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Are There Effects at the Ecosystem Level? August 21, 2007 Robert L. Knight, Ph.D. Wetland Solutions, Inc. (www.wetlandsolutionsinc.com) Springs and Nutrients.

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Presentation on theme: "Are There Effects at the Ecosystem Level? August 21, 2007 Robert L. Knight, Ph.D. Wetland Solutions, Inc. (www.wetlandsolutionsinc.com) Springs and Nutrients."— Presentation transcript:

1 Are There Effects at the Ecosystem Level? August 21, 2007 Robert L. Knight, Ph.D. Wetland Solutions, Inc. (www.wetlandsolutionsinc.com) Springs and Nutrients

2 Florida’s Springs A Resource in Danger: Rising Nitrate Nitrogen Lower Flows and Aquatic Plant Management, Downstream Dams, Increased Recreation, etc.

3 Dr. Howard T. Odum and Florida Springs Ecology “Father” of Springs Ecology and author of: Trophic Structure and Productivity of Silver Springs, Florida (Ecological Monographs,1957) and Primary Production Measurements in Eleven FL Springs… (L&O, 1957)

4 Silver Springs: Ecosystem Study Area 1,200-m Study Area and Sampling Stations

5 Silver Springs Biomass Pyramid (Odum 1957) Primary Producers Sagittaria / Aufwuchs (809 g/m 2 ) Herbivores Turtles, Snails, Mullet (36.8 g/m 2 ) 1 o Consumers Fish and Midges (10.7 g/m 2 ) Top Consumers Bass, Birds, and Alligators (1.53 g/m 2 ) Detritus Feeders Bacteria and Crayfish (5 g/m 2 )

6 Upstream/Downstream Oxygen Change Method ( ) Silver Springs Ecosystem Function (Odum 1957)

7 Ecosystem Metabolism Measured from Main Boil to 1,200-m Station: –Gross Primary Productivity = 6,390 g/m 2 /y (57,100 lbs/ac/yr) –Net Community Productivity = 768 g/m 2 /y (6,900 lbs/ac/y) –Community Respiration = 6,000 g/m 2 /y (53,600 lbs/ac/y)

8 Primary Productivity in Eleven FL Springs (Odum 1957) Relationship Between Visible Light and Gross Primary Production

9 Silver Springs Energy Flow Summary (Odum 1957) Florida’s springs have complex and highly adapted ecologies that have maximized the productive use of available energy inputs, including especially sunlight, nutrients, and current velocity.

10 Energy Basis of Control in Aquatic Ecosystems (Knight 1980) Doctoral Research Under Dr. H.T.Odum, : –Repeated upstream/downstream whole system metabolism studies –Conducted mesocosm experiments to determine the effects of consumer (snails and fish) density on ecosystem metabolism

11 Diel Oxygen Curves ( ) Silver Springs Ecosystem Function (Knight 1980)

12 In Situ Flow-Through Mesocosms Silver Springs (Knight 1980)

13 Silver Springs Ecosystem Summary (condensed from Knight 1980) Major alterations were observed for some 1 o consumers (catfish and mullet were largely replaced by gizzard shad), presumably due to installation of Rodman Dam in 1968 Whole ecosystem metabolism was little changed after 24 years Mesocosm experiments demonstrated that optimal consumer densities helped to maximize ecosystem metabolism

14 Silver Springs 50-Year Retrospective Study (Munch et al. 2006) SJRWMD and FDEP Funded WSI and UF DFAS: –Repeated Odum and Knight’s whole ecosystem studies –Estimated springshed nitrogen loads

15 Average Monthly Diel Oxygen Changes ( ) Silver Springs Ecosystem Function (WSI 2007)

16 Ecosystem Metabolism Comparison (1952 to 2005) Silver Springs Ecosystem Function Over 50 Years

17 Silver Springs Nitrate-N Concentrations (1955 – 2004)

18 Silver Springs: A 50-Year Restrospective Study Net Ecosystem Productivity vs. Nitrate-N

19 Silver Springs: A 50-Year Retrospective Study Summary of Findings (good news ) The overall structure and function of Silver Springs appears similar to qualitative observations from the 1950’s and 1970’s Discharge continues to be higher than most other first magnitude springs in Florida Water quality essentially unchanged (except nitrate) Total species richness for plants, birds, fish, and reptiles are similar to historic records Rates of ecosystem productivity are still high compared to most aquatic and terrestrial ecosystems

