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12.
Shark interactions in pelagic longline fisheries 总被引:1,自引:0,他引:1
Eric Gilman Shelley Clarke Nigel Brothers Joanna Alfaro-Shigueto John Mandelman Jeff Mangel Samantha Petersen Susanna Piovano Nicola Thomson Paul Dalzell Miguel Donoso Meidad Goren Tim Werner 《Marine Policy》2008
Substantial ecological, economic and social problems result from shark interactions in pelagic longline fisheries. Improved understanding of industry attitudes and practices towards shark interactions assists with managing these problems. Information on fisher knowledge and new strategies for shark avoidance may benefit sharks and fishers. A study of 12 pelagic longline fisheries from eight countries shows that incentives to avoid sharks vary along a continuum, based on whether sharks represent an economic disadvantage or advantage. Shark avoidance practices are limited, including avoiding certain areas, moving when shark interaction rates are high, using fish instead of squid for bait and deeper setting. Some conventionally employed fishing gear and methods used to target non-shark species contribute to shark avoidance. Shark repellents hold promise; more research and development is needed. Development of specifically designed equipment to discard sharks could improve shark post release survival prospects, reduce gear loss and improve crew safety. With expanding exploitation of sharks for fins and meat, improved data collection, monitoring and precautionary shark management measures are needed to ensure that shark fishing mortality levels are sustainable. 相似文献
13.
Dissolved organic carbon (DOC) flux dynamics were examined in the context of other biogeochemical cycles in intertidal sediments inhabited by benthic microalgae. In August 2003, gross oxygenic photosynthetic (GOP) rates, oxygen penetration depths, and benthic flux rates were quantified at seven sites along the Duplin River, GA, USA. Sediments contained abundant benthic microalgal (BMA) biomass with a maximum chlorophyll a concentration of 201 mg chl a m?2. Oxygen microelectrodes were used to determine GOP rates and O2 penetration depth, which were tightly correlated with light intensity. Baseline and 15N-nitrate amended benthic flux core incubations were employed to quantify benthic fluxes and to investigate the impact of BMA on sediment water exchange under nitrogen (N)-limited and N-replete conditions. Unamended sediments exhibited tight coupling between GOP and respiration and served as a sink for water column dissolved inorganic nitrogen (DIN) and a source of silicate and dissolved inorganic carbon (DIC). The BMA response to the N addition indicated sequential nutrient limitation, with N limitation followed by silicate limitation. In diel (light–dark) incubations, biological assimilation accounted for 83% to 150% of the nitrate uptake, while denitrification (DNF) and dissimilatory nitrate reduction to ammonium (DNRA) accounted for <7%; in contrast, under dark conditions, DNF and DNRA accounted for >40% of the NO3 ? uptake. The N addition shifted the metabolic status of the sediments from a balance of autotrophy and heterotrophy to net autotrophy under diel conditions, and the sediments served as a sink for water column DIN, silicate, and DIC but became a source of DOC, suggesting that the increased BMA production was decoupled from sediment bacterial consumption of DOC. 相似文献
14.
Integrated biogeochemical and hydrologic processes driving arsenic release from shallow sediments to groundwaters of the Mekong delta 总被引:3,自引:0,他引:3
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Caroline A. Canham Clément Duvert Leah S. Beesley Michael M. Douglas Samantha A. Setterfield Fiona L. Freestone Steven Clohessy Robyn C. Loomes 《水文研究》2021,35(5):e14180
Riparian trees play a critical role in the ecological function of rivers, yet are threatened by anthropogenic change to the hydrological cycle. Identifying the sources of water used by riparian trees can inform sustainable water policy. We used isotopic analysis complemented by measurements of plant water relations to assess water sources for riparian trees at two sites with contrasting hydrogeological processes; one with an alluvial aquifer overlaying an aquitard, and one where fault-induced preferential pathways in the aquitard allowed the flow of deeper, older groundwater from a regional aquifer to the alluvium. At both sites, plant water potential, stomatal conductance, and plant water isotope composition in the xylem sap of riparian trees were collected from two landscape positions, the riverbank and floodplain. We used a Bayesian mixing model (MixSIAR) to assess differences in the proportion of water sources for sites and landscape positions. We found that xylem water isotope values differed between the two sites in line with their hydrogeological characteristics, with trees at the regional aquifer site using water sourced from the regional groundwater and trees at the site with only an alluvial aquifer present using a mixture of water sources, with no dominant source identified. Higher plant predawn water potential values at the regional site indicated greater water availability and support the inference that plants were using more groundwater at the regional site compared to the alluvial site. Trees closer to the river had higher isotope values, indicative of surficial water sources i.e. shallow soil water and river water. Our findings show that the water sources used by riparian trees reflect local hydrogeology and resource availability. Water managers should identify and protect plant water sources to ensure maintenance of riparian trees. 相似文献
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18.
