# Characterisation of Coastal Sediment Properties from Spectral Reflectance Data
## 2 Study Area and Methods  
The study area examined, from which surface sediments were sampled, is at Oyster Bay, Eastern Cape Province, South Africa (Figure 1). Prevailing winds in this region are towards the northeast (in summer) and the west/northwest (in winter). Tidal range is high microtidal/low mesotidal and swell waves from the Southern Ocean have a significant wave height of >5 m [37]. Oyster Bay is an asymmetrical zeta-shape embayment [38] with an extensive sandy beach that is 6.1 km in total length and with a variable beach width of 30 to 290 m at low tide. Bedrock headlands to the east and west define the overall shape of the bay. An extensive supratidal zone is present, containing parallel-aligned transverse dunes with crests that are 40-50 m apart, similar to those found elsewhere along the South African coast [39]. Dune migration periodically blocks off the mouth of the incoming Klipdrift River. The landward boundary of the supratidal dunes at the back of the beach is marked by dune migration into a zone of highly vegetated and variably cemented linear palaeodunes that extend for \(\sim\)40 km along this coastline. These ridges broadly correspond to the Nahoon Formation of the late Pleistocene Algoa Group, covering the period of marine isotope stages 5 to 2 inclusively [40; 41; 42]. Holocene-age dunes in this region, fronting the eroded older dunes, correspond to largely unvegetated foredunes of the Schelm Hoek Formation and are composed of unconsolidated calcareous aeolian sand [43]. Surficial (top 5 cm) sediment samples (\(\sim\)400 g each, \(n=134\), labelled 6-139) were collected in the field across the beach-supratidal dune system in the centre of the Oyster Bay embayment (Figure 1c). A random sampling approach was used but covering the full width of the beach including the intertidal zone. These samples were bagged, labelled, and sampling locations and their geometric settings marked using a Garmin Etrex 20 handheld GPS (\(x\)\(y\) accuracy \(\pm\) 3 m). In addition, shells of different species (that were broken and did not contain organisms) were also collected from the intertidal zone. Samples were of the Cape brooding oyster (_Ostrea athertoni_, sample 1), Brown mussel (_Perna perna_, sample 2), Agulhas ridged nut clam (_Lembulus belcheri_, sample 3), Southern cuttlefish (_Sepia australis_, sample 4), and a mixed shell sample combining these and other shell species found within the intertidal zone (sample 5) (Figure 2). In the laboratory, shell samples (\(n=5\)) were dried and crushed using a pestle and mortar to generate broken fragments >2 mm diameter. Sediment samples were dried, sieved to remove the >2 mm fraction, and a subsample (\(\sim\)50 g) evaluated for CaCO\({}_{3}\) content using the loss on ignition method. In this  
Figure 1: (**a**) Location of the study area at Oyster Bay, Eastern Cape, South Africa; (**b**) large-scale geomorphic setting of Oyster Bay with the sampling region (panel **c**) shown in the red box; (**c**) distribution of sediment sampling points 006–139 (background image in (**c**) from Google Earth, image date 25 August 2013, which is the latest available image before the sampling period). method, the subsample was weighed, combusted in a muffle furnace for 5 h at 950 \({}^{\circ}\)C, and reweighed. Combustible CaCO\({}_{3}\) content (% of sample mass) was then calculated. Three replicates were undertaken for each sample, and the results averaged. Variation between the replicates was commonly <0.1%. The grain size distribution for each sample was measured using a Mastersizer 3000 Hydro EV for the size range 0.01-2000 \(\upmu\)m with a subsample size of ~5 g. Each subsample was sonicated for 20 s prior to measurement, and five individual grain size distribution patterns were measured using the Mastersizer, and the average taken. The key grain size distribution parameters (\(D_{10}\), \(D_{50}\), \(D_{90}\), kurtosis, skewness, standard deviation and mean) generated by the Mastersizer software were used for analysis.