1. Adding suspended sediment to the NRWQN
Deborah J. Ballantine and
Robert J. Davies-Colley
Acknowledgements: Funding from NIWA Capability Fund (CF112440) and NIWA field teams who will do sampling

2. Outline of talk Background information on NRWQN
Sediment monitoring in New Zealand
Sediment issues
What NIWA proposes doing
Science questions
Looking to the future

3. Background to the NRWQN
National Rivers Water Quality Network (NRWQN) operational from January 1989.
Provides reliable scientific information on the nation’s rivers.
Information used to detect trends in water quality and to help with understanding the functioning of NZ’s rivers.
Stable in its operation and design throughout its 20 year history.
no changes to monitoring sites, apart from minor shifts in precise sampling locations
only one change in variables measured
no change in methods of measurement
valuable resource due to its consistency
NRWQN data increasingly augmented by Regional Council SoE data.

4. Background to the NRWQN cont’d
77 sites on 35 rivers
Drain about 50% of NZ land area
33 South Island, 44 North Island
Sites at or close to flow monitoring stations
Samples collected by NIWA field teams monthly
Samples analysed for:
physico-chemical - %DO, pH, water temperature,conductivity
nutrients - TN, TP, NOx-N, NH4-N, DRP
optical – visual clarity, turbidity, CDOM
bacterial – E. coli.

5. NRQWN Applications

6. Applications of NRWQN data
State of the Environment (SoE) Reporting
NRWQN data has been used by MfE in two State of the Environment (SoE) reports for New Zealand
Two decades of NRWQN data used for trend analysis.
Water resource management
NRWQN data used by NIWA, regional councils and other environmental research and consulting agencies, for addressing practical problems of river water quality management .
International reporting
World Health Organisation’s Global Environmental Monitoring System (GEMS) programme.
Scientific research
To advance scientific understanding of New Zealand river ecosystems
e.g. used to calibrate national-scale models of the delivery to the sea of materials from the New Zealand landmass.

7. Sediment Sampling

8. Suspended sediment sampling in New Zealand
1950s - in response to soil conservation problems, carried out by Ministry for Works.
1960s and 1970s - extended to catchments of interest for hydroelectric power development.
1980s - small basins to establish effects of land use and land use change on sediment loads.
Stalled in 1990s due to a lack of funding.
Currently done on an ad-hoc basis by regional councils and for specific research projects.
Hicks D.M., Quinn J., Trustrum N Stream sediment load and organic matter. In Freshwaters of New Zealand, Harding J, Mosley P, Pearson C, Sorrell B (eds). NZ Hydrological Society and NZ Limnological Society: Christchurch.

9. Why add suspended sediment to the NRWQN?
NRWQN does not include suspended sediment monitoring.
Considered too expensive to include indefinitely.
NRWQN includes sediment-related optical variables
Turbidity and visual clarity. 
Other NZ water quality networks lack suspended sediment
Lack of national scale information on suspended sediment, particularly relating to water quality.
Sediment work, emphasising sediment mass fluxes, is traditionally done as an add-on to hydrometric work.

10. Why add suspended sediment to the NRWQN?
Visual clarity and other optical water quality variables are usually measured as part of water quality surveys.
Suspended sediment (SS) is measured at numerous sediment sites in New Zealand, but not along with visual clarity
Very few datasets with paired SS-visibility measurements in NZ
e.g. Motueka River and a few Regional SOE sites that are also ‘sediment’ sites
Special studies of sediment loads done independently of water quality.
There has been insufficient ‘cross-over’ between related disciplines.

