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LTDI [id:]

Method: Lake Trophic Diatom Index Method [Lake Trophic Diatom Index Method]

1. General information

1.01 GIG: Central-Baltic, Northern
Relevant intercalibration types:
Not intercalibrated to date. Environment Agency, England & Wales is planning a package of work, for UK experts to lead on IC of Diatoms in Lakes, across GIG?s. Martyn Kelly to lead. From December 2009 to review what diatom methods types of lakes data
1.02 Category: Lakes
1.03 BQE: Benthic Diatoms
1.04 Country: United Kingdom
1.05 Specification: none
1.06 Method name: Lake Trophic Diatom Index Method
1.07 Original name: Lake Trophic Diatom Index Method
1.08 Status: Method is/will be used in First RBMP (2009), Second RBMP (2015)
1.09 Detected pressure(s):
Eutrophication, General degradation Specification of pressure-impact-relationship:
Yes, with quantitative data (e.g. against range of sites reflecting continuous gradient). Relationships between LTDI score and the pressure metrics Chlorophyll a, SRP, TP, Total Oxidised Nitrogen and Total Nitrogen were tested from c200 lakes. Significant relationships were found for TP and TN, type specific r2 values ranged from 0.48-0.69, no significance was found in low alkalinity lakes. Full data have been presented in: Use of diatoms for evaluating ecological status in UK freshwaters. SCO301030/SR1 Environment Agency, 2007 and in Kelly et al., 2008. Assessment of ecological status in U.K. rivers using diatoms. Freshwater Biology 53: 403-422.
Pressure-impact-relationship:
Yes, with quantitative data (e.g. against range of sites reflecting continuous gradient of pressure).
1.10 Internet reference:
http://www.wfduk.org/bio_assessment/bio_assessment/river%20phytobenthos%20method%20statement
1.11 Pertinent literature of mandatory character:
Water Framework Directive - United Kingdom Advisory Group (WFD-UKTAG) (2008 UKTAG lake assessment methods. macrophytes and phytobenthos phytobenthos - diatom assessment of lake ecological quality (DARLEQ1).
http://www.wfduk.org/bio_assessment/bio_assessment/lakes_phytobenthos_darleq
Use of diatoms for evaluating ecological status in UK freshwaters. Environment Agency report, 2007. SCO301030/SR1.
Environment Agency England & Wales use these operational instructions and National
Standards (regularly reviewed):
EA Ref. No. 027_07 Sampling diatoms from rivers and lakes
EA Ref. No. 087_07 Fixing phytoplankton and diatom samples with Lugol's iodine
EA Ref. No. 028_07 Diatom sample digestion and slide preparation
EA Ref. No. 029_07 Diatom slide analysis, recording and archiving
EA Ref. No. 198_07 Quality Assurance Scheme for diatom samples
EA Ref. No. 387_09 Interpreting and reporting freshwater ecology data
1.12 Scientific literature:
Kelly, M.G., L. King, G. Clarke, H. Bennion & M. Yallop, 2006. Recommendations for sampling littoral diatoms in lakes for ecological status assessments. Journal of Applied Phycology 18: 15-25.
Kelly, M.G., S. Juggins, H. Bennion, A. Burgess, M. Yallop, H. Hirst, L. King, B.J. Jamieson, R. Guthrie & B. Rippey, 2007. Use of diatoms for evaluating ecological status in UK freshwaters. Environment Agency Report SC030103/SR.
Kelly et al., 2008. Assessment of ecological status in U.K. rivers using diatoms. Freshwater Biology 53: 403?422.
Kelly, M.G., L. King, R. Jones, P. Barker & B.J. Jamieson, 2008. Validation of diatoms as proxies for phytobenthos when assessing ecological status in lakes. Hydrobiologia 610: 125-129.
Kelly, M.G., H. Bennion, A. Burgess, J. Ellis, S. Juggins, R. Guthrie, B.J. Jamieson, V. Adriaenssens & M. Yallop, 2009. Uncertainty in ecological status assessments of lakes and rivers using diatoms. Hydrobiologia 633: 5- 15.
Yallop, M., H. Hirst, M. Kelly, S. Juggins, B.J. Jamieson & R. Guthrie, 2009. Validation of ecological status concepts in UK rivers using historic diatom samples. Aquatic Botany 90: 289-295.
Kelly et al., 2008. Assessment of ecological status in U.K. rivers using diatoms. Freshwater Biology 53: 403?422.
Kelly, M.G., H. Bennion, A. Burgess, J. Ellis, S. Juggins, R. Guthrie, B.J. Jamieson, V. Adriaenssens & M. Yallop, 2009. Uncertainty in ecological status assessments of lakes and rivers using diatoms. Hydrobiologia 633: 5- 15.
Kelly, M.G., L. King, G. Clarke, H. Bennion & M. Yallop, 2006. Recommendations for sampling littoral diatoms in lakes for ecological status assessments. Journal of Applied Phycology 18: 15-25.
Kelly, M.G., L. King, R. Jones, P. Barker & B.J. Jamieson, 2008. Validation of diatoms as proxies for phytobenthos when assessing ecological status in lakes. Hydrobiologia 610: 125-129.
Kelly, M.G., S. Juggins, H. Bennion, A. Burgess, M. Yallop, H. Hirst, L. King, B.J. Jamieson, R. Guthrie & B. Rippey, 2007. Use of diatoms for evaluating ecological status in UK freshwaters. Environment Agency Report SC030103/SR.
Yallop, M., H. Hirst, M. Kelly, S. Juggins, B.J. Jamieson & R. Guthrie, 2009. Validation of ecological status concepts in UK rivers using historic diatom samples. Aquatic Botany 90: 289-295.
1.13 Method developed by: Dr Martyn Kelly
Email of developer: MGKelly@bowburn-consultancy.co.uk
Institute of developer: Bowburn Consultancy
1.14 Method reported by: Jane Jamieson
Email of person reporting the method: jane.jamieson@environment-agency.gov.uk
Email of institute reporting the method: Environment Agency (EA)
1.15 Comments: none

