Benthic Algal (Periphyton) Growth Rates in Response to Nitrogen and Phosphorus: Parameter Estimation for Water Quality Models

Abstract

Nitrogen (N) and phosphorus (P) are significant pollutants that can stimulate nuisance blooms of algae. Water quality models (e.g., Water Quality Simulation Program, CE‐QUAL‐R1, CE‐QUAL‐ICM, QUAL2k) are valuable and widely used management tools for algal accrual due to excess nutrients in the presence of other limiting factors. These models utilize the Monod and Droop equations to associate algal growth rate with dissolved nutrient concentration and intracellular nutrient content. Having accurate parameter values is essential to model performance; however, published values for model parameterization are limited, particularly for benthic (periphyton) algae. We conducted a 10‐day mesocosm experiment and measured diatom‐dominated periphyton biomass accrual through time as chlorophyll a (chl a) and ash‐free dry mass (AFDM) in response to additions of N (range 5–11,995 µg nitrate as nitrogen [NO3‐N]/L) and P (range 0.89–59.51 µg soluble reactive phosphorus/L). Resulting half‐saturation coefficients and growth rates are similar to other published values, but minimum nutrient quotas are higher than those previously reported. Saturation concentration for N ranged from 150 to 2,450 µg NO3‐N/L based on chl a and from 8.5 to 60 µg NO3‐N/L when based on AFDM. Similarly, the saturation concentration for P ranged from 12 to 29 µg‐P/L based on chl a, and from 2.5 to 6.1 µg‐P/L based on AFDM. These saturation concentrations provide an upper limit for streams where diatom growth can be expected to respond to nutrient levels and a benchmark for reducing nutrient concentrations to a point where benthic algal growth will be limited.

Transport of N and P in U.S. streams and rivers differs with land use and between dissolved and particulate forms

“…Dissolved N and P concentrations exceeded highest reported half‐saturation constants for increasing leaf litter breakdown rates in 94% of cases for DIN (0.052 mg/L), and 59% of cases for DIP (0.021 mg/L; Fig. 1d, e), and were above highest half‐saturation constants for algal growth (Schmidt et al 2019) for 85% of values for DIN (0.186 mg/L) and 87% of values for DIP (0.004 mg/L).…”

“…We compared observed TN and TP concentrations to the most conservative (i.e., highest) TN and TP thresholds for benthic algae, macroinvertebrates, and fish communities reported in Evans‐White et al (2013). We then compared observed DIN and DIP concentrations to reported half‐saturation constants from Michaelis‐Menten/Monod‐type models of algal growth (Schmidt et al 2019), and leaf litter breakdown rates (e.g., Kominoski et al 2015). The second part of our analysis was also exploratory and sought to visualize relationships among total, dissolved, and particulate N and P as a function of the proportion of watershed land use characterized as urban, agricultural, or forested.…”

Nutrient limitation of algae and macrophytes in streams: Integrating laboratory bioassays, field experiments, and field data

“…The nutrient benchmarks derived here from the NDS and field survey data are considerably higher than benchmarks derived from some artificial stream studies [69][70][71]. For instance, Schmidt et al [70] showed P saturation occurred between about 12 and 29 μg/L P when N was not limiting and N saturation occurred between 150 to 2,450 μg/L when P was not limiting [70]. Phosphorus concentrations which saturate cellular level growth kinetics are very low, at less than 1 μg/L of soluble reactive P, yet in nature, much higher P levels are usually required to cause more dense accumulations of periphyton [69].…”

“…These changing saturation processes and >20 fold differences in P saturation concentrations caution that saturation thresholds derived from fresh benthic colonization laboratory assays may not be directly applicable to natural, established algal communities that develop throughout the growing season. For example, Schmidt et al [70] designed their tests (short-term with strong current to overcome any diffusion gradients) to produce maximum growth to define rate constants in numerical models, where in application limiting factors such as layer diffusion, sloughing, and light limitation would be adjusted by other mathematical functions.…”

On a non-standard two-species stochastic competing system and a related degenerate parabolic equation

“…In addition, aquatic species like Plecoglossus altivelis altivelis eat but cannot digest them [18]. On the other hand, non-filamentous algae, such as diatoms serving as staple foods of the fish, are more tolerant against turbulence but possibly have smaller intrinsic growth rates (Schmidt et al [16] for periphyton and Morin et al [12] for diatoms.). They are competing on the riverbed, and tracking and predicting their population dynamics are important industrial problem; however, least attention has been made on modelling and analysis of the population dynamics except for the engineering model [17].…”