Ecological Principles and Processes

Transcription

1 Ecological Principles and Processes Stream Ecosystems and Biomonitoring Name Ecological Principles & Processes workbook Module 8 Biomonitoring 8/1

2 Introduction In most streams and rivers there is a diverse community of animals and plants associated with the stream bed (benthos). This benthic community includes plants (algae), bacteria, fungi (and other tiny things), and macroinvertebrates (that can be seen with the naked eye). Aquatic macroinvertebrates include various sorts of worms, molluscs, and crustaceans, but in most streams the larvae of insects are dominant. Macroinvertebrate communities differ between streams. Sometimes this might be related to physical features of the stream such as size (big rivers and small streams will have different species), water velocity, temperature and frequency of floods. Other factors that might affect community composition are related to energy sources. For example open, shallow streams where full sunlight reaches the stream bed will support a very productive periphyton layer of algae on the substrate. This provides food for animals that either scrape the algae from surfaces, or suck the contents from algal cells. In contrast, in shaded streams, algal growth will be limited but the input of leaf litter from surrounding vegetation provides an alternative energy source. Some animals can feed directly on large leaf fragments. Coarse leaf material is broken down in streams by invertebrate feeding and also by physical abrasion. Fine particles of detritus provide food for other animals. The different food resources, and the ways in which animals feed on them, are the basis of a functional classification widely used in stream ecology Functional category Food type Feeding mode Shredder Grazer Filterer Collector Browser Predator Decomposing leaves and wood Benthic and epiphytic algae Fine suspended organic matter Fine detritus in sediments Algae and detritus Live animals Chewing, boring Scraping, piercing Nets, hairs, mucus Gathering, burrowing Sweeping, gathering Engulfing, sucking Note: "Browsers" are generalist stone surface feeders combining grazer and collector modes. Streams with different energy sources (food types) will have invertebrate communities that differ in their functional organisation. Other ways in which stream communities differ are related to human influence. Changes to the catchment (e.g. changing forest to farmland) alter the physical characteristics of the stream (less stability) and alter energy inputs (less detritus, more algae). Pollution also affects community structure because different species have different levels of tolerance Ecological Principles & Processes workbook Module 8 Biomonitoring 8/2

3 to pollution. Some stream insects are very sensitive to additions of toxic compounds (heavy metals), to altered temperature and ph, and to lowered oxygen concentration caused by the breakdown of organic matter such as sewage effluent. However, some animals can tolerate severe pollution; they may even require a highly 'enriched' environment. This suggests that we could use stream communities as indicators of pollution levels. Biological indices of pollution will be especially valuable when the pollution is intermittent (e.g. only when the monitoring agency is not looking). Spot tests using chemical methods might miss a critical event. But the animals in the stream have to survive all year (most have an annual life cycle), so any pollution event will be reflected in the community composition. We will use two simple indices based on this concept of sensitive, indicator species. The EPT index is simply the percentage of individuals in the sample that belong to either Ephemeroptera (mayflies), Plecoptera (stoneflies) or Trichoptera (caddisflies) - three groups of generally sensitive species. The Macroinvertebrate Community Index (MCI) uses different scores (1-10) for each type of animal that reflects its sensitivity to pollution. These scores were established through extensive research of stream communities in streams where the pollution status was known from independent tests. Although based on similar schemes used in other countries, the MCI had to be developed specifically for New Zealand since most of our aquatic invertebrates are endemic. Unlike the EPT index, the MCI uses simply the presence of species, not the numbers. To calculate the MCI: sum the scores of the species present; divide by the number of species (this gives the average score); and then multiply by 20 (to give a convenient scale). MCI Si = 20 n Experience with the MCI in stony streams has established the following calibration: Status MCI Clean water (pristine) > 120 Doubtful quality or mild enrichment Moderate pollution Severe pollution < 80 No such calibration is available for the EPT but it can be used comparatively; higher EPT means better water quality. Ecological Principles & Processes workbook Module 8 Biomonitoring 8/3

