subscribe: Posts | Comments

Measuring delta health on a global scale

Classic shape of Nile River delta    Classic shape of Nile River delta





I have previously noted that the major river deltas of the world are in a dynamic balance between growth and shrinkage. Recent human alterations of the watersheds on which deltas depend (and sea level rise via climate change) are rapidly altering this balance of power in complicated ways.

A deltaic landscape expands when river sediments increase and shrinks when sediments decline and/or sea level rises. Readers of this blog are aware that the Mississippi/Atchafalaya River delta system is shrinking dramatically. It is instructive to recognize how the changes in our backyard relate to deltas around the world.

Clearing land for agriculture and development increases sediment runoff and expands deltas but dam construction reduces sediment runoff and shrinks deltas. Rapid rise in sea level from climate change (currently at 3 mm/year and accelerating) threatens to virtually eliminate deltaic ecosystems.

Compare these two satellite views of the Yellow River delta in China put on the web by a geology graduate student named Brian R. (no last name given). 

Yellow River delta 1979

Yellow River delta 1979

Yellow River delta 2000

Yellow River delta 2000









He offers these thoughts on the dramatic changes: 

Compared to the earlier image, the 2000 shot shows an increase in developed land and a slight decrease in vegetation. The most striking difference between the two images, however, is the shape of the coastline. A steady supply of sediment expanded the Yellow River delta until it pushed into Bo Hai like a giant hook. Sediment colored the coastal waters bright blue. This delta-building process has added several hundred square kilometers of land to China’s coast.

I wonder if the change from a “smoother” coastline to the more “birdsfoot” river-dominated morphology has mostly to do with the land use changes? That is, a more restricted river course would preclude frequent avulsions and construction of the distributive dispersal pattern. A more restricted river course would result in more spatially focused growth. I don’t know … just thinking out loud.

Editor’s note: Brian R’s hypothesis on the deveopment of a “bird’s foot” configuration conforms with the historical changes to the modern delta of the lower Mississippi that accompanied the historic restriction of the river course. 

A new study compares the environmental health of major deltas around the world, including our own Mississippi system.  This study, published in the Bulletin of Atomic Scientists, provides an excellent global overview of the complicated interplay between riverine watersheds and ocean forces, and the ephemeral deltaic landscapes that reflect this interplay. One of the authors is well-known Louisiana coastal authority John Day, Professor Emeritus at LSU.

The article notes that increases in freshwater use for agriculture throughout riverine watersheds results in a reduction in the productivity of deltaic vegetation (wetlands) and a shift toward the marine side of the equation. This conclusion is relevant to both the ongoing issues of gulf hypoxia and the prospect of large scale river diversions to nourish our coastal wetlands. 

The authors note that from a global perspective over two billion humans, almost one third of everyone alive today, live on deltaic systems including ours. To put this statistic in perspective we know that about two million Louisianans who live south of I-10 are at risk. Small comfort that we represent only 0.001 % of the world population facing similar risks!

A complementary paper published in the Proceedings of the National Academy of Sciences and summarized in describes a methodology for collecting sediment cores offshore of major delta systems as a forensic tool to quantify human alterations to watersheds. The key authors, both pre-Katrina Tulane faculty members, are Tom Bianchi, now at Texas A&M and Mead Allison, now at the University of Texas, Austin.  

Bianchi and Allison interpret the sequence of sediment layers in these cores to measure past changes in nitrogen application in the watersheds from agricultural fertilizers, records of past flooding and hurricane events, all useful for predicting effects of climate change and other management issues.They have collected samples from deltas all over the world, including the Mississippi delta and the (Huanghe) Yellow and Yangtze in China. 

By using their methodology, human activity in some watersheds can be traced back more than 5,000 years ago to some of the first cities in Mesopotamia, along the Nile and in regions of China. The authors note that the world’s largest 25 rivers drain about one-half of the Earth’s surface and transport 50 percent of the fresh water and 40 percent of particulate materials into the ocean.

Chinese river deltas are currently threatened as the country attempts to manage severe water shortages, over-grazing and desertification for a growing population by manipulating natural water sources from their major rivers through damming and diversions. Over the last 20 years, China has become the world’s largest consumer of fertilizers and two of its rivers, the Yellow and the Yangtze, are among the top five in the world in terms of  discharge.

