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Eutrophication and Algal Proliferation in Florida’s Springs

Eutrophication and Algal Proliferation in Florida’s Springs. Forest Hydrology Spring 2014. Water Quality and Aquatic Health. Tenet #1: Contaminants from land end up in the water Industrial, urban, agricultural chemicals Tenet #2: Aquatic systems may respond, often in undesirable ways

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Eutrophication and Algal Proliferation in Florida’s Springs

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  1. Eutrophication and Algal Proliferation in Florida’s Springs Forest Hydrology Spring 2014

  2. Water Quality and Aquatic Health • Tenet #1: Contaminants from land end up in the water • Industrial, urban, agricultural chemicals • Tenet #2: Aquatic systems may respond, often in undesirable ways • Habitat viability • Aesthetics (color, aroma, clarity) • Function (support C storage, N removal, flow) • Human use potential (e.g., drinking or irrigation water)

  3. Eutrophication • Def: Excess C fixation • Primary production is stimulated. Can be a good thing (e.g., more fish) • Can induce changes in dominant primary producers (e.g., algae vs. rooted plants) • Can alter dissolved oxygen dynamics (nighttime lows) • Fish and invertebrate impacts • Changes in color, clarity, aroma

  4. Reduction in Water Clarity = Changes in Bottom Habitats http://www.sjrwmd.com/publications/pdfs/fs_lapopka.pdf More P Less P

  5. Eutrophication may stimulate the growth of algae that produce harmful toxins Red Tide

  6. Dead Zone in the Gulf of Mexico http://serc.carleton.edu/microbelife/topics/deadzone/

  7. Scope of the Problem in Florida Source: USEPA (http://iaspub.epa.gov/waters10/state_rept.control?p_state=FL&p_cycle=2002)

  8. What Causes Eutrophication? • Leibig’s “Law of the Minimum” • Some element (or light or water) limits primary production • Adding that thing will increase yields (GPP) • What is limiting in forests? Crops? Lakes? Pelagic ocean? Justus von Liebig

  9. What Limits Aquatic Production?

  10. Typical Symptoms: Alleviation of Nutrient Limitation • Phosphorus limitation in shallow temperate lakes • Nitrogen limitation in estuarine systems (GPP) V. Smith, L&O 2006 V. Smith, L&O 1982

  11. Global Nitrogen Enrichment • Humans have massively amplified global N cycle • Terrestrial Inputs • 1890: ~ 150 Tg N yr-1 • 2005: ~ 290+ Tg N yr-1 • River Outputs • 1890: ~ 30 Tg N yr-1 • 2005: ~ 60+ Tg N yr-1 • N frequently limits terrestrial and aquatic primary production • Eutrophication Gruber and Galloway 2008

  12. Local Nitrogen Enrichment Arthur et al. 2006 • The Floridan Aquifer (our primary water source) is: • Vulnerable to nitrate contamination • Locally enriched as much as 30,000% over background (~ 50-100 ppb as N) • Springs are sentinels of aquifer pollution • Florida has world’s highest density of 1st magnitude springs (> 100 cfs)

  13. Mission Springs Chassowitzka (T. Frazer) Mill Pond Spring WeekiWachee WeekiWachee 1950’s 2001

  14. Core Question: What Causes Algae to Reach Nuisance Levels? GROW FASTER LOST MORE SLOWLY

  15. Hnull: N loading alleviated GPP limitation, algae exploded (conventional wisdom) • Evidence generally runs counter to this hypothesis • Springs were light limited even at low concentrations (Odum 1957) • Algal cover/AFDM is uncorrelatedwith [NO3] (Stevenson et al. 2004) • Flowing water mesocosms show algal growth saturation at ~ 110 ppb (Albertin et al. 2007) • Nuisance algae exists principally near the spring vents, high nitrate persists downstream (Stevenson et al. 2004)

  16. N Enrichment in Springs Fall 2002 (closed circles) and Spring 2003 (open triangles) From Stevenson et al. 2004 Ecological condition of algae and nutrients in Florida Springs DEP Contract #WM858 No correlation between algae and N

  17. N Enrichment and Primary Production[No Significant Association] • More N does not mean more GPP (GPP)

  18. Visualizing the Problem Silver Springs (1,400 ppb N-NO3) Alexander Springs (50 ppb N-NO3)

  19. Qualitative Insight: Comparing Assimilatory Demand vs. Load • Primary Production is very high • 8-20 g O2/m2/d (ca. 1,500 g C/m2/yr) • N demand is proportional • 0.05 – 0.15 g N/m2/day • N flux (over 5,000 m reach) is large • Now: ca. 30 g N/m2/d (240 x Ua) • Before: ca. 2.5 g N/m2/d (20 x Ua) • In rivers, the salient measure of availability may be flux(not concentration) • Because of light limitation, this is best indexed to demand • When does flux:demandbecome critical?

  20. Core Question: What Causes Algae to Reach Nuisance Levels? LOST MORE SLOWLY GROW FASTER

  21. Algal Loss Rates - Scouring • Flow has widely declined, in areas a lot • Silver Springs • White Springs • Kissingen Spring • Lower discharge means lower scour • Algal cover varies with flow velocity (King 2014)

  22. Algal Loss Rates - Grazing • Algal cover is predicted by: • Dissolved oxygen (DO) • Grazer density • DO is keystone variable for aquatic animal health • Proxy for groundwater age?

  23. Observational Support:Grazers and Algae are Correlated Combined model (snails, flow, canopy) explains over 70% of algae variation Evidence of threshold effect? Liebowitzet al. (in prep)

  24. Experimental Confirmation: Snails Control Algae • Enclosed & excluded snails

  25. What Kills Snails? • Changes in DO • Flow varying? • Changes in salinity/[Ca] • Human disturbance

  26. Complex Ecological Causes

  27. Questions?mjc@ufl.edu

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