Applications of stable carbon and oxygen isotope analysis to some aspects of coastal environmental change. Edward James Twiddy The copyright of this thesis rests with the author. No quotation from it should be published without the written consent of the author and information derived from it should be acknowledged. Thesis submitted for the degree of Doctor of Philosophy. University of Durham, Department of Geography. December 1996. Abstract. Applications of stable carbon and oxygen isotope analysis to some aspects of coastal environmental change. Edward J. Twiddy, University of Durham, December 1996. Two projects were undertaken to assess the possibility of using the stable isotope composition of plant cellulose in reconstructions of coastal environments. One was specific to the common reed, Phragmites australis (Cav.) Trinius ex. Steudal, which is often found as a macrofossil in coastal sediment sequences. Analysis of material from 3 contemporary communities at Roudsea Marsh, Cumbria, U.K., which are subject to different frequencies of inundation by the tide, did not produce coherent or consistent intra- or inter-community patterns in either 5 13 C or 5 180. Local tide gauge records and data on sediment characteristics, soilwater salinity and isotopic composition, and plant habit all pointed towards significant chemical and physical differences between the three communities analysed. However, the extent of intra-community and intra-plant variation in both the isotopic ratios was such that it was impossible to assign particular values of 513C or 5 180 to particular communities. The possible reasons for this are discussed. The second project focused on a species-poor saltmarsh in western Scotland at Kentra Bay, Argyll. Here the contemporary marsh is backed by an extensive raised bog (Kentra Moss), below which are late Holocene sub-fossil saltmarsh deposits. The project compared 5 13 C values from all the species present in 4 contemporary saltmarsh communities in Kentra Bay with 5 13 C values from bulk plant cellulose extracted from the sub-fossil saltmarsh peats below Kentra Moss. Microfossil and stomatal density data were also collected to assess the efficacy of this approach, but the sub-fossil data bore no resemblance to the contemporary data. Possible reasons for this are discussed. It is concluded that although neither project directly adds to our understanding of coastal palaeoenvironments, both highlight other possible coastal applications of this technique. i Table of Contents Page no. Abstract. i Abbreviations used in the text. xi Acknowledgements. ?di Chapter 1. Aims, Scope and Limitations. 1.1 Introduction and aims. 1 1.2 Summary. 10 Chapter 2. Stable isotopes and the theory of isotopic discrimination during cellulose synthesis. 2.1 Stable isotopes and thermodynamic fractionation. 12 2.2 Stable isotopes and plants. 16 2.3 Carbon isotope uptake and discrimination by plants. 17 2.3.1 Factors influencing stomatal conductance. 24 2.4 Oxygen isotope fractionation during cellulose formation. 26 2.5 A summary of developments in the analysis of the stable isotope composition of sub-fossil plant material in palaeoenvironmental reconstructions. 29 2.6 Complicating factors which might influence 5 13 C and 5 180 values. 32 2.6.1 The preservation of cellulose. 32 2.6.2 The seasonality of isotopic values. 34 2.6.3 Variations in 5 values that are not the product of environmentally 34 driven factors. 2.6.4 Selective soilwater utilisation and the implications for 5 180 values. 36 2.7 The deuterium effect. 39 2.8 Summary. 40 It Chapter 3. A study of Phragnzites australis (Cav.) Trinius ex. Steudal. 3.1 Background, aim and potential. 43 3.2.Possible complications and limitations. 44 3.3 Research design and strategy. 49 3.4 Methodologies adopted to answer these questions. 50 3.4.1 Measurement of altitude and relationship to tidal inundation. 50 3.4.2 Measurement of soil sample characteristics. 50 3.4.3 Measurement of the habit ofPhragmites in each community. 51 3.4.4 The measurement of stomata] density. 52 3.4.5 Measurement of the 5 180 value of soilwater from the rhizosphere in each community. 52 3.4.6 Measurement of the isotopic composition of Phragmites cellulose. 54 3.5 Results of analyses on environment of growth and variations in plant physiognomy. 57 3.5.1 Altitude and frequency of inundation. 57 3.5.2 The sediment analyses. 63 3.5.3 Plant habit. 68 3.5.4 Stomatal density variations. 71 3.5.5 Soilwater isotopic composition. 74 3.5.6 Summary of these results. 80 3.6 Results of the 6 13 C and 5 18 0 analyses ofPhragmites cellulose. 83 3.7 Discussion 95 3.8 Summary. 97 iii Chapter 4. A cross-community investigation of 8 13C values in the flora of a contemporary saltmarsh, and their relationship to 513C values from sub-fossil saltmarsh peats. 