In situ ground water denitrification in stratified, permeable soils underlying riparian wetlands

The ground water denitrification capacity of riparian zones in deep soils, where substantial ground water can flow through low-gradient stratified sediments, may affect watershed nitrogen export. We hypothesized that the vertical pattern of ground water denitrification in riparian hydric soils varies with geomorphic setting and follows expected subsurface carbon distribution (i.e., abrupt decline with depth in glacial outwash vs. negligible decline with depth in alluvium). We measured in situ ground water denitrification rates at three depths (65, 150, and 300 cm) within hydric soils at four riparian sites (two per setting) using a 15N-enriched nitrate "push-pull" method. No significant difference was found in the pattern and magnitude of denitrification when grouping sites by setting. At three sites there was no significant difference in denitrification among depths. Correlations of site characteristics with denitrification varied with depth. At 65 cm, ground water denitrification correlated with variables associated with the surface ecosystem (temperature, dissolved organic carbon). At deeper depths, rates were significantly higher closer to the stream where the subsoil often contains organically enriched deposits that indicate fluvial geomorphic processes. Mean rates ranged from 30 to 120 microg N kg(-1) d(-1) within 10 m versus <1 to 40 microg N kg(-1) d(-1) at >30 m from the stream. High denitrification rates observed in hydric soils, down to 3 m within 10 m of the stream in both alluvial and glacial outwash settings, argue for the importance of both settings in evaluating the significance of riparian wetlands in catchment-scale N dynamics.     

Explaining the Performance of Mature Municipal Solid Waste Recycling Programs

This paper assesses the contextual, programmatic and decision-making factors that affect the performance of mature municipal solid waste recycling programs. Tobit models were prepared for cities with populations of less than or more than 25?000 to facilitate analysis of recycling performance. Recycling participation rates were found to be higher among cities in both groups that offered more convenient recycling programs and whose residents had a higher mean household income. The larger cities that achieved higher participation rates employed a decision-making process known as ‘collaborative learning’, imposed sanctions on improper sorting recyclable materials, and had a larger non-minority population. Among smaller cities, higher participation was attained by using variable fee pricing for solid waste collection and by mandating household participation. The study findings suggest that future research should focus on improved ways to characterize and measure the decision-making processes used to make policy changes in order to facilitate analysis of the causal and temporal relationships between decision-making processes and program performance.     

An exploration of place as a process: The case of Jackson Hole, WY

A variety of theoretical positions and frameworks have been advanced to account for how places become “places”—in other words, how places become meaningful. Most existing frameworks share the idea that a place is a complex concept, given life by people attaching meaning to a physical setting in a variety of ways. This paper explores how places evolve as ever-shifting points of meaning that mark changes in people's lives in response to a variety of influences. Data collected from in-depth personal interviews in and around Jackson, Wyoming, are used to explore the conceptualization of place as a process, rather than a static entity. Three key themes or dimensions that were frequently described by interviewees are examined: (1) life stage/course, (2) searching for a feeling, and (3) commitment to a place. Not only did some respondents describe what made places important to them (the components, such as social ties, or favorite activities), they also described how these attributes worked together to create and maintain place meanings over the course of their lives. During the interviews, it was noted that these dimensions and processes were expressed explicitly as well as implicitly.     

In situ measurements of nitrate leaching implicate poor nitrogen and irrigation management on sandy soils

Minimizing the risk of nitrate contamination along the waterways of the U.S. Great Plains is essential to continued irrigated corn production and quality water supplies. The objectives of this study were to quantify nitrate (NO(3)) leaching for irrigated sandy soils (Pratt loamy fine sand [sandy, mixed, mesic Lamellic Haplustalfs]) and to evaluate the effects of N fertilizer and irrigation management strategies on NO(3) leaching in irrigated corn. Two irrigation schedules (1.0x and 1.25x optimum) were combined with six N fertilizer treatments broadcast as NH(4)NO(3) (kg N ha(-1)): 300 and 250 applied pre-plant; 250 applied pre-plant and sidedress; 185 applied pre-plant and sidedress; 125 applied pre-plant and sidedress; and 0. Porous-cup tensiometers and solution samplers were installed in each of the four highest N treatments. Soil solution samples were collected during the 2001 and 2002 growing seasons. Maximum corn grain yield was achieved with 125 or 185 kg N ha(-1), regardless of the irrigation schedule (IS). The 1.25x IS exacerbated the amount of NO(3) leached below the 152-cm depth in the preplant N treatments, with a mean of 146 kg N ha(-1) for the 250 and 300 kg N preplant applications compared with 12 kg N ha(-1) for the same N treatments and 1.0x IS. With 185 kg N ha(-1), the 1.25x IS treatment resulted in 74 kg N ha(-1) leached compared with 10 kg N ha(-1) for the 1.0x IS. Appropriate irrigation scheduling and N fertilizer rates are essential to improving N management practices on these sandy soils.     

Mycorrhizae increase arsenic uptake by the hyperaccumulator Chinese brake fern (Pteris vittata L.)

