Water Quality

What is water quality?

Water quality refers to the physical, chemical, and ecological characteristics of water.

It is a measure of the condition of water relative to the requirements of one or more living species (animals, plants, fungi, and bacteria). The most common standards used to assess water quality relate to the health of ecosystems, the safety of human contact, and the use for drinking water.

Regional Councils around New Zealand measure the water quality of our rivers, lakes, and streams to get an idea about whether the water is suitable for a range of uses, as well as the effect of different land use pressures (i.e., urbanisation, farming, forestry, etc.) on the condition of our freshwater resources.

What controls water quality?

There are two main factors controlling water quality outcomes – the landscape and us. Water quality varies widely between regions around New Zealand, even where there are similar land uses and pressures. This is because the natural landscape can have a much bigger influence on water quality outcomes than land use on its own. By understanding the functions that the landscape is performing to minimise the pressures of land use, we can match our land use decisions to what is most suited to the land.

How do we protect water quality?

The quality of our rivers, streams, wetlands, and estuaries is closely linked to land use decisions made on both a public and a private scale. Many of the land areas are privately owned and you, as someone using the land, can make a significant contribution to protecting waterways through well informed management practices.

Protecting water quality is not only healthy for the environment, it is can also lead to social and economic benefits. By understanding the concept of Physiographic Environments you, the farmer, can identify the issues surrounding your land and contribute significantly to the protection of your waterways from many of the issues which may currently be present. With the cooperation of other neighbouring farmers, planning on a catchment scale will provide a framework to restore impaired waterways and protect water quality in healthy streams.

Everyone is part of the problem. Everyone needs to be part of the solution.

What are the main environmental contaminants affecting water quality?

There are four contaminants identified under the New Zealand Government’s National Policy Statement for Freshwater Management for reduction to improve water quality in New Zealand. In the wrong place or at high concentrations, nutrients such as nitrogen and phosphorus, sediment, and microbes can become environmental contaminants.

Excessive nutrients can change the balance of nutrient cycling within a lake or river and can result in excessive algae or plant growth, depleted oxygen levels, fish deaths, and reduced recreational use of water resources. Sediment can also cause problems smothering aquatic habitats and transporting sediment-bound nutrients (particularly phosphorus), ammonium, and microbes. Microbial contaminants (such as E. coli) from animal waste can make water unsafe for drinking or recreational contact.

By understanding how these contaminants get into waterways we can develop solutions to minimise their loss from the land.

What are nutrients?

Nutrients are chemicals needed by plants and animals for growth, especially nitrogen and phosphorus. We typically add them to land as fertilizer to improve plant growth or they are returned to the land through animal excrement.

Nitrogen (N) and phosphorus (P) in the environment typically occur as dissolved ionic forms or bound to dissolved or particulate organic molecules. The dissolved ionic forms are most biologically available and readily assimilated by stream plants. Nutrient concentrations are normally low in pristine waterways and higher in waterways that are impacted by human activities (for example fertilizer leachate/runoff, wastewater, and effluent discharges).

What is nitrogen?

Nitrogen (chemical symbol N) is both the most abundant element in the atmosphere and, as a building block of proteins and nucleic acids such as DNA, a crucially important component of all biological life. It has three main forms in the environment: molecular, organic, and inorganic. Nitrogen in the environment is cycled from one form to another depending upon the environmental and biological conditions.

In its molecular form, nitrogen is a gas (N2) and makes up about 80% of the Earth's atmosphere.

Organic nitrogen refers to the diverse array of nitrogen-containing organic molecules, ranging from simple amino acids, proteins and nucleic acids, to large and complex molecules, such as humic substances (or plant material) in soil and water.

The main forms of inorganic nitrogen that occur are:

