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Elevated nitrogen and phosphorus concentrations in urbanizing southwest Washington streams
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In southwest Washington, rapid population growth and associated land use change have resulted in elevated stream nutrient con-centrations. To evaluate the extent and nature of human alterations to stream nutrient concentrations in this region, we compiled four water years of total phosphorus (TP) and dissolved inorganic nitrogen (DIN) data from two long-term monitoring programs. We also quantified watershed characteristics likely to affect aquatic nutrient loading, and tested for correlations between these characteristics and stream nutrient concentrations. Average nutrient concentrations in study streams were significantly elevated relative to EPA recommended nutrient criteria in all sites for DIN and in nine out of 14 sites for TP. Of the watershed characteris-tics investigated, percent "impervious" (+) and percent "forested" (-) were the best predictors of TP concentration (R 2 = 0.41 and 0.64, respectively, + and – indicate the slope of the regression). Percent "developed" (+) and percent "forest and woody wetland" (-) were the best predictors of DIN concentration (R 2 = 0.75 and 0.73, respectively). In urban streams, the mean dry season DIN concentration was significantly higher than the mean wet season DIN concentration, but this pattern was reversed in less urban watersheds. Urban streams also had significantly higher DIN than non-urban streams. The strong relationship between DIN and "developed land" suggests that as southwest Washington's population continues to grow, targeted N management will become increasingly important. The strong negative relationship between "forest and woody wetland" and both TP and DIN concentration suggests that this land use type is particularly important in reducing stream nutrient loading.)NTRODUCTION Over the last several decades, high levels of nutrient loading and associated degradation of water quality have been extensively documented in freshwater systems across the United States (USEPA 2006, USGS NAWQA 2010). This pat-tern can largely be attributed to human activities, which have more than doubled the rate at which biologically available nitrogen (N) and phosphorus (P) are mobilized across the landscape (Vitousek et al. 1997, Bennett et al. 2001, Galloway 2008). At the global scale, anthropogenic sources of biologically available riverine nutrients exported to the coastal zone are now greater than natural sources (Seitzinger et al. 2005). Within the United States, 47% and 39% of wadeable streams exhibit elevated total N (TN) and total P (TP) concentra-tions relative to reference conditions respectively (Herlihy and Sifneos 2008).
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... In cities around the world, higher pollutant loads and flashier hydrographs resulting from impervious surfaces in urban areas have contributed to the degradation of water bodies and the emergence of an ''urban stream syndrome'' (Walsh et al. 2005a). Attributed to the presence of fossil fuel emissions, fertilizers, and human waste, reactive nitrogen (Nr) is one pollutant observed to be more abundant in urbanized versus undeveloped, non-agricultural watersheds (Baron et al. 2013;Deemer et al. 2012;Groffman et al. 2004). Excessive nitrogen (N) transport from cities can, in turn, cause a suite of regional ecological problems, including harmful algal blooms and hypoxia (Baron et al. 2013;Zhang et al. 2015). ...
... After initial measurements, stormwater was dosed with KNO 3 to achieve a concentration of *2.0 mg NO 3 -N/L, a concentration common in the Portland, OR/Vancouver, WA metropolitan area (Deemer et al. 2012;Hook and Yeakley 2005). Although DIN concentrations in real-world, urban stormwater are unlikely to remain constant throughout multiple precipitation events, 2.0 mg L -1 is a reasonable estimate of urban DIN concentrations for the Pacific NW US. ...
... Although DIN concentrations in real-world, urban stormwater are unlikely to remain constant throughout multiple precipitation events, 2.0 mg L -1 is a reasonable estimate of urban DIN concentrations for the Pacific NW US. In a recent review of the water chemistry of Pacific NW urban streams, DIN concentrations ranged from 2 to 3.5 mg N L -1 during the entire rainy season (Deemer et al. 2012). Following NO 3 enrichment, an air pump was used to mix the influent for at least 1 h prior to application. ...
Reported nitrogen (N) retention efficiencies for bioretention swales vary widely, but reasons for this are not well-understood, in part because almost no studies have measured (or characterized controls on) bioretention swale denitrification. Here, we apply a novel N2:Ar-based approach, in coordination with more established approaches, to estimate denitrification rates and compare bioretention N dynamics during artificial storms of two sizes (3.05 and 5.08 cm days⁻¹) and following 4 inter-storm periods (initial storm with no prior storm, 1-, 7-, and 13-days). Denitrification rates during storms occurring after 7-days (520 ± 150 µmol N m⁻² h⁻¹) were significantly higher than those during an initialization storm (13 ± 34 µmol N m⁻² h⁻¹) or during a storm occurring one day after a previous storm (−63 ± 65 µmol N m⁻² h⁻¹). No significant differences in N processing were observed between 3.05 and 5.08 cm days⁻¹ storms. Somewhat surprisingly, in all experiments [O2] remained near saturated, and N2O emissions were very low or undetectable. Mesocosms were largely a net sink for dissolved inorganic N (DIN) and a net source of dissolved organic N (DON). Denitrification was neither a dominant nor consistent pathway for N removal, accounting for a maximum of 23 ± 11% of DIN removal. Future research should continue to evaluate N assimilation as a N removal pathway in bioretention swales, as well as characterize N dynamics during unsaturated conditions associated with smaller rain events and during periods between the large storms examined here.
