A grain-size correction for metal pollution indexes in river sediments

According to the List of Hazardous Substances of the Agency of the Toxic Substances and Disease Registry(ATSDR 2017),some metallic elements such as Pb or Cd are still considered as the most polluting elements in the world.These elements accumulate in sediments,and there are various methods available that differentiate lithogenic sources from anthropogenic sources.For that,the natural geochemical background is required,however,its definition is far from unanimous:it can be a global or local value,single or statistically estimated value,depending on the studies.Our study is focused on the Suba
e River in the state of Bahia,Northeastern Brazil,which was historically contaminated by lead metallurgy.The river sediments were sampled at 21 locations:one at the discharge point of the plant's rainwater basin,ten upstream,and ten downstream.The total contents of Fe,Ti,Mn,Pb,Zn,Cu,Cr,particle-size distribution,and organic matter were analyzed.The conventional geochemical indexes,i.e.,the pollution degree(mCd),pollution load index,and enrichment factor indicated contamination by Zn,Pb,Cr,and Cu.Then,a new enrichment factor is introduced,assuming that the sediments come from erosion of soils in the watershed.After obtaining the natural concentrations of metals in the clay,silt,and sand fractions of uncontaminated reference soils,we corrected the pollution indexes by calculating a new individual background in each sediment sample,according to its grain size distribution.This new approach provided more precise indexes in the assessment of sediment pollution,by highlighting higher contamination of Zn and Pb(around 50%)and at the same time the absence of Cr and Cu contamination,two metals not involved with the metallurgical activity.     

Ice-rafted detritus events in the Arctic during the last glacial interval, and the timing of the Innuitian and Laurentide ice sheet calving events

Ice-rafted detritus (IRD) layers in the Arctic Ocean not only indicate the source of this detrital sediment, but give insights into the ice drift and ice sheet history. Detrital sand-sized Fe oxide mineral grains that are matched to precise sources using the microprobe chemical fingerprint of each grain, along with elevated coarse IRD abundance and radiocarbon ages, are used to define IRD peaks from the Innuitian and Arctic portions of the Laurentide ice sheets. Because grains from these two areas can be entrained by sea ice from the shelves just offshore of the calving areas, peaks in these grains must be correlated to coarse IRD to identify iceberg calving events, and to distinguish them from sea-ice rafting. The sequence of IRD peaks deposited by icebergs from these two ice sheets indicate that both ice sheets calved bergs at accelerated numbers, six or seven times, from 11 to 36 Kya. The relatively short times between most of these IRD events suggest that the ice sheets did not completely collapse with each IRD event, except the last event. Although there is some indication that one ice sheet may have begun calving bergs before the other, the resolution of the Arctic cores does not allow definitive determination of this. This emphasizes the need for higher resolution cores from the central Arctic, as well as from near the terminus of large Pleistocene ice sheets. Sea-ice rafting occurs throughout the last glacial stage, even during some glacial IRD events, as indicated by Fe grains from non-glacial sources.     

A method of evaluating effects of antecedent precipitation on duststorms and its application to Yuma,Arizona, 1981–1988

Precipitation causes several short- and long-term effects on wind-induced surface erodibility and subsequent dust emission. Among the principal effects considered by this paper are soil moisture, soil crusts, and vegetation. A quantitative method is developed to assess these effects using differences between the potential and the actual amounts of dust emitted from dust sources as inferred from surface meteorological measurements obtained downwind from those sources. The results of this assessment must be interpreted with caution, however, when the size and location of dust sources are unknown.Using meteorological data recorded near Yuma, Arizona at the Yuma Marine Corps Air Station (YMCAS), the method is applied to calculate the potential and actual amounts of dust emitted from upwind dust sources during the spring and fall/winter seasons between January 1, 1981 and May 31, 1988. (Spring is considered to be the period between February 1 and May 31; fall/winter, between October 1 and January 31.) Because summer precipitation is intermittent and wind patterns are localized, summer meteorological data are not used to evaluate regional correlations between precipitation and dust storms. For the period between 1981 and 1988, a correlation of -0.60 was found between fall/winter precipitation and the actual amount of dust emitted from sources upwind of YMCAS during the following spring. A particularly strong reduction in dust emission was noted during the springs of 1983 and 1984 following the start of an El Nino event in fall/winter 1982. Photographs taken at a geological and meteorological data-collection (Geomet) site, located in the natural desert 25 km southeast of YMCAS, show a correspondence between increased antecedent precipitation recorded at the site and increased vegetation. Whereas the annual precipitation totals at YMCAS and the Geomet site from the beginning of 1982 through 1984 are high, their seasonal totals, especially during the fall/winter seasons, are disparate. This fall/winter precipitation disparity may account for evidence suggesting that significant vegetation growth occurred at dust sources upwind of YMCAS by spring 1983, but that such growth did not occur at the Geomet site until fall/ winter of 1983. Spatial inhomogeneity in fall/winter precipitation probably contributed to the relatively low correlation (-0.60) between fall/winter precipitation recorded at YMCAS and the actual amount of dust emitted from upwind sources during the following spring.     