The comparison images of the Yellow River delta above show the effects of 21 years of this discharge. In contrast, south Louisiana is suffering from a massive decline in river-borne sediments, thanks to dams on the Missouri River.

In summary, the world’s major deltas reflect geological processes and human alterations over vast watersheds in the context of climate change. This means that saving coastal Louisiana requires thinking far beyond the footprint of the deltaic “veneer” on which we live. Unfortunately, for two decades we have focused on the veneer and devoted only a miniscule effort thinking beyond (and beneath) our coastal zone. It’s as though we ‘ve hired painters to restore a house with termite-ridden beams. 

Len Bahr

Be Sociable, Share!
  1. You can find some attention-grabbing closing dates on this post however I don’t know if I see all of them middle to heart. There is some validity but I’ll take hold opinion until I look into it further. Great post , thanks and we want a lot more! Added to FeedBurner as nicely

  2. I completely realize everything you’ve got stated. Really, I browsed via your various other articles and I do feel that you’re surely correct. Best wishes with this specific internet site.

  3. Aw, it was quite a good post. In thought I have to put in writing such as this moreover – taking time and actual effort to produce a excellent article… but what / things I say… I procrastinate alot by way of no indicates manage to get something completed.

  4. I would like to show my gratitude for your kindness for men and women that totally need to have help with this certain content. Your really own dedication to getting the message all-around became particularly good and have in most cases encouraged girls a lot like me to achieve their goals. This informative guideline implies so a lot to me and much more to my workplace colleagues. Thanks a lot; from each one of us.

  5. I precisely necessary to thank you so significantly however once more. I do not know the items I would’ve taken care of without these secrets contributed by you regarding this dilemma. It seemed to be a extremely frightful crisis for me, but encountering a new well-written tactic you processed it forced me to jump with contentment. Now i am happier for the function and hope you are aware of an incredible job you happen to be getting into educating individuals by way of your internet blog. Probably you haven’t come across any of us.

  6. Aw, this was an exceptionally good post. In concept I would like to place in writing such as this moreover – spending time and actual effort to create a outstanding article… but so what can I say… I procrastinate alot by way of no indicates locate a strategy to go completed.

  7. Extremely good publish, thanks so significantly for sharing. Do you have an RSS feed I can subscribe to?

  8. I went over this internet web site and I believe you’ve a great deal of great data, bookmarked (:.

  9. I am continually searching online for ideas that can assist me. Thank you!

  10. I like what you guys are up also. Such intelligent work and reporting! Keep up the excellent works guys I¡¦ve incorporated you guys to my blogroll. I think it’ll improve the value of my web site :)

  11. Once you conduct yourself as a spoiled little princess it’s good to expect to be thought of as a spoiled child, the sought after triple A review is always in danger and only an idiot wouldn’t have been conscious of this piece of information.

  12. HeidiHoe says:

    No I don't jest…..

    The ocean level has been higher than at present before; it will happen again; and perhaps anyone who lives within this dynamic interface between land and ocean should ponder this fact.

    No matter what defenses we Humans muster olde Ma Nature will find a way around them……

    No problem with living in this dynamic interface; feel free to ante up the costs of doing so…..

  13. Walter Sikora says:


    The last time there was a significant rise in sea level, at the end of the last glacial period, when the Wisconsin glaciation completely melted, there was no human infrastructure to speak of and those few humans that lived near the coast simply moved inland. Even though the actual physical impact on humans at that time was minimal, the psychological effect even back then was huge as evidenced by the fact that nearly all surviving cultures have great flood story in their mythology, including our culture i.e. Noah and Biblical flood. Are implying that in the 21st-century, with major population concentrations and huge infrastructure development in coastal areas world wide, that there is nothing to worry about from sea level rise, particularly when such a scenario is avoidable? Surely you jest.

  14. HeidiHoe says:

    More thoughts on global warming here:

    As I understand, the ocean's level was at one time perhaps 300 feet +/- LOWER than at present; meaning that some previous "coastlines" and "wetlands" are currently lying in perhaps 300 feet of water….

    Also, I understand that the ocean's level was at one time perhaps 50 feet +/- HIGHER than at present; meaning that some previous "coastlines" and "wetlands" are perhaps quite dry at present…….

    Time comes, time goes; changes go on……..

Leave a Reply