To clarify, there are many small gardens and fields in the town, irrigated with water from the desalinization plant. The other main source of food are fishermen (which is one of the reasons you are building a dock). Overseer Jorgal, your predecessor, ran the plant at about three and a half times its current rate of production and traded the excess water for stuff, most notable mercenaries. Although not that rare, chemically pure water is valued in the larger settlements due it being guaranteed safe to drink and for a variety of chemical processes which require pure, distilled water. To quote the end of turn inventory spoiler thingy:
Food Supplies: Adequate. A sudden shortage could cause problems.
The biological and plant life is holding up quite well. The biggest problem has been the various abominations created by genetic plagues, some of which skipped over species boundaries. The main ones that affect you (from the point of view of things that created monsters or something usable, since I doubt you wanna hear all about liver atrophy in burrowing moles) are things like giganticism, increased aggression and prolonged life. These actually stem from experimental medical cures, but your character doesn't know anything about it at this point...
For a few examples that you would be aware of, we have the zoanthropes and horned horses already described. Also, in the distant North it is well known that Nurnberg and it's fellow city states spend much of their effort curtailing the growth of the Black Forest, who's enormous trees grow anything up to ten meters a year and leach all the goodness from the soil.