Ecosystem services provided by the exotic bivalves Dreissena polymorpha, D. rostriformis bugensis, and Limnoperna fortunei

The ecosystem services approach to conservation is becoming central to environmental policy decision making. While many negative biological invasion-driven impacts on ecosystem structure and functioning have been identified, much less was done to evaluate their ecosystem services. In this paper, we focus on the often-overlooked ecosystem services provided by three notable exotic ecosystem engineering bivalves, the zebra mussel, the quagga mussel, and the golden mussel. One of the most significant benefits of invasive bivalves is water filtration, which results in water purification and changes rates of nutrient cycling, thus mitigating the effects of eutrophication. Mussels are widely used as sentinel organisms for the assessment and biomonitoring of contaminants and pathogens and are consumed by many fishes and birds. Benefits of invasive bivalves are particularly relevant in human-modified ecosystems. We summarize the multiple ecosystem services provided by invasive bivalves and recommend including the economically quantifiable services in the assessments of their economic impacts. We also highlight important ecosystem disservices by exotic bivalves, identify data limitations, and future research directions. This assessment should not be interpreted as a rejection of the fact that invasive mussels have negative impacts, but as an attempt to provide additional information for scientists, managers, and policymakers.

Binding of Nitrodiphenylamines to Reverse Micelles of AOT in n-Hexane and Carbon Tetrachloride: Solvent and Substituent Effects

The absorption spectra of N-[2-(trifluoromethyl)-4-nitrophenyl]-4-nitroaniline (1), N-[4-nitrophenyl]-4-nitroaniline (2), and N-[2-nitrophenyl]-4-nitroaniline (3) were analyzed in reversed micelles of AOT (sodium 1,4-bis (2-ethylhexyl sulfosuccinate) in n-hexane and carbon tetrachloride. For 1 and 2 the intensity of the band characteristic for the pure solvent decreases as the AOT concentration increases and a new band develops. This new band is attributed to the solute bound to the micelle. These changes allowed us to determine the binding constant (Kb) between these compounds and AOT. Kb at W0 = [H2O]/[AOT] = 0 in n-hexane varies from 81 for 1 to 5092 for 2. Although similar trends are observed for carbon tetrachloride, the values of Kb are smaller than those for n-hexane. The possible solute-solvent interactions of these compounds were analyzed by means of Taft and Kamlet's solvatochromic comparison method. The strength of binding is interpreted considering their hydrogen-bond donor ability as well as their solubility in the pure solvents. For 1 Kb decreases as W0 is increased, while for 2 no variation was observed. These effects are discussed in terms of nitrodiphenylamine-water competition for interfacial binding sites. Moreover, the effect of the solute size and the presence of the trifluoromethyl group in 1 are important factors to consider in explaining its binding behavior. The spectra of 3 change very little with AOT concentration and only a slight bathochromic shift is observed. Thus, 3 acts as nonhydrogen bond donor solute, merely sensing a slight change in the polarity of its microenvironment. Copyright 1998 Academic Press.

Micropolarity of Reversed Micelles: Comparison between Anionic, Cationic, and Nonionic Reversed Micelles

The interface polarity of benzyl-n-hexadecyldimethylammonium chloride (BHDC) cationic reversed micelles in benzene was studied and compared with those of the anionic systems of sodium 1,4-bis-2-ethylhexylsulfosuccinate (AOT) in benzene and hexane. The nonionic reversed micelles of the poly(oxyethylene)n dodecyl ethers type surfactants Brij 30 in benzene, cyclohexane, and decane and C12E5 in hexane, heptane, and decane were also investigated. 1-Methyl-8-oxyquinolinium betaine (QB) was used as optical probe. The influence of surfactant concentration and W = [H2O]/[surfactant] were analyzed as a function of the absorption bands shifts in the visible, B1, and in the UV, B2, and the absorbances ratio of these bands. At W = 0 the polarity sensed in the micelle interfaces of AOT-hexane and AOT-benzene is entirely similar while for BHDC-benzene is quite smaller. The detected interaction between the QB and BHDC may favor the entrance of QB into the oil side of the micelle interface thus sensing a less polar environment. At W >/= 10 once the polar heads of the surfactants are completed hydrated, the anionic as well as the cationic surfactants show the same behavior. The polarity of Brij 30 and C12E5 in the aliphatic hydrocarbons is comparable. However at W = 0 their micropolarity is higher than that of AOT-hexane, showing that the formation of hydrogen bond between QB and the free OH groups of these surfactants is the major factor affecting the microenvironment. In all the studied systems even at the maximum possible W, the polarity sensed by QB never reaches the value of pure water, that is, never reaches the bulk water phase prevailing in the micellar core.