Dissolved Organic Matter Features of Three Adjacent Eastern Mediterranean Urbanized Watersheds

Landscape urbanization broadly affects ecosystems in coastal watersheds, but, until now, the influence of nonpoint source urban inputs on dissolved organic matter (DOM) amount, composition, and source is poorly understood. To understand how DOM composition varied with urbanization, fluorescence excitation-emission matrices (EEMs) were determined for urban and non-urban waters from upstream to downstream sites along three adjacent coastal watersheds that flow into the Mediterranean Sea. Two humic DOM fluorescent components (humic-like and fulvic-like peaks) and two proteinic components (tyrosine-like and tryptophane-like peaks) were identified by EEM fluorescence. The results indicated that urbanization had an important influence on DOM concentration and composition, with urban waters having a high degree of DOM variation due to different land uses surrounding each body of water. Urban waters show a higher DOM fluorescence index (FI), the highest fluorescence intensity of protein-like manifested also by BIX values, and a lower value of the humification index (HIX) than non-urban waters which were dominated by allochthonous inputs. In addition, the EEM was compared in dry and wet season where higher DOM amounts and FI appeared in summer due to autochthonous production coming from algae growth compared to allochthonous input from rainfall dominated in wet season. The concentration of DOC increased from upstream to downstream for the three rivers, especially Beirut River. The increase in DOC values was observed in both dry and wet seasons by 39 and 19 times respectively compared to upstream (0.93 - 0.91 mgC/L).

Selective metal leaching from technosols based on synthetic root exudate composition

This study focused on metal release from technosols induced by synthetic root exudate(SRE).The effect of SRE composition on metal release was studied using six technosols.This was done by treating the technosols with SRE solutions having varying concentrations of low molecular weight organic acids (LMWOAs),namely oxalic,citric,and malic acids.Consequently,the physico-chemical parameters (p H and electric conductivity),Ca,Mg,Fe,Zn,and Cu release (by atomic absorption spectroscopy,AAS),chemical changes (by Fourier transform infrared,FT-IR),and organic parameters (by fluorescence) were investigated.Metal release showed to be dependent on the SRE composition and technosol characteristics.Citric acid selectively released Ca,Mg,Zn,and Cu from technosols in a concentration-dependent manner;oxalic acid showed a significant role in the release of Mg and Fe.Under relatively high LMWOA concentrations,particulate organo-mineral complexes precipitated.Additionally,technosol weathering was seen by the dissolution of humic substances and ferriallophanes,which in turn caused metal release.However,re-precipitation of these phases showed to re-sorb metals,thus underestimating the role of LMWOAs in metal release.Therefore,the selective metal leaching was highly dependent on the SRE composition and LMWOA concentrations on one hand,and on the mineral,organic,and organo-mineral components of the technosols on the other.The understanding of such processes is crucial for proposing and implementing environmental management strategies to reduce metal leaching or for the beneficial re-usage of metals (e.g.,for agromining) from technosols.