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Impact of Urbanization

Grades 9-10 | Argumentative | Source-Based

Source Lexile®: 1210L-1580L

Learning Standards





Prompt: In the early 1800s, there were fewer than one billion people living on the planet. A mere 200 years later, the human population had increased to over seven billion. With this growth in population came a gradual shift toward urbanization, people moving from rural or undeveloped areas to urban city living.


Today, more than half of the Earth’s population lives in towns or cities. Cultivating the land in these places to meet humans’ needs often has a profound impact on the ecosystems and environment.


Read the following sources on the effects of urbanization. Then, write an essay that makes a claim about the extent to which urbanization and human activity impact the environment and biodiversity. Use evidence from the sources to support your claim. Be sure to acknowledge and refute the counterclaim that addresses the other side of the argument.





Source 1

Houston’s Flooding Shows What Happens When You Ignore Science and Let Developers Run Rampant

by Ana Campoy and David Yanofsky

August 29, 2017



Since Houston, Texas was founded nearly two centuries ago, Houstonians have been treating its wetlands as stinky, mosquito-infested blots in need of drainage.


Even after it became a widely accepted scientific fact that wetlands can soak up large amounts of flood water, the city continued to pave over them. The watershed of the White Oak Bayou river, which includes much of northwest Houston, is a case in point. From 1992 to 2010, this area lost more than 70% of its wetlands, according to research by Texas A&M University.


In the false-color satellite images below, plants and other vegetation appear green, while urbanized and developed areas appear blue and purple. Examine the images to see how northwest Houston has changed since 1986.




In recent days, the flooding caused by Hurricane Harvey has raised water levels in some parts of the watershed high enough to completely cover a Cadillac. The vanished wetlands wouldn’t have prevented flooding, but they would have made it less painful, experts say.


The Harvey-wrought devastation is just the latest example of the consequences of Houston’s gung-ho approach to development. The city, the largest in the US with no zoning laws, is a case study in limiting government regulations and favoring growth—often at the expense of the environment. As water swamps many of its neighborhoods, it’s now also a cautionary tale of sidelining science and plain common sense. Given the Trump administration’s assault on environmental protections, it’s one that Americans elsewhere should pay attention to.



A distaste for regulation


Wetland loss is one of the many effects of lax rules. The construction of flood-prone buildings in floodplains is another one: the elderly residents of La Vita Bella, a nursing home in Dickinson, east of Houston, were up to their waists in water before they got rescued. The home is within the Federal Emergency Management Agency’s (FEMA) designated flood zone.


Yet another consequence is that too few people have flood insurance. Although federal rules require certain homeowners to carry it, those rules are based on outdated flood data. Only a little over a quarter of the homes in “high risk” areas in Harris County, where Houston sits, have flood insurance. The share is even lower, 15%, in many other areas that will also no doubt suffer water damage from Harvey.


And that’s before Trump came into office and started removing layers of regulation. Just 10 days before Harvey struck, the president signed an executive order that rescinded federal flood protection standards put in place by his predecessor, Barack Obama. FEMA and the US Housing and Urban Development Department, the two federal agencies that will handle most of the huge pile of cash expected for the rebuilding of Houston, would have been forced to require any rebuilding to conform to new, safer codes. Now, they won’t.


“What’s likely to happen is we’re going to spend tens of billions of dollars rebuilding Houston exactly like it is now, and then wait for the next one,” says Rob Moore, a senior policy analyst on water issues for the Natural Resources Defense Council.


To take another example: Obama had greatly expanded the number of wetlands protected by the Clean Water Act. This federal law requires developers who destroy wetlands to mitigate the ecological effects, for instance by creating new wetlands elsewhere. In February, the Trump administration said it would repeal (paywall) Obama’s decision, meaning a lot more wetlands would lose that protection. (The repeal process is still unfolding.)


Not that Houston has ever been a stickler for federal rules. To get a permit under the Clean Water Act, developers who build in protected wetland areas must submit paperwork showing they’ve completed mitigation measures. In 2015, Texas A&M and non-profit research group HARC analyzed a sample of permits issued from 1990 to 2012 in the greater Houston area. They found that in fewer than half of the cases had the developers submitted complete paperwork, and in two thirds of the cases, there was no documentation that any type of mitigation had happened. Another study by the same two groups looked at a dozen projects that had obtained permits, and found that only two of them had successfully offset wetland destruction, seven were partially successful, and three were complete failures.


