Chapter 4 - Metabolism of Streams and Rivers: Estimation, Controls, and Application

Abstract

Ecosystem metabolism is a fundamental property of streams and rivers that comprises carbon fixation as gross primary production (GPP) and mineralization as respiration by all organisms in the ecosystem (ER). Ecologists estimate GPP and ER at a stream reach scale by measuring dissolved oxygen throughout a day and converting these data to metabolism given an estimate of the air-water gas exchange flux. Use of this method has increased greatly in the past decade due to ease of data collection and statistical modeling methods, in particular estimates of the difficult to measure gas exchange. Here, I review recent improvements in methods to estimate GPP and ER, examine physical and biotic controls on rates, and address future applications of this technique. Nearly, all streams are heterotrophic (i.e., GPP<ER). Light availability is the dominant control on GPP, observed in both spatial surveys and time series analyses. When GPP is high and variable, it strongly controls rates of ER due to autotrophic respiration by the algae. Streams respond variably to hydrologic disturbance depending on the size of the flood and the substrate. Temperature and nutrients are secondary controls on GPP and ER relative to light and hydrologic disturbance. Despite a weak relationship of nutrients controlling rates of GPP and ER, metabolism can strongly increase rates of nutrient demand in rivers. Stream metabolism responds to human alteration of streams and rivers and holds promise as a metric to quantify human impacts. In particular, time series of daily metabolism may be quite sensitive to human impacts to streams and rivers, although this topic is only beginning to be explored.