Hi all
I can't find what I am looking for so I am asking here.  I have a
dataset that looks something like this. 

Year   season  percent_below
2000 Winter     6.9179870   
2000 Spring     1.6829436   
2000 Summer     1.8463501   
2000 Autumn     3.8184993   
2001 Winter     2.8832806   
2001 Spring     2.5870511   
2001 Summer     0.0000000   
2001 Autumn     4.7248240   
2002 Winter     4.4532238   
2002 Spring     3.7468846   
2002 Summer     1.0784311   
2002 Autumn     3.7061533   

I have plotted this nicely using 
barchart(percent_below ~ factor(Season, levels=Season), data= dataset1,
group=Year)
This gives me a barplot by season with each year shown in that season.  
Now the tricky part.  My data is from 2000 to 2007 and 2007 is an
important year.  I have an upper and lower limit for percent_below for
2007 for each season.  I would like to add the upper and lower limit of
2007 as a black line to each season.  The upper and lower limit will be
different for each season.  This is being done so for a comparison so I
need it done this way.
Thanks in advance for the help.

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