Experimental and multivariate analysis of biogeochemical indicators of change in wetland ecosystems

Eutrophication in subtropical wetland ecosystems can lead to extensive displacements of vegetative communities and as a result changes in overall environmental conditions (loss of slough habitat, substrate quality for e.g.). This has generated a demand for a set of sensitive indicator(s) that prelude the structural changes in vegetative communities in response to nutrient enrichment. Microbial communities play a critical role in nutrient cycling, mediating and responding to nutrient levels. Consequently, multiple microbial parameters have been shown to individually respond to nutrient enrichment. However, in this complex array of indicator forms, which is the most sensitive response?; In order to get a handle of the full scale of microbial response measures, this study encompasses three scales and two systems. Short term microbial ecophysiological responses were explored in a controlled lab experiment. Microbial response and microbially mediated organic matter turnover under controlled nutrient conditions was measured at the mesocosm scale. A cross system comparison was carried out at the field scale, one system currently still an expression of significant nutrient loading (WCA-2a in the Everglades), and a second responding to system dynamics associated with historical nutrient loads (Blue Cypress Marsh Conservation Area).; Microbial ecophysiological response measures vary in time and in space as well as a function of the changes in the biogeochemistry. In BCMCA, we were capable of describing ‘longer’-term changes (over the two year period) as well as accounting for the annual trend in these variables. In assessing whether an indicator is a coherent response measure, this particular study resulted in the qualitative differentiation between indicator response to the direct perturbation and as a result of the changes brought upon larger system changes such as plant community shifts. In contrasting the groups of measures in the experimental work, measures directly associated with the nutrient impact (N & P) as the most coherent response measures. Microbial nutrient acquisition (extracellular enzyme activity; EEA), microbially mediated nutrient turnover and microbial nutrient content were the “best” indicators of nutrient enrichment. The smaller scale, controlled mesocosm experiment seem to confirm that the most direct microbial indicators of nutrient impact are those directly associated to the perturbation.