Water quality - Guidance standard for the surveying of macrophytes in lakes

This guidance standard defines a method for surveying aquatic macrophytes in lakes - primarily for the purpose of assessing ecological status, using these organisms as an element of biological quality. The information provided by this method includes the composition and abundance of the aquatic macrophyte flora.
For a complete assessment of ecological status, other elements of biological quality should also be assessed.
The general principle of the approach described in this European Standard may also form the basis for the monitoring and assessment of macrophytes in lakes, for example, for conservation purposes.

Wasserbeschaffenheit - Anleitung zur Erfassung von Makrophyten in Seen

Diese Anleitung legt ein Verfahren für die Erfassung aquatischer Makrophyten in Seen, hauptsächlich zur Bewertung des ökologischen Zustands als biologisches Qualitätselement fest. Die hier gegebenen Informationen schließen die Zusammensetzung und die Häufigkeit aquatischer Makrophytenflora ein.
Für eine vollständige Bewertung des ökologischen Zustands sollten auch andere biologische Qualitäts-elemente bewertet werden.
Das Prinzip des in dieser Europäischen Norm beschriebenen Verfahrens kann ebenfalls als Grundlage für die Untersuchung und Bewertung von Makrophyten in Seen für z. B. naturschutzfachliche Fragestellungen dienen.

Qualité de l'eau - Guide pour l'étude des macrophytes dans les lacs

La présente norme-guide définit une méthode pour étudier les macrophytes aquatiques dans les lacs - principalement dans le but d'en évaluer l'état écologique, en se servant de ces organismes comme élément de la qualité biologique. Les informations fournies par cette méthode sont, entre autres, la composition et l'abondance de la flore des macrophytes aquatiques.
Pour une évaluation complète de l'état écologique, il convient d'estimer également d'autres éléments de la qualité biologique.
Le principe général de l'approche décrite dans la présente Norme européenne peut également constituer la base de la surveillance et de l'évaluation des macrophytes dans les lacs, par exemple à des fins de conservation.

Kakovost vode - Navodilo za preiskave višjih vodnih rastlin jezer

General Information

Status
Published
Publication Date
16-Oct-2007
Current Stage
9093 - Decision to confirm - Review Enquiry
Completion Date
09-Feb-2022

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2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Kakovost vode - Navodilo za preiskave višjih vodnih rastlin jezerWasserbeschaffenheit - Anleitung zur Erfassung von Makrophyten in SeenQualité de l'eau -

Guide pour l'étude des macrophytes dans les lacsWater quality - Guidance standard for the surveying of macrophytes in lakes13.060.70Preiskava bioloških lastnosti vodeExamination of biological properties of water13.060.10Voda iz naravnih virovWater of natural resourcesICS:Ta slovenski standard je istoveten z:EN 15460:2007SIST EN 15460:2007en01-december-2007SIST EN 15460:2007SLOVENSKI

STANDARD
SIST EN 15460:2007

EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN 15460October 2007ICS 13.060.70 English VersionWater quality - Guidance standard for the surveying ofmacrophytes in lakesQualité de l'eau -

Guide pour l'étude des macrophytesdans les lacsWasserbeschaffenheit - Anleitung zur Erfassung vonMakrophyten in SeenThis European Standard was approved by CEN on 1 September 2007.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the CEN Management Centre or to any CEN member.This European Standard exists in three official versions (English, French, German). A version in any other language made by translationunder the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as theofficial versions.CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMITÉ EUROPÉEN DE NORMALISATIONEUROPÄISCHES KOMITEE FÜR NORMUNGManagement Centre: rue de Stassart, 36

B-1050 Brussels© 2007 CENAll rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 15460:2007: ESIST EN 15460:2007

