Evaluating the Role of a Semi-Aquatic Amphibian in Consumer-Driven Nutrient Dynamics of Appalachian Headwaters

The flow of nutrients between upland and aquatic ecosystems has a large influence on physical and biological properties of aquatic systems. Semi-aquatic species may have a more active role in the movement of nutrients between terrestrial and aquatic habitat when activity or foraging patterns are biased to one habitat over the other. The potential role of a species (consumer nutrient dynamics, CND) within an ecosystem is in part influenced by individual size, excretion and egestion rates, and population-level biomass. We set out to identify the role of the black-bellied salamander (Desmognathus quadramaculatus) in Appalachian headwater CND. We first measured individual excretion over a 24-hr period to estimate hourly rates of ammonium and soluble reactive phosphorous (SRP) excretion, relative to individual mass. We then estimated size-mass relationships, biomass, and aerial excretion for black-bellied salamanders by estimating the abundance of three distinct size-classes (larvae, small adult, and large adult), using a series of connected Bayesian hierarchical models. Our results indicate strong predictive ability of individual size on mass (r2 = 0.99), mass on ammonium (r2 = 0.97), and mass on SRP (r2 = 0.87) excretion. We predicted larval salamanders to occur at 64x greater densities than adults, resulting in ~5x more larval biomass than adults. Overall, areal N excretion met ~13% of summer stream N demand, based on published values for similar streams in the region. These results indicate that black-bellied salamanders may meet a small portion of stream N-demand and can function as a pathway for the flow of terrestrial resources into aquatic habitat.