Michael R. Hoffmann

Global Biodiversity Conservation Priorities

The location of and threats to biodiversity are distributed unevenly, so prioritization is essential to minimize biodiversity loss. To address this need, biodiversity conservation organizations have proposed nine templates of global priorities over the past decade. Here, we review the concepts, methods, results, impacts, and challenges of these prioritizations of conservation practice within the theoretical irreplaceability/vulnerability framework of systematic conservation planning. Most of the templates prioritize highly irreplaceable regions; some are reactive (prioritizing high vulnerability), and others are proactive (prioritizing low vulnerability). We hope this synthesis improves understanding of these prioritization approaches and that it results in more efficient allocation of geographically flexible conservation funding.

Effectiveness of the global protected area network in representing species diversity

The Fifth World Parks Congress in Durban, South Africa, announced in September 2003 that the global network of protected areas now covers 11.5% of the planets land surface. This surpasses the 10% target proposed a decade earlier, at the Caracas Congress, for 9 out of 14 major terrestrial biomes. Such uniform targets based on percentage of area have become deeply embedded into national and international conservation planning. Although politically expedient, the scientific basis and conservation value of these targets have been questioned. In practice, however, little is known of how to set appropriate targets, or of the extent to which the current global protected area network fulfils its goal of protecting biodiversity. Here, we combine five global data sets on the distribution of species and protected areas to provide the first global gap analysis assessing the effectiveness of protected areas in representing species diversity. We show that the global network is far from complete, and demonstrate the inadequacy of uniform—that is, ‘one size fits all’—conservation targets.

Photocatalytic production of hydrogen peroxides and organic peroxides in aqueous suspensions of titanium dioxide, zinc oxide, and desert sand

The formation of H_2O_2 and organic peroxides in illuminated aqueous suspensions of ZnO, TiO_2, and desert sand in the presence of O_2 and organic electron donors has been studied. The photocatalytic rate of formation of H_2O_2 on ZnO was shown to depend on the O_2 partial pressure, on the concentration of organic electron donors, and on the concentration of H_2O_2.

Global gap analysis: Priority regions for expanding the global protected-area network

Abstract Protected areas are the single most important conservation tool. The global protected-area network has grown substantially in recent decades, now occupying 11.5% of Earths land surface, but such growth has not been strategically aimed at maximizing the coverage of global biodiversity. In a previous study, we demonstrated that the global network is far from complete, even for the representation of terrestrial vertebrate species. Here we present a first attempt to provide a global framework for the next step of strategically expanding the network to cover mammals, amphibians, freshwater turtles and tortoises, and globally threatened birds. We identify unprotected areas of the world that have remarkably high conservation value (irreplaceability) and are under serious threat. These areas concentrate overwhelmingly in tropical and subtropical moist forests, particularly on tropical mountains and islands. The expansion of the global protected-area network in these regions is urgently needed to prevent the loss of unique biodiversity.

Photocatalytic Production of H2O2 and Organic Peroxides on Quantum-Sized Semiconductor Colloids

Illuminated (320 ≤ X ≤ 370 nm), aqueous suspensions of transparent quantum-sized (Q-sized) ZnO semiconductor colloids in the presence of carboxylic acids and oxygen are shown to produce steady-state concentrations of H_2O_2 as high as 2 mM. Maximum H_2O_2 concentrations are observed only with added electron donors (i.e., hole scavengers). The order of efficiency of hole scavengers is as follows: formate > oxalate > acetate > citrate. Isotopic labeling experiments with ^(18)O_2 are consistent with the hypothesis that hydrogen peroxide is produced directly by the reduction of adsorbed oxygen by conduction band electrons. Quantum yields for H_2O_2 production are near 30% at low photon fluxes. However, the quantum yield is shown to vary with the inverse square root of absorbed light intensity [Φ ∝ ((I_(abs))^(-1)½)], with the wavelength of excitation, and with the diameter of the Q-sized colloids. The initial rate of H_2O_2 production is 100-1000 times faster with Q-sized ZnO particles (D_p = 4-5 nm) than with bulk-sized ZnO particles (D_p = 0.1 µm).

Photocatalytic oxidation of organic acids on quantum-sized semiconductor colloids.

A detailed analysis of the reaction products and mechanisms of the photocatalytic oxidation of acetate in the presence of quantum-sized ZnO colloids (Dp ≈ 40 A) is presented. The principal oxidation products and reaction intermediates are determined to be CO_2, HCO_2^-, CHOCO_2^-, HCHO, CH_3OOH, CH_3COOOH, and H_2O_2. Formate and glyoxylate, which are found as intermediates in the photooxidation of acetate, also serve as effective electron donors on illuminated ZnO surfaces. The proposed relative reactivity of electron donors toward photooxidation is in the following order: CHOCO_2- > HCO_2^- > HCHO > CH_3CO_2^- ≥ H_2O_2 CH_3COOOH > CH_3OOH. Observed product distributions are discussed in terms of pathways involving direct oxidation of surface-bound acetate by valence band holes (or trapped holes) and the indirect oxidation of acetate by surface-bound hydroxyl radicals. The product distribution observed at low photon fluxes is not consistent with oxidation primarily by free hydroxyl radicals. A mechanism involving the reaction of an intermediate carbon-centered radical with > ZnOH surface sites is proposed. When electron donors are strongly adsorbed to semiconductor surfaces, surface-mediated reactions appear to play a dominant role in the determination of the time-dependent product distributions.

