I myself am not a fan of ground level decks. They typically have ventilation issues trapping moisture under the deck. The lower part of beams/joists tend to retain moisture which causes the wood to swell. The tops exposed to sun and air moving across the deck tend to dry out and as a result shrink. The differential moisture content tends to cause the wood framing members to cup and twist. A friend of mine did not heed my advice and built one. five years later he was having to repair it. When clients want me to design ground level decks I do my best in convincing them to construction a ground level patio. If you must have a wood working project then add a pergola or sunshade to the patio.
I see you're gotten a lot of imput. I'd like to add a few items. I have attached the "Prescriptive Residential Wood Deck Guide" http://www.awc.org/publications/DCA/DCA6/DCA6-09.pdf
as published by he American Wood Council based upon the 2009 International Residential Code. This guide should answer most of your questions. It will provide tables for beams and joists.
I would check with you local building department and determine if a building permit is necessary for your project, and if they have an deck design guidelines. Some jurisdiction have a list of requirements you have to meet. If you build a deck and a permit is required (and you failed to obtain one) you can be fined, and at the worst be required to take down the deck. A few quick questions don't cost and can save you money.
I'm a little confused by your sketch. What size are the joists? I see you said 16' in length. You also stated you're using pressure preservative spruce-pine-fir?
Deck construction although fairly simple and straighforward must be done correctly. Deck collapses are common and often results in serious injuries. A lot of research has been done in the last few years in the proper construction of decks, and every three years additional requirements come on. I understand your's is a ground level deck. I'm making a blanket statement about decks in general.