Trend detection in water-quality and load time-series from agricultural catchments of Ylaneenjoki and Pyhajoki, SW Finland

: Carlos A. Gonzales-Inca, Ahti Lepistö, Timo Huttula

Publisher: FINNISH ENVIRONMENT INST

: 2016

: Boreal Environment Research

: BOREAL ENVIRONMENT RESEARCH

: BOREAL ENVIRON RES

: 21

: 1-2

: 166

: 180

: 15

: 1239-6095

: 1797-2469

: http://www.borenv.net/BER/pdfs/ber21/ber21-166.pdf

Long-term water quality (WQ) and load trends were studied in the catchments of Ylaneenjoki and Pyhajoki in SW Finland, where agricultural water protection measures have been implemented since the mid-1990s. A univariate Mann-Kendall (MK) trend test, a multivariate Mann-Kendall (MMK) trend test, and a multivariate Mann-Kendall trend test applied to the WQ data flow-normalized by a semi-parametric model (FN-MMK) were used. The results of all methods were similar when the nutrient concentration data were used, but they differed when using the nutrient load data. The FN-MMK test was intended to detect trends caused by anthropogenic impact. In the clay-soil-dominated catchment of Ylaneenjoki there were increasing trends in the concentrations and loads of total nitrogen, nitrate-nitrogen, dissolved reactive phosphorus, and a decreasing trend in suspended solid concentrations. However, no increasing or decreasing trends were detected for the majority of the concentrations or loads in sand-soil-dominated catchment of Pyhajoki. This suggests different responses to comparable environmental and anthropogenic pressures in these two river basins.