SciBlogs

Understanding groundwater quality – why it’s not easy Waiology Dec 11

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By Chris Daughney and Magali Moreau

Un-muddying the Waters : Waiology : Oct-Dec 2013Groundwater resources are very important for New Zealand. Groundwater supplies about a third of our abstractive water needs and an even greater proportion of the water required by the agricultural sector.

There is understandably much concern about groundwater quality, particularly in terms of nitrate. High concentrations of nitrate in groundwater that is used for drinking can impair oxygen transport through the bloodstream, particularly in infants. High concentrations can also pose risks to aquatic ecosystems where nitrate-rich groundwater discharges to rivers, lakes and estuaries.

So what is the state of health of New Zealand’s aquifers, as far as nitrate goes? There are a couple of reasons why this question is not easy to answer.

The first challenge is to determine the concentration of nitrate that we should expect in the absence of human influence. It is hard to define this “baseline” because many of our aquifers are already impacted to some degree by human influence, meaning that nitrate concentrations are not representative of natural conditions. One elegant way to estimate the baseline condition is to compare the age of groundwater to the concentration of nitrate that it contains. Application of this technique shows that nitrate concentrations in New Zealand’s groundwater were typically below 1 mg/L (as NO3-N) before the export meat industry started. A similar conclusion was reached in a separate study that used a statistical technique (without water dating) to show that nitrate concentrations above 1.6 mg/l are probably indicative of human influence, whereas nitrate concentrations above 3.5 mg/L are almost certainly caused by human activity.

Idealised shape of the capture zone for a well in a homogeneous isotropic unconfined aquifer. The regional groundwater flow direction is from right to left (modified from Ministry of the Environment, British Columbia 2004).

Idealised shape of the capture zone for a well in a homogeneous isotropic unconfined aquifer. The regional groundwater flow direction is from right to left (modified from Ministry of the Environment, British Columbia 2004).

The second difficulty is that capture zones have been mapped for very few wells in New Zealand. A capture zone is the area of land through which rain or river water enters the aquifer and is ultimately extracted from the well of interest. The land use activities within the well’s capture zone can alter the groundwater quality. So if the capture zone has not been mapped, if we find nitrate concentrations above the baseline, the source of the nitrate may not be identifiable. This leaves us asking “where did this nitrate come from?”

A third difficulty is that groundwater flow is relatively slow. This results in a time lag between nitrate infiltration into the aquifer in a well’s capture zone and detection of that nitrate at the well some distance away. The groundwater dating techniques mentioned above can assist us to understand these time lags, but there are still many locations around New Zealand at which groundwater ages remain unknown. This leaves us with the question “when did this nitrate enter the aquifer?”

Returning to the question posed above, what is the state of health of New Zealand’s aquifers, as far as nitrate goes?

A recent survey evaluated the concentrations of nitrate in groundwater from over 900 wells across the country, using measurements made between 1995 and 2008. Roughly 1/3 of the tested wells had median nitrate concentrations above 3.5 mg/L, which as mentioned above is the upper threshold for natural conditions. The wells with above-baseline nitrate concentrations were found across the country, indicating pervasive degradation of groundwater quality. At roughly 5% of the wells tested, the nitrate concentration was in excess of the drinking water standard that is set for protection of human health.

Although relationships between groundwater nitrate concentrations and well depth were observed, no relationships to land use or land cover around the wells were detected. This lack of relationship between groundwater quality and land use around the wells is in fact a common result that has been observed in several studies in New Zealand and overseas. It can be explained by the factors presented above: it is hard to understand relationships between groundwater quality and land use unless the age and source (capture zone) of the groundwater are known.

Given the importance of groundwater to this country, and given the evidence that groundwater quality is pervasively degraded relative to natural conditions, there is urgency for better understanding of our aquifers. Determining groundwater age and mapping capture zones must become priority activities. Without the ability to unequivocally relate cause (land use) to effect (increasing nitrate concentrations), we will keep telling each other “it wasn’t me!”


Dr. Chris Daughney is the Director of the National Isotope Centre, and Magali Moreau is a groundwater geochemist, both GNS Science.

References
Ministry of Environment (British Columbia). (2004) Well Protection Toolkit Step 2 (electronic resource). 24 p.; last accessed 30/01/2013.
Morgenstern, U.: Daughney, C.J. 2012. Groundwater age for identification of baseline groundwater quality and impacts of landuse intensification – The National Groundwater Monitoring Programme of New Zealand. J. Hydrol., Vol. 456–457: 79–93.
Daughney, C.J.; Raiber, M.; Moreau-Fournier, M.; Morgenstern, U.; van der Raaij, R.W. 2012. Use of hierarchical cluster analysis to assess the representativeness of a baseline groundwater quality monitoring network : comparison of New Zealand’s national and regional groundwater monitoring programs. Hydrogeology journal, 20(1): 185-200
Daughney, C.; Randall, M. 2009. National Groundwater Quality Indicators Update: State and Trends 1995-2008, GNS Science Consultancy Report 2009/145. 60p. Prepared for Ministry for the Environment, Wellington, New Zealand.

Vague expectations get vague results: Freshwaters need targets Waiology Dec 09

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By Mike Scarsbrook

Un-muddying the Waters : Waiology : Oct-Dec 2013You’ll have heard this saying before. You may have even used it as an excuse when talking to your boss at the end of the year. It is equally valid in managing our water resources. If we cannot provide clarity on what we are trying to achieve, how can we expect anyone to make effective decisions and change behaviours?

