Waterwatch Australia national technical manual

Module 3 - biological parameters
Waterwatch Australia Steering Committee
Australian Government Department of the Environment and Heritage, 2004
ISBN 0 6425 4856 0

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Introduction

Module 3 Biological Parameters concentrates on macroinvertebrate (water bugs) monitoring and also includes an introduction to undertaking habitat surveys. Module 3 is designed to raise awareness of waterway health amongst school groups and to help community groups effectively use macro-invertebrates to assess the health of their waterways.

Within Australia there is a huge diversity of animals that live together in our waterways. They include frogs, platypus, fish, birds and macro-invertebrates. Of all the animals however, it is the macro-invertebrate group that appears to be the most useful indicator of waterway health.

What is a macro-invertebrate?

A macro-invertebrate is an animal without a backbone. They are a diverse group of animals. Most freshwater macroinvertebrates are very small but many can still be seen with the naked eye.

There are many kinds of macro-invertebrates in our waterways. They include worms, snails, mites, bugs, beetles, dragonflies and freshwater crayfish. A group of different macroinvertebrates living together in the same aquatic habitat is called a ‘biological community’. Biological communities inhabit all types of waters from rushing mountain streams with rocky bottoms, to sluggish meandering rivers with sandy or muddy bottoms, to heavily vegetated ponds and farm dams. Some common examples of macro-invertebrates are illustrated in Figure 1.

Figure 1: Examples of common macro-invertebrates
Figure 1: Examples of common macro-invertebrates Note: organisms are not to scale or actual size. Source: South Australia Snapshot 97 Critter Catalogue

Macro-invertebrates have proved to be a useful indicator of the ‘state of health’ or condition of a waterway and are now the basis of rapid biological assessment techniques used across the whole country. Therefore, if your Waterwatch group wants to assess the health of your local waterbody, it would be sensible to measure the ‘water bug’ populations.

To assess the condition of the waterbody it is also important to survey its physical and chemical characteristics, see Module 4 Physical and Chemical Parameters. It is also a good idea to do a habitat survey at your site to note of any possible changes in the surrounding environment that may have affected the health of your waterway. All these surveys put together will show you what sort of habitat the waterbody and its surroundings offer to fauna.

Macro-inverterbate types and classification

As for other animals and plants, the classification system for macro-invertebrates is hierarchical. Within the animal kingdom, macro-invertebrates belong to various phyla. Each phylum comprises several classes, each class comprises several orders, and so on down to genus and species. As an example, here is the classification of a common freshwater shrimp.

Kingdom Animalia
Phylum (plural phyla) Arthropoda
Class Crustacea
Order Decapoda
Family Atyidae
Genus (plural genera) Paratya
Species australiensis

By convention, genus and species names are written in italics and the species name is entirely in lower case.

Where do macro-invertebrates live?

Understanding about macro-invertebrates will help you assess the health of your waterway. Knowing where macroinvertebrates live, why they live where they do and how they have adapted to live where they live will help you understand your local waterway (see Table 1).

Table 1: Habitats of macro-invertebrates
Freshwater habitats
Macro-invertebrates that may be living there
Edgewater includes overhanging vegetation from banks Fast-moving bugs and beetles, freshwater shrimp
Bottom - mud, sand, silt, gravel, rocks Worms, fly larvae, bivalve mussels
Aquatic plants - plants under the surface as well as those growing through the water and floating Gripping insects, caddis flies, damselflies, shrimp, snails
Flowing water - riffles, pools and runs Gripping insects, caddis flies, beetle larvae that have burrowed into logs and under rocks, mayflies and stoneflies

Your waterway will probably have several different habitats suitable for macro-invertebrates. Macro-invertebrates are found in still water and flowing waters.

We can broadly categorise aquatic habitats as moving water (rivers, creeks and streams) or still water (wetlands, backwaters, lakes and pools). Moving water can contain four different habitats - riffles, runs, pools and edgewater (see Figure 2).

Figure 2: Plan view and cross-sections of a pool, riffle and run – varying flows and depths create a variety of habitats for macro-invertebrates
Figure 2: Plan view and cross-sections of a pool, riffle and run - varying flows and depths create a variety of habitats for macro-invertebrates. Source: TVA Clean Water Initiative, 1995

Riffles are shallow rocky sections of streams with fast flowing turbulent water. The rocks provide a variety of living places and a large surface area onto which macro-invertebrates can attach. Food is continually swept along in the current from upstream. Since riffles provide a variety of living places, current conditions and food, they often support a diversity of macro-invertebrates.

