Understanding the factors that shape variation in productivity and respiration across ecosystem is a fundamental question in ecology. Previous studies have identified external nutrient subsidies, light availability, disturbance, and ecosystem size as important drivers in ecosystem metabolism across aquatic habitats. However, because of the logistical challenges of estimating metabolism for a large sample of ecosystems arrayed across multiple environmental gradients, few studies have been able to examine the relative importance of these drivers or test hypotheses about how they interact to shape ecosystem metabolism. Here we examine the effects of nutrients, shading, ecosystems size and frequency of flooding on ecosystem productivity and respiration in a system that includes hundreds of riverine rock pools in the James River, Virginia. We use the diel dissolved oxygen profiles measured across many rock pools to estimate components of ecosystem metabolism - net primary production (NPP), respiration (R) and gross primary production (GPP). We then related these responses to variations in rock pool size, leaf litter input, canopy cover, and flooding frequency using a model selection approach.
Results/Conclusions:
Pools varied considerably in environmental characteristics of size (1.96 – 16.69 m2), shading (0 – 100%), litter input and flooding frequency. Rock pools show considerable variation in ecosystem metabolism, ranging from net autotrophic to net heterotrophic. Mean GPP was 2.06 g O2/m2/d but varied more than threefold across pools. Mean R was 4.38 g O2/m2/d and varied up to ten folds across pools. Therefore, NPP had substantial fluctuation with low values at -5.26 g O2/m2/d and values up to 4.08 g O2/m2/d. Initial analyses indicate that pool shading is the most important driver of this variation.