Analysis of Temporal Trends in New Zealand's Groundwater Quality Based on Data from the National Groundwater Monitoring Programme

New Zealand's National Groundwater Monitoring Programme (NGMP) aims to provide a national perspective on groundwater quality, and to identify spatial and temporal trends in groundwater chemistry. In this investigation we assessed temporal trends in water quality at each NGMP site using the seasonal Mann-Kendall test and the seasonal Kendall Sen slope estimator. Hierarchical cluster analysis was conducted using the seasonal Kendall Sen slope estimator rates of change of 15 analytes from 108 NGMP sites, in order to define a set of categories representing distinct patterns of trends in groundwater quality that may be associated with specific causes. Cluster analysis revealed five trend-based clusters, with temporal patterns in groundwater quality that appear to relate to either natural water-rock interaction or human influence. The latter are possibly associated with changes in pumping regime and/or changes in land use in the groundwater recharge zone. Assignment of any monitoring site to one of the trend-based clusters defined in this investigation can provide a simple means of summarising temporal trends in water quality.

[1]  B. Biggs,et al.  Water quality in low‐elevation streams and rivers of New Zealand: Recent state and trends in contrasting land‐cover classes , 2004 .

[2]  Timothy A. Cohn,et al.  Estimation of descriptive statistics for multiply censored water quality data , 1988 .

[3]  Peter J. Rousseeuw,et al.  Robust regression and outlier detection , 1987 .

[4]  P. White,et al.  Hydrochemistry of New Zealand's aquifers. , 2001 .

[5]  M. Close.  EFFECTS OF IRRIGATION ON WATER QUALITY OF A SHALLOW UNCONFINED AQUIFER , 1987 .

[6]  Jim C. Loftis,et al.  Multivariate tests for trend in water quality , 1991 .

[7]  S. Yue,et al.  Power of the Mann–Kendall and Spearman's rho tests for detecting monotonic trends in hydrological series , 2002 .

[8]  M. R. Rosen,et al.  New Zealand guidelines for the collection of groundwater samples for chemical and isotopic analyses , 1999 .

[9]  D. Helsel,et al.  Baseline models of trace elements in major aquifers of the United States , 2005 .

[10]  G. Frapporti,et al.  Hydrogeochemistry of Dutch groundwater: classification into natural homogeneous groupings with fuzzy c-means clustering , 1993 .

[11]  An analytical model of contaminant transport from diffuse sources in saturated porous media , 1989 .

[12]  J. Lester,et al.  Influence of Environmental Factors , 1986 .

[13]  Linear trend analysis: a comparison of methods , 2002 .

[14]  Sylvia R. Esterby,et al.  Review of methods for the detection and estimation of trends with emphasis on water quality applications , 1996 .

[15]  William Dixon,et al.  Review of aquatic monitoring program design , 1996 .

[16]  Keith Turner,et al.  Evaluation of graphical and multivariate statistical methods for classification of water chemistry data , 2002 .

[17]  G. Drecht,et al.  The quality of the groundwater in the Netherlands , 1998 .

[18]  G. McBride,et al.  EFFECTS OF CLIMATE VARIABILITY ON RIVERS: CONSEQUENCES FOR LONG TERM WATER QUALITY ANALYSIS 1 , 2003 .

[19]  H. Broers,et al.  Regional monitoring of temporal changes in groundwater quality , 2004 .

[20]  David G. Smith,et al.  Trends in New Zealand's National River Water Quality Network , 1996 .

[21]  J. Rimstidt,et al.  Trace element distribution in US groundwaters: a probabilistic assessment using public domain data , 2002 .