The influence of stream size on the food quality of seston

Abstract

During 1979 and 1980, seston was investigated for food quality for aquatic consumers in 5 Quebec, Canada streams ranging in size from 1st-9th order. Course particulate organic matter (CPOM; > 1 mm), fine particulate organic matter (FPOM; 53 .mu.m - 1 mm) and very fine particulate organic matter (VPOM; 0.5-53 .mu.m) were examined for the percentage of ogranic matter, the C-N ratio, the amount of chlorophyll a, the respiration rate of associated microbes, and the nature of the particles. The percentage of organic matter ranged from 42-64% for CPOM, 21-35% for FPOM and 32-82% for VPOM. The majority of chlorophyll was associated with FPOM and CPOM, but chlorophyll-bearing particles constituted only 6-34% (.hivin.x = 15.1%) of the seston load. Highest respiration rates (.hivin.x = 15-35 mg O2 .cntdot. g ash-free dry mass-1 .cntdot. h-1) were associated with VPOM, nearly an order of magnitude greater than mean rates associated with FPOM or CPOM. C to N ratios decreased with particle size, and the lowest ratios and highest percentage of N were found in the large rivers. EM indicated a more diverse array of particles downstream. The results suggest that seston undergoes rapid and directed changes in food quality as particles move downstream.