EN 15460:2007 (E) 2 Contents Page Foreword..............................................................................................................................................................3 Introduction.........................................................................................................................................................4 1 Scope......................................................................................................................................................5 2 Normative references............................................................................................................................5 3 Terms and definitions...........................................................................................................................5 4 Principle..................................................................................................................................................6 5 Equipment..............................................................................................................................................7 6 Survey planning.....................................................................................................................................9 7 Survey procedure................................................................................................................................12 8 Aquatic macrophyte identification.....................................................................................................17 9 Fixation and preservation...................................................................................................................17 10 Data collation and classification........................................................................................................18 11 Quality assurance................................................................................................................................19 Bibliography......................................................................................................................................................20

SIST EN 15460:2007

EN 15460:2007 (E) 3 Foreword This document (EN 15460:2007) has been prepared by Technical Committee CEN/TC 230 “Water analysis”, the secretariat of which is held by DIN. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by April 2008, and conflicting national standards shall be withdrawn at the latest by April 2008. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights. WARNING — Working in or around water is inherently dangerous. This standard does not purport to address the safety problems associated with its use. It is the responsibility of the user to establish appropriate health and safety practices and to ensure compliance with national regulatory conditions where they exist. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom.

SIST EN 15460:2007

EN 15460:2007 (E) 4 Introduction Macrophytes are an important component of aquatic ecosystems and can be used to facilitate monitoring of ecological status. The requirement for the use of macrophytes in monitoring is inherent in numerous European and national directives, e.g. Urban Waste water Treatment Directive (91/271/EEC), and the Nitrates Directive (91/676/EEC). Macrophytes are one of four obligatory biological quality elements identified in the Water Framework Directive (Council Directive establishing a framework for a community action in the field of water policy, 2000/60/EC), and should be used in the ecological classification of all lakes. In addition to their important ecological role, the use of macrophytes as indicators of ecological status in standing waters is based on the fact that certain species and species groups are indicators for specific standing water types and are adversely affected by anthropogenic impact. In certain situations the lack of macrophytes is also a natural characteristic of certain types of aquatic habitat. For example, in lakes with high humic content or high turbidity, macrophytes may be virtually absent due to the reduction in light penetration. Many lakes show alternating states with clear water in some years and turbid water in others associated with the dominance or absence of macrophytes but with the same anthropogenic impact. A wide range of sampling and survey methodologies have been developed for specific applications including conservation, drainage impact, management, ecological habitat, enhancement etc. The methodology of this guidance standard is recommended specifically for the surveying of macrophytes in both natural and artificial fresh water lakes, for the purpose of monitoring ecological status or the status of the macrophyte vegetation itself. It could be used, however, as the basis for general monitoring of water quality or other applications. According to the precise use to which this guidance standard is to be put, it is essential for specifiers and users to agree and clearly record, any necessary variations or optional procedural details prior to use.

SIST EN 15460:2007

EN 15460:2007 (E) 5 1 Scope This guidance standard defines a method for surveying aquatic macrophytes in lakes - primarily for the purpose of assessing ecological status, using these organisms as an element of biological quality. The information provided by this method includes the composition and abundance of the aquatic macrophyte flora. For a complete assessment of ecological status, other elements of biological quality should also be assessed. The general principle of the approach described in this European Standard may also form the basis for the monitoring and assessment of macrophytes in lakes, for example, for conservation purposes. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

Not applicable 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 amphiphyte plant that can grow submerged in the water up to completely above the water, typically under fluctuating water level conditions 3.2 aquatic macrophytes larger plants of fresh water which are easily seen with the naked eye, including all aquatic vascular plants, bryophytes, stoneworts (Characeae) and macro-algal growths (see EN 14184)

NOTE For this method, this term is taken to include macrophytes growing in the water and in the wash zone, including hydrophytes, helophytes, amphiphytes, as well as supra-littoral species in the wash zone (such as Carex). 3.3 belt transect band of defined width oriented at right angles to the shoreline or bank, which starts at the water line including the wash and inundation zones starting at the highest seasonal waterline and in lakes extends to the lowermost limit of the aquatic macrophyte vegetation NOTE 1 The aquatic vegetation (species composition, abundance, cover) is analysed within this transect. The transect can be virtual or physically delineated. NOTE 2 The lowermost limit can change over years, either the belt transect is then extended to the lowermost limit that can be expected ever, or the lowermost limit or the belt transect is left variable through the years. 3.4 ecological status expression of the quality of the structure and functioning of aquatic ecosystems, expressed by comparing the prevailing conditions with reference conditions (see EN 14184) NOTE As classified in accordance with Annex V of the EC Water Framework Directive (2000/60/EC). SIST EN 15460:2007