Runs are generally deep and slow and the water surface is smooth. Smaller particles, like sand and gravel, tend to settle on the bottom. This limits the variety of living places for macro-invertebrates. In addition, occasional floods will wash sand and gravel and any macro-invertebrates downstream. Food is suspended in the water, deposited on the bottom or may grow in the stream bed. Since the physical habitat is not as stable as riffles, there are fewer and less of a variety of macro-invertebrates living in runs.

Pools usually have sandy or muddy bottoms with fewer types of macro-invertebrates present than in riffles. The habitat is less suitable so macro-invertebrates will attach to plant stems, roots, logs and other submerged objects.

Edgewater habitats may have emergent plants, sheltered overhangs with suspended root mats and leaf packs in quiet back eddies. The composition of macro-invertebrates will tend to differ from that in riffles. Animals survive best in places that provide protection, camouflage and food sources.

Special adaptations

Animals living in fast-moving water must be able to ‘hang on’ and, at the same time, catch their food. You can often find examples of adaptations in your sample. Some special adaptations include streamlined bodies, suction parts, special hooks and fine filters.

In contrast, animals living in still or slow-moving water don’t have to hang on and food is not brought to them in the current. Slow moving waters tend to house macro-inveterbates that are a wider range of sizes and shapes and are more mobile.

Characteristics of the aquatic environment that affect macro-invertebrates

The physical, chemical and biological characteristics of a river vary from its headwaters to the lowlands and these in turn influence the composition of macro-invertebrate communities downstream. Methods of assessing the physical habitat are described in Module 1 Background. Methods describing how to measure physical and chemical qualities of water which affect macro-invertebrates are described in Module 4 Physical and Chemical Parameters. Some important features of the waterway that affect macro-invertebrates are listed below.

Physical characteristics that affect macro-invertebrates

Aquatic chemistry and its effects on macro-invertebrates

The water in your catchment is a complex mixture of chemicals. The stream is affected by the composition of rain water, the geology of the catchment itself (such as limestone), animals in the water and by human activities. The most important chemical characteristics that affect macro-invertebrates are:

Biological characteristics that affect macro-invertebrates

The river is a living community of plants and animals which is dependent on getting food, oxygen and sunlight. The pattern of activity varies with the seasons. Macro-invertebrates are affected by:

Human-caused changes in macro-invertebrate numbers and diversity

In order to survive, macro-invertebrates need specific ranges of environmental conditions, such as temperature, oxygen levels, pH and salinity. Changes in the water quality can therefore affect macro-invertebrates by decreasing variety (numbers of different types of macro-invertebrates), and leave only those species tolerant of poor water quality. In general, diverse communities tend to be more stable than less-diverse ones, and it is generally assumed that high levels of variety are desirable for a healthy community.

Pollution, while it can reduce the variety of species in the community, may lead to a greater number of those species that survive polluted conditions. These species usually increase in number because of the lack of other species, some of which compete with them for food and some of which feed on them.

Human activities in a catchment or within the stream itself can significantly alter the characteristics of macro-invertebrate communities and therefore affect animals higher in the food chain. Changes in sediment load, clearance of stream form, and increases in nutrient and effluent input all affect community structure.

Suspended solids can reduce light penetration and therefore limit photosynthesis, with consequences for macroinvertebrate diversity and numbers. Sediment deposited on the stream bed can smother bottom-dwelling communities and alter habitat by filling in holes and depressions.

Riparian vegetation supplies food in the form of organic material (leaves, bark, etc.). Removal of this food source will not only affect macro-invertebrates that feed on it, but also increase the amount of light reaching parts of the stream that the overhanging vegetation previously shaded. Loss of shade may result in an increase in algal production - conditions that will favour selected macro-invertebrates. Increased solar radiation may also raise surface water temperatures, further affecting the number and diversity of macro-invertebrates.

Removal of snags (woody debris) and the formation of channels will alter macro-invertebrate diversity significantly, by reducing the variety of habitat available for colonisation. Removal of snags is particularly important in sandy reaches of a stream, where they may be the only habitat for colonisation. It can also affect macro-invertebrate communities by destabilising the river bed.

Barriers, such as dams, can alter the natural flow, temperature and water chemistry through controlled releases from the cold bottom layer of the dam, disrupting the various life stages of many stream macro-invertebrates. They also obstruct the animals’ drift or movement down the stream.

