Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Evolving Designer Ecosystem Sheds Light on Unintended Consequences

04.09.2008
What are the consequences of human-made tinkering with land cover and hydrology on surrounding native desert ecosystems and biodiversity? This question forms the backdrop for a case study proffered by an ASU research team and published in the journal BioScience, which found that one of the most profound impacts of urbanization is the “reconfiguration of surface hydrology.”

Amidst the semi-arid stretches of Phoenix, a visitor might blink twice at the sight of a sailboat cutting across the horizon. Tempe Town Lake, on the northern edge of Arizona State University (ASU), is just one of a multitude of lakes, small ponds, canals and dams combining flood control, water delivery, recreational opportunities and aesthetics, and altering perception of water availability and economics in the area.

What are the consequences of such human-made tinkering with land cover and hydrology on surrounding native ecosystems and biodiversity? This question forms the backdrop for a case study proffered by an ASU research team and published in the journal BioScience, which found that one of the most profound impacts of urbanization is the “reconfiguration of surface hydrology.”

Lead author John Roach, now with Simbiotic Software in Missoula, Mont., ASU professors Nancy Grimm and J. Ramon Arrowsmith and other former graduate students mapped water resources and connectivity and tracked land-use change in the Indian Bend Watershed (IBW). The researchers, associated with the Central Arizona-Phoenix Long Term Ecological Research project (CAP-LTER) and the Integrative Graduate Education and Research Training (IGERT) in Urban Ecology funded by the National Science Foundation, found that construction of artificial lakes and canal systems along with extensive groundwater pumping have had “unintended impacts on nutrient cycling.”

“As Phoenix grew from a small settlement to the large urban center it is today, it built an extensive canal network to bring water from the Salt, Verde, and Colorado rivers to agricultural fields and city taps,” says Roach. “While these canals enabled farmers to grow crops in the desert, they also cut across stream channels, disrupting the flow of water and sediments from tributary networks to the main channel. In pristine streams, sandbars and other patches created where these sediments collect are often ideal places for nutrient cycling. By starving streams of their historic supply of this material, canals accidentally alter the way nutrients are cycled in stream ecosystems.”

Humans have altered water systems in the Phoenix area as far back as 300 B.C. The Hohokam people constructed an extensive series of canals for irrigation in the region (until 1450 AD). A new group of settlers arrived in the 1860s and immediately began building “ditches” or simple irrigation canals. Construction continued through the 1900’s as dams were built to harness the Salt and Verde rivers and the canal system was expanded to bring more land under cultivation. As the area became more urban, flood control became more important, necessitating construction of the Indian Bend Wash greenbelt, one of the first non-structural flood management structures in the United States. These activities altered surface water availability, dramatically increasing the timing and spatial distribution of stream flow.

“Prior to these alterations, channel systems like those of Indian Bend Wash were ephemeral, storm precipitation-driven systems with only a limited connection to the groundwater (via loss from the channel bed),” notes Ramon Arrowsmith, professor with School of Earth and Space Exploration in ASU’s College of Liberal Arts and Sciences. “Now, the surface and subsurface hydrologic network is short circuited with water entering the channel from well and canal sources, and water leaving by important evaporation, seepage, and canal redirection.”

The authors emphasize how modern urban water systems shatter any limitations imposed by the topographic contours of a region. The Central Arizona Project cuts a blue swatch across the Sonoran Desert and subdivides watersheds, to deliver a reported 1.7 × 109 m3 per year (or 1.5 million acre-feet) of surface water to the area. In addition, the pumping of ground water has dropped the water table 90 meters and connected surface and subsurface flows, “not only increasing the spatial and temporal availability of water, but having the unintended effect of increasing the flux of NO3 through urban waterways by returning nitrogen leached from historic fertilizer applications to surface flows.”

One concern is the potential impact on riparian species, the “integrity of native ecosystems and the continued delivery of goods and services from these ecosystems.”

Streams in deserts are often overlooked in their importance because of their ephemeral nature; however, streams in general have been shown to be critical to the removal of excess nitrogen from agricultural fields and waste water run-off from urban areas. Denitrification, a bacterially-mediated process, converts nitrate to nitrogen gas, which then is released harmlessly to the atmosphere. High nitrogen loads from urban areas can overwhelm streams’ capacity to remove nitrates and the resulting pollution of downstream rivers has been linked to the proliferation of coastal dead zones.

“We were surprised by how frequently the concentration of nitrate in surface waters was determined by the turning of a tap,” Roach notes. “Because the groundwater below the greater Phoenix ecosystem contains a lot of nitrate, when groundwater wells are tuned on, the concentration of nitrate in the canals and streams receiving this water goes up. This nitrogen, in turn, can act as fertilizer, stimulating unwanted growth and producing changes in what the stream looks like that are independent of the decision to deliver more water to city lawns.”

The present study underscores the importance of understanding the structure and function of natural streams and arid ecosystems and how they are impacted by human-altered systems, water distribution and design. The authors point out that the unintended consequences “must be carefully evaluated – especially in arid and semiarid cities – if managers are to have any hope of mitigating them.”

Grimm, a professor in the School of Life Sciences and member of the Global Institute of Sustainability at ASU, sums their study up: “Our findings contribute to answering the more general question of how fundamental ecosystem services – those processes of ecosystems that provide a natural resource or regulate properties of the resource, for example – change when people make large alterations to streams during the course of urban development. Perhaps our case study will help define how to best design such ecosystems to meet the need to provide multiple services – in this case, protection from flooding, recreation, and regulation of nutrient concentrations reaching downstream systems.”

John Roach
JohnRoach21@gmail.com
Nancy Grimm
nbgrimm@asu. edu
(480)965-4735
Ramon Arrowsmith
ramon.arrowsmith@asu.edu
(480)965-3541
Margaret Coulombe
margaret.coulombe@asu.edu
480-727-8934

John Roach | Newswise Science News
Further information:
http://www.asu.edu

More articles from Ecology, The Environment and Conservation:

nachricht Bioinvasion on the rise
15.02.2017 | Universität Konstanz

nachricht Litter Levels in the Depths of the Arctic are On the Rise
10.02.2017 | Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung

All articles from Ecology, The Environment and Conservation >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Impacts of mass coral die-off on Indian Ocean reefs revealed

21.02.2017 | Earth Sciences

Novel breast tomosynthesis technique reduces screening recall rate

21.02.2017 | Medical Engineering

Use your Voice – and Smart Homes will “LISTEN”

21.02.2017 | Trade Fair News

VideoLinks
B2B-VideoLinks
More VideoLinks >>>