Columbia subject headings:
Humic acid.
Humus.
Sediments (Geology)
Soil chemistry.
Water chemistry.
Harvard subject headings:
Humic acid.
Humus
Sediments (Geology)
Soil chemistry.
Soils--Humic acid content
Water chemistry.
Princeton subject headings:
Humic acid.
Humus.
Sediments (Geology)
Soil chemistry.
Water chemistry.