Use (or non-use) of articles before abstract nouns

I know I have asked a similar question before but this time I have examples taken from COCA and they do puzzle me. I would love to hear explanations from native speakers.

The following (incomplete) sentences taken from COCA show three different ways of article usage before "reduction of something".

(1) $1.5 billion could be used for things like restoration of fish and wildlife, the reduction of mercury pollution and greenhouse gas reduction.

(2) Fasting imposes a reduction of calorie intake, which is particularly significant if the hours of darkness are few

(3) A key goal of the optimization phase is reduction of communication over-head via a range of techniques, including execution of communication in parallel

Can you say "a reduction of mercury pollution" instead of "the reduction of mercury pollution" in (1)? Likewise, can you say "the reduction of calorie intake" instead of "a reduction of calorie intake" in (2)? If you can, what difference in meaning would that make in each case?

My guess is that, in using "a", the speaker (or writer) has in mind some image of what is to be reduced, whereas in using "the", the speaker (or writer) has in mind more of the fact of reduction itself than what is to be reduced, lacking a better description.

Even if my guess is right, (3) still remains to be explained. Is the lack of article before "reduction of communications over-head" a case of ellipsis? If not, why don't you need an article here as in the other two examples? What difference does the absence of an article make in comparison with "the reduction of communication over-head" or "a reduction of (in) communication over-head"? Can you or should you use "a" or "the" in this case?

In addition, there is another issue in (1). There is no article in front of "restoration". Why is there no article here, whereas there is a definite article in front of "reduction"?

The general principle here is just that the focusses on a specific instance of something, whereas a implies one among many possibilities.

Thus in #1, the reduction of mercury pollution implies either that it's just one example of a type of pollution that could be reduced, or that mercury pollution is a clear example of things you might spend $1.5 billion on. But it's optional regardless of the exact sense intended.

In #2, if the hours of darkness are few implies we're specifically talking about how many hours of darkness there are at the time/place of fasting. There's no special grammatical rule applicable here, but idiomatically I'm sure most native speakers would include the in such contexts.

In #3, a range of techniques simply implies that the writer isn't concerned with exactly which range of techniques he's talking about. If in fact he meant the particular techniques actually used by his company, for example, he could have said our range, More rarely, in contexts where he's thinking of the complete range of possible techniques, he might use the definite article. But it would be generally considered "ungrammatical" to have no article at all in this construction.

Note that these are very fine nuances that won't normally apply anyway. In all the "articles" I've looked at above, and in comments below, any of definite | indefinite | zero article could be used, and it's unlikely many if any variations would strike most people as "odd".

@Fairdinkum, I think that the reason why the indefinite article is necessary in "Fasting imposes a reduction of calorie intake" is because it makes it clear that there are other possibilities for reductions of calorie intake (fasting is not the only one).

As for the use or non-use of the definite article, I agree with the other commenters that it is immaterial in the cases of example 1 and 3.