Variability patterns differ between standing stock and process rates

TL;DR: The overall variability of primary production is dominated by fluctuations at low frequencies, such as the annual, whereas in stocks and chlorophyll in particular, higher frequencies contribute substantially to the overall variance, suggesting that using standing stocks instead of rate measures leads to an under- or overestimation of food shortage for consumers during distinct periods of the year.

Abstract: Standing stocks are typically easier to measure than process rates such as production Hence, stocks are often used as indicators of ecosystem functions although the latter are generally more strongly related to rates than to stocks The regulation of stocks and rates and thus their variability over time may differ, as stocks constitute the net result of production and losses Based on long-term high frequency measurements in a large, deep lake we explore the variability patterns in primary and bacterial production and relate them to those of the corresponding standing stocks, ie chlorophyll concentration, phytoplankton and bacterial biomass We employ different methods (coefficient of variation, spline fitting and spectral analysis) which complement each other for assessing the variability present in the plankton data, at different temporal scales In phytoplankton, we found that the overall variability of primary production is dominated by fluctuations at low frequencies, such as the annual, whereas in stocks and chlorophyll in particular, higher frequencies contribute substantially to the overall variance This suggests that using standing stocks instead of rate measures leads to an under- or overestimation of food shortage for consumers during distinct periods of the year The range of annual variation in bacterial production is 8 times greater than biomass, showing that the variability of bacterial activity (eg oxygen consumption, remineralisation) would be underestimated if biomass is used The P/B ratios were variable and although clear trends are present in both bacteria and phytoplankton, no systematic relationship between stock and rate measures were found for the two groups Hence, standing stock and process rate measures exhibit different variability patterns and care is needed when interpreting the mechanisms and implications of the variability encountered