Metal release from serpentine soils in Sri Lanka

Ultramafic rocks and their related soils (i.e., serpentine soils) are non-anthropogenic sources of metal contamination. Elevated concentrations of metals released from these soils into the surrounding areas and groundwater have ecological-, agricultural-, and human health-related consequences. Here we report the geochemistry of four different serpentine soil localities in Sri Lanka by coupling interpretations garnered from physicochemical properties and chemical extractions. Both Ni and Mn demonstrate appreciable release in water from the Ussangoda soils compared to the other three localities, with Ni and Mn metal release increasing with increasing ionic strengths at all sites. Sequential extraction experiments, utilized to identify “elemental pools,” indicate that Mn is mainly associated with oxides/(oxy)hydroxides, whereas Ni and Cr are bound in silicates and spinels. Nickel was the most bioavailable metal compared to Mn and Cr in all four soils, with the highest value observed in the Ussangoda soil at 168?±?6.40 mg kg^?1 via the 0.01-M CaCl₂ extraction. Although Mn is dominantly bound in oxides/(oxy)hydroxides, Mn is widely dispersed with concentrations reaching as high as 391 mg kg^?1 (Yudhaganawa) in the organic fraction and 49 mg kg^?1 (Ussangoda) in the exchangeable fraction. Despite Cr being primarily retained in the residual fraction, the second largest pool of Cr was in the organic matter fraction (693 mg kg^?1 in the Yudhaganawa soil). Overall, our results support that serpentine soils in Sri Lanka offer a highly labile source of metals to the critical zone.     

Seasonal baseline of nutrients and stable isotopes in a saline lake of Argentina: biogeochemical processes and river runoff effects

The seasonal variability of inorganic and organic nutrients and stable isotopes and their relations with plankton and environmental conditions were monitored in Lake Chasicó. Principal component analysis evidenced the strong influence of the river runoff on several biogeochemical variables. Silicate concentrations were controlled by diatom biomass and river discharge. Higher values of nitrate and soluble reactive phosphorus (SRP) indicated agricultural uses in the river basin. Elevated pH values (～9) inhibiting nitrification in the lake explained partially the dominance of ammonium: ～83 % of dissolved inorganic nitrogen (DIN). The low DIN/SRP ratio inferred nitrogen limitation, although the hypotheses of iron and CO₂ limitation are relevant in alkaline lakes. Particulate organic matter (POM) and dissolved organic matter (DOM) were mainly of autochthonous origin. The main allochthonous input was imported by the river as POM owning to the arid conditions. Dissolved organic carbon was likely top-down regulated by the bacterioplankton grazer Brachionus plicatilis. The δ¹³C signature was a good indicator of primary production and its values were influenced probably by CO₂ limitation. The δ¹⁵N did not evidence nitrogen fixation and suggested the effects of anthropogenic activities. The preservation of a good water quality in the lake is crucial for resource management.     

Soil respiration,labile carbon pools,and enzyme activities as affected by tillage practices in a tropical rice–maize–cowpea cropping system

In order to identify the viable option of tillage practices in rice–maize–cowpea cropping system that could cut down soil carbon dioxide (CO₂) emission, sustain grain yield, and maintain better soil quality in tropical low land rice ecology soil respiration in terms of CO₂ emission, labile carbon (C) pools, water-stable aggregate C fractions, and enzymatic activities were investigated in a sandy clay loam soil. Soil respiration is the major pathway of gaseous C efflux from terrestrial systems and acts as an important index of ecosystem functioning. The CO₂–C emissions were quantified in between plants and rows throughout the year in rice–maize–cowpea cropping sequence both under conventional tillage (CT) and minimum tillage (MT) practices along with soil moisture and temperature. The CO₂–C emissions, as a whole, were 24 % higher in between plants than in rows, and were in the range of 23.4–78.1, 37.1–128.1, and 28.6–101.2 mg m^?2 h^?1 under CT and 10.7–60.3, 17.3–99.1, and 17.2–79.1 mg m^?2 h^?1 under MT in rice, maize, and cowpea, respectively. The CO₂–C emission was found highest under maize (44 %) followed by rice (33 %) and cowpea (23 %) irrespective of CT and MT practices. In CT system, the CO₂–C emission increased significantly by 37.1 % with respect to MT on cumulative annual basis including fallow. The CO₂–C emission per unit yield was at par in rice and cowpea signifying the beneficial effect of MT in maintaining soil quality and reduction of CO₂ emission. The microbial biomass C (MBC), readily mineralizable C (RMC), water-soluble C (WSC), and permanganate-oxidizable C (PMOC) were 19.4, 20.4, 39.5, and 15.1 % higher under MT than CT. The C contents in soil aggregate fraction were significantly higher in MT than CT. Soil enzymatic activities like, dehydrogenase, fluorescein diacetate, and β-glucosidase were significantly higher by 13.8, 15.4, and 27.4 % under MT compared to CT. The soil labile C pools, enzymatic activities, and heterotrophic microbial populations were in the order of maize?>?cowpea?>?rice, irrespective of the tillage treatments. Environmental sustainability point of view, minimum tillage practices in rice–maize–cowpea cropping system in tropical low land soil could be adopted to minimize CO₂–C emission, sustain yield, and maintain soil health.     