  • Nitrate (NO3-) is the preferred form of nitrogen nutrition for most species of plants. Nitrate is highly soluble and is easily transported through the soil if not used by plants and microorganisms. Sources of nitrate include inorganic fertilizer, animal wastes including farm dairy effluent, septic tanks and sewage systems. Nitrate also occurs as a result of nitrification of the ammonia in animal waste by bacteria in the soil. It is toxic at high concentrations. The majority of nitrate is released through microbial mineralisation processes irrespective of the form of input.
  • Nitrite (NO2-) is formed during the process of nitrification but its concentration is often low compared to other forms of inorganic nitrogen.
  • Ammoniacal nitrogen (NH4+ / NH3(g)) is represented by ammonia (NH3) and ammonium (NH4+). Which form dominates in water is dependent on pH, with ammonia concentrations increasing as pH increases. In most natural waters with pH values less than 7.5, ammonium is the dominant form. Ammonium is less mobile than nitrate as it is strongly attracted to negatively charged clay minerals. Where it occurs, ammonia is highly toxic to fish and other aquatic organisms.
The nitrogen cycle is a complex biogeochemical cycle in which nitrogen is converted from its inert atmospheric molecular form (N2) into a form that is useful in biological processes. This figure shows the reservoirs of where nitrogen is stored in red, the actors that use it (i.e., us, animals, microorganisms), the processes that nitrogen undergoes (yellow) and the forms of nitrogen in the environment (white).

In a farm system, the primary inputs of nitrogen to the soil are effluent from livestock, plant materials, and fertiliser (although there will also be atmospheric depositions as well). Fertiliser and urine inputs are generally in the form of urea ((NH2)2CO), which is quite rapidly converted to ammonium and ammonia (collectively they are known as ammoniacal nitrogen). Regardless of the source of nitrogen, the processes in the nitrogen cycle always apply.

The two main forms of inorganic nitrogen in the soil are ammonium (NH4+) and nitrate (NO3-). Ammonium and ammonia co-exist, with the proportion of each dependent on pH, soil temperature, and moisture. Ammonia may be lost to the atmosphere in response to volatilisation. In addition to fertiliser and urine, ammoniacal nitrogen is released during the breakdown of organic matter (which can be dung or dead plant material). In response to breakdown, mineralised nitrogen may be sequestered or released by the microbial biomass into solution. The conversion from ammonium to nitrate (nitrification) is a biologically mediated process involving microorganisms that is also influenced by soil pH, moisture, and temperature.

Ammonium and nitrate are both available for plant uptake, but there are important differences in their characteristics. Nitrate is highly mobile in soil due to its negligible adsorption characteristics, but ammonium is generally much less mobile because it tends to adsorb to the soil particles, particularly in soils with a high clay content. Nitrate is subject to denitrification, which is the gaseous loss of nitrogen as both nitrogen gas (N2) and nitrous oxide (N2O, a harmful greenhouse gas). If nitrate is not denitrified to gaseous forms, it can be lost to water through leaching. Ammonium is also lost to the atmosphere by volatilisation through the emission of ammonia gas (NH3) (This is the smell we associate with urine). Both denitrification and volatilisation processes respond to short-term daily climate and soil factors and can be highly episodic.

In most mineral or non-wetland soil types, the dominant form of nitrogen below the root zone is nitrate nitrogen, with a potentially important contribution from small dissolved organic nitrogen forms. Other forms of nitrogen, particulate organic N, larger dissolved organic forms, and ammonium seldom percolate to these depths due to physical exclusion (filtering), they are held by the soil or plant roots, and other biogeochemical processes. These forms of nitrogen tend to accumulate at or near the soil surface and can be more easily transported with runoff.

For artificially drained soils (mole-pipe drainage type), the potential range of nitrogen forms transported during drainage will vary according to the soil's carbon content, soil water residence time, and the effectiveness of the drainage system.

What forms of nitrogen are ecologically important?

The organic and inorganic forms of nitrogen are the forms that are ecologically important. It is these compounds that are added as nutrients (i.e., fertilisers) to enhance plant growth. However, as they are highly soluble, they can easily become environmental contaminants in the wrong location such as in rivers, lakes, and groundwater. In surface water, this can cause nuisance aquatic weeds and algae to flourish. Nitrite and ammonia become toxic at high concentrations.

How do I know what form of nitrogen is being lost from the land?

In areas dominated by mineral soils, the dominant form of nitrogen is nitrate. Areas of highest inherent nitrate risk are often associated with well drained soils and shallow alluvial aquifers that occur across a catchment. The lowest nitrate risk areas are associated with areas of organic or peat soils. Organic and ammoniacal (TKN) nitrogen is often a minor component of total nitrogen in areas of mineral soils. However, it can be significant during periods of heavy rainfall. Runoff events may supply significant increases of organic and ammoniacal nitrogen to a stream network.

How is nitrogen measured in water?

