Does fine sediment source as well as quantity affect salmonid embryo mortality and development?

Area of Science:

• Environmental Science
• Aquatic Ecology
• Fisheries Science

Background:

• Fine sediments negatively impact benthic spawning fish, primarily studied via sediment quantity in egg pockets.
• Emerging evidence highlights the importance of sediment source and post-hatch alevin fitness.

Purpose of the Study:

• To investigate the independent and combined effects of fine sediment quantity and source on brown trout (Salmo trutta) and Atlantic salmon (Salmo salar) incubation.
• To determine if sediment source influences alevin fitness beyond embryo mortality.

Main Methods:

• Simulated incubation environments for brown trout and Atlantic salmon embryos.
• Exposure to varying quantities of fine (<63 μm) sediment from four distinct sources: agricultural topsoils, damaged road verges, eroding river banks, and treated sewage.
• Assessment of embryo mortality and post-hatch alevin fitness.

Main Results:

• Both sediment mass and source significantly influenced alevin mortality and fitness, acting independently.
• Brown trout exhibited greater tolerance to sediment mass and source compared to Atlantic salmon.
• Sediment source's impact is linked to organic matter content and catchment oxygen consumption.

Conclusions:

• Sediment source is a critical, previously underestimated factor in fine sediment's impact on fish reproduction.
• Management strategies should consider sediment source characteristics, not just quantity, to mitigate ecological impacts.
• Understanding catchment processes influencing sediment composition is key to protecting sensitive fish populations.