01985nas a2200145   4500008004100000245008800041210006900129300001300198490000700211520145900218100001801677700001601695700001501711856011301726       2002                        eng d00aNitrogen and phosphorus relationships to benthic algal biomass in temperate streams0 aNitrogen and phosphorus relationships to benthic algal biomass i  a865 -8740 v593 aKnowledge 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 nutrientperiphyton 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 KolmogorovSmirnov statistical technique established significant breakpoints of about 30 µg total P·L1 and 40 µg total N·L1, above which mean chlorophyll values were substantially higher. Ecoregion effects on nutrientchlorophyll 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.1 aDodds, W., K.1 aSmith, V.H.1 aLohman, K.  uhttp://knz.lternet.edu/content/nitrogen-and-phosphorus-relationships-benthic-algal-biomass-temperate-streams