1. improving mechanistic models and their application in restoration
Effects of water depth change on phosphorus flux in benthic microbial mats:
improving mechanistic models and their application in restoration
Andres Sola Evelyn Gaiser, and Luca Marazzi – Southeast Environmental Research Center (SERC), Florida International University, Miami FL, USA
1) Introduction
To improve our understanding of biogeochemical dynamics in the Everglades, we need to study periphyton mats, important regulators of nutrient and carbon cycling and indicators of environmental changes. Phosphorus flux in and out of periphyton mats is likely to be altered by changed inundation patterns caused by increased freshwater flows to restore the Everglades. we conducted a microcosm experiment to test the direct effects of low vs high inundation frequency on nutrient concentrations and ratios (Fig. 1), following a preliminary analysis of nutrient data from Shark River Slough (SRS) across seasons and years (Fig. 2).
3) Experimental Design
5) Results
According to ANOVA analysis, mat TP was significantly higher in HV and LV than in C, but did not vary significantly between HV and LV (Fig. 4a)
Water TP was most often higher in LV than in HV and C (Fig. 4b)
LV mats became white due to the remaining carbonates (Fig. 5)
LV experienced large initial flux of N into the water before the mats reabsorbed it after ~1 week (thus increasing N:P ratio; Fig. 6)
Variance was greater in HV and LV than in C samples (Figs. 4-6)
Conditioning Phase
Final Rewetting
Figure 3. Timeframe of rewetting and dry down phases.
4) Results: TP Concentrations
Figure 5. After 5 days of wet conditions, HV and C mat samples retained
brown color associated with the presence of live algae.
Figure 1. Miniature greenhouse with Plexiglas roof and clear vinyl wall.
2) Methods
We collected 72 mat samples from nearby Chekika, placed them into beakers: Control (C), High Variance (HV), and Low Variance (LV) (high and low inundation frequency). After a 6-day drying phase, we kept C wet, dried and rewetted HV, and kept LV samples dry over ~ 30 days (Fig. 3). We then exposed all the samples to a final rewetting period. We retrieved five 1cm3 mat cores and 10mL water samples from each beaker, from which we analyzed total phosphorus (TP) and total nitrogen (TN) in mat and water.
Water Depth and Mat Nutrient Ratios in SRS ( )
(from last year’s FCE ASM poster)
Figure 6. Water N:P ratio during the final rewetting phase.
6) Next Steps
We are currently producing and analyzing mat TN and Chlorophyll a data to fully assess nutrient uptake and release from periphyton mats. These data will be used to model the rate of P and N release and uptake from mats under different drying and wetting cycles. This will help us determine the causes of the variance we observed in our long-term FCE-LTER data (Fig. 2).
Acknowledgements:
We thank the American Water Resources Association (AWRA) and the Miccosukee Tribe of Indians Endowment and SERC for funding, and SERC lab staff for supervising the analyses; Rudolf Jaffé, John Kominoski, & Jennifer Richards for their advice; Franco Tobias, Rafael Travieso, Viviana Mazzei, Kristen Dominguez & Monica Flores for their collaboration. The data were collected through the Florida Coastal Everglades Long-Term Ecological Research program (National Science Foundation Grants DEB , DBI , & DEB
Figure 2. a) Water depth; b) mat N:P molar ratios across sites (marine water inputs tend to increase P concentrations).
Figure 4. (top) Mat total phosphorus (TP); (bottom) water TP
during the final rewetting phase.