Sale
Clowes, C.D.; Kennedy, E.M.; Arnot, M.J. Bland, K.J.; Dahl, J.A.; Te Koha, T.A.; McKay, A-M.; McElroy, T. 2024 Late Holocene vegetation history from a new sediment core, Urenui River, Taranaki, New Zealand. Lower Hutt, NZ: GNS Science. GNS Science report 2024/46. 36 p.; doi: 10.21420/GER4-H219
Abstract:
GNS Science’s ‘Coastal Change and Adaptation’ research project, part of the ‘Changing Climate and Environments’ programme (formerly Global Change Through Time programme), has been investigating coastal processes within several ‘case study’ regions around Aotearoa New Zealand, including recently in north Taranaki, where team members have been engaging with Te Runanga o Ngati Mutunga and Taranaki Regional Council. A particular goal has been to characterise potential impacts of climate change on coastal environments (e.g. drivers of and changes in coastal erosion along the north Taranaki coastline), as well as past environmental and ecological conditions within the small estuaries that form at the area’s river mouths. The palynological analysis reported here is part of a larger project to analyse and report historic sediment accumulation rates within Urenui River mouth: a tidal river estuary located in north Taranaki. Understanding historic sediment accumulation rates will help to inform how sediment catchment loads can be managed in order to protect estuarine habitats. Taranaki Regional Council is currently implementing the National Policy Statement for Freshwater Management (2020) and developing a new Land and Water Plan. Understanding historic estuarine sediment accumulation rates is an important consideration for determining appropriate targets for in-stream sediment loads in rivers and streams in order to prevent adverse impacts in the downstream estuarine receiving environment. Building upon a previous analysis of gouge auger cores (Clowes et al. 2023), four new larger-diameter, continuous vibracores, up to c. 4.6 m long, were collected in 2023. This study reports the results of a palynological analysis from one of those cores, Urenui VC-04, located in a key part of the estuary system, directly opposite the river mouth. Although the top few centimetres of core Urenui VC-04 are unequivocally modern (see below),four radiocarbon analyses, of which the shallowest was at ~34 cm below the modern estuary surface, have all yielded dates c. 7600 years before present or older. This result implies that the bulk of the sediments within the core dates are from before human occupancy in Aotearoa New Zealand and that there is a significant hiatus within the 35–30 cm interval. Today, the lower reaches of Urenui River flow through predominantly open pastural land, although strips of remnant and secondary coastal forest are also present. Plant taxa commonly encountered in the core material include lycophytes, ferns (notably tree ferns), podocarps (most commonly rimu) and dicotyledons ranging from small herbs (asters and amaranths) to tall trees. Generally, the samples from Urenui VC-04 resemble a forest litter, or perhaps streamside vegetation source. All are overwhelmingly dominated by fern spores and podocarps, although this may be more reflective of pollen production and taphonomy rather than abundance of individual plants. Although one or two sporadic pine grains were found low in the core, these are almost certainly contaminants, and no significant changes occur until the uppermost ~30 cm, where there is an increase in charcoal, pine becomes common and an almost coeval (though not substantial) increase in herbs and grasses is seen. We interpret these changes as indicating a sharp increase in land-clearance / farming activity and possibly the appearance of pine plantations or pine shelter belts from the hypothesised hiatus. Previous studies elsewhere in Aotearoa New Zealand have mostly focused on different estuary types, often larger than that present in Urenui River; consequently, the findings of this project may also be applicable for other regions with small tidally influenced river estuaries. Additionally, Urenui Estuary is associated with important cultural, recreational and ecological values. The findings will also be of particular interest to local iwi, Ngati Mutunga, who have an important connection with this estuary and have been actively carrying out cultural monitoring and catchment restoration activities (auths)
