Considering the Civ that gets them a. is generally one of the first civs founded and b. only gets polders total, and considering that high pop cities need health buildings which require masonry anyway, maybe a significant buff, or potential from buffs due to research, is necessary? Maybe for a start the +1 food from irrigation doesn't require fresh water access? (The main bonus from irrigation here would be reducing the water levels, so that food can be grown more effectively without drowning the plants, I think? Generally it is for fenland and such) Plus soe other buffs, or else give Girnir some more bonuses?
Wait should this go in the Balance thread?
Breeding pen last time I checked still had the HELP_TEXT_BREEDING_PENS message thing as it's help text.