A 20‐Year View of Monitoring Ecological Quality in English and Welsh Rivers

Ormerod

2012

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103

120

Rivers are among the world's most modified ecosystems, with poor water quality representing a prominent problem for over 200 years, especially in urban areas. In Western Europe, however, industrial decline, tighter regulation and improved wastewater treatment have combined over recent decades to create conditions conducive to extensive restoration and positive biological change. Here, we evaluate the river macroinvertebrate fauna of England and Wales in relation to water quality, physical habitat and climate over almost two decades. We predicted that biological recovery would be characterized by: (i) greater taxon richness and prevalence of pollution-sensitive taxa, (ii) larger changes in more heavily urbanized catchments, and (iii) temporal trends in assemblage structure that correlated with improving water quality. Family level richness increased on average by nearly 20% during 1991-2008, accompanied by a widespread shift towards taxa characteristic of well-oxygenated and less polluted waters. Changes were largest in the most urbanized catchments. A combination of natural gradients and anthropogenic pressures explained the variation among sites, whereas temporal changes correlated with improving water quality and variations in discharge. Positive trends were not universal, however, and there was localized deterioration in some streams draining upland areas and in the lowland south east. Our results are consistent with a large-scale ecological recovery of English and Welsh rivers since 1990, probably continuing a trend from the mid-20th century. Based on these results, we suggest: (i) freshwater communities are resilient to long-term anthropogenic pressures, (ii) biodiversity benefits can arise from investment and long-term restoration intended largely to enhance ecosystem services such as drinking water and sanitary concerns, and (iii) long-term monitoring data collected for statutory purposes-based in this case on nearly 50 000 samples-can address scientific questions at spatial and temporal extents seldom achieved in research programmes.

Section: Discussionmentioning

confidence: 99%

Large‐scale, long‐term trends in British river macroinvertebrates

Ormerod

2012

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103

120

“…Testing these ideas about climate change effects on field populations has, in the past, been restricted by a scarcity of basic ecological data. However, extensive data on benthic macroinvertebrates and water chemistry in UK rivers now offer a major opportunity to assess responses of stream organisms to warming in interaction with other stressors (Environment Agency, 2002;Vaughan & Ormerod, 2012a). These data suggest strong improvement in water quality over two decades (Vaughan & Ormerod, 2012b), and present an important opportunity to examine interaction with long-term climate warming over this time period (Durance & Ormerod, 2009).…”

Section: Introductionmentioning

confidence: 99%

Field and laboratory studies reveal interacting effects of stream oxygenation and warming on aquatic ectotherms

Verberk

Durance

et al. 2016

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118

Aquatic ecological responses to climatic warming are complicated by interactions between thermal effects and other environmental stressors such as organic pollution and hypoxia. Laboratory experiments have demonstrated how oxygen limitation can set heat tolerance for some aquatic ectotherms, but only at unrealistic lethal temperatures and without field data to assess whether oxygen shortages might also underlie sublethal warming effects. Here, we test whether oxygen availability affects both lethal and nonlethal impacts of warming on two widespread Eurasian mayflies, Ephemera danica, Müller 1764 and Serratella ignita (Poda 1761). Mayfly nymphs are often a dominant component of the invertebrate assemblage in streams, and play a vital role in aquatic and riparian food webs. In the laboratory, lethal impacts of warming were assessed under three oxygen conditions. In the field, effects of oxygen availability on nonlethal impacts of warming were assessed from mayfly occurrence in 42 293 UK stream samples where water temperature and biochemical oxygen demand were measured. Oxygen limitation affected both lethal and sublethal impacts of warming in each species. Hypoxia lowered lethal limits by 5.5 °C (±2.13) and 8.2 °C (±0.62) for E. danica and S. ignita respectively. Field data confirmed the importance of oxygen limitation in warmer waters; poor oxygenation drastically reduced site occupancy, and reductions were especially pronounced under warm water conditions. Consequently, poor oxygenation lowered optimal stream temperatures for both species. The broad concordance shown here between laboratory results and extensive field data suggests that oxygen limitation not only impairs survival at thermal extremes but also restricts species abundance in the field at temperatures well below upper lethal limits. Stream oxygenation could thus control the vulnerability of aquatic ectotherms to global warming. Improving water oxygenation and reducing pollution can provide key facets of climate change adaptation for running waters.

“…Long-term monitoring of river macroinvertebrates in the UK provides one such opportunity, with an extensive monitoring network covering thousands of rivers (Vaughan & Ormerod, 2012a). For many years, gross pollution from wastewater discharge was probably the major stressor of these rivers, but treatment has improved over recent decades while discharges from heavy industry have declined (Langford et al, 2009), resulting in large reductions in point-source pollution, especially in the vicinity of urban areas (Vaughan & Ormerod, 2012a; Figure S1). At the same time as urban water quality has improved, however, there has been evidence of a trend towards increasing water temperatures, at least until the mid-2000s (Ormerod & Durance, 2012; Figure S1).…”

Section: Introductionmentioning

confidence: 99%

“…Considering the importance of separating climatic effects from other potential stressors on river ecosystems, there is a need for long‐term studies so that the temporal variability in both organisms and environment can be captured, rates of change quantified and events (e.g., droughts) characterized (Jackson & Füreder, ). Long‐term monitoring of river macroinvertebrates in the UK provides one such opportunity, with an extensive monitoring network covering thousands of rivers (Vaughan & Ormerod, ). For many years, gross pollution from wastewater discharge was probably the major stressor of these rivers, but treatment has improved over recent decades while discharges from heavy industry have declined (Langford et al ., ), resulting in large reductions in point‐source pollution, especially in the vicinity of urban areas (Vaughan & Ormerod, ; Figure S1).…”

Section: Introductionmentioning

confidence: 99%

Linking interdecadal changes in British river ecosystems to water quality and climate dynamics

Ormerod

2014

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Macroinvertebrate communities in Western European rivers have changed substantially in recent decades. Understanding the causes is challenging because improvements in water quality have coincided with climatic variations over this period. Using data covering >2300 rivers and 21 years (1991-2011) across England and Wales, we analysed family-level distributions and nationwide trends in prevalence (proportion of sampling locations where an organism was present) to diagnose the causes of ecological change. Our aims were to: (i) reveal the taxa driving assemblage-level trends; (ii) identify the main changes in family-level prevalence and distribution patterns; and (iii) test whether changes were accounted for by improving water quality, increasing temperatures or variations in discharge. While previous analyses revealed increasing richness among British river invertebrates, a partial turnover of taxa is now evident. Two distinct components of temporal trend have comprised: (i) overall increases or decreases in taxon prevalence over 21 years, which correlated with pollution sensitivity and discharge; and (ii) short-term variations in prevalence that correlated primarily with temperature and nutrient concentrations. The longer-term changes in prevalence were reflected in expansions or contractions in families' distributions linked to water quality, with little evidence of shifts consistent with increasing temperatures. Although these monitoring data had limitations (e.g., family-level data, few headwaters), they provide no clear evidence of long-term climate effects on invertebrates; the one feature consistent with climate warming - a small northward expansion of the range of many taxa - was accounted for by large improvements in water quality in northern England. Nevertheless, changes linked to discharge and temperature over the shorter-term (<2 years) point to the climatic sensitivity of invertebrate communities. It is therefore likely that any long-term climatic changes since 1990 have been outweighed by the strength and geographical extent of the recovery from poor water quality.