Does nutrient enrichment decouple algal-bacterial production in periphyton? part II: Evidence from experimental streams

Experimental streams were used to explore the coupling between periphytic algal and bacterial production. Twelve artificial streams received low nutrient water from a nearby created wetland and appropriate dosing with NaH₂PO₄ to establish three experimental phosphorus (P) levels: 1. low P (background ≈ 8 µg/L PO₄-P), 2. medium P (background + 20 µg/L PO₄-P), and 3. high P (background + 100 µg/L PO₄-P). Each P level was replicated in four experimental streams. Rocks with intact periphyton were collected from nutrient poor (Rocky Creek = RC) and nutrient rich (North Bosque) streams in central Texas and transplanted into all experimental streams. Experimental conditions were maintained 28 days. At the end of that time, periphyton photosynthesis (PS) and bacterial biomass production (BBP) were measured simultaneously using a dual-label radioassay (¹⁴C-HCO₃– uptake and ³H-L-leucine incorporation into protein). PS and BBP were measured after light and dark incubations. The degree of coupled production between algae and bacteria within a stream was estimated as the covariation (i.e., correlation or covariance) between PS and BBP derived from unshaded replicates in each stream. Preliminary results indicate that decoupling may occur with increased P, but may also depend on the legacy of P content in periphyton.