Processes that regulate the production, transport, and processing of nutrients contained in particles (seston) in riverine systems are relatively unknown. This limitation impedes our ability to understand the role of stream seston in carbon (C) and nutrient (nitrogen [N], phosphorus [P]) dynamics at the continental scale. We accessed available NEON seston data, and quantified how particulate nutrient concentrations varied among 20 NEON wadeable stream sites within 14 NEON domains from 2014-2020. We also used biweekly respiration assays on filtered and unfiltered samples to evaluate particulate bioavailability across a nested hydrologic gradient (Alabama, USA), including Mayfield Creek (MAYF, small forested headwater), Black Warrior River (BLWA, mid-order & mixed land use), and Tombigbee River (TOMB, high order and highly modified river). We used these data to begin addressing two predictions. First, we predicted seston composition would depend on continental-scale patterns in geology and climate, and second, that seston would act as an integrated signal of terrestrial and in-stream biogeochemical processes that varies according to seasonal or hydrologic context.
Results/Conclusions
Across sites, C was tightly coupled to N (r2 = 0.85) compared to P (r2 = 0.28). Particles were relatively P-rich (median molar C:P = 167, median molar N:P = 13), but this was dependent on watershed size: smaller watersheds had higher C:P compared to larger watersheds. Among domains, Atlantic neotropical (D04) sites had the lowest C:N, whereas the Northern Plains (D06) had the lowest C:P and N:P, on average. Temporal patterns of particulate C:N and C:P were also domain- and watershed-size-dependent, suggesting distinct particle sources and processing across space and time. For example, particulate C:N and C:P varied seasonally in forested Posey Creek (Virginia, USA), while in the larger Arikaree River (Colorado, USA) particulate C:N and C:P were more consistent across seasons. Preliminary data from the nested hydrologic gradient suggests that particulate bioavailability is highly site-dependent, with particulates having the highest bioavailability in the mid-order site (BLWA). These patterns point to an important role of particulate processing in streams across the US.
