Where's Nina?

So here's a little challenge for you. It wasn't my watch so I didn't do the blog for the puzzle, (don't look at that until you need to check the answer!) but there was a most entertaining enigma over yesterday's Times Quick Crossword. Some solvers complained that some of the answers were a bit hard to get, but then the setter dropped by to say...

Felix (or Dimitry today) says:

There is a Nina in this puzzle I have just remembered, which probably accounts for a couple of the obscurities.
I do apologise and hope it didn't spoil people's enjoyment too much.
F

So what is a Nina? As described more fully here, "A Nina is a special feature of the crossword grid: a word, words or phrase hidden within a pattern of cells in the completed grid." 

Well the crossword itself wasn't too challenging and took me less than 5 minutes, but here was an additional challenge... what is the Nina? Well the good news is, that to solve it you don't need any cryptic crossword solving skills at all - it's all in the grid of answers. So here it is...

Well this was much harder than the crossword itself! I just couldn't see it. And what did our setter mean by "Dimitry today"?

I replied...

Where are you Nina?

"The puzzle gave me no trouble, although I'd never heard of a BENGAL cat. Then. having come here, I find there is a Nina to be found and spent twice as long looking for it than solving. Best I can find is that the puzzle is NON-U. As for "(Dimitry today)", DIMITRY = John Grimshaw = Joker, so is there a hidden joke?"

I had noticed that the grid didn't include the letter "U". But that and the link to Joker were complete red herrings. Felix came back with..

RE: Where are you Nina?

In fairness the Nina is probably impossible to see unless you know what you are looking for.
Even if you look up March 6 anniversaries and find out what a certain Dimitry (not JG) was up to you still might not spot it.
Hence my apology for the self indulgence. 

Well, to save you the trouble of looking it up, yesterday was the 150th anniversary of Dimitry Mendeleev announcing his discovery of the Periodic Table of elements.

I tried finding them in the grid... but I got to Vanadium, and there was no V. Hmm. Stuck. But somebody else on the crossword blog came up with the oh so clever answer. But don't go and look yet. I've another clue for you!

Rather spookily.. or maybe it is just serendipity... or the Baader-Meinhoff effect... on the same day I came across this puzzle in the Codebreakers Puzzle Book my sister-in-law had sent me for Christmas....

TABLE OF RIVERS

Which river could follow next in the list?

Humber (1)

Hebron (2)

Liffey (3)

Beaulieu (4)

Brahmaputra (5)

The numbers are important... as they are for the crossword Nina.

The next river is, of course, the Clyde.

And the route to getting to the answer is the same for both puzzles! Can you work it out?