Physical Environment
The west coast of the Ngati Whatua rohe is characterised by wide open beaches, backed by sand dunes.
The western coast in the north of the North Island is influenced by the West Auckland Current, which flows down the coast toward the south. Further south, this meets the Westland Current, which flows northwards. The point of convergence of these two currents has moved up and down the coast over prehistoric time, and this has caused variations in the composition of the sand along the coast.
The open coastline of the western coast in Ngati Whatua rohe is exposed to these southwesterlies, which generate a high wave energy environment. In general, the prevailing southwesterly wave action causes long-shore drift of sediment along the coast from the south to the north. However, the western coast of Northland sweeps around to the north-west so that the southwesterly swell is nearly perpendicular to the coast. This reduces the long-shore movement, so that the sediment brought into the area exceeds that moving out, resulting in accretion (build-up) of sediment. It is this build-up of sediment over a long time that has resulted in the sand dunes characteristic of the coast to the north and south of the Kaipara Harbour.
Applied Geology Associates (1982) describe the coast from the South Kaipara Head as consisting of “ a wide belt of post-glacial dunes which broaden towards the Kaipara Harbour entrance. These geologically recent dunes front, and lap onto older, more weathered and consolidated dune sands of earlier Quaternary age ”.
The uplifted marine terraces on South Kaipara peninsula form a geological site of regional significance. Their significance lies in the fact that they are preserved uplifted Pleistocene marine terraces, with six terrace levels in total at approximately 8, 20, 40, 70, 110, and 170 metres above sea level. Their uplift level is 0.3 mm per year (DOC, 1990).
The coast north of the harbour is formed by a continuous stretch of Quaternary sand, extending as far north as Maunganui Bluff and inland to the Kaihu and Wairoa Rivers and rising to 200 metres in height. It is known to have been prograding (building up) since Holocene times, but was subject to previous depositional and erosional cycles as the convergence of the West Auckland and Westland currents migrated north and south. The prominent dunes consist of a complex of mainly coastal sediments in the west, and fluviatile (river) sediments in the east (i.e. the eastern side of the Pouto Peninsula). “ The western side of the barrier is bounded by accumulating sand deposits, which broaden to the south. These are backed by a 60 metre high wall of present and former sea cliffs. Richardson (1975) divided the barrier into the geomorphic divisions of drifting dune sands, young fixed dunes, old fixed dunes and inland high terraces. The latter are dissected in places by streams. Although there have been significant changes in the shoreline, particularly at North Kaipara Head during the last century, the erosion and accumulation suggest redistribution of sand rather than loss or gain of sediment for the beach ” (Applied Geology Associates, 1982).
The Bayley's Beach dunesands (at the northern end of the northern barrier) are of geological significance, in that they show the history of the rises and falls in sea level since the Pliocene (Kenny & Hayward, 1993).
From extensive sampling along the coast, Schofield (1970) established several sand facies (sediment groups with similar characteristics) on the west coast from Taranaki northwards, based on median grain size, mineralogical content, and the proportions of minerals present. Two facies are relevant to the western coast of the Ngati Whatua rohe: the Egmont Blacksand subfacies, and the West Auckland Sand facies. “ The Egmont Blacksand subfacies are rich in titanomagnitite, a source of iron for steel manufacture. The titanomagnetite content of the sands generally decreases northwards from Taranaki, but there is a marked increase in concentration on the southern side of headlands ” (Applied Geology Associates, 1982). On the coast of the Ngati Whatua rohe south of the South Head of the Kaipara Harbour, the Egmont Subfacies is integrated into the West Auckland Sand Facies, which continues northwards. In general, the sand from the beach and dunes south of the Harbour is a fine sand of 50 % to 65 % quartz and 18 % to 20 % heavy minerals. A study by Nicholson (1958) suggested that heavy mineral content increases rapidly southward, from 1 % near the heads up to 41 % at Muriwai. The West Auckland Sand Facies from North Head northwards has a dominant quartz content (averaging about 56 % of the sediment with shell removed) and a low heavy mineral content of about 5 % compared with the Blacksand subfacies to the south. It comprises a mixture of sediment from the Waikato River, providing feldspar rich sands derived from the central North Island rhyolitic volcanoes, plus a contribution from the weathering of the Waitemata Group sandstones of the Auckland area, and the quartz rich sands derived from the north that are now concentrated at Parengarenga Harbour on the east coast. This mixture is probably due to the migration of the convergence of the West Auckland and Westland currents up and down the coast during prehistoric times.
