Vegetated roofs for managing stormwater quantity in cold climate

Vegetated roofs, i.e. green roofs, were continuously measured for runoff to quantify their capacity to manage stormwater in a field experiment in southern Finland, with distinct seasonality and varying weather conditions. Attention was paid to heavy storms to study the potential in mitigating urban flooding. In addition, the impact of biochar amendment (10% v/v) on rainfall retention was studied. Meadow vegetation was established on crushed brick based substrate either by introducing plants as seedlings and seeds or by using pre-grown readymade mats. Annual retention varied from 40% to 70%. The highest retention, ca. 80%, was found in summer even though it was the rainiest season. Wintertime retention was 30-40%. The coarse substrate enabled infiltration even when frozen and, thus, the roofs operated also in winter. Heavy storms occurred mainly in summer, the season with the highest hydrologic performance of the roofs, resulting in >80% peak attenuation and slow release of runoff. In individual rain events, runoff from meadow roofs was largely a function of rainfall depth. However, retention was weakly explained by the amount of rainfall or by other variables, such as rainfall intensity or antecedent dry period, indicating the difficulty in capturing the complex phenomena behind variable weather conditions. Biochar improved retention only slightly, at maximum by ca. 10%. The empirical evidence of this study highlights vegetated roofs as a feasible technology to be applied in urban runoff management even in cold climate.Peer reviewe

Using biochar to purify runoff in road verges of urbanised watersheds: A large-scale field lysimeter study

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The ability of selected filter materials in removing nutrients, metals, and microplastics from stormwater in biofilter structures

Creative solutions to manage stormwater include ecologically based designs, such as biofilter structures. A laboratory experiment was established to study the ability of biofilters to remove nutrients, metals, total suspended solids (TSS), and total organic C originating from roadside stormwater as melted snow. Special attention was paid to the removal of P. In addition, the fate of microplastics (MPs) in the biofilters was followed. The materials selected for biofilters were (a) crushed light-expanded clay aggregates without biochar or amended with biochar, (b) Filtralite P clay aggregates, (c) crushed concrete, or (d) filter sand. A layer to support grass growth was placed above these materials. Stormwater was rich in TSS with associated P and metals, which were substantially retained by all biofilters. Filtralite and concrete had almost 100% P removal, but the high pH had adverse effects on plants. Light-expanded clay aggregates had lower retention of P, and, when mixed with biochar (30% v/v), the leaching of P increased and N retention was improved. None of the materials was ideal for treating both nutrients and metals, but sand was generally best. Vegetation improved N retention and stormwater infiltration. Plant roots formed preferential pathways for water and associated substances, evidenced by the accumulation of MPs along root channels. No MPs were found in discharge. Given the high loading of suspended solids and associated contaminants in snowmelt from traffic areas and their efficient retention in biofiltration, results of this study suggest the implementation of such stormwater management solutions along road verges.Peer reviewe

Responses of food web to hypolimnetic aeration in Lake Vesijärvi

We studied the responses of a food web, especially fish and zooplankton, to summertime aeration, pumping of oxygen-rich epilimnetic water to the hypolimnion in Lake Vesijärvi, southern Finland. The aim of hypolimnetic aeration was to reduce internal loading of phosphorus from sediment. The population of smelt (Osmerus eperlanus L.), the main planktivore of the pelagial area, collapsed during the two 1st years of aeration due to increased temperature and low oxygen concentrations in the hypolimnion. The population recovered after the 4th year of hypolimnetic aeration, when oxygen conditions were improved. Despite elevated hypolimnetic temperature, smelt reached exceptionally high abundance, which led to a significant reduction in cladoceran body size. The density of perch (Perca fluviatilis L.) increased at first, but then decreased when the proportion of smelt and cyprinids increased. Biomasses of Daphnia decreased probably as a result of the disappearance of dark, low-oxygen deep-water refuge against fish predation and low availability of nutritionally high-quality algae. Occasionally filamentous cyanobacteria, such as turbulence tolerant Planktothrix agardhii (Gomont), were abundant, suggesting deteriorated food resources for zooplankton. The responses of food web were controversial with respect to the aim of the management, which was to prevent the occurrence of harmful algal blooms.Peer reviewe

