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, 100m 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 loaddependent 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 Prelated 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.
Total Phosphorus
1000
TP Water (µg l-1)
TP Periphyton (µg g-1)
100
10
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, gaisere@fiu.edu, Ecology