Heather Viles

Interannual, decadal and multidecadal scale climatic variability and geomorphology

Abstract Climatologists have identified and started to explain a range of different modes of climatic variability which seem to be essential components of behaviour of the global climatic system. Of potentially high geomorphological importance are oscillations in climate over interannual to century scales. A range of geomorphological impacts of such climatic oscillations has been recognised, such as alterations in streamflow and sediment yield, mass movement frequencies and coastal erosion, some recent findings on which are reviewed here. Geomorphological impacts of interannual, decadal and multidecadal scale climatic variability vary from place to place and time to time, and are often complexly related to impacts of tectonic and human factors. The importance of improved understanding of decadal scale climatic variability for the progress of geomorphology in general is discussed in terms of the development of geomorphic ideas.

Biogeomorphology revisited: looking towards the future

Although biogeomorphological research is well-established, with many studies on a range of two-way interrelations between organisms and geomorphology in different environments, there is little consensus over what constitutes biogeomorphology, why it might be useful and where it is heading. Starting with definitions of core biogeomorphic processes, we consider the need for future biogeomorphological studies to evaluate the crucial links between bioprocesses, biological community dynamics and ‘inorganic’ earth surface processes. Five key applications of biogeomorphological research are identified; the roles of organisms in environmental reconstruction, trace fossil analysis, extraterrestrial geomorphology, environmental engineering and the built environment. Some key research directions and methodological challenges for future biogeomorphological research include expanding the spatial and temporal coverage of datasets, investigating the role of bioprocesses in landform development, tackling scale issues, investigating the relevance of nonlinear dynamical ideas to biogeomorphology and developing better sampling and monitoring techniques for bioprocesses.

Scale issues in weathering studies

A review of the major scale issues in weathering studies reveals concerns over the fundamental spatio-temporal distributions of weathering phenomena, as well as issues of upscaling microscope-based observations, and linking different scales of observations in explanations of landform development. Various strategies are proposed which can be used to tackle these issues, many rooted in non-linear dynamical systems ideas. As an initial step, spatio-temporal scale distributions are estimated here for weathering processes, landforms and controls based on a range of empirical data. Two case studies, of phytokarst in Grand Cayman and blistering and scaling of building stones, are presented to illustrate the types of data that might be used to establish more convincing scale linkages in weathering investigations.

The late-Holocene tufa decline in Europe

Over much of Europe, it has been postulated that in the late Holocene (since c.2500 BP) there was a marked decline in the deposition of tufa. There has been considerable debate about the causes of this phenomenon, with some authors postulating the importance of natural climatic changes, and others asserting that miscellaneous human influences have been crucial. This article discusses the role that various changes, both natural and anthropogenic, may have played, and suggests ways in which the large number of possible hypotheses can be tested.

Ecological perspectives on rock surface weathering: Towards a conceptual model

A wide range of information is now available on the ecology of rock surface microorganisms (including bacteria, fungi and algae) and lichens and their role in weathering in particular locations. External environmental conditions as well as rock characteristics determine the type of rock surface community, and thus the style of biological weathering. A simple, preliminary conceptual model can be drawn, which relates biological weathering activity to an environmental stress gradient and which is applicable at a range of scales. Further research needs carrying out to test and extend this model in order to make some progress towards the important goal of assessing the overall importance of biological weathering to geomorphology.

Coastal problems: geomorphology, ecology and society at the coast

The coastal context how coasts work sandy coastlines - beaches and dunes rocky coasts - cliffs and platforms coastal wetlands coral reefs cold coasts managing the coast - coping with coastal problems.

Bioconstruction, bioerosion and disturbance on tropical coasts: coral reefs and rocky limestone shores

The ecology of tropical carbonate coasts, including coral reefs and rocky limestone shores, is susceptible to disturbance that may have linked effects on geomorphology. Biogeomorphology, which considers the interrelations between biological and geomorphological processes, is particularly well-suited toward the understanding of such carbonate systems. Field observations and experimentation on tropical and temperate coasts by both biologists and geomorphologists, and the development of ecological theory, have come to stress the importance not of stable, successional littoral communities but rather of nonequilibrial, multistate systems. These ideas now need to be incorporated into improved models of coastal dynamics. Case studies from the Central Pacific, the Caribbean and the western Indian Ocean illustrate the interactions between external environmental variability and internal biological processes. These studies show how changing the balance between bioconstructional and bioerosional processes can interrupt a systems development and, in some cases, shift carbonate-based systems between healthy and degradational states. A better understanding of the spatial and temporal complexities present in carbonate coastal and shallow marine environments is an important precursor to effective coastal zone management on these prevalent tropical shorelines.

Experimental investigations into the interactions between moisture, rock surface temperatures and an epilithic lichen cover in the bioprotection of limestone

Abstract This paper examines the links between moisture, epilithic lichens, rock surface temperatures and weathering. Field and laboratory experiments were conducted in order to investigate the combined effect of surface wetness and Verrucaria nigrescens (an epilithic lichen) on limestone temperature fluctuations. Exposure blocks with and without a lichen cover were subjected to short-term temperature fluctuations and two types of moisture events: artificial showers ( 8 ml rainfall) and larger storms ( 40 ml rainfall). The experiments showed that larger storms are more likely to dampen temperature fluctuations at the rock surface, especially in the presence of an epilithic lichen cover, providing evidence for a mechanism of bioprotection. The conclusion is that the epilithic lichen retains moisture, which reduces thermal stress in the surface of the limestone.

Soiling and microbial colonisation on urban roadside limestone: a three year study in Oxford, England

Abstract An exposure programme has been carried out to study the impact of traffic on building limestone soiling and decay. After 1–3 years of exposure it was found that busier roads experience faster soiling, and all sites show extensive colonization by bacteria, fungi, and phototrophs, deposition of particulate matter and calcite dissolution. In all cases, fungal colonisation is preferentially located within hollows on the stone surface. Fungi appear to be an important component of soiling as confirmed by SEM observations and isolation experiments. However, no clear pattern of microorganism colonisation has been observed between sites, although the urban background site experienced higher colonization of all organisms after three years.

Eukaryotic Microorganisms and Stone Biodeterioration

Eukaryotic microorganisms (especially green algae and fungi) can have a significant impact on the structure and appearance of stone cultural heritage. This paper reviews current knowledge on the role of eukaryotes in the biodeterioration of stone. Considerable uncertainty remains over community-level interactions and the response of lithobiontic communities to environmental change. Three inter-linked approaches to future research are proposed: (1) long-term ecological field studies; (2) diversity studies based on new molecular techniques and (3) laboratory-based simulation studies. The overall goal of these research efforts should be the formulation of robust models of stone deterioration that integrate biotic and abiotic factors and can be used to aid prediction and management of eukaryotic growths on stone cultural heritage.