D. E. Line

Field study of the ability of two grassed bioretention cells to reduce storm-water runoff pollution.

Two grassed bioretention cells including internal storage zones (ISZs) were monitored for 16 months in central North Carolina. Each cell had a surface area of 106 m2 and fill media depths were 0.75 and 1.05 m for the north (North) and the south (South) cells, respectively. Asphalt parking lot inflow and outflows were analyzed for nitrogen and phosphorus forms and fecal coliform (FC). Outflow volumes and peak flows for individual storms were generally less than those of inflow. Overall, except for N O2,3 –N , effluent nitrogen species event mean concentrations (EMCs) and loads were significantly (α=0.05) lower than those of the inflow, and nitrogen species load reductions ranged from 47 to 88%. Apart from fall and winter, during which a longer hydraulic contact time seemed to be needed, the ISZs appeared to improve denitrification. Total phosphorus (TP) and OP O4 -P EMCs were significantly lower than those of the inlet. Reductions were 58% (South) and 63% (North) for TP and 78% (North) and 74% (South) for ...

Changes in a Stream's Physical and Biological Conditions Following Livestock Exclusion

Runoff from dairy cow pastures can degrade the quality of surface waters. Weekly grab samples were collected for 7.5 years from a small stream draining a 56.7–ha, mostly dairy cow pasture and analyzed for fecal coliform and enterococci (streptococci). In situ measurements of pH, dissolved oxygen, temperature, conductivity, and turbidity were made during most grab sampling events. Fecal coliform and enterococci levels for samples collected during the 2.25 years prior to the installation of livestock exclusion fencing were more than 300% greater at the downstream monitoring station compared to the upstream station. After fencing, fecal coliform and enterococci levels decreased 65.9% and 57.0%, respectively. The decreased bacteria levels were significantly different, indicating that livestock exclusion fencing was effective at reducing bacteria levels in the stream. While the levels of dissolved oxygen, pH, temperature, and specific conductivity downstream relative to upstream following fencing generally documented improved water quality, the changes were not statistically significant. Conversely, decreases in turbidity and suspended sediment levels following fencing were significantly different. Levels of most of the physical parameters and bacteria were not significantly different at the upstream monitoring site following the installation of the alternate water supply in the pasture upstream. Thus, the alternate water supply, without fencing, was not effective at improving water quality in the upper pasture.

Bioretention Outflow: Does It Mimic Nonurban Watershed Shallow Interflow?

Bioretention, a key structural practice of low impact development (LID), has been proved to decrease peak flow rates and volumes, promote infiltration and evapotranspiration, and improve water quality. Exactly how well bioretention mimics predevelopment (or “natural”) hydrology is an important research question. Do bioretention outflow rates mirror shallow groundwater interevent stream recharge flow associated with natural or nonurban watersheds? Streamflow from three small, nonurban watersheds, located in Piedmont, part of central North Carolina, was compared with bioretention outflow from four cells also in North Carolina’s Piedmont region. Each benchmark watershed drained to a small stream, where flow rate was monitored for an extended period of time. After normalizing the flow rates and volumes by watershed size, data were combined to form two data sets: bioretention outflow and stream interevent flow. Results indicate that there is no statistical difference between flow rates in streams draining unde...

Tracking Salmonella Contamination in Various Watersheds and Phenotypic and Genotypic Diversity

Salmonella enterica is an important foodborne pathogen, and contamination of surface and ground water that may result from various human activities, such as animal production and urbanization, may contribute to the public health burden. The aims of this study was to determine the sources of Salmonella contamination in four different types of watersheds and to assess the relative contribution of multidrug-resistant strains. Eighty-six water samples collected from four different watershed systems, including those impacted by swine production (n = 12), residential/industrial (n = 34), crop agriculture (n = 12), and forestry (n = 28), were cultured for Salmonella and further characterized by serotyping, antimicrobial susceptibility testing, and pulsed-field gel electrophoresis genotyping. Salmonella prevalence was high in all four watersheds: residential/industrial area (58.8%), forestry (57.1%), crop agriculture (50%), and swine production (41.7%). Majority of the Salmonella isolates (87.1%) were pansusceptible. Multidrug resistance up to eight antimicrobials (R-type: AmStTeAxChCeKmGm) was detected in water samples that originated from swine production systems only. Serovars identified included Anatum, Gaminara, and Inverness (18.3% each) and Muenchen and Newport (8.7% each), Bredeny (7.6%), and Montevideo (6.8%). Pulsed-field gel electrophoresis analysis indicated genotypic relatedness among Salmonella recovered from residential/industrial and forestry-associated watersheds (genotypic cluster types A, C, D, E, F, G, H, and J), sites with relatively close geographic proximity. Swine-production-associated isolates were distinctly different from the others (genotypic cluster types B and I), corroborating the phenotypic findings. Overall, the findings suggest that all the various watersheds, including natural forest, remain important contributors of Salmonella contamination. While swine-production-associated water samples were not found to have a disproportionately high prevalence, it was the most important reservoir of multidrug-resistant strains.