EN 15460:2007 (E) 6 3.5 habitat specific environment in which a species lives (see EN 13946, EN 14407) 3.6 helophyte plant that is normally rooted under water with emergent shoots, typically growing in marginal or marshy areas (see EN 14184) 3.7 hydrophyte aquatic plant that is normally rooted under water with floating or submerged leaves, or totally free floating (see EN 14184) 3.8 maximum depth of the vegetation lowermost limit of the aquatic macrophytes which are adherent to or rooted in the sediment 3.9 metric measurable part or process of a biological system empirically shown to change in value along a gradient of human influence 3.10 monitoring site lake, or body of water within a lake, in which aquatic macrophytes are surveyed for the assessment of ecological status and/or other purposes 3.11 reference site (RefS) lake or body of water within a lake representing the reference conditions for a given ecological type 3.12 reference conditions conditions reflecting a totally undisturbed state, lacking human impact, or near-natural with only minor evidence of distortion (see EN 14184) NOTE Reference conditions can be defined using field sites or, where necessary, using expert judgement or predictive modelling techniques 3.13 sample smallest unit of area to be sampled, typically a belt transect consists of a series of samples, continuous or discrete (with intervals), but samples may be scattered (stratified) randomly as well (non-transect methods) 3.14 supra-littoral survey location section of shoreline and adjacent submerged areas surveyed for aquatic macrophytes 3.15 taxon (pl. taxa) taxonomic unit, for example family, genus or species (see EN 14707) 4 Principle This European Standard describes a methodological approach for determining the ecological status of lakes using aquatic macrophytes. The status of a lake is assessed by establishing its deviation from the natural conditions of a lake of a similar ecological type. If natural conditions in comparable lakes no longer exist to SIST EN 15460:2007

EN 15460:2007 (E) 7 serve as a background or a reference site (RefS), it is necessary to reconstruct this background based upon whatever records exist. This may involve using data from lakes of a similar type in other European countries. NOTE Even within similar lake types there can be significant biogeographical variation in the naturally occurring species. The presence of aquatic macrophyte taxa in the individual lakes is recorded. Macrophyte abundance, measured in terms of the spatial extension of taxa or macrophyte beds, and/or macrophyte abundance estimates or biomass, is assessed by different methods adapted to the scale and purpose of the study. Numerical derivatives or metrics of the macrophyte composition and abundance in a lake survey can be used to identify the divergence from type-specific, natural conditions.

5 Equipment: the following equipment list is suggested. 5.1 Equipment common to all surveys 5.1.1 High resolution maps of survey area, preferably laminated. 5.1.2 Range of plastic bags and hard plastic containers, for retaining specimens or the temporary storage of macrophytes requiring laboratory identification. NOTE Mosquito netting or lace bags are easier to use than plastic bags in water. 5.1.3 Waterproof labels 5.1.4 Pencils or pens, with indelible ink. 5.1.5 Field data recording system, using either waterproof sheets, a small cassette recorder or water-resistant portable computer;

5.1.6 Floras, relevant field keys and identification guides, and iconographs (illustrations), appropriate to the habitats under consideration; 5.1.7 Records from any previous macrophyte surveys of the lakeunder survey 5.1.8 Personal protective clothing 5.1.9 First aid kit 5.1.10 Notebook, preferable with hard back and water repellent paper. NOTE A pre-prepared pro forma is helpful in the field. This can be a pro forma count sheet with a list of taxon names and space beside each on which the abundance estimates can be made, or a notebook organised in such a way that taxon identities and numbers can be clearly recorded, or a computer program with facilities for direct entry of data. It is recommendable that design of the recording sheets or programs takes into account the requirements of any Quality Assurance programmes that are in place. Alternatively, field notes can be dictated into a small cassette recorder or digital dictaphone with flash memory. 5.2 Additional equipment for diving surveys 5.2.1 Wet-suit, snorkelling or SCUBA equipment; 5.2.2 Sinkable measuring tape, with concrete weight (or leaded line graduated along its length at appropriate points e.g. 5 m distances) to mark survey transects. 5.2.3 Dive (Alpha) flag, to attach to boat or buoy. SIST EN 15460:2007