And that’s only projects subject to federal regulations. The researchers found that the vast majority of wetland-disrupting activities aren’t subject to those rules. “The inevitable resultant freshwater wetland loss is therefore often uncounted and unmitigated,” they wrote.



Draining the swamp


Largely unobstructed either by rules or by natural features such as mountains, the Houston area sprawled. Between 1992 and 2010 alone, nearly 25,000 acres (about 10,000 hectares) of natural wetland infrastructure was wiped out, the Texas A&M research shows. Most of the losses were in Harris County, where almost 30% of wetlands disappeared.


Altogether, the region lost the ability to handle nearly four billion gallons (15 billion liters) of storm water. That’s equivalent to $600 million worth of floodwater detention capacity, according to the university researchers’ calculations.


To be sure, that’s a drop in the bucket of what Harvey will eventually unleash. The estimate was already at nine trillion gallons a couple of days after the storm made landfall. But saving and restoring wetlands is nonetheless an important part of making Houston more storm resistant, says Mary Edwards, a wetlands specialist at Texas A&M’s AgriLife Extension.


Much of the destroyed wetlands were covered with pavement to accommodate the region’s explosive population growth. So these days, even a run-of-the-mill storm causes water to gush down the streets and can lead to flooding. “We generated a lot of runoff and until now we haven’t been able to keep up,” she said.


It won’t be long before remaining undeveloped places in the Houston area are swallowed up. Take a look at the Brays Bayou watershed in southwestern Houston. The maps below show how the area lost nearly half of its wetlands, shown in purple, as development (the gray areas) expanded. The area has flooded for the past three years in a row.


It’s not just wetlands that are being destroyed. Prairies, which also act as flood water sponges, have been decimated too. Below, maps show the change in the Katy Prairie, west of downtown Houston. By 1996, much of it was gone, but another 10% had been lost by 2010, while the developed acreage grew by 40%, data from HARC shows.




These maps don’t show what has happened over the past seven years. Bill Bass, the HARC geospatial technology expert who put them together for Quartz, says the National Oceanic and Atmospheric Administration (NOAA), which compiles the data he used, hasn’t released its latest installment, for 2015. That’s the result of another example of short sightedness; NOAA, one of the government agencies best equipped to generate information for tracking and responding to climate change, has been underfunded for a while, and Trump has proposed cutting its budget even more.



More people = more storm refugees


Houston has been stuck in a vicious circle. More people means more subdivisions, and more subdivisions means more runoff. That results in more flooding, which ends up affecting more people.


John Jacob, a wetlands expert who runs Texas A&M’s Coastal Watershed Program, has been warning about the dangerous effects of bulldozing natural flood barriers for years. The mission of his program is to share the science with communities to help them better cope with the fact that many of them live not much above sea level in hurricane country. He says he sees signs that Houstonians are finally coming to terms with the need to change their ways.


“The idea that we just don’t care is radically changing,” says Jacob. “The real estate people, to them Houston is a one-night stand. The rest of us want this to be a place where our grandkids are happy and safe… This storm just cements that there’s consequences to the way we’ve done stuff.”





Source 2

An Unfolding Tragedy: Australia's Vulnerable Koala Population Battles Extinction

Updated May 19, 2017


Koalas have inhabited broad regions of Australia for the past 25 million years, but the combined threats of urbanization, climate change, and land clearing are pushing populations in New South Wales and Queensland towards the edge of extinction.


Australia's koala population faces extinction across large parts of New South Wales (NSW) and Queensland as urbanization, land clearing, and climate change threaten the vulnerable species' habitats.


Experts are warning of an "unfolding tragedy" which could see koalas wiped out of regions including the Koala Coast southeast of Brisbane and the Pilliga Forests area in northern NSW.


Populations close to Byron Bay, Ballina, Port Macquarie, and Gunnedah in NSW are also under threat, while koala numbers in regions near Mackay and Toowoomba in Queensland have suffered declines of up to 80 percent.


Koala numbers have diminished in Queensland by a total of 53 percent, according to analysis of the past 20 years and projections of the next two decades.


In NSW, the koala population fell by a total of 26 percent over the same period.


A report released by WWF-Australia to coincide with Endangered Species Day found "habitat loss continues to be the key threatening process to the long-term survival of the koala and is being compounded by numerous other threats."


Koalas have inhabited broad regions of Australia for the past 25 million years. They are currently listed as a vulnerable species in NSW, Queensland, and the Australian Capital Territory.