What should a waterbody draining a highly modified catchment look like? Should it be physically, chemically and biologically indistinguishable from a paired waterbody in an unmodified catchment? Should it be swimmable and fishable? Should it achieve environmental bottom lines, but no more? Should it remain in its current state, or move to an agreed, alternate state? Over what timeframes should change occur?

These are not questions for scientists, regional council staff, or economists to answer. They need to be answered through the frameworks provided in law and under the guidance of instruments such as the National Policy Statement for Freshwater Management (2011).

Communities have been given a more clearly-defined role in water resource management under the NPS for Freshwater Management. Reforms of the RMA, currently under consideration by our government, may even enshrine collaborative processes for community engagement in our legislation. However, the challenge for communities under a collaborative model is no less fraught than the existing Schedule 1 process in the RMA. Drawing the line between what is acceptable, or unacceptable in terms of water quality across a range of values, many of which are conflicting, or even mutually exclusive, is a massive challenge for New Zealand.

From a dairy industry perspective we support the limit setting process set out in the NPS for Freshwater Management and we broadly support the National Objectives Framework that guides the setting of clear freshwater objectives. Having communities more robustly define the water quality outcomes they want is a healthy and desirable attribute of a mature society. Farmers, as part of the community want clear direction on what is acceptable and not acceptable. Furthermore, the dairy industry is fully committed to supporting farmers to meet the limits or constraints a fully-informed community deems appropriate. We are investing heavily in research, development and extension to prepare landowners for farming within limits. There will inevitably be disagreements on the details of methods and pace of change, but the drive to engage all sectors of the community in decision-making is encouraging.

Communities recognise different suites of values in highly-modified catchments versus unmodified catchments. Contaminant concentrations, driven by catchment modification, do underpin the expression of values (e.g. levels of faecal indicator bacteria indicate suitability for recreation), but changes in contaminant levels may or may not change the state of any particular value. To interpret increasing contaminant concentrations as decreasing water quality is unhelpful, particularly in the context of science’s role in informing communities and decision-makers, and especially when the water quality outcomes have not even been clearly defined.

The recent PCE report on land use intensity would have come as no surprise to anyone involved in water quality debates. The report highlighted the relationship between land use intensity and levels of nutrients in rivers. The final figure in that report showed a future prediction of increasing land used for dairy farming and associated increases in nitrate concentrations. The PCE’s analysis provides a very accessible summary of the issues around land use and contaminant loads, but contributes little to the more important debate about what is acceptable or unacceptable in terms of water quality outcomes for catchments where land use is intensifying. Is a 20, 30 or even 50% increase in nitrate loads over the next 10 years acceptable to the community? Science (and economics, matuaranga maori, plus other disciplines) can help inform the community on what are the likely effects of those nutrient increases on the water quality outcomes the community, but the ultimate decision on acceptability rests with communities through the legislated frameworks provided to them.

Let’s not give anyone the excuse of not having clear expectations of what we are asking them to achieve. And let’s not set anyone up to fail in setting unrealistic or unachievable expectations.


Dr Mike Scarsbrook is Environment Policy Manager at DairyNZ.

How does agriculture affect New Zealand’s water quality? Waiology Dec 05

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By Bob Wilcock

Un-muddying the Waters : Waiology : Oct-Dec 2013About 40% of the land area of New Zealand is in some form of agriculture. Sheep and beef farming are the most extensive (33%) followed by dairy farming at 6%, and the remainder being horticulture and cropping. Based on a large number of comparative land use studies we have a good understanding of how agriculture affects water quality and know that about 97% of the nutrient loads entering our freshwaters are from diffuse sources, in contrast with point-sources such as pipes and wastewater discharges.

Effluent from a cowshed over 1 km away. (J. Horrox)

Effluent from a cowshed over 1 km away. (J. Horrox)

Pastoral land use contributes three principal pollutant types: the nutrients nitrogen (N) and phosphorus (P), sediment, and faecal microbes. Nutrient enrichment of waterways can lead to unwanted growth of plants (waterweeds and algae). Excess sediment may cause siltation, impair oxygen transfer processes and degrading water clarity. Faecal matter and its associated pathogens presents a risk to human and animal health through waterborne infectious diseases. The extent of this risk is assessed by measuring water concentrations of the benign indicator organism, Escherichia coli (E. coli).

The cumulative effects of more than one of these contaminant may be greater than the sum of their individual parts. For example, elevated levels of N and P may stimulate vigorous plant growth that results in high pH levels during late afternoon and thereby exacerbate the toxicity of ammonia to fish and aquatic insects.

Cattle crossing in Southland. (A. Wright-Stow)

Cattle crossing in Southland. (A. Wright-Stow)

Inputs from specific land uses to waterways are characterised by their ‘yields’, which are the loads of pollutant per unit area per year. Significant differences occur in the amounts of contaminant delivered to surface waters, according to slope and elevation of land. Nitrogen enters surface waters via leaching to groundwater, whereas sediment, faecal matter and P enter streams mostly in surface runoff. Hill-country farms have lower stocking rates than flatland farms, but greater runoff potential because of the steeper landforms. This affects sediment, P and faecal microbes in particular. In contrast, N losses are highest on flatter lands, where the highest stocking rates are.

