Stream Insects Face Instability and Synchrony Due to Climate-Driven Warmer, Wetter Winters

Climate change is causing warmer and wetter winters in the UK, which may have negative impacts on the insect populations in streams.

A long-term study by Cardiff University has shown that stream insects are affected by the fluctuations of the North Atlantic Oscillation, a large-scale atmospheric pressure system that influences the weather patterns over the Atlantic region.

The study, which spanned four decades, revealed that warm and wet winters led to bigger changes in insect populations that were synchronized across 10 streams in Wales.

These effects reduced the diversity and stability of the insect communities, which are important for the functioning of freshwater ecosystems.

The effects of the North Atlantic Oscillation on stream insects

(Photo : ROSLAN RAHMAN/AFP via Getty Images)

The North Atlantic Oscillation (NAO) is a phenomenon that describes the difference in air pressure between two regions over the Atlantic Ocean: the Icelandic Low and the Azores High.

Depending on the pressure difference, the NAO can be either positive or negative.

A positive NAO means that the pressure difference is large, which results in stronger westerly winds that bring warm and moist air to northwestern Europe. Meanwhile, a negative NAO means that the pressure difference is small, which results in weaker westerly winds that bring cold and dry air to the region.

The NAO affects the climate and weather of the UK, especially in winter.

According to the researchers, the NAO can change the average temperature in upland Wales by up to 3°C and the rainfall by up to 40%.

These changes are similar to the projected effects of climate change, which makes the NAO a useful indicator of how global warming may affect the UK's rivers.

The researchers used data from the Llyn Brianne Stream Observatory, one of the longest-running catchment projects in the world, to investigate how the NAO influenced stream insect populations.

The observatory consists of 10 streams that originate from the Llyn Brianne reservoir in central Wales.

The streams have been sampled for water quality, flow patterns, temperature, and insect species since 1981.

The researchers found that the NAO had a significant effect on the stream insect populations over the years of the study.

They observed that warm and wet winters, which occurred more frequently during positive NAO phases, led to higher variability and synchrony in insect abundance and biomass across the 10 streams.

This means that the insect populations changed more drastically and in the same direction in response to the climatic conditions.

The researchers also found that the insect communities became less similar and more unstable between warmer years, which implies that the diversity and resilience of the stream ecosystems were reduced.

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The implications of the study for freshwater conservation

The study has important implications for the conservation and management of freshwater ecosystems, which are facing multiple threats from human activities and climate change.

Stream insects are vital for the functioning of freshwater ecosystems, as they provide food for fish and other animals, decompose organic matter, cycle nutrients and regulate water quality.

They are also sensitive indicators of environmental change, as they respond quickly to changes in water temperature, flow, chemistry and habitat.

The researchers suggested that the effects of the NAO on stream insects may have cascading effects on other aspects of the stream ecosystems, such as fish populations, food webs and nutrient cycling.

They also warned that the effects of the NAO may interact with other stressors, such as pollution, land use change, invasive species and disease, to further degrade the stream ecosystems.

The researchers called for more research and monitoring to understand the mechanisms and consequences of the NAO effects on stream insects and other freshwater organisms.

They also recommend that freshwater conservation and management strategies should consider the effects of the NAO and climate change on stream ecosystems, and adopt adaptive and flexible approaches to cope with the uncertainty and variability of the future climate.