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What happens to nitrates that flow into the sea?

  1. Jul 20, 2004 #1
    I live in a beautiful tropical valley, with a river, near to it, that flows into the sea when there is heavy rainfall. It is planted in avodcados mangos bananas ect and I know it is chemically fertilized. I know this area for 25 years and have noticed that all living things have nearly vanished close to shore, the water is crystal clear but nothing alive. There used to be abundance of octopus, shrimp, sea horses, squid, scools of all kinds of fish and many things that lived on the bottom like crabs and flying fish.

    What I want to know can the nitrates from fertilizer accumulate in the silt near shore and destroy the habitate or might it be somthing else? If this is the cause and it was stopped how long would the sea take to recuperate? Do the nitrates fall to the bottom or are they in suspension? This is only a agricultural area no chemical waste of any type or factory are dumped into the sea.

    I saw a film on BBC about Fiji that had a problem with nitrates from fertilizer killing the coral reefs. They buildt retention ponds with plants that ate the nitrates and reduced the pollution to replant corral reefs.
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  3. Jul 20, 2004 #2


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    Nitrates are very water soluble, and not going to be accumulating in near shore sediments. Nitrogen (as ammonia or nitrate, or nitrite), phosphorus, and potassium are limiting nutrients in sea water, and unless someone's washing trainloads of fertilizer down the river, it's not likely to be the source of a clear water desert problem. You might be seeing river water so thoroughly cleaned of other trace elements and necessities of life by the agricultural activities that there's nothing left in the runoff to feed the estuarine biota --- but, not too likely the case. Excess fertilizer in runoff usually leads to eutrophication, too much biological growth, and consequent dead plant and animal matter accumulating in an area. Algae blooms killing coral reefs by suffocation, sediments turning anaerobic, that sort of thing.

    Do you have access to any water quality studies at various points in the river that you mentioned? I haven't heard of any river clean-ups being so wildly successful that nothing could grow in the outflow, but at the same time, people are getting more and more economical in their applications of fertilizer in agricultural endeavors, and you may be looking at a very unusual case in which the application rates are just perfect --- nothing running off but water that the crops have stripped of everything useful.
  4. Jul 21, 2004 #3
    Bystander, the river that flows into the sea, stops in the summer and has a slow run off during the rest of the year. The area is about 100 kilometers square, with mountainsides that all eventually lead to the river valley.

    When there is a heavy rain a lot of mud is carried into the sea for a few 100 meters. There is no green algae beds near the shore as there once was. The river itself has green vegetation on both sides, when the water flow is low a lot of green algae builds up and the frog population explodes.

    No, not of the river water but did do a sample of a mountain spring, in the main area of agriculture 9K inland from the sea. We found levels of nitrates, that seeped into the groundwater, that were at some times, according to the lab that did the testing, to high. We drank this water, instead of tap clorine water, for several years and developed an alergy, a kind of tickle in the throat and then a need couph to try and clear the throat. It stopped when we stopped drinking this water as only source.

    Are you saying that, a certain amount of runoff is beneficial?

    We had a dam buildt a ways from here and the sand silt that was dug out, was used to rebuild the sea shore for many kilometers. There was a big stink with greenpeace here about that sediment having high amounts of lead and mercury, heavy metals in the silt. There used to be sand crabs in the sea and mollusks that could be found in the sand on the sea shore. That has disappeared. If this is the case will it recover eventually. Will this material unlike nitrates stay in the sand near shore?
  5. Jul 21, 2004 #4
    If the problem is heavy metals instead of fertilizer.
    Yes, HM polution will buildup in the sediment.
    I don't know by heart the effects of mercury and lead in marine life.
    However a chem. chart should provide the answer in this case.
    The effects of mercury and lead on marine life have been well researched and documented.
    Although highly toxic the concentrations have to be very high to completely whipe out all life in an area.
    I couldn't tell you what the recovery time for the area will be.
    This because i have no way to tell the concentrations, and the pace by which it is being whashed away by the sea.
  6. Jul 22, 2004 #5


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    Lead and mercury don't worry me too much in the situation you've described. What does start to look a little suspicious is the amount of mining activity, current and past, in the drainage area --- upstream from the dam? Mine tailings into the lake, hauled to shore to remedy beach erosion, low pH river water high in nitrates leaching silver from the beach sands? Very sterile ocean. You've described "live" freshwater downstream from this dam, nitrates in aquifers feeding the drainage, and a dead ocean. Not too obvious just what the problem(s) might be.

    Other thing to think about; how much commercial fishing offshore? Today vs. 20-30 years ago? Circulation of eastern N. Atlantic Ocean isn't something I've got handy off the top of my head --- is there any chance you're looking at some sort of cyclical eddy from some of the various sterile gyres? The Sargasso is the only example that comes immediately to mind, but I'm sure there are others.

    "Runoff beneficial?" The marine biota do not derive nourishment from distilled water --- it has to contain something in the way of nutrients or you've got a wet desert.
  7. Jul 22, 2004 #6
    There was silver and copper mining in the old days but I believe it is now over. Why is silver a problem? I know colloidal silver will eliminate fungus bacteria and viruses. I use this for medicinal purpuposes as my own medicine, in limited quantities. Could large quantities of silver being leached out of the sand, destroy enough microrganisms, that lead up the bio chain? It seems there is a chain of problems that are leading up to the main problem. Its the shoreline to within 300 meters off shore, where water depths, then go beyond free diving.

    There is a abundance of commercial fishing offshore, that does not seem to be of concern, although it is not what it use to be. It was 25 years ago when I first pulled out a 2 meter octupus, that is leg to leg. How long is cycle? It is now prohibited to fish them. Jaque Yves Cousteau was here in Almuñecar and doing research in the Mediterranean Sea in 1976, he said "on quote", what a pity the Mediterranean is dying. Its only when we examine our memory do we understand what he was trying to say. One meter Jew fish or Grouper if you want to call them, when smaller were pulled out off shore, in the same area we are talking about in 1960. :cry:

    River basin and delta show green algae and bio life. Is there any other factors you can think of that might also contibute to the problem? Other than lots of tourists and motorboats.
  8. Jul 22, 2004 #7
    Do you think that mining shellings from centuries of dumping, could buildup enough heavy metals in the river silt? These mines were open in Roman times over 2,000 years ago. The HM would just sit there until it was dug up for a big dam and then dumped on seahore!
  9. Jul 22, 2004 #8


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  10. Jul 22, 2004 #9
    Yes i think so.
    While with other substances, there are a lot of cases where dug up (or more precise dredged up) sediment which has been dumped at sea has whiped out the life in the surrounding area.
    A lot of these chemicals build up in a food chain, where each level is dependant on the other.
    In the end you kill the top predator, resulting in an decrease in the lower levels.
    In a worse case scenario the material is released is such high concentrations (when beeing dumped) that the concentrations reach LC50 values and higher.

    How much time was there between the dumping of the sand and the total whipe out?
  11. Jul 22, 2004 #10
    The dam project took 15 years to build. I think three times they dumped sand and gravel from the river bottom on our beaches. The last time, they did a major fill along the beaches, it seemed to finish the job. Certain things were wiped out first, like seahorses, sepia and schrimp, not far off shore, the sucker fish and sea sand crabs were the last to go. Sea urchens survived it but they live only on rocks 5 meters off the bottom. Now that you mention it the last fill, changed things for good in one season, it seemed, as I only dive in July August Sept..
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