Improvements in Quantifying the Phosphorus Concentration in Lake Water

Publisher Website
Google Scholar
Abstract
Vertical and horizontal patterns in limnetic P concentrations ([P]) were detected in an oligotrophic lake by dividing the total P pool into 2 fractions: dissolved and particulate matter smaller than 250 .mu.m (smaller fraction) and particulate matter larger than 250 .mu.m (larger fraction). The smaller fraction was estimated from samples collected with a water bottle, and the larger fraction was estimated with tow net samples taken at several stations and to various depths. Samples were digested with potassium persulfate which gave less variable results than other acid digestion techniques. The average variance associated with the mean [P] (n = 3) for samples collected and analyzed was < 0.05 mg P/m3. During summer stratification there was a consistent metalimnetic maximum in the smaller fraction, and there were small but significant differences in the concentrations found at 2 stations < 1 km apart. During the same period the larger fraction was a significant portion (14-28%) of the P pool in the epilimnion which varied from 3-5 m in depth. It was a relatively constant portion of the P in the trophogenic zone (0-10 m) and in the 0-20-m portion of the water column, i.e., 10-14% and 7.3-8.8%, respectively. In a separate experiment by removing from 1.0 to 2.4 .times. 10-2 mg/m3. This reduction occurred because the larger fraction contained zooplankters with relatively high but variable amounts of P and which occur in densities too low to be adequately sampled with the smaller fraction.