Effect of N and P enrichment on periphytic algal community succession in a tropical oligotrophic reservoir

This enrichment experiment was conducted to evaluate how nutrient availability drives colonization and succession of a periphytic algal community in a Brazilian tropical oligotrophic reservoir. Four treatments were designed using enclosures (n = 3): control (no nutrient addition), P+ (isolated phosphorus addition, N-limiting condition); N+ (isolated nitrogen addition, P-limiting condition), and NP+ (phosphorus and nitrogen combined addition, no limitation). Glass microscope slides were used for periphyton growth. Samplings were carried out at short, regular intervals (3-5 days) over 31 days. Isolated P addition promoted the highest structural organization, and both NP+ and P+ promoted the highest biomass accrual. Control condition favored Chromulina elegans (chrysophyte) dominance, whereas enrichment favored different species descriptors belonging mainly to cyanobacteria (N+) and green algae (P+, NP+). Phosphorus was the main environmental driver in the community structural changes. All periphyton attributes were significantly affected by enrichments in the advanced successional stages, when species were strongly associated to different amendments. Periphytic algal community was quite sensitive to enrichments, allowing identification of successional sequences in each treatment; however, colonization time is relevant when monitoring strategies are considered.