Hedonic housing prices and the demand for clean air

This paper investigates the methodological problems associated with the use of housing market data to measure the willingness to pay for clean air. With the use of a hedonic housing price model and data for the Boston metropolitan area, quantitative estimates of the willingness to pay for air quality improvements are generated. Marginal air pollution damages (as revealed in the housing market) are found to increase with the level of air pollution and with household income. The results are relatively sensitive to the specification of the hedonic housing price equation, but insensitive to the specification of the air quality demand equation.     

Denitrification in alluvial wetlands in an urban landscape

Riparian wetlands have been shown to be effective "sinks" for nitrate N (NO3-), minimizing the downstream export of N to streams and coastal water bodies. However, the vast majority of riparian denitrification research has been in agricultural and forested watersheds, with relatively little work on riparian wetland function in urban watersheds. We investigated the variation and magnitude of denitrification in three constructed and two relict oxbow urban wetlands, and in two forested reference wetlands in the Baltimore metropolitan area. Denitrification rates in wetland sediments were measured with a 15N-enriched NO3- "push-pull" groundwater tracer method during the summer and winter of 2008. Mean denitrification rates did not differ among the wetland types and ranged from 147 +/- 29 microg N kg soil(-1) d(-1) in constructed stormwater wetlands to 100 +/- 11 microg N kg soil(-1) d(-1) in relict oxbows to 106 +/- 32 microg N kg soil(-1) d(-1) in forested reference wetlands. High denitrification rates were observed in both summer and winter, suggesting that these wetlands are sinks for NO3- year round. Comparison of denitrification rates with NO3- standing stocks in the wetland water column and stream NO3- loads indicated that mass removal of NO3- in urban wetland sediments by denitrification could be substantial. Our results suggest that urban wetlands have the potential to reduce NO3- in urban landscapes and should be considered as a means to manage N in urban watersheds.     

Regional Turnover and Fluctuation in Populations of Five Plants Confined to Serpentine Seeps

Abstract: Spatial patterns in population turnover were analyzed for five plant species confined to a patchy and isolated habitat, serpentine seeps: annuals Helianthus exilis and Mimulus nudatus and perennials Senecio clevelandii , Astragalus clevelandii , and Delphinium uliginosum . A 3-year survey showed that, over a preceding 15-year period, 32 of 132 known populations in a 4200-ha area disappeared, and 65 new populations appeared. Populations that disappeared were significantly more isolated from conspecific populations than were surviving populations. Populations that disappeared were also marginally significantly closer to human-caused disturbances than were populations that survived. Vacant sites in which new populations appeared were significantly less isolated from conspecific populations than sites remaining vacant. Spatial patterns in population density were analyzed for three of the species for 3 years at 50 sites in a 20 × 40 km region. From 1997 to 1998, population densities of each species changed synchronously throughout the region. From 1998 to 1999, one species (   Mimulus nudatus ) again showed synchrony, and populations of the other two species (   Helianthus exilis , Delphinium uliginosum ) remained asynchronous and spatially uncorrelated. The five species we studied all appear to be persisting well at the regional scale, despite recent disturbance to the study region. These results suggest that for rare plants in isolated habitats, the spatial configuration of populations may have an important influence on local population persistence.     

Improving collaboration in the implementation of global biodiversity conventions

Eight conventions make up the biodiversity cluster of multilateral environmental agreements (MEAs) that provide the critical international legal framework for the conservation and sustainable use of nature. However, concerns about the rate of implementation of the conventions at the national level have triggered discussions about the effectiveness of these MEAs in halting the loss of biodiversity. Two main concerns have emerged: lack of capacity and resources and lack of coherence in implementing multiple conventions. We focused on the latter and considered the mechanisms by which international conventions are translated into national policy. Specifically, we examined how the Strategic Plan for Biodiversity 2011–2020 and the associated Aichi Biodiversity Targets have functioned as a unifying grand plan for biodiversity conservation. This strategic plan has been used to coordinate and align targets to promote and enable more effective implementation across all biodiversity-related conventions. Results of a survey of 139 key stakeholders from 88 countries suggests streamlining across ministries and agencies, improved coordination mechanisms with all relevant stakeholders, and better knowledge sharing between conventions could improve cooperation among biodiversity-related conventions. The roadmap for improving synergies among conventions agreed to at the 13th Convention on Biological Diversity's Conference of Parties in 2016 includes actions such as mechanisms to avoid duplication in national reporting and monitoring on conventions and capacity building related to information and knowledge sharing. We suggest the scientific community can actively engage and contribute to the policy process by establishing a science-policy platform to address knowledge gaps; improving data gathering, reporting, and monitoring; developing indicators that adequately support implementation of national plans and strategies; and providing evidence-based recommendations to policy makers. The latter will be particularly important as 2020 approaches and work to develop a new biodiversity agenda for the next decade is beginning.     

