The Effects of Leached Phosphorous From Various Plant Species and Implications for the Local Watershed
Alissa Van Epps, Lauren McElroy, and Lexi Krikelas
• Eutrophication is a process whereby lakes and streams receive excess nutrients, causing excessive plant growth and algal blooms. Algal blooms reduce dissolved oxygen in lakes and streams as plant material decomposes, which may in turn result in the death of other ecologically beneficial organisms.
• The most important contributing nutrient is phosphorus (P). P is found in the leaves of trees, and is essential for growth. However, when these leaves fall to the ground, their nutrients (including P) may be leached out and carried into lakes and streams.
• We hypothesized that different species of trees contribute different amounts of P to the watershed, and that these amounts vary depending on specific precipitation patterns.
• We collected 4 gallon-sized bags of 5 different leaf species that were then identified as follows: basswood (Tilia americana), White Pine (Pinus strobus), Autumn Blaze (Acer sachariuum x A. rubrum), Silver Maple, (Acer sachariuum), and Norway Maple (Acer platamoides).
• All leaves were placed in paper bags and set in a drying oven for one week to prevent the growth of mold. The dry leaves were weighed and tested as described below.
Soak Test
• 1,000 milliliters (or 1 liter) of deionized water was combined with 100 grams of each species of leaves in a gallon size jar. Each jar was then covered and allowed to stand for 4 hours.
• Phosphorous levels were then measured using standardized procedures of the PhosVer 3 with Acid Persulfate Digestion Method Hach Test, taking 2 samples for each leaf species to minimize error.
Flush Test
• 500 milliliters (or 0.5 liters) of deionized water was poured over 50 grams of the first species of leaves, and the process was repeated for the remaining 4 species.
• Phosphorous levels were then measured using standardized procedures of the PhosVer 3 with Acid Persulfate Digestion Method Hach Test, taking 2 samples for each leaf species to minimize error.
• Three flush tests were completed within 30 minutes increments, to again minimize error. These results were averaged.
As shown above, the White Pine species leached the least amount of P at 0.075 mg/dry gram of leaf while the Silver Maple species leached the greatest amount of P at 0.221 mg/dry gram of leaf.
As shown below, the White Pine species leached the least average amount of P at 0.005 mg/dry gram of leaf while the Silver Maple species leached the greatest average amount of P at 0.137 mg/dry gram of leaf.
• Possible errors in the soak test include the fact that the leaves sat in water for too long. What this told us was that when leaves sit in puddles of rain, it creates an environment conducive for the excessive and potentially quick release of P from the leaves. This leached P will either become surface runoff that goes directly into the watershed, or will collect by storm and sewer drains.
• In comparing these two tests, our results indicated that one heavy rainfall capable of producing large remaining puddles for leaves to soak in can be more harmful than the results of three smaller rainfalls. More specifically, after leaves were soaked for 4 hours, more P was leached than any of the flush tests results, including the average.
• This leads us to suggest that the public must be more careful where they put their piles of leaves after raking. When the public rake their leaves, they are to be put on the terrace, rather than in the street. This small task could cut back the amount of leached P in the lake in many ways.
• We would also suggest that further research be conducted about the amount of P leached from rainfall to rainfall. As seen in our flush test results, each flush produced different levels of P, that were not necessarily consistent among species or tests.
Check out the following links for further information about:
Love Your Lakes Don't Leaf Them Campaign
Edgewood Wingra Watershed Project
Edgewood Watershed Education Connection (EWEC)
We would like to thank the Edgewood Community, especially Jim Lorman, Suzanne Kercher, & Tim Andrews for their contributions toward our research.