Dunedin & Coast FMU (Freshwater Management Unit)

The main land use in the Dunedin & Coast FMU is plantation forestry (28%). Dry stock farming includes sheep and beef (19%); mixed sheep, beef, and deer (4%); beef (5%) and sheep farming (8%), and also covers a significant portion of the FMU. Dairy farming occurs on close to 8% of the area and around 7% is for urban use.  

Notable trends in land use change over the past 30 years have been an increase in dairy farming by 38%, public conservation estate by 55%, plantation forestry by 19%, and urban land use by 4%. Dry stock farming has decreased by 14%, although it remains one of the main land use activities in the Dunedin & Coast FMU.  

Brown soil covers 48% of the area, and Pallic soil covers 39%. This includes the north and south of Dunedin city and most of the Tokomairaro catchment. Brown soils are well-drained with moderate permeability and found mostly in plantation forests. Pallic soils have poor drainage and moderate to slow permeability and are mainly used for high-producing grasslands. Melanic soils are mainly around the Otago Harbour, are well-drained, and have moderate to rapid permeability. 

Dunedin & Coast land use summary

Surface water use in this area is relatively low. In the northern part of the FMU, Dunedin city water supply includes water take consents on the Leith and Waitati catchments. However, as most of the city’s water supply comes from the neighbouring Taieri FMU, these takes are now only for emergency supply and are not currently used. In the southern part of the FMU, surface water is used for dairy sheds and stock water, mining and landfill activities, rural domestic water supply, and a small amount of irrigation. 

Water quality is monitored at eight river and stream sites, and ecological monitoring is undertaken at three river sites in the FMU.

The results of this monitoring show high bacteria and nutrient concentrations at at every site other than the Waitati River, and nutrient concentrations were highest in the urban streams. .

Long term trend analysis of the Water of Leith, Kaikorai Stream and Tokomairaro show each site has degrading nutrient concentrations, however in the last 10 years all sites indicate improvement. 

Of the four sites monitored for aquatic health, two (Kaikorai and Lindsays Creek) do not meet the required standard for the Macroinvertebrate Community Index (MCI). This is likely to be because of the urban nature of the environment. 

Pressure from land use includes large areas of hard standing (hard surfaces on which heavy vehicles may be parked) in Dunedin, which require a network of stormwater drains. These drains then result in discharges of contaminants, which often have high bacteria and nutrient concentrations, into local rivers and streams. 

Dunedin & Coast FMU Water Quality State and Trends Technical Report

Introduction to water quality

Dunedin & Coast water quality summary

Groundwater use is low. The primary groundwater resource is the Tokomairaro Groundwater Management Zone, and its main uses include domestic supply, stock water, irrigation, and dairy sheds. The consented allocation is a small proportion of the current Mean Annual Recharge. Quarterly monitoring results generally show good groundwater quality, with low E. coli and nitrates. However, there is only one monitoring bore in this FMU currently. 

Dunedin is known as the “wildlife capital of New Zealand” due to the rare and endangered species near the city and has areas of outstanding biodiversity, including the Otago Peninsula, a renowned wildlife and eco-tourism destination, and Orokonui Ecosanctuary, a wildlife reserve with rare species including forest birds, reptiles, and plants. 

Rare and threatened freshwater ecosystems within the FMU include lagoons, dune slacks, estuaries, and wetlands. These ecosystems are often threatened by processes such as land use change and invasive species. Little is often known about the extent and/or condition of these ecosystems. 

The Dunedin & Coast FMU has many species that depend on freshwater habitats, including fishes, invertebrates, plants, and birds. There have been 44 threatened freshwater-dependent species identified within the FMU. Native freshwater fishes include three non-migratory galaxias, four migratory galaxias (whitebait), two eel and five bullies. The lamprey and all non-migratory galaxias in this FMU are threatened. 

Freshwater invertebrates include koura, shrimp, and mussels. Threatened freshwater-dependent plants include Crassula peduncularis and Carex strictissima. 

Many native birds depend on freshwater ecosystems as permanent or mobile residents, including the threatened Australasian bittern and the at-risk, black-billed gull. Information is often missing at a species level, particularly for freshwater invertebrates, non-vascular plants, and algae. 

Exotic fishes include goldfish, perch and four salmonids. Many native freshwater species are under threat and continue to decline. 

Natural wetlands in the Dunedin & Coast FMU are mainly associated with estuaries and lower reaches of rivers and streams. Flaxlands are the most common wetland vegetation type with oioi restiad rushland widespread in coastal wetlands and carex in upland areas. The wetlands are generally small and scattered along water courses and around the coast. The Okia Flat wetland and the Tokomairaro River Swamp are the largest wetland systems, both over 170 hectares.  

Within the Dunedin & Coast FMU 16 sites are recognised as Regionally Significant Wetlands. These are presently classified as swamp (8 sites), several grading to salt marsh (2), marsh (4) and bog (1). 

Starting with the bog site, the flat crest of Swampy Summit (48 hectares) holds several tarns with margins of sphagnum bog grading to tussock and shrubland. The substrate is peat, which in places is exposed as dried, wind-eroded surfaces that reveal subfossil stumps of a former pink pine woodland, as well as quartz pebbles derived from moa gizzard stones; two indications of bog history and change over time, in both flora and fauna.  

Additional bog communities occur in stream heads to the east of Swampy Summit, in basins having peat to 6 metre depths, variously with communities of sphagnum, carex sedgelands, mountain flax, with surroundings of subalpine scrub and regenerating cedar cloud forest.  

One other bog site is recognised: Black Swamp, an isolated 6-hectare dome of peat on a ridge crest inland from Milton, having wire rush, sphagnum, and sedge communities, and heath scrub including manuka and dracophyllum, within surrounding farmland.  

Coastal wetland sites that do not appear to have yet been identified within the Dunedin & Coast FMU are those of Purakaunui Inlet and Blueskin Bay (including the Orokonui arm). 

One aspect of wetland botanical interest lies in the latitudinal distribution limits of plants, for example species that are more common in northern New Zealand come south only as far as their cold tolerance may allow, hence sea rush (Juncus kraussii), reaching a southern limit in Pūrākaunui Inlet, and the tall sedge Bolboschoenus caldwellii at Tomahawk Lagoon. 

There are seven estuaries within the Dunedin & Coast FMU, with natural or modified ecosystems depending on surrounding land use. Tokomairaro and Kaikorai estuaries are the most impacted by sedimentation and increases in nutrients due to upstream land use and are in a “fair” and “poor” state, respectively.  

The Kaikorai Estuary has experienced high modification and habitat loss due to urban development. The Blueskin Bay catchment is less modified, with native and plantation forests and low-intensity agriculture. Because of this, the estuary is in a “good” state, although it is vulnerable to habitat loss and modification of estuary margins.  

Papanui and Hoopers inlets both have large seagrass beds — a good sign of estuarine health. However, like all estuaries, they are susceptible to human activity and vulnerable to modification. 

The Dunedin & Coast FMU also contains several coastal lagoons. Little is known about most of these ecosystems. The Tomahawk Lagoon is a regionally significant wetland and wildlife sanctuary under stress from nutrient and habitat alteration and experiences harmful algal blooms.