Foraminiferal record of sewage outfall impacts on the inner Manukau Harbour, Auckland, New Zealand

Abstract

The fossil foraminiferal faunas preserved in intertidal sediment in six cores document the impact of human activities on the ecosystems of the north-east arm of the Manukau Harbour, Auckland, New Zealand. They indicate that Polynesian forest clearance and horticulture had negligible impact on the harbour biota. Before 1960, organic-rich discharges from four large meat works around the head of Mangere Inlet produced changes in nearby foraminiferal faunas but did not affect faunas in the more seaward part of the arm. Initial early European increases in organic nutrients from the meat works resulted in the development of weak hypertrophic zones around the outfalls, characterised by higher absolute abundances of benthic foraminifera and ostracods and possible benthic algal blooms. Higher organic nutrient levels in one core closer to an outfall produced eutrophic and anoxic conditions with no foraminifera (abiotic zone the meat works and other outfalls progressively closed. This change coincided with a sharp increase in zinc (Zn) and lead (Pb) levels in sediments throughout the arm, attributed to a rapid increase in motor vehicle numbers and stormwater run-off. The MSTP discharged vast quantities of nutrient-and mud-rich fresh water into the seaward part of the arm, resulting in an order of magnitude increase in sedimentation rates throughout most of the arm and a widespread change in the foraminiferal faunas. Foraminiferal abundance generally decreased and species diversity increased with the appearance of numerous juvenile foraminiferal shells carried in by the incoming tide from subtidal habitats nearer the harbour mouth. Also appearing in large numbers in the post-1960 sediment are planktic foraminifera, large diatom valves, and sponge sterrasters, all of which are inferred to have been transported in. The sudden increase in displaced microfossils may be a result of a combination of fresh water-induced flocculation and increased "stickiness" of the substrate from the growth of benthic algal mats, resulting from the high nutrient output from the MSTP.

Microfossils of introduced starch cultigens from an early wetland ditch in New Zealand

“…The pollen sum was at least 250 grains, excluding Leptospermum type, herbaceous swamp plants and ferns except Pteridium (pollen was not counted in samples S7, S9 and SI1; slides were only scanned for cultigen pollen). Absence/presence of European-introduced pollen types were used to identify samples as pre-European or European (Hayward et al 2004, Matthews et al 2005. Following convention, common taxa are excluded from the base count for graphing purposes, but are still expressed as a percentage of the pollen sum.total, and may therefore exceed 100% in the pollen diagram.…”

Human‐induced marine ecological degradation: micropaleontological perspectives

“…New Zealand studies in the North Island harbors indicated that Polynesian forest clearance caused minor but initial ecological degradation starting at 1500 (Hayward et al 2006). European land clearance since~1840 and late-20th-century urbanization had a much larger impact on the marine ecosystem (Hayward et al 2004;Matthews et al 2005;Hayward et al 2006;Grenfell et al 2007;Hayward et al 2008). Details of North Island harbors' ecological degradation is complex and involves industrial and domestic sewage disposal, introduction of Asian date mussels and cordgrass, land clearance/deforestation, urbanization, and oyster farming (see, Hayward et al 2004;Matthews et al 2005;Hayward et al 2006;Grenfell et al 2007;Hayward et al 2008).…”

Ecological Impact of the Introduction to New Zealand of Asian Date Mussels and Cordgrass—The Foraminiferal, Ostracod and Molluscan Record

“…Many coastal areas were partially cleared of forest by pre-European Maori colonisers (700-200 years ago) but studies in estuarine and harbour cores indicate that this had only minor effects on sediment loads and foraminiferal faunas (e.g. Swales et al 2002a;Hayward et al 2004aHayward et al , 2006Matthews et al 2005). In the mid-late 19th century, after European colonisation, much of the native forest of northern New Zealand was more extensively cleared and converted to pastural farmland.…”