The sand barriers that form the northern and southern heads to the Kaipara Harbour both contain freshwater dune lakes. There are approximately 35 lakes in the South Kaipara Peninsula. Very few of the lakes have any stream outlets, and any water loss occurs either by evaporation or infiltration through the ground that contains them. The three lakes at the northern end of the peninsula (South Head Lake, and Lakes Ototoa and Kuwakatai) differ from the others in that they are formed in a depression in the South Head formation. This means that they are held in relatively impermeable basins, 45-90 metres above sea level. The lakes are recharged through precipitation and run-off from the surrounding land. In contrast, the other lakes are formed in depressions in recent sand dune formations about 14 metres above sea level. These lakes are fed from the water table (Auckland Regional Authority, 1976; Auckland Regional Water Board, 1983). The levels in both southern and northern lakes on the peninsula are falling. In the southern lakes this has been blamed on the use of water by the pine forests. However, some studies indicate that the source of water is from the water table on the east of the lakes, whereas the pines are predominantly on the west, so this is inconclusive. It is possible that the pines have resulted in an overall decrease in the level of the water table, as has occurred in other forested areas. It has been suggested that falling levels in the northern lakes are related to climate change.
Freshwater wetlands on the Pouto Peninsula (north head of the harbour) are situated in a region of consolidated Pleistocene sand dunes with more recent Holocene dunes near the coast. Most wetlands formed within basins in the Pleistocene dunes, except Lakes Humuhumu, Kanono and Kahuparere, which are between the older and newer dunes. Lake Humuhumu is the deepest lake, with a maximum depth of 16 metres (Cromarty, 1996). The lakes receive most of their water from precipitation and ground water, and there is some concern about the impact of the adjacent pine forest on their levels also. Water is also extracted from the lakes for pastoral farming and horticulture.
The region has a temperate climate, with temperatures ranging from an average of 10.7 o C in July to 19 o C in February. The annual rainfall averages 1,100 mm in the north, and 1,200 mm in the south, and the number of hours of sunshine 2,000 (Cromarty, 1996).
Flora & Fauna
Flora and fauna occurring on the reefs on this coastline are typical of northern exposed hard shorelines. The species diversity is high, often with distinct zones of plants and animals, ranging from the lichens, periwinkles, and limpets at the top of the intertidal zone, through barnacles, turfing algae and numerous species of mollusca in the mid-tidal zone, to dense kelp beds with associated populations of mollusca, kina, crabs and other crustacea. Paua and rock lobster occur sub-tidally, and at the low tide mark.
Off the coast, a diversity of fish species occurs, including snapper, trevally, gurnard, kahawai, kingfish and barracouta. Mullet also occur seasonally closer to the shore. Beds of mussels ( Perna canaliculus ) are found subtidally.
The flora and fauna of the beaches are typical of exposed northern sand beaches. On such sandy beaches, the inter-tidal animals are robust and capable of moving quickly to avoid being dislodged or smothered by sand. Species diversity is comparatively low, and usually dominated by small crustacea (i.e. amphipods ("sea slaters") and occasionally isopods (e.g. "sand hoppers"), and by bivalve mollusca (for example, tuatua).
Common on the upper beach are the sand hopper ( Talorchestia quoyana ) and the sea slater Scyphax ornatus . The dominant shellfish, tuatua ( Paphies subtriangulata ) and toheroa ( Paphies ventricosa ) are located in the mid to low inter-tidal zone of the shore. Both species are patchy in distribution, and local knowledge is usually necessary to locate the denser beds. On the west coast of Northland the toheroa has been exploited to such an extent that harvesting is highly restricted, but tuatua, which occur lower down the beach, are still generally present in numbers that make the species attractive to gather.