EN 15460:2007 (E) 8 5.3 Additional equipment for boat surveys 5.3.1 Boat suitable for local conditions, with appropriate safety equipment. Where a boat is used, a means of communication from the boat to designated shore-based staff, with access to rescue services. NOTE

The use of an experienced boat handler familiar with local conditions or as a minimum detailed bathymetric maps for the survey area is recommended for safe surveying. Accurate bathymetric data are crucial in delineating littoral zones, bed slopes etc. Where the data are not available, it should be an integral part of any vegetation survey. At a practical level, the use of transducer depth finders is recommended, which will operate to depths of up to approximately 73 m. 5.3.2 Double-sided rake grapnel and/or multi-point grapnel, attached to a suitable length of rope. NOTE 1 The double-sided rake grapnel is preferable on relatively smooth, uniform substrates. On stony terrain with large interstices, the multi-point grapnel will tend to be more effective as it can slip into areas that a double rake cannot access. However, grapnels and rakes are inefficient for sampling smaller aquatic macrophyte species, a grab and netting techniques can be more effective. NOTE 2 Double rake grapnels can be fabricated from two 32 cm garden rakes with 6 cm prongs at 2 cm intervals welded back to back with an attachment point for a rope. Rakes with longer prongs at smaller intervals can be preferred as they can be more efficient in sampling some situations. So called ‘grass rakes’ with 10 cm prongs transversely mounted are more suitable than ordinary garden rakes, especially for smaller specimen on soft sediments. NOTE 3 The efficiency of rakes can be increased by folding fine maze wire netting around the rake teeth; in very soft sediments and with only very tiny plants a grab and handnet can be used as effective alternatives. The rope should be of sufficient length to allow the deployment and recovery of the rake/grapnel. It should be of a sufficiently heavy gauge to allow pressure to be applied when the grapnel is snagged but not of excessive thickness that will lead to problems with deployment and recovery. Hemp ropes are less prone to kinking. Alternatively, extendable handles can be used that are effective to depths of approximately 3,5 m [3]. 5.3.3 Rake, with rigid extendable handle. 5.3.4 Graduated floating line and weighted mooring buoy 5.4 Additional equipment 5.4.1 Geographical Positioning System (GPS) 5.4.2 Polarising sunglasses 5.4.3 Underwater viewing aid/bathyscope, viewing tube, bucket or box with clear Perspex base. 5.4.4 Camera with polarising lens 5.4.5 Underwater ‘drop’ camera, waterproof camera mounted to a cable or pole, that can lowered into the water. 5.4.6 Sanitised wipes 5.4.7 Binoculars 5.4.8 Hand lens, ×10 and ×20 magnification. 5.4.9 White plastic trays 5.4.10 Equipment to measure water depth, e.g. rod marked with intervals of 1 cm to 2 cm; or for deep, less vegetated areas, a hand-held echo-sounder. SIST EN 15460:2007

