River ecosystem metabolism is useful for understanding energetics and carbon cycling in flowing waters. Net ecosystem production (NEP) provides information on whether a river is autotrophic (NEP > 0) or heterotrophic (NEP < 0) and carbon dynamics within the ecosystem. Are there any consistent patterns in the timing of autotrophy or heterotrophy?
I used circular statistics to calculate the mean timing of days with positive or negative NEP for a few hundred rivers. Additionally, the coherence (or dispersion) was also calculated to see if the timing of these events was concentrated in a specific time of year for each site.
A total of 44% of sites had a mean timing of autotrophy in summer and another 38% in spring. By contrast, 40% of sites had a mean timing of heterotrophy in summer and 37% in autumn. While summer has high percentages of both autotrophy and heterotrophy, it appears that positive NEP is more likely to happen in the spring and negative NEP in the autumn. This is a simple conclusion in agreement with conceptual understanding of biogeochemical cycling, but useful to see it so clearly highlighted in the data.
