Taiari/Taieri FMU (Freshwater Management Unit)

The Taieri FMU covers about 570,000 hectares of land. The main land covers are exotic grasslands, tall tussock grasslands and exotic forests. High-producing exotic grasslands are the most common vegetation and occupy around 35% of the area. These exotic grasslands are used for intensified grazing and are widespread across the Maniototo, Waipiata, Kyeburn, Middlemarch and the lower Taieri.  

Low-producing grasslands that brown off over summer, such as those found on steep hill and high-country cover 27%, while tall tussock lands cover 22% and exotic forests occupy 5% of the area. They mainly occur in parts of the Waipori, Waihola, Riverside and Salisbury catchments. 

Brown soils are the most common, covering 48% of the FMU in areas such as Waipori, Parera, Salisbury, Leeflat, and Paerau. These soils mainly support the high and low-producing exotic grasslands and exotic forests.  

Pallic soils cover 33% of the area, have variable permeability, generally poor drainage and occur in areas such as Shannon, Matarae, Kiteroa, Sutton, Middlemarch, Patearoa and Naseby. Parts of Maniototo and Patearoa have semi-arid soils, which cover 7% of the FMU, and recent soils, including alluvial floodplains of the Taieri River, cover around 6%. 

Dry stock farming is the most common land use occurring on 71% of the FMU. This is pasture grazing and includes sheep and beef (57%); mixed sheep, beef, and deer (8%); and sheep (6%). Conservation estate covers around 10% of the FMU, with forestry accounting for 5% and dairy farming 4%.  

Notable changes in land use over the past 30 years include an increase in dairy farming (31%), conservation estate (58%), forestry (7%), urban area (15%), and nurseries/vineyards/orchards (18%). Dry stock farming has decreased by 8% but remains the primary land use in the Taieri area.  

Taieri FMU land use summary

Weather and climate are diverse in the Taieri catchment, ranging from generally hot, dry summers and cold, frosty, dry winters upstream of Sutton to cooler, wetter conditions in its lower reaches.  

Upstream of Sutton, the catchment is sheltered by the Southern Alps from the westerly airstream, which drives much of the weather over New Zealand. Apart from the headwaters, the area is also sheltered from the southern and easterly quarters by hills and mountains.  

Temperatures can range from -13°C in winter to above 38°C in summer, and annual rainfalls range from about 1600mm in the Taieri headwaters to 400mm in the Maniototo Basin and the Strath Taieri. 

Downstream of Sutton, the catchment becomes more exposed to southerly and easterly quarter weather systems. Temperatures are much less extreme, and annual rainfalls range from around 1200mm on the coastal hills to between 600mm-700mm on the Taieri Plains.  

The Taieri is an important water source for irrigation, and low flows are significantly affected during the irrigation season. Two hydroelectricity plants are operating in the FMU: one in the Upper Taieri and the other in the Waipori catchment. Most of the Dunedin City water supply comes from the Taieri River downstream of Sutton. 

In its lower reaches, the Taieri River flows out onto the Taieri plains. It becomes tidal from around Allanton to Taieri Mouth on the East Coast. 

Water quality in the Taieri is generally good; however, some lower Taieri Plain tributaries are degraded. Some sites here have the poorest water quality in the Otago region. Water quality is affected by pressures such as intensive agricultural land use, urban land uses and stream modification. To check water health, ORC collects water quality and ecology data for rivers, streams, and lakes. We also analyse long-term data to find trends in water quality over time. Some sites in this FMU have only been monitored for less than five years, so some water quality states and trends are interim results. 

About half of the 22 river monitoring sites did not meet the required standard for suspended fine sediment, which indicates water clarity. However, visual clarity in these catchments may be affected by naturally occurring dissolved organic matter, such as tannins, and may not be directly attributable to suspended sediment Five sites in the lower Taieri did not meet the required standard for E. coli (human health indicator).  

Two sites, Taieri at Creamery and Owhiro Stream, did not meet the required standard for Dissolved Reactive Phosphorus. Excess phosphorus can cause algae growth and poor river health. Lakes Waipori and Waihola are situated in a wetland area that covers 2000 hectares. Lake Waihola has ‘C’ band results for nutrients and chlorophyll-a (a measure of algae in the water). This result is consistent with the shallow, nutrient-enriched state of the lake. 

