To expand on roundy’s thoughts, it would be interesting to follow a few ponds long term. Pick a half dozen or so ponds about to be constructed or renovated and provide ongoing in-depth articles over a several year period. Updates can be once or twice a year. I would pick a range of pond sizes and locations.
Another idea would be to have a couple pages with Forum Posts of the Month. There are some great discussions that many people may be missing because they fall off the Recent Posts sidebar. The could be copied directly from the forum or edited/summarized for the magazine.