Evaluation of nitrogen dioxide photolysis rates in an urban area using data from the 1997 Southern California Ozone Study

The photolysis of nitrogen dioxide and formaldehyde are two of the most influential reactions in the formation of photochemical air pollution, and their rates are computed using actinic flux determined from a radiative transfer model. In this study, we compare predicted and measured nitrogen dioxide photolysis rate coefficients (j_NO2). We used the Tropospheric Ultraviolet-Visible (TUV) radiation transfer model to predict j_NO2 values corresponding to measurements performed in Riverside, California as part of the 1997 Southern California Ozone Study (SCOS’97). Spectrally resolved irradiance measured at the same site allowed us to determine atmospheric optical properties, such as aerosol optical depth and total ozone column, that are needed as inputs for the radiative transfer model. Matching measurements of aerosol optical depth, ozone column, and j_NO2 were obtained for 14 days during SCOS’97. By using collocated measurements of the light extinction caused by aerosols and ozone over the full height of the atmosphere as model input, it was possible to predict sudden changes in j_NO2 resulting from atmospheric variability. While the diurnal profile of the rate coefficient was readily reproduced, j_NO2 model predicted values were found to be consistently higher than measured values. The bias between measured and predicted values was 17–36%, depending on the assumed single scattering albedo. By statistical analysis, we restricted the most likely values of the single scattering albedo to a range that produced bias on the order of 20–25%. It is likely that measurement error is responsible for a significant part of the bias. The aerosol single scattering albedo was found to be a major source of uncertainty in radiative transfer model predictions. Our best estimate indicates its average value at UV-wavelengths for the period of interest is between 0.77 and 0.85.     

Hierarchical regulation of nitrogen export from urban catchments: interactions of storms and landscapes.

In urban catchments of arid central Arizona, we investigate how the export of mineral and organic nitrogen (N) in storm runoff is regulated by interactions between local landscape characteristics and broader scale storm features. First, we test whether N export is more a function of (1) processes that affect N concentration in runoff or (2) the propensity of the catchment to convey rainfall as runoff. With data pooled across catchments, the mass of N in export (load) is determined by processes regulating runoff N concentration. There are exceptions when catchments are examined individually, where N load from some catchments is determined by the hydrologic responsiveness of the catchment. Second, we investigate the relationship between N export and catchment features. Loads per catchment area were greater from more impervious catchments, probably because impervious catchments held more N in a mobilizable phase and conveyed more rainfall as overland flow. Loads per area were lower from larger catchments, possibly owing to more N-retention hot spots in larger catchments. Catchments with the greatest N exports were those with commercial land use, and loads decreased as development became less prevalent or as residential replaced industrial land use. Third, we investigated how catchment features moderated direct responses of N export to storms. Export was less correlated with storm features in catchments that were larger, more pervious, and less industrial. Results support an "N build and flush" hypothesis, which purports that there is little biotic processing of N deposited to arid, urban surfaces with little organic matter. The rate and duration of deposition determine the size of the mobile N pool. Any amount of rainfall capable of generating overland flow would entrain nearly all mobilizable N and export it from the catchment. Nonetheless, these results suggest that, even with daunting seasonal and interannual variability in storm conditions, material export can be reduced by managing intrinsic catchment features.     

Intragroup dynamics of a cooperative breeder: An anlysis of reproductive roles in the acorn woodpecker

Summary The acorn woodpecker is a cooperative breeder generally thought to breed promiscuously within groups, but alternative patterns of reproductive investment can be expected and remain to be examined. With this feature of mating system in mind, we studied the reproductive roles of individuals in a single group of this species in central coastal California over a three-year period. Particularly detailed observations were made in 1979, when the group consisted of two potentially breeding sibling males and a single breeding female. One male (298) contributed significantly more than 297 in virtually all aspects of nest and fledgling care. These include (1) feeding nestlings, (2) nest sanitation, (3) nocturnal incubation and brooding, (4) feeding fledglings, and (5) escorting fledglings. In the few observed and rarely occurring dominance interactions, 298 prevailed. These results suggest that 298 had a higher probability of fathering the group's two 1979 offspring than did his brother. Thus, the two males differed substantially in their parental roles within the group, and very likely in reproductive roles, also. At present stage of knowledge, monogamy in groups with one female and more than one potential reproductive male is no less likely than promiscuity. These findings are discussed with respect to the evolution of cooperative breeding in this species.     

Sustainable urban development-the public health dimension

Public health in England developed during the first half of the nineteenth century with concern for sanitation in urban areas. Since that time environment, behaviour, social relationships, health services and genetic constitution are all recognized to contribute to health and disease in populations. Sustainable development is now of global concern, and its foundations-economy, environment and society-are similar to the determinants of health. However, while improved environment will have an important contribution to health, the broader social objectives are also needed to avoid the downward cycle of inequality and cultural deterioration that has occurred in some western cities. Epidemiological studies at University College London are particularly concerned with these social dimensions, and research opportunities exist for collaboration with environmental sciences in a number of areas, including intersectoral work, societies in social transition, collaboration with business, and research within through the European Union.     