In general, the order for yields from greatest to least, is as follows:
N: flat > rolling ~ easy ~ steep land
P: steep > easy ~ rolling > flat land
Sediment: steep > easy > rolling ~ flat land

The major source of E. coli in most farming systems is via overland flow from ruminant faeces and this is likely to be greatest on steeper land, although this is not the case where large herds of cattle are allowed direct access to waterways.

Box plots showing the median concentration, bounded by the 25th and 75th percentiles, the 10th and 90th percentiles as whiskers, and outliers as dots, for N, P and sediment annual loads for each stock class of land use.   ‘None’ refers to non-agricultural rural land uses, such as exotic plantation and native forest, while ‘mixed’ refers to a catchment with more than one stock land use class (McDowell & Wilcock 2008).

Box plots showing the median concentration, bounded by the 25th and 75th percentiles, the 10th and 90th percentiles as whiskers, and outliers as dots, for N, P and sediment annual loads for each stock class of land use. ‘None’ refers to non-agricultural rural land uses, such as exotic plantation and native forest, while ‘mixed’ refers to a catchment with more than one stock land use class (McDowell & Wilcock 2008).

A comparative study of different sorts of pastoral farming found that dairy farms on flat land at low elevations lost the most N, but very little sediment, although it was not statistically different from forest, sheep and mixed land uses. Deer farming tends to be on rolling land at a significantly greater elevation than dairy, but not other land uses. Deer farms lost significantly more sediment than any other farming type but had similar losses of N, except for dairy farming. The remaining land uses (sheep and mixed), were in lands with similar slope, elevation, and sediment and N loss. However, it should be noted that loads reported from non-agricultural land uses demonstrated the least loss of N, P, sediment or E. coli.

Estimates have been made using the SPARROW (SPAtially Referenced Regressions On Watershed attributes) model to estimate their relative contributions of nitrogen (N) and phosphorus (P) to freshwaters and to the coasts of New Zealand. Dairying and sheep+beef farming each contribute 30-40% of N entering freshwaters and the coast, with forests contributing most of the remainder. About 50% of P entering freshwaters and the coast is in sediment, about 20% from sheep+beef farming and 10% from dairying.

A broad suite of mitigation measures is available to farmers and offers some hope that increased production need not be accompanied by water quality degradation, so long as they are widely adopted (PDF; Waikato Regional Council’s ‘menus of practices’).


Dr Bob Wilcock is a NIWA Principal Scientist and Programme Leader – Causes and Effects of Water Quality Degradation

References
Elliott, A.H.; Alexander, R.B.; Schwarz, G.E.; Shankar, U.; Sukias, J.P.S.; McBride, G.B. (2005). Estimation of nutrient sources and transport for New Zealand using the hybrid mechanistic-statistical model SPARROW. Journal of Hydrology (NZ) 44: 1–27. (Abstract and PDF)
McDowell, R.W.; Wilcock, R.J. (2008). Water quality and the effects of different pastoral animals. New Zealand Veterinary Journal 56(6): 289-296. (Abstract)

Estuary water quality for ecosystem health and recreation, Christchurch Waiology Dec 04

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By Lesley Bolton-Ritchie

Un-muddying the Waters : Waiology : Oct-Dec 2013The quality of the water in an estuary influences the health, abundance and survival of the plants and animals that live in or pass through it and the suitability of estuary water for contact recreation. For the plants and animals it is the concentration of toxicants and oxygen in the water that can affect the survival of species and excessive nutrient concentrations can affect the growth of nuisance macroalgae, phytoplankton and microphytobenthos. For contact recreation it is the concentration of faecal indicator bacteria and hence the likely presence of pathogens that can affect human health.

Aerial view of the Estuary of the Heathcote and Avon Rivers/Ihutai. Red areas – Coastal AE water, the remainder of the estuary is classified Coastal CR water.

Aerial view of the Estuary of the Heathcote and Avon Rivers/Ihutai
Red areas – Coastal AE water, the remainder of the estuary is classified Coastal CR water.

The following is a case study on water quality in the Estuary of the Heathcote and Avon Rivers/Ihutai in the south-east of Christchurch. The Canterbury Regional Coastal Environment Plan has assigned two water quality classes to this estuary. The red shaded areas in the map are designated as Coastal AE water, i.e. for the maintenance of aquatic ecosystems. The remainder of the estuary is designated as coastal CR water, i.e. for contact recreation and the maintenance of aquatic ecosystems.

For many years Christchurch tertiary treated wastewater was discharged into this estuary. This wastewater was a source of ammonia nitrogen, phosphorus, faecal indicator bacteria and pathogens to estuary water. Ammonia nitrogen often occurred at potentially toxic (to marine life) concentrations at sites in the vicinity of the wastewater discharge point. When the Christchurch City Council applied to Canterbury Regional Council to renew its’ resource consent to discharge this wastewater into the estuary, it was declined. On 4 March 2010 the wastewater discharge was diverted away from the estuary; the wastewater is now discharged into Pegasus Bay some 3 km from shore.

Ammonia nitrogen concentrations around the time of high tide at Penguin Street, South Shore, January 2007 – December 2012.

Ammonia nitrogen concentrations around the time of high tide at Penguin Street, South Shore, January 2007 – December 2012.

