Water Quality of Hydrologic Systems Posters
Presiding: T Meixner, University of Arizona; J Hogan, University of Arizona; J Zepeda-Arce, University of Minnesota
H13A-01 1330h
Regional Analysis of One Dimensional Nitrate Transport Through the Vadose Zone Using a Geographic Information System
Wilmot Township is located in southwestern Ontario within the Grand River Watershed. The township is approximately 266 square kilometers, of which 80 percent is classified as farmland. A majority of the region relies on groundwater as the source of drinking water and it is therefore important to determine the effect of crop fertilization on the groundwater quality. The purpose of this study is to determine the one-dimensional transport of nitrate through the vadose zone to the water table with attenuation due to biodegradation. The model is simulated over a 30-year period to investigate the impact of seasonal applications of nitrate fertilizers on the concentration at the water table. Based on land use/land class maps, ArcView GIS is used to spatially define the location of fertilizer applications. Fertilizer sources are determined from Statistics Canada's Agricultural Census and include livestock manure and popular commercial fertilizers for the past 30 years. A physically based and readily implemented methodology for estimating recharge, as developed by Jyrkama (2003), is used to approximate the advective velocity through the soil column. This research methodology can be applied at the watershed scale. Future large-scale modeling will be performed on the Grand River Watershed, which is approximately 7000 square kilometers. Municipalities can utilize this model as a management tool to determine the extent of contamination and delineate site sensitive locations, such as well-head protection zones. This research is a first step in developing agricultural contaminant loadings for a regional scale surface water and groundwater model.
H13A-02 1330h
Watershed Characteristics Influencing Stream Nutrient Concentrations Across a Rural-to-Urban Land Use Gradient
We assessed the influence of several watershed-scale features on mean annual stream inorganic nitrogen (N) and phosphorus (P) concentrations in 23 urbanizing catchments (rural-to-urban) dominated by non-point source inputs. Population density was not a strong predictor of N or P concentrations across the gradient, while residential land use (%) explained 52% of the NO3 variability both across the gradient and even more variability (0.70%) in a subset of catchments with intermediate population densities (suburban, 100 to 620 people / km2). A multiple regression using percent wetlands and septic density explained a similar amount (51 and 73 %) of the NO3 variability across the rural-to-urban gradient and within suburban watersheds, highlighting the potential role of septic wastewater and wetlands as N sources and sinks, respectively. Isotopic data (15N-NO3) suggested that wastewater was the dominant source of NO3 in suburban and urban watersheds. While residential land use was the best single predictor, it provided little information on mechanisms controlling stream chemistry. In contrast, the use of wetland percentage and septic density in a multiple regression explained as much variability and suggested key sources and sinks for management at the watershed-scale.
H13A-03 1330h
Accumulation of Nitrogen in the Pore Water of Anoxic Lake Sediments
The impact of soil runoff nitrogen on the Silver Lake of Iowa was assessed in this study. Currently, the lake cannot support its designated uses as a recreational water body. Extensive algal blooms characterize the lake in late summer, lowering the dissolved oxygen content in water (< 2.0 mg/L). The goal of this study was to map the buildup of nitrogen in the pore water of lake sediments and come up with recommendations for restoration strategies. Sediment cores were taken from 20 sites along 5 transects in the lake. In the top 5 cm of the sediments, the pore water nitrogen ranges between 1.8 and 733.1 micro-gm of nitrate per gm of sediments. The average concentration is 94 micro-g/gm. Vertically, nitrate concentrations were measured at 90 micro-g/gm at 0-10 cm, 95 micro-g/gm at 10-20 cm, and 19 micro-g/gm at 20-30 cm. The sharp decline in nitrate below the 20 cm depth in the sediment is attributed to biochemical reduction of nitrate through denitrification in relatively older, much anoxic sediments. The above results indicate that sediments in Silver Lake are heavily contaminated with N trapped in the pore water. The primary sources of N are the surrounding croplands and an active hog lot on the southeastern lakeshore. The average rate of sedimentation in the lake has been 1 cm/year in the last 32 years. Upon sedimentation, the pore water N is slowly released to the lake water, thereby dramatically limiting the lake's capability to process incoming nutrients. The mass distribution of N in the lake was estimated as 3.66 x 103 kg (65%) in bottom sediments, 172 kg (3%) in suspended particulates, and 1.83 x 103 kg (32%) in the dissolved phase. Some of the recommendations made through this study include dredging the top 25 cm of lake sediments, applying buffer strips along the lake's northern and eastern shorelines, and reducing the application of N and P-based fertilizers.