Hundreds of thousands of koalas were culled for the fur trade after European settlement, a practice which did not cease until the 1930s, while another early threat to the population came from land clearing for agriculture.


Dr. Christine Adams-Hosking, from the Global Change Institute at the University of Queensland, told SBS World News that threats from agriculture have been exacerbated by habitat destruction tied to urbanization, mining, and climate change.


"We're seeing very dramatic declines [in koala numbers] in some areas while in other areas they're still holding on," said Dr. Adams-Hosking, who wrote the WWF-Australia report.


"It's a real tragedy when you think they've been here for tens of millions of years and that within such a short time frame we can be losing them at such a rapid rate.”


"It's just an unfolding tragedy for all wildlife and the koala is a good spokesperson for that. Something needs to be done.”


"It also should be teaching us a lesson that if you look at the koala as the iconic flagship species [in Australia], then what we're doing is very wrong on all levels."


Asked whether localized extinctions will occur among some populations in the future, Dr. Adams-Hosking said: "I don't think there's any doubt of that.”


"If we look at the Koala Coast, which was historically a real stronghold for koalas in southeast Queensland, they declined by 80 percent between 1996 and 2014. That's not a sustainable decline."


The encroachment of urban development on koala habitats has also led to injuries and deaths among koala populations due to increased road traffic and domestic animals.


WWF-Australia said more than 2,000 koalas were taken to wildlife hospitals in southeast Queensland suffering fractures over a 13-year period.


Vehicle collisions and dog attacks caused 93 percent of the fractures, WWF-Australia added, with only 2 percent of the injured koalas surviving their injuries.


WWF-Australia has also released analysis which reveals tree-clearing in southern Queensland likely killed 179 koalas over a two-year period, further pushing the region's koala population towards extinction.


Dr. Martin Taylor, a WWF-Australia conservation scientist, said the koalas would have died after bulldozers destroyed their forest habitats.


"Bulldoze their trees and you kiss the koalas goodbye – they're forced to look for new homes and are then killed by cars or dogs," Dr. Taylor said.


"The only solution is state government action to rein in excessive tree-clearing."


Despite the widespread declines in population numbers, Dr. Adams-Hosking said researchers are cautiously optimistic about the future of some relatively unstudied koala communities.


Koalas have recently been observed in the Southern Highlands and at Campbelltown in western Sydney, where the populations are believed to be stable or even increasing.


But Dr. Adams-Hosking cautioned that only a united approach to saving Australia's koalas will be able to arrest the decline.

"Somehow we have to have enough will from everybody: [from] all levels of government, all levels of communities, and all industries to actually care enough about wildlife.”


"We just need the will from everybody to actually stop and think and plan... [to avoid] the 200-year-old mentality of: 'Let's just go in there and clear [land] and use it as we like'.”


"That's a 200-year-old mentality that has to change before we're going to save our biodiversity."


Source 3

House Sparrow Decline Linked to Air Pollution and Poor Diet

by Frontiers in Ecology and Evolution

October 3, 2017



City sparrows suffer from more stress than their country cousins, find Spanish researchers, especially during breeding season.


Despite being well-adapted to urban life, house sparrow numbers are falling. A study in open-access journal Frontiers in Ecology and Evolution finds that, compared to sparrows living in the country, urban-dwelling birds show clear signs of stress linked to the toxic effects of air pollution and an unhealthy diet. This could have health implications for people living in cities.

"We find that house sparrows living in the city are suffering from more stress than those living in the countryside, and we link this to differences in air quality and diet," says Amparo Herrera-Dueñas, who completed this work in collaboration with the Department of Zoology and Physical Anthropology at the Complutense University of Madrid, Spain.


"It is particularly bad for urban birds during the breeding season when they are torn between allocating resources towards fighting the toxic effects of pollution or towards laying healthy eggs, both of which aren't helped by their poor diet."


She adds, "If our cities are unhealthy for birds, which is what our study is suggesting, then as their neighbors, we should be concerned, because we are exposed to the same environmental stressors as house sparrows."



Stress measured in urban, suburban, and rural sparrows


Herrera-Dueñas and her colleagues used a non-invasive method to sample the blood of hundreds of sparrows from rural, suburban, and urban areas around the Iberian Peninsula in Spain.


