(With J.P.C. Harding, D.H.N. Spence. Authors not listed on title page). Methods for the use of Aquatic Macrophytes for assessing water quality 1985. METHODS FOR THE EXAMINATION OF WATERS AND ASSOCIATED MATERIALS. Her Majestys Stationery Office, London, 176 pp. ISBN 0-11-752000-4
This booklet describes methods for surveying water quality in rivers and lakes by observing the larger aquatic plants. Rivers are passages of aquatic life traversing countries and regions, passages which connect in one direction only: downstream. Wider water bodies, lakes, are usually sited intermittently on rivers. Connections for plants between river systems are only by transport, usually birds, so species may be absent solely because incoming transport failed. However, if assemblages or patterns of species are absent, this can be ascribed to an unsatisfactory habitat which is hindering development. The methods in this booklet make use of the larger freshwater plants (commonly termed aquatic macrophytes or macrophytae), including flowering plants (angiosperms) with ferns, horsetails (pteridophytes), mosses and liverworts (bryophytes) and larger algae.
Freshwater macrophytes have often been neglected as pollution monitors, being regarded only as weeds which may hinder flow. Where macrophytes occur, however, the habitat range of the site can be deduced from the species present. (If species are absent, the primary cause, which need not be water quality, can be identified, even when pollution is severe.) Each species has a range of tolerance to each habitat factor, comprising a range in which it can grow well, peripheral ranges in which it can grow less well or occur less frequently, and conditions from which it is excluded. When some but not all the habitat factors are known, the vegetation can be used to assess the remaining factors. Consequently if water and soil quality can be deduced, both the pollution, and the base-line quality of the clean water can be assessed.
As a diagnostic tool, macrophytes have several advantages. They are large, most being easily recognised from a distance. They are few in number, diagnosis within a region usually being possible from about 50 species. They are stationary, so their absence is easily ascertained. Most are rooted, and so reflect soil as well as water quality (soil status is usually more stable). In its simpler forms macrophyte monitoring is exceptionally rapid, and so can be recommended for initial surveys and when man-power is limited.
The main disadvantages of macrophyte monitoring are that most species die back in winter, so preventing recording at that time, and that assessment is possible only in places where clean-water vegetation could be expected to be both plentiful and predictable. In rapid current scours, deep lakes and heavy shade, for instance, macrophytic vegetation is necessarily negligible, and cannot be much further decreased by pollution.
Completely clean, and grossly polluted waters give equivalent indicates with all forms of monitoring, botanical, zoological or chemical. In moderately polluted waters, however, different groups of organisms may react differently to different types of pollution, and show the maximum impact of the pollution at different distances from the inflow, hence using more than one method of assessment may add greatly to the total understanding of the pollution. Thus plants can oxygenate water and so are less susceptible to oxygen sag downstream of oxygen-consuming effluents than are macro-invertebrates. Conversely some indicators can migrate and so escape intermittent pollution which plants cannot avoid. Trace metal and other requirements are also species dependent.
The primary factors influencing freshwater vegetation are:
Water force (related to landscape and precipitation)
Rock type and land use
Rock type and land use
Circulation and disturbance
Those are made up of various components:
Flow (in rivers) or Circulation (for lakes), Disturbance, Substrate texture and stability, Depth, Light reduction (turbidity, shade) Width (or rivers), Area (of lakes), Water (chemical) quality, Substrate (chemical) quality, Bank type, Propagule availability.
Effects of past history, and long term changes in, for instance, weather.
These combine in different ways, for instance, turbidity may be due to the run-off particles (which are dependent on rock type, land use, topography and precipitation), to phytoplankton, or to pollution. The effect is the same, the cause is different.
Freshwater vegetation is influenced by many of man's activities, including:
Activities normally considered polluting
Effluent, both treated and untreated. Organic wastes from houses, farms, boats and factories. Industrial wastes from factories, mines, etc.
Agricultural run-off, fertilizer, biocides and increased soil particles.
About this series
Warning to Users
Hazards (including a section with advice on the safe Use of Boats).
A The surveying and assessment of Macrophytes in Watercourses.
A1 Summary of the method: biota determined; vegetation surveyed; basis of use for pollution assessment; basis of operation; limit of detection; form of data; range of application; bias; logistics.
A2 Introduction: macrophytes; types of record.
A3 Equipment needed: equipment in the field; equipment in the laboratory; introductory literature.
A4 Planning and survey: season; day; number of sites to record; choice of sites.
A5 Surveying: site identification; physical characteristics; banks above normal water level; plants of the channel; abundance.
A6 Records to be completed in the laboratory: complete records; preliminary analysis; further analysis.
A7 Rock Types.
A8 Interpretation: important variables; indices.
A9 Use of the Method: Table A1; Table A2; Table A3; Figure A1; Table A4; Figure A2; Table A5; Figure A3; Figure A4; Example of the use of the method for determination of a Stream Damage Rating Index with a worked example.