Lithological controls on biological activity and groundwater chemistry in Quaternary sediments

Depth profiles of solute chemistry and sulfate isotopic compositions are presented for groundwater and pore water in a sequence of Quaternary glacial outwash sediments. Sand units show evidence for hydraulic connection to the surface and thus modern sources of solutes. Finer‐grained sediments show a general pattern of increasing solute concentrations with depth, with sulfate derived from ancient rainwater and pyrite oxidation in the soil/drift. In these sediments sulfate has undergone bacterial sulfate reduction (BSR) to produce biogenic sulfide. In clay sediments, with d₁₀ ≤ 1·6 µm, high concentrations of sulfate and acetate now co‐exist, implying that BSR is inhibited. The correlation with smaller sediment grain size indicates that this is due to pore size exclusion of the sulfate reducing bacteria. Mechanical restriction of microbial function thus provides a fundamental limitation on microbial respiration in buried clay‐rich sediments, which acts as a control on the chemical evolution of their pore waters. Copyright © 2009 John Wiley & Sons, Ltd.     

Vegetation succession in deglaciated landscapes: implications for sediment and landscape stability

Landscapes exposed by glacial retreat provide an ideal natural laboratory to study the processes involved in transforming a highly disturbed, glacially influenced landscape to a stable, diverse ecosystem which supports numerous species and communities. Large‐scale vegetation development and changes in sediment availability, used as a proxy for paraglacial adjustment following rapid deglaciation, were assessed using information from remote sensing. Delineation of broad successional vegetation cover types was undertaken using Landsat satellite imagery (covering a 22 year period) to document the rate and trajectory of terrestrial vegetation development. Use of a space‐for‐time substitution in Glacier Bay National Park, Alaska, allowed ‘back‐calculation’ of the age and stage of development of six catchments over 206 years. The high accuracy (89.2%) of the remotely sensed information used in monitoring successional change allowed detection of a high rate of change in vegetation classes in early successional stages (bare sediment and alder). In contrast, later successional stages (spruce and spruce–hemlock dominated forest) had high vegetation class retention, and low turnover. Modelled rates of vegetation change generally confirmed the estimated rates of successional turnover previously reported. These data, when combined with the known influence of terrestrial succession on soil development and sediment availability, suggest how physical and biological processes interact over time to influence paraglacial adjustment following deglaciation. This study highlights the application of remote sensing of successional chronosequence landscapes to assess the temporal dynamics of paraglacial adjustment following rapid deglaciation and shows the importance of incorporating bio‐physical interactions within landscape evolution models. © 2014 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.     

Streambank sediment loading rates at the watershed scale and the benefit of riparian protection

Streambank erosion is a pathway for sediment and nutrient loading to streams, but insufficient data exist on the magnitude of this source. Riparian protection can significantly decrease streambank erosion in some locations, but estimates of actual sediment load reductions are limited. The objective of this research was to quantify watershed‐scale streambank erosion and estimate the benefits of riparian protection. The research focused on Spavinaw Creek within the Eucha‐Spavinaw watershed in eastern Oklahoma, where composite streambanks consist of a small cohesive topsoil layer underlain by non‐cohesive gravel. Fine sediment erosion from 2003 to 2013 was derived using aerial photography and processed in ArcMap to quantify eroded area. ArcMap was also utilized in determining the bank retreat rate at various locations in relation to the riparian vegetation buffer width. Box and whisker plots clearly showed that sites with riparian vegetation had on average three times less bank retreat than unprotected banks, statistically significant based on non‐parametric t‐tests. The total soil mass eroded from 2003 to 2013 was estimated at 7.27 × 10⁷ kg yr.^?1, and the average bank retreat was 2.5 m yr.^?1. Many current erosion models assume that fluvial erosion is the dominant stream erosion process. Bank retreat was positively correlated with stream discharge and/or stream power, but with considerable variability, suggesting that mass wasting plays an important role in streambank erosion within this watershed. Finally, watershed monitoring programs commonly characterize erosion at only a few sites and may scale results to the entire watershed. Selection of random sites and scaling to the watershed scale greatly underestimated the actual erosion and loading rates. Copyright © 2016 John Wiley & Sons, Ltd.     

Science-based coastal management in Fiji: Two case studies from the NGO sector

The effectiveness of coastal management in developing countries is widely perceived to be inhibited by a lack of scientific data on the coastal zone. To try to fill this need for information, donors and big international non-governmental organizations are increasingly initiating large-scale, science-driven conservation programs, with the goal of creating and using management relevant transdisciplinary datasets. In Oceania, these programs are entering a context where local ecological knowledge is already informing existing community-based approaches to coastal management. This paper examines two large-scale programs in Fiji, the Marine Management Area Science initiative and the Vatu-i-Ra and Cakau Levu Reefs Seascape Project, and offers insight relevant to the planning and implementation of similar programs where local management systems are already in place. Research methods used to examine the programs included document analysis, direct observation, and semi-structured interviews with key stakeholders over multiple field visits to Fiji in 2009 and 2010. Results suggest that as donors, non-governmental organizations, and partners move forward in implementing these programs, there must be active steps taken to bridge boundaries between disciplines and among knowledge systems, evaluate the added value of science for all stakeholder groups, and build opportunities for datasets to be used after donor funding ends.     

