YuZe (Tony) Yang; Artem Buryak; Runze He; Haonan Li
Even though more than 71% of the earth’s surface area is covered in water, 97% of them are found in the earth’s oceans. While that seems to be plenty, saltwater can almost never be used for consumption, cultivation of crops, and most industrial uses. The process of desalination is very energy-intensive and inefficient, which makes the rest 3% of the freshwater resources all the more valuable to the world’s ever-growing human population.
Since 1524 when Giovanni da Verrazano, the first European discovered the New York Harbor, the Hudson River was always an essential harbor for the New Amsterdam settlement, present-day New York City. Nowadays, the primary drinking water for the city is from the upper Hudson River, where the Croton, the combined Catskill, and the Delaware watershed are located.
The state of New York has more than 7600 freshwater sources, as well as portions of two of the five North American Great Lakes and over 70,000 miles of rivers and streams. Beyond being our critical supplies of drinking water, they also provide flood control, recreation, tourism, agriculture, fishing, power generation, and manufacturing. Natural water systems are also an important factor in the local climate, humidity, temperature, and rainfall, as well as providing critical habitats for aquatic plants, fish, reptiles, birds, and mammals.
Species diversity is an important aspect of the water system; it helps maintain the food chain, working closely with all other ecosystems on the earth. The study of how such organisms interact with each other and with their environment is called Aquatic Ecology. One interesting of such is that organisms are not solely benefactors of their environment, instead, they contribute to the maintenance and sustainability of their environment as well, creating near equilibriums that can continuously sustain life.
One such example is that almost all aquatic plants, from water lilies to algae, are able to clean water by filtering out minerals, ammonia, nitrates, and nitrites, as well as converting carbon dioxide into oxygen, which aerates the water and sustains life for other organisms. Furthermore, the produced oxygen allows aerobic bacteria to break down organic contaminants, as well as nitrogen and phosphorus in the process.
Living organisms can influence other aspects of their environments. A common example is that beaver dams can change the flow of water, in turn, they provide habitat for many other organisms, as well as control floods by slowing the movement of water. Similarly, it is also the case with a prime example of an invasive plant species of the Hudson River Region: the European horned water chestnut, or Trapa natans, a species introduced to the region in the 1800s.
Invasive species, like their name suggests, are species from other parts of the world that have been accidentally introduced to a region away from their native habitats. Quite often due to a lack of natural predators, parasites, or diseases, these species often flourish and reproduce at an amazing pace, often at the expense of native species. There are many types of aquatic invasive species, from plants, algae, to fish, reptiles, fungi, and bacteria. And for the scope of this essay, we will explore invasive species introduced to the Hudson River region due to human intervention, their impact on the native habitat, and the methods to halt or counteract their spread or influences.
In its native habitat across the ocean, the European horned water chestnut is kept in check by native insect parasites. However, as these parasites are not found in Native America, the plant reproduces rapidly without its natural predator and colonizes freshwater lakes, forming impenetrable floating mats of vegetation. Not only they are a danger for boaters and swimmers, they also block much of the light from the surface, killing native plants beneath the surface. As an annual plant, the thick layers of water chestnut that die each year decompose, leading to a reduced level of oxygen inside the surrounding water; that combined with a lack of other aquatic plants, can potentially kill fish and other organisms.
There have been several ongoing approaches in an effort to halt the infestations of the European water chestnut in the Hudson River area, and they can mainly be classified into mechanical, chemical, biological methods. If they are reported and dealt with in time, small-scale infestations can be cleaned up by hand pulling from canoes or kayaks, and due to the annual nature of the plant, this method can be effective as long as seed formation is prevented.
For large-scale infestations, the clean-up process may have to involve mechanical harvesters or chemical methods such as aquatic herbicides, and ideally before the fruits ripen, forming a bank of seeds as they dropped to the bottom of the water. If the clean-up happens too late, repeated annual cleaning is required for five to twelve years to ensure complete eradication, which is extremely expensive; and that is given that no plants float off-site and spread elsewhere during the clean-up process.
Alternatively, chemical methods can be employed, however with numeral limitations and downsides, and are used only as a last resort. Some of such downsides include public perception of using chemicals on public waters, as well as herbicides’ tendency to also affect non-target species. As a result, there are state regulations in place to regulate the use of chemical herbicides, though some aspects of these regulations are debated. According to the 2015 Aquatic Invasive Species Management Plan published by the New York State Department of Environmental Conservation, on an aquatic herbicide 2,4-D, one that has been tested to be non-adverse on non-target species, that “6 NYCRR § 327.6(c) only allows the aquatic herbicide 2,4-D to be used for… emergent plants having a large part of their leafy growth projecting above or lying flat on the water surface. That regulation would prevent the use of 2,4-D to control a submerged aquatic invasive species, even if it was the most efficacious herbicide available. This and similar regulations should be revised or repealed.”
