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Historic Freshwater State

Water quality

Surface Water Quality – WQI measures

Surface water, being above ground waterways, are easily recognizable across the Marlborough landscape – such as our iconic braided rivers. Surface water courses gain their flow through catchment areas as well as underground springs in some cases. A catchment is the area of land from which all rainfall and streams flows out into a river, a lake or the sea. The catchment of large rivers can be divided into smaller sub-catchments, which usually represent the tributaries.

The Surface Water Quality State of the Environment (SOE) monitoring has been operational in Marlborough since 2007. The programme measures 56 sites regionally, five of which are in the Marlborough Sounds Complex (MSC) FMU.

The Water Quality Index (WQI) serves as a consolidated score reflecting the quality of river water. It is derived from nine chemical and physical parameters measured on a monthly basis. The WQI ranges from 0 to 100 with higher values indicating better water quality. The WQI simplifies comparisons of water quality across various waterways and serves as a valuable tool for identifying degraded waterways and prioritising improvement actions.

The five index classes represent water quality, with “marginal” and “poor” categories requiring improvement. The higher the index number, the better the water quality and accordingly the closer to “excellent” WQI rating. Read more about our surface water SOE monitoring programme below:

Go to our SOE monitoring programme page

The below table shows the historical WQI indices for the Marlborough Sounds Complex FMU monitoring sites. This data is also shown on the graph below – please note this graph is historic; the Kaituna River is not part of this FMU area. The WQI for the Graham, Kenepuru, Waitohi, and Linkwater Rivers and Cullens Creek monitoring sites are summarised into the below chart.

WQI graph, Marlborough Sounds 2007-2015

We can see from the graph that the WQI for several of the monitoring sites has fluctuated but remained within the same index band. In contrast, the Graham River and Cullens Creek WQI indices gradually declined in the early to mid-2010s. We can also see from the below chart that a large proportion of the indices were in the ‘marginal’ or ‘poor’ categories.

The 2016 surface water SOE report provides insight as to the decline in water quality at the Graham River and Cullens Creek monitoring sites at this time:

“The Graham River has the second largest proportion of native vegetation in the catchment and was originally chosen as a reference site for the other smaller catchments in this group. The Water Quality Index had been in the ‘good’ category between 2009 and 2013, confirming the reference status. However, in the last two years the water quality has deteriorated and has now reached the lowest value since monitoring began in late 2007. The main cause for the reduction in the Water Quality Index is a significant increase in turbidity. Field notes point to gravel extraction and bank erosion near the sampling site as the cause. Sporadically high E. coli concentrations in the Graham River are measured during rainfall periods, but also during low flows, which is likely an indication of direct stock access to the waterway. The guidelines for the dissolved nutrients, phosphorus and nitrogen are rarely exceeded and analysis of the data has shown no relationship with high E. coli concentrations. The example of the Graham River shows that the anthropogenic modification of a relatively small proportion of the catchment can have significant implications for the water quality of a waterway.”

“E. coli concentrations in Cullens Creek are higher than those in Linkwater Stream. This is despite a longer history of permanent fencing along Cullen Creek, which has mature riparian vegetation along most of its length. It appears that remaining stock access or run-off during irrigation and rainfall is having a substantial effect on the water quality of the creek.”

Marlborough Sounds Complex SOE monitoring sites – historic quality measures

Monitoring site

2007-2009

2010-2012

2011-2013

2012-2014

2014-2016

2016-2018

Graham River

N/A

Good

Good

Fair

Fair

Good

Kerepuru River

Fair

Fair

Fair

Fair

Fair

Fair

Waitohi River

N/A

Fair

Fair

Fair

Fair

Fair

Cullens Creek

N/A

Fair

Fair

Fair

Marginal

Fair

Linkwater

N/A

Marginal

Marginal

Marginal

Marginal

Marginal

The historic quality measures in the above table are further summarised across all years and for all three sites into the below chart. We can see from the chart that the majority of WQI measures are either marginal or poor, with a small number of excellent or good measures. The latest WQI summary up to 2022 is in the Marlborough Sounds Complex Current Freshwater State page.

