SUMMARY
Intermediate Productivity and Disturbance
We considered applications of the Intermediate Disturbance Hypothesis in urban settings, using a 2005 study by Marzluff on birds and a separate study on vascular plants (Mayor et al. 2012). While Marzluff found convincing support for bird diversity peaking at intermediate levels of human settlement, the corresponding finding for native vascular plants by Mayor et al. was criticized for fitting a questionable hump-shaped curve to highly scattered data.

Urban Trees and Soils!
The average urban tree lives for about ten years in contrast to trees in areas with less anthropogenic disturbance, which may live for centuries. Some aspects of urban settings may promote tree survival, such as elevated CO2 levels, access to sewage water, greater nitrogen availability through fertilization and atmospheric deposition, prolonged growing seasons, and reduced shading and competition due to lower tree densities. However, urban trees also face substantial challenges, such as poor soil quality, minimal water pooling, and restricted growing spaces. The high-cost "tree in a box" trend in many cities is proving to be a waste of money because of the challenges that urban trees face.

Urban soils are highly altered through human activities. For example, street-cleaning activities tend to interrupt potential nutrient recycling sources by removing fallen leaves and decomposing animals. Additionally, excavating land disrupts soil horizons and homogenizes the distribution of nutrients throughout the soil. Soil bulk density may be increased by compression from heavy traffic or decreased due to mixing. As we saw in Kirsten Schwarz' lecture, urban soils may also house high densities of toxic materials. In a previous lecture we also saw that carbon and nitrogen levels are significantly lower in urban soils beneath pavement than open soils! As a final example (in a list that should probably be shorter in a summary), soil microorganisms and their activities may also be altered in urban settings.

We also looked at an interesting hypothetical, qualitative graph by Rich Pouget on carbon density homogenization over time. The expectation is that different habitats originally show a wide range of carbon densities, with deserts hosting the lowest levels of carbon densities. Over time, through agricultural conversion most ecosystems experienced reduced carbon densities. Subsequently, urban conversion resulted in increasing carbon densities with all ecosystems converging to a narrower range relative to original carbon densities.

Urban Climates
We began this portion of the class lecture looking at the hypothetical profile of air temperature spanning from rural areas to urban centers (and all places in between). The idea of the “urban heat island” was first proposed by naturalist Luke Howard in 1818 (the same scientist who spent years manually drawing and classifying clouds!). As expected, urban areas were a few degrees warmer than rural areas given the same amount of incoming solar radiation. The magnitude of heating lessens with land surfaces that have combinations of urban and rural characteristics. For example, residential suburban areas that are human-dominated landscapes with a fair amount of vegetation saw moderate temperatures bisecting the maximum temperatures in urban areas and minimum temperatures seen in rural areas. The deadly heat wave in Paris in 2003 really brought the impacts of the urban heat island into the public eye, and it was brought to attention that air conditioners may have amplified the heat wave instead of cooling people down. We discussed briefly how some urban areas were using plants to create "cool islands" in the city, through the creation of green roofs on downtown buildings.
We introduced the Earth’s surface radiation balance in the lecture as well. In essence, the amount of incoming energy must balance with outgoing energy.

Incoming energy consists of:
  • Incoming solar radiation (Insolaton) – in the form of direct and diffuse radiation
  • Counterradiated longwave radiation from the atmosphere (Greenhouse Effect)
  • Anthropogenic heat flux (energy added through human activities)
Outgoing energy consists of:
  • Emitted longwave radiation
  • Sensible heat transfer (via conduction and convection)
  • Latent heat transfer (through the evaporation of water)
  • Ground heat flux
In the traditional meteorological perspective, the anthropogenic heat flux and ground heat flux are not considered. However, in the context of urban ecology both of these terms are added. In conclusion, as one or more of the incoming energy terms increases, one or more of the outgoing energy terms must also increase in order for this balance to be maintained. This compensation of energy and fluxes involved in this balancing act is heavily dependent on individual urban centers being analyzed.
We also began to discuss the concept of albedo. Albedo is the proportion of incoming shortwave radiation reflected by a surface, which is reported as a percentage ranging from 0 to 100% with increasing reflectivity. Urban areas traditionally have low albedos due to a host of black/dark-colored man-made structures and impervious surfaces. This results in heated urban centers relative to vegetated areas and contributes to the urban heat island (UHI) effect. As absorbed energy slowly radiates back to the atmosphere throughout the evening and night, urban nighttime temperatures remain higher than temperatures in surrounding rural areas.
BLOGS

Steve:
Hey guys! I just wanted to share this story. It was written by Ernest Thompson Seton and is an essay in a great collection called "Wild Animals I Have Known." This is about a wild crow that he named "Silverspot," and anecdotally illustrates well what Marzluff showed empirically, namely that crows are crazy smart. Give it a read if you have a minute - Amanda, you'll really love this! The one about the wolf, "Old Lobo," is great too.

