Biogeochemical response to aqueous sulfate additions in Everglades wetland mesocosms

Transcription

1 iogeochemical response to aqueous sulfate additions in Everglades wetland mesocosms Mike Jerauld 1, Scott D. Jackson 1, Forrest E. Dierberg 1, Michelle Kharbanda 1, William F. Deusk 2, Thomas. Deusk 1, and inhe Gu 3 1 D Environmental, Inc. 2 Water Resource Group, LLC 3 South Florida Water Management District

2 ackground Surface water sulfate Potential deleterious effects of sulfate enrichment: 1. Internal eutrophication 2. Enhanced Hg methylation 3. Sulfide toxicity Scheidt and Kalla, 27 2

3 Experimental Design Treatment groups Unenclosed control Control enclosure +Sulfate 3 mg/l a +Sulfate 12 mg/l +Sulfate 24 mg/l +Sulfate 48 mg/l a Seasons 2 and 3 only 3

4 Mesocosm Operation 2-week Sampling Cycle 2. stopper 2-way valve Supply water Sump 1. Water exchange (5X volume) 3. Post- spike collection t = 2-wk Spiking solution 4. Pre-spike collection (immediate) Spiking 4

5 Monitoring Sample collection Surface water (t = 2wk) Porewater (1/season) Soils (initial and final) Mercury (selected events) nalytes Sulfate Sulfide P species THg & MeHg lkalinity Diss. Iron DOC & optical mmonia-n ph & Eh & D.O. 1 Wet season 1 (21-211) Wet season 2 ( ) Wet season 3 ( ).8 Water depth (m) pr-1 Jul-1 Oct-1 Jan-11 pr-11 Jul-11 Oct-11 Jan-12 pr-12 Jul-12 Oct-12 Jan-13 pr-13 Depth Routine SW Sample Day 2 SW Sample Mercury Soil PW 5

6 Results Sulfur Chemistry 48 Sulfate (mg/l) mg/l Unenc. Unenclosed Ctrl Control S(3) SO4 S(12) SO4 S(24) SO4 S(48) SO4. 25 c. porewater sulfate Sulfate (mg/l) mg/l a. surface water sulfate Surface water sulfate Porewater sulfate Unenc. Unenclosed Control Ctrl S(3) SO4 S(12) SO4 S(24) SO4 S(48) SO C D Sulfate reduction (mg/l/d) mg/l/d mg/l Sulfide (mg/l) d. porewater sulfide e. porewater redox potential Soil bulk redox potential 2 b. surface water sulfate depletion Surface water sulfate depletion C Unenc. Unenclosed Control Ctrl S(3) SO4 S(12) SO4 S(24) SO4 S(48) SO4 Porewater sulfide C Unenc. Unenclosed Control Ctrl SO4 S(3) S(12) SO4 S(24) SO4 S(48) SO4 C C D C Eh (mv) mv C C C Unenc. Unenclosed Control Ctrl SO4 S(3) S(12) SO4 S(24) SO4 S(48) SO4 6

7 Results Phosphorus P Concentration (μg/l) P Concentration (μg/l) SRP DOP PP CD D CD C C C C D CD C D Unenc. Ctrl S(3) S(12) S(24) S(48) Unenclosed Control SO4 (3) SO4 (12) SO4 (24) SO4 (48) 7

8 Internal Eutrophication (Smolders et al., 26) 1. nion exchange 2. lkalinization 8 Unlikely: Generally uncommon. Soil ion-extractable P was only.2 mg/kg (.5% of soil TP). Unlikely: High native alkalinity, biological alkalinity buffering mg CaCO 3 /L Surface water alkalinity Weeks into monitoring season 1 xis Title Unenclosed Encl. Cont. SO4 (3) SO4 (12) SO4 (24) SO4 (48)

9 Internal Eutrophication (Smolders et al., 26) 3. Mineralization of organic P Unlikely: P conserved during decomposition Soil TOC:TP = 7-1 3% soil TP as microbial biomass Mass remaining (% of initial) Time (days) Cheesman et al., 21 Change in P (μg/g) (relative to initial) 9

10 Internal Eutrophication (Smolders et al., 26) 4. Mobilization of iron-bound P Unlikely: Pools of P were small compared to iron stores Soil iron-bound P: 1-2 mg/kg (2.5-5% of TP) Threshold for P release Iron:P ratios (Guerts et al., 28) Mesocosms Soil Porewater

