Sediment plays an extremely important role in the function of ecospheres. It is where most insoluble minerals and nutrients are found which allows the plants to grow. It also has the greatest influence on the pH of the ecosphere. Sediment taken from stagnant bodies of water such as ponds and vernal pools tend to have more nutrients which can cause higher ammonia levels and then eventually a crash. River sediment is much less nutrient dense however pond sediment tends to contain much more life which is why I tend to use both in mine. I usually use 1/3 pond sediment to 2/3 river sediment and mix a little gravel to help plants anchor themselves.