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The River Continuum Concept (RCC) posits that stream biota and ecological processing exhibit predictable change along a continuous gradient from the headwaters downstream to the mouth of a river. According to the RCC, longitudinal variation in stream metabolism (primary production and respiration) arises in response to channel widening and decreased canopy cover. However, the RCC does not consider variation in metabolic rates across streams of the same order within the network. It also does not consider temporal variation as a result of changing discharge, light and temperature, or make predictions regarding the relative magnitude of this variation across stream orders. The Suwannee River Watershed in Northern Florida is comprised of tannic blackwater, clear alluvial, and spring-fed streams where differing physical, chemical and biological features cause variations in in-stream metabolic rates within stream order. We deployed dissolved oxygen sensors in 12 headwater streams to measure metabolic rates over a period of several months. We also collected light, temperature, stage, flow, water quality samples in order to consider the effect of the differing physical, chemical and biological features on metabolic processing. Similar data was also collected in higher-ordered rivers downstream of these headwater locations. Preliminary results suggest that variations in metabolism within stream order may be equal or greater in magnitude to variation in means across orders. The results also suggest headwater to streams to be temporally more dynamic, and that this variation becomes dampened in larger order downstream reaches. These additional sources of variation are important to consider in conjunction with longitudinal variation when characterizing metabolic activity on the network level. |