Antioxidant responses in the leaves of mercury-treated Eichhornia crassipes (Mart.) Solms.

Eichhornia crassipes (Mart.) Solms. plantlets were grown in 0.1 and 1.0 ppm treatment solutions of Hoagland’s hydroponic solutions modified with Hg(NO₃)₂ in order to examine the specific cellular and biochemical mechanisms involved in the tolerance of this plant exposed to mercury. This study assessed the responses of chloroplast pigments, i.e., carotenoids and chlorophylls, and evaluated the enzymatic and nonenzymatic antioxidant systems. Inductively coupled plasma-atomic emission spectrometry (ICP-AES) revealed varying Hg²⁺ levels in the young and mature leaf tissues, with greater amounts of Hg²⁺ found in the tissues of the young leaves. Total chlorophyll levels, notably those of chlorophyll a, chlorophyll b, and carotenoids, showed significant elevation in young leaf tissues, while a decrease in their levels was observed in mature leaf tissues in comparison to those of the control plants. These results lend support to the protective role of increased chlorophyll and carotenoid levels in the photosynthetic apparatus of young E. crassipes leaves in the presence of Hg²⁺. The antioxidant responses of Hg-treated E. crassipes plants were also measured, revealing a highly significant increase in catalase units, catalase and ascorbate peroxidase activities, and mercury-binding thiols in leaves from Hg-treated plants. Moreover, substantial differences in the degree of oxidative injury between the cells in leaves from the control and Hg-treated plants were evidenced by the lipid peroxidation activities monitored. The Hg-treatment-induced significant decrease in malondialdehyde (MDA) levels was observed in 0.1-ppm Hg(NO₃)₂-exposed plants, while a highly significant increase in MDA levels was noted in 1.0-ppm Hg(NO₃)₂-exposed plants. The high degree of lipid peroxidation at 1.0-ppm Hg treatment was evidently counteracted by the compensatory protective mechanism brought about by the increased levels in chloroplast pigments and the enhanced activities of the antioxidant systems. E. crassipes responded to mercury treatments by enhancing the synthesis of chlorophyll and carotenoid pigments, enzymatic, and nonenzymatic antioxidant substances, concomitantly increasing the antioxidative activities, thus rendering E. crassipes capable of tolerating Hg-induced stress. The potential of E. crassipes as a phytoremediator is evident.     

Cumulative influences of a small city and former mining activities on the sediment quality of a subtropical estuarine protected area

This study aimed to evaluate the sediment quality in the estuarine protected area known as Cananéia-Iguape-Peruíbe (CIP-PA), located on the southeastern coast of Brazil. The study was designed considering possible negative effects induced by the city of Cananéia on the sediment quality of surrounding areas. This evaluation was performed using chemical and ecotoxicological analyses. Sediments were predominantly sandy, with low CaCO₃ contents. Amounts of organic matter varied, but higher contents occurred closer to the city, as well as did Fe and Total Recoverable Oils and Greases (TROGs) concentrations. Contamination by Cd and Cu was revealed in some samples, while concentrations of Zn were considered low. Chronic toxicity was detected in all tested sediments and acute toxicity occurred only in sediments collected near the city. The principal component analysis (PCA) revealed an association among Cd, Cu, Fe, TROG, fines, organic matter, CaCO₃, and chronic toxicity, whereas acute toxicity was found to be associated with Zn and mud. However, because Zn levels were low, acute toxicity was likely due to a contaminant that was not measured. Results show that there is a broad area within the CIP-PA that is under the influence of mining activities (chronic toxicity, moderate contamination by metals), whereas poorer conditions occur closer to Cananéia (acute toxicity); thus, the urban area seems to constitute a relevant source of contaminants for the estuarine complex. These results show that contamination is already capable of producing risks for the local aquatic biota, which suggests that the CIP-PA effectiveness in protecting estuarine biota may be threatened.     

