Coastal Restoration Trust of New Zealand

Coastal Dune Ecosystem Reference Database

Effect and Timing of Increased Freshwater Runoff into Sheltered Harbor Environments Around Auckland City, New Zealand. Technical Report

Hayward, B. W., Grenfell, H.R., Sabaa, A.T., Morley, M.S., Horrocks, M.
Journal / Source
Estuaries and Coasts
Estuarine sediment, Late Holocene, Waitemata Harbour, Faunal changes, Freshwater runoff
This paper reports on the research undertaken in the sheltered fringes of the Auckland's Waitemata Harbour, New Zealand. Two short cores of late Holocene, low tidal, estuarine sediment were analysed to record the changes through time since human colonization. THREATS IDENTIFIED AND/OR DESCRIBED: Urbanisation, catchment modification SCOPE OF SPECIES, HABITATS AND ECOSYSTEMS IMPACTED: Benthic fauna, estuaries SPATIAL EXTENT OF THREAT STUDIED: Waitemata Harbour TEMPORAL EXTENT OF THREAT STUDIED: Hundreds of years from human colonisation DATASETS USED IN THE ANALYSES: Sediment core fauna and physical characteristics METHODOLOGY USED TO IDENTIFY AND DETERMINE SEVERITY OF THREAT: Core biota and physical characteristics linked to major changes in local land-use KEY FINDINGS OF THE ANALYSIS: Changes observed include: abrupt decline and disappearance of marine molluscs, a major decline and virtual disappearance of ostracods, an abrupt decline in calcareous foraminifera (mostly Ammonia spp.), a rapid increase in abundance of agglutinated foraminifera, large diatoms, and freshwater thecamoebians, and an increase in sedimentation rate, but no consistent trend in change of grain size. At the head of the Waitemata Harbor, in Lucas Creek estuary, three phases of foraminiferal faunal change occurred: minor changes during initial Polynesian forest clearance (1500-1800 AD), a major change in early European times (1840-1870 AD) with clearance of most of the remaining native forest, and another small change in very recent times (1990s) with urbanization in the Lucas Creek catchment. On the eastern, seaward fringes of the Waitemata Harbor, in the smaller Tamaki Estuary, no faunal changes occurred in association with complete forest clearance and establishment of pastoral farming in Polynesian and early European times (before 1950s). Major foraminiferal and other faunal changes occurred in the late European period (1960s-1970s) coincident with the onset of major urbanization spreading throughout the Tamaki catchment. Increased freshwater runoff may be primarily responsible for many of the observed biotic changes in the urbanized estuaries of New Zealand.
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