Linking scales of flow variability to lotic ecosystem structure and function

Biggs, B. J. F., Nikora, V. I., & Snelder, T. H. (2005). Linking scales of flow variability to lotic ecosystem structure and function. River Research and Applications, 21(2-3), 283-298.

While biotic interactions have major influences on ecosystem, Biggs et al. argue that the abiotic environment constrains the biotic interactions playing a greater role in ecosystem. "An organism must be able to survive, grow and reproduce under a given set of abiotic conditions, before the habitat defined by those conditions can be considered viable for that species."  Abiotic conditions are the non-living chemical and physical factors in the environment as opposed to the biotic which is the living component of a community. Over evolutionary time species gradually adapt to specific habitats both abioticly and bioticly .  These abiotic environments act as evolutionary forces that drive the development of different sets of traits.  These forces are not static, and are extremely variable in both time and space. These forces can be climatic such as rain, wind, flooding, and flow variability.

Biggs et. al, punished work in River Research and Applications (River Res. Applic. 21: 283–298, 2005) linking flow variability to the lotic ecosystem structure and function.  Having a study area of New Zealand and focusing on rivers with a ranging difference in flow variability, they show that temporal variations in flow strongly influences the functional processes and structures of lotic ecosystems. They hypothesized that the lotic ecosystem is sensitive to flow variability at temporal scales, but also sensitive on scale of magnitude. They show that "infrequent, but high magnitude flow variations influence lotic ecosystem structure and function at high system levels (i.e. communities) through drag processes (resulting in ‘drag-disturbance’) whereas more frequent, but lower magnitude events influence ecosystem structure and function more through mass-transfer processes (controlling growth of individuals)."

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While this reserached focuses on New Zealand, this concept of climatic senstivity in lotic ecosystems is critical in the age of climate change.  As with the Rivers in New Zealand, many rivers have variations in flow that is controlled by inter-annual variations in climate.  Year to year variations in New Zealand are driven by two Oscillations, the El Nino Southern Oscillation (ENSO) phenomenon superimposed by the Interdecadal Pacific Oscillation (IPO).  During El Nino there tends to be greater precipitation and higher more frequent flow events in the south and west of new Zealand. These inter-annual variations in flow regime have major implications river ecosystems due to the frequent flood disturbances in come years, and low flows in other years.  The figure below from the article shows the hydrograph of three rivers in New Zealand, where the inter-annual variation is apparent with the peaks in flow rates. The Bottom Chart is they hydrograph from the source of the two river above, while the source is relatively stable, down stream there is a strong variations related to runoff from storm events.

Biggs et. al. believes that ecological effects of horological variability follow a hierarchically principles, with effects of flow variation on communities by large scale events and event effects at lower levels with smaller scale flow variations.  They hypothesize that flow variability is the underlying reason for the temporal and spatial patterns of biological characteristic are different scales in the lotic ecosystem.

They conclude that "high energy flow events are generally catastrophic to lotic ecosystem structure and function for periods of time that vary depending on the resistance and resilience of the different populations."

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Wiley Online Library - http://onlinelibrary.wiley.com/doi/10.1002/rra.847/abstract

Deforestation and Climate Variability effects on the Araguaia River, Brazil

Deforestation is impacting river systems like the Araguaia, which forms a natural border between the Brazilian states of Goias, Mato Grosso, Tocantins, and Pará.  The Araguaia River is a rare example of rapid geomorphologic response of a large alluvial river to land cover and land use change.  Deforestation alters the hydrological, geomorphological, and biochemical states of streams.  This occurs due to decrease evapotranspiration and increased runoff, river discharge, erosion and sediment fluxes from the land surface.  Over the past 4 decades, Brazil has experienced rapid regional development and land use change due to high demand of cattle feed, beef, and other agricultural commodities like sugar cane.  At the same time during the 1990s parts of Brazil has experienced increases in precipitation.  Determining how river systems respond to multiple changes require further study to link and quantify land use change and geomorphic responses.

Professor Edgardo Latrubesse was a Co-Principle Investigator (PI)  of an international project in Brazil named “Land use Impacts on the Water Resources of the Cerrado Biome” which was supported by NASA, Earth Science Enterprises and developed in collaboration  the Wood Hole Research Center, University of Goias Brazil,  and University of Brasilia.  Professor Latrubesse, with an international team of researchers, studied the river’s watershed, relating land use change to geomorphic response in the river system.  Their results are reported in the Journal of Biogeochemisty which shows that agricultural expansion has impacted the system. The team used modeling methods to simulate the watershed without land cover change, which suggested that about 1/3 of the observed discharge increase in the 1990s can be attributed to the observed increase in precipitation (Climate Variability). The simulation with land cover change compared to that without land cover change in the 1990s suggested that the remaining 2/3 of the observed discharge increase was most likely the result of some other factor such as a net decrease in evapotranspiration that occurred when native vegetation was replaced with more shallow rooted, less water-demanding pastures and crops.

Their paper can be found at:

Coe, M. T., E. M. Latrubesse, M. E. Ferreira, and M. L. Amsler (2011), The effects of deforestation and climate variability on the streamflow of the Araguaia River, Brazil, Biogeochemistry, 1–13.

The Power of Naming: The Toponymic Geographies of Commemorated African-Americans

Tretter, E. M. (2011). The Power of Naming: The Toponymic Geographies of Commemorated African-Americans. The Professional Geographer, 63(1), 34-54. doi:10.1080/00330124.2010.537936

(http://www.informaworld.com/openurl?genre=article&issn=0033-0124&volume=63&issue=1&spage=34)

The names that we give our streets, schools, parks, and other places in our landscape reflect our collective culture and history.  These place names can shape regional identities, give a neighborhood character, and recognize great people in our society.  Dr. Martin L. King Jr. is the most commemorated African-American in the United States, and in fact around the World.  Dr. King makes up nearly 2/3 of all African-American commemorations in the United States.  How does the other 1/3 of commemorative place-naming of notable African-Americans shape our American landscape?  

Image via WikipediaDr. Elliot Tretter has recently published a study on commemorative place-naming of notable African-Americans in the February 2011 issue of the Professional Geographer.  His study explores how there are regional characteristics associated with where African-Americans are commemorated, particularly pertaining to cities.   Dr. Tretter uses a variety of Internet-based mapping tools to collect a dataset on the regional variation of the commemoration of thirty famous African-Americans (fifteen men and fifteen women).

Dr. Tretter’s finding show that while Dr. King may have reached a universal symbol of African-Americans transcending limits, other African-Americans figure have not.  He found that African-American commemorations do follow a geographical pattern. In the fact, the patterns show that commemorations are in places associated with African-American.  These figures therefore are not recognized as universal members of a nation and remain symbols of a separate “black nation”.

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The Black Nation

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