The role of antecedent groundwater heads in controlling transient aquifer storage and flood peak attenuation in karst watersheds

Transient storage of floodwaters in aquifers is known to attenuate peak flows in rivers and drive subsurface dissolution. Transient aquifer storage could be enhanced in watersheds overlying karst aquifers where caves facilitate surface and groundwater exchange. Few studies, however, have examined controls on, or magnitudes of, transient aquifer storage or flood peak attenuation in karstic watersheds. Here we evaluate flood peak attenuation with multiple linear regression analyses of 10 years of river and groundwater data from the Suwannee River, which flows over the karstic upper Floridan aquifer in north-central Florida and experiences frequent flooding. Regressions show antecedent river stage exerts the dominant control on magnitudes of transient aquifer storage, with recharge and time to peak having secondary controls. Specifically, low antecedent stages result in larger magnitudes of transient aquifer storage and thus greater flood attenuation than conditions of elevated antecedent stage. These findings suggest subsurface weathering, including cave formation and enlargement, caused by transient aquifer storage could occur on a more frequent basis in aquifers where groundwater table elevation is lowered due to anthropogenic or climatic influences. Our work also shows that measures of groundwater table elevation prior to an event could be used to improve predictive flood models. © 2018 John Wiley & Sons, Ltd.     

Molluscs as multidisciplinary models in environment toxicology

The primary goal of this paper is to stimulate discussion and promote the use of mollusc models and multidisciplinary research approaches in the field of environmental toxicology. Molluscs are effective models because they are ubiquitous, have highly conserved control and regulatory pathways that are often homologous to vertebrate systems, and are extremely sensitive to anthropogenic inputs. We have attempted to provide initial references as an avenue into the literature and as a means for researchers to expand their thoughts to regions outside of their own area of expertise. The authors are particularly interested in developing multidisciplinary international collaborative efforts.     

Effects of hydrocarbon contamination on a free living marine nematode community: results from microcosm experiments

Anthropogenic inputs of crude and refined petroleum hydrocarbons into the sea require knowledge of the effects of these contaminants on the receiving assemblages of organisms. A microcosm experiment was carried out to study the influence of diesel on a free living nematode community of a Tunisian lagoon. Sediments were contaminated by diesel that ranged in concentration from 0.5 to 20 mg diesel kg⁻¹ dry weight (dw), and effects were examined after 90 days. Gradual changes in community structure were revealed depending on the quantity of diesel administrated. In the medium (1 mg diesel kg⁻¹ and 5 mg diesel kg⁻¹ (dw)) and high (10 mg diesel kg⁻¹, 15 mg diesel kg⁻¹ and 20 mg kg⁻¹ (dw)) treated microcosms, most univariate measures, including diversity and species richness, decreased significantly with increasing level of diesel contamination whereas nematode assemblage from the low treated microcosm (0.5 mg diesel kg⁻¹ (dw)) remained unaffected. Results from multivariate analyses of the species abundance data demonstrated that responses of nematode species to the diesel treatments were varied: Chaetonema sp. was eliminated at all doses tested and seemed to be intolerant species to diesel contamination; Pomponema sp. and Oncholaimus campylocercoïdes were significantly affected at all diesel contamination levels but they were not eliminated, these species were categorized as “diesel-sensitive”; Hypodontolaimus colesi, Daptonema trabeculosum and Daptonema fallax which significantly increased respectively at 0.5, 1 and 5 mg diesel kg⁻¹ (dw) concentrations and appeared to be “opportunistic” species at these doses whereas Marylynnia stekhoveni which increased at all high doses (10, 15 and 20 mg diesel kg⁻¹ (dw)) seemed to be a “diesel-resistant” species.     

Effects of mechanical and chemical processes on the degradation of plastic beach debris on the island of Kauai, Hawaii

Plastic debris is accumulating on the beaches of Kauai at an alarming rate, averaging 484 pieces/day in one locality. Particles sampled were analyzed to determine the effects of mechanical and chemical processes on the breakdown of polymers in a subtropical setting. Scanning electron microscopy (SEM) indicates that plastic surfaces contain fractures, horizontal notches, flakes, pits, grooves, and vermiculate textures. The mechanically produced textures provide ideal loci for chemical weathering to occur which further weakens the polymer surface leading to embrittlement. Fourier transform infrared spectroscopy (FTIR) results show that some particles have highly oxidized surfaces as indicated by intense peaks in the lower wavenumber region of the spectra. Our textural analyses suggest that polyethylene has the potential to degrade more readily than polypropylene. Further evaluation of plastic degradation in the natural environment may lead to a shift away from the production and use of plastic materials with longer residence times.     

Antifouling biocides in discarded marine paint particles

Antifouling paint fragments collected from marinas and leisure boat maintenance facilities and in the vicinity of abandoned boats have been chemically characterised. High concentrations of Cu (23-380 mg g⁻¹) and Zn (14-160 mg g⁻¹) in the samples (n = 14) are consistent with the use of these metals in the principal biocidal and non-biocidal pigments in contemporary antifouling formulations. Up to about 2% and 7% of the respective metals were solvent-extractable, suggesting that organo-forms of Cu and Zn (e.g. pyrithiones) were also present. Of the organic biocides, dichlofluanid was present in most samples and at concentrations up to about 20 mg g⁻¹. Chlorothalonil and Irgarol 1051® were only detected in one and four cases, respectively, and Sea Nine 211® was not detected in any sample. Results are discussed in terms of UK legislation regarding biocide usage and the likely effects and fate of discarded paint particles in coastal environments where boats are repaired or moored.     