"We took a small blood sample from each bird, according to its weight and physical condition, and released them unharmed," she explains. The samples were analyzed for signs of oxidative stress, which can be used to measure how much an environmental stressor, such as pollution, is weakening the bird's natural defenses.



Urban sparrows show higher levels of free radical damage


"Air pollutants or an unhealthy diet can promote the formation of free radicals. These molecules are the by-product of a normal functioning body, so our cells have developed a mechanism to counteract them. However, under demanding conditions, the production of free radicals can overwhelm these antioxidant defenses, causing oxidative stress. When this happens, free radicals can accelerate the aging of cells. In humans, this has been linked to respiratory diseases, such as asthma, as well as cardiovascular disorders and cancer," says Herrera-Dueñas.


The researchers found that urban sparrows suffered higher levels of free radical damage in comparison to rural birds. In addition, the blood samples revealed that city-dwelling sparrows were trying to fight off these damaging molecules, but, in comparison to their rural counterparts, their natural defenses had a lower capacity to do so.


Need to improve urban environment


"We need to work hard to improve the quality of the urban environment, for example, air quality and the design of green areas. Even the leftovers that we throw in the bin at the park should encourage us to reflect on ourselves: more nuts and fruit and fewer chips and cookies would be better for humans as well as for birds," Herrera-Dueñas advises.


She adds, "During this project, I observed that the breeding season is particularly challenging for adult house sparrows, but unfortunately, I do not have information on how their offspring are coping. I hope to investigate how the stresses of urban life at an early age influence the condition of these birds as they reach adulthood."


Source 4

Effects of Urbanization on Stream Ecosystems



Urban Development Results in Multiple Stressors That Can Degrade Aquatic Ecosystems by Altering the Hydrology, Habitat, and Chemistry of Streams





Results of the USGS investigation of the Effects of Urbanization on Stream Ecosystems (EUSE) found that no single environmental factor was universally important in explaining why the health of streams decline as levels of urban development increase. Across all nine metropolitan study areas, changes in the condition of the aquatic biological communities from urban development were related in varying degrees to alterations in stream hydrology, habitat, and chemistry. Even within a single study area, the three biological communities that we surveyed—algal, fish, and invertebrate—responded differently to urban development and altered environmental factors. A primary reason that the responses are different between the algal, invertebrate, and fish communities is that they have different life cycles and requirements for food, shelter, and reproduction; consequently, their responses typically vary with stressors that arise from urban-related changes in stream hydrology, habitat, and water chemistry.



Hydrology—Urban Development Leads to Increased Variability in Streamflow





Urban development typically increases the amount of water entering a stream after a storm and decreases the time that it takes for the water to travel over altered land surfaces before entering the stream. Efforts to reduce flooding by draining water quickly from roads and parking lots can result in increased amounts of water reaching a stream within a short period of time, which can lead to stream flashiness and altered stream channels. Additionally, rapid runoff reduces the amount of water available to infiltrate the soil and recharge the aquifers, which often results in lower sustained streamflows, especially during summer. Furthermore, when the hydrology of a stream is altered, the physical habitat of a stream often becomes degraded from channel erosion or lower summer flows that reduce spawning, feeding, and living spaces of the aquatic biota.



Habitat—Urban Development Can Alter Stream Channels



Urban development can result in alterations to stream habitat either directly, such as from modifications to channel and riparian areas (left), or indirectly, such as from higher streamflows that reshape the channel (right).


Stream habitats can be severely degraded where urban development occurs along the streambanks, such as where a stream has been straightened by channelization or where man-made structures have replaced natural riparian vegetation. Additionally, urban development that occurs throughout a watershed (but not necessarily directly along the streambank) can result in degraded habitat within a stream channel through flow alteration and sediment erosion. Urban development often results in deeper stream channels or an increase in the stream-channel cross-sectional area. The magnitude of these effects depends on natural environmental factors, such as the geology and soils that can influence the geomorphic characteristics of a stream and its watershed.



Chemistry—Concentrations of Contaminants in Water Increase with Urban Development





Concentrations of contaminants, including nitrogen, chloride, insecticides, and polycyclic aromatic hydrocarbons (PAHs), increased with urban development, although few measurements exceeded any human or aquatic-life benchmarks. The total concentration of insecticides increased with urban development in seven of the nine study areas. The number of individual insecticides detected, as well as the relations between these insecticide concentrations and level of urban development, varied across the study areas and appeared to coincide with regional pesticide-use patterns. For instance, higher concentrations of the insecticides chlorpyrifos and chlordane were detected in urban streams in the Atlanta, Dallas, and Raleigh study areas because of the historical use of these compounds for termite control in these areas. These results underscore the importance that regional differences need to be taken into account when comparing the influence of urban development on aquatic biota in different areas.



