Spatial and temporal variations in shallow wetland groundwater quality

SummaryWetlands worldwide are threatened by environmental change. Differences in groundwater composition is one of the factors affecting wetland terrestrial floristic biodiversity. However, few studies discuss variations in wetland groundwater composition. This study presents an analysis of local-scale spatial and short-term temporal variations in 15 groundwater composition parameters of the 7 km2 Naardermeer wetland nature reserve in The Netherlands. Data is available from a network of 35 groundwater wells with 2–4 filters each, at depths between 50 and 800 cm, which were sampled about monthly over a 1-year period, totalling 1042 chemical analysis from 103 filter screens.Relative standard deviations indicate large differences in variation between parameters. Largest spatial and temporal variations were found for nutrients (NO3-, PO43-, NH4+) and redox sensitive parameters (Fe, Mn), and lowest variations for macroions and SiO2. A horizontal zonation in groundwater concentrations has been found related to soil type and soil wetness, with largest horizontal decrease in NO3- and SO42-, and largest increase in Fe and SiO2, going in the groundwater flow direction from dry sandy soils to wet peat/clay soils. No clear horizontal patterns have been found for the macroions. Spatial zonations in the north–south direction and with depth are absent for all parameters.Spatial and temporal variations were found to be related. 3D-maps indicate highest temporal fluctuations at filter screens with lowest median concentrations for NO3-, SO42- and Fe, but the reverse pattern for SiO2. High temporal variations of nutrients and redox sensitive parameters could not be traced back to a seasonal trend.The spatial and temporal variability of groundwater quality parameters as presented in this study, together with their reported effects on different vegetation types, may be used to design efficient monitoring schemes by nature managers having set specific vegetation development targets for different spatial locations.

Temporal median concentrations per filter screen for the parameters SiO2, Fe, NO3- and SO42-. Isosurfaces correspond to indicated median concentrations (from low to high: blue–green–orange). Dots indicate filter screens.Figure optionsDownload as PowerPoint slideHighlights
► Local-scale (five locations/km2) and short-term (monthly) variation in wetland groundwater parameters is analysed.
► Largest variations were found for nutrients and redox sensitive parameters, lowest for macroions and SiO2.
► A concentrations zonation exists for NO3-, SO42-, Fe and SiO2 related to soil type and soil wetness.
► No clear patterns have been found for the macroions.
► High temporal variations could not be traced back to a seasonal trend.