Waterwatch Australia national technical manual

Module 1 - background
Waterwatch Australia Steering Committee
Environment Australia, June 2003
ISBN 0 6425 4856 0

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Compiling your waterway profile (continued)

Getting to know your catchment

A water catchment is an area or basin of land bounded by ridges, hills or mountains from which all surface run-off water drains to a river, stream, lake, wetland or estuary.

What happens in a catchment?

When it rains, water drains to the lowest point on the land, forming small creeks that feed into larger streams and rivers as they run downhill. In this way water can drain into a river from an area that is often many square kilometres in area. Natural features, such as ridges, hills or mountains form the boundaries of a catchment. From these high points, all water flows down to the lowest point (like water in a bathtub flowing to the plug hole). In the case of a natural catchment, the low point could be a wetland, lake, junction with a river, or river mouth where it enters the sea.

Catchments vary in size and makeup. Large ones are bordered by mountain ranges and include hundreds of small sub-catchments. Each sub-catchment may itself be bordered by low hills and ridges and drained by smaller creeks or gullies. What happens in all of these smaller catchments and streams will affect the wellbeing of the main river. So, water quality at one spot along the river will be influenced by what has happened upstream and will itself affect water quality downstream.

Advantages of using the catchment idea

We all live in catchments. Catchments are ideal units to work with when looking at land use and management issues because many things are linked by water, and what happens in one part of a catchment is likely to affect other parts. For example, a soil erosion problem on a farm near the top of a catchment may contribute to silting of creeks and rivers lower down. Monitoring the water will reveal a composite picture of all the environmental processes taking place in the catchment.

Another advantage in using the catchment idea is that we can select an area (sub-catchment, catchment or region) of a size that suits the issues and interests of each group. If the issue faced by the community is a major one, such as diffuse pollution along a large river, land use in a catchment covering thousands of square kilometres may need to be examined by a coalition of Waterwatch groups.

On the other hand, if a small group wants to do something about a local problem, it may be best to work within a smaller sub-catchment area. For example, a school may be interested in a sub-catchment that covers the school grounds to help explain the principles of ecosystems. A farmer may be interested in revegetating the stream banks and monitoring the improving condition of the water leaving their property in a small sub-catchment. Efforts at the sub-catchment scale contribute to improving the larger catchment area.

Where does water go?

To understand how waterways get polluted, we have to understand how water moves through the environment. This is called the water cycle (see Figure 1.2).

Figure 1.2: The water cycle
Figure 1.2: The water cycle

Rivers and streams receive water in four ways:

The water cycle is completed by evaporation from water bodies and evapo-transpiration from plants, and condensation and rainfall.

Does it matter which pathway water follows to the stream?

Yes it does! Water which falls from the clouds is usually fairly pure but the water quality of run-off and baseflow can be very different.

The baseflow, which comes from groundwater, is full of dissolved minerals, and is described as being 'hard'. Soap will not easily lather in hard water. Turbidity, suspended solids and nutrient levels are normally low. However, materials that have been trapped or stored underground can leach out into the groundwater that makes up the baseflow. These could be either natural, such as iron from iron-rich sediments, or man-made, such as petroleum products from leaking underground tanks.

Run-off water picks up few dissolved minerals during flow over the soil and is often described as 'soft'. However, run-off can pick up a variety of contaminants while flowing across the ground surface. These include leaves, animal waste, detergent, fertiliser and soil, which make the water turbid and increases nutrient levels. In addition, run-off over pavement in urban areas will pick up oil, various chemicals and litter.

In floods the proportion of run-off water in the stream increases and the quality of water may worsen. It is very helpful to know how the flow (volume per time) of your stream has changed in order to interpret your water quality data (see Figure 1.3).