Climate change effects on an endemic-rich edaphic flora: resurveying Robert H. Whittaker's Siskiyou sites (Oregon, USA)

Species with relatively narrow niches, such as plants restricted (endemic) to particular soils, may be especially vulnerable to extinction under a changing climate due to the enhanced difficulty they face in migrating to suitable new sites. To test for community-level effects of climate change, and to compare such effects in a highly endemic-rich flora on unproductive serpentine soils vs. the flora of normal (diorite) soils, in 2007 we resampled as closely as possible 108 sites originally studied by ecologist Robert H. Whittaker from 1949 to 1951 in the Siskiyou Mountains of southern Oregon, USA. We found sharp declines in herb cover and richness on both serpentine and diorite soils. Declines were strongest in species of northern biogeographic affinity, species endemic to the region (in serpentine communities only), and species endemic to serpentine soils. Consistent with climatic warming, herb communities have shifted from 1949-1951 to 2007 to more closely resemble communities found on xeric (warm, dry) south-facing slopes. The changes found in the Siskiyou herb flora suggest that biotas rich in narrowly distributed endemics may be particularly susceptible to the effects of a warming climate.     

Aspects of iron and nitrogen nutrition in the red tide dinoflagellateGymnodinium sanguineum

Iron-stress-mediated effects on biochemical constituents of the red tide dinoflagellateGymnodinium sanguineum Hirasaka were examined in 1988 by comparing Fe-replete and Fe-deplete batch cultures. The influence of nitrogen source (NO₃ or NH₄) on characteristics of Fe-deplete cells was also studied [i.e., Fe-deplete/NO₃-grown (= — Fe/NO₃) vs Fe-deplete/NH₄-grown (= — Fe/NH₄)]. Common to both N sources were reductions of chlorophylla (chla) and Fe quotas (per cell volume) by 75% and ca. 1.5 orders of magnitude, respectively, under Fe depletion. The Fe requirement ofG. sanguineum exceeded those of certain neritic diatoms by one to two orders of magnitude. — Fe/NH₄ cells exhibited 30 to 50% greater N quotas and free amino acid:protein ratios than did Fe-deplete cells grown on NO₃. In vivo fluorescence:chla increased with Fe deficiency particularly in — Fe/NO₃ cultures, surpassing — Fe/NH₄ values by ca. two-fold. Effects of Fe depletion were consistent with this element's essential role in the biosynthesis of chla and components of the photosynthetic electron transport (PET) system, and also in NO₃ utilization. Fe:N ratios were larger (1.5-fold) for iron-deficient NO₃-grown than NH₄-grown cells, likely reflecting the Fe content of NO₃ assimilatory enzymes [nitrate (NR) and nitrite (NiR) reductase] and of electron transport components needed to provide reductant, coupled with a diminished capacity of — Fe/NO₃ cells to acquire and assimilate nitrogen. Indicators of PET efficiency suggested that under iron stress, supply of Fe for NR and NiR is partly at the expense of iron-containing PET components. Utilization of nitrate by NO₃-grown cells was inhibited sufficiently by Fe depletion to yield symptoms bordering on N deficiency. In an ecological context, the most important effect mediated by nitrogen source may be the determination of critical Q_Fe (i.e., Fe required to just sustain maximal growth), thereby regulating the degree of growth limitation for a given subsaturating iron concentration.     