Horse mackerel egg identification using DNA methodology

Egg identification in plankton samples is usually needed for purposes of stock assessment. Until recently, only morphological characters were used for identifying the eggs of different fish species. Late developmental stages are easily distinguishable due to pigmentation as well as egg and oil globule size range. However, for early stages, these characteristics are difficult to be discriminated and may overlap with other species. European horse mackerel species (Trachurus trachurus, T. mediterraneus, T. picturatus) overlap significantly in their spawning areas in some European waters. Because of the fact that their eggs are morphologically similar, genetic methodologies are needed to identify eggs and larvae to species correctly. In the present study, formalin‐ and ethanol‐preserved eggs were tested to estimate the efficacy of genetic methodologies for species identification of eggs when different preservatives are used. A 370‐bp fragment of cytochrome b was successfully amplified followed by restriction fragment analysis with two restriction enzymes aiming to identify the eggs to species. Horse mackerel egg identification was accomplished with the maximum success in ethanol‐preserved eggs. However, it seems that various preservatives had different effects on the DNA quality of eggs as genetic identification was less successful in formalin‐preserved eggs. Preserving in ethanol a part of the eggs obtained in plankton surveys is suggested for purposes of accurate genetic identification, even if their morphological features are distorted in time.     

Ecophysiological responses to elevated CO<Subscript>2</Subscript> and temperature in <Emphasis Type="Italic">Cystoseira tamariscifolia</Emphasis> (Phaeophyceae)

Ocean acidification increases the amount of dissolved inorganic carbon (DIC) available in seawater which can benefit photosynthesis in those algae that are currently carbon limited, leading to shifts in the structure and function of seaweed communities. Recent studies have shown that ocean acidification-driven shifts in seaweed community dominance will depend on interactions with other factors such as light and nutrients. The study of interactive effects of ocean acidification and warming can help elucidate the likely effects of climate change on marine primary producers. In this study, we investigated the ecophysiological responses of Cystoseira tamariscifolia (Hudson) Papenfuss. This large brown macroalga plays an important structural role in coastal Mediterranean communities. Algae were collected from both oligotrophic and ultraoligotrophic waters in southern Spain. They were then incubated in tanks at ambient (ca. 400–500 ppm) and high CO₂ (ca. 1200–1300 ppm), and at 20 °C (ambient temperature) and 24 °C (ambient temperature +4 °C). Increased CO₂ levels benefited the algae from both origins. Biomass increased in elevated CO₂ treatments and was similar in algae from both origins. The maximal electron transport rate (ETR_max), used to estimate photosynthetic capacity, increased in ambient temperature/high CO₂ treatments. The highest polyphenol content and antioxidant activity were observed in ambient temperature/high CO₂ conditions in algae from both origins; phenol content was higher in algae from ultraoligotrophic waters (1.5–3.0%) than that from oligotrophic waters (1.0–2.2%). Our study shows that ongoing ocean acidification can be expected to increase algal productivity (ETR_max), boost antioxidant activity (EC ₅₀ ), and increase production of photoprotective phenols. Cystoseira tamariscifolia collected from oligotrophic and ultraoligotrophic waters were able to benefit from increases in DIC at ambient temperatures. Warming, not acidification, may be the key stressor for this habitat as CO₂ levels continue to rise.     

Radiocarbon application in dating “complex” hot and cold CO2-rich mineral water systems: A review of case studies ascribed to the northern Portugal

The use of radioactive isotopes plays a very important role in dating groundwater, providing an apparent age of the systems in the framework of the aquifers conceptual modelling making available important features about the water fluxes, such as recharge, horizontal flow rates and discharge. In this paper, special emphasis has been put on isotopic constraints in the use of δ¹³C and ¹⁴C content as a dating tool in some hot (76 °C) and cold (17 °C) CO₂-rich mineral waters discharging in the Vilarelho da Raia–Pedras Salgadas region (N-Portugal). The radiocarbon content determined in these CO₂-rich mineral waters (¹⁴C activity from 4.3 up to 9.9 pmc) is incompatible with the systematic presence of ³H (from 1.7 to 7.9 TU). The δ¹³C values of the studied CO₂-rich mineral waters indicate that the total C in the recharge waters is being masked by larger quantities of CO₂ (¹⁴C-free) introduced from deep-seated (upper mantle) sources. This paper demonstrates that a good knowledge of mineral water systems is essential to allow hydrologists to make sound conclusions on the use of C isotopic data in each particular situation.     

Impact of intensive fish farming on methane emission in a tropical hydropower reservoir

Fisheries and aquaculture are important sources of food for hundreds of millions of people around the world. World fish production is projected to increase by 15% in the next 10 years, reaching around 200 million tonnes per year. The main driver of this increase will be based on fish farming management in developing countries. In Brazil, fish farming is increasing due to the climate conditions and large supply of water resources, with the production system based on Nile tilapia (Oreochromis niloticus) farming in reservoirs. Inland waters like reservoirs are a natural source of methane (CH₄) to the atmosphere. However, knowledge of the impact from intensive fish production in net cages on CH₄ fluxes is not well known. This paper presents in situ measurements of CH₄ fluxes and dissolved CH₄ (DM) in the Furnas Hydroelectric Reservoir in order to evaluate the impact of fish farming on methane emissions. Measurements were taken in a control area without fish production and three areas with fish farming. The overall mean of diffusive methane flux (DMF) (5.9?±?4.5 mg CH₄ m^?2 day^?1) was significantly lower when compared to the overall mean of bubble methane flux (BMF) (552.9?±?1003.9 mg CH₄ m^?2 day^?1). The DMF and DM were significantly higher in the two areas with fish farming, whereas the BMF was not significantly different. The DMF and DM were correlated to depth and chlorophyll-a. However, the low production of BMF did not allow the comparison with the limnological parameters measured. This case study shows that CH₄ emissions are influenced more by reservoir characteristics than fish production. Further investigation is necessary to assess the impact of fish farming on the greenhouse gas emissions.