Unlocking wetland ecologies and agriculture in prehistory through sulphur isotopes.

Since the advent of farming, water has been central to agricultural productivity. However, the way in which people made use of natural water resources in the past, or manipulated these resources to meet their needs, is not adequately understood. While archaeologists can find indirect evidence of water management systems used in the past through the irrigation infrastructure and tools that these practices left behind, or from texts detailing agricultural strategies, they currently do not have adequate methods to directly determine the water conditions a particular field/crop/animal was raised under, particularly in landscapes where the use of wetlands may have been significant. This information is important for several reasons. The harnessing of water resources in the past are thought to have been fundamental to increasing crop productivity, ensuring food security and creating an agricultural surplus; these factors are all thought to have enabled population growth and the development of increasingly complex societies. However, the harnessing of water resources is also thought to have had significant environmental consequences such as a loss of biodiversity and increased greenhouse gas emissions. Understanding these developments and impacts has implications for our current food production systems, especially in meeting the challenges of maintaining agricultural productivity under an ever-increasingly unpredictable climate.

To address this issue, our project will develop a new tool for detecting agricultural water use by past populations. Specifically, we will use fossil animal and plant remains to understand water use in agriculture through sulphur isotope analysis. Sulphur in plants and animals comes from the soil upon which the plant grew, or the animal fed. Current data shows that the amount of water in the soil likely influences plant sulphur isotope values. If this relationship can be quantified, sulphur isotopes in archaeological material can be used to infer past watering regimes. Our project will study sulphur isotopes in modern soils and plants in a controlled growth experiment. We will grow plants under a number of different water regimes and measure the plant sulphur isotope compositions. This analysis will allow us to quantify the relationship between watering and plant isotopes, which will then allow us to apply this method to archaeological samples.

To test that the method works on archaeological samples we will apply the new method to two specific archaeological case studies, where indirect evidence suggests agricultural developments were linked to changing water availability or use. Specifically, we will analyse archaeological material from the Thames river valley, where agricultural practices have been linked to the natural cycle of river flooding, and from Thailand, where agricultural production of rice is thought to have shift from low-maintenance dry systems to high-maintenance wet systems in response to climate change. These applications will allow us to validate the method, enabling it to be applied to other archaeological contexts. This will facilitate better understanding of how water resources were harnessed in the past in different locations around the world, providing important information on agricultural resilience, sustainability and management under different climate systems; information that is vital to ensuring our current food production systems stand up to the challenges faced by climate change.