It looks too broad to be Riccardia, looking at the other flora it looks like it is probably limy water, so <"Pellia endiviifolia"> possibly.Could it be Riccardia chamedryfolia?
The Hart's-tongue fern (Asplenium scolopedrium) and Herb Robert (Geranium robertianum) are plants you would associate with base rich conditions, so I guessed the water had some bases in it.the GH/KH was surprisingly high.
I associate it with the tops of stones in limestone streams, but I don't think it needs to be continually wet. It is the only liverwort (that looks like this) that you find in very base rich water. <"Pellia epiphylla"> can look almost identical, and is also really common, but it grows in less base rich conditions.Sounds likely to be the pellia you describe. Is it an aquatic species or just likes wet spots near water?
I'm pretty sure that one is <"Conocephalum conicum">, it looks quite big and chunky, and you can see the very obvious pale dots (air pores), it is a common Liverwort in any damp, bare places.I found this growing on the brickwork of a canal lock in Staffordshire.