salinity <-
structure(list(site_number = c("I", "I", "I", "I", "I", "I", 
"I", "I", "I", "I", "I", "I", "II", "II", "II", "II", "II", "II", 
"II", "II", "III", "III", "III", "III", "III", "III", "III", 
"III", "III", "III"), salinity_ppt = c(37.539999999999999, 37.009999999999998, 
36.710000000000001, 37.030000000000001, 37.32, 37.009999999999998, 
37.030000000000001, 37.700000000000003, 37.359999999999999, 36.75, 
37.450000000000003, 38.850000000000001, 40.170000000000002, 40.799999999999997, 
39.759999999999998, 39.700000000000003, 40.789999999999999, 40.439999999999998, 
39.789999999999999, 39.380000000000003, 39.039999999999999, 39.210000000000001, 
39.049999999999997, 38.240000000000002, 38.530000000000001, 38.710000000000001, 
38.890000000000001, 38.659999999999997, 38.509999999999998, 40.579999999999998
)), class = c("spec_tbl_df", "tbl_df", "tbl", "data.frame"), row.names = c(NA, 
-30L), spec = structure(list(cols = list(site_number = structure(list(), class = c("collector_character", 
"collector")), salinity_ppt = structure(list(), class = c("collector_double", 
"collector"))), default = structure(list(), class = c("collector_guess", 
"collector")), skip = 1L), class = "col_spec"))