Experimental Phosphorus Enrichment in Everglades National Park: Approach and Methods

Experimental phosphorus enrichment in Everglades National Park: III. Application to large-scale pattern of enrichment in Everglades Marshes.

Evelyn E. Gaiser, Daniel Childers, Krish Jayachandran, Ronald Jones, David Lee, Greg Noe, Thomas Philippi, Jennifer Richards, Leonard Scinto, Joel Trexler Florida International University, Miami, FL

To determine the relevance of results of experimental P enhancement studies to enrichment patterns in the larger Everglades ecosystem, we assessed the distribution of the same abiotic and biotic parameters along transects that parallel P gradients in 5 Everglades marshes. The experimental P-dosing study, described in detail in other GEER presentations in this same session, added P at 0, 5, 15 and 30 ppb above ambient concentrations to the upstream end of 4 channels in 3, 100- m long flow-through flumes. Responses in the water, microbial community, periphyton, flocculent detritus, soils, macrophytes and fauna were measured at select stations downstream from inputs for a period of 4 years. Our hypothesis was that low -level additions of P to the water column would induce an ecosystem state change in the Everglades that would eventually lead to the types of disturbed ecosystems that occur in enriched areas elsewhere in the system. We therefore measured the same variables along transects that extend from canal-water inputs to the unimpacted interior of WCA-1, WCA-2A, WCA-3A, Shark River Slough and Taylor Slough. Transects were sampled in both the wet and dry seasons.

In the P-addition experiment, we detected a cascade of responses consistent with our hypothesis that microbial parameters would be the first to respond, followed by the floc, soils and finally the plant and animal communities. Biotic alterations were first detected at upstream stations and progressed downstream at load- dependent rates. These changes, while related to upstream dose concentration, preceded P enhancements in the surrounding water column, indicating rapid biotic uptake and downstream spiraling. Extending these findings to the marsh transects, we expected to find little correlation of water column P with biotic structure and function except in areas with a long history of enhancement that are now saturated in P. In addition, we expected to find a sequence of alterations downstream of canal inputs, with disruptions in periphyton assemblages indicated significantly downstream of enhanced P inputs, enriched soils, or altered plant communities.

In all basins we found a significant negative correlation of periphyton tissue P content with distance from inflow, and this relationship was always stronger than similar distance-water column TP concentration relationships. Periphyton biomass was depressed and assemblage composition altered at sites adjacent to canals. Using data from the experimental control channels in ENP as a model for an unenriched marsh, we detected departures from ambient conditions further downstream from canal sources for attributes of the periphyton community (TP content, biomass, composition) than for soil nutrient content or plant composition. In comparisons to similar data from these basins collected in 1989, we found P- related impacts to be migrating downstream in WCA-2A and WCA-1. The within-marsh patterns of change are related to changes in P concentration in canal-water inputs.

Figure 1. TP concentration in water and periphyton tissue across a 17 km transect from S-12C inflow structure to the interior of Shark River Slough, Everglades National Park, showing a significant decline in periphyton TP away from the canal without a significant change in water TP.

1000 TP Water (µg l-1) TP Periphyton (µg g-1)

100 Phosphorus 10 Total

1 0 5 10 15 20 Distance from Input (km)

In summary, our P-enrichment experiments and transect surveys indicate that the microbial community responds quickly to changes in P-input and can provide an indication of impending ecosystem change. Changes in periphyton attributes were followed temporally and spatially by changes in the soil parameters and the plant and animal communities in a predictable manner in both experimental and natural settings. That these changes are correlated with alterations in upstream nutrient loading but not necessarily the water column P concentration at a given site suggests that biotic data, rather than water quality, be used to monitor and predict the degree of current or pending ecosystem alteration. Evelyn Gaiser, Department of Biology and the Southeast Environmental Research Center, Florida International University, Miami, FL, 33199. Phone: 305-348-6145, Fax: 305-348-4096, [email protected], Ecology