Limited Animal-Facilitated Nutrient Transfer across an Aquatic–Terrestrial Interface in a Southern African Savanna

Abstract

Animal-mediated nutrient transfer facilitates nutrient cycling in marine, freshwater and terrestrial ecosystems via the deposition of aquatically-derived nutrients such as nitrogen (N) and carbon (C). This mode of nutrient transfer has not been studied in southern African river systems. We investigated nutrient deposition associated with defecation, urination, and scent-marking at latrine sites of a semi-aquatic predator species (African clawless otters Aonyx capensis) in a riparian zone of a Bankenveld savanna ecosystem. We provide a comparison of stable nitrogen isotopes (δ15N) measured in soil, vegetation and faecal material, between latrine and paired control sites. Latrine sites displayed higher δ15N values than the paired non-latrine sites, but only at the area of direct deposition (soil surfaces). This effect dissipated as the distance from direct contact increased, while no significant difference in δ15N values was detected for sub-surface soil samples. Plants displayed varying trends of enriched δ15N values between the latrine and paired control sites. These results suggest that several factors and processes such as leaching, mineralization, ammonia volatilization, and nitrogen acquisition influence the nutrient availability within latrine-soil-vegetation systems in riparian zones of African savanna ecosystems.