Coastal wetlands in and : Understanding rainfed groundwater dependent ecosystems to underpin conservation management

Nick Robins and Charlie Stratford BGS and CEH Groundwater Dependent Ecosystems 27 February 2013 THE TEAM: •Centre for Ecology and Hydrology / British Geological Survey •University of Southampton •University of Groningen •Natural England •Countryside Council for Wales •Ecological Surveys (Bangor) •Geological Survey of Northern Ireland •Sefton Borough Council THE COASTAL DUNE WETLANDS: •Sandscale – Furness •Ainsdale – Sefton Coast •Newborough Warren – Anglesey •Whiteford Burrows – Gower • Burrows – North •Holme – North Norfolk •Magilligan – Co. Londonderry The coastal dune wetlands of England and Wales

Masters of sand dune hydrology are the Dutch. Their differ in that they are deeper with a saline wedge below and used to filter Rhine water for supply and as coastal defence structures. Magilligan is different: thick and very big I’m not licking any water off this beach! coastal dune spit system. Classic groundwater ridge two thirds way inland towards estuarine marsh at estuary mouth. Carboniferous Limestone hills to the north...

...and a typical long-term dipwell record in dune slacks at Ainsdale, Sefton Coast High frequency hydrograph data for Whiteford Burrows, Gower. Note the TREES and NOT TREES issue (RED SQUIRRELS or RABBITS?)

Hourly Rainfall Well 11 in open dunes Well 6 in trees Well 4 nearest beach

5 30 Quiet response beneath trees 25 4.8

Flashy open 20 warren 4.6

15

4.4

Moderated by beach as fixed 10 (mm) (mm) Rainfall Rainfall head boundary

Water Level Level Level (m(maOD) aOD) Water Water 4.2 5

4 0 09-Oct-08 09-Nov-08 10-Dec-08 10-Jan-09 10-Feb-09 13-Mar-09 Whiteford Burrows The great storm of April 1995 300 250 200 150 Richter analysis – 100 hydroecological 50 indicators of change 0 Percentage change Percentage Braunton -50 Whiteford -100 Ainsdale events Flood duration Flood Drought duration Drought

Frequency of drought drought drought ofof Frequency Frequency 150

Frequency of floodfloodofofevents events Frequency Frequency 100

50 Percentage change due to 0 long term decline in effective Braunton

Percentage change Percentage -50 rainfall at Braunton Burrows, Whiteford rapid storm event foreshore -100 Ainsdale erosion at Whiteford Burrows, and long term foreshore

erosion at Ainsdale events Winter mean Winter events Summer mean Summer Flood duration Flood Flood magnitude Flood Drought duration Drought Frequency offlood Frequency Drought magnitude Drought Frequency of drought ofdrought Frequency Surface outflow (0 l/s) no standing water

4 845/12.3

8 1968/14.2

7 3080/13.0

32630/12.4

5 734/12.8 Primary slack

2 602/13.5 Whiteford Burrows: 6 870/12.9 monitoring Tors Slack 1 627/13.7

Key: 6 - dipwell number 870/12.9 - Conductivity ( µ S/cm) / temperature ( o C) Whiteford primary slack 26 May 2011 BRAUNTON BURROWS

Grain size profile D4. Hazen approximation gives K of ~10 m/d

Moisture content depth profiles for dipwells D2, D3 and D4 showing water table in D4 in December 2011 and February 2012 Well Temperature SEC DO depth (m HCO 3 Site Date RWL (mbgl) bgl) (oC) (µS/cm) pH (mg/l) Eh (mg/l) High dune

Dnew 4 15/02/2012 5.93 9.2 10.4 804 7.9 13.4% 23 285

Dnew - 5 15/02/2012 5.06 9.2 12.1 687 8.0 6.7% 107 330 Dune slack

1 25/02/2010 top of casing 1.97 7.9 719 7.3 0.4 139 373

2 25/02/2010 0.51 1.97 8.9 597 7.5 0.23 133 291

3 25/02/2010 0.35 1.97 8.3 835 7.7 0.15 248 307

7 15/11/2012 12.2 599 7.6 0.5 148 306 Bedrock Borehole (Pilton Mudstone Formation)

GC 14/11/2012 artesian 24 and 63 12.0 877 7.2 0.9 23 254

Braunton Burrows L and δ 2H profiles. Peaks, if annual, suggest downward piston flow of ~1 m/yr Problem: need downward Cause : perturbation of piston flow of ~2 m/yr to shift climate with wet all the effective rainfall down summers and dry winters. the unsaturated zone with porosity of 30% and moisture content of 13%.

Mean residence time Age dating with SF6. Sampling 1.5 ccSTP/L EA

CFC not used as Dipwell Site Eastings Northings Date SF 6 (fmol/l) ± 2 years water in vadose and 1 Dune slack 245849 135363 25/02/2010 2.65 (2004) 6 saturated zones 2 Dune slack 245222 135738 25/02/2010 2.49 (2003) 7 tends to be 3 Dune slack 244765 135888 25/02/2010 2.73 (2005) 5 depleted in oxygen Dnew 4 High dune 244902 135684 15/02/12 1.76 (1996) 16 and CFC may have Dnew 5 High dune 244760 135731 15/02/12 2.06 (1999) 13 become degraded. GC Bedrock 24648 13748 14/11/12 1.310 (1992) 20 Moisture profiling –Braunton Burrows Rainfall Water Level 5.5 8

5 6

4.5 4

4 2 Rainfall (mm) Rainfall

Water Level (maOD) Water 3.5 0 0.45 0.4 0.35 0.3 0.25 0.2

Soil Moisture Moisture Moisture Soil Soil (m3/m3) (m3/m3) 0.15 19/08/12 16/09/12 14/10/12 11/11/12 Date Soil Moisture @ 10 cm Soil Moisture @ 20 cm Soil Moisture @ 40 cm Soil Moisture @ 1 m So why monitor and measure?

To advise national strategy for conservation management.

What has it all got to do with the ecology anyway?

Plant species according to pH, depth to water, flooding, nutrient supply etc.

Hydrogeological and hydrological enquiry underpins ecological understanding and informs the managers.