Influence of evaporative cooling by urban forests on cooling demand in cities

Trees provide important ecosystem services to urban human society. Their absence can lead to more pronounced environmental and social consequences, for example the urban heat island effect. Evapotranspiration (Et) from trees reduces air temperature in the urban microclimate by converting sensible heat to latent heat. Quantification and valuation of the ecosystem services provided by urban trees is important for improving cost-benefit evaluations in support of protecting tree planting and maintenance budgets and, thus, for building climate change resilience into cities. Inclusion of Et cooling could improve ecosystem service valuation models by producing a more complete picture of the benefits that urban trees provide to society. This study explores two approaches for evaluating climate regulation as an ecosystem service of urban trees. Firstly, an enthalpy-based approach was adopted to valuate latent heat of evaporation from tree transpiration (in three case study urban forests) by equating it to an equivalent service from an active direct evaporative cooling system. Secondly, energy savings to air-conditioned buildings was modelled using TRNSYS and TRNFLOW simulation programs with and without air precooled and humidified by urban trees. Trees are shown to provide substantial urban cooling with an annual valuation of £84 m estimated using the enthalpy-based approach, or ranging from £2.1 m to £22 m using TRNSYS and TRNFLOW dynamic simulation programs; both for inner London case study. The latter savings arose from a modelled 1.28 – 13.4% reduction in air-conditioning unit energy consumption. Challenges around assumptions of homogeneity in both built form and urban forest canopy effects are discussed. The case study examples highlighted differences in Et cooling between tree species, with Castanea sativa, Prunus avium, Quercus petraea, Platanus hybrida and Fagus sylvatica typically providing more Et cooling than any of the other tree species commonly found in urban forests. The research highlighted a shortage of published Et data, particularly for urban environments

Interactive effects of composted green waste and earthworm activity on tree growth and reclaimed soil quality: a mesocosm experiment

On reclaimed landfill sites, the addition of organic matter such as composted green waste (CGW) to soil-forming materials can support tree survival and growth. CGW addition may also assist the establishment of sustainable earthworm populations, and in turn these organisms can promote further soil development through their burrowing and feeding activity. Despite such potentially mutual benefits, little research has been carried out into CGW and earthworm interactions with trees on reclaimed land. A twelve month, open field nursery experiment revealed the responses of the interactions between two tree species; Alnus cordata (Betulaceae) and Acer platanoides (Sapindaceae), CGW and the earthworms Aporrectodea longa (Lumbricidae) and Allolobophora chlorotica (Lumbricidae) in reclaimed soil. Controlled mesocosm conditions permitted a detailed investigation into the factors affecting tree growth and nutrient uptake, soil nutrient cycling and earthworm population dynamics. Results revealed that A. cordata growth was unaffected by CGW or earthworm addition. There was, however, a significant positive synergistic effect of earthworm activity and CGW addition on A. platanoides growth. CGW addition significantly increased levels of organic carbon and essential plant macro-nutrients in reclaimed soil while earthworm activity assisted decomposition of both leaf litter and CGW. Findings showed that CGW may serve as a suitable early source of organic matter to support earthworm population establishment on reclaimed sites. This experiment demonstrates that CGW improves reclaimed soil quality, thereafter supporting tree establishment and growth on reclaimed landfill

The canopy cover Webmap of the United Kingdom’s towns and cities

Urban trees and other green infrastructure are advocated as a cost-effective sustainable solution to ameliorate the socio-economic and environmental challenges of urbanisation. UK research has only recently started to quantify urban trees. Tree canopy cover percentage (TCC) is a useful indicator of tree presence. Its estimation can be reproducible, simple, fast, and cost-effective; it can also be evaluated through citizen science, improving people’s appreciation for urban trees and widening the data collection resource pool. This research summarises a citizen science assessment of the TCC of the UK’s 5,749 urban wards. Descriptive statistics are presented spanning local authority to country. The area-weighted mean (and standard error) of TCC across urban wards was 17.3 ± 0.1%. Nationally, the TCC were 11.8 ± 0.5%, 15.7 ± 0.5%, 17.5 ± 0.2%, and 18.1 ± 0.5%, for Northern Ireland, Scotland, England, and Wales, respectively. Results show that only 27.6% of urban wards had a TCC higher than 20%, previously suggested as a minimum target for UK towns. The findings highlight substantial geographical variance in TCC equity, as well as a negative correlation between TCC and deprivation. This information will be of value in urban forest strategy and management

Investigating tree foliar preference by the earthworms Aporrectodea longa and Allolobophora chlorotica in reclaimed and loam soil

Afforestation can improve the delivery of ecosystem services from reclaimed landfill sites. Tree health is a key determinant of ecosystem service delivery, and is directly impacted by soil quality; which is driven by biological processes in the soil, reliant on leaf litter inputs to function. Different tree species have different litter quality, affecting the degree to which they support biological processes in soils and the development of abundant and diverse soil faunal communities. In recognition of their key role in improving soil structure and fertility - key attributes of soil quality, earthworms have often been the subject of research as a part of land reclamation, and these organisms have displayed preferences for specific types of leaf litter. This work utilised a choice chamber design to measure the foliar material palatability of two tree species used in land restoration (Alnus cordata and Acer platanoides) as a food source for two common European earthworm species (Aporrectodea longa and Allolobophora chlorotica), and the effect of a reclaimed soil quality on earthworm growth, survival and feeding preferences. The research revealed that both earthworm species initially preferred the foliar material of A. cordata over A. platanoides, with the leaves of the latter requiring higher degradation to become palatable to earthworms. The consumption of fresh leaves showed these are a suitable food source for earthworms in choice chamber experiments, which historically have instead relied on senescent leaf litter. Finally, high survival rates of both A. longa and A. chlorotica in the reclaimed soil treatment, in addition to consumption of leaf material of two tree species now widely used on reclaimed landfill sites, demonstrated that these earthworm species are suitable candidates for inoculation to reclaimed land

Further validation of the HPCD-technique for the evaluation of PAH microbial availability in soil.