Figure 1.3: Increase in stream flow after rain at 0 hours
Figure 1.3: Increase in stream flow after rain at 0 hours

Whether or not water from rain falling in your catchment flows across the surface or soaks into the soil depends on many factors including slope, amount of rainfall and most importantly, ground cover. During heavy rain or storms, run-off water rapidly increases the level and flow of rivers. In some streams, flow may increase quickly because of hard man-made surfaces such as roads, footpaths and parking areas. Clearing of land to make way for cities and towns or for farming increases run-off into waterways (see Figure 1.4).

Figure 1.4: Effect of cities on the pathway of water from rain to rivers
Figure 1.4: Effect of cities on the pathway of water from rain to rivers

In some catchments, stream flow may take a long time to respond to rainfall. In forested country, run-off is slowed by vegetation and water soaks into the ground. In relatively flat country, water also infiltrates the ground. Eventually however, all rain will make its way through the catchment and become stream flow. Baseflow maintains the low flow in waterways in the dry season long after there has been rain in the catchment. In these areas, stream flow will rise slowly, but also fall slowly.

Knowing the pattern of stream flow in a catchment is important in interpreting water quality data, because run-off and baseflow come from different sources with different levels of water quality.

How does water quality naturally change along a stream?

Some characteristics of a stream, such as water temperature, flow rate, water depth, stream bed and food sources, will naturally change as it flows from headwaters to a lake, wetland or the sea (see Table 1.2).

Table 1.2: Typical changes in physical characteristics, food production and macro-invertebrates of a river from the upper to lower catchment
 
Upper catchment
Middle catchment
Lower catchment
Physical characteristics
Altitude High Decreasing Low
Slope Steep Generally decreases Flat
Velocity Fast Generally decreases Slow
Depth Shallow Deeper Deepest
Width Narrow Generally increases Wide
Bottom Rocky stream-bed All types Gravel, sand, silt or mud
Turbidity Clear water Generally increases More turbid
Percentage shading High Generally decreases Low
Temperature Cold Increasing Warmer, possible stratification (layering)
Dissolved oxygen High Generally decreases Lower
Nutrients Low Generally increases Higher
Food production
Plant growth Minor Attached algae and large rooted plants Free floating algae and large plants at margins of river
Food source for macro-invertebrates Mainly coarse pieces of streamside vegetation (dead leaves) Increasing proportion of fine particles Mainly fine particles
Macro-invertebrates
Feeding types Shredders and collectors dominate Grazers and collectors dominate Filtering collectors dominate
Body shapes Adapted to fast moving water e.g. streamlined body shape Wide variety of body shapes Adapted to slow moving water e.g. burrowers
Abundance Low Generally higher Generally lower
Diversity Low Generally higher Generally lower
 

Before interpreting your monitoring results, it is helpful to know what natural changes take place along the watercourse. Once you have listed these natural changes, you can then better identify human-caused changes to the stream.

Upper catchment

In the upper areas of the catchment, such as in mountain regions or foothills, streams are often fast-flowing. This means the stream has the energy to erode its bed and bank, and carry large amounts of rock and gravel downstream.

Vegetation has a greater influence on both the ecology and physical environment of small streams in the upper catchment than in larger streams. Headwaters in forested areas are often shaded from the sun's warming rays by overhanging tree branches. These streams are often fed by groundwater that seeps to the surface at a constant cool temperature. This stream environment shows only small daily or seasonal changes in water temperature. Aquatic insects adapted for cooler water may be found here, for example the stonefly larva.

Headwater streams in non-forested areas, or streams fed largely by run-off from the land, tend to show greater changes in water temperature both during the day and from season to season. Here, sunlight and air temperature have a greater impact on water temperature.

The type of stream bottom or substrate - boulders, cobbles, gravel, sand or silt - is determined in part by the speed of the current and by bedrock. Boulders, cobbles and bedrock are characteristic of fast-flowing streams and offer many living places for aquatic macro-invertebrates.