EN 15460:2007 (E) 9 5.5 Equipment for collecting additional data

5.5.1 Conductitivity meter 5.5.2 Depth meter 5.5.3 pH meter 5.5.4 Secchi disc NOTE A secchi-disc to indicate the depth of light penetration, and equipment to measure the depth and level of the water can be useful in interpreting the resulting data. A hand-held conductivity and pH meter can also be useful, especially if surveying lakes with different water chemistry. 6 Survey planning 6.1 General Survey planning is very much dependent on the purpose of the study and the procedure described here is primarily for the purpose of assessing ecological status. At the beginning of a survey the geographic region(s), the hydromorphological lake typology and the expected reference conditions characteristic for the type of lake under investigation should be defined. 6.2 Establishing reference conditions Ecological reference conditions for each hydromorphological lake type need to be established before the ecological status of a monitoring site can be assessed. This can be achieved either by surveying reference sites (RefS) within a specific type or, where suitable RefS cannot be found, by modelling or expert opinion. Historical data from unimpacted sites may also be invaluable. Reference sites (lakes, or bodies of water within a lake), should be as close as possible to natural conditions with respect to their species composition and the abundance of each species, physical and chemical variables and hydromorphological background. Hazardous substances should either be totally absent or close to the limit of detection. Nutrient concentrations and the levels of acidification should be close to background levels taking into account the influences of the local geology and geographical location. Catchment pressures from, for example, agriculture and forestry should be low and significant point-discharges should be absent. The selection of reference sites (RefS) should be based on information from regional or national surveys that have data on the species composition, distribution and diversity of the aquatic vegetation. 6.3 Monitoring sites The ecological status of a lake or body of water within a lake (a monitoring site) is measured in terms of the deviation of the aquatic macrophyte flora from the reference conditions for the same lake type. For most practical purposes the lake is the waterbody unit and not the individual areas surveyed for macrophytes. Where the concentration of lakes is high, as for example in Scandinavia, it is impractical and unnecessary to survey macrophytes in all lakes. In these circumstances a representative subset of monitoring sites can be surveyed to reflect the range of lake types represented and the extent to which these are influenced by specific human pressures. When selecting representative lakes from lake clusters use similar criteria to those listed in Clause 6.2. SIST EN 15460:2007

EN 15460:2007 (E) 10 6.4 Survey protocols In the case of heavily modified or artificial water bodies the survey procedure may differ from that described in this guidance standard, depending on the extent of the hydromorphological changes or differences, but only when certain elements of the procedure cannot be implemented because of the hydromorphological deviation from the reference conditions. For instance: if banks of the lake have been modified, through embankment, consolidation or other means, the littoral zone, the wash zone and the inundation zone might be absent or reduced too much to serve as a relevant element in the quality assessment. Lake macrophyte surveys can be undertaken at different levels of sophistication and intensity. This can involve the surveying of: i) several discrete transects, or short lengths of shoreline in lakes with shallow littoral zones, which are regarded as representative of the visible and littoral flora of the study lake (quick survey) involving the identification of species present and a crude estimate of abundance;

ii) multipoint transects, or longer lengths of shoreline as a means of defining the best positioning for survey locations under approach (i); or

iii) contiguous transects or stretches of shoreline; or iv) complete surveys of the lake (or body of water within a lake) to produce species inventories and in the selection of representative transects.

The survey protocol may vary between these different approaches depending on the purpose of the survey. For example, less intensive data collection may be appropriate for preliminary (quick) surveys designed to locate representative survey locations. The first two approaches require relatively little time and may be useful for the routine assessment of ecological status. They allow only representative survey locations to be described, but they can be useful for spatial and temporal monitoring. A longer stretch of a shoreline is surveyed first, using the second approach to demonstrate the “evenness” of a) physical and b) biological variables. Representative survey locations are then selected within those stretches, and surveyed using the first approach. Contiguous survey stretches cover the full length of the shoreline, but are labour intensive and so may not be suitable for routine use. The last approach fulfils more specialist needs. For example, this can be part of the procedure to find reference sites (RefS) for different ecological lake types such as those with acute inclines into deep water but also those with shallower littoral areas.

It is a labour-intensive approach not to be applied for routine surveys. It is for use in special cases, e.g. long-term monitoring and for detailed background information for ecological classification.