Synergistic effect of calcium and bicarbonate in enhancing arsenate release from ferrihydrite 总被引:1,自引:0,他引:1
Many groundwater systems contain anomalously high arsenic concentrations, associated with less than expected retention of As by adsorption to iron (hydr)oxides. Although carbonates are ubiquitous in aquifers, their relationship to arsenate mobilization is not well characterized. This research examines arsenate release from poorly crystalline iron hydroxides in abiotic systems containing calcium and magnesium with bicarbonate under conditions of static and dynamic flow (pH 7.5-8). Aqueous arsenic levels remained low when arsenate-bearing ferrihydrite was equilibrated with artificial groundwater solution containing Ca, Mg, and HCO3−. In batch titrations in which a solution of Ca and HCO3− was added repeatedly, the ferrihydrite surface became saturated with adsorbed Ca and HCO3−, and aqueous As levels increased by 1-2 orders of magnitude. In columns containing Ca or Mg and HCO3−, As solubility initially mimicked titrations, but then rapidly increased by an additional order of magnitude (reaching 12 μM As). Separately, calcium chloride and other simple salts did not induce As release, although sodium bicarbonate and lactate facilitated minor As release under flow. Results indicate that adsorption of calcium or magnesium with bicarbonate leads to As desorption from ferrihydrite, to a degree greater than expected from competitive effects alone, especially under dynamic flow. This desorption may be an important mechanism of As mobilization in As-impacted, circumneutral aquifers, especially those undergoing rapid mineralization of organic matter, which induces calcite dissolution and the production of dissolved calcium and bicarbonate. 相似文献
19.
Inorganic nitrogen dynamics in intertidal rocky biofilms and sediments of the Douro River estuary (Portugal) 总被引:1,自引:0,他引:1
Catarina M. Magalhäes William J. Wiebe Samantha B. Joye Adriano A. Bordalo 《Estuaries and Coasts》2005,28(4):592-607
In this study rates of oxygen, ammonium (NH4
+), nitrate (NO3
−), nitrite (NO2
−), and nitrous oxide (N2O) fluxes, nitrogen (N) fixation, nitrification, and denitrification were compared between two intertidal sites for which
there is an abundant global literature, muddy and sandy sediments, and two sites representing the rocky intertidal zone where
biogeochemical processes have scarcely been investigated. In almost all sites oxygen production rates greatly exceeded oxygen
consumption rates. During daylight, NH4
+ and NO3
− uptake rates together with ammonification could supply the different N requirements of the primary producer communities at
all four sites; N assimilation by benthic or epilithic primary producers was the major process of dissolved inorganic nitrogen
(DIN) removal; N fixation, nitrification, and denitrification were minor processes in the overall light DIN cycle. At night,
distinct DIN cycling processes took place in the four environments, denitrification rates ranged from 9 ± 2 to 360 ± 30 μmol
N2 m−2 h−1, accounting for 10–48% of the water column NO3
− uptake; nitrification rates varied from 0 to 1712 ± 666 μmol NH4
+ m−2 h−1. A conceptual model of N cycle dynamics showed major differences between intertidal sediment and rocky sites in terms of
the mean rates of DIN net fluxes and the processes involved, with rocky biofilm showing generally higher fluxes. Of particular
significance, the intertidal rocky biofilms released 10 times the amount of N2O produced in intertidal sediments (up to 17 ± 6 μmol N2O m−2 h−1), representing the highest N2O release rates ever recorded for marine systems. The biogeochemical contributions of intertidal rocky substrata to estuarine
and coastal processes warrant future detailed investigation. 相似文献
20.