Example of using Pandas for renaming columns

gist_column_rename_using_pandas.py

# ...
# The nutrients dictionary holds a panda data frame with columns week, and "PO4_mgP_m3" or "DIN_mgN_m3". 
# for simplicity I rename the columns holding the values as value.

for station in nutrients.keys():
    for year in nutrients[station].keys():
        nutrients[station][year]["PO4"].rename(columns={"PO4_mgP_m3":'value'}, inplace=True)
        nutrients[station][year]["DIN"].rename(columns={"DIN_mgN_m3":'value'}, inplace=True)

# Example of use    
nutrients["B1"][2010]["PO4"].keys()