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 that they deliver the desired improvements in biological condition.
Hydrochemical data provided by a network of high‐frequency (15 or 30 min) automated monitoring stations over 3 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 1–90 days before 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.
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 resulting from one stressor frequently lead to confounding effects on stressor‐specific indices.
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.
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.
Detrimental impacts of excessive fine‐grained sediment inputs to streams and rivers are well established. What is less well understood is the susceptibility of different elements of the freshwater ...biota to such perturbations and how such knowledge of their susceptibility could aid in identifying where excessive fine‐grained sediment is impairing ecological condition. Following the collection of biological and sediment data from 179 streams across England and Wales, representative of a range of river types over a gradient of fine sediment loading, objective statistical approaches were applied to establish relationships between the macroinvertebrate assemblage and fine‐grained sediment inputs to river channels. Having factored out that portion of the biological variation associated with natural environmental gradients, a model comprising mass of organic sediment in erosional areas of the stream bed predominantly associated with the first axis of the partial canonical correspondence analysis (pCCA), and mass of fine‐grained sediment in the surface drape of depositional areas and % organic content in erosional areas (associated with the second axis of the pCCA) as explanatory variables best accounted for the residual variation in the macroinvertebrate assemblage. The relative position of taxa along both axes of the pCCA, provided a ranking of taxa in relation to the two gradients of fine‐grained sediment and provided the basis for a new empirically derived diagnostic index for fine‐grained sediment stress in rivers. Two sub‐indices were derived to capture the assemblage responses to both the gradient of organic sediment in erosional areas and the gradient of total fines in depositional areas. The two sub‐indices were then combined to derive the new combined fine sediment index (CoFSIₛₚ). The index was tested on an independent test data set (comprising 127 samples from 83 sites) and was found to provide a robust indication of benthic fine‐grained sediment conditions (Spearman's rank correlations ρ = −0.519 to −0.703). The strength of correlation with the total fine‐grained sediment gradient was always greater than that for other routinely used indices, confirming that CoFSIₛₚ offered additional explanatory power when assessing this stressor of aquatic environments.
1. Improved water quality, through a reduction in diffuse pollution from agricultural sources, is an expected benefit of agri-environment schemes, but this has yet to be demonstrated in practice. ...Here, we evaluate the impact of Welsh agri-environment schemes on water quality and freshwater ecosystem condition through a combined monitoring and modelling framework. 2. To determine the influence of the agri-environment schemes on ecosystem condition, spatially independent catchments dominated by a single scheme (>40% of catchment) were compared to control catchments dominated (>70%) by agricultural land that was not part of any scheme. Biological indicators of water quality were monitored at the outfall of each catchment and a spatially explicit modelling framework of diffuse pollutant emissions applied to each of the 80 catchments. 3. Direct comparison (scheme/non-scheme) was unable to identify any significant effect of agri-environment scheme participation. However, derived biological indicators that reflected organic pollution, eutrophication and pesticide run-off were strongly correlated with modelled concentrations of corresponding diffuse pollutants, thus providing a ground-truth for the models. Scenarios that assessed the correct counterfactuals (i.e. the influence of scheme entry on pollutant output) were developed for the whole of Wales. The models indicated an important effect of scheme entry on water quality, but this effect was not evenly distributed across the landscape. 4. Synthesis and applications. Our results indicate that agri-environment schemes can deliver improvements in water quality, through a reduction in diffuse pollution from agricultural sources. However, it is not easy to demonstrate scheme effectiveness; the combination of field survey and modelling used here provides a framework for addressing these difficulties. A spatially targeted approach for agri-environment scheme options to protect water resources from diffuse pollution is likely to be most effective at delivering water quality improvements.
Twelve sites of tyre track pools and puddles situated in woodland, heath and pasture in Dorset UK were examined to determine their macroinvertebrate species richness and community changes over the ...course of one year.
174 taxa were found with Diptera (59) and Coleoptera (48) contributing 61% of the total. The most frequently occurring and ubiquitous groups were nematoceran dipterans, Oligochaeta, Coleoptera, Crustacea and Lamellibranchiata.
Species richness varied with season and on average was highest in March and November samples. On average only 26% (range 16–40%) of the combined total number of taxa found in spring (March) and autumn (November) samples from a site were also found there in each of these seasons individually, indicating a high species turnover through the year.
The tyre track pools contributed to local aquatic biodiversity by adding 29 taxa to previously published taxa lists from aquatic habitats in the area. The relative richness of the tyre track pools is attributed to their successional variation in a heterogeneous landscape.
Conservation value of 9 of the 12 sites was rated Very high to High and nine regionally notable or rare taxa were recorded. It is suggested that the important conservation status of the tyre track pools warrants greater recognition and further intensive study.
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