Characterizing Storm Hydrograph Rise and Fall Dynamics With Stream Stage Data1

Abstract: Storm‐flow transients (i.e., hydrograph rise and fall dynamics) may represent an important aspect of understanding streamflow dynamics. However, little is known about how temporal resolution of transient data and climate variability may color these potential indicators of hydrologic pattern or condition. Warm‐season stream stage and rainfall were monitored continuously (5 min) during the 2002 water year in eight tributaries of the Little Miami River (Ohio), which drain 17‐58 km² catchments. Rise rates generated using 5‐min data were different than those generated with mean daily data [calculated with the Indicators of Hydrologic Alteration (IHA) software], though fall rates were similar for fine and coarse temporal data. This result suggests that data with low temporal resolution may not be adequate to fully represent the dynamics of storm rise rates. Conversely, fall rates based on daily stage data (via IHA) were similar to those based on the 5‐min data, and so daily mean data may be appropriate for characterizing fall rates. We next analyzed the possible correlations between rainfall variability and storm‐flow stage dynamics. We derived rise and recession rates from storm stage hydrographs by assuming exponential rise and decay of a runoff peak. We found that raw rise rates (R_raw) were correlated with both the maximum rainfall rate and the time to the centroid of a rain event. We subsequently removed the trend based on these rainfall characteristics, which yielded new representations of rise rates abbreviated as R_rate and R_tcent, respectively, and that had lower variability than the uncorrected (raw) data. Fall rates were found to be independent of rainfall characteristics. Due to the predominant influence of stream hydrology upon aquatic biota and nutrient fluxes, our work suggests that these stage data analysis protocols can refine or otherwise reduce variability in these indices by accounting for relevant factors such as rainfall forcing. These protocols for derivation of transient indices should be tested for their potential to improve correlations between stream hydrology and temporally aligned biotic data and dissolved nutrient fluxes in streams.     

Streambank Soil and Phosphorus Losses Under Different Riparian Land‐Uses in Iowa1

Abstract: Phosphorus and sediment are major nonpoint source pollutants that degrade water quality. Streambank erosion can contribute a significant percentage of the phosphorus and sediment load in streams. Riparian land‐uses can heavily influence streambank erosion. The objective of this study was to compare streambank erosion along reaches of row‐cropped fields, continuous, rotational and intensive rotational grazed pastures, pastures where cattle were fenced out of the stream, grass filters and riparian forest buffers, in three physiographic regions of Iowa. Streambank erosion was measured by surveying the extent of severely eroding banks within each riparian land‐use reach and randomly establishing pin plots on subsets of those eroding banks. Based on these measurements, streambank erosion rate, erosion activity, maximum pin plot erosion rate, percentage of streambank length with severely eroding banks, and soil and phosphorus losses per unit length of stream reach were compared among the riparian land‐uses. Riparian forest buffers had the lowest streambank erosion rate (15‐46 mm/year) and contributed the least soil (5‐18 tonne/km/year) and phosphorus (2‐6 kg/km/year) to stream channels. Riparian forest buffers were followed by grass filters (erosion rates 41‐106 mm/year, soil losses 22‐47 tonne/km/year, phosphorus losses 9‐14 kg/km/year) and pastures where cattle were fenced out of the stream (erosion rates 22‐58 mm/year, soil losses 6‐61 tonne/km/year, phosphorus losses 3‐34 kg/km/year). The streambank erosion rates for the continuous, rotational, and intensive rotational pastures were 101‐171, 104‐122, and 94‐170 mm/year, respectively. The soil losses for the continuous, rotational, and intensive rotational pastures were 197‐264, 94‐266, and 124‐153 tonne/km/year, respectively, while the phosphorus losses were 71‐123, 37‐122, and 66 kg/km/year, respectively. The only significant differences for these pasture practices were found among the percentage of severely eroding bank lengths with intensive rotational grazed pastures having the least compared to the continuous and rotational grazed pastures. Row‐cropped fields had the highest streambank erosion rates (239 mm/year) and soil losses (304 tonne/km/year) and very high phosphorus losses (108 kg/km/year).     

