Wading bird guano enrichment of soil nutrients in tree islands of the Florida Everglades

- Tree island soil P concentration and δ15N values exceed other Everglades soils.
- Characteristics of Everglades tree island soil may indicate guano deposition.
- Deposition of stable guano P can exceed other P sources to tree island soil.

Differential distribution of nutrients within an ecosystem can offer insight of ecological and physical processes that are otherwise unclear. This study was conducted to determine if enrichment of phosphorus (P) in tree island soils of the Florida Everglades can be explained by bird guano deposition. Concentrations of total carbon, nitrogen (N), and P, and N stable isotope ratio (δ15N) were determined on soil samples from 46 tree islands. Total elemental concentrations and δ15N were determined on wading bird guano. Sequential chemical extraction of P pools was also performed on guano. Guano contained between 53.1 and 123.7 g-N kg− 1 and 20.7 and 56.7 g-P kg− 1. Most of the P present in guano was extractable by HCl, which ranged from 82 to 97% of the total P. Total P of tree islands classified as having low or high P soils averaged 0.71 and 40.6 g kg− 1, respectively. Tree island soil with high total P concentration was found to have a similar δ15N signature and total P concentration as bird guano. Phosphorus concentrations and δ15N were positively correlated in tree island soils (r = 0.83, p < 0.0001). Potential input of guano with elevated concentrations of N and P, and 15N enriched N, relative to other sources suggests that guano deposition in tree island soils is a mechanism contributing to this pattern.