Biological and Inorganic Factors in the Destruction of Limestone Coasts

About this book

These investigations were carried out mainly on the coast of the northern Adriatic near Rovinj (Istria, Yugoslavia). The general applicability of the results achieved there was tested by comparison with Bermuda, Florida and Marseille.

The process of destruction of a limestone coast is explained in terms of a complex interrelationship of biological and inorganic factors.

The physical and chemical parameters relevant to the waters of tidal- and rockpools were determined over periods of 24 hours. They showed that the rockpool waters are incapable of dissolving the carbonate substrate inorganically. These waters are always oversaturated with respect to CaCO₃, day and night. Variations in their alkalinity can be partly biologically explained, since it is shown that cyanophytes can assimilate bicarbonate. It is therefore not necessarily valid to use variations in alkalinity to calculate CaCO₃ dissolution or precipitation in milieus with high biological productivity. The rockpool floors are densely populated by epi- and endolithic algae, fungi and lichens which prevent any direct exchange between the water and the carbonate substrate and consequently inhibit inorganic dissolution which is of limited significance in coastal destruction.

The coastal profile is subdivided according to obvious colour zones. Both morphological and biological zonations conform to this subdivision.

Endolithic and epilithic algae (Cyanophyceae, Chlorophyceae), fungi and lichens corrode the rock through etching processes. Grazing gastropods rasp away the microflora together with rock particles. The morphological forms resulting from biological corrosion and biological abrasion may be termed biokarst.

Both modes of destruction contribute to deposition in the subtidal zone. A first estimate for the northeastern Adriatic suggests that the destruction of limestone coast contributes about 15 % of the total sedimentation rate.

The rate of destruction varies from zone to zone and has not yet been quantified for all zones. On average it amounts to 0.25-1.0 mm per year. Applications to fossil sediments are offered in terms of distribution, ecology, and boring behaviour of the endolithic microflora as well as their fossilization potential.

Contents

1. Introduction 5
1.1 The general setting of the investigation 5
1.2 Situation of the area of investigation 5
1.3 Selection of the area of investigation 7
1.4 The problem of subdividing the littoral zone 9

2. Main section: The investigations and their results 13
2.1 The coastal profile on Garzotto Point 13
2.11 The phenomenological classification 13
2.111 Thenotch 13
2.112 WE, White Zone 16
2.113 GB, Yellow—Brown Zone 16
21114 DB, Dark-Brown Zone 16
2.115 BS, Blue—Black Zone 17
2.116 GR, GreyZone 17
2.117 HA, Zone of Halophytes 17
2.118 Fl, Zone of Lichens 17
2.12 The rock—pools 18
2.2 The destructive processes and their causes 18
2.21 Statement of the problem 18
2.22 Method of approach 20
2.3 The inorganic factors 20
2.31 Introduction 20
2.32 The theoretical basis 21
2.33 The problem of CaCO₃ saturation 24
2.34 Measurements in the rock-pools: results and discussion 26
2.341 Rock—pool DB (a mixed water pool) 26
2.342 Rock—pool ha (a rain water pool) 32
2.343 Rock- pool BS (stable stratification of pool water) 36
2.344 Rock—pool BS (evaporation of pool waters) 37
2.345 Rock-pool DB (last stage of evaporation) 37
2.35 Conclusions 37
2.36 Redox—potential measurements in rock-pools and hollows 46
2.37 The inorganic microrelief 46
2.38 Coastal karren (lapies) 47
2.4 The biological factors 48
2.41 The biological zonation and its causes 48
2.42 The organism groups 48
2.43 Destructive biological processes 48
2.431 Endolithic organisms 49
2.432 Epilithic and grazing organisms 51
2.433 Chasmolithic organisms 51
2.434 Endolithic fauna 51
2.44 The endolithic algae, lichens and fungi (biological corrosion) 52
2.441 Taxonomy 52
2.442 Distribution and ecology 54
2.443 The boring behaviour of the endolithic flora and its effect on the substrate 58
2.444 Reasons for the endolithic mode of life 62
2.45 The grazing organisms (biological abrasion) 63
2.451 Distribution and ecology 64
2.452 Effect on the substrate 66
2.5 Comparison with other areas 67
2.51 Bermuda   68
2.52 Florida Keys 69
2.53 Marseille. Les Calanques 72

3. Synopsis 72
3.1 The interaction of biological and inorganic factors 72
3.2 The morphogenesis 73
3.3 The rate of destruction 75
3.4 The relativity of the bionomic and morphological zonation 76
3.5 Conclusions 78

4. The geological relevance 78
4.1 The sedimentological relevance 78
4.11 Destructionofprimaryhardbottoms 78
4.12 Destruction of secondary hard bottoms 79
4.13 Destruction of sediment grains 79
4.2 Applicability and geological significance 79
4.3 The fossilization potential and geological record 81

5. Results I 82

6. References 83

Appendix:
7. Methods 95
7.1 Field surveying 95
7.2 Measurement methods 95
7.21 Temperature and relative humidity 95
7.22 Light intensity 95
7.23 pH measurement 95
7.24 Eh measurement 95
7.3 Removal of water samples 96
7.4 Chemical determination methods 97
7.41 Chloride content 97
7.42 Calcium content 97
7.43 Titration alkalinity 97
7.44 Oxygen concentration 97
7.45 Rock analyses 97
7.5 Biological material 97
7.51 Sampling and preparation of algae and fungi 97
7.52 Sampling oflichens 98
7.53 Sampling and evaluation of the Littorina distribution 98
7.54 Algal cultures 98

8. Documentation 99
8.1 The coastal profiles 99
8.2 Alphabetical list of epi- and endolithic lichens 101
8.21 Distribution of the lichen species, Adriatic coast 102
8.3 Alphabetical list of the epi-and endolithic algae and fungi 103
8.31 Distribution of the algae and fungi, Adriatic coast 103
8.4 Photographic plates 108

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