Studies of the effects of urbanization on stream ecosystems have usually focused on single metropolitan areas. Synthesis of the results of such studies have been useful in developing general conceptual models of the effects of urbanization, but the strength of such generalizations is enhanced by applying consistent study designs and methods to multiple metropolitan areas across large geographic scales. We summarized the results from studies of the effects of urbanization on stream ecosystems in 9 metropolitan areas across the US

Three cyanobacteria ( Microcystis aeruginosa Kütz. emend. Elenkin, Merismopedia tenuissima Lemmermann, and Oscillatoria sp.) and one diatom ( Aulacoseira granulata var. angustissima O. Mull. emend. Simonsen) were isolated from the tidal freshwater Potomac River and maintained at 23 Њ C and 40 mol photons и m Ϫ 2 и s Ϫ 1 on a 16:8 L:D cycle in unialgal culture. Photosynthetic parameters were determined in nutrient-replete cultures growing exponentially at 15, 20, 25, and 30 Њ C by incubation with 14 C at six light levels. P B max was strongly correlated with temperature over the entire range for the cyanobacteria and from 15 to 25 Њ C for Aulacoseira , with Q 10 ranging from 1.79 to 2.67. The ␣ values demonstrated a less consistent temperature pattern. Photosynthetic parameters indicated an advantage for cyanobacteria at warmer temperatures and in light-limited water columns. P B max and I k values were generally lower than comparable literature and field values, whereas ␣ was generally higher, consistent with a somewhat shade acclimated status of our cultures. Specific growth rate ( ), as measured by chlorophyll change, was strongly influenced by temperature in all species. Oscillatoria had the highest at all temperatures, joined at lower temperatures by Aulacoseira and at higher temperatures by Microcystis. Values of for Aulacoseira were near the low end of the literature range for diatoms consistent with the light-limited status of the cultures. The cyanobacteria exhibited growth rates similar to those reported in other studies. Q 10 for growth ranged from 1.71 for Aulacoseira to 4.16 for Microcystis. Growth rate was highly correlated with P B max for each species and the regression slope coefficients were very similar for three of the species. Abbreviations: I , photon flux density (light level); I k ϭ P B max и␣ Ϫ 1 ; I opt , photon flux density at which P B max is reached where photoinhibition is present; P B , photosynthetic rate/Chl a ; P B max , maximum of P B -I curve; ␣ , slope of P B -I curve; , specific growth rate 1

This paper presents the results of a study on the use of continuous stage data to describe the relation between urban development and three aspects of hydrologic condition that are thought to influence stream ecosystems—overall stage variability, stream flashiness, and the duration of extreme‐stage conditions. This relation is examined using data from more than 70 watersheds in three contrasting environmental settings—the humid Northeast (the metropolitan Boston, Massachusetts, area); the very humid Southeast (the metropolitan Birmingham, Alabama, area); and the semiarid West (the metropolitan Salt Lake City, Utah, area). Results from the Birmingham and Boston studies provide evidence linking increased urbanization with stream flashiness. Fragmentation of developed land cover patches appears to ameliorate the effects of urbanization on overall variability and flashiness. There was less success in relating urbanization and streamflow conditions in the Salt Lake City study. A related investigation of six North Carolina sites with long term discharge and stage data indicated that hydrologic condition metrics developed using continuous stage data are comparable to flow based metrics, particularly for stream flashiness measures.

health may occur between low and moderate levels of urban intensity. Additionally, many of the responses showed that at urban index values greater than 35, there was a threshold effect where the response variable no longer changed with respect to urban intensity. Recognizing and understanding this type of response is important in management and monitoring programs that rely on decisive interpretations of variable responses. Any biological, physical, or chemical variable that is used to characterize stream health over a gradient of disturbance would not be a reliable indicator when a level of disturbance is reached where the variable does not respond in a predictable manner.