Emilie K. Stander

Ecological Engineering Practices for the Reduction of Excess Nitrogen in Human-Influenced Landscapes: A Guide for Watershed Managers

Excess nitrogen (N) in freshwater systems, estuaries, and coastal areas has well-documented deleterious effects on ecosystems. Ecological engineering practices (EEPs) may be effective at decreasing nonpoint source N leaching to surface and groundwater. However, few studies have synthesized current knowledge about the functioning principles, performance, and cost of common EEPs used to mitigate N pollution at the watershed scale. Our review describes seven EEPs known to decrease N to help watershed managers select the most effective techniques from among the following approaches: advanced-treatment septic systems, low-impact development (LID) structures, permeable reactive barriers, treatment wetlands, riparian buffers, artificial lakes and reservoirs, and stream restoration. Our results show a broad range of N-removal effectiveness but suggest that all techniques could be optimized for N removal by promoting and sustaining conditions conducive to biological transformations (e.g., denitrification). Generally, N-removal efficiency is particularly affected by hydraulic residence time, organic carbon availability, and establishment of anaerobic conditions. There remains a critical need for systematic empirical studies documenting N-removal efficiency among EEPs and potential environmental and economic tradeoffs associated with the widespread use of these techniques. Under current trajectories of N inputs, land use, and climate change, ecological engineering alone may be insufficient to manage N in many watersheds, suggesting that N-pollution source prevention remains a critical need. Improved understanding of N-removal effectiveness and modeling efforts will be critical in building decision support tools to help guide the selection and application of best EEPs for N management.

HYDROLOGIC DESCRIPTION OF FORESTED WETLANDS IN NORTHEASTERN NEW JERSEY, USA—AN URBAN/SUBURBAN REGION

The hydrology of wetlands located in urban landscapes is likely to be affected by the numerous effects of urban development on the water cycle. Although urbanization is affecting an increasingly large amount of wetland area, there have been few studies documenting hydrologic patterns in such wetlands. We have studied a set of 21 forested wetlands distributed through northeastern New Jersey, USA, a region characterized by dense residential and commercial development. The sites varied widely in area (6–500 ha), and all were bordered by urban land uses. In ten sites, water levels were monitored for 2.5 yr in shallow wells and piezometers; in all sites, qualitative indicators of hydrology, vegetation, and soil indicators of wetland hydrology were sampled. The sites were placed in five hydrogeomorphic (HGM) classes (depression, slope, riverine, mineral flats, and mineral flat-riverine) and also in three qualitative classes of hydrologic disturbance (low, medium, and high). We examined water-level dynamics, variability, the occurrence of discharge/recharge conditions, and the frequency of occurrence of hydrologic indicators across both HGM and disturbance classifications. Qualitative indicators of hydrology did not reveal differences in hydrology that were apparent from the quantitative data, the soils, and the vegetation. Mineral flat-riverine sites were the most wet, and the riverine sites the most dry, but hydrologic disturbance tended to blur distinctions among HGM classes by creating relatively dry conditions in most site types. Sites with a high level of hydrologic disturbance also tended to be more “flashy,” regardless of HGM class. We conclude that the utility of HGM classifications and qualitative indicators of hydrology in urban/suburban landscapes are limited by the high degree of variability in both the extent and particularly the sources of hydrologic disturbance. We conclude that the hydrology of wetlands in an urban region reflects not only the hydrogeomorphic setting but also the unique set of disturbances from current and historical land-uses found at each site.

Rapid Assessment of Urban Wetlands: Do Hydrogeomorphic Classification and Reference Criteria Work?

The Hydrogeomorphic (HGM) functional assessment method is predicated on the ability of hydrogeomorphic wetland classification and visual assessment of alteration to provide reference standards against which functions in individual wetlands can be evaluated. The effectiveness of this approach was tested by measuring nitrogen cycling functions in forested wetlands in an urbanized region in New Jersey, USA. Fourteen sites represented three HGM classes and were characterized as “least disturbed reference” or “non-reference” based on initial visual assessment. Water table levels and in situ rates of net nitrogen mineralization, net nitrification, and denitrification were measured over one year in each site. Hydrological alterations, resulting in consistently low or flashy water table levels, were not correlated with a priori designations as reference and non-reference. Although the flat-riverine wetland class had lower net nitrification and higher denitrification rates than riverine or mineral flat wetland classes, this difference was attributable to the lack of hydrologically-altered wetlands in the flat-riverine class, and thus more consistently wet conditions. Within all HGM classes, a classification based on the long-term hydrological record that separated sites with “normal,” saturated hydrology from those with “altered,” drier hydrology, clearly distinguished sites with different nitrogen cycling function. Based on these findings, current practices for designating reference standard sites to judge wetland functions, at least in urbanized regions, are ineffective and potentially misleading. At least one year of hydrological monitoring data is suggested to classify wetlands into groups that have different nutrient cycling functions, particularly in urban landscapes.

Mapping the Design Process for Urban Ecology Researchers

The integration of research into the design process is an opportunity to build ecologically informed urban design solutions. To date, designers have traditionally relied on environmental consultants to provide the best available science; however, serious gaps in our understanding of urban ecosystems remain. To evaluate ecosystem processes and services for sustainable urban design and to further advance our understanding of social-ecological processes within the urban context, we need to integrate primary research into the urban design process. In this article, we develop a road map for such a synthesis. Supporting our proposals by case studies, we identify strategic entry points at which urban ecology researchers can integrate their work into the design process.

