TEMPORAL CHANGES IN THE YADKIN RIVER FLOW VERSUS SUSPENDED SEDIMENT CONCENTRATION RELATIONSHIP1

ABSTRACT: Dynamic linear models (DLM) and seasonal trend decomposition (STL) using local regression, or LOESS, were used to analyze the 50‐year time series of suspended sediment concentrations for the Yadkin River, measured at the U.S. Geological Survey station at Yadkin College, North Carolina. A DLM with constant trend, seasonality, and a log₁₀ streamflow regressor provided the best model to predict monthly mean log₁₀ suspended sediment concentrations, based on the forecast log likelihood. Using DLM, there was evidence (odds approximately 69:1) that the log₁₀ streamflow versus log₁₀ suspended sediment concentration relationship has changed, with an approximate 20 percent increase in the log₁₀ streamflow coefficient over the period 1981 to 1996. However, sediment concentrations in the Yadkin River have decreased during the decade of the 1990s, which has been accompanied by a concomitant increase in streamflow variability. Although STL has been shown to be a versatile trend analysis technique, DLM is shown to be more suitable for discovery and inference of structural changes (trends) in the model coefficient describing the relationship between flow and sediment concentration.     

Bioconcentration, biomagnification and metabolism of 14C-terbutryn and 14C-benzo[a]pyrene in Gammarus fossarum and Asellus aquaticus

The contribution of bioconcentration and biomagnification of 14C-terbutryn and 14C-benzo[a]pyrene via food and water to the bioaccumulation in Gammarus fossarum and Asellus aquaticus was investigated in single species-tests. In this investigation the uptake of 14C-terbutryn and 14C-benzo[a]pyrene via food and water by G. fossarum (L.) and A. aquaticus (L.) was examined. Bioconcentration factors (BCFs) and biomagnification factors (BMFs) were determined. Calculated BCFs were clearly higher than BMFs, indicating that water is the primary route of uptake. The uptake of terbutryn and benzo[a]pyren via water in G. fossarum and A. aquaticus is faster than uptake via food. The elimination and metabolism of the two chemicals by G. fossarum and A. aquaticus were studied. Terbutryn was eliminated almost completely in both species. In general, the elimination of terbutryn from G. fossarum and A. aquaticus was fast with half-life of 5 h. The elimination of terbutryn by G. fossarum after biomagnification is slower than after bioconcentration. No difference was found in elimination of terbutryn by A. aquaticus after biomagnification and after bioconcentration. Metabolites of terbutryn in G. fossarum and A. aquaticus were analyzed by HPLC. After the bioconcentration experiment a higher percentage of metabolites was found in G. fossarum than in A. aquaticus. This was confirmed for the experiment with uptake via food. The spectrum of metabolites was similar in both species, with hydroxyterbutryn being the major metabolism product in water. 14C-B[a]P could nearly completely be eliminated by G. fossarum (rest of activity 2%) after uptake via water. 14C-B[a]P could not be eliminated by G. fossarum and A. aquaticus after uptake via food. The metabolite could not be identified.     

Toxicity assessment of a common laundry detergent using the freshwater flagellate Euglena gracilis

Synthetic detergents are among the commonly used chemicals in everyday life. Detergents, reaching aquatic environments through domestic and municipal wastewater, can cause many different effects in aquatic organisms. The present study was aimed at the toxicity evaluation of a commonly used laundry detergent, Ariel, using the freshwater flagellate Euglena gracilis as a biotest organism. Different parameters of the flagellate like motility, swimming velocity, cell shape, gravitactic orientation, photosynthesis and concentration of light harvesting pigments were used as end points for the toxicity assessment. No Observed Effect Concentration (NOEC) and EC₅₀ values were calculated for the end point parameters at four different incubation times, i.e. 0, 6, 24 and 72 h. After 72 h incubation, swimming velocity of the cells was found to be the most sensitive parameter giving NOEC and EC₅₀ values of 10.8 and 34 mg L⁻¹, respectively. After 72 h exposure to the detergent, chlorophyll a and total carotenoids were significantly decreased in cultures treated with Ariel at concentrations of 50 mg L⁻¹ and above while chlorophyll b significantly decreased at concentrations above 750 mg L⁻¹. The maximum inhibitory effect on the quantum yield of photosystem II was observed after 24 h exposure and thereafter a recovery trend was observed. Motility, gravitaxis and cell shape were strongly impaired immediately upon exposure to the detergent, but with increasing exposure time these parameters showed acclimatization to the stress and thus the NOEC values obtained after 72 h were higher than those immediately after exposure.     

Alternative carbon dioxide modelling approaches accounting for high residual gases in LandGEM

High Canadian waste disposal rates necessitate landfill gas monitoring and accurate forecasting. CO₂ estimates in LandGEM version 3.02 currently rest on the assumptions that CO₂ is a function of CH₄, where the two gases make up nearly 100% of landfill gas content, leading to overestimated CO₂ collection estimates. A total of 25 cases (five formulas, five approaches) compared annual CO₂ collection at four western Canadian landfills. Despite common use in literature, the 1:1 ratio of CH₄ to CO₂ was not recommended to forecast landfill gas collection in cold climates. The existing modelling approach significantly overestimated CO₂ production in three of four sites, resulting in the highest residual sum of squares. Optimization resulted in the most accurate results for all formulas and approaches, which had the greatest reduction in residual sums of squares (RSS) over the default approach (60.1 to 97.7%). The 1.4 Ratio approach for L _o:L _o-CO2 yielded the second most accurate results for CO₂ flow (mean RSS reduction of 50.2% for all sites and subsection models). The annual k-modified LandGEM calculated k’s via two empirical formulas (based on precipitation) and yielded the lowest accuracy in 12 of 20 approaches. Unlike other studies, strong relationships between optimized annual k’s and precipitation were not observed.

     

Attribution of Carbon Dioxide Fluxes to Crop Types in a Heterogeneous Agricultural Landscape of Argentina

The increasing proportion of agricultural lands worldwide makes it necessary to intensify the research concerning the carbon exchange at agricultural sites. In order to determine the Net Ecosystem Exchange (NEE) in an agricultural landscape in the province of Buenos Aires, Argentina, we carried out eddy covariance measurements with a flux tower, which was placed between two agricultural fields. Therefore, the measured CO₂ flux represents the accumulated flux from both areas, i.e., from different crop types. We here present an analysis method which attributes the flux to the two crop types. For this analysis, we applied the Hsieh footprint model to identify the contributing source area to the flux measurement. We then applied a multiple regression analysis to calculate the NEE in the growing season 2011/2012 for each field separately. The pronounced differences in the time courses of the CO₂ fluxes in the two fields can be explained by the different sowing times and different growth stages of both cultivations. The time courses furthermore show that the CO₂ uptake of the plants was strongly affected by the drought which lasted from December 2011 to January 2012. For the growth cycle of maize (216 days), the NEE was ?240 g C m^?2 and for the growth cycle of soybean (154 days) ?231 g C m^?2. In order to obtain the NEE of a complete agricultural cycle (from harvest to harvest), we also considered the NEE of autumn and winter 2011. Uncertainties of the spatially partitioned NEE are quantified and discussed.