Aquatic Biota—Loss of Sensitive Species was the Most Consistent Biological Response to Urban Development


In this example from the Atlanta study area, urban development resulted in the loss of Ephemeroptera, Plecoptera, and Trichoptera (EPT) species, many of which are sensitive to stressors such as streamflow flashiness, habitat loss, and chemical contaminants.


Urban development generally results in a shift in the species composition of the algal, invertebrate, and fish communities. However, the most consistent change in any of the biological communities was the loss of sensitive invertebrate species and a shift to a community with a higher percentage of species more tolerant to physical and chemical stressors. A loss in the numbers of aquatic insect species that occurred in the groups Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies) (EPT), was a common response in all study areas where urban development occurred in forested watersheds. The number of EPT species is a biological-condition metric that is used in many biomonitoring programs across the country because it is sensitive to stressors from environmental degradation. A reduction of more than 50 percent of EPT species was observed in some study areas as the percentage of urban development increased in the watersheds from low to high levels.



The Invertebrate Community Begins to Degrade at the Earliest Stages of Urban Development



An often assumed response in how a biological community degrades with urban development is an initial resilience to change in biological condition over low levels of development. Then, after the community undergoes a rapid change in condition with increasing levels of urban development, an exhaustion response occurs (a "flat line" response) when only a few tolerant species are left in the community. The observed response, however, differed from this hypothetical depiction. The aquatic invertebrate communities begin to degrade with the onset of urban development, which indicates that some species are highly sensitive to physical and chemical changes associated with urban development. There was no evidence that biological communities were resilient to even low levels of urban development, based on the observation that sensitive species were being lost over the initial stages of development in relatively undisturbed watersheds. Likewise, over moderate to high levels of urban development, no exhaustion response was observed to indicate the biological community was degraded so severely that only the most tolerant species remained. Consequently, the absence of an exhaustion response indicates that stream-restoration efforts could have a rehabilitating effect on the biological condition of a stream regardless of the level of urban development in the watershed.



Regional Differences in Pre-urban Land Cover Influenced How Stream Ecosystems Responded to Urban Development



The types of land cover undergoing urban development varies among metropolitan areas, which is important because the way in which stream ecosystems respond to urban development is related to pre-urban land cover. Forest is the predominant pre-urban land cover in Boston, Portland, Salt Lake City, Birmingham, Atlanta, and Raleigh, whereas in Milwaukee, Denver, and Dallas, the predominant pre-urban land cover is some form of agriculture. Generally in watersheds converted from agricultural to urban, the streams have endured some degree of degradation prior to the initial stages of urban development. Thus, the response of stream biota to the stressors associated with urban development can appear weaker in agricultural watersheds compared to forested watersheds. For example, in comparing the aquatic invertebrate communities between the most and least developed sites in the nine study areas, the loss of EPT (mayfly, stonefly, and caddisfly) species was less in the Milwaukee, Denver, and Dallas areas than in the other six areas where pre-urban land cover is forest. The reason for this difference is not because biological communities in the agricultural regions are more resilient to stressors from urban development, but because the biological communities had already lost sensitive species to stressors from pre-urban agricultural land use activities.



Better Predictions of How Urban Development Affects Stream Health Can Be Made With Regional Models that Evaluate Multiple Stressors



In a pilot investigation using data from the Boston study area, a model was developed specifically for New England to predict how different combinations of urban-related stressors associated with stream hydrology, habitat, and chemistry affect stream health. Such tools can be used to evaluate how changes in multiple stressors can affect biological endpoints and the likelihood of attaining the desired stream-health goal. A biological condition gradient (BCG) was integrated in the model to provide a scale of stream health, which is based on the values of three biological endpoints that are sensitive to the presence and absence of certain species in the invertebrate community. The model was structured to predict the probability of attaining six tiers of stream health, which makes it possible to evaluate different management scenarios for protecting streams in urbanizing areas. For example, the model predicted that the likelihood of attaining a healthy stream would be only about 25 percent when levels of urban development exceeded 31 percent in a watershed. However, as seen in the figure, applying management actions that reduce flashiness and improve water quality increase the likelihood of attaining a healthy stream to about 70 percent.











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