Last September, two invasive aquatic plants, water lettuce (Pistia stratiotes) and water hyacinth (Eichhornia crassipes), were discovered in the Lehigh Canal in Bethlehem PA. Both species are floating plants, like duckweeds but much larger, and they often grow in dense mats in tropical and subtropical regions. Although this was the first confirmed occurrence in natural habitat within Pennsylvania, both species are sensitive to freezing temperatures so they have not not been regarded as major threats in the Northeast. A description of the discovery of these populations and some background on the species, including a discussion of recent work suggesting that the overwintering potential may be greater than previously thought, can be found in my post from last year (New invaders in the Lehigh Valley? Or Just Summer Visitors?).
The discovery last year prompted several questions. In particular, are these populations really persisting from year-to-year and therefore surviving freezing temperatures? I suspected that they were introduced last summer from someone’s pond and that they would not survive the winter. However, the winter was mild and the recent discovery of some overwintering populations in the lower Great Lakes gave me pause. I road my bike along the canal towpath last week to have a look.
I was wrong. Both species have overwintered. A harbinger of things to come? Below are some pictures, and I’ll update this post with more later in the summer.
13 Jan 2017
After arriving in Bogota late last night, I awoke to sunshine and the sounds of traffic this morning. In addition to myself and Jaime Escobar, our crew includes Mark Brenner and Jason Curtis from the University Florida, who are here to collect lake-sediment cores from high-elevation lakes in the paramo. After a breakfast of eggs, fresh fruit, and good coffee we took a taxi across Bogota to a place where we could store the lake coring equipment, as we won’t need it until next week.
My first impression of Bogota was that driving in this city of 9 million people is a
terrifying thrilling experience. Although lanes may or may not be marked, any lane delineation is clearly just a suggestion. Vehicles seem to drive wherever they please, weaving in and out of traffic while motorcycles (and there are a lot of them) drive between the cars and trucks. The roads twisted and turned and I felt like we were driving in circles at times, even when we weren’t navigating the traffic-merging madness of a roundabout. Jugglers and dancers performed at some of the stoplights, and I couldn’t help but admire them for their bravery, as pedestrians do not appear to have the right-of-way. The one piece of advice I received before coming to Colombia was not to drive, and this was definitely excellent advice.
In the early afternoon we flew from Bogota west to Manizales, which is a city of about 400,000 people. The view of the Colombian landscape was fantastic, with mountains covered in coffee and plantains. Coffee is planted even on the very steep slopes. The flight was a bit bumpy as we dropped into Manizales, and I was glad that I only had a muffin for lunch.
Our hotel was just outside the city and was very nice with beautiful gardens, wetlands, and a fenced area with several ostriches and a deer. The hotel property backed up against a nature reserve, and the diversity of rain forest vegetation and birds was impressive. I wished I had been able to fit my binoculars into my luggage! It was fun to see a number of floating plants and floating-leaved plants that my EES-386 students will soon know, including abundant Azolla, Salvinia, water hyacinth (Eichhornia crassipes), and water lilies (Nymphaea sp.). Some pictures of the hotel ground are below.
We then drove into Manizales to meet with scientists in the Departamento de Ciencias Geológicas at the University of Caldas. We had a tour of their labs and facilities, and discussed our plans for exploration of the paramo tomorrow. Several of the geologists will join us in the field.
Back in June an alligator was found in the Lehigh Canal. Apparently it wasn’t the first one found in the broader Lehigh Valley.
But perhaps just as surprising are a couple of potentially new plant arrivals. Or are they just summer visitors? Last week I noticed sizable populations of two aquatic plant species, water lettuce (Pistia stratiotes) and water hyacinth (Eichhornia crassipes), in the canal at Sand Island in Bethlehem. Both of these species float unattached on the water surface, like the more common duckweeds, and they often grow in dense mats that make fishing and boating difficult, crowd out other plant species, and alter water chemistry and light penetration. To my knowledge, neither species is confirmed to occur naturalized in Pennsylvania but it is not uncommon to see them cultivated in backyard ponds (USDA Plants: water hyacinth, water lettuce).
The populations of water lettuce and water hyacinth in the Lehigh Canal consist of scattered colonies extending from about the Hill-to-Hill Bridge (Route 378) east past the New Street Bridge (Fahy Bridge), to about the point where the Sand Island Trail meets the towpath (D&L Trail). The total distance is about a half mile. The water lettuce appears to cover a slightly greater distance than the water hyacinth, and the plants are generally smaller in height as you head east (downstream) from the Main Street Bridge.