The Predatory Bird Monitoring Scheme: identifying chemical risks to top predators in Britain

The Predatory Bird Monitoring Scheme (PBMS) is a long term (>40 y), UK-wide, exposure monitoring scheme that determines the concentration of selected pesticides and pollutants in the livers and eggs of predatory birds. This paper describes how the PBMS works, and in particular highlights some of the key scientific and policy drivers for monitoring contaminants in predatory birds and describes the specific aims, scope, and methods of the PBMS. We also present previously unpublished data that illustrates how the PBMS has been used to demonstrate the success of mitigation measures in reversing chemical-mediated impacts; identify and evaluate chemical threats to species of high conservation value; and finally to inform and refine monitoring methodologies. In addition, we discuss how such schemes can also address wider conservation needs.     

Historical marine ecology: examining the role of fisheries in changes in North Sea benthos

The organisms living on and in the sea floor, the benthos, represent an important ecological group. Although some (shellfish) have an economic value, most do not, and so little long-term data are available. We have identified three sources of historic benthic data for the North Sea, a regional sea that has been subjected to multiple human impacts for at least several hundred years. Each dataset has its limitations, but by their use together some issues emerge. Wider community shifts were observed in the shorter term and a number of extirpations at the scale of the North Sea were seen over longer time scales. The extirpated taxa share a number of characteristics consistent with an effect of fisheries such as fragile morphology. We must concentrate now on furthering our understanding of the ecological significance of shifts in dominance of particular functional units and protecting those habitats and species most vulnerable to fisheries-driven extirpation.     

Sorption of imidazolium-based ionic liquids to aquatic sediments

Ionic liquids (ILs) have received much attention as "green" alternatives to traditional solvents because they do not evaporate, eliminating concerns over fugitive emissions. However, if ionic liquids are used in industrial applications, they may enter aquatic systems via effluent, and their fate and transport may be influenced by sorption to sediments. In this study, we conducted batch mixing experiments with four alkylmethylimidizolium-based ILs and four types of aquatic sediments to asses the capacity for natural aquatic sediments to remove these chemicals from the water column. The concentration isotherms were non linear with point estimates of the distribution coefficient (K(d)) decreasing with increasing concentration. Apparent distribution coefficients ranged from 7.9 to 95.7l kg(-1) at an initial concentration of 0.5mM and were positively related to sediment organic matter (SOM) content. These K(d) values indicate that the ILs did not sorb strongly to the tested sediments. Increased alkyl chain length did not lead to increased sorption suggesting that hydrophobic interactions were not the most important sorption mechanism. We conclude that aquatic sediments have a limited capacity to sorb alkylmethylimidazolium ILs and that the transport of these contaminants in aquatic systems will not be strongly attenuated by sediments.     

PAHs in background soils from Western Europe: influence of atmospheric deposition and soil organic matter

The levels and distribution of polynuclear aromatic hydrocarbons (PAHs) were determined in soil samples from background locations in the UK and Norway, to investigate their spatial distribution and the controlling environmental factors. Concentrations ranged between 42 and 11200 microg kg(-1) (geometric mean 640 microg kg(-1)) and 8.6 and 1050 microg kg(-1) (150 microg kg(-1)) dry weight in the UK and Norwegian soil, respectively. Proximity to sources and locations susceptible to high atmospheric depositional inputs resulted in higher concentrations. Statistically significant relationships were observed between PAH and total organic carbon (TOC) in the Norwegian samples. High molecular weight PAHs correlated with black carbon (BC) in UK-woodland soil. These observations support the hypothesis that TOC plays an important role in the retention of PAHs in soil and that PAHs are often combined with BC during combustion emissions. PAHs with 4 and more rings comprised approximately 90% of total PAHs in the UK soil, but only 50% in the Norwegian soil. The mixture of PAHs implied that fractionation occurred during long-range atmospheric transport and deposition. The lighter PAHs with lower K(ow) values more readily reached the most remote sites. The heavier PAHs with higher K(ow) values remained in closer proximity to sources.     