The procedure described in this guidance standard relates to the first approach, using belt transects. If using alternative approaches, such as shoreline (walk-around) surveys, care should be taken to demonstrate that the resulting data are as representative as possible

of the flora and conditions present. 6.5 Transect surveys The most widely used method for surveying macrophytes in lakes is based on belt transects (3.3). This approach allows mapping of the distribution of individual species and abundance of aquatic macrophytes, it provides robust data sets that can be used to generate indices and metrics, and it is a cost effective means of data collection. The number and positioning of survey locations at which belt transects are surveyed should allow a representative flora and the extent of colonisation to be recorded, reflecting the extent of human impact on the lake. These decisions should be made, as far as is possible, before the initiation of fieldwork. SIST EN 15460:2007

EN 15460:2007 (E) 11 NOTE 1 A quick survey is recommended to investigate variability across and between the lakes and to determine which lakes are representative It is strongly recommended that the important and/or representative sections of the shoreline are walked prior to survey. This allows the opportunity for pilot surveys of several short transects in order to obtain a general impression of the vegetation and to identify likely safety hazards. Preliminary walks will also provide information on seasonal variation of the aquatic vegetation. Where this is not possible due to the extent of the helophyte reed growths this may be undertaken from a boat or using aerial photographs. Survey locations should include the principal habitats and components of bathymetry of the lake – including inlet and outlet points (although only where no perceptible flow), embayments, exposed areas, islands etc. – and represent the various land-use types in the immediate catchment. Where possible, the natural conditions of substrate, water depth, bank-side shading etc. should be similar to those at survey locations at the reference site(s), if included in the study, so that differences in the flora due to anthropogenic impact can be distinguished more easily from differences due to natural hydromorphological conditions. The number of survey locations/transects can be derived empirically [3] or from mathematical considerations [4]. The objectives of the survey, the requirements and constraints of the subsequent data analysis (one transect equates to one sample for multivariate analysis), the degree of confidence required from the data, and the resources and expertise available commensurate with achieving that confidence, should all be taken into account. In all cases, sufficient transects will need to be surveyed to generate representative data, particularly with respect to identifying the maximum number and abundance of species, but also to ensure that changes in the macrophyte assemblage due to anthropogenic factors such as land-use can be distinguished from changes due to natural factors, such as differences in geology, altitude, or exposure. Surveyors should be aware that the number of species recorded will increase with increasing number of transects surveyed. Sufficient transects should be surveyed in order to determine the Species Saturation Number (SSN – when the number of species recorded does not increase with an additional transect). NOTE 2 Example of a survey strategy [3]: A minimum of 4 transects are surveyed for each land-use type around the lake. Additional transects within each land-use type are surveyed if – when surveying the 4th transect – the SSN has not been reached for that land-use type, or if there is a marked variation in abundance of one or more species. If the land-use type occurs in other areas around the lake, then only one transect is required at each of these additional areas, provided the SSN is still met (otherwise the basic requirement of a minimum of 4 transects applies). Transects can be of varying widths and lengths (usually 1 m to 5 m in width) but this should be standardised as far as possible, particularly when comparing lakes that are defined as having the same or very similar hydromorphological characteristics. It is recommended that each transect surveyed is the same in terms of its width as for the corresponding reference site. However, as with river aquatic macrophyte surveying (see EN 14184), much of the data can be compared directly by mathematical scaling. The start point for a transect is at the shoreline from the highest water level (as demarcated by the litter line, which can be several metres from the water’s edge) and from here the transect runs perpendicular to the shore. GPS or a compass can be used to fix the direction of the transect. In smaller lakes visual landmarks can be helpful in fixing the transect direction. Each transect should be surveyed to the depth at which no further plant growth occurs, where possible, confirming this by the use of divers or drop cameras. In very shallow lakes (< 3 m mean depth) there may not be a defined end to the aquatic macrophyte colonisation area. Alternative strategies that may be considered include setting a maximum length to the belt transect, surveying across the entire width of the lake (suitable for smaller lakes) or applying the principle of stopping observations when no new taxa are identified. The latter approach will not establish the depth limit of plant colonisation or the extent of the macrophyte beds to be determined, which are important parameters. 6.6 Timing of initial and subsequent surveys As far as possible, macrophyte surveys of lakes should be undertaken between late Spri

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