Delayed Impacts Of Land-use Via Groundwater
On Lake Taupo, New Zealand
Author(s)
J. C. Hadfield, U. Morgenstern & J. J. Piper
Abstract
The near pristine quality of water in Lake Taupo has begun to deteriorate, largely
as a result of farming. Groundwater investigations were undertaken to estimate
potential future land-use impacts and the lag in effects. The lake is a sink for
groundwater migrating indirectly via baseflow dominated streams and to a lesser
extent by direct seepage. Land-use impacts are increasing as contaminated water
progressively replaces older, higher quality groundwater.
The age of groundwater in Lake Taupo catchment was estimated by
measuring the cosmogenic isotope tritium and atmospheric trace gases CFC and
SF6. Mean residence times of samples ranged from about 20 to 75 years. Higher
nitrogen concentrations occur in groundwater with a greater fraction of water
recharged since farm development some 40 years ago.
Numerical groundwater modeling predicts nitrogen mass loading to the lake
from current land-use will continue to increase for a substantial period of time
(> 100 years). This lag relates to the considerable time required to replace old
pristine groundwater with nitrogen enriched water from farming. Modeled
nitrogen flux via groundwater of some 300 tonnes annually may potentially be
expected, with 25,000 tonnes stored in the groundwater system. A proposed
initiative to reduce manageable nitrogen loading from the catchment by 20%
would be a useful mitigation measure.
Keywords: groundwater, diffuse contamination, dating, lag, nitrogen, model,
Lake Taupo.
Keywords
groundwater, diffuse contamination, dating, lag, nitrogen, model,
Lake Taupo.
Related Book
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