Channel design is an important component of stream restoration, but little is known of the interplay between hydrogeomorphic features and ecosystem processes within designed channels. Water velocity, transient storage, and nutrient uptake were measured in channelized (prerestoration) and naturalized (postrestoration) reaches of a 1-km segment of Wilson Creek (KY) to assess the effects of restoration on mechanisms of nutrient retention. Stream restoration decreased flow velocity and reduced the downstream transport of nutrients. Median travel time was 50% greater in the restored channel due to lower reach-scale water velocity and the longer length of the meandering channel. Transient storage and the influence of transient storage on travel time were largely unaffected except in segments where backwater areas were created. First-order uptake rate coefficients for N and P were 30- and 3-fold higher (respectively) within the restored channel relative to its channelized state. Changes in uptake velocities were comparatively small, suggesting that restoration had little effect on biochemical demand. Results from this study suggest that channel naturalization enhances nutrient uptake by slowing water velocity. Solute injection experiments revealed differences in the functional properties of channelized, restored, and reference streams and provided a means for quantifying benefits associated with restoration of ecosystem services.

1. We surveyed eighty‐five lakes located in the Adirondack Mountain Region of New York State, U.S.A., to characterize the attenuation of photosynthetically active (PAR) and ultraviolet radiation (UVR) in relation to dissolved organic carbon (DOC) concentrations and pH. Attenuation of PAR was quantified in situ. Attenuation was also inferred by measuring the light absorption of filtered lake water samples at wavelengths (300, 340 and 440 nm) representing UV‐B, UV‐A and PAR. 2. Substantial variation in transparency was observed among lakes in this region. Attenuation depths (z1%) for PAR ranged from 0.5 to greater than 20 m, while inferred values for UV‐B and UV‐A ranged from a few centimetres to > 5 m. Median values of UV‐A penetration (0.75 m) and UV‐B penetration (0.45 m) corresponded to 11% (UV‐A) and 6% (UV‐B) of lake maximum depth. 3. Much of the variation in PAR and UVR attenuation was explained by differences in lake DOC. Univariate power models based solely on DOC accounted for 85% (PAR), 90% (UV‐A) and 91% (UV‐B) of the variation in absorption. 4. Attenuation and absorption coefficients were generally lower for recently acidified lakes compared to acidic and circumneutral lakes which have not undergone recent acidification. However, differences among these three groups of lakes were not statistically significant. Our results suggest that the effects of acidification on the optical properties of a regional population of lakes, even in an area experiencing widespread acidification, are relatively subtle in comparison with other factors contributing to inter‐lake variability. 5. The presence of near‐shore wetlands is probably a key factor influencing regional variability in DOC and light climate among Adirondack lakes. Temporal variability in climatic factors influencing wetland DOC production and export may mask more subtle influences on lake DOC associated with anthropogenic acidification.

Phytoplankton production in riverine systems is regulated by hydrologic processes and coupled optical dynamics, which determine the light dosages experienced by phytoplankton during transit within a defined reach. We used data on river stage, discharge, and channel geomorphometry to model changes in light availability experienced by phytoplankton during transit within a 122-km navigational pool of the Ohio River. Whole-pool estimates of phytoplankton production were derived from photosynthesis-irradiance relationships and modeled values of light availability. Derived estimates of primary production showed good agreement with whole-pool mass balances for algal carbon. The sum of upriver inputs and autochthonous production agreed to within 10% of downriver export. During a summer with above normal discharge (1998), phytoplankton production within the pool corresponded to Ͻ10% of phytoplankton inputs from upstream and tributary sources. During lower flows in 1999, phytoplankton production in the pool exceeded external inputs of algal carbon. Modeled estimates of primary production were used to predict seasonal and longitudinal variation in algal abundance assuming a constant C : chlorophyll ratio. Model results showed good agreement with measured chlorophyll values and supported the hypothesis that biomass development was constrained by light availability and transit time within the pool. The model overestimated chlorophyll in late summer when grazing might limit biomass accumulation. The cumulative irradiance experienced by phytoplankton during transit within the pool was found to be a good predictor of autotrophic potential and for interpreting complex interactions arising from seasonal hydrologic cycles and the influence of water regulation structures.

Longitudinal variation in factors affecting phytoplankton production were analyzed to better understand the mechanisms that cause the formation of a chlorophyll maximum within the tidal freshwater James River. Phytoplankton production was two-to threefold higher in the region where persistent elevated chlorophyll concentrations occurred. Near this site, the morphology of the James transitions from a narrow, deep channel to a broad expanse with shallow areas adjoining the main channel. Shallower depths resulted in greater average irradiance within the water column and suggest that release from light limitation was the principal factor accounting for the location of the chlorophyll maximum. Grazing rates were low indicating that little of the algal production was directly consumed by zooplankton. Low exploitation by zooplankton was attributed to poor food quality due to high concentrations of non-algal particulate matter and potential presence of cyanobacteria. Metabolism data suggest that two thirds of net primary production was respired in the vicinity of the chlorophyll maximum and one third was exported via fluvial and tidal advection. Comparison of water column and ecosystem metabolism indicates that the bulk of respiration occurred within the sediments and that sedimentation was the dominant loss process for phytoplankton.

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