Inside The New York Botanical Garden

Testing the Waters

Posted in Science on July 18 2013, by Owen Robinson

A recent graduate from Pelham Memorial High School, Owen Robinson worked as a volunteer Forest Intern at the NYBG in the summer of 2012. He will begin as a freshman at the University of Virginia this fall, where he hopes to continue his pursuit of science research as a part of the Echols Scholar Program.

Norway maple leaf pack
Norway maple leaf pack

Last summer I conducted a project to determine whether or not invasive trees are negatively impacting aquatic macroinvertebrate populations. Aquatic macroinvertebrates are small, invertebrate insects that play essential roles in their ecosystems, acting as an energy bridge between outside plant life and the rest of their aquatic environment. They do this by breaking down tree leaves.

Invasive trees are an established and worsening problem in our region, one that impacts plant biodiversity as well as some mammalian and avian populations. As little research has been dedicated to my particular focus, I wanted to determine whether the leaves from these invasive trees were less beneficial to aquatic macroinvertebrate populations than the leaves of native trees. If this proved the case, there would be reason to work harder against the takeover of invasive plant species.

To test whether or not invasive trees are less conducive to healthy macroinvertebrate populations, I constructed leaf packs that allowed macroinvertebrate colonization when placed in water. The packs mirrored what theoretically occurs in a stream or river when leaves fall into the water; when the leaves are deposited in running water, they tend to group together and form “natural” leaf packs as they encounter obstacles. I constructed four types of leaf packs, each containing 30 grams of leaves from a different tree species. Of the three containing invasive specimens, I chose Tree of Heaven, Norway maple, and knotweed; the fourth native control pack contained equal measures of American beech, red oak, and sweetgum leaves.

While knotweed is not, in fact, a tree, this Japanese shrub forms monocultures in riparian zones, meaning it blocks out the growth of all other plants along the streams or rivers it colonizes. It acts just like a tree in this case because of the similar amounts of leaf litter it puts into these aquatic environments.

Set of leaf packs suspended in the Bronx River
Set of leaf packs sitting in the Bronx River

After putting a total of 13 sets of leaf packs—or 52 packs total—into the Bronx River and letting them sit for three weeks, I analyzed the macroinvertebrate colonization and conducted statistical tests to determine which packs fostered the healthiest populations. In the end, I found that populations were more diverse in the native leaf packs, and at statistically significant levels and with more consistently high yields of macroinvertebrates. In other words, this data strongly suggests that invasive trees are not only impacting land species negatively, but possibly entire aquatic ecosystems.

I have presented my work at the Garden in several science competitions that exhibit research from around the country, and most recently at the Westchester Science and Engineering Fair, where I was awarded the Momentive Performance Materials Innovation Award and fourth place in the Environmental Science category. It’s awesome that this research, which I poured so much hard work and love into, was recognized and received with such high praise. I’m really glad I had the opportunity to intern at The New York Botanical Garden, and look forward to this fall when I attend the University of Virginia through the Echols Scholar program. Once there, I hope I will have similar opportunities for more exciting research.


Sandy Wolkenberg said:

This is a particularly timely, fascinating, and urgent area of study and your thoughtful and creative implementation of the experiment is impressive indeed! Congratulations on the awards you have received for your work and, hopefully it will lead you to continue your involvement and study of the impact of invasives on our aquatic populations and on our environment. Bravo!

Damian said:

Beautiful work, Owen, and worthy of further study and conversation. I spend many hours on the Bronx River and, unfortunately, have to teach words like , “monoculture” , “invasive species” and “Japanese knotweed” to folks who paddle or walk with us. Miles of the river are lined with knotweed, including Giant knotweed, Japanese knotweed and the hybrid of the two that know populates our area. Many urban river issues focus on human inputs, including sewage that enters the river in Westchester and causes lower water quality, and can only be corrected through municipal action. Your study, however, may point the way to a more personal interaction to improve water quality. A macro invertebrate study last year by Alejandro Baladron showed that water quality in the Bronx River improved as the water coursed through the NYBG and that may be the result of efforts to reduce invasives and increase biodiversity. As some aquatic insects themselves actually improve water quality by filtering water ( Caddisfly), providing an appropriate source of food may help with that filtering. While we wait for Westchester to make the necessary changes to reduce illicit connections to the river, maybe a concerted effort to increase biodiversity on the banks of the river from the NYBG to points north could help improve water quality at the local level.Thank you Owen.

Diane Murgalo said:

Well said Sandy. I concur…Bravo! I wish you success with your studies at the University of Virginia – Echols Scholar program and in your future endeavors.

Ray Bucko said:

So what are the concrete results of you findings? Is the garden removing ‘invasive’ species even as I type? NICELY done article. We need brain candy more than eye candy!