Application of ultrasonic assisted extraction of chemically diverse organic compounds from soils and sediments

The objective of this research was the development, optimization, and demonstration of an ultrasonic assisted extraction (UAE) based method for organic anthropogenic waste indicators (AWIs) with a range of physicochemical properties from soil and sediment samples. The optimized method was designed to be cost effective compared to existing extraction methods, which may require large quantities of consumables, produce substantial volumes of organic waste, or require costly instrumentation or equipment. Reagent grade sand, soil collected from the native grassland in proximity to Eastern Washington University (EWU), and sediment samples collected from the Spokane river were used as sample matrices during method development. These matrices were fortified with eight AWIs of varying chemical properties that are representative of a variety of household, industrial, and agricultural sources. The recoveries of the AWIs spiked onto these matrices were determined in the extracts using gas chromatography/mass spectrometry (GC/MS). These values reflect the efficiency of the method for extraction of these analytes from representative environmental matrices. Recoveries ranged from 46.1% to 110% in the fortified soil and from 49.2% to 118.6% in the fortified sediment samples, which is comparable with existing methods for the study analytes. The optimized method was then used to quantify AWIs in a biosolid-amended soil. Indole and p-cresol were detected in the biosolid-amended soil.     

Evaluation of post-Katrina flooded soils for contaminants and toxicity to the soil invertebrates Eisenia fetida and Caenorhabditis elegans

This research evaluated soil samples from a New Orleans neighborhood in the Chalmette, Saint Bernard Parish, that had been inundated by flooding associated with Hurricane Katrina. The goal was to determine if ecological risks persisted from flood waters that had come in contact with hazardous surface chemicals before inundating this low-lying neighborhood for a prolonged period. Research objectives were to establish the presence or absence of volatile organic and heavy metal contaminants, and then asses the toxicity of this soil to Eisenia fetida in a soil exposure assay and Caenorhabditis elegans in a simulated porewater exposure assay. Soil analysis revealed detectable levels of metals and organics in the surface soil at each location. No contaminant was detected in concentrations above human health screening values. Chromium and mercury were detected at levels in excess of typical ecological risk values. Soil extracts revealed concentrations of nitrate, sulfate, and chloride above those from an unflooded background sample. Toxicity testing resulted in no acute effects to either test species, but did show bioaccumulation of arsenic, cadmium, and lead in E. fetida exposed to several samples. The combination of mercury and sulfate provide the potential for mercury methylation should flooding and prolonged inundation occur again.     

Warming and drought change trace element bioaccumulation patterns in a Mediterranean shrubland

A field experiment consisting of drought and warming manipulation was conducted in a Mediterranean shrubland dominated by the shrubs Erica multiflora and Globularia alypum. The aim was to investigate the effects of the climatic changes predicted by IPCC models for the coming decades on trace element concentration and accumulation in aboveground biomass, plant litter, and soil. Warming increased concentrations and aboveground accumulation of some trace elements related to plant root uptake, such as Al, As, Cr, Cu, and partially Pb. This effect was more general in E. multiflora than in G. alypum. The stronger effects were increases in Al leaf concentrations (42%) and aboveground accumulation (500gha(-1)) in E. multiflora, in As stem biomass accumulation (0.2gha(-1)) in E. multiflora, and in Cr leaf concentrations (51%) in G. alypum and stem aboveground accumulation in E. multiflora (1.1gha(-1)). These species-specific increases were related to greater retranslocation, photosynthetic capacity and growth in E. multiflora than in G. alypum. Warming decreased the concentrations of some trace elements in leaf litter, implying the existence of an increased leaf retranslocation. Drought increased As (40%) and Cd (55%) in E. multiflora stems, whereas it decreased Cu (50%) in leaves, Ni (28%) in stems and Pb (32%) in leaf litter of G. alypum. The increasing concentrations of some trace elements in E. multiflora and not in G. alypum were related to a greater growth reduction in E. multiflora than in G. alypum. Warming increased As soil solubility (67%) and decreased total soil As (21%). Those changes were related to a greater Fe mobilization in warming plot and to a greater plant capture. Drought increased Hg (350%) concentrations in soils but had no significant effects on trace element accumulation in aboveground biomass. The different response to warming and drought in the two dominant species implies uneven changes in the quality of the plant tissues that may have implications for herbivores. This may be specially important for the performance of the studied Mediterranean ecosystems under the warmer and drier conditions predicted by the next decades by the GCM and ecophysiological models.