Within months of the diversion of the wastewater there was up to a 90% decrease in ammonia nitrogen and phosphorus concentrations in estuary water. This decrease was interrupted by the 2010-2011 earthquake sequence when raw sewage was discharged to the rivers and directly into the estuary because of broken infrastructure (raw sewage was discharged directly into the estuary in the Penguin Street area).

The dissolved inorganic nutrients in the wastewater also meant more than enough nutrients in estuary water to allow for the prolific growth of the nuisance algae sea lettuce and the red algae Gracilaria chilensis.

Sea lettuce (green) and Gracilaria chilensis (red) on the mudflats.

Sea lettuce (green) and Gracilaria chilensis (red) on the mudflats.

While there are still post-earthquake issues with infrastructure, in the main the quality of the river water flowing into the estuary now has the largest influence on nutrient concentrations in estuary water. Both rivers arise from springs that are fed from groundwater in the shallow aquifers. Notable concentrations of nitrate occur in the spring water (PDF). It is the nitrates in the spring water that now have the greatest influence on dissolved inorganic nitrogen concentrations in estuary water. However, there are other nutrients sources to the river and directly into the estuary including stormwater (at least 67 outlets into the estuary), point source discharges from industrial sites, infrequent sewage overflows, catchment geology and the presence of large numbers of waterfowl (PDF).

When wastewater was discharged into the estuary the suitability for recreation grade at all estuary sites was Poor or Very Poor. With the removal of the wastewater sites now have either a Poor or Good grade http://ecan.govt.nz/services/online-services/monitoring/swimming-water-quality/Pages/Default.aspx. The three sites that still have a Poor grade are within the area classified as coastal AE water. The concentration of faecal indicator bacteria at these sites is primarily influenced by faecal indicator bacteria loads in river water (from waterfowl and dogs; PDF) and one area supports an abundance of waterfowl.

Future improvements in nutrient and faecal indicator bacteria concentrations in estuary water can be achieved by improved stormwater quality and reducing the number of industrial point source discharges. It is unlikely that waterfowl or dog numbers will decrease. As this is an urban estuary there will always be human influences on water quality. However, the aim is to minimise the impact on aquatic ecosystems and to allow people to be able to use the estuary for contact recreation without having their health compromised.


Lesley Bolton-Ritchie is a coastal water quality and ecology scientist at the Canterbury Regional Council.

Water quality models – are they good enough for management? Waiology Dec 02

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By Sandy Elliott

Un-muddying the Waters : Waiology : Oct-Dec 2013Water quality models are making their way to a farm or catchment near you – so what are they, and how good are they?

Models are being used in New Zealand to address water quality impacts of land use from national to farm scales. At national scale, the CLUES model was recently linked to a land-use evolution model to predict future changes in water quality in a study for the Parliamentary Commissioner for the Environment (see figure for an example of the predictions). The Freshwater Reforms propose that models be used in community deliberation processes for catchments. Down on the farm, the leaching model OVERSEER is being used under the Waikato Regional Plan Variation No 5 to regulate nutrient emissions in the Lake Taupo catchment.

Predicted nitrogen yield increase from 2008 to 2020.

Predicted nitrogen yield increase from 2008 to 2020.

How do water quality models work?

Most water quality models are built around mass budgeting approaches, whereby the water quality constituents are generated and transformed according to approximate mathematical representation of the processes or rates – an example is the dynamic point-scale crop growth and leaching model APSIM. But others are purely statistical, such as a recent model to estimate median concentrations for every stream reach in New Zealand as a statistical function of catchment characteristics (PDF) – and there are various mixtures of these approaches. New Zealand has a fairly rich array of climate, landuse, hydrometric, and water quality data to drive and calibrate these models. And models of different environments are being linked. For example recent modelling in the Ruataniwha Basin linked OVERSEER, a groundwater model, and a stream periphyton growth model.

How do model errors affect their usefulness?

All models entail errors and uncertainty, which arise from errors in inputs such as rainfall or land use, uncertainty in estimating various coefficients, or inappropriate representation of the processes. And often as we look closer – for example at fine time scale or an individual stream reach in the figure above – the errors get larger. Even at the large scale of a catchment and annual timescales, we can expect a standard error of around 30% for nitrogen loads for CLUES, and larger errors for phosphorus, sediment, and microbial indicators. Uncertainty in OVERSEER has also been discussed, which is particularly relevant when the model is used for regulatory purposes. And using purely statistical models or throwing more and more detail into the model doesn’t solve the problem.

So in a sense all models are wrong: but are they so wrong that they are useless? Here are a few thoughts on this topic:

  1. Over time, water quality models are getting better. For example, the first versions of OVERSEER provided only crude estimates of nitrogen leaching losses, but now the situation has improved considerably. Other models, such as flood models, were once on the fringes but are now relied on for predicting hazards, and this gives hope for water quality modelling.
  2. There are more data available for input to models and for calibration of parameters. For example, the amount of water quality data for calibrating models has exploded, from about 70 sites in 1990 to about 1000 now, and this allows improved calibration of models such as CLUES.
  3. Information technology and number-crunching power continues to increase, making more detailed modelling tractable and advanced uncertainty methods possible.
  4. We are getting more savvy at using models in a relative sense, fusing observations with model predictions. We can use the projected factor change in model predictions for different scenarios to adjust measured concentrations, which reduces errors in predictions of future conditions.
  5. Techniques for establishing and communicating uncertainty are improving. In the climate arena, probabilistic model predictions using a range of models are becoming routine, and knowledge of uncertainty helps decision-makers decide what weight to give the model predictions. We haven’t seen this much in water quality modelling yet, but it is bound to come.
  6. People are starting to take a more mature view of modelling, rather than a completely trusting or disbelieving attitude. This involves a more knowledge about strengths and weaknesses of a models, a bigger knowledge base of applications, smarter ways of driving the models, and better representation and communication of their uncertainty.

