Optimization of an Alternative Methodology for Simultaneous Analysis of Nitrite and Nitrate in Water from Urban Stream by Capillary Electrophoresis under Direct UV Detection

An alternative methodology for simultaneous determination of nitrite and nitrate by capillary zone electrophoresis using direct detection UV at 210 nm under reverse electrosmotic flow is proposed. The choice of the electrolyte composition has taken account: the mobility of the anion buffer and of the solutes;the low absorbance of the buffer in 210 nm;high base line stability and analysis time. The electrolyte optimized has consisted of 100 mmol.L–1 TRIS/HCl buffer and 0.15 mmol.L–1 CTAB at pH 8.2. The proposed method was applied successfully in the analysis of nitrite and nitrate in samples from urban stream in the absence of usual sample pretreatment.

Water quality impacts of small-scale hydromodification in an urban stream in Connecticut, USA

Introduction:Construction activities in and along urban streams increase the sediment input into surface waters,causing an overall decline in water quality and aquatic ecosystems.In this case study,we investigate the water quality impacts of local hydromodification in an urban stream(discharge 0.4 m^(3)/s).At the site of interest,workers removed a stream crossing consisting of an embankment with culverts and replaced it with a small bridge(single span of 25 m)in an effort to improve flow capacity.Methods:Water samples were taken at four sites along the North Branch Park River in Connecticut,Northeastern United States.Turbidity and dissolved oxygen(DO)were measured in situ,and nitrate and total phosphorus(TP)were measured in the laboratory.Benthic macroinvertebrate samples were also collected and analyzed for taxon richness and Shannon-Weaver species diversity.Data were compared between upstream and downstream sites and before,during,and after hydromodification.We used one-way ANOVA combined with the post hoc Turkey test to derive statistical significance.Results:During construction,turbidity increased temporarily by 60.9%[from 2.48 Nephelometric Turbidity Units(NTU)over ambient to 4.00 NTU].Once construction was completed,DO increased locally from 11.0 to 13.0 mg/L.Benthic macroinvertebrate taxon richness and species diversity declined by 61.6 and 32.6%respectively,with no recovery observed in the year following construction.Water quality was only affected within 50 m downstream.Nitrate and TP concentrations were unaffected.Conclusions:Small-scale hydromodification temporarily increased the turbidity as a result of increased sediment input,approaching the maximum level for clean water(5 NTU).Benthic macroinvertebrate communities declined in the immediate downstream vicinity of construction but are expected to recover soon given that turbidity recovered to pre-construction levels,and DO increased.These outcomes emphasize that environmental assessment is important not only for large-scale hydromodification but also for smaller scale stream modifications.

Hyporheic Zone Flow Disruption from Channel Linings： Implications for the Hydrology and Geochemistry of an Urban Stream, St. Louis, Missouri, USA

Cement channel linings in an urban stream in St. Louis, Missouri increase event water contributions during flooding, shorten transport times, and magnify geochemical variability on both short and seasonal timescales due to disruption of hyporheic flowpaths. Detailed analyses of water isotopes, major and trace elements, and in situ water quality data for an individual flood event reveal that baseflow contributions rise by 8% only 320 m downstream of the point where this particular channel changes from cement-lined to unlined. However, additional hydrograph separations indicate baseflow contributions are variable and can be much higher（average baseflow increase is 16%）. Stream electrical conductivity（EC） and solute concentrations in the lined reach were up to 25% lower during peak flow than in the unlined channel, indicating a greater event flow fraction. In contrast, during low flow, stream EC and solute concentrations in the lined reach were up to 30% higher due to the restricted inflow of more dilute groundwater. Over longer timescales, EC, solute concentrations, turbidity, and bacterial loads decrease downstream signifying increasing contributions of dilute baseflow. The decreased connectivity of surface waters and groundwaters along the hyporheic zone in lined channels increases the hydrologic and geochemical variability of urban streams.

Hydrologic Time Scale:A Fundamental Stream Characteristic

A new,fundamental catchment attribute called the hydrologic time scaleτgoverns the rate of delivery of runoff to a particular site,and is equal to∫Qdt/∫|dQ|,where Q is discharge and t is time.The value ofτfor any gauged site is readily calculated from tabulated discharge data by replacing the integrals with sums.This quantity,coupled with the square root of catchment area,√A,form a coordinate pair that embodies the characteristic time and length scales for any catchment,which govern its flow dynamics.The fitting constants used in several unit hydrograph models are simple multiples ofτ,so knowledge ofτallows rapid calibration of these models for the particular site,facilitating flow prediction from rainfall data.Values ofτreflect many different landscape attributes,but for multiple sub-basins in watersheds with homogeneous land use and lithologic conditions,they correlate linearly with √A.The ratio √A/τprovides a characteristic velocity that is high for channelized,floodprone rivers,for flashy urban streams with high impervious cover,and for sites downstream of hydropower dams.Sites with low velocities are resistant to flooding,as their landscapes have a greater ability to delay the delivery of runoff by retention,detention,and infiltration into the groundwater system.