Production and growth rates of Egeria densa in the Sacramento-San Joaquin Delta, California

1. Production and growth rates of Egeria densa in the Sacramento-San Joaquin Delta, California Toni G. Pennington & Mark D. Sytsma Center for Lakes & Reservoirs Portland State University Portland, Oregon APMS 2005, San Antonio, Texas

2. Models of growth & production • Important to know conditions that favor/limit growth of nuisance aquatic plants under variable climates • Light availability, temperature, nutrients, water velocity, alkalinity • Better inform management decisions • Herbicide application time, herbivore requirements • To predict effects of changing plant assemblages on water quality and vice versa • Restoration, changes in turbidity APMS 2005, San Antonio, Texas

3. Submersed macrophyte Dioecious Reproduces by fragmentation Introduced through aquarium trade Widely naturalized (Japan, New Zealand, Australia, Denmark, Germany, France, Chile) Impedes recreation & navigation Alters pH and temperature Controlled by herbicides and mechanical means Egeria densa (Brazilian elodea) APMS 2005, San Antonio, Texas

4. E. densa distribution in US www. plants.usda.gov APMS 2005, San Antonio, Texas

5. www. ucce.ucdavis.edu APMS 2005, San Antonio, Texas

6. Purpose • To describe seasonal phenological responses of Egeria growing in Western waterways to improve management efforts • Accomplished by determining seasonal changes in: • nitrogen allocation • rates of photosynthesis & growth APMS 2005, San Antonio, Texas

7. Hypotheses • Egeria exhibits changes in nitrogen allocation between plant parts and seasons • There are seasonal differences in maximum photosynthetic rate, light saturation, and growth rates of Egeria APMS 2005, San Antonio, Texas

8. Methods & results overview • Study site • Seasonal nitrogen allocation • Photosynthetic response • Maximum photosynthetic rate (Pmax) • Photosynthetic efficiency • Light saturation levels • Growth rate APMS 2005, San Antonio, Texas

9. Methods - study site • Sacramento-San Joaquin Delta, CA (Disappointment Slough) • Upper San Francisco Bay • 700 mi. of channels and sloughs • California Bay-Delta Restoration Project Ray Sterner, John Hopkins Univ. APMS 2005, San Antonio, Texas

10. Methods – nitrogen allocation • Plants collected monthly Dec 2003 to June 2005 • Separated into: • Tips (upper 3 cm) • Lower stems (1st 15 cm from root crown) • Root crowns • Roots • Dried at 70ºC and ground • Analyzed on CHN elemental analyzer APMS 2005, San Antonio, Texas

11. Results - nitrogen allocation • In tips: highest in winter ( 5.5%) and lowest in late summer (3.5%) • Lower stems: 2.7% • Root crowns: 3.6% • Roots: 2.7% APMS 2005, San Antonio, Texas

12. Methods – production rate • Monthly from Dec 2003 to June 2005 bet. 10 am and 2 pm • Incubated 15 cm tips in 300 ml BOD bottles in shipboard circulating water bath • Five light levels: 0 to 100% of surface irradiance • Measured DO, pH, and DIC to model Pmax, photosynthetic efficiency and light saturation APMS 2005, San Antonio, Texas

13. Photosynthesis versus Irradiance (P vs I) curves Pmax Light saturation (I sat) Michaelis – Menten P = (Pmax * I) Ik + I Photosynthetic efficiency APMS 2005, San Antonio, Texas

14. Same Pmax • Different saturation APMS 2005, San Antonio, Texas

15. Results – production rates • For some months, maximum production rates were not achieved • Why? Low ambient light APMS 2005, San Antonio, Texas

16. Results – Photosynthetic efficiency (-) surface irradiance (+) %N in upper stems APMS 2005, San Antonio, Texas

17. Results – monthly Pmax • Where maximum photosynthetic rate was observed, model and observed mean Pmax in close agreement • Positive but weak relationship between Pmax and temperature (p = 0.06) APMS 2005, San Antonio, Texas

18. Results - light saturation • Light saturation for Egeria ranged from 130 to 690 µE m-2 s-1 and averaged 400 µE m-2 s-1 • Low saturation levels positively associated with increased N content APMS 2005, San Antonio, Texas

19. Methods – seasonal growth rate • ~20 plants tagged on six occasions • Measured for tip, stem and branch/bud growth • Potted in Delta sediment and allowed to grow ~ three weeks in situ APMS 2005, San Antonio, Texas

20. Results – growth rates • Tips: 0.2 to 0.7 cm . d-1 • Stems: 0.02 to 0.3 cm . d-1 • Branch/bud: 0.03 to 0.8 cm . d-1 • Cumulative: 1 cm d-1 April 2005 APMS 2005, San Antonio, Texas

21. Conclusions • Maximum nitrogen content observed in tips during the winter and least in roots compared to all plant parts • Nitrogen content positively associated with photosynthetic efficiency and negatively associated with light saturation • i.e. more nitrogen = more efficient with less light • Maximum photosynthetic rates occurred during the summer, however that relationship to temperature was weak • Maximum growth rate occurred during in April and growth continued through the winter APMS 2005, San Antonio, Texas

22. Egeria under ideal temperature conditions in the Delta No “winter-type” growth form as observed in S. Carolina and Japan Rapid spring growth suggests early season systemic herbicide application Capable of adapting to low light Reduced photosynthetic efficiency with increased light Low light saturation levels during the winter Summary APMS 2005, San Antonio, Texas

23. Acknowledgements California Bay-Delta Authority USDA-APHIS Perry Lake Management Aquatic Ecosystem Restoration Foundation Staff & Students at the Center for Lakes & Reservoirs San Marcos River, Texas 1998 APMS 2005, San Antonio, Texas