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 • Habitat viability • Aesthetics (color, aroma, clarity) • Function (support C storage, N removal, flow) • Human use potential (e.g., drinking or irrigation water) 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 http://www.sjrwmd.com/publications/pdfs/fs_lapopka.pdf Reduction in Water Clarity = Changes in Bottom Habitats Eutrophication may stimulate the growth of algae that produce harmful toxins Red Tide Dead Zone in the Gulf of Mexico http://serc.carleton.edu/microbelife/topics/deadzone/ Scope of the Problem in Florida Source: USEPA (http://iaspub.epa.gov/waters10/state_rept.control?p_state=FL&p_cycle=2002) 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 What Limits Aquatic Production? 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 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 Local Nitrogen Enrichment • 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) Arthur et al. 2006 Mission Springs Chassowitzka (T. Frazer) Mill Pond Spring Weeki Wachee 1950’s Weeki Wachee 2001 Core Question: What Causes Algae to Reach Nuisance Levels? GROW FASTER LOST MORE SLOWLY • 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 uncorrelated with [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) 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 N Enrichment and Primary Production [No Significant Association] • More N does not mean more GPP (GPP) Visualizing the Problem Silver Springs (1,400 ppb NNO3) Alexander Springs (50 ppb N-NO3) 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:demand become critical? Core Question: What Causes Algae to Reach Nuisance Levels? GROW FASTER LOST MORE SLOWLY 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) 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? Observational Support: Grazers and Algae are Correlated Ln (Filamentous Algae Biomass) 8 6 4 2 0 -2 -4 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 Ln (Gastropod Biomass) Combined model (snails, flow, canopy) explains over 70% of algae variation Evidence of threshold effect? Liebowitz et al. (in prep) Experimental Confirmation: Snails Control Algae • Enclosed & excluded snails What Kills Snails? • Changes in DO – Flow varying? • Changes in salinity/[Ca] • Human disturbance Complex Ecological Causes Questions? mjc@ufl.edu