qgis - Calculate volume from raster (GRASS) with depth per cell

I'm trying to calculate the volumes of depression areas filled with water. I have the depth for each cell in the raster, and I'm trying to get the total volume of cells adjacent to each other. Which I then, in step 2, need to remove all the bodies of water lower than a given threshold and then convert the file to vector/shp format.

I've trying using the r.clump and then r.volume function in qgis, but I keep getting this error:

ERROR: r.volume: Sorry, is not a valid parameter ERROR: Required parameter not set: (Name of input raster map representing data that will be summed within clumps)

C:\PROGRA~1\QGIS2~1.18\bin>v.out.ogr -s -e input=centroids0814b2718bf14943909f424cebd714fb type=auto output="C:\Users\JGJ\AppData\Local\Temp\processing503b826c304e474ebc5a9862a9dd29e1\b97bc604e110497ab8dde2cc3da478e7" format=ESRI_Shapefile output_layer=centroids ERROR: Vector map not found

C:\PROGRA~1\QGIS2~1.18\bin>exit Converting outputs Loading resulting layers

The following layers were not correctly generated. Centroids You can check the log messages to find more information about the execution of the algorithm

I could not get the above to work, but managed a workaround.

I have converted raster to vector, and calculated each polygons volume. I have a lot of polygons I want to dissolve into a lot of larger polygons, which can be done with Dissolve. However each of the small polygon has a volume too it, that needs to be summed up. If I do a dissolve it just adds the total volume of all the polygons in the layer, and not those that get dissolved. Added a concept picture.