Kill the Weeds, Not the Fish!

Transcription

1 Kill the Weeds, Not the Fish! Dr. Chuck Cichra University of Florida / IFAS School of Forest Resources & Conservation Program in Fisheries & Aquatic Sciences

2 My goal is for you to have a better understanding of: How water bodies function and How and why fish kills occur (Use this info in weed management)

3 All Plants Need Water, Light, and Nutrients

4 Aquatic Plants are No Different Algae Macrophytes

5 New Ponds are Clean Clear Water Few Algae / Plants

6 Over Time Ponds Become More Fertile, Plants Become More Abundant Green Water (Algae) Lots of Plants Eutrophication = Enrichment ( increased nutrients P and N ) of a water body

7 Where Do the Nutrients Come From????

8 Natural Phosphate Deposits Well Water: Often Full of Phosphorus

9 Stormwater Ponds are Built to Catch Storm Runoff / Nutrients (P and N) Lawn fertilizers, leaves, sticks, grass clippings,

10 Livestock and Other Agriculture Human Waste

11 Nutrients = Plants Macrophytes ( large plants ) Algae ( phytoplankton )

12 Fertilization Purposeful Addition of Nutrients to the Water

13 Blocknet Total Fish (kg/ha) Fish blocknet data on 60 Florida lakes Oligotrophic Mesotrophic Eutrophic Hypereutrophic Trophic State (chlorophyll)

14 So if nutrients (N and P) don t kill fish, then what causes fish kills?

15 A lot of People Believe that Toxins (Pesticides) Cause Most Fish Kills

16 Aquatic Herbicide Toxicity (ppm) Expected application rate Bluegill 96-hr LC-50 Copper low alkalinity Endothall alkylamine salt Copper high alkalinity ,4-D Diquat Endothall dipotassium salt Fluridone Carfentrizone >1000 Glyphosate NA >1000 Imazapyr NA >1000

17 Humans Can Directly Cause Fish Kills However, Most Fish Kills are Natural Generally due to Low Dissolved Oxygen in the Water

18 It s Important to Understand the Dynamics of Oxygen in Water

19 Why? To Prevent Fish Kills The last thing that applicators and homeowners/public want to see!

20 So how much oxygen is enough for fish? 210,000 ppm of oxygen in the air that we breathe!

21 Sources of Oxygen: Diffusion ( Agitation ) Photosynthesis

22 Diffusion of Oxygen Into Water

23 Response of Fish to Low Oxygen

24 Agitation Speeds up Diffusion of Oxygen into Water

25 Man-Made Agitation = Aerators Natural Agitation = Waves

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29 Fish / Aquatic Life Can Die!!! (during cloudy periods) Why? Especially, if the water is hot!

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31 Sometimes, Plants (Algae) Die! Then, No Oxygen Production, but Oxygen is Consumed by Decaying Plant Material

32 Effects of Submersed Plants on the Vertical Distribution of Oxygen in the Water Column Stratification can also affect the distribution of herbicides in the water column.

33 Floating Plants Can Block Sunlight => Little or No Photosynthesis

34 What about deep lakes?

35 Density Differences due to Water Temperature Differences - Prevent Mixing Warmer Less Dense Colder More Dense

36 Cross-sections of Deep and Shallow Lakes Bad Water: High H 2 S, Low Dissolved Oxygen, High CO 2, High BOD

37 Summer Thunderstorm! Pond turnover water is turbid

38 So, How do we use this Information in Aquatic Plant Management?

39 Algae - Should We Spray? How Much? -- Watch the Weather! Education If you kill the plants, the nutrients are still there!

40 Submersed Plants Spray Portion of Plants, Herbicide Selection, Time of Year, Aerate -- Weather

41 Floating Plants - Use of Herbicides: Partial Treatments, Herbicide Selection, Weather Bite the Bullet and Spray?

42 Floating Plants Grass Carp: Aerate & Use Herbicides to Improve Efficacy

43 Aeration can break up algae blooms (i.e., Homogenize the lake) Can bring nutrients to the surface increase algae blooms

44 Aeration can be used to destratify a pond - Be Careful When you Start! Shallower ponds are more forgiving

45 Shift between large plants and phytoplankton (algae) be careful! Herbicides Grass Carp Nutrients still in the pond!

46 Effects of Drought? No Water: No Fish! ( Fish stir up bottom sediments and water is hot )

47 For more information: UF/IFAS Extension Circulars

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