Nitrogen and phosphorus relationships to benthic algal biomass in temperate streams

TLDR

Understanding what limits benthic algal biomass is essential for grasping stream energy flow and eutrophication. The study aims to link water‑column nutrients and other factors to periphytic biomass and test whether ecoregion concepts apply to these relationships. The authors compiled seasonal periphyton biomass, nutrient, and stream characteristic data from ~300 sampling periods and analyzed benthic chlorophyll and nutrient concentrations from 620 US National Stream Water‑Quality Monitoring Network stations. Models of mean and maximum benthic algal biomass explained about 40 % of variance with total N and P, showing breakpoints at ~30 µg P L⁻¹ and ~40 µg N L⁻¹ where chlorophyll rises sharply; ecoregion effects were weak and confounded by anthropogenic land use, so separating natural from human influences requires caution.

Abstract

Knowledge of factors limiting benthic algal (periphyton) biomass is central to understanding energy flow in stream ecosystems and stream eutrophication. We used several data sets to determine how water column nutrients and nonnutrient factors are linked to periphytic biomass and if the ecoregion concept is applicable to nutrient–periphyton relationships. Literature values for seasonal means of biomass of periphyton, nutrient concentrations, and other stream characteristics were collected for almost 300 sampling periods from temperate streams. Data for benthic chlorophyll and nutrient concentrations from a subset of 620 stations in the United States National Stream Water-Quality Monitoring Networks were also analyzed. The greatest portion of variance in models for the mean and maximum biomass of benthic stream algae (about 40%) was explained by concentrations of total N and P. Breakpoint regression and a two-dimensional Kolmogorov–Smirnov statistical technique established significant breakpoints of about 30 µg total P·L –1 and 40 µg total N·L –1 , above which mean chlorophyll values were substantially higher. Ecoregion effects on nutrient–chlorophyll relationships were weak. Ecoregion effects were cross-correlated with anthropogenic effects such as percent urban and cropland area in the watershed and population density. Thus, caution is necessary to separate anthropogenic effects from natural variation at the ecoregion level.