EVALUATING THE EFFECTIVENESS OF TWO STORMWATER WETLANDS IN NORTH CAROLINA

Two constructed stormwater wetlands in North Carolina were monitored to document their efficiencies at reducing nitrogen, phosphorus, and sediment loads in runoff from urban areas. Inflow to and outflow from the two wetlands were monitored during at least ten storm events, and flow-proportional samples of each were collected and analyzed. The first wetland (CMS), located in the Piedmont region, had a relatively low wetland surface to drainage area ratio of 2.2%, while the second (UNC), located in the mountains region, had less storage and a wetland surface to drainage area ratio of 4.7%. The UNC wetland had a much more diverse and extensive plant community. For the CMS wetland, the median load reduction efficiencies of nitrogen forms ranged from 47% to 54%, while the corresponding reductions for the UNC wetland ranged from 57% to 71%. The median reduction efficiencies for phosphorus forms for the CMS wetland ranged from 59% to 76%, while those for the UNC wetland ranged from -95% to 70%. The median reduction efficiencies for TSS were 72% and 88% for the CMS and UNC wetlands, respectively. The median load reduction efficiencies of nitrogen forms, total phosphorus, and sediment for the UNC wetland were greater than for the CMS wetland and were considerably greater than corresponding median efficiencies of other completed studies. These results indicate that both of these wetlands were, in general, more efficient at reducing pollutant loading than many others reported in the literature. The greater efficiencies may be the result of a relatively high surface area to drainage area ratio and a diverse plant community in the UNC wetland and a considerable storage capacity of the CMS wetland.

Efficiencies of temporary sediment traps on two north carolina construction sites

Sediment export from construction sites is receiving increasing scrutiny, and correspondingly the efficiencies of sediment controls are being questioned. Sediment or total suspended solids (TSS) and total phosphorus (TP) concentrations in outflow from, as well as sediment accumulation, in three temporary sediment traps located on North Carolina construction sites were monitored to assess the efficiencies of the traps. The trapping efficiency of the trap located on a Coastal Plain site (Woodsong) was 69%, while the efficiencies of two traps located on a Piedmont site (Carpenter) averaged 59%. In addition, the Carpenter trap retained 30% of the TP coming off the site, while the Woodsong trap retained 9%. Sediment size analyses of a limited number of samples indicated that the Woodsong trap retained 91%, 43%, and 21% of the sand, silt, and clay primary particles entering the trap, while the Carpenter traps retained 68%, 72%, and 40% of the sand, silt, and clay particles entering it. The turbidity of outflow samples was also measured and correlated to TSS concentrations. A relatively strong linear correlation was found for data from the Carpenter traps (r2 = 0.96), and a weaker correlation was documented for the Woodsong trap (r2 = 0.64). These data indicate that for sites with high TSS concentrations in runoff and relatively little organic matter left on the site, TSS may be computed from turbidity; however, more data is needed to confirm this assertion.

Evaluating the Effectiveness of Two Stormwater Wetlands in North Carolina

Two constructed stormwater wetlands in North Carolina were monitored to document their efficiencies at reducing nitrogen, phosphorus, and sediment loads in runoff from urban areas. Inflow to and outflow from the two wetlands were monitored during at least ten storm events, and flow-proportional samples of each were collected and analyzed. The first wetland (CMS), located in the Piedmont region, had a relatively low wetland surface to drainage area ratio of 2.2%, while the second (UNC), located in the mountains region, had less storage and a wetland surface to drainage area ratio of 4.7%. The UNC wetland had a much more diverse and extensive plant community. For the CMS wetland, the median load reduction efficiencies of nitrogen forms ranged from 47% to 54%, while the corresponding reductions for the UNC wetland ranged from 57% to 71%. The median reduction efficiencies for phosphorus forms for the CMS wetland ranged from 59% to 76%, while those for the UNC wetland ranged from -95% to 70%. The median reduction efficiencies for TSS were 72% and 88% for the CMS and UNC wetlands, respectively. The median load reduction efficiencies of nitrogen forms, total phosphorus, and sediment for the UNC wetland were greater than for the CMS wetland and were considerably greater than corresponding median efficiencies of other completed studies. These results indicate that both of these wetlands were, in general, more efficient at reducing pollutant loading than many others reported in the literature. The greater efficiencies may be the result of a relatively high surface area to drainage area ratio and a diverse plant community in the UNC wetland and a considerable storage capacity of the CMS wetland.

