Reproduced from Journal of Environmental Quality. Published by ASA, CSSA, and SSSA. All copyrights reserved. Cascading Ecological Effects of Low-Level Phosphorus Enrichment in the Florida Everglades Evelyn E. Gaiser,* Joel C. Trexler, Jennifer H. Richards, Daniel L. Childers, David Lee, Adrienne L. Edwards, Leonard J. Scinto, Krish Jayachandran, Gregory B. Noe, and Ronald D. Jones ABSTRACT The Everglades is a flowing-water wetland that is historically oligotrophic (reviewed in Noe et al., 2001). Few studies have examined long-term ecological effects of sus- Decades of P enrichment have significantly degraded tained low-level nutrient enhancement on wetland biota. To deter- portions of this wetland, prompting studies to determine mine sustained effects of phosphorus (P) addition on Everglades marshes we added P at low levels (5, 15, and 30 gL -1 above ambient) the levels of P input that would afford protection to for 5 yr to triplicate 100-m flow-through channels in pristine marsh. remaining federally protected marshland. Enclosure stud- A cascade of ecological responses occurred in similar sequence among ies suggested that water column P levels in excess of treatments. Although the rate of change increased with dosing level, 10 gL -1 (ppb) cause biotic change in the Everglades treatments converged to similar enriched endpoints, characterized (McCormick and O’Dell, 1996). However, enclosure most notably by a doubling of plant biomass and elimination of native, studies are designed to dose with a predetermined mass calcareous periphyton mats. The full sequence of biological changes of P m -2 yr -1 , which is difficult to relate to actual marsh occurred without an increase in water total P concentration, which water column concentrations (Noe et al., 2002; Gaiser remained near ambient levels until Year 5. This study indicates that et al., 2004). While enclosure studies have provided use- Everglades marshes have a near-zero assimilative capacity for P with- ful biotic metrics of P enrichment in the Everglades out a state change, that ecosystem responses to enrichment accumulate over time, and that downstream P transport mainly occurs through (McCormick and Stevenson, 1998), they do not address biota rather than the water column. long-term cumulative effects of nutrient influx to this flowing-water system. One flow-through experimental dosing study was con- ducted in marshes of Water Conservation Area 2A (Rich- F looded grasslands are generally highly productive and thus thought to be a sink for nutrients that fuel ardson et al., 1995) upstream of protected areas, and found significant alterations in communities exposed to water high standing crops of vegetation (Kadlec and Knight, 1996). Particularly in warmer climates, rapid growth of total phosphorus (TP) concentrations exceeding 15 g L -1 (approximately 5 gL -1 P above background con- vegetation and attached periphyton allow efficient re- moval of incoming nutrients and subsequent burial in centrations). In that study P was continuously added at quantities sufficient to raise the water column concen- the sediments (Vymazal, 1995). A study by Richardson and Qian (1999) compiled data from 126 wetlands and tration throughout the channels to predetermined lev- els, and biological responses were related to the sur- showed that the average long-term assimilative capacity of P for North American wetlands is close to 1 g m -2 rounding water column TP concentration. However, large areas of marsh near canal inputs in this and other marshes yr -1 . Assimilative capacity was defined therein as the amount of P absorbed with no significant ecosystem have been shown to be dramatically altered ecologically without the water column being significantly enriched state change and no downstream transport of P. The convention to express assimilation on an annual basis (Smith and McCormick, 2001; Childers et al., 2003), indicating that biotic changes can occur before enhance- implies that marshes have the ability to continuously re- move some excess P at a constant rate without incurring ments are measured in the water column. In P-limited systems, excess P is rapidly and efficiently sequestered change, regardless of exposure duration. However, few studies have tested the assimilative capacity of wetlands by biota and mainly transported downstream through biota rather than the water column (Gaiser et al., 2004). over time scales greater than a few years, and no long- term experimental investigation of P assimilation has Experimental manipulations aimed at elevating marsh water P concentration to a certain level therefore rely taken place in the Everglades, where one of the largest restoration projects in history is currently underway. on loading rates that exceed the naturally high rate of assimilation, creating an enrichment design that is different from the mode of P transport downstream of E.E. Gaiser, D.L. Childers, L.J. Scinto, and K. Jayachandran, South- most canal inputs. east Environmental Research Center; E.E. Gaiser, J.C. Trexler, J.H. In flowing-water systems subject to elevated nutrient Richards, D.L. Childers, and D. Lee, Department of Biological Sci- inputs, it is particularly important to document the se- ences; and K. Jayachandran, Department of Environmental Studies, Florida International University, Miami, FL 33199. A.L. Edwards, quence of changes taking place during the eutrophica- Center for Biodiversity, Illinois Natural History Survey, Champaign, tion process before the attainment of an enriched end- IL 61820. G.B. Noe, U.S. Geological Survey, Reston, VA 20192. R.D. point. Detecting the onset of state change is imperative Jones, Department of Biology, Portland State University, Portland, to calculate the assimilative capacity of the system for OR 97207. Received 26 May 2004. *Corresponding author (gaisere@ fiu.edu). the added nutrient, and knowing the progressive se- quence of alterations can provide a model to predict Published in J. Environ. Qual. 34:– (2005).  ASA, CSSA, SSSA 677 S. Segoe Rd., Madison, WI 53711 USA Abbreviations: TP, total phosphorus. 1