A Decision-Support System for Prioritizing Restoration Sites on the Mississippi River Alluvial Plain

Conversion of forested wetlands to agricultural use and the resulting fragmentation of the landscape has led to concerns for the functional integrity of the Mississippi River Alluvial Plain ecosystem. We describe an effort spearheaded by The Nature Conservancy to initiate a multi-decade partnership dedicated to creating and implementing a viable, cooperative, landscape-level restoration project in the Mississippi River Alluvial Plain. Important phases of the process during the first 5 years were (1) initiation of the development of an extensive network of partners, including state and federal agencies, private land owners, conservation groups, academicians, and other interested citizens; (2) development of a geographic information system (GIS) for the entire extent of the ecosystem; and (3) for one watershed, the Tensas basin in northeastern Louisiana, refinement of a high resolution GIS to generate more detailed land-use conversion statistics to demonstrate the feasibility of a semi-objective, landscape-scale restoration planning procedure, including methodology for prioritization of existing wetland forest patches and areas most suitable for reforestation and connection via corridors.     

AN ANALOG COMPUTER DEMONSTRATION OF DOUBLE-PEAKED INSTANTANEOUS UNIT HYDROGRAPHS1

The properties of an instantaneous unit hydrograph model consisting of two cascades of linear reservoirs in parallel were explored with the aid of an analog computer. By proper choice of the model parameters it is possible to produce two-peaked instantaneous unit hydrographs. The relative magnitudes and locations of the two peaks can be varied by changing the values of the parameters. An example of the use of the analog computer to select the parameters of the model giving the best fit to an observed runoff hydrograph is also included. The analog computer used in the study was the ASTRAC II developed at the University of Arizona.     

Living with a large reduction in permited loading by using a hydrograph-controlled release scheme

The Total Maximum Daily Load (TMDL) for ammonia and biochemical oxygen demand for the Pee Dee, Waccamaw, and Atlantic Intracoastal Waterway system near Myrtle Beach, South Carolina, mandated a 60-percent reduction in point-source loading. For waters with a naturally low background dissolved-oxygen concentrations, South Carolina anti-degradation rules in the water-quality regulations allows a permitted discharger a reduction of dissolved oxygen of 0.1 milligrams per liter (mg/L). This is known as the 0.1 rule. Permitted dischargers within this region of the State operate under the 0.1 rule and cannot cause a cumulative impact greater than 0.1 mg/L on dissolved-oxygen concentrations. For municipal water-reclamation facilities to serve the rapidly growing resort and retirement community near Myrtle Beach, a variable loading scheme was developed to allow dischargers to utilize increased assimilative capacity during higher streamflow conditions while still meeting the requirements of a recently established TMDL.As part of the TMDL development, an extensive real-time data-collection network was established in the lower Waccamaw and Pee Dee River watershed where continuous measurements of streamflow, water level, dissolved oxygen, temperature, and specific conductance are collected. In addition, the dynamic BRANCH/BLTM models were calibrated and validated to simulate the water quality and tidal dynamics of the system. The assimilative capacities for various streamflows were also analyzed.The variable-loading scheme established total loadings for three streamflow levels. Model simulations show the results from the additional loading to be less than a 0.1mg/L reduction in dissolved oxygen. As part of the loading scheme, the real-time network was redesigned to monitor streamflow entering the study area and water-quality conditions in the location of dissolved-oxygen sags. The study reveals how one group of permit holders used a variable-loading scheme to implement restrictive permit limits without experiencing prohibitive capital expenditures or initiating a lengthy appeals process.     

Nutrients on Asphalt Parking Surfaces in an Urban Environment

Amounts of readily soluble nutrients on asphalt parking lot surfaceswere measured at four locations in metropolitan Phoenix, Arizona, U.S.A. Using a rainfall simulator, short intense rainfall events were generated to simulate `first flush' runoff. Samples were collected from 0.3 m² sections of asphalt at 8 to 10 sites on each of four parkinglots, during the pre-monsoon season in June-July 1998 and analyzed for dissolved NO₃ ^--N, NH₄ ⁺-N, soluble reactive phosphate (SRP), and dissolved organic carbon (DOC). Runoff concentrations varied considerably for NO₃ ^--N and NH₄ ⁺-N (between 0.1 and 115.8 mg L^-1) and DOC (26.1 to 295.7 mg L^-1), but less so for SRP (0.1 to 1.0 mg L^-1), representing average surface loadings of 191.3, 532.2, and 1.8 mg m^-2 respectively. Compared with similar data collected from undeveloped desert soil surfaces outside the city, loadings of NO₃ ^--N and NH₄ ⁺-N on asphalt surfaces were greater by factors of 91 and 13, respectively. In contrast, SRP loads showed little difference between asphalt and desert surfaces. Nutrient fluxes in runoff from a storm that occurred shortly after the experiments were used to estimate input-output budgets for 3 of the lots under study. Measured outputs of DOC and SRP were similar to those predicted using rainfall and experimentally determined surface loadings, but for NH₄ ⁺-N and particularly for NO₃ ^--N, estimated rainfall inputs and surface runoff were significantly higher than exports in runoff. This suggests that parking lots may be important sites for nutrient accumulation and temporary storage in arid urban catchments.