2. Data acquisition

Field sampling/surveying

2.01 Sampling/Survey guidelines:
EN 13946, 2003. Water Quality ? Guidance Standard for the Routine Sampling and Pretreatment of Benthic Diatoms from Rivers.
Kelly, M.G., A. Cazaubon, E. Coring, A. Dell?Uomo, L. Ector, B. Goldsmith, H. Guasch, J. Hürlimann, A. Jarlman, B. Kawecka, J. Kwandrans, R. Laugaste, E.-A. Lindstrom, M. Leitao, P. Marvan, J. Padisak, E. Pipp, J. Prygiel, E. Rott, S. Sabater,H. van Dam & J. Vizinet, 1998. Recommendations for the routine sampling of diatoms for water quality assessments in Europe. Journal of Applied Phycology 10: 215-224.
King, L., G. Clarke, H. Bennion M.G. Kelly & M.L. Yallop, 2006. Recommendations for sampling littoral diatoms in lakes for ecological status assessments. Journal of Applied Phycology 18: 15-25.
Validation of diatoms as proxys for phytobenthos when assessing ecological status in lakes and "Sampling littoral diatoms in lakes for ecological status assessments: a literature review". EA Science reports:
Environment Agency England & Wales also uses these operational instructions and National Standards (regularly reviewed):
EA Ref. No. 027_07 Sampling diatoms from rivers and lakes
EA Ref. No. 087_07 Fixing phytoplankton and diatom samples with Lugol's iodine
EA Ref. No. 028_07 Diatom sample digestion and slide preparation
EA Ref. No. 029_07 Diatom slide analysis, recording and archiving
EA Ref. No. 198_07 Quality Assurance Scheme for diatom samples
EA Ref. No. 387_09 Interpreting and reporting freshwater ecology data
2.02 Short description:
In standing waters, if cobbles are the dominant littoral substratum, collect samples from cobbles.
If cobbles or small boulders are absent or the bed is dominated by fine sediments with only a few large stones, collect samples from submerged stems of emergent plants such as Phragmites australis, Sparganium erectum, Glyceria maxima or Typha spp. Phragmites australis is widespread in UK standing waters and should be used wherever possible.
To apply the method, samples of benthic diatom species should be collected by brushing or scraping the upper surface of cobbles or small boulders obtained from the littoral zones of lakes in order to remove the biofilm with a clean toothbrush. This passed to a tray with a little stream water. The resulting suspension collected in a plastic bottle, fixed with Lugol?s iodine and stored prior to analysis.
Where the bed of the lake is dominated by fine sediments, samples should be collected from submerged stems of emergent macrophytes such as Phragmites australis, Sparganium erectum, Glyceria maxima or Typha species.
The national standard method should be followed ? Environment Agency National Standard Ref. No. 027_07 Sampling diatoms from rivers and lakes. EN 13946 : 2003 Water quality ? Guidance standard for the routine sampling and pre-treatment of benthic diatoms from rivers.
2.03 Method to select the sampling/survey site or area:
Expert knowledge, Random sampling/surveying, Stratified sampling/surveying Other method to select the sampling/survey site or area:
The main requirement for a sampling site is that it is typical of the lake being assessed. Choose a section of shore that has suitable substrata for sampling and can be identified against a permanent physical feature so that we can easily recognise and re
2.04 Sampling/survey device:
Airlift sampler, Artificial substrate, Brush, Corer, Dredge, Dredge, Grab, Grapnel, Hand net, Multiple Opening/Closing Net and Environmental Sampling System (MOCNESS), Plankton net, Rake, Scraper, Spoon, Surber or Hess sampler, Water sampler
Other phytobenthos sampling device: Toothbrush
Any other sampling device: Toothbrush
2.05 Specification:
toothbrush, strong scissors, white plastic tray, wide-mouthed plastic sample bottles with watertight lids, waterproof permanent marker pen or another means of labelling samples, (house bricks with holes in, and polypropylene rope ? only if using introduce
2.06 Sampled/surveyed habitat:
Specification of sampled habitat:
Generally cobbles but other habitats when cobbles are not present. Sample habitat is chosen based on that which is appropriate for optimising the presence of diatoms at a site.
Sampled habitat: All available habitats per site (Multi-habitat)
2.07 Sampled/surveyed zones in areas with tidal influence: Intertidal zone
2.08 Sampling/survey month(s):
Great Britain (England, Wales and Scotland): Spring (May) and Autumn (September to end of November), Northern Ireland: Spring and Summer
2.09 Number of sampling/survey occasions (in time) to classify site or area:
At least six replicates are required within a three-year classification period to ensure 95% confidence of class at the middle of status classes.
2.10 Number of spatial replicates per sampling/survey occasion to classify site or area: 1
2.11 Total sampled/surveyed area or volume or total sampling duration to classify site or area:
If cobbles or small boulders are absent or the bed is dominated by fine sediments with only a few large stones, samples are collected from submerged stems of emergent plants such as Phragmites australis, Sparganium erectum, Glyceria maxim

