St. Croix River Watershed Trends Analysis Water Quality Data for 2007 and 2018
In this report, ECCC provides the results of trend analyses for water chemistry data obtained at both the Forest City and Milltown stations. Mann-Kendall trend tests (or the Seasonal variant of the test) were conducted for each water quality parameter, to identify monotonic changes in concentrations for a suite of parameters over a long time period. Trends were assessed for most parameters over a 12 year period from 2007 – 2018, and for selected metal parameters (antimony, arsenic, beryllium, chromium, cobalt, copper, lead, nickel, molybdenum, selenium, titanium, vanadium, and zinc) over an eight year period from 2011 – 2018. The shorter time period for metals was due to changes in laboratory methodology in 2010, which improved sensitivity and lowered detection limits. These new trend analyses are the first step in investigating long-term changes within the St. Croix watershed.