Predicting Trophic Level Responses To Phosphorus Concentrations In The
Everglades
Curtis J. Richardson
Duke University Wetland Center
Durham, NC
The Everglades are one of the most P limited wetlands in the world. The effects of
varying levels of P additions are often debated but an understanding of the process that
control P cycling and concentrations are essential to our being able to properly assess the
P concentrations that will allow for the restoration of the structure and function of the
Everglades. We present results from a 6 year phosphorus (P) dosing experiment in the
Everglades and long-term gradient studies that suggest that the 10 ppb (g/L) P threshold
often given for average annual concentrations in oligotrophic waters (“natural pristine
lakes”) is not appropriate for defining oligotrophic wetland status in the Glades due to
differences in ecosystem structure (periphyton versus phytoplankton) seasonal water
depth affects on P concentrations, and natural nutrient gradients (i.e., higher exterior
nutrient concentrations in wetlands gradate to lower interior nutrient levels) that exist in
wetlands versus lakes. We show that biotic responses to water column concentrations
for the Everglades is highly predictable across trophic levels but estimates of uncertainty
and confidence intervals must be utilized to accurately bound biotic P thresholds
responses, which change with water depths and across seasons. Bayesian change point
analyses indicate that long-term water column phosphorus concentrations above 15.6 ppb
(g/L) P results in an ecological imbalance for both flora and fauna attributes.
Curtis J. Richardson
Duke University Wetland Center
Nicholas School of the Environment and Earth Sciences
Levine Science Building
Durham, NC 27708
Phone:919-613-8006
Fax: 919-613-8101