Lotic Ecosystem Response to a Chlorine Disturbance

Area of Science:

• Ecology
• Environmental Science
• Aquatic Ecosystems

Background:

• Laboratory stream ecosystems were subjected to repeated chlorine additions to assess impacts.
• The study examined the influence of circulation regimes and grazer density on ecosystem responses.

Purpose of the Study:

• To investigate the resistance and resilience of stream ecosystems to repeated chlorine disturbances.
• To determine the effects of flow regime (once-through vs. recirculated) and snail density on ecosystem resistance and resilience.

Main Methods:

• A 2x2 factorial design was used with eight laboratory streams, manipulating circulation regimes and grazer (snail Elimia clavaeformis) densities.
• Chlorine was added repeatedly, and periphyton biomass, carbon fixation rates, and microbial activity were measured.

Main Results:

• Periphyton resistance to chlorine was greater in once-through streams and in streams without snails, attributed to higher biomass buffering.
• Ecosystem resilience was generally not affected by flow or snail density, but chlorophyll-specific carbon fixation and microbial activity showed greater resilience in recirculated streams with snails.
• Streams without snails and those with once-through circulation generally exhibited higher structural parameters and carbon fixation rates.

Conclusions:

• Periphyton mat physiognomy and integrity are crucial for ecosystem resistance (buffering capacity) and resilience (nutrient cycling).
• Chlorine concentrations below 1.0 mg/L can significantly alter periphyton structure and function.
• Nutrient cycling was minimally affected, allowing faster recovery in recirculated systems than anticipated.