Overall, I think water quality models have met the usability threshold, and this will only get better with time.


Dr Sandy Elliott is a catchment modeller at NIWA.

Emerging organic contaminants: A threat to New Zealand freshwaters? Waiology Nov 29

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By Sally Gaw

Un-muddying the Waters : Waiology : Oct-Dec 2013Emerging organic contaminants are a burgeoning and extremely diverse class of contaminants that are not routinely monitored and that have the potential to have adverse ecological and human health effects.

Emerging organic contaminants (EOCs) include both naturally occurring and synthetic chemicals. Many of these contaminants may have been present in the environment for a long time but are only now have they become detectable due to advances in analytical chemistry. EOCs include active ingredients in personal care and domestic cleaning products, pesticides, plasticisers, pharmaceuticals, steroid hormones excreted by humans and animals, surfactants and veterinary medicines. Many EOCs are everyday chemicals in widespread use in consumer products. Much research is being devoted internationally to understanding the sources, environmental fate and adverse effects of EOCs.

Discharges from wastewater treatment plants are a major source of emerging contaminants entering aquatic environments. (P. Emnet)

Discharges from wastewater treatment plants are a major source of emerging contaminants entering aquatic environments. (P. Emnet)

The contaminants can enter surface and groundwater through a range of different pathways. Wastewater discharges are recognised as a major source of EOCs into aquatic ecosystems. In urban areas other potential sources include stormwater, sewer overflows, leachate from landfills and re-use of wastewater for irrigation. Rural sources include runoff from farmland, disposal of animal waste, septic tank effluents and the use of veterinary medicines in aquaculture.

The environmental fate of EOCs tends to be contaminant-specific, depending on the composition of the contaminant and in some cases the concentration and the presence of other contaminants. Potential removal pathways include photodegradation, biodegradation and sorption. Sediments can act as a sink from which EOCs can be later released. Some EOCs can bioaccumulate in aquatic organisms, however the mechanisms of uptake are not well understood. EOCs are not readily removed by conventional wastewater treatment processes as they tend to be water soluble. And while many EOCs degrade quickly in the environment, ongoing discharges into waterbodies can result in environmental concentrations and hence exposure of aquatic organisms remaining relatively constant.

The majority of EOCs are typically present in aquatic ecosystems at parts-per-trillion to parts-per-billion concentrations. Despite these low concentrations, a range of adverse effects have been reported in wildlife including endocrine disruption effects on growth and reproduction, genotoxicity, organ damage, and changes in behaviour. Exposure to environmentally relevant concentrations of ethinylestradiol an active ingredient in contraceptive pills can cause reproductive effects and behavioural changes in fish. Similarly the non-steroidal anti-inflammatory diclofenac can cause kidney damage in fish at concentrations routinely measured in wastewaters in North America and Europe. The presence of antibiotics and anti-microbial compounds can lead to the development of antibiotic resistance in pathogenic bacteria creating serious risks for human health. Exposure to EOCs can also alter the nutrient processing capacity and natural food web structure of aquatic ecosystems. For example the anti-microbial compound triclosan can alter the species diversity of algal communities. In most aquatic ecosystems, EOCs will be present as mixtures alongside other environmental stressors. The combined effects of mixtures of EOCs and the presence of multiple stressors on aquatic organisms are poorly understood. EOCs may be the tipping point for endangered species and aquatic food chains.

There is very limited data available on EOCs in New Zealand. What we do have indicate that EOCs are present in wastewater and environmental matrices at comparable concentrations to those measured internationally. The sensitivity of New Zealand’s unique aquatic fauna to EOCs is unknown. Further data will be needed to understand and reduce the impacts of EOCs on freshwater ecosystems in New Zealand including identification of the key EOCs of concern. Risks specific to New Zealand due to usage patterns or sensitivity of aquatic organisms and receiving environments also need to be identified. This information will underpin future policy and regulatory decision making for EOCs to protect New Zealand’s waterways.


Dr Sally Gaw is a Senior Lecturer in Environmental Chemistry and Director of the Environmental Science Programme at the University of Canterbury.

References:
Corcoran J, Winter, MJ, Tyler CR (2010) Pharmaceuticals in the aquatic environment: A critical review of the evidence for health effects in fish. Critical Reviews in Toxicology. 40:287-304.
Pal A, Gin KY-H, Lin A Y-C, Reinhard M (2012) Impacts of emerging organic contaminants on freshwater resources: Review of recent occurrences, sources, fate and effects. Science of the Total Environment 408: 6062–6069
Rosi-Marshall EJ, Royer TV (2012) Pharmaceutical Compounds and Ecosystem Function: An Emerging Research Challenge for Aquatic Ecologists. Ecosystems. 15: 867-880

Nitrate in Canterbury groundwater Waiology Nov 27

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By Carl Hanson

Un-muddying the Waters : Waiology : Oct-Dec 2013Nitrate concentrations in Canterbury groundwater have been prominent in the media recently. Headlines have included phrases like “ticking time bomb”, “scaremongering” and “freaking out much of Canterbury”.

