Set up a drip system, or even an irrigation system. City water (Chloramines) landing in the pond are not significant in this small quantity. If there is no soil for a plant to grow in, then no plant will grow there. Over many years moss or lichen may grow with no irrigation. Moss in more shade, lichen in the sun. Lichen will die in chlorinated water.
If there is soil nearby a low spreading plant might be planted nearby that will trail into the area. There are some that would need careful attention to water the first summer or two, then could get by with once a month water when it does not rain, say June, July, August and September. Perhaps Arctostaphyllos 'Emerald Carpet'
. Asparagus sprengeri
is another possibility, but would need more than once a month water in the summer.
To fix the concrete: There is a Brickyard Masonry store in Sacramento, out Jackson Road/16, then south on South Watt to Elder Creek. Also, Silverado is also out that way, on Jackson Road/16. Ask for a type of mortar like product that is not the same mortar as is used for brick or stone work, but is a stronger one. Heavy Duty Masonry Coating, by Quikrete. There are instructions on the package (40 lb bag) for adding an acrylic additive and water. Then paint it on with a very coarse brush. (Ask for one of these brushes when you buy the product). You can add color to the material. It comes in grey or white. You can reseal the whole pond, if you want. 1 bag will cover about 90-100 square feet with 2 coats. The bag is not labeled for under water use, but there is a catalog that these stores use to order these products. In that catalog this product is listed for ponds and swimming pools.
If the cracks are much smaller, then perhaps something in a caulking tube would do the job. Look for something that might be labeled as 'below grade', though that is not the same as a pond or underwater. At least it is OK in a wetter location than 'interior or exterior use'.