4.1 Background, aim and potential. 100 4.2 Limitations. 102 4.3 Structure of research strategy. 104 4.4 Methods adopted to answer these questions. 106 4.4.1 Establishing the number and altitude of vegetation communities at Kentra Bay. 106 4.4.2 Establishing the diversity of the species mix within the saltmarsh flora. 107 4.4.3 Establishing the density of stomata and measuring other variations in physiognomy that might be related to 5 13 C values. 109 4.4.4 Establishing the variations in 6 13 C values of the contemporary saltmarsh flora. 110 4.4.5 Establishing that the buried sediment units below Kentra Moss represent similar communities to those presently found in Kentra Bay. 112 4.4.6 Establishing the extent to which 8 13 C from sub-fossil cellulose can elucidate sea-level histories. 114 4.5 Results of these analyses. 115 4.5.1 The altitude and floristic composition of the zones identified and analysed at Kentra Bay. 115 4.5.2 The contemporary foraminiferan assemblages. 123 4.5.3 Variations in leaf physiognomy across the saltmarsh. 131 4.5.4 The contemporary 6 13 C values. 134 4.5.4.1 Results from Kentra Bay. 135 4.5.5 The 6 13 C values of bulk cellulose taken from the two cores on iv Kentra Moss. 139 4.6 Discussion. 148 4.7. Summary. 152 Chapter 5. Conclusions and Implications. 5.1 Conclusions from the 5 13 C and 5 180 data. 154 5.1.1 Data from the Phragmites project at Roudsea. 154 5.1.2 Data from the study of contemporary and ancient material at Kentra. 155 5.2 Implications of these results. 157 References. 162 Appendices. Appendix 1. Surface sediment analysis methods. 224 Appendix 2. Collection and preparation of samples for counting leaf stomatal densities. 226 Appendix 3. Isolation of a-cellulose from bulk plant material. 227 Appendix 4. Production and isolation of CO2 from a-cellulose for 5 13 C analysis. 228 Appendix 5. Production and isolation of CO2 from a-cellulose for 5 180 analysis. 229 Appendix 6. Tidal data recorded at Heysham 1975-1994; incidence of inundation at or above Mean High Water Spring Tide (4.5m. 0.D.) and up to Highest Astronomical Tide (5.6m. 0.D.). 231 Appendix 7. Roudsea Marsh surface sediment analysis, 06/04/94 - 05/10/94. 232 Appendix 8. Roudsea Marsh Phragmites australis density and V minimum/maximum height of aerial shoots. 244 Appendix 9. Roudsea Marsh Phragmites australls plant habits. 247 Appendix 10. Roudsea Marsh Phragmites australis stomatal density raw counts. 250 Appendix 1 1 a. Roudsea Marsh Phragmites =stains intra-plant comparisons• Plant numbers, heights and length of leaves analysed. 253 Appendix 1 lb. Roudsea Marsh Phragmites australis intra-plant comparisons of stomatal density. Zones 1, 2 and 3. 254 Appendix 12. Collection and preparation of samples for establishing contemporary foraminiferan populations. 257 Appendix 13. Kentra Bay levelling data for zones KB1 - KB7 in metres O.D. 258 Appendix 14. Kentra Bay loss on ignition (%) data from three repeat samples, 10/93 - 07/94. 258 Appendix 15. Kentra Bay foraminifera counts by zone for three repeat samples, 10/93 - 07/94. 259 Appendix 16 Kentra Bay stomatal density raw data. 260 Appendix 17. Kentra Bay stomatal density data, by species and zone. 264 Appendix 18. Kentra Bay Armeria maritima salt gland densities by zone. 265 Appendix 19. Kentra Bay contemporary 5 13 C data, by species and zone. 267 List of tables. Table 2.1 The proportion of 5 13 C and 5 180 in nature and typical ranges of 5 values. 13 Table 2.2 Carbon isotope fractionations associated with photosynthesis. 18 Table 3.1 Isotopic standards used during the analyses of Phragmites isotopic composition. 56 vi Table 3.2 Variations in environment and Phragmites physiognomy at Roudsea. 81 Table 3.3 Variations in sediment quality, salinity and soilwater isotopic composition in three cores from zones 1, 2 and 3. 82 Table 3.4.1 Plant habit and isotopic composition of Phragmites in zone 1, Roudsea. Inter-plant variations; intra-plant variations. 88 Table 3.4.2 Plant habit and isotopic composition of Phragmites in zone 2, Roudsea. Inter-plant variations; intra-plant variations. 89 Table 3.4.3 Plant habit and isotopic composition of Phragmites in zone 3, Roudsea. Inter-plant variations; intra-plant variations. 90 Table 4.1 Summary data by zone relating to the contemporary succession analysed at Kentra Bay. 121 Table 4.2 5 13 C values for individual Armeria plants sampled on two separate dates; seasonal comparisons and intra-zone variations. 138 Table 4.3 Kentra Moss core 21 data; Troels-Smith stratigraphy, loss on ignition (%), summary of microfossil evidence and radiocarbon dates (Shennan et al. 1995 and unpublished data) with stable carbon isotope values of sub-fossil cellulose.