What I want to do in this article is to present the state of nitrate concentrations in Canterbury groundwater, and the trends we see in those concentrations, as objectively as I can, avoiding any emotive language.

First, the concentrations. Based on the data from our regional long-term monitoring programme, which includes approximately 300 wells distributed across the region, nitrate concentrations in Canterbury groundwater fall into two groups:

  • About 30% of the samples we collect have concentrations less than 1 mg/L (recorded as nitrate nitrogen).
  • The rest of the samples have concentrations distributed over a broader range, with an average of about 5 to 6 mg/L and the highest concentrations exceeding 20 mg/L.

Risk of finding groundwater in Canterbury with nitrate concentrations above the MAV (C. Hanson).

Risk of finding groundwater in Canterbury with nitrate concentrations above the MAV (C. Hanson).

Groundwater with low nitrate concentrations is found in the areas coloured green on the map to the right. This groundwater is derived mainly from alpine rivers, which have low nitrate concentrations themselves. In addition, the groundwater in some areas is anoxic as a result of organic material in the aquifer sediments. We find this particularly along the northern coast of the Canterbury Plains, where the land has historically been covered by swamps. Nitrate is generally not compatible with anoxic environments.

Groundwater with higher concentrations is found in the areas coloured yellow and red on the map in Figure 1. This covers most parts of the region where groundwater is used. The red colouring shows areas where we frequently measure concentrations greater than the New Zealand drinking-water standard (the Maximum Acceptable Value, or MAV, equal to 11.3 mg/L when reported as nitrate nitrogen).

In the yellow areas, concentrations are variable. They change from one location to another, they change with depth, and they change over time. Nitrate concentrations often display a seasonal pattern, with the highest concentrations occurring in the springtime after winter rainfall. Within these yellow-coloured areas, concentrations are generally below the MAV, but they may exceed the MAV in some years and/or at some locations.

There have been some questions in the media as to the source of the nitrate contamination. In my opinion, farming is the main source. Point sources like septic tanks and wastewater discharges contribute discrete, localised plumes of contamination, and in some cases the resulting concentrations are quite high. But we see elevated nitrate concentrations across the entire region. Nitrate contamination is ubiquitous. If you drill a well almost anywhere within the yellow and red areas on the map above, you will find groundwater with nitrate concentrations that are higher than they would be naturally. Contamination of this extent can only be explained by diffuse leaching from the farmland that covers the region. There are no other plausible sources.

Regarding trends, we can say comfortably that nitrate concentrations are increasing. Over the past ten years (2003-2012), we’ve noted increasing trends in about 30% of the wells in our regional-scale long-term monitoring programme. In contrast, we find decreasing trends in only 3% of the wells. Concentrations in the rest of the programme wells rise and fall over time but show no clear long-term trends, either upward or downward.

Trends in nitrate concentrations in Canterbury groundwater, 2003 to 2012 (C. Hanson).

Trends in nitrate concentrations in Canterbury groundwater, 2003 to 2012 (C. Hanson).

The results have been similar since our monitoring programme began in the 1980s. For any time period that we look at, we find that while most of the wells in the survey show no clear trend, the trends that do show up are mostly increasing. The increases are distributed across the region.

Concentrations have probably been increasing since farming began in Canterbury. As more land has been cultivated and farmed, as more fertiliser has been added to increase crop production, and as more stock have been grazed on the paddocks, the nitrogen balance in the soil has increased, and more nitrate has been available to leach into the groundwater.

Finding ways to minimise nitrate leaching from farming is a key part of Environment Canterbury’s work under the Canterbury Water Management Strategy.


Carl Hanson leads the groundwater quality team at Environment Canterbury.

Nuisance periphyton – too much of a good thing Waiology Nov 25

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By John Quinn

Un-muddying the Waters : Waiology : Oct-Dec 2013Periphyton is the name given to the community of algae that grows on river and lake beds, and it has a Dr Jekyll and Mr Hyde reputation.

As thin films and short/sparse filaments – the good Dr Jekyll – it is an important fuel at the base of healthy aquatic food webs, turning nutrients and sunlight into a food for invertebrates, which are in turn food for fish and waterbirds. In the process, they reduce the nutrient levels downstream or in a lake, helping to control eutrophication. Ecologist Maurice Lock once described periphyton as the “light and energy transducer of streams”. When viewed under a microscope, the species are also stunningly beautiful.

Dr Jekyll periphyton - thin films with about 10% cover by filamentous green algae. (J. Quinn)

Dr Jekyll periphyton – thin films with about 10% cover by filamentous green algae. (J. Quinn)

But its Mr Hyde side comes to the fore when periphyton forms abundant blooms that can degrade the looks, smell and taste of waterbodies, clog streambeds, and cause extreme fluctuations in pH and dissolved oxygen that harm sensitive aquatic organisms. When thick periphyton sloughs off the bed it can foul anglers’ lines, clog water intakes and sully the view for drift-feeding fish and humans alike. What’s more, the dark mats dominated by cyanobacteria, like Phormidium, can produce toxins that have been responsible for many dog deaths over the last decade.
Mr Hyde periphyton downstream of a wastewater treatment plant on the same river as the Dr Jekyll site showing almost complete cover of the bed by filamentous algae and mats. (J. Quinn)

Mr Hyde periphyton downstream of a wastewater treatment plant on the same river as the Dr Jekyll site showing almost complete cover of the bed by filamentous algae and mats. (J. Quinn)


It’s not surprising then that periphyton is one of the key river attributes assigned quality bands and bottom lines in the government’s recent National Objectives Framework proposals.