Effectiveness of LID for Commercial Development in North Carolina

AbstractThe purpose of this project was to characterize runoff and pollutant export from three commercial sites: one with no storm water control measures (NoTreat), one with a wet detention basin (WetBasin), and one with low impact development (LID) measures. The sites were located in the Piedmont and Coastal Plain physiographic regions of central North Carolina. Rainfall, runoff, and pollutant concentrations were monitored at each site for more than one year by using automated rain gauges and samplers. The storm event mean concentrations (EMCs) of total kjeldahl nitrogen (TKN), nitrate+nitrite nitrogen (NOx-N), and total phosphorus (TP) in runoff were generally less than corresponding EMCs for many other urban areas in the United States. Also, EMCs were similar to those found for eight parking lots in North Carolina. Storm runoff to rainfall ratio was greatest for the NoTreat site and least for the WetBasin site, which was anticipated because the NoTreat site had no detention/storage and the WetBasin sit...

WATERSHEDSS GRASS-AGNPS MODEL TOOL

A modeling tool that utilizes a raster-based geographic information system to build an input file for the spatially distributed pollutant runoff model, AGNPS, was developed as a component of the WATERSHEDSS decision support system. In addition to automatically computing input data from basic soils, topography, and land use maps, this modeling tool adds the capability to input point source, channel characteristic, and pesticide application data for userselected areas in the watershed. The tool was used to simulate runoff and sediment, nitrogen, and phosphorus loads for a small gaged watershed located in North Carolina. Output from the tool was compared to observed runoff and pollutant loads for 11 storms. Statistical comparisons between observed and model-simulated loads at two monitoring stations showed no significant difference between observed and predicted runoff volumes and nitrogen, phosphorus, and sediment loads, indicating that the modeling tool provides reasonable estimates of pollutant loads from storm events.

Constructed Storm-Water Wetland Installation and Maintenance: Are We Getting It Right?

Constructed storm-water wetlands (CSWs) have become one of the more popular storm-water control measures (SCMs). CSWs offer a hybrid between larger detention technologies like storm-water wet ponds and newer green infrastructure technologies. The systems are characterized as being predominately shallow retention practices, with water elevations sufficiently low to support diverse flora and fauna. Figs. 1(a–c) illustrate several successful examples of CSWs. Many researchers have found that CSWs remove sediment, nutrients, and metals from storm-water runoff (Greenway 2004; Hathaway and Hunt 2010; Line et al. 2008; Kohler et al. 2004; Wadzuk et al. 2010). One of the principal drivers for the use of storm-water wetlands is the amount of credit awarded to them by various governmental agencies with respect to nutrient removal and sequestration [North Carolina Department of Environment and Natural Resources (NCDENR) 2009]. The apparent improvement in nutrient capture from storm-water runoff over that of storm-water wet ponds is one of the main reasons designers choose CSWs over the more traditional wet pond. Extensive coverage of vegetation allows for several pollutant removal mechanisms: filtration of particles, stabilization of sediments, nutrient uptake, microbialrhizophere interaction to promote nitrification and denitrification, and the provision of increased surface area for biofilm/periphyton growth (Greenway 2004). In regions where thermal loads threaten cold water fisheries, CSWs have been shown to release cooler water to streams than do wet ponds because of the shading caused by the vegetation—but absent from wet ponds (Jones and Hunt 2010). Some concerns have also presented themselves with respect to CSWs, which have prevented the practice from outright replacing the wet pond. Foremost among them is the threat of mosquito infestation that wetlands invariably face in relation to the public (QDNR 2000). Research has shown that exorbitantly high mosquito populations need not accompany CSWs, provided they are diversely vegetated (Greenway et al. 2003; Hunt et al. 2006). However, if wetlands are allowed to become monocultures of specific mosquito-protective plants, such as Typha spp. (commonly referred to as cattails in the United States), they can become the very mosquito breeding grounds that the public fears (Greenway et al. 2003; Hunt et al. 2005). If storm-water wetlands are to be constructed, they must both (1) meet their intended water quality (and hydrologic) design goals and (2) not be a public nuisance. Anecdotal observation of CSWs constructed worldwide shows how many well-intended CSW designs fail. Two principal reasons were identified: One appears to be that not enough care was taken to ensure the storm-water wetlands’ normal pool elevation was appropriately shallow (that is, often the elevation of water in CSWs is too deep). The cause has been previously identified by Greenway et al. (2007). The second is clogging of the outlet structure that artificially raises the elevation above normal pool for extended periods of time. In both cases, simple preventative actions could be taken to ensure constructed storm-water wetlands maintain their designed integrity. The purpose of this forum is to document how poor design and inadequate management of two CSWs caused each to effectively become wet ponds, which results in (1) a reduced efficiency in the removal of some pollutants; (2) a degradation of biodiversity, which leads to an increased risk of having the wetlands become mosquito breeding grounds; and (3) degraded aesthetics.