Periphytic algae dynamics in lentic ecosystems in the Brazilian semiarid

Area of Science:

• Ecology
• Limnology
• Aquatic Ecology

Background:

• Hydrological periods are key drivers of aquatic community structure in semiarid regions.
• Periphyton, a community of algae, is sensitive to environmental changes and plays a crucial role in aquatic ecosystems.
• Understanding periphyton dynamics is vital for managing eutrophic water bodies, especially in water-scarce environments.

Purpose of the Study:

• To investigate the impact of hydrological periods on periphytic algal community structure in Brazilian semiarid eutrophic ecosystems.
• To test the hypothesis that decreased precipitation during dry periods favors periphytic algal development (richness and density).
• To identify the main factors influencing periphytic algal community dynamics, including hydrological periods, substrate type, and abiotic variables.

Main Methods:

• Field sampling of periphytic algae on macrophytes and rocks in three shallow, eutrophic ecosystems over a four-year period (2007-2010).
• Bi-monthly sampling intervals to capture seasonal variations.
• Simultaneous analysis of key abiotic variables (e.g., pH, nutrient concentrations, temperature, dissolved oxygen).

Main Results:

• Periphytic algal communities showed dominance shifts between diatoms, cyanobacteria, and chlorophytes across hydrological periods.
• Dry periods were characterized by alkaline waters, high nitrate and total phosphorus, favoring high densities of diatoms (Bacillariophyceae).
• Rainy periods exhibited warmer, oxygenated waters with high ammonia and soluble reactive phosphorus, where diatoms remained dominant but less dense, while cyanobacteria and chlorophytes increased.

Conclusions:

• Hydrological periods significantly altered the *dynamics* of periphytic algal communities, evidenced by class alternations, but not overall community composition.
• Ecosystem's morphometric, chemical, and physical characteristics were more influential on periphytic algal community dynamics than hydrological periods or substrate types.
• The findings highlight the complex interplay of factors regulating periphyton in semiarid aquatic ecosystems, suggesting broader ecosystem properties are critical for community structure.