Go to the Marlborough Sounds Complex Current Freshwater State page

Ground Water Quality

There are no significant groundwater aquifers in the Marlborough Sounds FMU, which is a function of both the area’s geology and its formation as drowned river valleys. The largest aquifer in the region is located in the Linkwater area, which is a low-lying alluvial plain of 5 kilometres in length that separates the head of Queen Charlotte Sound/Totaranui and the Mahakipawa Arm of the Pelorus/Te Hoiere Sound. Another smaller aquifer is located in the Tuamarina Valley.

Due to the natural downwards tilting of the region to the north, the creeks and streams flowing north into the Linkwater area have more extensive catchments, wider valleys, and higher flows than those flowing south. This has determined the way the aquifer has formed and is thought to be alluvium of up to 100 metres thick. The Linkwater Aquifer is unique amongst the Marlborough Sounds catchments as it lacks a perennially flowing river and has two seaward coastal boundaries. Drilling in the area showed that around 50,000 years ago, the area was a lake.

Water quantity

The requirement for water takes are not on the scale of the Wairau FMU but there are still a number of water takes in the area. These are primarily from creeks and streams for community domestic supplies for residences and visitor accommodation.

Within the Linkwater catchment, groundwater is used for pasture and crop irrigation. While there has always been some irrigation of crops and pasture in the Linkwater area, water demand increased significantly following the 1998 and 2001 summer droughts. The first systematic investigation of groundwater resources at Linkwater was commissioned by the MDC in early 2006. This baseline study included a review of the local geology, but the focus was on the application of environmental isotopes and hydrochemistry to understand aquifer dynamics. Mineral exploration in the mid-1990s systematically drilled around 170 test wells across the Cullen Creek fan to assess the economic viability of placer gold deposits within the alluvium.

The history of the underground phase of gold mining at Cullensville is very pertinent to groundwater hydrology in the area. The first phase of gold mining took place in the 19th century and continued off and on until about 1940. Groundwater originating from schist basement rock caused significant problems for historic underground gold mining operations that took place around Cullen Creek. This basement rock sourced groundwater is likely to still contribute to aquifer recharge. However, it is unlikely that sufficient quantities of groundwater occur in the schist bedrock for irrigation. Although it is fractured and jointed, the permeability of the schist is too low to store or transmit sufficient quantities of water.

Historic mine shafts dating from the 19th century onwards have modified the natural direction of groundwater flow in some areas. For example, a significant flow of groundwater emerges continuously from a vertical, disused mine shaft approximately 500 metres north of the information board at the historic Cullensville settlement. The old mine workings presumably provide a preferred pathway for groundwater, which in this case flows out at the surface and contributes to the natural surface flow of Cullen Creek Mine shaft water represents an important contribution to the baseflow of Cullen Creek under summer conditions.

Special investigation

The WQI and SOE water quality monitoring discussed above was preceded by a pilot study on small streams in the Marlborough Sounds, their ecology, water quality, and associated values. Interestingly, many of the factors discussed above were identified in the 2003 study, such as high levels of suspended sediment (turbidity) and E. Coli.

This pilot study focused on streams in the Queen Charlotte Sound and aimed to characterise the ecological values of these streams and identify if water abstraction (domestic supply, holiday homes etc.) may threaten these values.

All the sites drained catchments with either native forest or regenerating native forest. The only exception to this was one site which has a catchment dominated by pine forest. Indices of stream health, calculated from the composition of the invertebrate communities, indicated healthy stream ecosystems at most sites, although the smaller streams studied tended to have lower diversity.

Water quality was generally good at most of the sites sampled. However, the smallest three sites had the poorest water quality with relatively high levels of suspended sediment and dissolved phosphorus and nitrogen. The concentrations of faecal indicator bacteria were also relatively high at several of the sites and above contact recreation guidelines at one site. Drinking water guideline concentrations for E. coli were exceeded at all of the sites.

The smallest stream sampled had a lower diversity of fish and invertebrate species compared with the other sites and the species that were found there were generally restricted to small poorly-connected pools. The conditions in this stream are probably representative of the changes likely to occur at other sites if significant amount of flow were abstracted for domestic use. Some examples of flow diversion through water supply systems were observed and have resulted in reductions in the amount of habitat available in some streams.

A conclusion of the study was that an education campaign and guidelines for people taking water from these streams may be sufficient to overcome many of the highlighted issues.

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