The headwaters of a river system are very important to the health of the entire river. Overhanging vegetation in forested areas provides much of the food required by stream organisms in the form of leaves, fruits, seeds, twigs and bark. Some of this material is fine, but most is coarse. Some macro-invertebrates collect this material, while others shred it. Both collector and shredder macro-invertebrates are common in forested streams.

In headwater streams that are not shaded by stream-bank vegetation, attached algae and rooted aquatic plants produce most of the available food.

Middle catchment

In the middle part of the catchment, the land is generally flatter and the stream flows more slowly. Usually there is a combination of erosion on the outside edge of bends (meanders) where the water flow is more rapid, and setting of sediment (deposition) on the inside of bends where the water flow is slower. During large floods, water spills out over banks onto the flood plain and deposits a layer of sediment.

Often, in these middle reaches, the stream bank and its trees no longer shade all of the water surface. Here the sun is able to warm the water through the day, particularly where the current slows to form pools. Water temperature tends to drop at night as the accumulated heat is given off to the cold air. Daily and seasonal changes in water temperature tend to be greatest here.

Attached algae become more abundant and grazer (plant eating) and collector macro-invertebrates dominate this section of the stream. Organisms like mayfly nymphs shear off pieces of algae growing on rocks. Collectors feed upon fine material (shredder faeces and small plant fragments) transported from upstream and from local vegetation.

Lower catchment

As the river widens and gathers more flow, it often becomes deeper and more turbid. Close to the sea or a large lake, it travels very slowly and deposits the large quantities of sediment it has been carrying from further upstream.

Here, vegetation has little effect on the physical shape of the channel. Aquatic plants with roots may grow in the turbid water along the shoreline and algae may grow in the shallows attached to stones or other objects. Collector macro-invertebrates are common in this stretch of the stream, filtering out minute food particles suspended in the water and gathering fine particles that have settled to the river bottom.

Dissolved oxygen levels are often reduced in the lower catchment. In slow moving areas the stream bottom becomes silty from a continuous supply of fine sediment from upstream. There is less mixing between the water and atmospheric oxygen with the result that oxygen levels are not replenished quickly in sediments. The breakdown of organic matter by bacteria further decreases dissolved oxygen levels in sediments. Organisms that tolerate lower oxygen levels are more common in this section of the river.

How does water flow affect water quality?

Flow rate affects water temperature, dissolved oxygen, turbidity and pollution levels.

Stream flow is altered by weirs and dams. These man-made obstructions reduce the flow of water downstream and even out the natural high and low flows to which many ecosystems, especially wetlands, have adapted.

Low stream flows

Under low-flow conditions (baseflow) water entering the watercourse is largely groundwater from sub-surface seepage. The visible presence of orange iron stains may be evidence of this. During low flows the waterway can become semi-stagnant resulting in:

Moderate stream flows

The best water quality usually occurs under moderate flow conditions where there is sufficient flow to ensure:

High stream flows

During and immediately after heavy rainfall, water flows over the surface of the ground, picking up pollutants, which results in:

Estuaries

Tidal movements almost totally dominate flow patterns in estuaries. Except in times of flooding, water in estuaries moves in and out with the tide. This affects:

It is usual practice to test water quality on an ebb tide (outgoing).

How does pollution affect streams?

Water in a stream is always moving and mixing. Pollutants that enter the stream travel some distance before they become well mixed. At the discharge site and immediately downstream, water quality might be very poor but stream water quality may recover as pollutants are diluted with more water. Unfortunately, most streams are often affected by more than one source of pollution.

Point source and diffuse pollution

Pollution is broadly divided into two kinds depending on the source. Point source pollution comes from a clearly identifiable source, such as a pipe, which discharges material directly into the waterway. Typical sources of such pollution include factories, wastewater treatment plants, and illegal pipes direct from homes and boats.

The source of diffuse pollution (non point source) is more difficult to identify because it originates over a broad area from a variety of causes. Examples include:

Solving point source and diffuse pollution problems

If the problem is caused by a point source, such as a pipe discharge into a lake, it can easily be identified and tested. Permits for discharging directly into waterways are required by law. If monitoring indicates a problem, a government agency can be asked to take action. These kinds of problems can be solved with engineering solutions.