Sample processing

2.12 Minimum size of organisms sampled and processed: n.a.
2.13 Sample treatment:
n.a.
2.14 Level of taxonomical identification:
Level: Species/species groups
Specification of level of determination: n.a.
2.15 Record of abundance:
Determination of abundance: Individual counts, Relative abundance
Abundance is related to: Area, Time, Volume
Unit of the record of abundance: n.a.
Other record of abundance: sampled 5 cobbles/small boulders free from algae
2.16 Quantification of biomass: n.a.
2.17 Other biological data:
Other photosynthetic organisms e.g. filamentous algae Cover of sewage fungus above and below stones, presence and density
2.18 Special cases, exceptions, additions: none
2.19 Comments: none

3. Data evaluation

Evaluation

3.01 List of biological metrics:
The LTDI is based on the weighted average equation of Zelinka and Marvan (1961).

WMS = Sum of (aj * sj) / Sum of aj
where aj is the abundance or proportion of valves of species j in sample; sj is the revised nutrient sensitivity class (1?5) of species j; WMS, the weighted mean score.
The second step was performed to present the TDI on a score ranging from 0 (very low nutrients) to 100 (very high nutrients).
3.02 Does the metric selection differ between types of water bodies: No
3.03 Combination rule for multi-metrics: Not relevant
3.04 From which biological data are the metrics calculated:
List of biological metrics: Aggregated data from multiple sampling/survey occasions in time

Reference conditions

3.05 Scope of reference conditions: Surface water type-specific
3.06 Key source(s) to derive reference conditions:
Scope of reference conditions:
Existing near-natural reference sites, Expert knowledge, Historical data
Other reference source: hindcasting methods, e.g. paleolimnology
3.07 Reference site characterisation:
Number of sites:
45 sites across Scotland, England and Wales and Northern Ireland were used to derive reference conditions for the method.
Geographical coverage: Scotland, England and Wales and Northern Ireland
Location of sites: Scotland, England, Wales
Data time period:
Reference sites were identified from Spr/Aut 2004-2006 Scottish sites also included 2003.
Criteria:
Derived using a number of methods including spatial state schemes, expert judgement and modelling. For the latter, hindcasting methods such as palaeolimnology (the study of the lake sediment record) are given as one such technique (Pollard and Huxham,1998; European Union, 2000).
In order to identify a set of reference sites to assist in tool development, a combination of the above methods were employed. One data source was the set of reference lakes identified in June 2005 by the phytoplankton classification project, following discussion with both SEPA and the Environment Agency, to support the development of a GB-calibrated morphoedaphic index model (MEI). The lakes are assumed to have no significant anthropogenic sources of phosphorus (P) and thus represent high status lakes in the context of their total P (TP) concentration. A second set of reference lakes was identified for the EU Rebecca project by the Centre for Ecology and Hydrology (CEH) based on an analysis of reference conditions for TP and chlorophyll a. This list is being used as a basis for the identification of intercalibration reference lakes for the Northern Geographical Intercalibration Group (GIG). A further set of high alkalinity reference lakes has been identified by the Central GIG on the basis that they have no point sources of P, < 10% non-natural land use and < 10 inhabitants km2. A list of the lakes used for each of the above purposes is documented in an Excel spread sheet (LTT_106a_GP_QRY_RefList_Mar06) and further details are given in TAG/LTT 106 (Phillips, 2006).
A further body of data for identifying potential reference lakes is the palaeoecological database held by the Environmental Change Research Centre (ECRC). Data were collated from all UK lakes where palaeoecological diatom studies have been undertaken.
3.08 Reference community description:
High relative abundance of Achnanthidium spp. (many sites also contained A. biasolettiana and/or A.microcephalum), attached taxa Gomphonema spp, and loosely-attached Fragilariophyceae (Fragilaria capucina was the most abundant, but Meridion circulare, Hannae arcus and Tabellaria flocculosa were all common at lower alkalinities), but few motile taxa. A few lower alkalinity sites were dominated by Achnanthes oblongella, and Cocconeis placentula was also abundant on some occasions.
3.09 Results expressed as EQR: Yes

