Release of colloidal particles in natural porous media by monovalent and divalent cations

We study mobilization of colloidal particles from natural porous media, such as soils and groundwater aquifers. Extensive laboratory scale column experiments of particle release from four different subsurface materials are presented. The important characteristics of the release process are (i) its non-exponential kinetics, (ii) the finite supply of colloidal particles and (iii) the strong dependence of the release kinetic on the nature of the adsorbed cations. Particle release depends most sensitively on the relative saturation of the medium with divalent cations. We propose a mathematic model, which captures all these aspects quantitatively, and can be used to describe the coupling between transport of major cations and the release of colloidal particles. The present experimental investigations as well as the developed modeling framework represent an important step towards the understanding of colloid-facilitated transport phenomena in natural porous media.     

Environmental PCBs in Guánica Bay,Puerto Rico: implications for community health

Guánica Bay, located in southwestern Puerto Rico, has suffered oil spills and other pollution discharges since the 1960s. Previous research showed elevated concentrations of polychlorinated biphenyls (PCBs) in coral reef and sediment. This research examined PCB concentrations in sediment and fish. Sediment and fish sampling in the bay was facilitated by community members. This study identified the second highest reported PCB level (129,300 ng/g) in sediment in the USA. Fish samples also showed elevated concentrations (1623 to 3768 ng/g), which were higher than the thresholds of safe levels of PCBs in fish for human consumption. The alarmingly high concentration of PCBs calls for proactive community engagement to bring awareness about contamination of the bay and more extensive sampling to test for the concentration of PCBs in seafood and the people of Guánica. This study also underscores the value of the involvement of local communities during sampling design aimed at identifying hot spots of contaminants.     

Sources and transformations of nitrogen compounds along the Lower Jordan River

The Lower Jordan River is located in the semiarid area of the Jordan Valley, along the border between Israel and Jordan. The implementation of the water sections of the peace treaty between Israel and Jordan and the countries' commitment to improve the ecological sustainability of the river system require a better understanding of the riverine environment. This paper investigates the sources and transformations of nitrogen compounds in the Lower Jordan River by applying a combination of physical, chemical, isotopic, and mathematical techniques. The source waters of the Lower Jordan River contain sewage, which contributes high ammonium loads to the river. Ammonium concentrations decrease from 20 to 0-5 mg N L(-1) along the first 20 km of the Lower Jordan River, while nitrate concentrations increase from nearly zero to 10-15 mg N L(-1), and delta(15)N (NO(3)) values increase from less than 5 per thousand to 15-20 per thousand. Our data analysis indicates that intensive nitrification occurs along the river, between 5 and 12 km from the Sea of Galilee, while further downstream nitrate concentration increases mostly due to an external subsurface water source that enters the river.     

Quantifying ground water inputs along the Lower Jordan River

The flow rate of the Lower Jordan River has changed dramatically during the second half of the 20th century. The diversion of its major natural sources reduced its flow rate and led to drying events during the drought years of 2000 and 2001. Under these conditions of low flow rates, the potential influence of external sources on the river discharge and chemical composition became significant. Our measurements show that the concentrations of chloride, calcium, and sodium in the river water decrease along the first 20-km section, while sulfate and magnesium concentrations increase. These variations were addressed by a recent geochemical study, suggesting that ground water inflow plays a major role. To further examine the role of ground water, we applied mass-balance calculations, using detailed flow rate measurements, water samplings, and chemical analyses along the northern (upstream) part of the river. Our flow-rate measurements showed that the river base-flow during 2000 and 2001 was 500 to 1100 L s(-1), which is about 40 times lower than the historical flow rates. Our measurements and calculations indicate that ground water input was 20 to 80% of the river water flow, and 20 to 50% of its solute mass flow. This study independently identifies the composition of possible end-members. These end-members contain high sulfate concentration and have similar chemical characteristics as were found in agricultural drains and in the "saline" Yarmouk River. Future regional development plans that include the river flow rate and chemistry should consider the interactions between the river and its shallow ground water system.     

Mollusc communities in Bulgarian fens: predictive power of the environment,vegetation, and spatial structure in an isolated habitat

Mollusc communities of previously unexplored Bulgarian fens were studied in order to determine and generalise the patterns of species richness and composition along the mineral richness gradient. The aim was also to compare predictive values of the environment, vegetation and spatial structure. Altogether, 44 mollusc species were recorded at 40 treeless fen sites. Species richness varied from 0 to 18 species per site, and it was positively associated with the mineral gradient and negatively with altitude. However, the best predictor was obtained using plant species composition. All explanatory variables had higher effect on land snails than on the entire mollusc assemblage (including aquatic species). Species richness and abundance were significantly and positively correlated with the species composition turnover; the communities were highly nested, with poor sites having subsets of the fauna found in the richest. The main direction of mollusc species turnover was highly associated with that observed for vegetation, and the main gradient of plant species composition was able to explain nearly 20% of total variation in mollusc data. We found that spatial structure explained by far the highest proportion of independent variation, which reflected the high level of geographical isolation of Bulgarian fens and regional differences independent of any environmental variation. Our results demonstrate (1) the general role of mineral richness gradient for structuring mollusc communities in fens, (2) the pivotal indicator role of plant species composition in predicting species composition of mollusc communities, despite being trophically independent and (3) the effect of isolation and origins of the habitat on species composition: most species have wide geographical distributions within the habitat type, and geographical patterns within Bulgaria may have a stochastic element.