... The exacerbation of urban river flooding by climate change will not only cause a significant loss of life and property, but will also contribute to the public health and social problems [Oven et al., 2012in Yoon et al., 2016. It is therefore vital that society develops urban river management systems that can cope with and reduce the impacts of the climate change, including the flood damage [Kim et Moreover, elevated concentrations of nutrients, metals and sediments have also been reported in urban streams [Deemer et al., 2012;Grayson et al., 1996;Hatt et al., 2004 in Wu et al., 2015]. Phosphorus and nitrogen from fertilizers applied to lawns, sediment and salts from roads, and increased runoff from roofs delivered to streams rapidly via storm sewers have been identified as potential contributors to the stream degradation in the urban areas [Adachi & Tainosho, 2005;Fissore et al., 2011;Negishi et al., 2007;Ragab et al., 2003in Wu et al., 2015. ...
The impact and occurrence of human-induced pollution sources have been investigated in one of the few remaining urban streams located in Attica, Greece. Baseline information is provided on the presence and concentration of physicochemical parameters, nutrients, total coliforms, hydrocarbons and phenols in 12 key points along the Pikrodafni stream. The aim was to evaluate the relative importance of key water quality variables and their sources. Indicator substances (i.e. concentrations of nitrate, ammonium, phosphate and total coliforms in certain stations indicating wastewater exposure; PAHs indicating petroleum sources) successfully related the water quality variables to pollution sources. Furthermore, a pollution pressure map has been developed with the activities identified from in-situ visits and Google Earth surveys, while the statistical analysis (CA and PCA) has contributed to the further exploration of the relative magnitude of pollution sources effects. Our results underline initially the importance of diffuse pollution management accompanied by the necessity for continuous environmental monitoring and the application of legal and environmental restoration actions if water quality is to be improved according to WFD 2000/60/EC.
... For example, increases in total discharge, peak discharge, and flashiness have been reported in urban streams as impervious land cover increases within a watershed (Nelson et al., 2009;Schoonover, Lockaby, & Helms, 2006;. Elevated concentrations of nutrients, metals and sediments have also been reported in urban streams (Deemer et al., 2012;Grayson, Finlayson, Gippel, & Hart, 1996;Hatt et al., 2004). Phosphorus and nitrogen from fertilizer applied to lawns, sediment and salts from roads, and increased runoff from roofs delivered to streams rapidly via storm sewers have been identified as potential contributors to stream degradation in urban areas (Adachi & Tainosho, 2005;Fissore et al., 2011;Negishi, Negochi, Sidle, Ziegler, & Nik, 2007;Ragab, Bromley, Rosier, Cooper, & Gash, 2003). ...
Urban stream condition is often degraded by human activities in the surrounding watershed. Given the complexity of urban areas, relationships among variables that cause stream degradation can be difficult to isolate. We examined factors affecting stream condition by evaluating social, terrestrial, stream hydrology and water quality variables from 20 urban stream watersheds in central Iowa, U.S.A. We used path analysis to examine and quantify social and ecological factors related to variation in stream conditions. Path models supported hypotheses that stream water quality was influenced by variables in each category. Specifically, one path model indicated that increased stream water conductivity was linked to high road density, which itself was associated with high human population density. A second path model revealed nitrogen concentration in stream water was positively related to watershed area covered by cropland, and that cropland increased as human population density declined. A third path model indicated phosphorus concentration in stream water declined as percent of watershed residents with college education increased, although the mechanism underlying this relationship was unclear and could have been an artifact of lower soil-derived nutrient input from watersheds dominated by paved surfaces. To improve environmental conditions in urban streams, land use planning strategies should include limiting or reducing road density near streams, installing treatment trains for surface water runoff associated with roads, and establishing vegetated buffer zones to reduce inputs of road salt and other pollutants. Additionally, education/outreach should be conducted with residents to increase understanding of how their own behaviors influence stream water quality.