There is currently considerable scientific interest in finding a chemical technique capable of predicting bioavailability; non-exhaustive extraction techniques (NEETs) offer such potential. Hydroxypropyl-beta-cyclodextrin (HPCD), a NEET, is further validated through the investigation of concentration ranges, differing soil types, and the presence of co-contaminants. This is the first study to demonstrate the utility of the HPCD-extraction technique to predict the microbial availability to phenanthrene across a wide concentration range and independent of soil-contaminant contact time (123 d). The efficacy of the HPCD-extraction technique for the estimation of PAH microbial availability in soil is demonstrated in the presence of co-contaminants that have been aged for the duration of the experiment together in the soil. Desorption dynamics are compared in co-contaminant and single-PAH contaminated spiked soils to demonstrate the occurrence of competitive displacement. Overall, a single HPCD-extraction technique proved accurate and reproducible for the estimation of PAH bioavailability from soil. (c) 2006 Elsevier Ltd. All rights reserved

Microbial interactions with organic contaminants in soil: Definitions, processes and measurement.

There has been and continues to be considerable scientific interest in predicting bioremediation rates and endpoints. This requires the development of chemical techniques capable of reliably predicting the bioavailability of organic compounds to catabolically active soil microbes. A major issue in understanding the link between chemical extraction and bioavailability is the problem of definition; there are numerous definitions. of varying degrees of complexity and relevance, to the interaction between organic contaminants and microorganisms in soil. The aim of this review is to consider the bioavailability as a descriptor for the rate and extent of biodegradation and, in an applied sense, bioremediation of organic contaminants in soil. To address this, the review will (i) consider and clarify the numerous definitions of brioavailability and discuss the usefulness of the term `bioaccessibility'; (ii) relate definition to the microbiological and chemical measurement of organic contaminants' bioavailability in soil, and (iii) explore the mechanisms employed by soil microorganisms to attack organic contaminants in soil. (C) 2007 Elsevier Ltd. All rights reserved

Can microbial mineralization be used to estimate microbial availability of organic contaminants in soil?

The aim of this study was to characterize the behaviour of a PAH-degrading bacterium to determine whether mineralization plateaus as a result of substrate removal, a decrease in microbial activity or nutrient availability in sterile soils over time. To investigate this, the mineralization of 14C-phenanthrene was measured until it plateaued; subsequently, additional 14C-phenanthrene, catabolic inocula or nutrients were introduced and mineralization was measured for a further 10 d. Cell numbers were also measured together with 14C-uptake into microbial biomass. Freshly added 14C-phenanthrene was rapidly metabolised by the microorganisms. Neither the addition of a catabolic inoculum nor nutrients affected the extent of 14C-phenanthrene mineralization. Cell numbers remained constant over time, with only a small amount of the 14C-activity incorporated into the microbial biomass. This study indicated that the termination of mineralization was due to the removal of available phenanthrene and not decreasing cellular activity or cell death. The mineralization values also correlated with 14C-phenanthrene extractability using β-cyclodextrin. Mineralization can estimate the microbial availability of 14C-contaminants in soil

Long-Term Fate of Polychlorinated Biphenyls and Polycyclic Aromatic Hydrocarbons in an Agricultural Soil.

Laboratory studies are useful for understanding the behavior of persistent organic pollutants (POPs) in soil, although such investigations do not always relate directly to field conditions. Outdoor lysimeter studies may be used to overcome this problem. This work aimed to investigate the behavior of two polycyclic aromatic hydrocarbons (PAHs) (fluoranthene and benzo[a]pyrene) and two polychlorinated biphenyls (PCBs; congeners 28 and 52) in soil, using lysimeters established in 1990 at the Agrosphere Institute (Forschungszentrum Jülich GmbH, Germany). The two PAHs were in one lysimeter, and the PCBs were in a second lysimeter. A further aim of the study was to determine soil half-lives for each of the contaminants. The overall decline in PAH concentrations was considerably greater than for the PCBs over the 152 month study. The PCBs exhibited greater chemical extractability than the PAHs and were demonstrated to have migrated through the soil column to a greater extent than the PAHs. Loss of PCBs from surface soil was not considered to have been congener specific for the two PCB congeners in this study. The two PAHs varied in their extents of total loss and movement through the soil column. Soil half-lives were determined as 10.9 y for [12C]PCB 28, 11.2 yr for [12C]PCB 52, 2.7 yr for benzo[a]pyrene, and 32 d (phase 1) to 38 yr (phase 2) for fluoranthene. These are shown to disagree with some previous estimates of POP half-lives in soil, suggesting that previous studies underestimated persistence by 10-fold or more