Increases in nutrients from catchment run-off (through erosion, salinity, sedimentation etc.) increase the potential for algal productivity. The macro-invertebrate community will respond to the changes in food supply and an increase in grazing macro-invertebrates will occur.

Sewage and industrial effluent contains many components, including toxic substances, such as heavy metals and pesticides, that can kill macro-invertebrates. As well, heated water reduces dissolved oxygen levels and disrupts macroinvertebrate metabolism which can also kill them. Severe organic pollution causes depletion of oxygen in the water and invertebrates are largely eliminated except for species such as tubificids (worms) and chironomids (midge larvae), which can tolerate low levels of oxygen. With less sever organic pollution, diversity is reduced but the abundance of tolerant species increases. The effect of pollution by toxic substances, like heavy metals, differs somewhat as different species have different tolerance ranges. However, as with organic pollution, the result is a reduction is species diversity and a change in the relative abundance of tolerant organisms.

What can macro-invertebrate communities indicate about the health of your waterway?

Monitoring, via sampling and identification, will reveal information about the macro-invertebrate community in your waterbody and will help you tell its story. When you sample you are collecting information on the community’s abundance, diversity, composition and pollution tolerance.

Abundance refers to the number of macro-invertebrates present. Large numbers of macro-invertebrates tend to be found in water enriched with nutrients. Small numbers may indicate erosion, toxic pollution or scouring by floodwaters.

Diversity refers to the number of different types of macroinvertebrate present. Healthy streams usually have a greater diversity than degraded streams, although the diversity in headwaters can be naturally low due to a lack of different types of food. Communities with many different species appear to be more stable and healthy than less diverse ones.

Composition refers to the proportion of different types of animals living together. A sample from healthy streams tends to contain a good number of mayflies, stoneflies and caddis flies. If the sample contains a lot of worms and midge larvae (chironomids), the stream is probably degraded.

Pollution tolerance refers to the tolerance of animals to organic pollution from sewage, industrial effluent and heated water. For example, most stonefly families are intolerant of pollution whilst worms are quite tolerant. Pollution tolerant animals do occur in natural streams where there is low dissolved oxygen, for example, in small clumps of leaves buried in sediment.

How does pollution affect macro-invertebrates?

Macro-invertebrates are sensitive to a range of pollutants and changes to habitat.

Organic pollutants come from sewage treatment plants, animal manure, and food processing industries. Organic wastes generally:

Increase in abundance. The initial release of organic pollutants in small amounts may cause an increase in abundance of all macro-invertebrates. However, as the amount of organic waste increases further, those macroinvertebrates that are best adapted to it will become more and more abundant. Poorly decomposed sewage or animal manure from upstream will be deposited on the bottom of the stream favouring gathering collectors, such as caddis flies. Fine particles of organic waste suspended in the water, such as well decomposed sewage, manure or processed coarser material from upstream, favour filtering collectors, such as black fly larvae. The abundance of animals in each feeding group at a site can suggest the type of pollution impact.

Lower dissolved oxygen. Heavy organic pollution will reduce macro-invertebrate diversity. Decay of dead plants and organic waste may lower dissolved oxygen to critical levels reducing the number of sensitive macro-invertebrates. For example, some families of stonefly larvae are very sensitive to pollution and cannot survive if dissolved oxygen falls below a certain level. They disappear first. Mayflies are a little more tolerant but are next to disappear as oxygen continues to fall. If dissolved oxygen levels become very low, only very tolerant animals, such as tubifex worms and chironomid larvae, will survive. If your sample contains many tubifex worms and chironomid larvae but little else, it indicates that the site is degraded by severe organic pollution.

Growth of aquatic plants. Excess nutrients can come from organic wastes, fertilisers and detergents, animal manure and erosion. In many streams, phosphorus appears to be in shortest supply, so small amounts of phosphorus added to waterways can produce a sudden growth of aquatic plants. Under favourable conditions, such as little wind and current, blue-green algae may bloom and produce toxins that can kill stock and harm humans.

Toxic pollution can come from various sources such as tip sites, industries and mines, and includes acids, solvents, petroleum compounds, pesticides, herbicides and heavy metals, such as cadmium, lead and zinc. These pollutants poison or harm living things. They can often be traced to point sources, such as discharge pipes. Most macro-invertebrates are killed by the comparatively high concentration of toxic substances found around discharging pipes. Both low abundance and low diversity of macro-invertebrates suggest toxic pollution of the waterway.