Boundary setting

3.10 Setting of ecological status boundaries:
High-good boundary derived from metric variability at near-natural reference sites
Using paired metrics that respond in different ways to the influence of the pressure
3.11 Boundary setting procedure:
The procedure for defining the class boundaries follows that of the DARES approach for rivers, which has been successfully intercalibrated. The method is based on the approach for many UK classification methods set out in
Phillips et al., 2003. The assessment of ecological quality of lakes in the Great Britain Ecoregion: an update on thinking and a possible approach for phytoplankton. TeemaNord 547: 35-39.
The good/moderate boundary was determined as the point at which the proportion of nutrient sensitive and nutrient tolerant taxa intersect when plotted on an axis of decreasing EQR (increased impact). At this point both the reference and impact communities are represented and thus the impact community, considered to be undesirable, is not yet dominant. There were insufficient reference sites to determine the high/good boundary from the distribution of EQR from type specific reference sites. Thus a point approximately mid-way (position depended on lake type) between the good/moderate boundary and an EQR of 1 was selected. The remaining gradient moderate to bad was divided into 3 equal classes, although only a moderate/poor boundary is used in the final method as it was considered that the diatom method in isolation could not identify bad status as defined in the WFD normative definitions.
3.12 "Good status" community:
A. minutissimum, F. capucina, F. vaucheriae and N. dissipata were present in a majority of sites at 99.5%, 69.2%, 70.6% and 70.6% respectively, but the maximum relative abundance recorded was lower than in samples at high status (62.5%, 25.7%, 26.0% and 41.6% relative abundance respectively). Other species including G. parvulum, A. pediculus, Planothidium lanceolatum, Reimeria sinuata and motile species including N. gregaria, N. lanceolata, Navicula minima and N. dissipata were present in over 70% of all samples in this status class. Concerning these species the highest maximum of relative abundance was recorded for G. parvulum (61.4%).

Uncertainty

3.13 Consideration of uncertainty: Yes
Specification of uncertainty consideration:
The approach assumes that the estimated diatom EQR is normally distributed with a standard deviation that is a modelled function of EQR. Using the estimated standard deviation and number of samples collected we determine the confidence that the observed mean EQR lies within particular class boundaries. The approach follows that of Ellis (1990) (available at http://publications.environmentagency. gov.uk/epages/eapublications.storefront/4b100774024a67a6273fc0a802960648/Product/View/GEHO1006BLOR&2DE&2DE). The approach is described in chapter 6 of the report: Use of diatoms for evaluating ecological status in UK freshwaters (Environment Agency report SCO301030/SR1, 2007). In the chapter we address two questions: What is the uncertainty associated with a single sample as an estimate of ecological status on the day that the sample was collected? How well does this sample reflect the long-term average condition of the biology? These questions are addressed separately. The former uses a nested analysis of variance that examines variation in metrics associated with variability on a slide nested within variability at a site. No attempt has been made to separate (natural) spatial variability from variability introduced by the operator but the latter sources of error were minimised by use of standard methods. Errors associated with making slides are relatively small and differences between lakes and rivers are minor. If analysts adhere to protocols, one slide per sample is sufficient to estimate the taxonomic composition and derived indices from a sample. The variance between replicate samples taken at one time from one location in lakes was much smaller than in rivers. There is a large amount of temporal variation at single sampling locations in rivers and reliable indications of status class will need to be based on repeated sampling from the same location. Results suggest that at least six replicates (i.e. two per year for three years or three per year for two years) will be required in order to provide a firm basis for regulation. A sampling intensity greater than this might be at risk of ?pseudo-replication?. The risk of misclassification depends on the proximity of the mean EQR for a site to the status class boundary. When the EQR value is very close to the boundary, the risk of misclassification will be approximately 50%, regardless of the number of samples available.
3.14 Comments: none

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