Flow Reduction in a Pesticide-Exposed Stream Mesocosm Affects Emerging Aquatic Insects and Alters Riparian Spider...

Area of Science:

• Ecology
• Environmental Science
• Hydrology

Background:

• Water scarcity impacts aquatic ecosystems by reducing streamflow, altering habitats, and increasing pollution.
• The effects of reduced streamflow on sediment pesticide concentrations and subsequent impacts on aquatic insect emergence and riparian spider communities are not well understood.

Purpose of the Study:

• To investigate the effects of simulated low-flow conditions on pesticide concentrations in stream sediments.
• To assess the influence of streamflow reduction on aquatic insect emergence and riparian spider abundance and community composition.

Main Methods:

• A 39-day mesocosm experiment with 12 artificial streams in Southwest Germany.
• Streams were randomly assigned to low-flow (0.4 L s⁻¹) or control (1 L s⁻¹) treatments.
• Sampling included daily water, weekly emerging insects, and bi-weekly sediment and riparian spider assessments.

Main Results:

• Sediment pesticide concentrations showed a slightly stronger increase from week 4 to week 6 under low-flow, but differences were not statistically significant due to high variability.
• Low flow significantly reduced the abundance of Ephemeroptera, Plecoptera, and Trichoptera (EPT) by 2.9-fold.
• While overall emerging insect and spider abundance were not significantly affected, the web-building spider Tetragnatha sp. decreased by 2.6-fold, while ground-hunting Lycosidae remained unaffected.

Conclusions:

• Hydrological alterations, such as streamflow reduction, can have complex cross-ecosystem effects, impacting both aquatic and terrestrial communities.
• The decline in EPT abundance and specific spider groups highlights the sensitivity of certain species to altered flow regimes in contaminated environments.
• Ecological impact assessments of hydrological changes must consider cascading effects between aquatic and riparian ecosystems, especially in polluted waters.