Intercropping Sedum Alfredii and Cicer Arietinum L. Does Not Present a Suitable Land Use Pattern For Multi-Metal-Polluted Soil

Background and aims Intercropping of hyperaccumulators with commercial crops is widely accepted in single-metal-polluted farmland. However, the ecological risks of non-hyperaccumulated metals in intercropping systems have not been revealed. Methods To evaluate Pb and Cu activation and absorption in an intercropped system of Sedum alfredii and Cicer arietinum L., sequential extraction and dissolved organic matter (DOM) characterization were used to describe the migration of metals in the intercropping system. Results This study found that the concentrations of DOM in the S. alfredii monoculture and intercropping system were significantly higher than those in the C. arietinum L. monoculture, and DOM from the former two cultivation strategies had significantly higher Cd, Pb, and Cu extraction capacity than those from the latter. Compared with the C. arietinum L. monoculture, C. arietinum L. intercropping had significantly lower Cd content owing to the depletion of Cd by S. alfredii. However, Cu and Pb concentrations in the former were significantly higher than those in the latter because S. alfredii mobilized these metals but did not hyperaccumulate them. Conclusion The results indicated that intercropping efficiently decreased the potential risk of Cd, but deteriorated the ecological risk of Pb and Cu. Therefore, intercropping does not present a suitable land-use pattern for multi-metal-polluted soil.

Submarine mud volcanoes as a source of chromophoric dissolved organic matter to the deep waters of the Gulf of Cádiz

Seafloor structures related to the emission of different fluids, such as submarine mud volcanoes (MVs), have been recently reported to largely contribute with dissolved organic matter (DOM) into the oceans. Submarine MVs are common structures in the Gulf of Cádiz. However, little is known about the biogeochemical processes that occur in these peculiar environments, especially those involving DOM. Here, we report DOM characterization in the sediment pore water of three MVs of the Gulf of Cádiz. Estimated benthic fluxes of dissolved organic carbon (DOC) and chromophoric DOM (CDOM) were higher than in other marine sediments with an average of 0.11 ± 0.04 mmol m−2 d−1 for DOC and ranging between 0.11 and 2.86 m−1 L m−2 d−1, for CDOM. Protein-like components represented ~ 70% of the total fluorescent DOM (FDOM). We found that deep fluids migration from MVs (cold seeps) and anaerobic production via sulfate-reducing bacteria represent a source of DOC and FDOM to the overlying water column. Our results also indicate that fluorescent components can have many diverse sources not captured by common classifications. Overall, MVs act as a source of DOC, CDOM, and FDOM to the deep waters of the Gulf of Cádiz, providing energy to the microbial communities living there.

Composition Wheels: Visualizing dissolved organic matter using common composition metrics across a variety of Canadian Ecozones

Dissolved organic matter (DOM) is a ubiquitous component of aquatic systems, impacting aquatic health and drinking water quality. These impacts depend on the mixture of organic molecules that comprise DOM. Changing climates are altering both the amount and character of DOM being transported from the terrestrial system into adjacent surface waters, yet DOM composition is not monitored as often as overall concentration. Many DOM characterization methods exist, confounding comparison of DOM composition across different studies. The objective of this research is to determine which parameters in a suite of relatively simple and common DOM characterization techniques explain the most variability in DOM composition from surface and subsurface sites. Further, we create a simple visualization tool to easily compare compositional differences in DOM. A large number of water samples (n=250) was analyzed from six Canadian ecozones for DOM concentration, ultraviolet-visible light absorbance, molecular size, and elemental ratios. Principal component analyses was used to identify quasi-independent DOM compositional parameters that explained the highest variability in the dataset: spectral slope, specific-UV absorbance at 255nm, humic substances fraction, and dissolved organic carbon to dissolved organic nitrogen ratio. A ‘Composition Wheel’ was created by plotting these four parameters as a polygon. Our results find similarities in DOM composition irrespective of site differences in vegetation and climate. Composition Wheels reveal two main shapes that correspond to common compositions of DOM regardless of site: DOM in the subsurface and DOM influenced by photodegradation The Composition Wheel approach uses easily visualized differences in polygon shape to quantify how DOM evolves by natural processes along the aquatic continuum and to track sources and degradation of DOM.

Removal and transformation of dissolved organic matter (DOM) during the treatment of partially stabilized leachate in membrane bioreactor

The removal of dissolved organic matter (DOM) during municipal solid waste leachate treatment in a membrane bioreactor (MBR) was investigated. The MBR was operated with fouled and cleaned membranes, at a time. DOM, mixed liquor, and effluent were characterized by fractionation and fluorescence excitation–emission matrix (EEM) spectroscopy. Results showed DOM removals of 82% during the MBR operation with the fouled membrane. The DOM characterization indicated that most of the hydrophilic compounds and protein-like substances could be significantly removed by microbial activities in the treatment processes. Furthermore partial removal or transformation of organic substances was observed during membrane filtration. The fouled membrane improved DOM rejection by only about 2% when compared to the cleaned membrane, which demonstrated the significance of irreversible foulants on DOM rejection. There were insignificant differences in DOM fractionation and EEM fluorescence spectra between water samples filtered through the fouled and cleaned membranes.

The dynamics of fluorescent dissolved organic matter in the Paranaguá estuarine system, Southern Brazil

The aim of this study was to investigate the dynamics of the fluorescent dissolved organic matter (FDOM) in Paranaguá Estuarine System (PES) as to infer about the contribution of allochthonous FDOM to the estuarine waters in relation to tidal condition and seasons. Fluorescence spectroscopy was used for such purpose and DOM characterization through fluorescence emission was performed using excitation wavelengths of λex 350 nm and λex 450 nm, the two main fluorescence groups known to be present in natural DOM. Relations between emission wavelength (λem) and environmental variables, and the relevance of these variables to the different tides and seasons were identified by principal component analysis. The results showed that the first class of fluorophores (λex 350 nm) changed from the river (freshwater) towards the estuary, whilst the second class (λex 450 nm) has a more conservative nature and does not change as significantly as the first. Allochthonous DOM contribution to the estuarine system is intensified during the rainy season, especially in spring tides, whereas in the dry season the ratio of autochthonous DOM to total DOM in PES waters increased. We concluded that the variation of maximum λem of the first class of fluorophores (λex 350 nm) is mainly related to allochthonous contribution, whilst the maximum of emission for the second class of fluorophores (λex 450 nm) is dependent on the contribution of the different sources of organic matter (freshwater and marine water DOM contribution).