Ecosystem, community, and population ecology 85components of organisms (Barbouret al.1987,Odum and Barrett2005). Thesulfur
cycleeffectively links fossil fuel, especially coal burning in factories and power
facilities, to nearby high sulfur dioxide levels in the air that damage plant and
human health. The associated acid precipitation acidifies lakes, dissolves mortar
and concrete, and degrades built structures, from gravestones and sculptures to
large buildings across the region.
The ‘‘atmosphere--organism”carbon cyclehas rapid exchanges of CO 2 between
organisms and the air in ecosystems. Plants absorb CO 2 from the air, and all
organisms in the food web metabolize organic (carbon-containing) compounds
in cellular respiration, which liberates CO 2 back to the air. Carbon is stored
in forest vegetation, cool soils, the sea, and the atmosphere. Carbon is stored
long term in limestone as well as in gas--oil--coal deposits which are rapidly
being combusted by concentrations of people in urban regions and elsewhere.
This process increasingly pumps carbon, i.e., CO 2 and CH 4 (methane), into the
atmosphere as greenhouse gas. Associated higher global temperature and sea-
level rise promise big problems for many urban regions.
In the ‘‘organism--soil”phosphorus cycle,phosphorus is absorbed by roots,
moved through the food chain, and returned to the soil in decomposition.
Rocksand ocean sediments are long-term storage reservoirs for phosphorus.
The more complex ‘‘atmosphere--organism--soil”nitrogen cycleincludes the basic
phosphorus-type model. In addition though, a series of bacteria with specialized
functions converts ammonia (NH 4 )tonitrite (NO 2 ), nitrite to nitrate (NO 3 ), nitrate
to nitrogen gas (N 2 )intheair,and nitrogen gas to ammonia.
Urban regions are bathed in nitrogen and phosphorus (Smith 1981, Gilbert
1991 ,Craul1999,Nowak1994,Santamouris2001,Sieghardtet al.2005). A con-
centration of high combustion engines used in transportation and industry cov-
ers the land with nitrogen oxides (NOX). These air pollutants are also major
components of acid precipitation. Fertilizers rich in nitrogen and phospho-
rus are poured onto farmland that remains the matrix cover in most urban
regions, so agricultural runoff into water bodies is rich in these mineral nutri-
ents. Market-gardening areas near cities are typically nitrogen and phosphorus
hotspots. Furthermore, human wastewater is rich in nitrogen and phosphorus,
so downstream of sewage treatment plants and across residential areas with
septic systems these mineral nutrients tend to be abundant.
An excess of nitrogen or phosphorus causeseutrophication(algal blooms due
tonutrient enrichment), so lakes, ponds, estuaries, bays, and near-shore sea
areas tend to be unnaturally green. Recreational swimming areas are degraded.
Recreational and commercial fishing may be improved or worsened, but the
species caught are different due to eutrophication. Heavily eutrophicated ponds
and lakes may lose their oxygen, and consequently many fish and other species,
at lower levels.