Measurement of soluble reactive phosphorus concentration profiles and fluxes in river-bed sediments using DET gel probes

DET (diffusive equilibrium in thin films) gel probes were used for sampling river-bed sediment porewaters, to characterise in situ soluble reactive phosphorus (SRP) concentration profiles and fluxes. DET probes were deployed in three contrasting rural streams: (1) a headwater ‘pristine’ stream, with minimal P inputs from low intensity grassland and no point sources, (2) an intensively cultivated arable catchment, and (3) a stream subject to high P loadings from sewage effluent and intensive arable farming. The DET results showed highly enriched porewater SRP concentrations of between ca. 400 and 5000 μg-P l⁻¹ in the sewage-impacted stream. In contrast, the arable and pristine streams had porewater SRP concentrations <70 μg-P l⁻¹ and <20 μg-P l⁻¹, respectively. Porewater SRP concentration profiles in both the sewage-impacted and arable-impacted streams showed well-defined vertical structure, indicating internal sources and sinks of SRP within the sediment. However, there was little variability in porewater SRP concentrations in the pristine stream. The DET porewater profiles indicated net diffusion of SRP (a) from the overlying river water into the surface sediment and (b) from subsurface sediment upwards towards the sediment–water interface. A mass balance for the sewage-impacted site showed that the influx of SRP into the surface sediments from the overlying river water was small (ca. 1% of the daily river SRP load). The DET results indicated that, in the arable and sewage-impacted streams, the surface ‘cap’ of fine sediment may play an important role in inhibiting upward movement of SRP from subsurface porewaters into the overlying river water, under steady-state, low-flow conditions.     

Seismic,petrologic, and geodetic analyses of the 1999 dome-forming eruption of Guagua Pichincha volcano,Ecuador

Guagua Pichincha, located 14 km west of Quito, Ecuador, is a stratovolcano bisected by a horseshoe-shaped caldera. In 1999, after some months of phreatic activity, Guagua Pichincha entered into an eruptive period characterized by the extrusion of several dacitic domes, vulcanian eruptions, and pyroclastic flows. We estimated the three-dimensional (3-D) P-wave velocity structure beneath Guagua Pichincha using a tomographic inversion method based on finite-difference calculations of first-arrival times. Hypocenters of volcano-tectonic (VT) earthquakes and long-period (LP) events were relocated using the 3-D P-wave velocity model. A low-velocity anomaly exists beneath the caldera and may represent an active volcanic conduit. Petrologic analysis of eruptive products indicates a magma storage region beneath the caldera, having a vertical extent of 7–8 km with the upper boundary at about sea level. This zone coincides with the source region of deeper VT earthquakes, indicating that a primary magma body exists in this region. LP swarms occurred in a cyclic pattern synchronous with ground deformation during magma extrusions. The correlation between seismicity and ground deformation suggests that both respond to pressure changes caused by the cyclic eruptive behavior of lava domes.     

Coda Q before and after the eruptions of 13 November 1985, and 1 September 1989, at Nevado del Ruiz Volcano, Colombia

 Coda Q^–1 was calculated at Nevado del Ruiz Volcano (NRV) before and after two phreatomagmatic eruptions (November 1985, September 1989) and for a period of stability (May 1987) using a functional form for coda derived from a single scattering model (Sato 1977). Substantial changes were found before and after the eruptions. The highest value of Q^–1 was found during the November 1985 eruption, an intermediate value for the September 1989 eruption, and the lowest value for May 1987. It seems that the changes in coda Q^–1 at NRV have a still-unknown relationship with the volume or magnitude of the eruption. A relatively strong frequency dependence was found for all periods. Also Q^–1 clearly changed with time, suggesting that the scattering was strong for the eruption of November 1985 and decreased for the eruption of September 1989, and that the intrinsic absorption probably increased. This suggests the possibility that crystallization is taking place in the NRV magma. The clear change of coda Q^–1 before and after the eruptions at NRV also suggests the possibility that coda Q^–1 is a premonitory tool of activity at this volcano. Received: 25 October 1996 / Accepted: 21 January 1998     

Crustal structure and tectonic setting of the south central Andes from gravimetric analysis

Based on terrestrial gravity data, in this paper we prepared a map of Bouguer anomalies, which was filtered to separate shallow and deep gravity sources. Based on a density model and gravimetric inversion techniques, the discontinuous crust-mantle boundary and the top of crystalline basement were modeled. Subsequently, the equivalent elastic thickness (Te) was evaluated, considering information from the crust-mantle discontinuity and topographic load, finding high Te values in the eastern Andean foothills and west of the Velasco range. These results are consistent with the positive isostatic and residual Bouguer anomaly values, which suggest the presence of high-density rocks in the mid-to upper crust. In addition, petrographic and geochemical analysis conducted in surface outcrops suggest a mantle origin.     

Effects of CO2 on benthic biota: An in situ benthic chamber experiment in Storfjorden (Norway)

Carbon capture and storage (CCS) methods, either sub-seabed or in ocean depths, introduces risk of CO₂ leakage and subsequent interaction with the ecosystem. It is therefore important to obtain information on possible effects of CO₂. In situ CO₂ exposure experiments were carried out twice for 10 days during 2005 using a Benthic Chamber system at 400 m depth in Storfjorden, Norway. pCO₂ in the water above the sediment in the chambers was controlled at approximately 500, 5000 and 20,000 μatm, respectively. This article describes the experiment and the results from measured the biological responses within the chamber sediments. The results show effects of elevated CO₂ concentrations on biological processes such as increased nanobenthos density. Methane production and sulphate reduction was enhanced in the approximately 5000 μatm chamber.