Sometimes a toxic pollutant may act in a selective way, especially if present in only low concentrations.For example, an insecticide washed into a stream from a diffuse source, such as intensive horticulture,may only kill the most sensitive invertebrates, while numbers of other types of invertebrates may not change. Macro-invertebrates from the mayfly and stonefly groups are usually the most sensitive to toxic pollutants. Caddis flies are normally considered moderately sensitive, while certain types of worms and chironomids are known to be the most tolerant.

Conditions gradually improve downstream from the pollution source as the toxins are diluted by tributary streams and groundwater. The variety of aquatic invertebrates gradually increases and eventually the clean water aquatic invertebrates reappear.

Physical changes to the waterway include construction works, removal of woody debris and streamside vegetation, erosion and straightening of the natural stream meanders. These changes reduce the variety of aquatic habitats available for different kinds of macro-invertebrates. Water bodies that are only slightly degraded may have lower numbers of sensitive groups like stoneflies. In waterways that lack a variety of habitats for animals, for example, concrete-lined channels, the abundance and diversity of invertebrates will be very low.

Urban areas. Physical degradation of aquatic ecosystems is particularly common in urban areas. Waterways are often realigned and channelled to stop them from meandering. They may be lined with concrete or even diverted underground in pipes. Concrete channels do not provide adequate shelter from predators or floods. Other streams may be left to follow their natural course but their riparian vegetation is often removed and replaced with grass or pavement.

Erosion. Clearing away stream-side vegetation, carrying out earth-works and removing gravel from the stream bed cause an increase in erosion and suspended solids in the waterway. In rural areas, stock grazing around waterways destroys riparian vegetation, causes banks to slump and increases erosion. This blocks light from reaching aquatic plants, reducing growth and resulting in fewer macro-invertebrates in the stream. In addition, sediment deposited on the stream bed can fill in deep holes, smother bottom dwelling plants and fill in gaps between rocks that are normally occupied by macro-invertebrates. Deep holes in the stream bed are the preferred habitat of some native fish, providing cold water refuges from the summer heat.

Overhanging stream-side vegetation. Removal of this food source (branches, fruit, leaves and bark) will not only reduce the population of shredder macro-invertebrates that feed on it, but also increase the amount of light reaching the stream. Loss of shade may result in algal growth, a condition which will favour grazer macro-invertebrates. So, as shredders decrease, grazers become more common. More sunlight will also raise surface water temperatures and lower dissolved oxygen levels, again harming sensitive macro-invertebrates.

Large woody debris (snags, logs and branches). Removal of large woody debris will significantly reduce the variety of living places available for macro-invertebrates. In large rivers, large woody debris is often removed to ensure safe boat travel. Woody debris is particularly important in sandy reaches of the stream where it may be the only suitable habitat available. De-snagging can also destabilise the river-bed and further reduce the variety of habitats available to macro-invertebrates.

Flow regulation and water extraction

Dams and weirs can change the natural seasonal flow pattern of rivers. They can also reduce the size and frequency of floods. Flow in some rivers is greatly reduced by the amount of water taken for irrigation. These changes can lead to increases in salinity and disruption of the reproductive cycles and growth of fish, macro-invertebrates and plants.

Not only do dams alter the natural flow pattern, but the water released from the bottom of a dam may also harm macro-invertebrates downstream. Water in a deep dam tends to form layers with a relatively warmer layer floating on top of a colder, denser bottom layer. The temperature difference can be quite marked, for example, 3-4°C. In addition, oxygen levels in the bottom layer can fall to zero due to bacterial decomposition and isolation from the atmosphere. Dissolved oxygen levels quickly return to normal when the discharge water in the river mixes with the air at the end of the discharge pipe. However, fish have be known to die beyond the end of the discharge pipe when there are large releases of water. Dams also block drift or movement of animals downstream to new habitats.

Introduction of exotic (feral) organisms

A large number of exotic organisms have been introduced into Australia and they have a major impact on our natural aquatic systems. For example, willow trees change aquatic habitats by blocking sunlight, altering the water chemistry and choking streams and rivers with mats of fine roots. European carp stir up the sediment in water bodies, uprooting plants and making the water murky. Brown and rainbow trout are voracious predators, eating large numbers of native fish and macroinvertebrates, including aquatic snails.

Exotics plants and animals change the abundance and diversity of aquatic invertebrates by predation, competition and habitat change. They can even cause the localised extinction of native organisms, however the exact impact of any exotic is hard to predict.

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