If the cause is diffuse pollution it is more difficult to solve, where identifying the sources is a challenge. Because diffuse pollution originates over a large area, it is necessary to monitor many sites to actually find the main source or sources of the problem. Surveying land use, stream hydrology and riparian vegetation can help determine the causes. Fixing diffuse pollution will require you to work with many different land managers.

What are wetlands?

Wetlands are areas featuring permanent or temporary shallow open water. They include billabongs, marshes, swamps, lakes, mud flats and mangrove forests. A wetland is virtually any land which is regularly or occasionally covered with water that is still or flowing, fresh, brackish, or saline, including areas of sea water which does not exceed a depth of six metres at low tide.

Wetlands usually occur next to creeks and rivers, near the coast and even in arid desert areas. They can range in size from a small swamp to a vast shallow lake.

There are many types of wetlands. Wetlands that contain water all year round are called permanent wetlands and those that only fill seasonally are called temporary wetlands. Another type, ephemeral wetlands, only occasionally contain water after heavy rains or during floods. This may occur very infrequently, perhaps once every ten or more years.

The quality of water in wetlands will vary depending on the location. The salinity (how salty or fresh the water is) determines the type of plants and animals present.

Some wetlands are valued landscapes because of their scenic beauty and popularity as recreational sites. However, their attractive appearance can sometimes lead to problems through overuse, for example, trampling, noise, pollution, bank erosion, and over-fishing.

Why are wetlands important?

Wetlands are among the world's most diverse and productive environments providing essential habitats for many species of plants and animals. Many wetlands are also essential for supporting human populations and their continuing loss or deterioration is a major global concern.

Wetlands are important for a number of reasons:

Water which moves down creeks and rivers can pick up all sorts of silt, rubbish and contaminants, particularly in stormwater runoff from city and suburban areas. When this water enters a wetland it slows down and its contents settle. Pollutants are naturally filtered and much of the washed-down material can be used as nutrients by wetlands plants, which in turn nourish birds, fish and other animals. Bacteria and viruses carried in the water are killed by exposure to plenty of sunlight as the water is spread over a large surface area. Some are also eaten by microscopic water life.

This filtered water can now gently flow out of the wetlands into a river system or out to sea. It is cleaner and healthier, protecting the health of plants, fish and other animals it meets downstream.

How can you tell if a wetland is healthy?

The vegetation growing in and around a healthy wetland will show no signs of stress. Healthy wetlands will often be surrounded by diverse and abundant communities of native plants, with few weeds. The area of vegetation surrounding a stream or wetland is sometimes called the buffer zone because the vegetation 'buffers' the stream or wetland and its animal communities from the adverse effects of land management activities within the catchment (see Figure 1.5).

Figure 1.5: Ways in which a riparian buffer can intercept runoff
Figure 1.5: Ways in which a riparian buffer can intercept runoff

The buffer zone does this by:

Inadequate buffer zones are one of the causes of degradation of wetlands and waterways.

Water quality will also give a good indication of wetland health. Poor water quality in the wetland might arise from the poor quality of inflows or from local contamination. Some wetlands along the Murray River, for example, have been badly affected by salinity. Often this will be obvious, as the soil will have traces of salt on the surface and some of the surrounding plants may be stressed or dead. Specialised types of plants that thrive on salty soil may be found here instead of the original plants.

One of the best ways to tell if a wetland is healthy is to take a sample of water and check for the presence of macro-invertebrates. If healthy, you can expect to find a diverse and abundant macro-invertebrate population. Conversely, expect low diversity and variable abundance in less healthy wetlands.

Changes to wetlands

In some natural wetlands the plant and animal communities have adapted to a cycle of drought and flood. There is a natural succession of plants as the environment changes. Flooding is often a trigger for many animals, such as fish and birds, to breed, and for growth and flowering of many plants.

