Add comparisons onto facet_wrap2 plot

Question

I have a plot of four locations and in each locations there are sets of three boxplots for three years.

I have a table of pairwise comparisons to show significance.

I'm interested in adding in significance labels to indicate pairs that are not significantly different.

Current Code

# library(ggh4x)
color <- c("light blue", "#B4EDD2","#E86A92","#F6AE2D")
scaledDaily$year <- as.factor(scaledDaily$year)

scaleBox <- scaledDaily %>%
  ggplot(aes(x=label2, y=mAODscale, fill=year)) +  
  geom_hline(yintercept=0, color='grey') +
  geom_boxplot() +
  labs(y="Scaled Water Depth (mAOD)", x="Location", fill="Year (Mar-Feb)") +
  guides(fill=guide_legend(ncol=1)) +
  facet_wrap2(~mere, ncol=1, trim_blank = TRUE, scales='free_x',
              strip=strip_nested(bleed=FALSE,  background_x=elem_list_rect(fill=color))) +
  theme_bw() +
  theme(text=element_text(size=14, 'Calibri'))

plot(scaleBox)

Test Data

This is not my actual data, I've made it up.

structure(list(lable2 = c("B1", "B1", "B1", "B1", "B1", "B1", "B1", 
"B1", "B1", "B2", "B2", "B2", "B2", "B2", "B2", "B2", "B2", "B2", 
"B3", "B3", "B3", "B3", "B3", "B3", "B3", "B3", "B3", "CH1", 
"CH1", "CH1", "CH1", "CH1", "CH1", "CH1", "CH1", "CH1", "CH2", 
"CH2", "CH2", "CH2", "CH2", "CH2", "CH2", "CH2", "CH2", "CH3", 
"CH3", "CH3", "CH3", "CH3", "CH3", "CH3", "CH3", "CH3"), mAODscale = c(0.561948848, 
0.851883432, 0.293151829, 0.683807808, 0.864472706, 0.380303934, 
0.324501709, 0.765022304, 0.900772901, 0.204731715, 0.877104175, 
0.56367162, 0.206528162, 0.353350116, 0.219628257, 0.840723901, 
0.716389918, 0.569798858, 0.707583441, 0.120064246, 0.275325307, 
0.438391155, 0.308969668, 0.350156436, 0.886955315, 0.693416677, 
0.710065022, 0.561948848, 0.851883432, 0.293151829, 0.683807808, 
0.864472706, 0.380303934, 0.324501709, 0.765022304, 0.900772901, 
0.204731715, 0.877104175, 0.56367162, 0.206528162, 0.353350116, 
0.219628257, 0.840723901, 0.716389918, 0.569798858, 0.707583441, 
0.120064246, 0.275325307, 0.438391155, 0.308969668, 0.350156436, 
0.886955315, 0.693416677, 0.710065022), year = c(1L, 1L, 1L, 
2L, 2L, 2L, 3L, 3L, 3L, 1L, 1L, 1L, 2L, 2L, 2L, 3L, 3L, 3L, 1L, 
1L, 1L, 2L, 2L, 2L, 3L, 3L, 3L, 1L, 1L, 1L, 2L, 2L, 2L, 3L, 3L, 
3L, 1L, 1L, 1L, 2L, 2L, 2L, 3L, 3L, 3L, 1L, 1L, 1L, 2L, 2L, 2L, 
3L, 3L, 3L), mere = c("hatch", "hatch", "hatch", "hatch", "hatch", 
"hatch", "hatch", "hatch", "hatch", "hatch", "hatch", "hatch", 
"hatch", "hatch", "hatch", "hatch", "hatch", "hatch", "hatch", 
"hatch", "hatch", "hatch", "hatch", "hatch", "hatch", "hatch", 
"hatch", "chapel", "chapel", "chapel", "chapel", "chapel", "chapel", 
"chapel", "chapel", "chapel", "chapel", "chapel", "chapel", "chapel", 
"chapel", "chapel", "chapel", "chapel", "chapel", "chapel", "chapel", 
"chapel", "chapel", "chapel", "chapel", "chapel", "chapel", "chapel"
)), class = "data.frame", row.names = c(NA, -54L))

Test Data Plot

In this test data plot. How would I for example put significance bars between Year 2 and 2 in the CH3 site. and the Year 1, 2, and 3 for B1. The significance tests I've run are Kruskal-Wallis and pairwise comparisons.