Exploiting radiation damage control on apatite (U–Th)/He dates in cratonic regions

Apatites from four pairs of samples of Precambrian basement from the western Canadian shield were analyzed by (U–Th)/He thermochronometry to test for the influence of radiation damage on apatite (U–Th)/He dates in this cratonic region. Recent studies have demonstrated that the accumulation of radiation damage increases the apatite He retentivity, so that apatites with a span of effective U concentrations, eU, that experienced the same thermal history may be characterized by a range of closure temperatures. In this investigation, each sample pair consisted of a mafic dike cross-cutting felsic gneisses from a single outcrop or nearby outcrops that contained apatites with a span of eU. The apatites yielded (U–Th)/He dates from 846 to 123 Ma, and were positively correlated with eU within each sample pair. These results can be explained using a model that tracks the evolution of He mobility in response to the accumulation of radiation damage. When coupled with regional geological constraints, the data appear to require partial to complete He loss due to burial and reheating in Phanerozoic time. New apatite fission- track dates and length data were obtained for five of these samples. The apatite fission- track dates are Proterozoic regardless of apatite eU. Thermal history simulations indicate that the apatite fission-track data are compatible with the (U–Th)/He results, although the thermal histories are not identical in detail and the fission-track results alone do not require Phanerozoic heating. Together the data are consistent with burial of this region by ≥ 1 km of Phanerozoic strata that were subsequently denuded, thus pointing toward significant Phanerozoic deposition in the North American cratonic interior hundreds of kilometers east of where previously documented. The results suggest that exploiting radiation damage control on apatite (U–Th)/He dates through investigation of surface sample apatites with a span of closure temperatures can impose tighter restrictions on thermal histories in low relief cratonic landscapes than was previously possible.     

Response of estuarine meio- and macrofauna to in situ bioremediation of oil-contaminated sediment

Numerous studies have demonstrated the efficacy of bioremediation for enhancing oil removal but the ecological effect on shoreline biota is unclear. Therefore, a field experiment was designed at an intertidal sandflat in SW England to assess the effects of nutrient addition to oiled sediments on meio- and macrofauna for a period of up to 45 weeks. Natural assemblages were exposed to different types of experimental treatments (no oil, oil alone, oil treated with slow-release fertiliser or liquid fertiliser). Bioremediation stimulated the microbial population and increased oil biodegradation. This, however, did not result in faster recolonisation rates of fertilised versus non-fertilised oiled sediments. Mild effects of oil and bioremediation treatments on benthic fauna were observed, including short-term shifts in dominance patterns. Decreased abundance of dominant species in the oiled compared to unoiled sediments resulted in significantly higher evenness of benthic assemblages within the first 11 weeks of the experiment.     

Spatial and temporal variation in hexachlorocyclohexane isomers in a temperate estuary

Hexachlorocylcohexanes (HCHs) are pesticides that persist in air and water of the Northern hemisphere. To understand the spatial and temporal variability in HCH levels in estuarine surface waters we measured concentrations of two HCH isomers (-HCH and γ-HCH) at six sites in the York River estuary at bimonthly intervals for a year. Bacterial abundance and activity were also monitored using acridine orange direct counts and uptake of tritiated substrates, respectively. -HCH was consistently observed to be significantly higher in marine water compared to river water entering the estuary, suggesting that the Chesapeake Bay or Atlantic Ocean is a larger source of this compound to the York River estuary compared to riverine input. Moreover, following periods of high freshwater flow into the estuary during spring and early summer, both - and γ-HCH mixing curves indicated an additional source of these pollutants to the estuary such as land-derived runoff or groundwater discharge. In contrast, during low freshwater flow (late summer and fall) the estuary was a sink for HCHs, with γ-HCH more rapidly removed from the estuary than -HCH. During the period of low freshwater flow, concentrations of both - and γ-HCH were negatively correlated with bacterial activity. Bacterial activity as opposed to abundance appears to control HCH degradation in estuarine surface waters.     

Entanglement of Australian sea lions and New Zealand fur seals in lost fishing gear and other marine debris before and after Government and industry attempts to reduce the problem

In recent years, Australian governments and fishing industry associations have developed guiding principles aimed at reducing the impact of fishing on non-target species and the benthos and increasing community awareness of their efforts. To determine whether they reduced seal entanglement in lost fishing gear and other marine debris, we analysed Australian sea lion and New Zealand fur seal entanglement data collected from Kangaroo Island, South Australia. Contrary to our expectations, we found that entanglement rates did not decrease in recent years. The Australian sea lion entanglement rate (1.3% in 2002) and the New Zealand fur seal entanglement rate (0.9% in 2002) are the third and fourth highest reported for any seal species. Australian sea lions were most frequently entangled in monofilament gillnet that most likely originated from the shark fishery, which operates in the region where sea lions forage--south and east of Kangaroo Island. In contrast, New Zealand fur seals were most commonly entangled in loops of packing tape and trawl net fragments suspected to be from regional rock lobster and trawl fisheries. Based on recent entanglement studies, we estimate that 1478 seals die from entanglement each year in Australia. We discuss remedies such as education programs and government incentives that may reduce entanglements.