These natural changes are disrupted by such events as permanent flooding or draining a wetland for agriculture. In the Murray-Darling Basin many wetlands have been partly or completely drained, while those wetlands adjacent to weirs on the Murray River are now permanently flooded.

As well, introduced pest species, for example, carp, mosquito fish and willows, can dramatically alter wetlands.

What is an estuary?

Estuaries contain a wide variety of habitats where fresh and salt water meet and mix in a continually changing environment.

Fresh water does not readily mix with salt water. Fresh water flowing from upstream is relatively light and rides over the more dense salt water from the ocean. This difference in density causes layering or stratification of the water, which in turn affects water quality and currents in the estuary. If tidal flow is very strong, the fresh and salt water layers may completely mix.

Unlike the one-way flow of rivers, water in estuaries often cycles backwards and forwards before finally leaving. Water-borne pollutants and sediment may remain in the estuary for a long time and harm plants and animals. This is particularly so in estuaries that are large but have a narrow opening to the ocean.

Why are estuaries important?

Estuaries support multi-million dollar fisheries and recreational activities throughout Australia. Sea grass beds in estuaries provide nursery grounds for fish, habitat for wildlife, nutrient uptake, shoreline protection, oxygen supply, recreation and ecotourism.

Changes to estuaries

Estuaries receive human sewage, farm runoff, industrial wastes and other contaminants. Toxic substances affect the health of fish, wildlife and humans; bacterial contamination threatens recreational users and shell fish farms; and nutrients trigger algal blooms. Algal blooms have caused destruction of sea grass beds and in turn the loss of habitat for prawns, and food for fish and dugong. The apparent silting up of some estuaries is due to an increase in the fine particle loads in rivers caused by changed land use such as sand mining or clearing vegetation for farms industry and urban settlement. High turbidity readings are particularly evident after heavy rainfall and particulates in the river water tend to clump together (floc) and settle out upon meeting the brackish and salt water in an estuary.

Measuring estuarine health

Although estuaries are complex systems with many habitats, plants and animals, and physical and chemical conditions, a few indicators are suitable for measuring environmental health. These include:

What is groundwater?

Groundwater is any water that is stored below the plant root zone; it is more commonly thought of as water which occupies openings, cavities and spaces in layers of rocks well beneath the surface of the earth. Where saturated rocks are permeable enough to transmit significant amounts of groundwater, they are called aquifers.

The source of most groundwater is rainfall and surface water which filters through the soil profile down into the aquifers. Groundwater varies considerably in quality, from pure water with little dissolved matter (in some cases better quality than most rivers and streams) to highly mineralised waters, sometimes more saline than sea water. Salinity is a measure of the amount of different inorganic chemical compounds (salts) which are dissolved in water (see Module 4).

Why is groundwater important?

About 97 per cent of the world's fresh water is stored under the ground in aquifers. The economy of many parts of Australia relies in part on the availability of groundwater supplies for:

Groundwater, however, is not just important for supply purposes. It plays a vital role in the water cycle. It may take a long time (possibly thousands or millions of years) but water which filters underground can flow out into rivers and eventually find its way back to the ocean.

Groundwater flows from the soil profile into rivers, it can sustain water flow long after rains have ceased in a catchment. Groundwater can, therefore, have a major impact on the volume and quality of surface water supplies. If groundwater quality and flow deteriorates, so too can the lakes and rivers connected with it.

Like surface water, groundwater quality can change over time. Changes in quality generally take place slowly and can be due to natural causes, such as fluctuating storage levels in aquifers arising from changes in rainfall. However, they can also be due to human actions such as:

Groundwater pollution

Groundwater pollution is very serious due to the great difficulty and costs involved in cleaning up polluted aquifers. Because of the relatively slow rates of groundwater flow in aquifers, it may take many years before contamination from a distant source reaches water supply bores.

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