The world's population is concentrated in urban areas. This change in demography has brought landscape transformations that have a number of documented effects on stream ecosystems. The most consistent and pervasive effect is an increase in impervious surface cover within urban catchments, which alters the hydrology and geomorphology of streams. This results in predictable changes in stream habitat. In addition to imperviousness, runoff from urbanized surfaces as well as municipal and industrial discharges result in increased loading of nutrients, metals, pesticides, and other contaminants to streams. These changes result in consistent declines in the richness of algal, invertebrate, and fish communities in urban streams. Although understudied in urban streams, ecosystem processes are also affected by urbanization. Urban streams represent opportunities for ecologists interested in studying disturbance and contributing to more effective landscape management.
Phosphorus (P) is one of the most important mineral nutrients in agricultural systems, and along with nitrogen (N), is generally the most limiting nutrient for plant production. Farming systems have intensired greatly over time, and in recent years it has become apparent that the concomitant increase in losses of N and P from agricultural land is having a serious detrimental effect on water quality and the environment. The last two decades have seen a marked increase in research into the issues surrounding diffuse losses of P to surface and ground water. This paper reviews this research, examining the issue of P forms in runoff, and highlighting the exceptions to some generally held assumptions about land use and P transport. In particular the review focuses on P losses associated with recent P fertilizer application, as opposed to organic manures, both on the amounts and the forms of P in runoff water. The effects of the physicochemical characteristics of different forms of P fertilizer are explored, particularly in relation to water solubility. Various means of mitigating the risk of loss of P are discussed. It is argued that the influence of recent fertilizer applications is an under-researched area, yet may offer the most readily applicable opportunity to mitigate P losses by land users. This review highlights and discusses some options that have recently become available that may make a significant contribution to the task of sustainable management of nutrient losses from agriculture.
One of the biggest challenges when conducting a continental-scale assessment of streams is setting appropriate expectations for the assessed sites. The challenge occurs for 2 reasons: 1) tremendous natural environmental heterogeneity exists within a continental landscape and 2) reference sites vary in quality both across and within major regions of the continent. We describe the process used to set expectations for the multimetric index of biotic integrity (MIBI) and observed/expected (O/E) indices generated from predictive models used to assess stream condition for the US Wadeable Streams Assessment (WSA). The assessment was based on a reference-site approach, in which the least-disturbed sites in each region of the US were used to establish benchmarks for assessing the condition of macroinvertebrate assemblages at other sites. Reference sites were compiled by filtering WSA sample sites for disturbance using a series of abiotic variables. Additional reference sites were needed and were obtained from other state, university, and federal monitoring programs. This pool of potential reference sites was then assessed for uniformity in site quality and comparability of macroinvertebrate sample data. Ultimately, 1625 sites were used to set reference expectations for the WSA. Reference-site data were used to help define 9 large ecoregions that minimized the naturally occurring variation in macroinvertebrate assemblages associated with continental-wide differences in biogeography. These ecoregions were used as a basis for developing MIBI and O/E indices and for reporting results. A least-disturbed definition of reference condition was used nationally, but we suspect that the quality of the best extant sites in ecoregions, such as the Northern Plains and Temperate Plains, was lower than that of sites in other ecoregions. For the MIBI assessment, we used a simple modeling approach to adjust scores in ecoregions where gradients in reference-site quality could be demonstrated conclusively. The WSA provided an unparalleled opportunity to push the limits of our conceptual and technical understanding of how to best apply a reference-condition approach to a real-world need. Our hope is that we have learned enough from this exercise to improve the technical quality of the next round of national assessments.
We analyzed nutrient data from a probability survey of 1392 wadeable streams across the 48 conterminous states of the US and from intensified survey data in 921 streams in the Pacific Northwest (PNW) to examine different methods of setting nutrient criteria and to develop a nutrient stream typology. We calculated potential nutrient criteria for total P (TP) and total N (TN) by 3 methods (ecoregion population 25th percentile of population, least-disturbed reference-site 75th percentile, and disturbance modeling) and compared them with existing draft US Environmental Protection Agency (EPA) criteria within 14 national nutrient ecoregions. All criteria derived from the methods were highly correlated; however, absolute values within ecoregions differed greatly among approaches. Population 25th percentiles of TP were almost always lower from statistically designed survey data than from found data. TN percentiles were more similar than were TP profiles, but they still tended to be lower from survey data than from found data. TP and TN population 25th percentiles were lower (often by a factor of 2–6) than reference-site 75th percentiles in all ecoregions. This result indicates that population 25th percentiles cannot be used as surrogates for reference-site 75th percentiles. Thirty-nine percent of the assessed national stream length exceeded TP criteria and 47% exceeded TN criteria when compared to nutrient criteria based on EPA Wadeable Stream Assessment reference-site 75th percentiles. In the PNW data set, all disturbance regression model estimates of background nutrient concentrations were lower than reference-site 75th percentiles. Regression tree analysis based on PNW reference sites used runoff, elevation, acid neutralizing capacity, forest composition, substrate size, and Omernik level III ecoregion as environmental class predictors to explain 46 to 48% of the total deviance in nutrient concentration. Reference-site nutrient concentrations varied widely among Omernik level III ecoregions in nutrient ecoregion II. Our analysis and the literature strongly suggest that 14 national nutrient ecoregions are too coarse to account for natural variation in stream nutrient concentrations. Setting appropriate national nutrient criteria will require finer-scale typology or classification of sites that better controls for natural variation.