20 Silver Springs: A 50-Year Retrospective Study Summary of Findings (bad news  ) Flow has decreased by about 20% NO 3 -N has increased by 176% Water clarity has decreased Nighttime dissolved oxygen has declined by about 19% Total plant and algal biomass increased by 88% Ecosystem productivity declined by 27% Insect productivity declined by 72% Fish biomass declined by 96%

21 Wekiva River and Rock Springs Run PLRG Analysis (Mattson et a. 2006) Corroborative Ecosystem-Level Findings (Wekiva, Rock, Alexander, Juniper Springs)

22 Multiple Spring Stressors Nutrient Increases Declining Discharge Other Stressors –Exotic plant and animal invasion and control –Recreational use –Sedimentation from upland development –Downstream water management Florida Springs: Ecosystem Studies

23 Synthesis of Recent Studies (cont.) Flora and Fauna –Benthic and attached algae populations are increasing, especially in the vicinity of spring boils –Macroinvertebrate productivity may be reduced –Fish populations have declined in the Silver River, possibly due in part to decreased NPP and other causes (Rodman Dam?) Florida Springs: Ecosystem Studies

24 Synthesis of Recent Studies (cont.) Ecosystem-Level Functions –Gross primary productivity is reduced –Community respiration shows little change –Net primary productivity is reduced –Ecological efficiency is reduced Florida Springs: Ecosystem Studies

25 Synthesis of Recent Studies (cont.) Problem: –It appears counter-intuitive that increased nitrate concentrations in springs lead to reduced plant productivity (gross and net) in spite of higher plant biomass (increased benthic and attached algae) Florida Springs: Ecosystem Studies

26 Synthesis of Recent Studies (cont.) Hypothesis: –Possible explanation is that spring systems are highly adapted to pre- development nutrient levels and have already maximized ecological efficiency –Increased nitrate concentrations, in concert with other structural changes such as loss of key consumers, leads to the opportunity for increased growth of “weedy” algal species Florida Springs: Ecosystem Studies

27 Synthesis of Recent Studies (cont.) Hypothesis: –“Weedy” algae are not as palatable to consumers and cover adapted aufwuchs species, shading them and reducing their populations –Although overall plant biomass increases due to reduced grazing, productivity declines due to dominance of less efficient “weedy” species But, this hypothesis does not fit all observed data??? Florida Springs: Ecosystem Studies

28 Key Ecosystem-Level Spring Research Needs Comparisons of Control and Affected Springs: –Define the range of normal and altered ecosystem metabolism in springs over a wide range of nutrient conditions, including upstream/downstream studies along nutrient gradients –Define the trophic-level biomass pyramids and energy flows in these reference spring systems Effects of Nutrients in Springs

29 Key Ecosystem-Level Spring Research Needs (cont.) Controlled Ecosystem-Level Studies: –Mesocosm studies in situ to determine the effects of nutrient levels on key primary producers and effects of consumers on various natural and “weedy” benthic and periphytic algal assemblages –Interactive effects of multiple stressors on springs ecology – nutrients, flow reductions, aquatic plant control, recreation, etc. Effects of Nutrients in Springs

30 Florida’s Springs “A long history of permanency is no guarantee of a future…” Howard T. Odum (1957)

31 Ecosystem-Level Effects – Chapter Outline Springs as Ecosystems –Springs Ecosystem Model –Environmental Forcing Functions –Energy Storages/Structure –Ecosystem-Level Processes Effects of Nutrients on Spring Ecosystems –Primary Producers –Community Metabolism –Community Structure –System Export –Human and Aesthetic Additional Research Needs and Questions Literature Cited

32 Silver Springs Ecosystem Structure (Odum et al. 1998)

33 Silver Springs Ecosystem Model (Odum et al. 1998)

34 Spring Ecosystems

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