Will a Shift in Algal Composition in. System Help Achieve the CLRMA

Transcription

1 Presented By: Craig Wolf Will a Shift in Algal Composition in Response to the Destratification System Help Achieve the Chlorophyll a Standard? CLRMA Denver, CO November, 2011

2 Where am I going Today! Background In-reservoir management strategy Results What s Next 2

3 Cherry Creek Reservoir Volume ~13,000 acre feet Surface area ~850 acres Mean depth ~ 8.5 feet Max depth ~ 25 feet Eutrophic Polymictic Use Classifications: Aquatic Life Warm 1, Recreation E, Agriculture, Water Supply Recreational State t Park 3

4 Reservoir Destratification System 123 aerators, ~8 miles of hose that covers ~200 acres of the total 850 surface acres Each aerator is adjusted to provide a total rate of flow of ~1.5 ft3/min/ac of air Circulates approximately 440 ac-ft per day of the total 13,000 ac-ft volume Capital Investment $970,000 Installation $26,000 annual maintenance $30,000 annual electric bill First seasonal operation, 2008 Operated the last four years generally from April to November of each year

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7 Nazca Lines of Peru

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9 Primary Objectives of the Destratification tifi ti System Designed to simulate a windy day on the reservoir Vertically mix (destratify) the water column Reduce periods of thermal stratification tifi ti Reduce suitable habitat conditions for cyanobacteria by vertical mixing Reduce scum-forming cyanobacteria (nuisance blooms) 9

10 Primary Objectives of the Destratification tifi ti System Designed to simulate a windy day on the reservoir Vertically mix (destratify) the water column Reduce periods of thermal stratification tifi ti Reduce suitable habitat conditions for cyanobacteria by vertical mixing Reduce scum-forming cyanobacteria (nuisance blooms) Increase dissolved oxygen concentrations in the deepest portions of the reservoir Reduce the release of phosphorus from the bottom sediments into the water column of the reservoir 10

11 Destratification Effectiveness Reduced the number of thermally stratified days from ~60 days to ~20 day (May-Oct) Storm events strongly influence stratification Shifted phytoplankton composition Minimized scum forming cyanobacteria Increased flagellated ll species Cryptomonads, dinoflagellates, and chlorophytes 11

12 Variability in Growing Season Phytoplankton Composition Other Euglenophyta Dinophyta Chrysophyta Cryptophta Bacillariophyta Chlorophyta Cyanophyta 100 Relativ ve Percent To otal Abundan nce Aeration Begins 12

13 Growing Season (Jul-Sep) Phytoplankton Abundance, Phytoplan nkton Abundan nce (cells/ml) Other Euglenophyta Dinophyta Chrysophyta Cryptophta Bacillariophyta Chlorophyta Cyanophyta 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct 13 Nov Dec

14 How Has the Destratification System and the Shift in the Phytoplankton Composition Effected Chlorophyll a? 14

15 Algal Response to Internal Loading 60 Photic 4m 5m 6m 7m Photic Chl Chlorophyll a (µg g/l) 10 SRP < MDL Oct-10 Sep-10 S Aug-10 A Jul-10 Jun-10 May-10 M Apr-10 Mar-10 Feb-10 Jan-10 Dec-09 D Nov-09 0 Oct Photic 4m 5m 6m 7m Photic Chl Oct Sep-11 Aug-11 Jul-11 Jun-11 May-11 Apr-11 Mar-11 Feb-11 Jan-11 Dec-10 0 Nov-10 0 Oct-10 Growing season chlorophyll p y peaks p of 30 to 45 µg/l are associated with flagellated algae that are beneficial b fi i l from f a food web approach Solu uble Reactive Phosp phorus ( g/l) 200 Chlorophyll a (µ µg/l) Soluble e Reactive Phosph horus ( g/l) 200

16 Has the Reservoir Achieved the New Chlorophyll Standard? Chloroph hyll a (µg/l) Historical Chlorophyll a "Goal" or Standard 15 µg/l Compliance Period Chlorophyll a Standard = 18 µg/l Aeration Begins Revised Standard Becomes Effective Growing Season (Jul-Sep) Mean ± 95% CI 16

17 Summary The new reservoir management strategy has been effective at minimizing i i i thermally stratified conditions Enhanced circulation provides more suitable habitat for flagellated species Competitive advantage for resources Reduced habitat for cyanobacteria Effective mixing constantly supplies the photic zone with SRP from internal load Created a stable bio-reactor with optimal growing conditions 17

18 What s Next It s a Good Thing We Took a Feasibility Approach with the new chlorophyll standard (18 µg/l), because for 17 years the beneficial i use approach (15 µg/l) was not achievable Wait for 20 years to see if the new chlorophyll standard (18 µg/l) is feasibly achievable given the current management strategy Destratification management is still in its infancy Ecological Equilibrium Zooplankton and forage fish response to change in food source? Anecdotal evidence that the beneficial uses have been protected, BUT need quantitative proof 18

19 Aquatic Food Web for Cherry Creek Reservoir 19

20 Thank you! Acknowledge g Cherry Creek Basin Water Quality Authority 20