourne' chalk stream in southern Eng-616 land (Wright et al, 1984;Berrie, 1992). However, 617 despite the marked differences in chalk and karst 618 stream communities, an inverse relationship between 619 flow permanence and both invertebrate abundance 620 and species richness is common to both environments 621 (Berrie & Wright, 1984;Meyer et al, 2003).…”

The role of season and social grouping on habitat use by Mute Swans (Cygnus olor) in a lowland river catchment

“…Numerous shallow lakes are also found within the catchment. Due to the mild climate and influx of groundwater water temperatures never decline below 5°C and so ice formation does not occur (Berrie 1992, Wood et al 2012b. Complaints of grazing damage to aquatic plants by swans started around 1996 (Ilsington Angling Club and Moreton Estate, pers.…”

“…Mute Swans are among the most abundant water birds within the lowland river catchments of Britain (Mason & Macdonald 2000, Mason et al 2006. Such rivers, typically rich in vegetation, are highly productive ecosystems (Berrie 1992). In particular, the lowland rivers dominated by cretaceous chalk geology (hereafter 'chalk rivers'), support diverse and productive wildlife communities as well as socioeconomically valuable agriculture and game fishing (Environment Agency 2004).…”

The invertebrate community of the chalk stream hyporheic zone: spatio-temporal distribution patterns

“…The relationship between groundwater level and river flow in chalk streams follows a clear seasonal pattern (Berrie, 1992). Rising groundwater levels in winter produce an extension of river flow, with rivers responding rapidly to precipitation, whereas the summer is characterised by a constant low baseflow (Grapes et al, 2005).…”