iso_site_type: Classify Groundwater Stable Isotope Measurements (Dynamic)
In cvoter/isoH2Obudget: Lake Water Budget Using Stable Isotopes

Classifies the site type of isotope measurements as precipitation, lake, upgradient, or downgradient. Upgradient vs. downgradient wells are determined by comparing the daily difference in lake levels and well levels in the 30 days leading up to isotope measurements.

iso_site_type(
  isotopes,
  dictionary,
  lake_levels = NULL,
  gw_levels = NULL,
  threshold = 0.01
)

`isotopes`	a data frame with isotopes measurements as formatted in the isotopes dataset, subset for a single lake.
`dictionary`	a data frame with site id numbers and static isotope site classifications as formatted in the dictionary dataset, subset to records for the lake of interest.
`lake_levels`	a data frame with daily water level measurements as formatted in the lake_levels dataset, subset to lake level records for the lake of interest.
`gw_levels`	a data frame with daily water level measurements as formatted in the lake_levels dataset, subset to groundwater level records at the lake of interest.
`threshold`	minimum median difference between lake levels and groundwater levels during the month of measurement in order to classify groundwater measurement.