library(readxl)
POC_and_Mass_flux <- read_excel("G:/Analyses/Explore/POC and Mass flux.xlsx", 
                                sheet = "monthly")
View(POC_and_Mass_flux)

plot(POC_and_Mass_flux$Uppperbound)
lines(POC_and_Mass_flux$lowerbound)
lines(POC_and_Mass_flux$Average)
points(POC_and_Mass_flux$MonthlyMassFlux)