Trend analysis found most sites to have some degrading trends. Degradation for nutrients, E. coli and turbidity (visual clarity) were calculated for most Taieri sites in our 20-year trend results. However, our 10-year analysis showed fewer sites with degrading trends for nutrients and improving trends for turbidity at most sites.  

For Lake Waihola, there were degrading long-term (18-year) trends for nutrients, E. coli, and turbidity. However, the 10-year analysis showed improving trends for turbidity and chlorophyll-a are likely. 

Taieri FMU Water Quality State and Trends Technical Report

Introduction to water quality

Taieri FMU water quality summary

The Taieri FMU has three aquifers: The Maniototo Tertiary, Strath Taieri, and the lower Taieri aquifers can be used for domestic supply, irrigation, stock water, and dairy sheds. However, the status and use of many bores in the FMU is unknown. 

The Maniototo is Otago’s largest aquifer by area. Groundwater in the Maniototo is found in two types of aquifer systems: shallow Quaternary deposits and deeper Tertiary sediments. According to the ORC database, there are 255 bores in the aquifer. Most bores are either less than 20 metres or 60 to 80 metres deep. We monitor groundwater quality in two bores, and results show high nitrate concentrations and some E. coli detections. Some nitrate results were moving towards the nitrate NZ Drinking Water Standards Maximum Acceptable Value (MAV) of 11.3mg/L. Arsenic concentrations did not exceed the limits in these two bores. However, due to the extensiveness of schist (a natural source of arsenic) in the area, it is recommended that bore users regularly test their water. 

The Strath Taieri basin is between the Rock and Pillar Range to the west and the Taieri Range to the east. It is a tectonic basin formed by the faulting/folding of the Otago Schist basement rocks. The Strath Taieri basin has a single unconfined aquifer. This aquifer consists mainly of silty gravel but also has iron pans (iron salts) and silt lenses (very fine silt) that form perched water tables above the regional water table, confined aquifers, and groundwater channels. The water table is shallow in most of the valley, at less than 5 metres below ground level, but is deeper to the west and beneath pockets of silt.  

There are 114 bores in the ORC database for the Strath Taieri basin. Groundwater quality in the Strath Taieri basin is monitored in one bore. The results show several E. coli exceedances, which are likely to be due to poor bore security. There was one exceedance of the dissolved arsenic MAV. However, it may have been an isolated event and could be due to an analytical error. We recommend checking arsenic concentrations in this area. The highest nitrate concentration was 4.7mg/L, which is slightly below half of the MAV, although most samples range between around 1.0 and 1.7mg/L. 

The lower Taieri aquifer sits in a tectonic depression filled with large layers of sand, gravel, silt, clay, and peat deposits. A fine-grained, low-permeability estuary deposit covers around three quarters of the aquifer (the Waihola Silt-Sand). This layer formed when the basin was a marine bay. The groundwater is mainly recharged by rainfall and infiltration from the Taieri River around Outram, the Silver Stream, and the Waipori River upstream of Berwick. Most of the groundwater recharge is in the Mosgiel area, and the flow is westward to low-lying areas such as the West Taieri Drainage Scheme and the Waipori–Waihola Lake wetlands complex.  

The ORC database shows 552 bores in the lower Taieri aquifer, although the status of many is unknown. Despite the high number of bores, groundwater use has decreased, particularly since the shutdown of the Dunedin City Council (DCC) groundwater takes. Many bore owners in the area do not use groundwater because the naturally high iron and manganese adversely affect the taste and colour of the water.  

The ORC monitors groundwater quality in four bores. The results show an increased risk of faecal contamination, with E. coli exceedances in three bores. Groundwater nitrate concentrations are all below the MAV of 11.3mg/L. However, some concentrations were over half the MAV i.e., over 5.5mg/L. This is likely due to dairy sheds, septic tanks, and poor bore-head protection. Sometimes nitrate leaching can be high but does not show in groundwater testing. This can be due to low-oxygen conditions, which break nitrate down. Dissolved arsenic concentrations were all below the MAV. 

Biodiversity within the Taieri FMU includes rare and threatened ecosystems and species. The vulnerable ecosystems include braided rivers, ephemeral wetlands, lake margins, salt pans, cushion bogs, and wetlands. These are often threatened by processes such as land use change and invasive species. Little is known about the extent and/or condition of these ecosystems.  