When a water sample is analysed for nitrogen, different techniques are applied to isolate the various forms. Nitrogen is typically analysed and reported as follows:
NNN Nitrate-Nitrite Nitrogen Nitrate + Nitrite
TKN Total Kjeldahl Nitrogen Total Organic Nitrogen + Total Ammoniacal (NH3 + NH4+)
DIN Dissolved Inorganic Nitrogen Nitrate-Nitrite Nitrogen + Total Ammoniacal (NH3 + NH4+)
TN Total Nitrogen TKN + NNN

The forms of nitrogen in water (organic and inorganic) and how it is measured (yellow boxes).

What is phosphorus?

Phosphorus (chemical symbol P) is an essential nutrient for life. Phosphorus is predominantly found as phosphate-based compounds (solid form) and is cycled through the lithosphere (the rigid outer surface of the earth), hydrosphere (all the water on the earth’s surface), and biosphere (the regions of the surface and atmosphere of the earth occupied by living organisms). In the environment, the weathering of rocks and minerals releases phosphorus in a soluble form where it is taken up by plants, and subsequently transformed into organic compounds. Unlike with nitrogen, the atmosphere does not play a significant role in the cycling of phosphorus. Organic phosphate is phosphorus that has been incorporated into plant or animal tissue (e.g., seeds, leaves). In soil, phosphate is absorbed by iron oxides, aluminium hydroxides, clay surfaces, and organic matter particles, and becomes incorporated in the soil particle. In natural waters, phosphorus typically occurs in both inorganic and organic forms. 

The phosphorus cycle is a slow process which involves the key steps of weathering and erosion, absorption by plants and animals, and return to the environment via decomposition and sedimentation. This figure shows the reservoirs of where phosphorus is stored in red, the actors that use it (i.e., us, animals, microorganisms), and the processes that phosphorus undergoes in the environment (yellow).

Why is too much phosphorus an issue?

Humans have had a significant impact on the phosphorus cycle due to a variety of human activities, specifically the use of fertiliser, the distribution of food products, and artificial eutrophication. P fertilisers increase the phosphorus levels in the soil and are particularly detrimental when lost into local aquatic ecosystems. When phosphorus is added to water at a rate typically achieved by natural processes, it is referred to as natural eutrophication. A natural supply of phosphorus over time provides nutrients to the water and serves to increase the productivity of the ecosystem. However, when levels of phosphorus are too high, the overabundance of plant nutrients enables the excessive growth of algae. A rapid increase in the population of algae in an aquatic ecosystem forms an algal bloom. Blooms can reduce the amount of light and oxygen available to other aquatic life. Some types of algae may be toxic if ingested or can be an irritant to skin and eyes.

In rivers, potentially toxic benthic algae generally form brown or black mats that grow on rocks in the riverbed. Benthic algae differ from harmless bright green algae, which often form long filaments.
Image credit: www.lawa.org.nz

How is phosphorus measured in water?

When a water sample is analysed for phosphorus, different techniques are applied to isolate the various forms. Phosphorus is typically analysed and reported as:

  • Dissolved Reactive Phosphorus (DRP)
  • Particulate Phosphorus (PP)
  • Total Phosphorus (TP)

The forms of phosphorus in water (organic and inorganic) and how it is measured (yellow boxes).

What is sediment?

Sediment is the loose sand, silt, clay, and other organic particles that are suspended in a waterway or settled on the bottom. Sediment can come from soil erosion or from the decaying (decomposition) of plants and animals. Water, wind, and ice help carry these particles to rivers, streams, lakes and aquifers. The heavier the rainfall the more likely sediment can be transported. Sediment is a natural part of a stream, lake, or river, and the type and amount found in waterways is influenced by the geology of the surrounding area. Natural processes that contribute sediment in waterways include instream scouring of the riverbed and banks, and erosion of sediment from the surrounding catchment from natural slips and any exposed soils. Sediment can enter streams from alongside a reach or from upstream via the many smaller interconnecting streams that form a river network within a catchment area. Soil type in the catchment can also affect the amount of suspended sediment. For example, streams in catchments with clay soils are likely to have naturally poorer water clarity than streams in sandy catchments. In slow-flowing lowland streams where sediment can be very fine, water clarity can be poor for long periods. This is due to the slow rate of flushing and the fact that very fine particles are held in suspension almost indefinitely. While sediment movement is a natural part of a functioning freshwater ecosystem, human activities around a waterway (such as dam or road construction or land use change from native forest to pasture) can greatly increase the amount of sediment that enters the system. This can have considerable effects on water quality and the plants and animals that live there. The addition of sediment to rivers and streams above normal levels is a serious issue across many parts of New Zealand.

