Seasonal and diurnal hydro-chemical variations in a recreated reed bed

Abstract. To help stem this decline, wetland areas are now being preserved and where possible created. This study investigated water quality in a recreated reed bed in south-west England designed specifically to provide habitat for birds. Since June 2000, continuous measurements of temperature, pH, electrical conductivity and dissolved oxygen have been logged. These data enable the partial pressure of CO₂ to be calculated. This paper looks at the data collected up to November 2001. Despite similar solar radiation and water temperature conditions in both 2000 and 2001, peak summertime values of dissolved oxygen dropped from >100% to <50% and pH values dropped from >7.7 to <7.2. Both also show a reduction in diurnal variation. Over the same period, the average partial pressure of CO₂ increased from 19.7 to 56.1. Analysis of the diurnal dissolved oxygen curves indicates a decrease in photosynthesis which, in the absence of a change in nutrient concentrations in the water, may result from surface plant growth or from a reduction in submerged plant cover. The implications of these changing hydro-chemical conditions are that the site will be less able to support such a wide diversity of aquatic fauna, which will reduce the effectiveness of the site as a habitat for some bird species.

Keywords: wetland, reed bed, hydrochemistry, dissolved oxygen, pH, continuous monitoring, Hamwall, Somerset Levels