Abstract. The concept of nitrogen (N) saturation has organized the assessment of N loading in terrestrial ecosystems. Here we extend the concept to lotic ecosystems by coupling Michaelis-Menten kinetics and nutrient spiraling. We propose a series of saturation response types, which may be used to characterize the proximity of streams to N saturation. We conducted a series of short-term N releases using a tracer ( 15 NO 3 -N) to measure uptake. Experiments were conducted in streams spanning a gradient of background N concentration. Uptake increased in four of six streams as NO 3 -N was incrementally elevated, indicating that these streams were not saturated. Uptake generally corresponded to Michaelis-Menten kinetics but deviated from the model in two streams where some other growth-critical factor may have been limiting. Proximity to saturation was correlated to background N concentration but was better predicted by the ratio of dissolved inorganic N (DIN) to soluble reactive phosphorus (SRP), suggesting phosphorus limitation in several high-N streams. Uptake velocity, a reflection of uptake efficiency, declined nonlinearly with increasing N amendment in all streams. At the same time, uptake velocity was highest in the low-N streams. Our conceptual model of N transport, uptake, and uptake efficiency suggests that, while streams may be active sites of N uptake on the landscape, N saturation contributes to nonlinear changes in stream N dynamics that correspond to decreased uptake efficiency.

SUMMARY 1. We monitored streams within the Gila River drainage in south‐western New Mexico, U.S.A., over a 5‐year period, to investigate the influence of ash input on water quality and stream biota following forest wildfires. 2. Nutrients [ammonium, nitrate, soluble reactive phosphate (SRP)], potassium and alkalinity were most affected by fires; all were increased in stream water following ash input. Concentrations of each returned to prefire conditions within 4 months. Ammonium and nitrate also increased in stream water as a result of atmospheric fallout (e.g. smoke) from fires outside the catchment. 3. Periphyton biomass was not affected significantly by wildfires, although there was a shift in diatom assemblage to smaller more adnate taxa. Cocconeis placentula was frequently the dominant postfire species. 4. The influence of wildfires on macroinvertebrates ranged from minimal to dramatic reductions in density depending upon the duration of ash flows and the characteristics of the ash material that entered each system. Macroinvertebrate densities returned to prefire conditions within 1 year. 5. An in‐situ ashing experiment was conducted on a first‐order stream in the Gila River drainage to monitor on‐site physiochemical and biotic responses during and after fire ash addition, for comparison with ash delivery from real wildfires on monitored streams. Physical–chemical parameters and algae and macroinvertebrates were monitored in an ashed and upstream reference reach for 13 months. Results generally substantiated findings from monitored streams. 6. Concentrations of major ions and nutrients, as well as turbidity, conductivity and pH, increased immediately in stream water below the point of ashing, while dissolved oxygen decreased. Changes in water chemistry were short‐lived (=24 h) except for SRP. The concentration of SRP in stream water was significantly higher in the ashed reach than the control reach for at least 1 month after ash input. 7. Periphyton biomass and diatom assemblages were not significantly altered in the ashing study, whereas macroinvertebrate density was measurably lower in the ashed reach for nearly a year. Macroinvertebrate drift was over 10‐fold greater in the ashed reach compared with the reference reach during ashing. Dissimilarity between macroinvertebrate communities in the reference and ashed reaches was significantly greater than variation within reaches for nearly a year.

BackgroundUrbanization can strongly impact the physiology, behavior, and fitness of animals. Conditions in cities may also promote the transmission and success of animal parasites and pathogens. However, to date, no studies have examined variation in the prevalence or severity of several distinct pathogens/parasites along a gradient of urbanization in animals or if these infections increase physiological stress in urban populations.Methodology/Principal FindingsHere, we measured the prevalence and severity of infection with intestinal coccidians (Isospora sp.) and the canarypox virus (Avipoxvirus) along an urban-to-rural gradient in wild male house finches (Haemorhous mexicanus). In addition, we quantified an important stress indicator in animals (oxidative stress) and several axes of urbanization, including human population density and land-use patterns within a 1 km radius of each trapping site. Prevalence of poxvirus infection and severity of coccidial infection were significantly associated with the degree of urbanization, with an increase of infection in more urban areas. The degrees of infection by the two parasites were not correlated along the urban-rural gradient. Finally, levels of oxidative damage in plasma were not associated with infection or with urbanization metrics.Conclusion/SignificanceThese results indicate that the physical presence of humans in cities and the associated altered urban landscape characteristics are associated with increased infections with both a virus and a gastrointestinal parasite in this common songbird resident of North American cities. Though we failed to find elevations in urban- or parasite/pathogen-mediated oxidative stress, humans may facilitate infections in these birds via bird feeders (i.e. horizontal disease transmission due to unsanitary surfaces and/or elevations in host population densities) and/or via elevations in other forms of physiological stress (e.g. corticosterone, nutritional).

