Fieldwork

3.2.1. Sample collection for the contemporary foraminiferal study

A total of 105 samples were collected from five surface transects across two saltmarshes. The locations of these transects can be seen in figure 3.1. A description of each of the transects follows. Twenty seven sediment samples were collected in November 2007 along a transect (OBSS1) 69 m in length across the width of Oglet Bay saltmarsh from the back of the high marsh, at the upland edge, to the low marsh. The samples were taken every 1.5 m until the slope of the saltmarsh decreased, when samples were then taken every 3 m. The

samples were not taken at equal vertical intervals (e.g.Horton and Edwards 2006; Edwards

et al., 2004) as it proved difficult due to the small microtopography of the saltmarsh. Most

of the samples taken for this transect were located within the Phragmites spp. (samples 1-

13). A second Oglet Bay transect (OBSS2) was carried in November 2008 where a total of 19 surface samples were collected over a distance of 39 m, the majority of samples (1-12)

being located within the Phragmites spp. Samples were collected every 1.5 m, again

increasing to 3 m on the flatter part of the marsh. A third transect (OBSS3) was carried out in early March 2009 in an area further west along the saltmarsh, in a location which was

not occupied by Phragmites spp. at the back of the marsh. A total of 30 surface samples

were taken, firstly every 1 m across the saltmarsh starting from the highest trash-line until 17 m whereby the slope decreased and samples were collected every 2 m. Decoy Marsh was sampled in January 2010, where 10 surface samples (DMSS1) were collected from the back of the ridge of Decoy Marsh, 100 m in length. Additional samples were collected in March 2010, a total of 19 surface samples (DMSS2) were collected, starting 30 m from the location of the first sample from DMSS1 (figure 3.1).

All samples were levelled to a fixed temporary benchmark and later levelled to an Ordnance Datum benchmark (Flush bracket, Hale, Childe of Hale Hotel, benchmark number 10558, 16.208 m OD). Sediment samples for analysis of both foraminifera and

environmental variables were collected. A standardised volume of 10 cm3 was taken for

foraminiferal analysis allowing comparisons with other studies including; Phleger and Walton (1950), Scott and Medioli (1980a), Horton et al. (1999a, 1999b, 2000, 2005), Gehrels et al. (2001, 2005, 2006). To ensure the correct volume of sample was collected at

each sampling point a small cylindrical pot was used which had a surface area of 10 cm2 and

was 1 cm deep. At the same time a volume of 30 cm3 was taken for analysis for other

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Figure 3.1 Location of modern surface transects from a) Oglet Bay b) Decoy Marsh (see figure 2). a)

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3.2.2. Core collection for the stratigraphic study of Oglet Bay saltmarsh

Systematic transects of cores were examined across the Oglet Bay saltmarsh, in order to provide information about the past environment and environmental conditions of Oglet Bay, to establish an appropriate location in which to take a core. A total of 50 cores were taken and examined using the Troels-Smith (1955) method of classification. The location of the cores can be seen in figure 3.2 and table 3.1. Each transect was spaced 50 m apart and in each transect between 2 and 5 cores were examined which were spaced 10 m apart. The length of the core retrieved was dependent on: reaching the underlying bedrock; whether the sediment was retrievable and not being re-sampled; or when the sediment was no longer penetrable. The depth varied between 0.13 m and 5 m. The same methodology was not conducted on Decoy Marsh due to the practical limitations of sampling due to restrictions relating to permission and the protection of rare bird species.

Figure 3.2 Location of a) red circles show sediment cores examined for lithology b) black circles show sediment cores collected for geochemical analysis from Oglet Bay.

Table 3.1 Location and altitude of cores analysed.

Core Name Grid Reference Location Altitude

(m OD)

OB1 345250, 381980 Low Marsh 4.482

OB4 345473, 382130 Mid-Marsh 4.822

OB5 345678,382019 Mid-Marsh 5.012

OB6 345689,382030 High Marsh 5.252

PB1 345786, 382125 Mid-Marsh 4.822

PB3 345498, 382122 Mid-Marsh 4.682

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3.2.3. Core collection for the geochemistry analysis of saltmarsh sediments

Several cores were collected from various locations across the saltmarsh (figure 3.2 and table 3.1) in order to determine if there is a distinct pattern in pollution across the saltmarsh as a whole. Each core was levelled to a temporary benchmark then later to Ordnance Datum. Core OB1 was located on the edge of the low marsh using 2 monolith tins 50 cm in length, a total of 95 cm with an overlap of 5 cm. Core OB4 was collected in the

Phragmites spp. vegetation zone close to the boundary of Phragmites spp. and Scirpus maritimus 26 m from the back of the saltmarsh in the same location as surface sample transect OBSS1. It was collected using a wide gouge corer (5.5 cm diameter) and was 74 cm in length. Core PB1 was collected at a similar location to the previous core OB4 and was 70 cm in length. Core PB3 was taken 20 m east along the saltmarsh from OB4, also taken

within the Phragmites spp. reeds and was 90 cm in length. Cores OB6 and OB5 were

collected from an area further east along the saltmarsh, in a location absent of Phragmites

spp. OB6 was collected from an upper marsh location and was 26.5 cm in length. OB5 was collected from a mid-marsh environment and was 83 cm in length. Cores were taken from different locations in order to find a core which maximised sediment depth, had the best potential for sea-level reconstruction based upon foraminifera preservation and species type as well as being representative of the marsh. The core analysed from Decoy Marsh (DMC1) taken from a high marsh location was 42 cm in length below which was only sand. The cores were returned whole to the laboratory where they were sliced every 1 cm. The cores PB1 and PB3 were very wet and unconsolidated therefore both were frozen in order to slice the core without compressing it, and thereby removing water and air, changing the dry bulk density of the sediment.

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3.2.4. Core collection for foraminiferal fossil analysis from Oglet Bay and Decoy

Marsh

Two cores were collected for fossil foraminifera analysis, one from each of the saltmarsh sites. OB5 was taken from Oglet Bay, and was collected from the eastern side of the

saltmarsh, in a location absent of Phragmites spp. (figure 3.3a). It was sampled from a mid-

to-high marsh environment and was 84 cm in length. DMC1 was collected from a high marsh location from Decoy Marsh (figure 3.3b) and was 42 cm in length.

Figure 3.3 Location of cores a) OB5 from Oglet Bay b) DMC1 from Decoy Marsh. a)

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