Water lettuce and water hyacinth are tropical or subtropical in origin. The two species have dramatically expanded their range in warmer regions in recent years, where they have cause considerable ecological and recreational impacts. However, given that both species are sensitive to freezing temperatures, they have not not been regarded as major threats in the Northeast. However, some uncertainty about this assumption has emerged in the last several years. For example, a few years ago populations were found in the lower Great Lakes (Adebayo et al. 2010), and resurveys found both species in three subsequent years (Maclsaac et al. 2016), raising concerns about the potential for the establishment of persistent populations in more northerly locations. Although freezing typically kills individuals of both species they can produce seeds that survive cold temperatures; in fact, water lettuce seeds can still be viable after a few weeks in solid ice (Pieterse et al. 1981). Maclsaac et al. (2016) suggested that the two species likely persist in the lower Great Lakes due to annual reintroductions by humans (both species are sold for ponds/aquariums), but also noted that at least in the case of water hyacinth, seasonal regeneration from viable seeds may be occurring.
For background, the Lehigh Canal was built in 1827 to transport anthracite coal from the upper Lehigh Valley, and it remained in operation until the early 1940s. Heavy transportation and industrial activity along the canal and river corridor, as well the development of the surrounding Allentown-Bethlehem-Easton region led to numerous environmental problems, including pollution, habitat degradation, the spread of invasive species, and eutrophication of the canal. However, the towpath along the canal is now a natural-area corridor and the old towpath is a great place to bike, run, hike, fish, bird, and observe nature from within the urban and suburban matrix of the Lehigh Valley. Near Sand Island in Bethlehem, the canal itself gets pretty green by mid-summer, as the slow-moving water warms and algae proliferate. Invasive eurasian water milfoil (Myriophyllum spicatum) and curly-leaf pondweed (Potamogeton crispus) are common submerged plants within the canal, and provide a favorable substrate for filamentous algae. The habitat is ideal for water lettuce and water hyacinth, except for the fact that it freezes in the winter.
Have these species been in the canal in previous summers? Are these populations persisting, or did this expansion occur just this year? Perhaps the two species came into the canal with the pet alligator 🙂 Although this was the first time I noticed the two floating species, I don’t frequent this particular area of the towpath often. Will they reemerge next summer? Are they producing viable seed? Lots of questions, and certainly something to watch. The observations have been submitted to iMap Invasives, a database of invasive species.
Of course, floating plants are also very good at moving. Maybe not as fast as an alligator, but fast enough for me to watch a cluster of water lettuce floating down the canal. Perhaps on its way to Easton?
Adebayo, A., E. Briski, O. Kalaci, M. Hernandez, S. Ghabooli, B. Beric, F. Chan, A. Zhan, E. Fifield, T. Leadley, and H. MacIsaac. 2011. Water hyacinth (Eichhornia crassipes) and water lettuce (Pistia stratiotes) in the Great Lakes: playing with fire? Aquatic Invasions 6: 91-96. DOI 10.3391/ai.2011.6.1.11.
MacIsaac, H.J., A.P. Eyraud, B. Beric, and S. Ghabooli. 2016. Can tropical macrophytes establish in the Laurentian Great Lakes? Hydrobiologia 767: 165-174. doi:10.1007/s10750-015-2491-y
Pieterse, A. H., L. Delange, and L. Verhagen. 1981. A study on certain aspects of seed germination and growth of Pistia stratiotes L., Acta Botanica Neerlandica 30: 47–57. doi:10.1111/j.1438-8677.1981.tb00386.x
The Pymatuning Wetlanders visited Presque Isle today, where we observed coastal processes and successional change. After a stop at the Tom Ridge Environmental Center, explored the peninsula to observe coastal wetlands and processes. This included a hike out to Gull point, located at the tip of the peninsula, to observe the youngest landscape and wetlands. We did some wading in Lake Erie to cool off, had lunch on the beach, on our way home we stopped for the long-promised ice cream. A fun day before tomorrow’s final exam.
The Pymatuning wetlanders learned about the role of wetlands in the broader earth system this morning, with a focus on biogeochemical cycles and climate change. This was followed by a quick overview of federal laws that protect wetlands, particularly the history and controversy surrounding the Clean Water Act.
We headed to Hartstown Swamp in the late morning, where the students were tasked with conducting an actual wetland delineation along a transect from the swamp to the upland. They received little to no help from me, and had to self organize, determine what data to collect, and then carry it out. They did a fantastic job, and integrating and applying their knowledge of wetland plants and soils. They have come a long way; in fact, just a couple weeks ago most of them struggled to provide a definition for the term “wetland.” Their data from along the transect was used to construct the diagram below, and we will discuss these results in the morning.