Research in NZ and overseas over the last couple of decades has led to guidelines for the levels of periphyton that separate the Dr Jekyll from Mr Hyde states, as both percentage cover/type and as biomass, in relation to different river values [PDF]. Refining these nuisance levels is an area of on-going research.

So what keeps periphyton in the desirable Dr Jekyll state? That comes down to the balance of growth-stimulating factors – mainly light, nutrients (nitrogen and phosphorus), temperature, steady flows and stable bed attachment sites – and controlling factors –high levels of flow disturbance and grazing by insects.

Conditions in summer are usually most conducive to periphyton blooms – long days and lots of sun; warm water increases algal growth rates and inhibits grazing; and the periods extend between spates (moderate flow spikes) that slough or scour the periphyton. So unfortunately, periphyton often blooms at the very time when people most want to use rivers for recreation and abstraction for irrigation, making them more of a nuisance.

Periphyton cover at National Rivers Water Quality Network sites is correlated with the percentage of pasture land use upstream, likely reflecting high nutrient inputs and light. Other research has shown periphyton increases below some point source wastewater discharges, after logging (unless riparian shade is retained), and in unshaded streams after urbanisation. On the other hand, maintenance and restoration of shade has been shown to reduce periphyton biomass.

So what can we do to manage periphyton in the desirable Dr Jekyll state? The main options are:

  1. Provide shade by enhancing riparian vegetation – this is most effective in small-medium streams with channels narrower than about 6 m, although trees with sprawling growth form can provide patches of heavy shade along rivers with wide channels where the main flow often hugs the banks.
  2. Control nutrient inputs – limiting the inputs of nitrogen and phosphorus so that concentrations are well below the optimal levels for periphyton development reduces biomass and/or the downstream extent of nuisance periphyton below inputs.
  3. Reduce fine sediment input –fines deposited during high flows, or due to insidious inputs, can be a source of phosphorus on the bed right where the periphyton need it. Fine sediment can also reduce grazer abundance by clogging their bed habitat and reducing the food quality of the periphyton.
  4. Manage stressors on grazing invertebrates – keep levels of toxicants like pesticides and ammonium well below stressful levels to maintain grazing rates that crop the periphyton
  5. Maintain scouring flows – avoid alterations to flow regimes that extend the periods for periphyton biomass build-up between spates that scour growths (typically flow increases to more than 3 times normal)
  6. Avoid spreading particular nuisance periphyton types like Didymo that are adapted to exploit low nutrient environments by following the Check/Clean/Dry protocols.

Dr John Quinn is Principal Scientist for Freshwater Ecology at NIWA.

Overcoming obstacles to setting water quality limits Waiology Nov 22

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By Ned Norton and Helen Rouse

Un-muddying the Waters : Waiology : Oct-Dec 2013In the previous Waiology series on Water governance, we referred to the National Policy Statement for Freshwater Management (NPSFM) (2011) requirement to set limits for water quantity and quality. So, how are councils getting on with limit-setting?

In May 2012 we surveyed planners for regional councils to find out how their current regional plans measure up against the NPSFM requirements to set limits, and found that 1 of 14 respondents said their current plan meets NPSFM requirements, 8 of 14 said their plan met requirements to some extent, and 5 of 14 said their plan did not meet NPSFM requirements.

Our survey also identified a number of potential obstacles that make limit-setting difficult. Some of the most common obstacles were costs (time,staff), availability of catchment-specific data, understanding existing/baseline conditions, balancing instream and out-of-stream values, lack of support for plan process (political or council staff), lack of clear process for getting parties together/getting agreement, and lack of understanding of (and difficulty communicating) complex issues and value trade-offs.

Solutions to these obstacles can be grouped into regulatory, non-regulatory and ‘other’ categories. Examples include national policy instruments, guidance documents, and improved information flow amongst researchers, practitioners, and communities. Suggestions made by the Land and Water Forum are being acted on by central government in the Freshwater reforms 2013 and beyond workstream, which will address to some extent the obstacles that can be solved with regulatory tools and guidelines. Sharing good practice and effectively communicating science are other avenues that many players can assist with. How these can be achieved is an important focus for our research.

A key challenge in setting limits for water quality associated with diffuse-source contaminants lies in being transparent about the links between desired outcomes (environmental, social, cultural, economic), the concentration of a contaminant in a waterbody (e.g. nitrogen, N), the associated total contaminant load limit (e.g. tonnes N/yr), and the allocation of the load limit amongst dischargers at a property level (e.g. kg N/ha/yr). Such transparency demonstrates that choices about outcomes come with consequences for limits and allocation, and vice versa. A related challenge lies in making the difficult decisions around the level to which multiple conflicting outcomes will be met, thus establishing what limits will be set. To see how councils are faring now with limit-setting generally and with this challenge in particular, we have been looking at some case studies to examine current progress.

