Combining Spatial and Palaeoecological Perspectives on Land-Use Change and Restoration of a Saltmarsh in Wairarapa Moana.

Abstract

This research investigates the impacts of land-use change on Te Pouaruhe, a saltmarsh in Wairarapa, New Zealand. The study uses this saltmarsh as an example to evaluate whether restoring previously drained wetland sections can return soil to baseline conditions using both temporal and spatial approaches. Surface soil cores (10-cm in depth) were collected across the wetland to compare drained areas with relatively undisturbed saltmarsh. Soil nutrients (Total Carbon, Organic Matter, Organic Carbon, Total Nitrogen, and Total Phosphorus), X-ray fluorescence (XRF)-derived elemental data, and 16S bacterial community profiles were used as indicators of restoration success, defined here as the soil’s capacity to accumulate and store carbon. Long-term land-use impacts were assessed from two 50-cm soil cores using palaeoecological techniques to compare modern soils with pre-European drainage conditions (c. 1960). Short-lived radionuclide dating (²¹⁰Pb and ¹³⁷Cs) was used to develop sediment chronologies, supported by grain-size analysis, XRF, 16S metabarcoding, and nutrient measurements. The findings show that the study site is part of a naturally transitioning environment. Rather than returning to a historical baseline, the saltmarsh has evolved from an estuarine mudflat through gradual sediment infilling. Consequently, restored soils are not reverting to a past state but are instead developing characteristics consistent with a productive wetland within a dynamic, shifting landscape. These findings challenge the assumption that restoration success should be measured against a fixed historical baseline, with implications for how restoration targets are defined in naturally transitioning coastal wetland systems globally.