11 Results Methylmercury.6.5 a. Surface water MeHg (ng/l) ns ns Un. Ctrl Un. Ctrl Un. Ctrl DryDown Feb212 Closeout Soil MeHg (ng/g dry) b. Soil ns ns Un. Ctrl Un. Ctrl Un. Ctrl DryDown Feb212 Closeout 11

12 Results Methylmercury SW MeHg (ng/l) SW MeHg (ng/l) SW MeHg (ng/l) SW MeHg (ng/l) a SW SO sulfate c. 4 (mg/l) SW MeHg (ng/l) SW MeHg (ng/l).6 b. y = x R² =.5195 P <.1 SW MeHg (ng/l) SW MeHg (ng/l) SW Ssulfide 2- (mg/l) d PW PW SO sulfate PW Ssulfide 2- (mg/l) 4 (mg/l) Post DryDown Hg Spike Closeout.2 SW MeHg (ng/l).6 SW MeHg (ng/l) y =.59x R² = SW sulfate consumed SW SO 4 cons. (mg/l/d) 12

13 Controls on Mercury Methylation Net methylmercury accumulation was not tightly coupled to sulfate reduction in this experiment Stimulatory effect of drydown cycle, as observed by previous investigators. Possible alternative controls 1. Hg bioavailability Observed by other investigators (e.g. Gilmour et al., 27) and other DE laboratory experiments 2. Demethylation Microbial syntrophy (ae et al., 214) 13 Degradation rate (μmol MeHg/m 2 /d) Marvin-DiPasquale and Oremland, CO2 / 14 CH 4 Ratio

14 Conclusions 1. This and previous studies* show sulfate enrichment is not a significant contributor to eutrophication in the Everglades 2. The role of sulfate as a contributor to methylmercury production and accumulation in the Everglades is less clear than previously believed 14 *Dierberg et al., 211; 212

15 cknowledgments Field Support Stacey Cote Dawn Sierer Finn Doug Hatton Patrick Owens Lab Support Nichole Larson Nancy Chan and many others Everglades gricultural rea Environmental Protection 15 District Thank you!

16 References ae, H.-S., F.E. Dierberg and. Ogram Syntrophs dominate sequences associated with the mercury-methylating gene hgc in the Water Conservation reas of the Florida Everglades. ppl. Environ. Microbiol. 8: Cheesman,.W.,.L. Turner, P.W. Inglett and K.R. Reddy. 21. Phosphorus transformations during decomposition of wetland macrophytes. Environ. Sci. Technol. 44: Dierberg, F.E., T.. Deusk, J.L. Henry, S.D. Jackson, S. Galloway and M.C. Gabriel Temporal and spatial patterns of internal phosphorus recycling in a south Florida (US) stormwater treatment area. J. Environ. Qual. 41: Dierberg, F.E., T.. Deusk, N.R. Larson, M.D. Kharbanda, N. Chan and M.C. Gabriel Effects of sulfate amendments on mineralization and phosphorus release from south Florida (US) wetland soils under anaerobic conditions. Soil iol. iochem. 43: Geurts, J.J.M.,.J.P. Smolders, J.T.. Verhoeven, J.G.M Roelofs and L.P.M. Lamers. 28. Sediment Fe:PO 4 ratio as a diagnostic and prognostic tool for the restoration of macrophyte biodiversity in fen waters. Freshwater iol. 53: Gilmour, C.C., D.P. Krabbenhoft, W. Orem, G. iken and E. Roden. 27b. ppendix 3-2: Status Report on the Control of Mercury Methylation and ioaccumulation in the Everglades. In 27 South Florida Environmental Report Volume I. South Florida Water Management District, West Palm each, FL. Marvin-DiPasquale, M.C. and R.S. Oremland acterial methylmercury degradation in Florida Everglades peat sediment. Environ. Sci. Technol. 32: Smolders,.J.P., L.P.M Lamers, E.C.H.E.T. Lucasseen, G. Van der Velde and J.G.M Roelofs. 26. Internal eutrophication: how it works and what to do about it - a review. Chem. Ecol. 22:

17 Results Iron Chemistry.5 a. surface water dissolved iron Dissolved Fe (mg/l) C C C C Unenclosed Control SO4 (3) SO4 (12) SO4 (24) SO4 (48) 2 b. porewater dissolved iron Dissolved Fe (mg/l) Unenclosed Control SO4 (3) SO4 (12) SO4 (24) SO4 (48) 17