Toheroa have special significance to Ngati Whatua – toheroa are said to have been brought to the western coast of Northland from Hawaiiki by Mareao, and seeded out for the use of his descendants (Jackson, 1997). Iwi have cared for the toheroa for generations in their role as kaitiaki. This still includes the reseeding of toheroa from the more dense populations at Bayley's Beach to North Head and Maunganui Bluff. The toheroa population is relatively fragile, due to years of over-exploitation by both commercial and recreational fishing, both of which are now prohibited. There is currently some concern about the impact of vehicle use on the beaches on toheroa populations. The population is also depleted by people taking toheroa illegally, both for personal consumption, and for illegal sale in Auckland. In addition, the population has a history of sporadic incidences of high mortality, the cause of which is unknown. It has been suggested in the past that this could be the result of a high level of predation by birds. However, this is most likely to occur in conjunction with the incidence of some sort of disease, which results in the shellfish becoming more vulnerable to predation (for example, by being slower to retract their siphons or burrow deeper in the sand).
Further up the shore, marram ( Ammophila areneria ), spinifex ( Spinifex hirsutus ) and pingao ( Desmoschoenus spiralis ) occur on the sand dunes, often with manuka/kanuka shrubland further back. Pingao is a rare native plant, and marram is an exotic species that has been planted to stabilise the sand on the dunes. Pingao is also regarded as a taonga by Mäori; it is used in fine weaving and tukutuku panels, which are enhanced by the brilliant golden colour of the dried leaf blades. Another locally rare species, Pseudopanax ferox occurs in the belt of native vegetation between the dunes of Rangatira Beach and the pines of Woodhill Forest. The wetlands in the dunes south of the harbour mouth are ranked as nationally significant in terms of their ecology. The three most northern lakes are oligotrophic (i.e. contain low nutrient levels, little phytoplankton and weed), with Lake Otatoa forming 100 hectares of open water. The more southern lakes are greatly impacted by littoral weed growth and eutrophication (high nutrient levels, causing high levels of weed and phytoplankton growth, and high oxygen demand in the water). Eutrophication can be a natural process, but is often accelerated by high levels of nutrients in run-off from the land caused by application of fertiliser. It is uncertain what the major contributing factors are in this case. Lake Otatoa contains trout, and is the only known significant location of koura ( Paranephrops planifrons ) (the native freshwater crayfish) in the Auckland region. At least one species of plant Hydrocotyle otatoa is endemic to Lake Otatoa, and the rare native dwarf inanga ( Galaxis gracilis ) has been introduced there. Among the bird species present on some or all of the lakes in this area are NZ dabchicks ( Podiceps rufopectus ), Caspian tern ( Hydroprogne caspia ) and Australasian bittern ( Botaurus stellaris poiciloptilus ), all of which are threatened species. The lakes are also seasonal feeding, breeding and roosting areas for other native and introduced water-fowl as a consequence of the range and variety of habitats available ( Department of Conservation, 1990a).
Toward the mouth of the harbour at the southern head, Papakanui Spit is the principal nesting area for the caspian tern and white-fronted tern on the Kaipara, and large numbers of Arctic migrant birds use the spit as a roost site, including the Bar-tailed Godwit ( Limosa lapponica baueri ), red-necked stint ( Calidris ruficollis ), and lesser knot ( Calidris canutus canutus ). There can be up to 10,000 wading birds at this roost site at any one time, with high numbers of NZ dotterel ( Charadrius obscurus ), variable oyster-catcher ( Haematopus unicolor ) and wrybill ( Anarhynchus frontalis ), as well as South Island pied oyster-catcher ( Haematopus ostralegus finschi ), turnstone ( Arenaria interpres interpres ) and fairy tern ( Sterna nereis ), (an endangered species). The adjacent Waionui Inlet is an important feeding site for the large numbers of wading birds previously noted, and wetland birds use the margins of the habitat (e.g. bittern, fernbird and crake). The Waionui wetlands form an extensive area of sand dunes, soaks and wetlands which are regionally rare, with good sequences of a diversity of ecotones (sequences where one type of ecosystem grades into another). The wetlands also contain two vulnerable native species, the fern Cyclosorus interruptus , and the Dwarf Mazus plant ( Mazus pumilio).
