Hydrologic modelling of niche construction at the Waitetoke Cultivation Complex, Ahuahu, Aotearoa New Zealand

The early Māori settlers of Ahuahu, a small island off the Coromandel Peninsula of Aotearoa New Zealand, engineered the environment to create a raised-bed irrigation system to grow taro (Colocasia esculenta). Three-dimensional computational fluid dynamic (CFD) modelling of water flow provides insights into how the irrigation system functioned. Excavation and coring data and a digital elevation model combine to simulate the hydrology of the raised-bed irrigation system at Waitetoke on Ahuahu. This modelling demonstrates that for operation, the system required a series of channels and weirs to divert water from a nearby spring. The slow-moving water delivered nutrients to the cultivation area and also promoted the growth of nitrogen fixing algae. Exogenous nutrients including wood ash and calcium carbonate along with fire modified rocks derived from nearby household hearths added to the cultivation matrix created ideal conditions for taro growth. Over the span of over two hundred years, Māori engaged in various forms of niche construction to enhance taro production by altering feedback relationships between the geomorphology of the area, a natural spring, the constructed channels and weirs, water, cultivars, algae, and soil nutrients.