Investigation of the Relationship Between the LIFE Index and RIVPACS
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Investigation of the relationship between the LIFE index and RIVPACS Putting LIFE into RIVPACS R&D Technical Report W6-044/TR1 R T Clarke, P D Armitage, D Hornby, P Scarlett & J Davy-Bowker CEH Dorset Publishing Organisation Environment Agency, Rio House, Waterside Drive, Aztec West, Almondsbury, Bristol BS32 4UD Tel: 01454 624400 Fax: 01454 624409 Website: www.environment-agency.gov.uk © Environment Agency 2003 June 2003 ISBN : 1844321495 All rights reserved. No part of this document may be produced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without the prior permission of the Environment Agency. The views expressed in this document are not necessarily those of the Environment Agency. Its officers, servants or agents accept no liability whatsoever for any loss or damage arising from the interpretation or use of the information, or reliance upon the views contained herein. Dissemination status Internal: Released to Regions External: Public Domain Statement of Use This report examines the potential for RIVPACS to enable standardisation of LIFE scores between sites in order to then estimate the relative severity of flow-related stress at a site. Keywords: LIFE; RIVPACS; Biological monitoring; macroinvertebrates; low flows; slow flows; ecological stress; Catchment Abstraction Management Strategies (CAMS); Resource Assessment and Management (RAM) Framework Research Contractor This document was produced under R&D Project W6-044 by : CEH Dorset, Winfrith Technology Centre, Winfrith Newburgh, DORCHESTER, Dorset DT2 8ZD Tel : 01305 213500 Fax : 01305 213600 Environment Agency Project Manager The Environment Agency’s Project Manager for R&D Project W6-044 was Doug Wilson, Head Office, Bristol. Further copies of this report are available from: Environment Agency R&D Dissemination Centre WRc, Frankland Road, Swindon, Wilts. SN5 8YF Tel: 01793 865000 Fax: 01793 514562 E-mail: [email protected] R&D Technical Report W6-044/TR1ii ACKNOWLEDGEMENTS The authors are grateful to Terry Marsh and Felicity Sanderson of CEH Wallingford for providing the flow gauging station data. It has been a pleasure to work with Doug Wilson, the Environment Agency’s manager for this R&D project. Many useful comments on an earlier draft were provided by the Project Board members and others, notably Doug Wilson, Chris Extence, Richard Chadd, Alice Hiley, John Murray-Bligh, Philip Smith, Juliette Hall, Stuart Homann and Brian Hemsley-Flint. R&D Technical Report W6-044/TR1iii R&D Technical Report W6-044/TR1iv EXECUTIVE SUMMARY In the UK, there are competing demands for both surface and groundwater resources. Sustained or repeated periods of low flows and/or slow flows are expected to impact on the plant and animal communities within rivers. To assess the potential impact of flow-related stresses on lotic macroinvertebrate communities, Chris Extence and colleagues from Anglian Region of the Environment Agency developed the Lotic-invertebrate Index for Flow Evaluation (LIFE). Extence et al. (1999) showed that for several individual sites, temporal variation in LIFE could be correlated with recent and preceding flow conditions. RIVPACS (River InVertebrate Prediction And Classification System), developed by CEH, the Environment Agency and their predecessors, is the principal methodology currently used by the UK government environment agencies to assess the biological condition of UK rivers. RIVPACS assesses biological condition at a site by comparing the observed macroinvertebrate fauna with the fauna expected at the site if it is unstressed and unpolluted, as predicted from its environmental characteristics. Biological condition is estimated currently using two Ecological Quality Indices (EQI) represented by the ratio (O/E) or observed (O) to expected (E) values of the number of Biological Monitoring Working Party (BMWP) taxa present and the ASPT (Average Score Per Taxon), denoted by EQITAXA and EQIASPT respectively. LIFE is based on the same macroinvertebrate sampling procedures as RIVPACS. In this R&D project, an assessment was made of the potential to use the RIVPACS reference sites and methodology to standardise LIFE across all physical types of site, as a ratio of observed to expected LIFE, denoted LIFE O/E. LIFE O/E then provides a standardised estimate of the severity of the impacts of any flow-related stress on the macroinvertebrate fauna at a site. The Environment Agency intend to use expected LIFE calculated using RIVPACS and LIFE O/E to determine the macroinvertebrate component in the Environmental Weighting (EW) system being developed within their Resource Assessment and Management (RAM) Framework for abstraction licensing and water resource assessments for Catchment Abstraction Management Strategies (CAMS). CEH have derived a numerical algorithm to provide predictions of the expected LIFE for any river site based on its values