Waikato River (centre) converging with the Waipā River (right) at Ngāruawāhia after flooding and heavy rainfall in 1998. The Waikato River catchment has a volcanic geology compared to the weaker sedimentary sand and mudstones of the Waipa River catchment which contributes a much higher sediment load.
Image credit: John Greenwood, J. Greenwood Photography
The Waipā River (left) joining the Waikato River (right) at Ngāruawāhia under normal flow conditions.

Why is sediment a problem?

High sediment concentrations in rivers degrades ecosystem health by smothering organisms and their habitat and reducing water clarity and light penetration. While elevated suspended sediment has the greatest effect during flood events, the accumulation of sediment in the stream bed can also result in reduced clarity and elevated turbidity under low flow conditions.

What land activities increase sediment loss?

Any activity that leaves bare soil exposed, such as cultivation (ploughing, fertilising, and drilling) and vegetation clearance can increase the amount of sediment that enters nearby waterways. Waterways near agricultural and horticultural land are especially vulnerable when there is little riparian vegetation to act as a buffer for increased runoff from the land. Sediments can carry nutrients and chemical contaminants that may be washed into waterways, especially after heavy rain.

What is water clarity and when is it a problem?

Water clarity refers to the ability of light to travel through water and has two important aspects, light penetration and visual clarity. Light penetration is important as it controls the amount of light in the water needed for aquatic plants to grow. Visual clarity indicates how much suspended sediment is in the water. Poor water clarity can have many adverse effects on stream and lake ecosystems. For example, murky water can make the water unsuitable for drinking by stock and make areas unsafe for swimming. High sediment can also harm aquatic life by clogging their gills which reduces their ability to take up oxygen. As fine particles settle in slower-moving downstream areas, the spaces between rocks and gravel are filled making the bottom habitat unsuitable for fish and other aquatic species.  Poor water clarity will also affect the amount of light reaching the river bottom, potentially limiting plant growth.

How is sediment measured in water?

When a water sample is analysed for suspended sediment, different techniques are applied to isolate the various forms, inorganic (mineral) and volatile (organic matter). Sediment in a water sample is typically analysed and reported as:

  • Total Suspended Sediment (TSS) = Inorganic + Volatile Forms (both < 0.2 mm in diameter).
  • Volatile Suspended Sediment (VSS)

Other measures, such as absorbance, clarity, and turbidity are measures of the optical properties of water that may be influenced by both dissolved and solid constituents. Dissolved organic carbon which comes from the breakdown of plant material in soils, also affects light penetration in water. The greater the reduction of light by suspended sediment and dissolved organic carbon, the lower the water clarity. Turbidity is influenced by the presence of ‘dissolved’ colloids that are smaller than the 2 microns used to define total suspended sediment. Therefore, the relationship between total and volatile suspended sediments, turbidity and clarity is not always simple.

What is microbial contamination?

Microbial pollution in aquatic environments is one of the crucial issues with regard to the sanitary state of water bodies used for drinking water supply, recreational activities, and harvesting of food due to a potential contamination by pathogenic bacteria, protozoa or viruses which make us sick.

How is microbial contamination measured?

Microbial contamination is monitored using indicator species that are present in the faeces of warm-blooded mammals and birds. In freshwater, the indicator species is Escherichia coli (E. coli) and is measured as a count under a microscope as Colony Forming Units per 100ml. E. coli is used as an indicator species for the presence of more harmful bacteria due to its comparative ease to detect and quantify. High concentrations of this bacteria exceeding water quality guidelines indicate faecal contamination which can be harmful to human health. Too much E. coli means that the water is unsafe to drink or swim in and can cause gastroenteritis, or infections of ears, eyes, nasal cavity, skin, and the upper respiratory tract. Water is only considered safe for drinking if there are very low concentrations of E. coli present.

Where do microbes come from?

Common sources of E. coli bacteria are animal waste, stormwater run-off, and untreated human wastewater discharges.  E. coli survives outside the body and can survive for up to six weeks in fresh water making it a useful indicator of faecal presence and therefore of disease-causing organisms in a river or lake.  Faecal concentrations are typically higher in pastoral streams, but even near-pristine streams are not totally free from E. coli because of faecal deposits by birds and wild animals. Sediment and microbes are deposited on and eroded from the soil surface and are, therefore, transported predominantly by surficial runoff (overland flow). However, artificial drainage can also act as a conduit for sediment and microbes to surface water bodies.