Chinese brake fern (Pteris vittata L.) is a hyperaccumulator of arsenic (As) that grows naturally on soils in the southern United States. It is reasonable to expect that mycorrhizal symbiosis may be involved in As uptake by this fern. This is because arbuscular mycorrhizal (AM) fungi have a well-documented role in increasing plant phosphorus (P) uptake, P and As have similar chemical properties, and ferns are known to be colonized by AM fungi. We conducted a factorial greenhouse experiment with three levels of As (0, 50, and 100 mg kg(-1)) and P (0, 25, and 50 mg kg(-1)) and with and without Chinese brake fern colonized by a community of AM fungi from an As-contaminated site. We found that the AM fungi not only tolerated As amendment, but their presence increased frond dry mass at the highest As application rate. Furthermore, the AM fungi increased As uptake across a range of P levels, while P uptake was generally increased only when there was no As amendment. These data indicate that AM fungi have an important role in arsenic accumulation by Chinese brake fern. Therefore, to effectively phytoremediate As-contaminated soils, the mycorrhizal status of ferns needs to be taken into account.     

The acetochlor registration partnership surface water monitoring program for four corn herbicides

A surface drinking water monitoring program for four corn (Zea mays L.) herbicides was conducted during 1995-2001. Stratified random sampling was used to select 175 community water systems (CWSs) within a 12-state area, with an emphasis on the most vulnerable sites, based on corn intensity and watershed size. Finished drinking water was monitored at all sites, and raw water was monitored at many sites using activated carbon, which was shown capable of removing herbicides and their degradates from drinking water. Samples were collected biweekly from mid-March through the end of August, and twice during the off-season. The analytical method had a detection limit of 0.05 microg L(-1) for alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)-acetamide] and 0.03 microg L(-1) for acetochlor [2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl)-acetamide], atrazine [6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine], and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)-acetamide]. Of the 16528 drinking water samples analyzed, acetochlor, alachlor, atrazine, and metolachlor were detected in 19, 7, 87, and 53% of the samples, respectively. During 1999-2001, samples were also analyzed for the presence of six major degradates of the chloroacetanilide herbicides, which were detected more frequently than their parent compounds, despite having higher detection limits of 0.1 to 0.2 microg L(-1). Overall detection frequencies were correlated with product use and environmental fate characteristics. Reservoirs were particularly vulnerable to atrazine, which exceeded its 3 microg L(-1) maximum contaminant level at 25 such sites during 1995-1999. Acetochlor annualized mean concentrations (AMCs) did not exceed its mitigation trigger (2 microg L(-1)) at any site, and comparisons of observed levels with standard measures of human and ecological hazards indicate that it poses no significant risk to human health or the environment.     

MODELING LIGHT ATTENUATION,SECCHI DISK,AND EFFECTS OF TRIPTON IN SENACA RIVER,NEW YORK,USA1

The development, testing, and application of a probabilistic model framework for the light attenuation coefficient for downwelling irradiance (K_d) and Secchi disc transparency (SD) that resolves the effects of several light attenuating constituents, including phytoplankton and nonliving particles (tripton), is documented. The model is consistent with optical theory, partitioning the magnitudes of the light attenuating processes of absorption and scattering according to the contributions of attenuating constituents as simple summations. The probabilistic framework accommodates variations in the character and concentrations of these constituents and ambient conditions during measurements, and recognizes a linear relationship between the magnitudes of absorption and scattering by tripton. The model is tested and applied for a 21 km reach of the Seneca River, New York, that features optical gradients caused by an intervening hypereutrophic lake and dam, and a severe infestation of the exotic zebra mussel. The model is applied to resolve the roles of phytoplankton and tripton in regulating measured longitudinal patterns of SD along the study reach of the river and increases in SD since the zebra mussel invasion, and to predict decreases in K_d since the invasion.     

BASE FLOW RECESSION RATES,LOW FLOWS,AND HYDROLOGIC FEATURES OF SMALL WATERSHEDS IN PENNSYLVANIA,USA1

This paper examines the relationships between measurable watershed hydrologic features, base flow recession rates, and the Q_7,10 low flow statistic (the annual minimum seven‐day average streamflow occurring once every 10 years on average). Base flow recession constants were determined by analyzing hydrograph recession data from 24 small (>130 km²), unregulated watersheds across five major physiographic provinces of Pennsylvania, providing a highly variable dataset. Geomorphic, hydrogeologic, and land use parameters were determined for each watershed. The base flow recession constant was found to be most strongly correlated to drainage density, geologic index, and ruggedness number (watershed slope); however, these three parameters are intercorrelated. Multiple regression models were developed for predicting the recession rate, and it was found that only two parameters, drainage density and hydrologic soil group, were required to obtain good estimates of the recession constant. Equations were also developed to relate the recession rates to Q_7,10 per unit area, and to the Q_7,10/Q₅₀ ratio. Using these equations, estimates of base flow recession rates, Q_7,10, and streamflow reduction under drought conditions can be made for small, ungaged basins across a wide range of physiography.     

BASE FLOW TRENDS IN URBANIZING WATERSHEDS OF THE DELAWARE RIVER BASIN1

Rapid land development is raising concern regarding the ability of urbanizing watersheds to sustain adequate base flow during periods of drought. Long term streamflow records from unregulated watersheds of the lower to middle Delaware River basin are examined to evaluate the impact of urbanization and imperviousness on base flow. Trends in annual base flow volumes, seven‐day low flows, and runoff ratios are determined for six urbanizing watersheds and four reference watersheds across three distinct physiographic regions. Hydrograph separation is used to determine annual base flow and stormflow volumes, and nonparametric trend tests are conducted on the resulting time series. Of the watersheds examined, the expected effects of declining base flow volumes and seven‐day low flows and increasing stormflows are seen in only one watershed that is approximately 20 percent impervious and has been subject to a net water export over the past 15 years. Both interbasin transfers and hydrologic mechanisms are invoked to explain these results. The results show that increases in impervious area may not result in measurable reductions in base flow at the watershed scale.