H13A-04 1330h
Concentrated Flow through a Riparian Buffer: A Case Study
Riparian buffers are often used for in-situ treatment of agricultural runoff. Although the benefits of riparian buffers are well recongized, concentration of flow can restrict the efficiency of contaminant removal. This study evaluates flow concentration at a agricultural site near Manhattan, Kansas. Manual and automated GIS analyses of a high-resolution digital elevation model were used to determine the fraction of runoff contributing to each buffer segment. Subsequent simulation of the system in WEPP (Water Erosion and Prediction Project) demonstrates the extent to which flow concentration affects buffer efficiency. Recommendations are presented for the design of adaptive-width buffers.
H13A-05 1330h
Assessing the Effectiveness of Forest Best Management Practices in two Louisiana Watersheds
A manual recommending Best Management Practices (BMP) for Louisiana foresters was produced in 2000. There is deficient information on the effectiveness of BMP reducing non point source pollution in streams located in forested areas of Louisiana. A new study assessing the effectiveness of forest BMP is being initiated and will be conducted in two small watersheds in Central Louisiana. The objectives of this study are to quantify changes in stream flow and water quality after BMP treatment, assess the magnitude of the impact, and develop a model that will quantify the impacts. To achieve this goal, two sampling approaches will be used to monitor water quality within the watershed over a two year period. An intensive method will sample storm water runoff in proximity to the treated area and an extensive method will sample water monthly at locations downstream from the treated area. With the collected data, an evaluation of BMP effectiveness based on changes in water quality and flow at the intensive and extensive monitoring sites will be produced. The research concept, methodology, and analytical procedures for this study are presented.
H13A-06 1330h
Analyses of Citizen - Collected Water Quality Data: Bridging the Gap between "Hot Spots" to Understanding Processes
Monitoring and stewardship of watershed systems is increasingly being undertaken by citizen and non-profit groups. Regular monitoring of water quality being done by many of these organizations is quality controlled and can yield continuous, high-quality data sets. In many cases these data are only being used for preliminary analyses: identifing so-called "hot-spots" or tracking improvement over time. However, these data are suitable for more intensive analyses, and techniques such as principal components analysis may yield more comprehensive understanding of the processes and modes of variability at work. Here, we analyze data from 13 citizen-monitored water quality parameters of the Neponset River and several tributaries in Eastern Massachusetts. We found that different modes of variability emerged from the main river vs. the tributaries and that factors such as stream size and land use could be correlated with specific identified components. This type of analysis could be used by many local watershed associations to better understand their watersheds and to aid in developing long term strategies for protecting and improving the health of the watershed systems.
H13A-07 1330h
Organic Carbon Fluxes From the Atchafalaya River Into the Gulf of Mexico
The continental flux of organic carbon to the ocean represents a significant component of the global carbon cycle. The total amount and timing of the fluxes may have crucial impacts on marine ecosystems and habitats, yet its seasonal and annual variations have not been well investigated. This study analyzed twenty-five years of total organic carbon (TOC) fluxes from the Atchafalaya River which transports thirty percent of the Mississippi River into the Gulf of Mexico. By utilizing the Atchafalya's long-term discharge and water quality data from 1978 thru 2002, the monthly and annual TOC fluxes were quantified, and their seasonality and interannual variation in relationship with the river's hydrologic conditions were investigated. The results showed that annual TOC fluxes from the Atchafalaya averaged 1,093,625 Mg, varying from 642,555 Mg in the dry year of 2000 to 1,466,981 Mg in the wet year of 1979. Monthly TOC fluxes from the river averaged 91,135 Mg and were highest from March to June (132,582 Mg mon-1) and lowest from August to November (49,117 Mg mon-1). The large variations in both monthly and annual TOC fluxes were closely related to the amount of the river's discharge.
