Contribution by leaves to Nutrient Levels in Lake Wingra Phosphorus Leaching from Sugar Maple and White Oak Leaves in Standing Water

By: Amanda Oliva, Emilie Reiss, Krista Moses and Trista Kuhl

Background & Questions Hypothesis Methods Results Conclusions & Recommendation

 

Background & Questions
• Phosphorus is a necessary nutrient for the growth of lake organisms, but too much phosphorus can increase the amount of algae in the lake, which is detrimental to the lake’s health.

• Our purpose was to find out how much phosphorus is released from leaves of two common trees in the Lake Wingra Watershed, namely White Oak and Sugar Maple.

 

 

Hypothesis
• We hypothesized that the amount of phosphorus leached from the leaves immersed in water would be low at first, then increase with time until they reached a plateau.

 

Methods
• Collected approximately 440 grams of each type of leaf from trees on the Edgewood College campus and placed them in two separate gallon jars with 3 liters of de-ionized water.

• Performed Hach Phosphorus Test on samples taken at six time intervals: 5 hours, and 1, 3, 7, 14, and 21 days.

• After an initial increase, phosphorus levels decreased, suggesting that bacteria may be consuming some of the phosphorus from the decomposing leaves in the water.
• Therefore, we conducted an additional test in which we boiled the leaves to kill the bacteria and release all remaining phosphorus.

 

 

Results
• Leached phosphorus levels in the Sugar Maple leaves were higher than those of the White Oak leaves (Figure 1).

• Phosphorus levels in the water increased dramatically between 5 hours and 3 days. White Oak levels then decreased and leveled off, while the Sugar Maple levels decreased initially and increased after 15 days.

• Maple leaves initially leached more phosphorus, but Oak leaves actually contained more total phosphorus (including phosphorus that was released after the leaves were boiled) (Figure 2).

 

 

Conclusions & Recommendations
• Our original hypothesis was not supported. While phosphorus levels did increase initially, they then dropped off instead of leveling off.

• A possible explanation for the decrease in phosphorus amounts was that microorganisms were consuming the phosphorus as it was released from the leaves. Boiling the leaves would have released this phosphorus from the bacteria, which is consistent with the results of our last test.

• We found 1.45 mg of phosphorus per 1 gram of dry Oak leaves, and 1.33 mg of phosphorus per gram of dry Maple leaves.

• To prevent increased levels of phosphorus in Lake Wingra, we recommend that:
-Watershed residents properly dispose of their leaves in a timely manner.
- Any leaves in the retention pond on the Edgewood College campus be removed at least every three weeks.

• Factors such as the presence of bacteria populations, water, and temperature can contribute to phosphorus levels and should be taken into account in deciding the frequency of leaf disposal.

 

 

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