Diverse species depend on freshwater habitats and ecosystems, including fishes, invertebrates, plants, and birds. There have been 72 threatened freshwater-dependent species identified within the FMU. Threatened freshwater fishes include the Central Otago roundhead galaxias, Taieri flathead galaxias, dusky galaxias, Eldon's galaxias, and lamprey.  

Freshwater invertebrates include koura, shrimp, mussels, and threatened caddisflies, moths, stoneflies, and clam shrimp. Cardamine mutabilis, Chenopodium detestans, Crassula peduncularis, and Triglochin palustris are examples of threatened freshwater-dependent plants found here.  

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

Exotic geese, willows and exotic fishes are found in the Taieri catchment, including perch and four salmonids. Many native freshwater species are under threat and continue to decline in number. 

Within the Taieri FMU, 33 sites are recognised as Regionally Significant Wetlands (RSWs) in the current Regional Plan: Water for Otago. These are classified as swamp (13 sites), marsh (8), fen (7), and inland saline (5).  

The wetlands of Lakes Waihola and Waipori are the remains of the Taieri Plain extensive wetland system which has been drained in the last 200 years. The area of 2,089 hectares includes both lakes, linked to the Waipori River by a bird’s-foot delta. These landforms were created by tidal fluctuations of the river. This wetland system, including Te Nohoaka o Tukiauau/Sinclair Wetlands, is well known.  

Six much smaller ponds with swamp and willow margins are recognised as RSW sites on the Taieri Plain. Takitoa Swamp (68 hectares), with flax, shrubland, and carex sedge grasslands, occupies the bed of a side valley at the top of the Taieri Gorge.  

The scroll plain of the upper Taieri is of a different origin and character to the lower area. These wetland systems are still present on a grand scale. They hold the broad river meanders of the current river course as it wanders across the floodplains, along with ponded oxbows and old water channels which show the river's history. These scroll plains are special to Otago, and ORC is working on better understanding them to support their ongoing management.  

Maungatua Summit Wetland Management Area (1213 hectares) has cushion bogs, tarns, and tussock tops. Subalpine shrublands and beech forest remnants surround it on the east side of the range.  

To the west of Maukaatua (Maungatua), and slightly lower, headwater fingers of the Pioneer Stream area drain north into Lake Mahinerangi. This area has the Loch Luella and Loch Loudon fen complexes (871 and 33 hectares). These have a cover of copper tussock, sphagnum bogs and fens, and are surrounded by pasture. 

Similar remnants are found in the Black Rock marshes on slopes rising to the Lammermoors. To the north, on drier rolling hills west of the Silverpeaks, red tussock and moss. Smaller wetlands are also present. The Peat Moss Hills (36 hectares) and Lamb Hill (37 hectares) wetlands are here. West again, several smaller wetlands are present in the Clarks Junction vicinity. 

Ephemeral wetlands are scattered, and their flora and fauna are diverse, rare, and often nationally threatened. These wetlands can have various origins, such as glacial moraines, dune hollows, oxbows, or sinkholes. But the characteristic type in inland Otago are surface depressions on the plateau crests of rolling schist country. These lack a surface outlet, so they pond in winter and spring when fed by rain and snow melt. In drier months, they often completely dry out, encouraging specific wetland flora and fauna for part of the year, such as low-growing turf vegetation. 

Examples of ephemeral wetlands in the Taieri FMU include Nenthorn Ridge (67 hectares), Red Bank (122 hectares), and the Styx (11 hectares) Wetland Management Areas. At Taieri Mouth, there are estuarine communities and wetland forests, also known as carrs. 

The Taieri River estuary is a shallow, short-residence time tidal river estuary (SSRTE). The zone between high and low tide (intertidal area) is 9.96% of the estuary. While the Taieri River is not named as a Coastal Protected Area (CPA 22), it is important in terms of ecological, scenic, recreational, and cultural values. The estuary is vulnerable to both nutrient and sediment stress. However, these stressors do not have much effect because of the small intertidal area, high flushing from the river, and lower light due to river depth. 

Only small patches of nuisance algae (quick-growing algae) and mud occur along the edges of the water around rushes. The estuarine area is mainly intact, with some historical reclamation of wetland areas, and large areas of rushland found along some margins. The margins of the estuary are where food web producers such as algae, eelgrass, rushes, and mangroves provide a huge amount of organic matter, producing up to ten tonnes of plant detritus per hectare each year.