Wednesday, May 21, 2008

Overcoming muddy sediments?

As I have noted in several previous blogs we have observed that the grass in most of our muddy bottom creeks and harbors around Long Island has disappeared. There are many theories as to why this happened, but on the top of the list is the stress associated with growing in muddy, highly organic, anoxic (lack of oxygen) sediments.

One theory is that low light and/or high water temperatures (or some other stressor) combined with sediment anoxia kills the plants by poisoning the meristem. This appears to have a significant impact on young seedlings.

Sulfide toxicity has been held out as the main culprit in this scenario. The problem is how can we control sulfur concentrations in the marine environment? The answer is we probably can’t since sulfur is everywhere!

One way around this may be to somehow alter the sediment is such a way that it does not go completely anoxic. This might be achieved by lowering the amount of organic matter and/or increasing sediment texture (from silts to sands). Since lowering organic matter is nearly impossible we have considered changing the texture by adding a thin layer of sand to the surface of the mud. In theory, this should allow oxygen to penetrate the surface sediments and prevent sulfide build-up at the base of the shoot.

We decided to try this out at Noyack Creek in Southampton where we already have a large number of seedlings that resulted form last year’s restoration work. Over the last couple days we set out 30 small tubes isolating individual seedlings on the bottom. The experiment involves doing nothing to the seedling (control) or either adding 1cm or 2.5cm of sand to the surface of the sediment surrounding the seedling. The hope is that we will see a difference in survival and growth between these three treatments in the coming weeks.

At this time all the seedlings look great and there is no sign of stress whatsoever. However, we observed a similar thing a few years ago when thousands of natural seedlings recruited to this site. That year the seedlings looked great during May and early June, but by the end of June they were ALL dead.

We’ll keep checking on our seedlings weekly to see what happens over the next two months. It would be nice if everything survives, but I must admit that I might be more pleased if only the sand treatments survive.


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