Question

SEP Construct an Explanation Salinity affects the species that live in each area. Suggest what effect the formation of the brine pool might have on the organisms living on the lakebed.

Answer 1

Claim: The formation of a dense brine pool on the lakebed will reduce the number and types of animals and plants there and shift the community toward salt‑tolerant and anaerobic microorganisms.

Evidence and reasoning:
- Salinity directly stresses organisms because they must regulate internal water and ion balance. Freshwater fish, most benthic invertebrates, and many algae cannot survive sudden, sustained high salinity — their cells lose water, enzymes malfunction, and osmoregulatory organs fail. Those species will die off or move away.
- Brine is very dense and will sink to the bottom, creating a sharply saline layer that limits mixing with overlying, fresher water. That stratification also limits oxygen transport to the lakebed, producing hypoxic or anoxic conditions.
- Anoxic, high‑salt conditions favor halotolerant and halophilic microbes (salt‑loving bacteria and archaea) and anaerobic metabolisms (sulfate reduction, methanogenesis). These microbes can form dense mats or biofilms and change nutrient and sulfur chemistry (for example producing H2S), which is toxic to many aerobic organisms.
- Some organisms adapted to hypersaline environments (e.g., certain brine shrimp, halophilic algae, extremophile bacteria/archaea) may increase in abundance, but overall species richness and the original food‑web structure on the lakebed will decline.

Predicted consequences (short and long term):
- Short term: mortality of sensitive benthic fauna, temporary increases in scavengers at the brine margin, formation of strong salinity and oxygen gradients.
- Long term: collapse or reorganization of the original benthic community, dominance by salt‑tolerant microorganisms and a simpler food web, altered nutrient cycling and possible production of toxic compounds (H2S).

How to test this explanation:
- Measure salinity, temperature, and dissolved oxygen profiles from surface to lakebed before and after brine formation.
- Monitor species composition and abundance of benthic invertebrates, fish (if present), algae, and microbes over time.
- Analyze chemical indicators of anaerobic microbial activity (sulfide, methane, sulfate reduction rates).

Summary: The brine pool will likely kill or drive away most freshwater benthic organisms, create anoxic, salty conditions on the lakebed, and favor halophilic and anaerobic microbes, reducing biodiversity and altering ecosystem functions.