Toby Fusco:
This lecture on urban climates was the first time all semester that I haven’t felt totally lost in the content we cover and discuss in class! Outside of Paige Warren’s presentation last week, this is my favorite topic thus far (I’m obviously a tad bit biased here!).

Urban heat islands are interesting and troubling environmental issues brought on by humans. A classic paper published in 1973 by T.R. Oke shows a fundamental approach to city size and the urban heat island. This work is referenced in many current papers written on this topic. All papers I’ve consulted for my research cite the Oke paper.

An interesting aspect of the urban heat island effect I’ve encountered during recent research is the effect of wind. Wind is a mechanism created within the atmosphere to transfer radiation in an attempt to equilibrate heat content and temperature. It appears that the effects of the urban heat island are most pronounced under weak wind regimes. The air in urban and rural areas is better able to stagnate. This stagnation of air leads to vast differences in the urban and rural areas including major differences in air temperatures.

I live in the Lakes Region of New Hampshire and there was one day this past summer I witnessed this phenomenon first hand. I taught an afternoon summer session course and left Boston around 5:30pm. The air temperature was 96°F and the wind was calm. When I arrived home at approximately 7:30pm, the temperature in New Hampshire was 78°F. The wind was almost calm throughout New England this particular day and this was close to the June Solstice so the sun had not set by the time I got home (though the amount/intensity of solar radiation had definitely lessened).

This feature can sometimes be witnessed in the winter season as well. In the Boston area, when we get cold and clear (and calm!) nights, temperatures overnight might be a balmy 20°F. In the suburbs just outside the city (within 15 miles or so), temperatures may be below 0°F. The calm winds do not rip the warmth away from urban centers and therefore they stay a bit warmer than the surrounding areas. Regardless of season, temperatures in urban areas are generally warmer in the overnight hours due to the re-radiating of energy back to the atmosphere that was acquired throughout the day. The difference is less noticeable (between 5 and 10°F between urban and rural areas) when the winds are blowing at a faster rate of speed.

In my project at the end of the semester, there will be much more on the urban heat island and wind and their influence on precipitation.

Sam Worley:

A part that was just skimmed over in class that really hit home for me in lecture... Back Bay is built on soil fill and wood piles, that were built on mud and clay.

HOW DID I NOT KNOW THIS?

The ground we walk on almost daily has the potential to collapse in approximately 10-20 years, although buildings are especially susceptible. The receding water is due mostly in part to urbanization. The increased amount of impervious surface in Boston through its history has led to a slow decline in the water table as less water is being absorbed into the ground, and more is being treated as run-off through sewer drains. This is an enormous problem to fix, requiring thousands of dollars just to monitor the water table around your property. If you find your piles are degrading, you're paying roughly $250,000 according to the Neighborhood Association of Back Bay (Neighborhood Association of the Back Bay on Pilings) or $500,000 according to Boston Civil Society of Engineers (Boston Civil Society of Engineers on Pilings).

This just blew my mind. How could the city of Boston be so careless? I know it was 150 years ago but jeez, did anybody have some foresight? What were the benefits besides rapid growth of filling this area? Did anyone think of the cost or future repercussions?
This just shows how much more careful we are now (hopefully ... Singapore... ) and how much thought really goes into the actions government and cities take in the 21st century (again.. hopefully).

The city of Boston really "filled" itself into a hole here.


Bahareh (B.) Sanaie:


Great posts Toby and Sam. Sam thanks! the Back Bay info was really informative.

This lecture so far was one of my favorite. The urban heat island is the area of my interest. In addition, that was a very first time I learned about Boston lands! Honestly, I was in ignorance when I heard it in the class and it took some time for my brain to digest this fact. I have heard about other land reclamation all around the world like Plam Jumirah* or Nagoya Centrair Airport in Japan but most of them happened recently, not 150 years ago! So, as we discuss in the class room the future of Boston is kind of foggy. Isn't it?

*A palm shape island (Palm Jumeirah)was added to Dubai (United Arab Emirate) using land reclamation which extended into Persian Gulf recently.