for the standard RIVPACS environmental predictor variables. This algorithm is compatible with the derivation of expected ASPT, gives appropriate lower weighting to taxa with lower expected probabilities of occurrence and hence should be used in preference to the current LIFECALCULATOR method. It is recommended that this new algorithm is incorporated into an updated Windows version of the RIVPACS software system to provide automatic calculation of observed LIFE, expected LIFE and hence LIFE O/E for any macroinvertebrate sample and river site. All analyses were based on family level log abundance category data from single season samples. The relative merits of using the minimum or average values of single season LIFE O/E or combined season sample LIFE O/E for annual assessments of flow related stress at a site need further investigation. Natural sampling variability alone can cause lower minimum values. An agreed standard method is needed for combining abundance category data for R&D Technical Report W6-044/TR1v historical samples (i.e. pre- 2002) to enable sites assessments for future samples to be compared with historical data to estimate changes and trends. Seventy percent of the total variation in LIFE across all the high quality RIVPACS reference sites was explained by differences between the biological groupings of sites formed in the development of RIVPACS; this explanatory power was as high as for ASPT. Amongst these high quality unstressed sites, observed LIFE was correlated with the physical characteristics of a site. LIFE was positively correlated with site altitude and slope and the percentage substratum cover of boulders and cobbles; it was negatively correlated with stream depth and in-stream alkalinity and the percentage cover of sand and fine silt or clay sediment. When based on its standard suite of environmental predictor variables, RIVPACS predictions of expected LIFE were very effective overall, with correlations between observed life and expected LIFE of 0.78 for the 614 RIVPACS reference sites. Expected LIFE can vary between 5.93 and 7.92. LIFE O/E was centred around unity for the RIVPACS reference sites, with a small standard deviation of 0.056, less than the equivalent standard deviation for EQIASPT. Observed and expected LIFE should be recorded to two decimal places and LIFE O/E to three decimal places. Variation in observed LIFE and LIFE O/E was assessed for over 6000 of the biological sites sampled in the 1995 General Quality Assessment (GQA) national survey. These sites covered a very wide range of types and biological quality of site, including some which had been impacted by varying degrees of flow-related stress. Although observed LIFE ranged from 4.60 to 9.45, 90% of GQA sites had values in the narrow range 5.91-7.85. A provisional six grade system for LIFE O/E was developed based on the frequency distributions of values of LIFE O/E for the high quality reference sites and the wide ranging GQA sites. The lower limits for the grades were set at 1.00, 0.97, 0.93, 0.88 and 0.83; the lower limit of 1.00 for the top grade was chosen to give compatibility with the GQA grading system based on EQIASPT. The LIFE and ASPT indices are naturally correlated to some extent; macroinvertebrate families which require fast flowing conditions tend to also be susceptible to organic pollution, and vice versa. However, amongst the GQA sites the correlation between LIFE O/E and EQIASPT is only 0.69; the correlation between LIFE O/E and EQITAXA is only 0.39. The LIFE and GQA grades for the GQA sites were cross-compared. The LIFE and BMWP scoring systems do not appear to be completely confounded; suggesting that it may be possible to use the biota to differentiate flow-related stress from organic dominated stress. However, the apparent lack of agreement in site assessments using the two scoring systems must be at least partly due to the effects of sampling variation on both sets of O/E ratios. This will be correlated variation as the O/E ratios for a site are all calculated from the same sample(s). Further research is needed urgently to assess the influence of sampling variation on the observed relationship between LIFE O/E and EQIASPT and thus the extent to which they can be used to identify different forms of stress. R&D Technical Report W6-044/TR1vi The sensitivity of RIVPACS predictions of expected LIFE to flow related characteristics at a site was assessed by simulating alterations to stream width, depth, discharge category and substratum composition. Within a site type, realistic changes led to relatively small changes, usually less than 0.3, in expected LIFE. This suggest that RIVPACS predictions of expected LIFE are robust and mostly vary with the major physical types of site. Ideally, the RIVPACS predictions of the ‘target’ or expected LIFE, should not involve variables whose values when measured in the field may have already been altered by the flow-related stresses whose effects LIFE O/E is being used to detect.