<ol>
<li><p>Most of the sediment and nutrients of the Mississippi River no longer reach the coastal wetlands, a phenomenon that has adversely affected the region's ecological balance.</p></li>
<li><p>Most major air pollutants cannot be seen, although large amounts of them concentrated in cities are visible as smog.</p></li>
</ol>
<p>But how is that possible, what about “the region’s” in question 1. Shouldn’t the apostraphe be omitted, since as it is now, it doesn’t refer to something possessive. “'s” is a shorter form for “is”, isn’t it?</p>
<p>And on question 2, how is that possible too? in “are visible”, shouldn’t it be changed to “are as visible” then complemented with “as smog”, to make a correctly structured form of “as something as something”.</p>
<p>I believe it is a possessive. The ecological balance of the region.</p>
<p>
</p>
<p>If you implement the as…as structure, you’re changing the meaning of the sentence. It is not a comparison between pollutants and smog. Rather, it is trying to say that it is visible in the form of smog.</p>
<p>That is a possessive apostrophe because it is the “ecological balance of the region” or “the region’s ecological balance.”</p>
<p>In #2, it is not to be a similie (“as…as…”). They are visible as smog, or you could say, they appear as smog. The sentence isn’t comparing them to smog but saying that they are smog.</p>
<p>Hold on, hold on. OK, number 2 is okay. Back to number 1:
's -> shorter form for “is”. For examples, “He’s stupid” or “He is stupid”.
s -> possessive case. “The carpenters car”. </p>
<p>Or am I mixed up, should it be the other way around?</p>