Eutrophication

So I am having breakfast and have been thinking more about eutrophication. The gulf is bothering me on lots of counts, one is that it was in trouble before this mess. Eutrophication is roughly were there is an increase in nutrients in an ecosystem. Which generally turns out to be bad.

Bad in the sense that it kills things, and it is generally hard to resolve. We tend to think of ecosystems being balanced in terms of plants and animals, but everything has to be balanced - meaning chemistry also. All biological systems operate with just the right amount of this and that in the system.

Fresh water is a bit easier to understand, so we can begin there. Wastes create ammonia, nitrites and then nitrates. The microbial populations are there already to convert one to the other. Nitrates are the less harmful and can then be used by plants. This is the nitrogen cycle, and why you need to let fish tanks operate a week or two prior to putting fish in.

Now if you suddenly start adding extra stuff here and there, then there is always a lag as the microbial populations catch up. And that is what happens in places like the gulf on a massive scale each summer.
There are lots of cycles happening like this, and seawater is much more complex in terms of chemistry, there are carbonate cycles for example which many marine animals depend on for making their skeleton or home. Corals absorb carbonates and release carbonates, and of course that is influenced by other factors of equilibrium. To go further, as the ph changes equilibriums change, eg. ammonia <> ammonium and so on.

The point is that they are very complex systems. Nature can compensate very well in most cases, but there are limits. So fundamentally I am starting to wonder what the limits are.

In case of the gulf it was already suffering massive dead zones each year from nutrient rich runoff. Think algae bloom then you get into problems of low light at depth, remember much benthic marine life depends on that light. And to make it worse at night the algae like all plants absorb oxygen. Then at the end of summer it all dies, decomposes and uses more oxygen from the water column.

So that is how you end up with hypoxic conditions, or in real terms a dead zone each year in the gulf the size of New Jersey.

Anyway I have heard reports about how oil decomposing bacteria will breakdown the oil - and use up oxygen. Which makes sense but here is where the experiment begins.

I cant remember the exact numbers, but the surface oil is over a huge area blocking out light in the middle of summer over a highly eutrophic zone. To make it worse, dissolved oxygen falls with increasing temperature.So straight off you will have algae population collapse - which really shouldn't have been there in the first place... Then the zooplankton go next - including this years spawning marine life, and on up the chain everything starts dying.

And we havent even got into straight out toxicity from the oil itself and worse the dispersant used. So eventually you get to a point where everything is dead - the death creating more hypoxic and eutrophic conditions and on and on.

So I am wondering ok, how does that runaway scenario stop? As far as I can tell not easily. If it was a river or open ocean, then there is more outflow, eg. Denmark or the Japan Sea as better examples of bad cases. In the case of the gulf the currents are actually weird. It takes a long time to flush out through the Florida Strait. The loop current means stuff can circulate there for years. (There must also be a fundamental limit to even what the open oceans can take also, but the larger scales help).

I suppose it is academic wondering, but it has got me thinking purely in terms of "how much can it take?"
I also should say I am not in the serious hippy category, but I am smart enough to know that the planet is a small place, and resources are finite. If the 500 000 tons of seafood (or whatever the number is) is no longer reaching peoples tables, then it means that they will find the food somewhere else. So it is a serious global problem. "Ok no shrimp...we will take the chicken wings..."