Abstract
1. Monitoring programmes worldwide use biota to assess the ‘health’ of water bodies. Indices based on biota are used to describe the change in status of sites over time, to identify progress against management targets and to diagnose the causes of biological degradation. A variety of numerical stressor-specific biotic indices have been developed based on the response of biota to differences in stressors among sites. Yet, it is not clear how variation in pressures within sites, over what time period, and in what combination has the greatest impact on different biotic groups. An understanding of how temporal variation in pressures influences biological assessment indices would assist in setting achievable targets and help focus catchment-scale mitigation strategies to ensure they deliver the desired improvements in biological condition.
2. Hydrochemical data provided by a network of high-frequency (15 or 30 mins) automated monitoring stations over three years were matched to replicated biological data to understand the influence of spatio-temporal variation in pollution pressures on biological indices. Hydrochemical data were summarised in various ways to reflect central tendency, peaks, troughs, and variation over 1 to 90 days prior to the collection of each biological sample. An objective model selection procedure was used to determine which hydrochemical determinand, and over what time period, best explained variation in the biological indices.
3. Stressor-specific indices derived from macroinvertebrates which purportedly assess stress from low flows, excess fine sediment, nutrient enrichment, pesticides and organic pollution were significantly inter-correlated and reflected periods of low oxygen concentration, even though only one index (ASPTWHPT: Average Score Per Taxon) was designed for this purpose. Changes in community composition due to one stressor frequently lead to confounding effects on stressor-specific indices.
4. Variation in ASPTWHPT was best described by dissolved oxygen calculated as Q5 over 10 days, suggesting that low oxygen events had most influence over this period. Longer-term effects were apparent, but were masked by recovery. Macroinvertebrate abundance was best described by Q95 of stream velocity over 60 days, suggesting a slower recovery in numbers than in the community trait reflected by ASPTWHPT.
5. Although use of ASPTWHPT was supported, we recommend that additional independent evidence should be used to corroborate any conclusions regarding the causes of degradation drawn from the other stressor specific indices. The use of such stressor specific indices alone risks the mistargeting of management strategies if the putative stressor-index approach is taken to be more reliable than the results herein suggest.
2. Hydrochemical data provided by a network of high-frequency (15 or 30 mins) automated monitoring stations over three years were matched to replicated biological data to understand the influence of spatio-temporal variation in pollution pressures on biological indices. Hydrochemical data were summarised in various ways to reflect central tendency, peaks, troughs, and variation over 1 to 90 days prior to the collection of each biological sample. An objective model selection procedure was used to determine which hydrochemical determinand, and over what time period, best explained variation in the biological indices.
3. Stressor-specific indices derived from macroinvertebrates which purportedly assess stress from low flows, excess fine sediment, nutrient enrichment, pesticides and organic pollution were significantly inter-correlated and reflected periods of low oxygen concentration, even though only one index (ASPTWHPT: Average Score Per Taxon) was designed for this purpose. Changes in community composition due to one stressor frequently lead to confounding effects on stressor-specific indices.
4. Variation in ASPTWHPT was best described by dissolved oxygen calculated as Q5 over 10 days, suggesting that low oxygen events had most influence over this period. Longer-term effects were apparent, but were masked by recovery. Macroinvertebrate abundance was best described by Q95 of stream velocity over 60 days, suggesting a slower recovery in numbers than in the community trait reflected by ASPTWHPT.
5. Although use of ASPTWHPT was supported, we recommend that additional independent evidence should be used to corroborate any conclusions regarding the causes of degradation drawn from the other stressor specific indices. The use of such stressor specific indices alone risks the mistargeting of management strategies if the putative stressor-index approach is taken to be more reliable than the results herein suggest.
| Original language | English |
|---|---|
| Article number | FWB14106 |
| Pages (from-to) | 1330-1345 |
| Number of pages | 16 |
| Journal | Freshwater Biology |
| Volume | 68 |
| Issue number | 8 |
| DOIs | |
| Publication status | Published - 8 May 2023 |
Bibliographical note
Funding Information:The authors gratefully acknowledge the funding provided by Defra projects WQ0211 and LM0304 (the Hampshire Avon Demonstration Test Catchment programme), access to the sites kindly granted by the landowners, support in the installation and maintenance of the automated monitoring by Robin Hodgkinson, and access to the Brixton Deverill gauging site and flow data provided by Geoff Hardwicke at the Environment Agency. Rothamsted Research receives strategic funding from the UK Biotechnology and Biological Sciences Research Council (BBSRC) and work on this paper by ALC was supported by grant BBS/E/C/000I0330.
Funding Information:
The authors gratefully acknowledge the funding provided by Defra projects WQ0211 and LM0304 (the Hampshire Avon Demonstration Test Catchment programme), access to the sites kindly granted by the landowners, support in the installation and maintenance of the automated monitoring by Robin Hodgkinson, and access to the Brixton Deverill gauging site and flow data provided by Geoff Hardwicke at the Environment Agency. Rothamsted Research receives strategic funding from the UK Biotechnology and Biological Sciences Research Council (BBSRC) and work on this paper by ALC was supported by grant BBS/E/C/000I0330.
Publisher Copyright:
© 2023 The Authors. Freshwater Biology published by John Wiley & Sons Ltd.