Parallel Nitrogen Cycles in Southwest Florida’s Tidal Rivers: Selective Remineralization of Algal Material Supports Fish Biomass Elon M. Malkin, David H. Hollander, Ernst B. Peebles University of South Florida College of Marine Science Southwest Florida: Land Development & Fisheries 1. Anthropogenic Land Development: N Drains into receiving waters 2. Estuarine Dependent Juvenile Fish: Occupy Receiving Waters Positively or negatively influenced by N 3. Sedimentary N Processing: N Transformation between land and fish Study Questions: •What is the source of sedimentary recalcitrant nitrogen? •What is the source of sedimentary labile nitrogen? •Which of these pools are associated with fish production? Study Sites: 8 Watersheds Feather Sound Alafia River Wildcat Creek Curiosity Creek McMullen Creek Frog Creek Myakka River Peace River SOM vs. Sedimentary Porewater NH4+ NH4+ Sediment Porewater NH4+ (SedNH4+) Labile Sediment Nitrogen Pool Recalcitrant Sediment Nitrogen Pool Sediment Organic Matter (SOM) NH4+ NH4+ NH4+ NH4+ NH4+ NH4+ NH4+ NH4+ NH4+ δ15N SOM, ‰ AIR 16 14 12 10 8 6 4 2 0 SOM vs. Sedimentary Porewater NH4+ SOM r2= 0.17 -2 0 2 4 6 8 10 δ15N SedNH4+, ‰ AIR 12 What is the Source of Recalcitrant SOM? Approach: δ15N System Averaging to Account for Advection •Sample Collection: (Primary producers, SOM) •Each primary producer δ15N value averaged across sites •Each SOM δ15N value averaged across sites •Mean values of 1oP plotted against mean SOM values Collection Sites 1 River A 2 1 2 River B 1 River C 2 3 1 average value per 1oP 1 average value for SOM 3 1 average value per 1oP 1 average value for SOM 3 1 average value per 1oP 1 average value for SOM Microalgae is not Recalcitrant N 12 δ15N, ‰ AIR 10 8 POM BMA r2= 0.45 r2= 0.33 6 4 2 0 -2 2 2.5 3 3.5 4 4.5 5 δ15N Sedimentary Organic Matter, ‰ AIR Vascular Plant Detritus is Recalcitrant N 12 Emergent Vegetation δ15N, ‰ AIR 10 8 Upland Plants r2= 0.83 6 4 r2= 0.91 2 0 -2 2 2.5 3 3.5 4 4.5 5 δ15N Sedimentary Organic Matter, ‰ AIR What is the Source of Sedimentary Labile NH4+? Approach: δ15N Site Specific Values to Maximize Data Points •Site Collections (various 1OP, sedimentary NH4+) •Site Specific Values of 1oP plotted vs. sedNH4+ Collection Sites 1 River A 1 River B 1 River C 2 2 2 3 3 values per 1oP, porewater NH4+, SOM 3 3 values per 1oP, porewater NH4+, SOM 3 3 values per 1oP, porewater NH4+, SOM δ15N, ‰ AIR Upland Plant Detritus is Not Labile N 16 14 12 10 8 6 4 2 0 Mangroves Upland Plants r2= 0.07 r2= 0.32 -2 0 2 4 6 8 10 12 δ15N Sedimentary Porewater NH4+, ‰ AIR δ15N, ‰ AIR BMA is Labile N 16 14 12 10 8 6 4 2 0 BMA r2BMA = 0.99 -2 0 2 4 6 8 10 12 δ15N Sedimentary Porewater NH4+, ‰ AIR δ15N, ‰ AIR POM is Labile N 16 14 12 10 8 6 4 2 0 POM r2BMA = 0.68 -2 0 2 4 6 8 10 12 δ15N Sedimentary Porewater NH4+, ‰ AIR Which N Pool Supports Fish Production? Approach: δ13C vs. δ15N plots for all available data: Fish vs. Benthic Microalgae (BMA) Particulate Organic Matter (POM) Upland Plants (UP) Mangroves (MAN) Emergent Vegetation (EM) Stable Isotopes Link 1oP to Fish 1OC (Benthic inverts) ΔN=3‰ δ15N ‰ AIR 10 9 8 7 6 5 4 3 2 1 0 -26 1OP -25 ΔC=1‰ -24 -23 δ13C ‰ PDB -22 Stable Isotopes Link 1oP to Fish 1OC (Benthic inverts) ΔN=3‰ 2OC (fish) ΔC=1‰ ΔN=3‰ δ15N ‰ AIR 10 9 8 7 6 5 4 3 2 1 0 -26 1OP -25 ΔC=1‰ -24 -23 δ13C ‰ PDB -22 What 1oP Support Fish Production? Fish δ15N, ‰ AIR 16 14 12 10 8 6 4 2 0 -30 -28 -26 -24 δ13C, ‰ PDB -22 -20 Mangroves Do Not Support All Fish Fish MAN δ15N, ‰ AIR 16 14 12 10 8 6 4 2 0 -30 -28 -26 -24 δ13C, ‰ PDB -22 -20 Emergent Plants Do Not Support All Fish δ15N, ‰ AIR 16 14 12 10 8 6 4 2 0 Fish MAN EM -30 -28 -26 -24 δ13C, ‰ PDB -22 -20 Upland Plants Do Not Support All Fish δ15N, ‰ AIR 16 14 12 10 8 6 4 2 0 Fish MAN EM UP -30 -28 -26 -24 δ13C, ‰ PDB -22 -20 Vascular Plants Do Not Support All Fish δ15N, ‰ AIR 16 14 12 10 8 6 4 2 0 Fish MAN EM UP -30 -28 -26 -24 δ13C, ‰ PDB -22 -20 Microalgae Supports Fish Production δ15N, ‰ AIR 16 14 12 10 8 6 4 2 0 Fish POM BMA TB & CH POM -30 -28 -26 -24 δ13C, ‰ PDB -22 -20 Benthic Invertebrates are Intermediates δ15N, ‰ AIR 16 14 12 10 8 6 4 2 0 Fish POM BMA INV TB & CH POM -30 -28 -26 -24 δ13C, ‰ PDB -22 -20 Conclusions: Parallel Nitrogen Cycles Vascular Plant Cycle: Recalcitrant OM is Buried Vascular Plants Bulk SOM Burial Microalgal Cycle: Labile OM is Remineralized POM Vascular Plants BMA Labile SOM Bulk SOM SedNH4+ Recycle Burial Foodwebs Are Associated with Labile Cycle POM Vascular Plants BMA Labile SOM Bulk SOM SedNH4+ Recycle Burial