H13A-08 1330h
A Mass Balance Analysis of Total Mercury Flux Through a Large, Managed Floodplain
The fate and transport of mercury are of critical concern in lowland floodplains worldwide. Increasing attention has been paid to the uncertainty of mercury sources and sinks in the Sacramento Valley, which is still recovering from decades of gold mining that used mercury for gold separation. Active in floods, Yolo Bypass is the largest flood-control bypass (or conveyance floodway) on the Sacramento River and is a key conduit for flow (up to 15,000 m(3)s(-1)) and the transport of fine sediment and adsorbed mercury to the San Francisco-Sacramento Bay-Delta. The 24,000 hectare bypass located in the lower Sacramento Valley has been recently implicated as a likely storage site for mercury with a high risk for methylation and transmission into the food chain at the primary wintering stop on the Pacific Flyway. In order to assess contaminant risk in the bypass, quantitative relationships between (1) total mercury concentration and suspended sediment concentration and (2) suspended sediment concentration and flow were developed for each of its major inputs and outputs using event-based sample data from various sources. These relationships were improved by incorporating dynamics of seasonal exhaustion and intraflood exhaustion (hysteresis) of sediment and mercury. From this characterization of how the flow-sediment-mercury transport system functions we were able to characterize the relative contributions of the various inputs. While the main inflow to the bypass is via flood weirs along the Sacramento River, two major creeks and an agricultural runoff canal made significant contributions to flow, sediment and mercury loads. Using the continuous record of flow to estimate sediment transport and sediment transport to estimate mercury flux we computed the net transfer of mercury through the bypass over a five-year period. Based on the volume and source of the expected change in flow and sediment, we were able to evaluate how mercury loading might change in the future due to proposed structural changes to the bypass. The research results have implications for mercury mitigation and floodplain restoration.
H13A-09 1330h
Arsenic Species Distribution in a Hydrologic System Near a Skarn Deposit
The purpose of this study is to understand the distribution of arsenic species in the hydrologic system and to compare sampling and analyzing methods. A well-known and historical iron mine, located in the suburb of Ulsan in Korea, has been identified as the source of environmental problems because of high arsenic contents. This mine formed as a calcareous skarn deposit represented by ore pipe in the boundary between early Tertiary granite and Cretaceous sedimentary rocks, Hayang Group. A total of 18 water samples, including eight groundwater, nine creek-water and a spring water, were collected around the mine. For total arsenic concentrations, samples were filtered then acidified by concentrated HNO3, and analyzed by HG-ICP-AES. For arsenic species analysis, samples were divided into two sub-samples. One was only filtered and analyzed by LC-ICP-MS within 24 h. The other was filtered then added phosphoric acid, and analyzed by LC-ICP-MS within 72 h. In results of total As analysis, a spring water showed the concentration of 300 ug l-1, and two groundwater samples around 70 ug l-1. Only one groundwater sample had an As concentration less than 10 ug l-1. In the downstream of studied two creeks, As concentrations were 42 and 53 ug l-1. For arsenic speciation, As(V) was the only present species in groundwater and the major one in surface water. In surface water, As(III) existed in a small fraction except one sample which showed higher As(III) concentration than As(V). And a surface water sample near the spring had As(III), As(V), DMA and unknown peak which showed before As(III), inferred as AsB. Two sub-samples for arsenic speciation showed similar results. Addition of phosphoric acid appeared successfully preserve samples for at least 72 h.
H13A-10 1330h
Toxicity and Geochemistry of Missouri Cave Stream Sediments
Water and sediment quality are among the most important variables affecting the survival of stygobites. In Tumbling Creek Cave, Taney County Missouri the population of the endangered cave snail, Antrobia culveri, has declined significantly over the past decade. The cause of the population decline is unknown but could be related to the quality of streambed sediment in which the cave snail lives. The objective of this study was to determine the toxicity and concentrations of heavy metals in the sediment of Tumbling Creek Cave and five other caves in Missouri. These sediments were analyzed to assess possible point sources from within the recharge areas of the caves and to provide baseline geochemical data to which Tumbling Creek Cave sediments could be compared. Standard sediment toxicity tests and ICP-MS analysis for heavy metals were conducted. Survival and reproduction of the amphipod, Hyalella azteca, did not differ significantly between cave sediments and a control sediment. However the growth of amphipods differed significantly among sites and was significantly reduced in sediments from Tumbling Creek Cave relative to controls. Concentrations of several metals in sediments differed substantially among locations, with elevated levels of zinc and copper occurring in Tumbling Creek Cave. However, none of the measured metal concentrations exceeded sediment quality guidelines derived to predict probable effects on benthic organisms and correlations between sediment metal concentrations and toxicity endpoints were generally weak. While elevated metal levels may play a part in the cave snail's decline, other factors may be of equal or greater importance. Ongoing analyses of persistent organic contaminants and total organic carbon in cave sediments, along with continued water quality monitoring, may provide data that will allow us to better understand this complicated problem.