Evidence for sensitivity of dune wetlands to groundwater nutrients

Abstract

. 2014. Evidence for sensitivity of dune wetlands to groundwater nutrients. Contact CEH NORA team at noraceh@ceh.ac.ukThe NERC and CEH trademarks and logos ('the Trademarks') are registered trademarks of NERC in the UK and other countries, and may not be used without the prior written consent of the Trademark owner.Manuscript for Science of the total environment ACCEPTED Dune slacks are seasonal wetlands, high in biodiversity, which experience considerable within-year and 24 between-year variations in water-table. They are subject to many pressures including climate change, 25 land use change and eutrophication. Despite their biological importance and the threats facing them, 26 the hydrological and nutrient parameters that influence their soil properties and biodiversity are poorly 27 understood and there have been no empirical studies to date testing for biological effects in dune 28Manuscript for Science of the total environment ACCEPTED 2 systems resulting from groundwater nutrients at low concentrations. In this study we examined the 29 impact of groundwater nutrients on water chemistry, soil chemistry and vegetation composition of dune 30 slacks at three distance classes (0-150 m, 150-300 m, 300-450 m) away from known (off-site) nutrient 31 sources at Aberffraw dunes in North Wales, whilst controlling for differences in water- (Provoost et al., 2011;Jones et al. 2011; Beaumont et 56 al. 2014). With regard to the latter; nutrients from atmospheric deposition have increased dramatically 57 from their pre-industrial levels of 2 -6 kg N ha -1 yr -1 (Fowler, 2004). As a consequence, the critical load 58 defined for dune slacks, 10-15kg N ha -1 yr -1 (Bobbink and Hettelingh, 2011), is exceeded across much 59Manuscript for Science of the total environment ACCEPTED 3 of Europe. While the effects of atmospheric deposition have received recent attention in dry dune 60 habitats (Plassmann et al., 2009; Remke et al. 2009;Jones et al. 2013), relatively little attention has 61 been given to the impact of other sources of nutrients in dune wetlands, indeed in wetlands in general, 62 and the issue of groundwater or surface water-derived nutrients is not explicitly considered within 63 atmospheric critical loads frameworks. In dune systems that are not isolated hydrologically from 64 surrounding groundwater, there is the potential for nutrient inputs to these habitats from agricultural and 65 other sources via groundwater to add to the nutrient load already received from atmospheric deposition. grasslands (Heil and Diemont, 1983). However, in dune slacks there is still relatively little empirical 82 evidence of nutrient impacts either from atmospheric deposition or from other sources, especially at 83 realistic N loads. One of the few studies, using high nutrient loads on dune vegetation at Braunton 84 Burrows demonstrated that Agrostis stolonifera dominated a dune slack following surface additions of N 85 and P (Willis, 1963). 86 87 Dune slack water tables tend to be at their highest in winter and fall in the summer m...

Using chemical, microbial and fluorescence techniques to understand contaminant sources and pathways to wetlands in a conservation site

“…By contrast, nitrate concentrations in Stream A, which drains the pastureland and flows onto the sand dune site, are significantly higher than those in stream B and previous studies have shown they can exceed the 50 mg/L threshold for designation of a nitrate vulnerable zone by the UK Environment Agency (Rhymes et al, 2014, Environment Agency, 2012. This implies that stream A has additional N inputs compared to stream B, these are likely to be from fertilisers leaching from the steep sloped pastureland adjoining the stream.…”

“…Annual long term average rainfall at the site is 847mm .There are a number of potential pathways by which nutrients and coliforms can enter the site, these include streams and ditches, surface runoff draining agricultural land and flowing onto the site, seepage of nutrients into the groundwater flowing under the site, and on-site sources such as grazing cattle and rabbits. Previous work has previously shown a nitrogen groundwater contamination gradient that extends into the site from the fertilised pastureland on the south east border with groundwater travelling in a south westerly direction (Fig 1) (Rhymes et al, 2014). To determine the nature and pathways of the contamination, measurements were made bimonthly for a 12 month period (i.e.…”

“…Samples were collected from the top 10cm of the water table at each well using a sterilised pump and tubing, which was disinfected with Trigene and flushed three times with deionised water between samples into 250 mL sterile plastic bottles. During periods of inundation, for up to 4 months between November and February (Rhymes et al, 2014), when water tables were above ground level in certain slacks, samples of the standing water above the piezometer were taken. Groundwater depth was measured monthly at each piezometer.For fluorescence and E. coli measurements, sampling was conducted for 4 of the 6 sampling periods.…”

“…Atmospheric nutrients have been demonstrated to have adverse impacts on the ecology of protected dune habitats , Plassmann et al, 2008, Field et al, 2014. However, the specific impacts of relatively low levels of nutrients from groundwater on aquatic habitats in dune systems have only recently been documented (Rhymes et al 2014). As well as nutrients, diffuse inputs of dissolved organic matter (DOM), and micro-organisms into groundwater and surface waters also occur via runoff, field drainage and leaching, as a result of agricultural practices such as slurry and fertiliser application.…”

“…The presence of TCs in surface or groundwater is usually considered evidence of recent faecal contamination, with E. coli remaining active for 16-45 days in the subsurface (Taylor et al, 2004). This study aims to use a combination of inorganic chemistry, DOM fluorescence and culturable E. coli and TC counts to evaluate the potential sources and pathways of nutrients and contamination to a sand dune site designated for its international nature conservation importance, known to be affected by nutrients from the surrounding agricultural land (Rhymes et al (2014). Building on the previous study, a further year of bi-monthly sampling was carried out to separately assess the degree of potential contamination and likely sources of contaminants from a) off-site sources entering the site from streams, b) off-site sources entering the site via runoff/overland flow, c) groundwater flowing under the site, and d) on-site sources.…”