Soil response to a 3-year increase in temperature and nitrogen deposition measured in a mature boreal forest using ion-exchange membranes

The projected increase in atmospheric N deposition and air/soil temperature will likely affect soil nutrient dynamics in boreal ecosystems. The potential effects of these changes on soil ion fluxes were studied in a mature balsam fir stand (Abies balsamea [L.] Mill) in Quebec, Canada that was subjected to 3 years of experimentally increased soil temperature (+4 °C) and increased inorganic N concentration in artificial precipitation (three times the current N concentrations using NH₄NO₃). Soil element fluxes (NO₃, NH₄, PO₄, K, Ca, Mg, SO₄, Al, and Fe) in the organic and upper mineral horizons were monitored using buried ion-exchange membranes (PRS? probes). While N additions did not affect soil element fluxes, 3 years of soil warming increased the cumulative fluxes of K, Mg, and SO₄ in the forest floor by 43, 44, and 79 %, respectively, and Mg, SO₄, and Al in the mineral horizon by 29, 66, and 23 %, respectively. We attribute these changes to increased rates of soil organic matter decomposition. Significant interactions of the heating treatment with time were observed for most elements although no clear seasonal patterns emerged. The increase in soil K and Mg in heated plots resulted in a significant but small K increase in balsam fir foliage while no change was observed for Mg. A 6–15 % decrease in foliar Ca content with soil warming could be related to the increase in soil-available Al in heated plots, as Al can interfere with the root uptake of Ca.     

Remote sensing in environmental police investigations: aerial platforms and an innovative application of thermography to detect several illegal activities

Being able to identify the environmental crimes and the guilty parties is central to police investigations, and new technologies enable the authorities to do this faster and more accurately than ever before. In recent years, our research team has introduced the use of a range of aerial platforms and an innovative application of thermography to detect several illegal activities; for example, illegal sanitary sewer and storm-drain connections, illicit wastewater discharges, and other “anomalies” on surface waters can be easily identified using their thermal infrared signatures. It can also be used to detect illegal solid/liquid waste dumps or illicit air discharges. This paper introduces first results of a Thermal Pattern and Thermal Tracking approach that can be used to identify different phenomena and several pollutants. The aims of this paper were to introduce a fingerprint paradigm for environmental police investigations, defining several specific signatures (patterns) that permit the identification of an illicit/anomalous activity, and establish a procedure to use this information to find the correlation (tracking) between the crime and the culprit or the source and the target.     

Community metabolism in a deep (stratified) tropical reservoir during a period of high water-level fluctuations

As long as lakes and reservoirs are an important component of the global carbon cycle, monitoring of their metabolism is required, especially in the tropics. In particular, the response of deep reservoirs to water-level fluctuations (WLF) is an understudied field. Here, we study community metabolism through oxygen dynamics in a deep monomictic reservoir where high WLF (~10 m) have recently occurred. Simultaneous monitoring of environmental variables and zooplankton dynamics was used to assess the effects of WLF on the metabolism of the eutrophic Valle de Bravo (VB) reservoir, where cyanobacteria blooms are frequent. Mean gross primary production (P _g) was high (2.2 g C m^?2 day^?1), but temporal variation of P _g was low except for a drastic reduction during circulation attributed to zooplankton grazing. The trophogenic layer showed net autotrophy on an annual basis, but turned to net heterotrophy during mixing, and furthermore when the whole water-column oxygen balance was calculated, considering the aphotic respiration (R _aphotic). The high total respiration resulting (3.1 g C m^?2 day^?1) is considered to be partly due to mixing enhanced by WLF. Net ecosystem production was equivalent to a net export of 3.4 mg CO₂?m^?2 day^?1 to the atmosphere. Low water levels are posed to intensify boundary-mixing events driven by the wind during the stratification in VB. Long-term monitoring showed changes in the planktonic community and a strong silicon decrease that matched with low water-level periods. The effects of low water-level on metabolism and planktonic community in VB suggest that water-level manipulation could be a useful management tool to promote phytoplankton groups other than cyanobacteria.