4 Sampling stream macroinvertebrates There are a number of methods for obtaining a sample of stream invertebrates: Kick sampling - relies on the movement of water in the stream to move invertebrates into a net when the substrate is disturbed. Kick sampling is not strictly quantitative because it is never clear what area of stream has been sampled, but it is very versatile - able to be used in a wide range of stream types and microhabitats. Surber sampling - also uses the water current and a net but a square frame attached to the net marks out a defined area (usually 0.1 m 2 ) within which the stones are scrubbed and the fine substrate stirred. Surber sampling is thus more quantitative, but only really accurate where the frame can be embedded into loose substrate. It is very difficult to use in bouldery rivers or deep slow rivers. Improvements on the Surber include completely enclosing the sample area with netting so that animals can t escape upstream (or drift in) but these are even less versatile. Artificial substrates: Kick sampling and Surbers only work well in swift flowing water (in riffles or runs). Sampling pools, or large deep rivers, can be done by placing removable structures that are colonised by invertebrates. The most common design uses a stack of perspex sheets with thin gaps between the sheets. Other designs use tiles or bricks. Whole stone sampling: To really find out how invertebrates utilise the microhabitats of a stream you need to look at the inhabitants of an individual stone (or other substrate unit, e.g. pieces of wood, clumps of moss). A small net held downstream of the stone will catch escapees as the stone is lifted. Periphyton sampling: The layer of algae, bacteria, fungi and trapped detritus on stones is an important food resource for stream communities. Excessive growths of periphyton can also be a good indicator of organic enrichment. Too much periphyton is visually unappealing and can interfere with recreation, but more importantly, the decay of dead periphyton can deplete oxygen levels, and some species of algae produce toxins. Periphyton can be scraped from a known area of substrate, dried and weighed, or the species identified. To get a better idea of the primary productivity of the periphyton, it is best to measure the level of photosynthetic pigments (usually Chlorophyll A). This is done by scraping a known area of substrate and extracting the Chlorophyll with acetone. The concentration of chlorophyll (green pigment) is measured with a spectrophotometer. The level of Chlorophyll is a good indicator of photosynthesis and potential primary production, but is also used in monitoring water quality where excess nutrients are a problem. Ecological Principles & Processes workbook Module 8 Biomonitoring 8/4

5 Biomonitoring Exercise Some samples have already been collected and processed from four sites on the Ngongotaha Stream. We will collect two more samples at each site, plus five samples from a further site, to add to the data. The Ngongotaha Stream arises in native forest on the Mamaku Plateau and flows into Lake Rotorua. We will sample it just inside the native forest where there are essentially no human impacts. Below this point the stream flows through Paradise Springs (a game park and tourist centre) and then through farmland. We will sample the stream at three points down the valley and also in a tributary. Water temperature and conductivity will also be measured. Conductivity is a measure of the amount of dissolved minerals in the water - another indicator of pollution. We are unable to analyse periphyton samples in this exercise but we will make a visual assessment of the type and amount of plant life in the stream at each site. Site Altitude Temperature Conductivity Periphyton observations 1 (forest) 2 (bridge) 3 (trib) 4 5 Do the physical measurements and amount of periphyton indicate any deterioration of water quality downstream? Ecological Principles & Processes workbook Module 8 Biomonitoring 8/5

6 What else (other than nutrient enrichment) will affect the biomass of periphyton in the stream? When the extra samples have been processed, enter the data in the table supplied and for each site (5 samples combined) calculate the MCI and EPT indices. Site MCI EPT Do these indices indicate any deterioration in water quality downstream? Is the change sudden or gradual? Ecological Principles & Processes workbook Module 8 Biomonitoring 8/6

7 What are the likely causes of lowered water quality in the Ngongotaha Stream and what could be done to improve the situation? Do the proportions of the different functional groups change along the stream, and if so, can you explain this in terms of energy sources to the stream ecosystem? Ecological Principles & Processes workbook Module 8 Biomonitoring 8/7

8 Ngongotaha Stream Taxon FFG MCI Order Site Site Site Site Site Sum Sum Sum Sum Sum Hydora Hydraenidae B 6 C B 8 C Orthocladiinae Tanytarsus Maoridiamesa Empididae Muscidae Austrosimulium Aphrophila Eriopterini C 2 D C 3 D G 3 D P 3 D P 3 D F 3 D P/B 5 D C 9 D Acanthophlebia B 10 E Austroclima Deleatidium Zephlebia Coloburiscus Ameletopsis Nesameletus B 9 E B 8 E B 7 E F 9 E P 10 E G 9 E Austroperla S 9 P Ecological Principles & Processes workbook Module 8 Biomonitoring 8/8

9 Stenoperla P 10 P Megaleptoperla P 9 P Zelandobius Zelandoperla B 5 P B 10 P Beraeoptera Confluens Olinga G 8 T G 5 T S/B 9 T Pycnocentrodes G 5 T Zelolessica Helicopsyche Costachorema Hydrobiosis Neurochorema Aoteapsyche Orthopsyche Oxyethira G 10 T G 10 T P 7 T P 5 T P 6 T F 4 T F 9 T G 2 T Archichauliodes P 7 M Potamopyrgus Oligochaeta Nematoda G 4 S C 1 W C 3 W Platyhelminthes P 3 W Nemertea P 3 W Ecological Principles & Processes workbook Module 8 Biomonitoring 8/9

10 Total Number No. of Taxa MCI EPT Browsers % Collectors Grazers Predators Shredders Filterers Functional Feeding Groups B = Browsers G = Grazers C = Collectors F = Filterers S = Shredders P = Predators Orders C = Coleoptera (beetles) D = Diptera (flies) E = Ephemeroptera (mayflies) P = Plecoptera (stoneflies) T = Trichoptera (caddisflies) M = Megaloptera (dobsonflies) S = Mollusca (snails) W = worms Ecological Principles & Processes workbook Module 8 Biomonitoring 8/10