Protected Areas and Effective Biodiversity Conservation

Increasing the collective contribution of protected areas toward preventing species extinctions requires the strategic allocation of management efforts. Although protected areas (PAs) cover 13% of Earths land (1), substantial gaps remain in their coverage of global biodiversity (2). Thus, there has been emphasis on strategic expansion of the global PA network (3–5). However, because PAs are often understaffed, underfunded, and beleaguered in the face of external threats (6, 7), efforts to expand PA coverage should be complemented by appropriate management of existing PAs. Previous calls for enhancing PA management have focused on improving operational effectiveness of each PA [e.g., staffing and budgets (6)]. Little guidance has been offered on how to improve collective effectiveness for meeting global biodiversity conservation goals (3). We provide guidance for strategically allocating management efforts among and within existing PAs to strengthen their collective contribution toward preventing global species extinctions.

Time-resolved microwave conductivity. Part 1.—TiO2 photoreactivity and size quantization

Charge-carrier recombination dynamics after laser excitation are investigated by time-resolved microwave conductivity (TRMC) measurements of quantum-sized (Q-) TiO_2, Fe^(III)-doped Q-TiO_2, ZnO and CdS, and several commercial bulk-sized TiO2 samples. After pulsed laser excitation of charge carriers, holes that escape recombination react with sorbed trans-decalin within ns while the measured conductivity signal is due to conduction-band electrons remaining in the semiconductor lattice. The charge-carrier recombination lifetime and the interfacial electron-transfer rate constant that are derived from the TRMC measurements correlate with the CW photo-oxidation quantum efficiency obtained for aqueous chloroform in the presence of TiO_2. The quantum efficiencies are 0. 4 % for Q-TiO_2, 1. 6 % for Degussa P25, and 2. 0 % for Fe^(III)-doped Q-TiO_2. The lower quantum efficiencies for Q-TiO_2 are consistent with the relative interfacial electron-transfer rates observed by TRMC for Q-TiO_2 and Degussa P25. The increased quantum efficiencies of Fe^(III)-doped Q-TiO_2 and the observed TRMC decays are consistent with a mechanism involving fast trapping of valence-band holes as Fe^(IV) and inhibition of charge-order recombination.

Chemical mechanism of inorganic oxidants in the TiO2/UV process: increased rates of degradation of chlorinated hydrocarbons

Particulate suspensions of TiO_2 irradiated with UV light at wavelengths shorter than 385 nm catalyze the autooxidation of chlorinated hydrocarbons such as 4-chlorophenol (4-CP). The addition of oxyanion oxidants such as CIO_2^-, CIO_3^-, IO_4^-, S_2O_8^(2-), and BrO_3^- increases the rate of photodegradation of 4-CP in the following order: CIO_2^- > IO_4^- > BrO_3^- > CIO_3^-. In the absence of TiO_2, CIO_3^- shows no photoreactivity toward 4-CP, while HSO_5^- and MnO_4^- exhibit rapid thermal reactivity with 4-CP. BrO_3^- appears to increase photoreactivity by scavenging conduction-band electrons and reducing charge-carrier recombination. With CIO_3^- as an oxidant, the degradation of 4-CP appears to follow three concurrent pathways. Kinetic equations for the rate of degradation of 4-CP as a function of [4-CP], [CIO_3^-], and [O_2] and of the light intensity are derived from a proposed mechanism.

Redox chemistry of iron in fog and stratus clouds

The redox chemistry of Fe in fog and cloudwater has been investigated at coastal and inland locations in the Los Angeles basin, in Bakersfield California, and in Delaware Bay. Samples were collected and analyzed for Fe (Fe(II)), Fe(III), total(Fe), sulfur (S(IV), S(VI)), organic ligands (formate, acetate, oxalate), total organic carbon (TOC), pH, major cations (sodium, calcium, magnesium, potassium, ammonium), chloride, sulfate, nitrate, peroxides, and aldehydes (HCHO); the amount of sunlight was also measured. The ratio Fe(II)/Fe(total) varied between 0.02 and 0.55. The concentration of Fe(II) varied between 0.1 and 5 micromole, and the concentration of total Fe varied between 2 and 27 micromole. The atmospheric redox cycle of Fe involves both dissolved and aerosol surface species and appears to be related to the presence of organic compounds which act as electron donors for the reduction of Fe(III). Fe(III) reduction is enhanced by light but significant Fe(II) levels were observed in the dark. We suggest that reduction of Fe(III) species by organic electron donors may be an important pathway that affects the speciation of Fe in both urban and rural atmospheres. It is possible that reactions involving Fe and organic compounds might be an important source of carboxylic acids in the troposphere.