The dunes behind the west coast beaches north of the harbour mouth are sparsely populated with spinifex and pingao. Behind this, the unconsolidated dunes support denser vegetation of toetoe ( Cortaderia toetoe ), Isolepis nodosa, Coprosma acerosa, Cassinia leptophylla, Muehlenbeckia complexa , and exotic plants including marram grass, pampas grass, and lupin. The jointed wire rush ( Leptocarpus similis ), jointed twig rush ( Baumea artiulata ), Typha orientalis, Scirpus lacustris , and manuka. The wetlands also support an association of plants which are special to this type of habitat, and are now extremely rare and restiricted to a few sites on the west coast of Northland, including the Marsh Fern ( Thelypteris confluens ) in dense swamps, Pseudopanax ferox (in shrublands), Hydatella inconspicua (in water less than 1.5 metres deep), and Hebe c.f. diosmifolia (in shrubland and forest). As mentioned earlier, pingao is also a rare species. The Pouto Peninsula also has two unmodified native forest remnants growing amidst mobile dunes, which is very unusual. The species include manuka, kanuka, kohekohe, karaka, cabbage tree, taraire, rewarewa and totara.
On the north head bluffs there is a grey petrel colony ( Procellaria cinerea ) with a large numbers of burrows. The wetlands of the Pouto Peninsula support substantial breeding populations of several species of birds and fish that have declined significantly elsewhere in New Zealand, including the NZ Dabchick, Australasian Bittern, Pacific Reef Egret (rare in this habitat type), Brown Teal, NZ Scaup, Banded Rail (rare in this habitat), Marsh Crake, Variable Oystercatcher, NZ Dotterel, and North Island Fernbird. A total of 56 different bird species have been recorded in the northern head lake area. Notable fish include the endangered and endemic dwarf inanga ( Galaxis gracilis) , which occurs in only seven lakes (Cromarty, 1996).
References:
Applied Geology Associates. 1982. Coastal sand and shingle resources of Auckland and Northland. Unpublished report to the Auckland Regional Authority, April 1982.
Auckland Regional Authority. 1976 . Report on a coastal resource area, Kaipara South Peninsula. Planning Division, Auckland Regional Authority, April 1976.
Auckland Regional Water Board. 1983. Preliminary investigation into the water resources of the Kaipara South Peninsula. Auckland Regional Authority Water Board Technical Publication No. 25, June 1983.
Cromarty, P. 1996 . A directory of wetlands in New Zealand. Compiled by P Cromarty for the NZ Department of Conservation, International Waterfowl and Wetlands Research Bureau, and the Ramsar Convention Bureau. Published by NZ Department of Conservation, Wellington.
Department of Conservation. 1990 . Coastal wetland inventory for northern New Zealand: Volume 1: Auckland Region (Draft). Department of Conservation, Wellington.
Jackson, M. A. 1997. Pouto Peninsula: An archaeological perspective; The evidence of Moira Annette Jackson, amended 10 April, 1997. Statement of Claim by Te Uri O Hau O Te Wahapu (Wai 271).
Kenny, J. A. & Hayward, B. W. 1993. Inventory of important geological sites and landforms in the Northland region. Geological Society of New Zealand Miscellaneous Publication No. 67 (2 nd Edition).
Nicholson, D. S. 1958. Borehole survey of North Island ironsands from New Plymouth to Kaipara Harbour. New Zealand Journal of Geology and Geophysics. 1 :617-634.
Richardson, R. J. H. 1975. The Quaternary geology of the North Kaipara Barrier. MSc. thesis, University of Auckland.
Schofield, J. C. 1970. Coastal sands of Northland and Auckland. New Zealand Journal of Geology and Geophysics. 18 :295-316.
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