TEMPORAL VARIABILITY IN OXYGEN METABOLISM OF AN ESTUARINE SHOAL SEDIMENT

Abstract

Benthic microalgal production of a submerged sandy shoal in the York River, Virginia was measured from March to December 1983, with particular emphasis on the variability in metabolic estimates over different time scales. Variation in rates was examined over the photoperiod, between successive sampling days, between tidal condition (mid-day high vs. low tide), and among seasons. The coefficient of variation for 4 to 22 estimates of hourly net production (NP) and respiration (R) over the photoperiod averaged 231% to 75%, respectively. Morning NP was significantly greater than afternoon NP over the study. Mean hourly NP and R were significantly different on successive days in 4 of 6 tests, and 2 of 6 tests, respectively. The coefficients of variation for average NP, R and chlorophyll a over these two-day periods ranged from 4 to 43%, 1 to 34% and 0 to 80%. R was significantly higher on days with mid-day low tides (noon ± 2 hours). Mean hourly NP was 49% greater on days with mid-day low tides and R was 70% greater. Hourly NP and R were significantly different among seasons. R peaked in summer and NP in fall. Coefficients of variation for mean hourly NP and R over the seasons were 57% and 59%, respectively. Plots of mean hourly NP and R by month were made using all data for a given month and these were compared to plots made by randomly selecting a single measurement for each month. The latter plots are based on 12 data points, the former on 185 points. The two types of plots produced very similar annual rate estimates but differed radically in their depiction of seasonal changes.