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<p>Periphyton-mediated nutrient uptake in urban streams plays a critical role in regulating watershed-scale biogeochemical fluxes. However, the effects of urbanization-induced nutrient loading and light regime shifts on this process remain poorly quantified. Using controlled microcosm experiments with naturally colonized epilithic periphyton from two urban headwater streams (open-canopied and canopied), we examined short-term (7-hour daytime incubation) nutrient uptake responses to elevated ambient concentrations of soluble reactive phosphorus (SRP), ammonium (AN), and nitrate (NN), as well as variable light intensities (open and shaded conditions). We found that proportional increases (1- and 3-fold) in background water column nutrient concentrations or abrupt alterations in light conditions had minimal impacts on overall periphyton nutrient uptake. However, our results indicated a significant positive correlation between the uptake rates of SRP and AN by periphyton and algal biomass. In contrast, the NN uptake rate exhibited an inverse relationship with algal biomass. Furthermore, random forest analysis results revealed that, in the nutrient enrichment experiment, the ambient AN concentration was the most crucial predictor for periphyton SRP and NN uptake. Meanwhile, the autotrophic index (the ratio of ash-free dry weight to chlorophyll-<i>a</i> content) exerted the greatest influence on periphyton AN uptake. In contrast, within the light control experiment, the ambient concentration emerged as the most preponderant factor affecting the nutrient uptake of periphyton. These findings advance the mechanistic understanding of periphyton nutrient cycling under pulsed urban stressors and heterogeneous light environments.</p>

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Limited effects of short-term nutrient enrichment or abrupt light changes on daytime periphyton nutrient uptake in urban streams

  • 期刊论文

  • 发表日期：

    2025年6月25日

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  • Yang Fu,
  • Ruzhong Li

摘要

Periphyton-mediated nutrient uptake in urban streams plays a critical role in regulating watershed-scale biogeochemical fluxes. However, the effects of urbanization-induced nutrient loading and light regime shifts on this process remain poorly quantified. Using controlled microcosm experiments with naturally colonized epilithic periphyton from two urban headwater streams (open-canopied and canopied), we examined short-term (7-hour daytime incubation) nutrient uptake responses to elevated ambient concentrations of soluble reactive phosphorus (SRP), ammonium (AN), and nitrate (NN), as well as variable light intensities (open and shaded conditions). We found that proportional increases (1- and 3-fold) in background water column nutrient concentrations or abrupt alterations in light conditions had minimal impacts on overall periphyton nutrient uptake. However, our results indicated a significant positive correlation between the uptake rates of SRP and AN by periphyton and algal biomass. In contrast, the NN uptake rate exhibited an inverse relationship with algal biomass. Furthermore, random forest analysis results revealed that, in the nutrient enrichment experiment, the ambient AN concentration was the most crucial predictor for periphyton SRP and NN uptake. Meanwhile, the autotrophic index (the ratio of ash-free dry weight to chlorophyll-a content) exerted the greatest influence on periphyton AN uptake. In contrast, within the light control experiment, the ambient concentration emerged as the most preponderant factor affecting the nutrient uptake of periphyton. These findings advance the mechanistic understanding of periphyton nutrient cycling under pulsed urban stressors and heterogeneous light environments.