THE LINKS BETWEEN LAND USE AND WATER QUALITY FOR FRESHWATER PEARL MUSSEL, MARGARITIFERA MARGARITIFERA, IN THE RIVER SOUTH ESK, SCOTLAND

Abstract

The freshwater pearl mussel, Margaritifera margaritifera, is an endangered species and its
population has decreased rapidly over the last century. Scotland is the home to half of the known populations
of M. margaritifera. Land use is a significant factor affecting water quality as well as the distribution of
freshwater pearl mussels. Thirty eight sites in River South Esk were selected to investigate the impacts of land
use on water conductivity, pH and the concentration of nitrate and phosphorus on the distribution of mussels.
M. margaritifera was more abundant in habitats in woodland with low and stable water nutrient level. Water
chemical analysis indicates that pollutant concentration is related to the vegetation of river catchments. River
water passing woodland has a relatively better quality and overhanging boughs of trees create shadows which
attract mussels. Livestock pasture catchments seem to have less significant chemical effects, but animal
activities may disturb the habitat of mussels and increase water turbidity. Water pollution in irrigated crop land
is relatively higher. Heather moorland is of less concern because of its inappropriate channel type for mussels.
Waters in the vicinity of housing, roads and bridges seem to be avoided by mussels. Margaritifera
margaritifera did not show any preference on the type of shadows. Living mussels have been discovered at the
sites which have shadows created by overhanging branches or high riverbanks.