For example, in Canterbury the Canterbury Water Management Strategy is driving a collaborative approach to limit-setting, which is now an option encouraged under the central government freshwater reforms. Community-based Zone Committees consider scenarios for water quantity and quality limits, explore the consequences of these scenarios with community involvement, and then decide on a ‘solution package’ containing a mix of limits and other regulatory and non-regulatory on-the-ground solutions that best meet the Committee’s suite of goals. Experience to date has shown, at least in heavily utilised catchments, that such decisions require iteration as the difficulty of achieving aspirational outcomes (environmental and economic) becomes clearer during the process. These processes have tended to arrive at solutions that acknowledge the need for significant time to attain all desired outcomes.

The collaborative, zone-based approach has been used to date in the Hurunui-Waiau, Selwyn Waihora, Hinds Plains, and South Canterbury Coastal Streams zones, and continues to evolve and improve as lessons are learned by all. The approach has required creative use of science tools (including models) and careful attention to communication techniques. It has also become critical to define Good Management Practice (GMP) in terms of on-the-ground practices that can be related to N losses in kg/ha/yr. Significant collaborative progress has been made by a Primary Sector group, Ngai Tahu and ECan, leading to an agreed limits framework for the Selwyn Waihora zone (see Irrigation New Zealand article). All the primary sector bodies have also committed to a multi-agency project that will define agreed GMP in kg/ha/yr across all landuse, soil and climate types in Canterbury by 2015.

These Canterbury case studies have all had their ups and downs, but there are undeniably positive signs of progress towards setting durable water quality limits via collaborative processes, compared to more adversarial and pessimistic times just a few years ago.


Ned Norton is a water resource management consultant working part time for NIWA and part time assisting Environment Canterbury. Dr Helen Rouse is a resource management scientist at NIWA.

The topics discussed above are part of our research under the Management of Cumulative Effects of Stressors on Aquatic Ecosystems project, funded by the Ministry of Business Innovation and Employment.

Science and policy merge in water plan Waiology Nov 20

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By Paul Reynolds

Un-muddying the Waters : Waiology : Oct-Dec 2013Recently the government released proposals for a national framework for setting freshwater objectives, including bottom lines for ecosystem and human health (for secondary contact). It has had an unusual reaction.

For the first time in my memory, we have had stakeholders from all quarters pretty much in strenuous non-disagreement with one another – in support of the proposal. That is not a common occurrence in the policy world. In particular, it is not common in environmental policy, where complex ‘wicked’ problems predominate and people often have trouble agreeing on the problem – let alone contributing constructively to the solution.

Developing the National Objectives Framework has been a challenge. It was first suggested by the independent group of water users who make up the Land and Water Forum. The government then took it up as a tool to support regional councils with the 2011 National Policy Statement for Freshwater management’s requirements to maintain or improve the overall water quality in their region, and safeguard freshwater’s life supporting capacity. Officials in the cross-agency Water Reform Directorate have worked with a raft of people and organisations from many differing perspectives and disciplines to come up with this first iteration.

Well over two decades ago, philosopher Jerome Ravetz suggested that policy makers should respond intelligently to the imperfections of science in forming policy decisions, but in a way that makes sensible use of the available science in the context of other information. His argument was not to delay or procrastinate on decision-making (often by calling for new or more research), but to have better policy processes with wider engagement, procedures of self-criticism, and quality control.

This is the approach we have taken with the framework. We acknowledge that we do not have perfect information. But this should not stop us from taking action. We especially recognise that policy makers alone cannot solve the challenges that we face. In this instance, the role of the science community has been pivotal.

To develop the framework from just a concept into a practical tool, the government brought together more than 60 experts from New Zealand’s freshwater science community to tell us – from a scientific viewpoint – what defines water quality in our rivers, lakes and aquifers. Estuaries, as many have noted, are not yet included. Neither, for that matter, are several attributes that we all recognise are important indicators of freshwater health, such as macroinvertebrate communities or sediment load. For those, I refer you back to Jerome Ravetz, with the commitment that should Ministers give the framework the go-ahead, work will continue on the science we need to understand further attributes for populating future versions of the framework.

We engaged scientists early in the process of developing the framework to gain consensus on the scientific evidence. The reasons for this are two-fold. The first is to give regional councils and their communities a tool that will help them have the difficult conversations around what they want for their water bodies. This is essentially a value judgement – and competing interests and values for our water is where the conflict usually lies. But good – which means achievable, affordable and lasting – decisions need to be underpinned by an understanding of both the scientific and economic implications that ultimately create the costs to communities.

Secondly, a robust national framework where the science has been settled is an attractive alternative to dragged-out case-by-case disputes in the Environment Court where the focus is the ‘accuracy’ of the science. We want to get agreed science out to our communities, so a collaborative and constructive conversation can occur about the values they hold for their water bodies.

Science of course, is not about what is ‘right’ or ‘wrong’ – it is about the weight of evidence. What we think we know now may change as evidence improves, and as our behaviour changes or adapts. Balancing the need to get the science as settled as possible, and the need to introduce more support for councils to successfully implement the NPS-FM, we decided to take a step-by-step approach to populating the framework. That’s why this version is simply the first cab off the rank. It is the start of the journey, not the end.


Dr Paul Reynolds is the Secretary for the Environment, Ministry for the Environment.

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