. (2015) 'Stormwater infrastructure controls runo and dissolved material export from arid urban watersheds.', Ecosystems., 18 (1). pp. 62-75. Further information on publisher's website:http://dx.doi.org/10.1007/s10021-014-9812-2Publisher's copyright statement:The nal publication is available at Springer via http://dx.doi.org/10.1007/s10021-014-9812-2.Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. General commentsOverall I was quite happy with the quality and scope of this paper. It is very well written and contains some important findings. Some general and more specific comments are provided below. I think the authors should have the opportunity to think about a few of my comments below; this calls for minor revision.While the paper concerns both hydrology and water quality, I think more attention is given to the latter. I would have liked to seen more results on hydrology. Maybe you could provide a graph (with associated discussion in the text) showing mean event runoff coefficients for each catchment? Given that the paper is already fairly long, this might not be possible. In any case, I recon you could expand your hydrological findings in a separate journal paper.• Response: We are planning a separate paper that details the hydrologic results of this work. However, since both reviewers requested more hydrologic data, we have added a table in the appendix that provides more details on runoff and storm characteristics (Table A1) In the discussion, you present a conceptual model of urban watershed ecosystem function and describe four periods of change. You suggest that the model is for arid urban catchments. I think it would be worth fleshing this section out a bit more. In doing this, maybe you could firstly describe in a general way, what is natural arid catchment hydrology.• Response: We have limited space to add more discussion here, and we already have some information on arid hydrology in the introduction (lines 191-194), and we reference key literature (Osterkamp and Freidman, 2000. We have however, included a bit more discussion about how this model might differ in other regions (now lines 611-618).Where I'm from, the "third" phase in your diagram is very different. We have been installing distributed stormwater infrastructure for the last 15 years. But, our systems are generally designed for pollutant-load reduction-aimed to protect our largest receiving water (a bay). These systems are not designed to restore/protect natural hydrology. Because of this, runoff/ratios tend to still be c...

Urbanization is frequently cited as a major driver of species losses worldwide; however, most studies in urban areas use a space-for-time substitution approach to document effects of urbanization through time. Ultimately, understanding the effects of urbanization on biodiversity requires long-term datasets. We examined long-term changes in bird assemblages at 12 riparian sites in the greater Phoenix metropolitan area and nearby Sonoran Desert region, featuring a range of human modifications and levels of water flow. Riparian areas in arid cities represent a key habitat type that is sensitive to human modification and supports high levels of species diversity. We used long-term data to: (1) explore variation in bird communities as a function of water permanence and degree of human-modification; (2) identify which environmental variables best describe differences found across riparian site types; and (3) assess how riparian bird communities, abundance, and species richness have changed through time. Engineered riparian sites supported more broadly distributed generalists; whereas, natural riparian sites supported more specialists. Sites with perennial flows had more vegetation and water compared to ephemeral sites and engineered sites had more impervious surface compared to natural sites. In nearly all comparisons, bird species richness, diversity, and abundance declined across riparian types during the period of study, even for common species. Bird communities in natural settings have changed more than communities at engineered sites. Overall, the riparian bird community is shifting toward urban dwelling, resident species that are characteristic of riparian sites with less water and more impervious surface.

This study conducts a comparative analysis of the effects of irrigation scheduling at two urban residential sites in the Phoenix, Arizona, metropolitan area: a xeriscaped site (gravel base with low water use plants) and a mesiscaped site (turf grass and shade trees). A model of soil moisture dynamics was calibrated to observed soil moisture data from irrigated and non‐irrigated sensors at the xeric site and an irrigated sensor at the mesic site. Model simulations were conducted at both irrigated sites to investigate effects of irrigation scheduling; plant stress parameters; and precipitation variability on soil moisture dynamics, water balance partitioning, and plant water stress. Results indicated a substantial difference in soil water storage capacity at the two sites. At the xeric site, seasonal variation of irrigation input was shown to be critical in avoiding losses from the rooting zone, while reducing plant water stress. At the mesic site, sensitivity to irrigation scenarios was lower, though small amounts of water savings were achieved with seasonal applications. The model was then used to determine the minimum annual irrigation required to achieve specified levels of plant stress using long‐term meteorological records. A bimodal schedule consisting of low winter and summer irrigation was identified as a means to conserve water while keeping moderate levels of dynamic water stress. Results from the quantitative model can potentially assist water and landscape managers in desert urban areas by identifying opportunities for water savings, while providing a deeper understanding of the ecohydrological differences between the two types of landscape designs. Copyright © 2014 John Wiley & Sons, Ltd.

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IntroductionUrbanization can considerably impact animal ecology, evolution, and behavior. Among the new conditions that animals experience in cities is anthropogenic noise, which can limit the sound space available for animals to communicate using acoustic signals. Some urban bird species increase their song frequencies so that they can be heard above low-frequency background city noise. However, the ability to make such song modifications may be constrained by several morphological factors, including bill gape, size, and shape, thereby limiting the degree to which certain species can vocally adapt to urban settings. We examined the relationship between song characteristics and bill morphology in a species (the house finch, Haemorhous mexicanus) where both vocal performance and bill size are known to differ between city and rural animals.ResultsWe found that bills were longer and narrower in more disturbed, urban areas. We observed an increase in minimum song frequency of urban birds, and we also found that the upper frequency limit of songs decreased in direct relation to bill morphology.ConclusionsThese findings are consistent with the hypothesis that birds with longer beaks and therefore longer vocal tracts sing songs with lower maximum frequencies because longer tubes have lower-frequency resonances. Thus, for the first time, we reveal dual constraints (one biotic, one abiotic) on the song frequency range of urban animals. Urban foraging pressures may additionally interact with the acoustic environment to shape bill traits and vocal performance.Electronic supplementary materialThe online version of this article (doi:10.1186/s12983-014-0083-8) contains supplementary material, which is available to authorized users.