Phosphatase activities of cyanobacteria as indicators of nutrient status in a Pyrenees river

Abstract

There is increasing evidence that fluvial systems are influenced by anthropogenic factors, and disturbance due to pollution and other human interference gives rise to specific problems. It is now imperative that we develop and apply novel and effective ways which allow us to monitor water quality. The present study was planned as part of a programme to develop biological monitoring methods to assess nutrient characteristics of upland calcareous streams and rivers. Phototrophs respond to environmental changes over a period of time, so organisms sampled at one time can potentially provide almost as much information about nutrients in the water as a number of individual chemical measurements. Phosphatase activity is often a good indicator of phosphorus limitation, and field materials could be used to study changes in nutrients dynamics. The calcareous River Muga, north-east Spain, at a site 10 km downstream from its source in the Pyrenees, was therefore chosen for the present study of surface phosphatase activities of the main cyanobacterial communities at different seasons to assess P limitation and establish the suitability of this method for use in monitoring catchment processes. Here we report seasonal changes of phosphatase activity in field populations of Schizothrix coriacea, Rivularia biasolettiana, Tolypothrix distorta var. penicillata and Nostoc verrucosum. All four cyanobacteria showed marked surface phosphomonoesterase and phosphodiesterase activity on each sampling period. Michaelis-Menten kinetic studies showed similar K m values for the four species suggesting similar affinity for organic P substrates. Light had no effect on phosphatase activities, indicating that there is no need to consider this factor in short-term field assays. However, there was an increase in phosphomonoesterase activity of Rivularia with rise in temperature over the range 10–35°C, which suggests adaptation to the frequent temperature changes in nature. Phosphorus limitation seems the main chemical factor influencing phototrophs in R. Muga. Combined observations on macroscopically visible phototrophs with assays of surface phosphatase activity provide a valuable means of assessing long-term changes in a catchment.