Novel Use of Time Domain Reflectometry in Infiltration-Based Low Impact Development Practices

AbstractLow impact development (LID) practices intercept storm-water runoff and infiltrate it through a range of media types and underlying soils. Hydrologic performance is typically evaluated by comparing inlet and underdrain outlet flows, but there is no standard practice for defining and measuring performance in LID structures designed without underdrains that infiltrate into the ground. Water content reflectometer (WCR) sensors were installed in the aggregate storage layer under permeable pavement and rain garden media to test their ability to measure the size and timing of the wetting front in infiltrating LID practices. WCR data were also used to monitor infiltration rates in the underlying soil beneath both practices. Bench-scale testing was performed to quantify the response of WCRs to saturated and unsaturated conditions and calibrate sensors to a range of water content values. Bench-scale testing revealed that WCRs installed in the aggregate were calibrated to volumetric water content (VWC) as t...

Hydraulic Test of a Bioretention Media Carbon Amendment

Rain gardens effectively remove some stressors from storm water, but in most cases they show much smaller removal rates of nitrate, likely due to the high sand and low organic matter content of rain garden media inhibiting denitrification. A bench-scale experiment was conducted to test the drainage capability of media containing shredded newspaper layers as a carbon amendment. Storm water was introduced at low and high rates to bins containing zero, one, and two layers of newspaper at varying depths. While there were differences in effluent volumes and flow rates between control and newspaper treatments, surface ponding occurred in all three treatments, suggesting that some other factor besides the newspaper had an effect on drainage properties. Grain size and clay mineralogy analyses indicated the migration of finer particles into the deeper soils, which could have inhibited drainage.

Rapid assessment of urban wetlands: Functional assessment model development and evaluation

The objective of this study was to test the ability of existing hydrogeomorphic (HGM) functional assessment models and our own proposed models to predict rates of nitrate production and removal, functions critical to water quality protection, in forested riparian wetlands in northeastern New Jersey. In particular, the relationship between rapidly measured structural indicators and complex nitrogen (N) cycling functions was evaluated as well as the ability of generalized biogeochemical models to predict rates of specific N cycling processes. Additional models were designed specifically to predict net nitrification and denitrification rates, using both rapid and non-rapid variables based on known controlling factors on these two processes. Existing models and our own rapid models were not able to describe net nitrification and denitrification rates in urban riparian wetlands. Our additional models based on non-rapid variables, quantified through long-term hydrological monitoring and laboratory analyses of soil properties, successfully described net nitrification rates, but surprisingly failed to adequately predict denitrification rates. The high variability in hydrological and soil properties and the complexity of site-specific relationships between disturbance, altered hydrology, and hydrologically driven N cycling processes in urban wetlands restricts our ability to predict denitrification rates using simple models. It is recommended that functional assessment models be designed to describe specific, process-based functions which are based on structural indicators that are well linked to process rates. These indicators should be based on measurements from at least one year of hydrological monitoring and from simple laboratory measurements of soil properties. Detailed studies of populations of wetlands may be necessary to validate specific forms of models.

Factorial Study of Rain Garden Design for Nitrogen Removal

AbstractNitrate (NO3−-N) removal studies in rain gardens show great variability in removal rates, and in some cases NO3−-N was exported. A three-way factorial design (2×2×4) was devised for eight outdoor unvegetated rain gardens to evaluate the effects of hydraulic loading (two sizes and two flow rates), the presence/absence of a buried wood chip layer (2), and the presence/absence of a subsurface saturated zone (SZ) (2) on nitrate-nitrite (NO3−-NO2−) removal. Captured stormwater runoff was used in this study. Results showed that the presence of a SZ reduced the NO3−-NO2− mass by 75% compared to a 7% reduction without this zone. The presence of a SZ significantly decreased ammonia-N (NH3-N) mass reduction (p<0.00001). The difference in total nitrogen (TN) mass reduction with the introduced SZ was not significant, largely due to NO3−-NO2− mass reduction that was offset by NH3-N mass increases in rain gardens with the SZ. The buried wood chip layer showed no significant effect on N removal. No significant i...

Permeable Pavement Demonstration at the Edison Environmental Center

There are few studies of full-scale, outdoor, replicated, functioning pervious pavement systems. More studies of pervious pavement operating in its intended use (parking lot, roadway, etc.) during a range of climatic events, daily usage conditions, and maintenance regimes are necessary in order to properly evaluate these systems. In accordance with this research need, the EPAs Urban Watershed Management Branch has installed an instrumented, working full-scale 110-space pervious pavement parking lot in Edison, NJ. EPA plans to monitor several environmental stressors in effluent and runoff. This parking lot demonstration site investigates differences among side-by-side pervious asphalt, pervious concrete, and permeable interlocking concrete paver systems. The parking lot consists of three sets of parking rows, each one surfaced with a different pervious pavement type, and driving lanes surfaced with conventional asphalt. The pervious pavement parking areas contain replicated subsections to collect the infiltrating water as well as sections that allow the filtered effluent to infiltrate into the underlying soil. The replication allows for statistical analyses of collected data. Investigated parameters include: volume, temperature, solids, indicator organisms, nutrients, metals, and semi-volatile organic compounds.

Enhancing Rain Garden Design to Promote Nitrate Removal

Rain gardens effectively remove some stressors from stormwater, but in most cases they show much smaller removal rates of nitrate, likely due to the medias high sand and low organic matter content that inhibit nitrate removal by denitrification. EPAs pilot-scale research explores the use of shredded, unprinted newspaper as a carbon source to fuel denitrification. A bench-scale experiment was conducted to test the drainage capability of media containing shredded newspaper layers. Stormwater was introduced at low and high rates to bins containing zero, one, and two layers of newspaper at varying depths. While there were differences in effluent flow rates between control and newspaper treatments, surface ponding occurred in all three treatments, suggesting that some other factor besides the newspaper had an effect on drainage properties. Grain size and clay mineralogy analyses indicated that migration of finer particles into the deeper soils could have inhibited drainage.