Human actions—mining phosphorus (P) and transporting it in fertilizers, animal feeds, agricultural crops, and other products—are altering the global P cycle, causing P to accumulate in some of the world’s soil. Increasing P levels in the soil elevate the potential P runoff to aquatic ecosystems (Fluck et al. 1992, NRC 1993, USEPA 1996). Using a global budget approach, we estimate the increase in net P storage in terrestrial and freshwater ecosystems to be at least 75% greater than preindustrial levels of storage. We calculated an agricultural mass balance (budget), which indicated that a large portion of this P accumulation occurs in agricultural soils. Separate P budgets of the agricultural areas of developing and developed countries show that the rate of P accumulation is decreasing in developed nations but increasing in developing nations.
Orthophosphate concentrations in the Tualatin River of northwest Oregon have historically been high enough for the formation
of seasonal algal blooms in the lower slow moving stretches of the river. Past work to decrease phosphate levels concentrated
on limiting agricultural runoff and reducing effluent from water treatment plants, yet phosphate levels have remained high.
Close examination of the Willamette Silt and underlying Hillsboro Formation in the Tualatin Valley has revealed that phosphate
is leaching from the substrata into the overlying drainage system through ground-water discharge. Hillsboro Formation samples
from subsurface borings as deep as 330 m contain up to 3.17 mg/1 orthophosphate as measured by saturated pastes. Three distinct
zones of phosphate concentrations are recognized in the HBD-1 core drilled at the Hillsboro airport; the top 65 m average
0.3 mg/1 orthophosphate, the next 60 m average 1.22 mg/1, and the bottom 138 m average 0.1 mg/1. Reductions in orthophosphate
concentrations below a depth of 150 m correspond with the presence of small vivianite nodules and crystals, and increased
abundances of magnetite, both which persist to the base of the Hillsboro Formation. Changing redox conditions with depth along
with phosphate complex adsorption onto iron oxides in the shallow zone best explain the observed relationships between phosphate,
vivianite, and magnetite concentrations in the sediments. Observations in other borings from the central and western Tualatin
Basin support the above hypothesis. Naturally large phosphate concentrations leaching from the Hillsboro Formation and into
the Tualatin River drainage system will always keep the river at risk of accelerated seasonal algal growth.
Ecologists have described an urban stream syndrome with attributes such as elevated nutrients and contaminants, increased hydrologic flashiness, and altered biotic assemblages. Ecosystem function probably also varies with extent of urbanization, although there are few stream networks in which this prediction has been studied. We examined functional characteristics of 6 tributaries of the Chattahoochee River near Atlanta, Georgia, USA, whose catchments differed in degree of urbanization. We conducted short-term NH4- and PO 4-addition experiments to measure nutrient uptake velocity, which is the rate at which a nutrient moves through the water column toward the benthos. Both NH4 and soluble reactive P uptake velocities decreased as indicators of urbanization (i.e., % of catchment covered by high-intensity urban development) increased. The amount of fine benthic organic matter (FBOM) also decreased with increasing urbanization, and uptake velocities were directly related to FBOM. Uptake velocities were not related to ecosystem metabolism (gross primary production [GPP], community respiration [CR], or net ecosystem production) as measured with diel oxygen curves. However, NH4 uptake velocity increased as total stream metabolism (GPP + CR) increased in these streams as well as in other North American streams, suggesting that biotic demand drives NH4 uptake velocities across a wide range of stream ecosystems. Measures of ecosystem function responded differently to urbanization: ecosystem metabolism was not correlated with indicators of urbanization, although breakdown rate of Acer barbatum leaves was positively correlated and nutrient uptake velocities were negatively correlated with indicators of urbanization. Elevated nutrient concentrations associated with urbanization are usually attributed to increased inputs from point and non-point sources; our results indicate that concentrations also may be elevated because of reduced rates of nutrient removal. Altered ecosystem function is another symptom of an urban stream syndrome.
Planners concerned with water resource protection in urbanizing areas must deal with the adverse impacts of polluted runoff. Impervious surface coverage is a quantifiable land-use indicator that correlates closely with these impacts. Once the role and distribution of impervious coverage are understood, a wide range of strategies to reduce impervious surfaces and their impacts on water resources can be applied to community planning, site-level planning and design, and land use regulation. These strategies complement many current trends in planning, zoning, and landscape design that go beyond water pollution concerns to address the quality of life in a community.