Aquatic plant nutrients, moss phosphatase activities and tissue composition in four upland streams in northern England

SummaryA study was made of the water chemistry, tissue nutrients and surface phosphatase activities of the 2-cm apices of three mosses in four upland streams in northern England, UK. This was part of a project to optimize methods for assessing nutrient fractions in environments with highly variable water chemistry. Aqueous N and P fractions showed the greatest variability followed by moss phosphatase activities, with nutrient composition of the shoot apices the least variable. There was no consistent pattern as to which aqueous N or P fraction was the most variable. The ratio between total inorganic N and total filtrable P ranged over three orders of magnitude in some streams. The interrelations between tissue N and P concentrations, tissue N:P ratio, phosphatase activities and aqueous variables showed:(1)Significant +ve relationship between tissue N and aqueous NO3–N in some populations, but not between tissue P and aqueous P concentration;(2)Significant +ve relationships between phosphatase activities and aqueous organic N, but none with aqueous organic P;(3)Significant +ve relationships between phosphodiesterase:phosphomonoesterase activities and aqueous organic N;(4)Significant −ve relationships between phosphatase activities and tissue P concentration;(5)Significant +ve relationships between phosphatase activities and tissue N:P.Both types of biological measurement are valuable for monitoring ambient nutrients in upland streams. Neither is clearly better than the other, so both should be included in surveys.