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The Charles River Watershed Association (www.crwa.org) has been involve with various urban environment -such as storm-water control- projects. Trees in urban environment have various values such as protecting and enhancing property value; controlling storm water erosion; and reducing local flooding. A tree pit structure which typically includes a box and soil mixture which is suitable for urban streets was suggested to Dorchester city by CRWA. The tree pit rather than providing some flood control would also improve quality of surface water way and reducing storm-water runoff volume, and increasing groundwater infiltration and recharge. On the other hand, some root barriers are implying underground to protect foundations from tree root damage.
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In CRWA we had some workshops for farmers at Massachusetts to reduce the amount of fertilizer base on the availability of nitrogen and phosphorous which would save them some money and reduce their cost plus its environmental benefits. Although, it was so hard to work with Gulf courses meanwhile their profit lays down in greener land which make them resistant to reduce the amount of N/P fertilizers.
We also talked about landfills. Most of the modern landfills are equipped with liner system which isolates the landfill contents (e.g. leachate) from the environment; however, scientists are still struggling with leachate treatment. In addition, young leachate which is released from municipal solid waste transfer stations contains high amount of nitrogen and phosphorus which need to be treated (not fully possible yet) before releasing to the environment. Malaysia challenging with this problem vastly in recent years especially because of eutrophication and blue-baby syndrome causing by excess amount of nitrogen and phosphorus which is released untreated from the landfills and transfer stations.
EPA: “Waste transfer stations are facilities where municipal solid waste is unloaded from collection vehicles and briefly held while it is reloaded onto larger long-distance transport vehicles for shipment to landfills or other treatment or disposal facilities”.

Ryan Foley:
One thing I found very interesting in lecture was the affect that the heat island had on the growing season of vegetation. I went home this weekend to Middlebury, VT and took this picture of my backyard:


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Granted, Middlebury is just over 100 miles north (and west) of Boston, I'm going to go out on a limb and make an educated guess that this much variation in tree color is due to more than just the difference in latitude.

Also, just to clear another question you might have- the difference between Middlebury and Boston's elevation is harmless.

Compare that to what you see a full 5 days later here, in Boston!


Bahareh: Wow! This photo is wonderful Ryan! I have no idea if there is any relation between heat island and the Fall in Vermont but this image is astonishing.

Lital:
Last year I did some research on the Urban Heat Island (UHI) effect, and came across an opposite phenomenon called the "Park Cool Island" (PCI) effect. While the UHI measures the temperature difference between urban environments and their surrounding suburban/rural environments, the PCI measures the temperature difference between the heat of the city and the cooler temperatures of parks, aka urban oases.

The basis of this idea is kind of similar to what Toby previously described in his blog post. When there are a lot of buildings densely compacted in a small area of land, wind isn't able to move air and heat gets trapped- part of the reason why we have the UHI. But we also have parks interspersed in between the buildings. By allowing the air to circulate, in addition to having vegetation that utilizes solar radiation and transpires water, we observe a great difference in temperature, sometimes up to 5-7 degrees celcius!

The paper I'm refering to (found here) studied the correlation between a lot of factors, not just wind; Lu et al also studied the shape of the park, the type of vegetation, the season, the cooling of building surfaces, and the green ratio. Breifly summarizing his conclusions, Lu et al found that the park area is the greatest factor in the PCI effect, PCI intensity peaks around 1 pm, and relative humditiy varies positively with PCI intensity.
I thought this paper was really informative and interesting, and I highly recommend taking the time to even skim it over while we are on this topic!


Maddy Huerta:
I found some interesting resources regarding urban heat islands while browsing the EPA website: Apparently from 1998 to 2002, there was a program called the Urban Heat Island Pilot Project (UHIPP) in which the EPA partnered with cities and helped them evaluate the impacts of urban heat islands as well as coming up with strategies to reduce the effects. The pilot cities in this program were Chicago, Baton Rouge, Sacramento, Houston, and Salt Lake City. There is a profile for each city (here's Chicago's) that looks at land use, "urban fabric", climate, geography, air quality and a bunch of other factors, and comes up with energy saving mechanisms and heat island reduction activities. This seems like a really interesting project, and I would have liked to see how other cities like Boston, New York, or Los Angeles would have been evaluated.

Another more up-to-date EPA resource I found is a page that allows you to look at urban heat island information where you live. Each state's page outlines past and current initiatives and mitigation strategies that are being carried out by different programs and organizations within the state. I looked at the Illinois page and I was really impressed by the number of initiatives that are in progress or have already been completed, (especially the Permeable Alleys project, where the Chicago Department of Environment reconstructs asphalt alleys using permeable pavement). However, I was disappointed to see that Massachusetts does not have one of these pages.


Michelle: Although I had been told in the past that most of Boston was built on dredged soils, I think the implications of that finally hit me this past Friday in class. Earlier, when we had gone over the sites that we looked at from the previous homework, and reviewed the area of the Big Dig, we all realized just how much change that area experienced. To think that the construction of the Big Dig took place through and around layers upon layers of man-made and altered soils that are supporting huge structures with the help of aging wooden poles is just incredible! The soil composition of the dredged soil that we added started out very different from the soil that naturally occurred in the marshy areas surrounding the original 789-acre Shawmut Peninsula. Instead of being full of peat, it was largely solid marine clays that were good for building on due to there stability. I wonder now if the soils layers have become more homogeneous with time and how this affects the stability of the soils underneath the city. Below is a link to what I consider a really cool article discussing how engineers of the Big Dig had to work around the challenges associated with working in and around such highly altered soil structures.

http://www.geotimes.org/oct02/feature_bigdig.html