Effect of nitrogen supply on nitrogen uptake,accumulation and assimilation in Porphyra perforata (Rhodophyta)

Porphyra perforata J. Ag. was collected from a rocky land-fill site near Kitsilano Beach, Vancouver, British Columbia, Canada and was grown for 4 d in media with one of the following forms of inorganic nitrogen: NO ₃ ^- , NH ₄ ⁺ and NO ₃ ^- plus NH ₄ ⁺ and for 10 d in nitrogen-free media. Internal nitrogen accumulation (nitrate, ammonium, amino acids and soluble protein), nitrate and ammonium uptake rates, and nitrate reductase activity were measured daily. Short initial periods (10 to 20 min) of rapid ammonium uptake were common in nitrogen-deficient plants. In the case of nitrate uptake, initial uptake rates were low, increasing after 10 to 20 min. Ammonium inhibited nitrate uptake for only the first 10 to 20 min and then nitrate uptake rates were independent of ammonium concentration. Nitrogen starvation for 8 d overcame this initial suppression of nitrate uptake by ammonium. Nitrogen starvation also resulted in a decrease in soluble internal nitrate content and a transient increase in nitrate reductase activity. Little or no decrease was observed in internal ammonium, total amino acids and soluble protein. The cultures grown on nitrate only, maintained high ammonium uptake rates also. The rate of nitrate reduction may have limited the supply of nitrogen available for further assimilation. Internal nitrate concentrations were inversely correlated with nitrate uptake rates. Except for ammonium-grown cultures, internal total amino acids and soluble protein showed no correlation with uptake rates. Both internal pool concentrations and enzyme activities are required to interpret changes in uptake rate during growth.     

Nitrogen cycling in a marine planktonic food chain: Nitrogen fluxes through the principal components and the effects of adding copper

Nitrogen cycling in a natural planktonic food chain was followed before and after perturbation by copper (10 g l^-1). Observations were separated into effects from artificial containment of the food chain and effects from the addition of copper. An initial reduction of seston-N and subsequent recovery, uniformly high settling rates of suspended particulate-N, and general decrease in zooplankton-N were attributed to the physical limitations imposed by the enclosures (e.g. elimination of normal mixing processes). Acute inhibition of nitrate assimilation by the seston, acute elevation of seston-N settling and chronic inhibition of zooplankton feeding, along with accelerated decline in zooplankton stocks, were attributed to copper stress. Since zooplankton stocks and fluxes were most drastically affected by copper, its overall effect on N-cycling through the planktonic food chain would depend largely upon the importance of zooplankton in regulating the production of the remaining seston.     

Algal plating as a tool for investigating allelopathy among marine microalgae

Chemical interactions among marine microalgae were studied in cultures of pennate diatoms on agar plates. Nine marine and freshwater pennate diatoms were surveyed as potential bioassay organisms; Cylindrotheca fusiformis was most favourable for assays because of its rapid and even growth on agar. Diatom and bacterial bioassays were used to screen cell and filtrate extracts of 14 microalgal cultures. A number of these algal species, which were grown axenically, produced extractable, intracellular and/or extracellular substances that inhibited the growth of C. fusiformis. Our results suggest that the culturing of pennate diatoms on a solid medium can provide a simple bioassay for screening algal extracts which potentially contain growth inhibitors involved in microalgal allelopathy.     

Conserving biodiversity that matters: practitioners' perspectives on brownfield development and urban nature conservation in London

Policies designed to conserve sites of nature conservation importance are an important aspect of city planning in the UK. London has led the way in putting in place a spatial hierarchy of sites of nature conservation importance designed to protect wildlife habitats from development. Some wasteland habitats associated with derelict and vacant land receive protection in this way but development pressure on these so-called 'brownfield sites' is high and is likely to continue. This paper examines how conservation professionals in the private, public and voluntary sectors are responding to the threats of biodiversity loss and opportunities for habitat creation posed by re-development of brownfield sites. The study draws on in-depth interviews conducted with conservation professionals and the practices employed by ecological advisers employed by developers seeking to re-develop wasteland sites. It finds that practitioners are negotiating their role in the re-development process in different ways. Key issues relate to the role of ecological science in codifying wasteland habitats, uncertainties about how best to evaluate the conservation importance of such sites and the strategies and tactics employed by different practitioners as they seek to mobilise a range of knowledges and practices to secure ecologically sensitive proposals. Scientific knowledge about wasteland habitats has not stabilised in ways that can consistently inform conservation policy and practice. As a result biodiversity issues of wasteland sites are often discounted in the re-development process. Investment in studies of the basic ecology of urban wastelands could provide a firmer scientific foundation on which conservation policies could build. At the same time, many conservation professionals involved in urban re-development are struggling to promote a pro-active approach to secure environmentally sensitive development. The knowledge and co-operation networks being mobilised to support this approach are fluid and unstable, and favourable development outcomes as yet are few. Formalising these networks to achieve more effective engagements with developers and the construction industry could consolidate ecological practices designed to conserve and re-create the biodiversity of wasteland habitats.