11. Sediment as a pollutant
Effects of suspended sediment on water quality and aquatic environments well known.
Affects clarity, drinking water quality, also recreation suitability.
Limits light penetration for photosynthesis.
Affects the health and feeding of aquatic organisms
Contributes to the loss of diversity and the dysfunction of community structure.
Fine-grained sediment deposition and accumulation on river channel beds degrades riverbed habitat quality.
Spaces between gravel particles get clogged.
Sediment is a vector for a range of contaminants and nutrients, e.g., particulate organic carbon (POC), phosphorus, delivered to rivers by soil erosion

13. Sediment as a pollutant
Affects drinking water quality
Limits light penetration for photosynthesis.
Affects the health and feeding of aquatic organisms
Contributes to the loss of diversity, loss of habitat, dysfunction of community structure and disrupts food chains.
Affects visual clarity
Loss of diversity and dysfunction of community structure – less tolerant organisms take over
Loss of habitat for fish spawning e.g. for salmon and trout

14. Sediment as a pollutant
Affects recreation e.g. swimming, fishing, boating
Reduced clarity is a major limitation to contact recreation (CR) in NZ rivers (Davies-Colley and Ballantine, 2010)
Approx 22 of 77 NRWQN sites are unsuitable for CR because of clarity
Fine-grained sediment deposition and accumulation on river channel beds degrades riverbed habitat quality.
Davies-Colley, R.J. and Ballantine, D.J. (2010). Suitability of NZ rivers for contact recreation: a pilot application of a water quality index to the National Rivers Water Quality Network (NRWQN). NIWA Internal Report 145. (National Centre for Freshwater).

15. Sediment as a vector for pollutants
Sediment is a vector for a range of contaminants and nutrients, e.g., phosphorus, E. coli, particulate organic carbon (POC)
Phosphorus storage in channel bed sediments
Nutrient transformations between sediment and water column
High POC transport in NZ rivers
Delivered to rivers by soil erosion
NZ (and other South Pacific islands) may contribute up to 35% of the global POC supply to the ocean from 3% of the land area (Lyons et al., 2002).
Lyons W.B., Nezat C.A., Carey A.E., Hicks D.M., (2002) Organic carbon fluxes to the ocean from high-standing islands: Geology, 30, p. 443– 446.

16. Why add suspended sediment to the NRWQN?
SS (and particulate organic carbon - POC) added to the NRWQN for a 5 year period.
to allow certain water quality variables to be inter-related to suspended sediment, and
to provide a basis for modelling sediment, visual clarity, and other particulate concentrations and fluxes.
High flows most important when SS and sediment-associated constituents are high.
Sampling throughout one year through high and low flows.
Further 3 years sampling through high flows, possibly followed by a limited amount of special flood sampling.

17. Why add suspended sediment to the NRWQN?
Over a 5 year period – hope to gain a better understanding of suspended sediment dynamics in NZ rivers.
Advance our understanding of fine suspensoids in rivers – and the impacts of turbid plumes and their associated contaminants on downstream waters (lakes and estuaries).
Useful to have datasets with suspended sediment, optical and water quality variables.

18. Median values for 6 months Jan – June 2011
Results so far…….
Strong relationship between both (log) clarity and (log) turbidity and (log) clarity and (log) suspended sediment
Median values for 6 months Jan – June 2011

19. Results so far….
PP (NRWQN TP – DRP) v SS
PON and POC v SS

20. Science Questions

21. Can we model visual clarity at the national scale?
What are the contaminants associated with fine sediment? (microbes, toxics, carbon, phosphorus)?
Can we predict light attenuation as a function of land use-geology interactions in catchments?
Predict how visual clarity changes when land use changes?
How does soil conservation and riparian management affect light attenuation in rivers and downstream waters?
Can we set targets for ecologically sustainable SS concentrations and bed sediment storage?
By measuring the carbon and phosphorus content of sediment in rivers (flow related), fluxes of SS can be used to calculate and model fluxes of particulate carbon and phosphorus
Help advance national scale modelling of SS and its optical effects

22. The future? Add continuous turbidity measurements to NRWQN sites
Add sediment gauging to a selection of NRWQN sites
Eventually have reliable information on suspended sediment and water quality
Useful for assessing impacts of SS on water quality

23. Any questions?

25. NZ sediment loads
New Zealand is a major sediment producer globally – accounts for about 1% of the input to the world’s oceans from less than 0.2% of the land area.
North Island 91 Mt/year.
South Island 118 Mt/year.
Interested to know how suspended and channel bed sediment impacts on water quality
Hicks, D.M., Shankar, U Sediment from New Zealand Rivers. NIWA, Wellington. NIWA Miscellaneous Chart 236.

26. The future?