Effects of Chloride Levels on Native
and Invasive Aquatic Plants

 


Myriphyllum spicatum or Eurasian Watermilfoil is an exotic species that was introduced into Lake Wingra in the 1960s

Abstract

Background and Questions

 Hypothesis

Methods

  Results 

Discussion

 Recommendations

Acknowledgements

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Ceratophyllum demersum  or Coontail is a native plant to Lake Wingra

 

                         

Abstract

Road salt (mostly sodium chloride) used as a winter de-icer on streets, sidewalks, and parking lots is known to negatively impact aquatic organisms as the salt is carried into lakes by rains and spring melts. This study compares salt tolerance levels of three species of aquatic plants, Eurasian milfoil (Myriophyllum spicatum), coontail (Ceratophyllum demersum), and lesser duckweed (Lemna minor). The purpose of this experiment was to determine whether the non-native species, M. spicatum, was more resistant to high salt levels than the native species, C. demersum and L. minor. Plants were exposed to a range of salt concentrations (100 mg/L; 500 mg/L; 1,000 mg/L; 5,000 mg/L; and 50,000 mg/L). Plant growth and reproduction were determined by measuring the length of plants and their respective levels of fragmentation. Increased salt levels resulted in a decline of growth and reproduction in C. demersum and L. minor, while levels of growth and reproduction in M. spicatum remained fairly constant at all salt levels. Algal density increased with increasing salt levels, suggesting high concentrations of salt may promote growth of algae at the expense of aquatic macrophytes, thus decreasing water clarity. This study supports other studies which show that road salt use in the Wingra watershed has detrimental impacts on aquatic ecosystems.

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Background and Questions

Text Box: • Road salt that is used as a winter de-icer is eventually carried into Lake Wingra. Studies have shown that increased levels of chloride negatively impact aquatic ecosystems. How do high levels of salt impact vegetation in Lake Wingra? • Myriophyllum spicatum, a non-native and invasive submerged plant, is the dominant submerged plant in Lake Wingra. Is this exotic species more salt resistant than the native species Ceratophyllum demersum (a submerged plant) and Lemna minor (a floating vascular plant)? • Do high salt levels in water influence algal blooms? Back to top

 

 

 


Lake Wingra
http://lakewingra.org/images/lake_watershed/stmarys.jpg
 

 


                    Lemna minor

 

 

 

 

 

 

 

 

 

 

 




Hypothesis

    

 

    

 

 

 

 

 

 

 

 

Text Box: M. spicatum grows better in high salt concentrations than both C. demersum and L. minor   Algal populations are larger in the higher salt concentrations Back to top

 

 

 

 

                                                      Methods

·       Equal-length fragments of C. demersum and M. spicatum were placed in 3 liter jars at four salt levels (0, 100, 500, and 1000 mg/L); fragments were measured at the end of the experiment 
 


 

·       C. demersum and M. spicatum reproduce by fragmentation. The number of fragments “dropped” by each plant was counted.

 

·       Number of algae per ml was determined using two methods:

§     The Palmer equation, which yields the number of algae most commonly found in organically polluted waters per ml

 

 

 

 

 

 

 

§     Counting the number of algae per 0.1 ml and converting to 1 ml

 

·       A separate experiment was set up for L. minor. One-hundred plants, each with four lobes, were placed in 100 ml jars at five salt levels (0, 50, 500, 5000, 50000 mg/L)

 

·       L. minor reproduces by fragmentation. New lobes form at the fronds and from these new fronds can form. We counted the new fronds to determine reproduction rates.

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 Text Box:         (Area of cover slip) x (number of individuals of each genus) (Area of one traverse) x (number of traverses) x (volume under cover slip)   Area of cover slip= 22mm x 22mm= 484 mm2 Diameter of field of 10 x objective lens= .95 mm Area of one traverse= 22 mm x .95 mm Area of traverse= 20.9 mm2

Results


Figure 1
 

The level of fragmentation of C. demersum is much higher in the control jars than in any of the other jars.
 The overall trend is that the level of fragmentation declines as the level of salinity raises. The overall trend for C. demersum is similar to that of L. minor.

 


Figure 2

 

  

 

The level of fragmentation of M. spicatum is low in comparison to the other two species. However, its fragmentation level remained stable. These results suggest that the environment created for M. spicatum in this experiment might not have been the most favorable. However, the plants did not exhibit widely different reactions to increased salinity.

 

 

 

 
C. demersum plants outgrew M. spicatum in the control jars and in the 100 mg/l concentration jars by an average of six times. However, as salt concentrations increased, the length of the fragments dropped dramatically. The results for M. spicatum show that although the plants did not grow as much as C. demersum, the length of the fragments remained constant at all salinity levels. The average lengths of the M. spicatum plants in the control jars are the same for the plants in the 1000 mg/l concentration jars.  


Figure 3


Figure 4

 

 

 

The results of algal density calculations show an opposite trend of that of C. demersum. Algal production was found to increase as salinity levels increased.

 

 
Both methods show a similar trend of algae growth, both of common genera and harmful genera found in organically polluted waters. No algae were detected or analyzed microscopically in the L. minor jars. Because of the size of the water sample (100 ml), most plants died sooner than the other two species. Also, judging by water color, there was no indication of abundant levels of algae developing in the treatments.

 

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Figure 5
 

 

 

 

 

 

 

 

 

 

Discussion
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Filamentous algae on a 500 mg/L jar. December 2006

 

 

 

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Recommendations
 

Text Box: · Overall trend showed that the rate of L. minor’s and C. demersum’s growth dropped dramatically while M. spicatum survived and reproduced at an almost constant rate   · High salinity in water appears to have more negative impact on native species than on invasive species. In this experiment, high chloride concentrations promote conditions that favor the non-native species, and put the native species at a disadvantage.   · Although reproduction rates decline with increasing salt. L. minor plants can tolerate up to 5 g/L · Our data suggests that high salinity concentrations contribute to high algal density. At 1 g/L salt, there were almost 20,000 more individuals than in the controls. Text Box: Finding thresholds of salinity tolerance for other aquatic species that are important sources of nutrients for waterfowl Identifying various species’ tolerance to low levels of oxygen (algal blooms promote oxygen depletion) Determining effects of high salt levels on invertebrates associated with C demersum
 



Water Celery (Vallisneria americana)
http://www.ecy.wa.gov/programs/wq/plants/native/images/watercelery.jpg
 

Coontail (Ceratophyllum demersum)
http://www.aquaticbiologists.com/images/coontail/coontail1.jpg 
 

 

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Acknoledgements

 

Special thanks to professors Suzanne Kercher and Jim Lorman;
and students Carly Garfield and Courtney Ramirez

 

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