For large infestations, long-term mechanical and chemical methods are proven to be simply too impractical and economically unsustainable, so new biological agents are being experimented to serve as long-term solutions to water chestnut infestations. One of such biocontrol species being studied is the leaf-beetle Galerucella birmanica, found in the native water chestnut ranges in Eurasia. Conversely, observations of the specials suggested that the leaf beetles may also attack native aquatic species in addition to the water chestnut. The New York State DEC is also funding other “[studies] of the effectiveness of predator insects from water chestnut’s native range,” although the results of these studies have yet to be implemented in the field.
Even though the total costs for managing water chestnut in Hudson River have not been disclosed to the public, one instance that is often cited that forms a nice parallel with Hudson River is the cleanup of Lake Champlain, a joint effort by the States of New York and Vermont. From 1982 through 2011, $9,600,000 has been spent on the control efforts of European water chestnut; while significant reductions in chestnut population have resulted from these efforts, every time the funds were reduced, the species rapidly grow back and even extends into other ranges.
Another prevalent invasive species in the Hudson River Region is the zebra mussels. Native to Eurasia, they were introduced to the Great Lakes by European cargo ships in the 1980s and reached the Hudson River in May 1991. Within a year, zebra mussels became dominant in the freshwater tidal region of Hudson River, constituting more than half of heterotrophic biomass, and they filter a volume of water equal to the entirety of Hudson River every 1-4 days during summer. As a result of the rapid increase in number, phytoplankton biomass fell by 80%, and zooplankton numbers fell by 70%, according to the Cary Institute of Ecosystem Studies. The ramifications of the zebra mussels’ rapid growth were that due to the loss of their planktonic food, native suspension feeders declined, such as the native pearly mussels, which previously numbered at one billion, went on the verge of disappearing entirely from the river. A study by the New York State DEC shows that the zebra mussel invasion greatly impacted the local ecological landscape up and down the food chain; for example, large changes were done to the local fish population, open-water fish such as shad and herring population suffered, while littoral fish such as sunfish prospered. Consequently, the zebra mussels’ invasion was noted as “one of the largest changes that humans have caused to the Hudson.”
In contrast to the previously explored case of water chestnut infestation, the zebra mussel population has been in a gradual decline for more than twenty years, all without human-induced biological or chemical intervention. Since the 2000s, the population of native mussels, previously falling by 20 to 60 percent each year, has stabilized and even began to increase; the numbers of crustaceans, worms, and other small invertebrates even came back to nearly pre-invasion levels. While billions of them still live in the river, their survival rates are now less than one percent compared to the 1990s. There are several explanations of this decline; one of which is the competitive adaptation from native mussels, and perhaps more importantly, native blue crabs who have adapted to feed more on zebra mussels, according to the Cary Institute.
The long terms effects of the two cases of invasive species in the Hudson River region outlined previously are similar in many ways, and different in others. One species has developed into an expensive nightmare for almost two hundred years, the other’s numbers started to diminish only twenty years after their introduction to the Hudson ecosystem. Nevertheless, they both negatively impact the well-being of native species inside their habitat and are both extremely difficult and costly to remove. According to the New York State Invasive Species Comprehensive Management Plan, the best approach is to prevent invasive species in the first place. In the case of the water chestnut, due to the severity of its impact, the plant has been prohibited to be sold or transported through state borders, and campaigns have been launched to better engage and inform the public regarding the dangers of human-introduced invasive species, and platforms such as Imapinvasives have been set up for the public to report sightings of these species. To quote a featured Audubon Society Staff in the NY State ISCM Plan: “Prevention is always the goal, but when an invasion has occurred, early detection and rapid response are ideal.”
Citation:
https://usa.hudsonreed.com/info/blog/new-york-city-gets-water/
https://response.restoration.noaa.gov/about/media/report-reveals-hudson-river-and-wildlife-have-suffered-decades-extensive-chemical-contam
https://www.researchgate.net/publication/343797515_River_Bank_Erosion_and_Environmental_Degradation
https://www.dec.ny.gov/lands/5104.html
https://www.sciencedirect.com/topics/earth-and-planetary-sciences/freshwater-ecosystem
https://www.ehow.com/info_7931670_aquatic-plants-clean-water.html
https://sustainability-innovation.asu.edu/news/archive/11515-2/
https://www.invasivespeciesinfo.gov/aquatic
http://nyis.info/invasive_species/water-chestnut/
https://www.humanesociety.org/resources/what-do-about-beavers
https://www.dec.ny.gov/docs/fish_marine_pdf/nysaisplan15.pdf
https://www.dec.ny.gov/lands/95817.html
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https://www.dec.ny.gov/docs/lands_forests_pdf/iscmpfinal.pdf
https://www.caryinstitute.org/news-insights/feature/zebra-mussels-losing-their-grip-hudson-river-ecosystem-rebounding
