"are there" or "they are"

What possibly could “are there” mean in the following sentence?

“When these bacteria die, the compounds of nitrogen remain in the soil and are there ready for other plants to use for their feeding.”

Hi Jraou

In the context, the word “there” refers to a location. The word “there” refers back to “in the soil”, so “are there” refers to the compounds that “are in the soil” in this case.
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As Amy said and a couple of examples, for display purposes only:

Don: They are there now, i.e. at home, if you want to call them.

Mally: Ah, they are there/at home. Good.

Sherry: Hi, I left my keys somewhere. Are they there, i.e. at your house?

Shelly: Yes, they are here.

Sherry: Ah, they are there/at your house. Good.

Here the words ‘are there’ shall be understood as ‘remain there’, ‘there’ referring to the soil already mentioned.

Or, “are there ready” shall be understood as ‘remain available’.

Thanks Yankee, nanucbe and Molly! You were such a great help!

BTW, “are there” is not necessary at all in that sentence. “When these bacteria die, the compounds of nitrogen remain in the soil ready for other plants to use for their feeding.”