def subset_wqt_by_gain(avg_wq_site_df, gain_field_name, gain_setting):
	"""
	Subsets daily water quality by specified gain setting
	:param avg_wq_site_df: average vertical profiles by site for specific date
	:param gain_field_name: field name that stores the gain settings
	:param gain_setting: gain setting (gn0, gn1, gn10, gn100)
	:return: water quality subseted by gain
	"""
	subset = avg_wq_site_df[avg_wq_site_df[gain_field_name] == gain_setting]
	return subset