Variations in marsh surface levels in the upper Tay Estuary

Abstract

SynopsisIn the upper Tay Estuary the marshes bordering the northern intertidal mud-flats are dominated by Phragmites communis in the west, with Juncus gerardi becoming more important eastwards, where Aster tripolium is also significant. Sedimentation on the surface of the marshes at Kingoodie and Invergowrie has been measured at monthly intervals over a twenty-three month period, using stake implants to provide local marker levels. The marsh surfaces were at their greatest heights in early summer and fell during autumn and winter. Maximum accretion rates were measured in spring on the outer marshes at both sites, where net accretion over the entire period was greatest. The net accretion in the Phragmites marsh was 2.5 mm, in the Aster belt 5 mm, in established Juncus 9 mm and in newly colonising Juncus 8.7 mm, whereas on the adjacent Kingoodie mud flats there was net stability over the twenty-three-month interval. Accretion was less at Invergowrie (3–5 mm) than at Kingoodie (2.5–9 mm). Monthly analysis of the upper 0.5 cm of the surface sediments showed the Invergowrie marsh sediments to be sandier than those of Kingoodie. Silts and clays deposited on the outer marsh surface in spring migrate landward during the summer and autumn. The apparent annual net accretion varied greatly with the specific month used for comparison, with 13 mm net losses based on November figures and 10 mm gains using January data.