Abstract:
A good quantitative understanding of phosphorus (P) delivery is essential in the
design of management strategies to prevent eutrophication of terrestrial
freshwaters. Most research to date has focussed on surface and near-surface
hydrological pathways, under the common assumption that little P leaches to
groundwater. Here we present an analysis of national patterns of groundwater
phosphate concentrations in England and Wales, Scotland, and the Republic of
Ireland, which shows that many groundwater bodies have median P concentrations
above ecologically significant thresholds for freshwaters. The potential risk to
receptor ecosystems of high observed groundwater P concentrations will depend on
(1) whether the observed groundwater P concentrations are above the natural
background; (2) the influence of local hydrogeological settings (pathways) on
the likelihood of significant P transfers to the receptor; (3) the sensitivity
of the receptor to P; and, (4) the relative magnitude of P transfers from
groundwater compared to other P sources. Our research suggests that, although
there is often a high degree of uncertainty in many of these factors,
groundwater has the potential to trigger and/or maintain eutrophication under
certain scenarios: the assumption of groundwater contribution to river flows as
a ubiquitous source of dilution for P-rich surface runoff must therefore be
questioned. Given the regulatory importance of P concentrations in triggering
ecological quality thresholds, there is an urgent need for detailed monitoring
and research to characterise the extent and magnitude of different groundwater P
sources, the likelihood for P transformation and/or storage along aquifer-
hyporheic zone flow paths and to identify the subsequent risk to receptor
ecosystems. (C) 2009 Elsevier B.V. All rights reserved.