Plant growth-promoting microbes improve stormwater retention of a newly-built vertical greenery system

On-site decentralized urban stormwater management has gained significant momentum in urban planning. Recently, vegetated roofs have been recommended as a viable decentralized stormwater management system and nature-based solution to meet the challenge of urban floods. However, as another type of unconventional green infrastructure, vertical greenery systems (VGS), also known as vegetated facades, have received much less research attention. Even though some researchers suggest that stormwater management by VGS is comparable to that of vegetated roofs, empirical evidence to substantiate this claim is limited. In this study, we conducted rain simulations on newly-built vegetation containers with water storage compartments. These vegetation containers were designed to be incorporated into a VGS specifically for stormwater management. We tested variables that could influence water retention efficiency and evapotranspiration of the containers under field conditions, i.e., inoculation of plant growth-promoting microbes (PGPMs) (Rhizophagus irregularis and Bacillus amyloliquefaciens), different substrate types (sandy loam and reed-based substrate), simulated rain quantity, natural precipitation, substrate moisture, and air temperature. The inoculation of PGPMs significantly reduced runoff quantity from the vegetation containers. Meanwhile, the well-ventilated sandy-loam substrate significantly reduced the remaining water in the water storage compartments over 1-week periods between rain simulation events, achieving high water-use efficiency. The selected microbes were established successfully in the containers and promoted the growth of 2 out of 5 plant species. R. irregularis colonization responded to substrate type and host plant species, while B. amyloliquefaciens population density in the substrate did not respond to these factors. Environmental conditions, such as antecedent substrate moisture, air temperature, and natural precipitation also influenced the efficiency of stormwater retention and/or evapotranspiration. In conclusion, this study provides instructive and practical insights to reduce urban flood risk by using VGS.Peer reviewe

Effect of weather conditions, substrate pH, biochar amendment and plant species on two plant growth-promoting microbes on vegetated roofs and facades

Background Vegetated building envelopes (VBEs), such as vegetated roofs and facades, are becoming more frequent in urban planning nowadays. However, harsh growing conditions restrain the application of VBEs. Plant growth-promoting microbes (PGPMs) might help ease the stresses, but first, it is necessary to investigate how to ensure their survival and growth under VBE conditions. Methods We conducted three experiments to test the impact of various factors on the microbial populations of inoculated PGPMs in VBEs, a mycorrhizal fungus Rhizophagus irregularis and a bacterium Bacillus amyloliquefaciens. The first experiment was conducted by inoculating the two PGPMs separately in Sedum roof plots, and the microbial populations associated with Poa alpina was monitored for two consecutive years under local weather conditions. The second experiment was conducted in a laboratory testing the effect of substrate pH (substrates collected from balcony gardens) on R. irregularis population associated with Trifolium repens and Viola tricolor. The third experiment was conducted on a meadow roof testing the effect of biochar amendment on R. irregularis population associated with Thymus serpyllum and Fragaria vesca. Results In the first experiment, Bacillus was found to associate with P. alpina, but Rhizophagus wasn't. Yet, the fungus induced high Bacillus population density in the Rhizophagus treated plots in the first year. In the second experiment, Rhizophagus abundance in T. repens was higher in the neutral substrate (6–6.5), while V. tricolor was more colonized in acidic substrate (5–5.5), suggesting an important interactive effect of substrate pH and plant species on Rhizophagus abundance. The third experiment suggested a negligible impact of biochar amendment on Rhizophagus abundance for both host plants. Conclusion Three experiments demonstrate that PGPM inoculation on VBEs is feasible, and various factors and interactions affect the PGPM populations. This paper provides reference and inspiration for other VBE research involving substrate microbial manipulation.Peer reviewe

Thermal behavior of green roofs under Nordic winter conditions

To understand how green roofs affect building energy performance under cold climatic conditions, a proper thermal analysis of the roof and its components is required. To address this, we measured the thermal conductivity of each layer of experimental green roofs, as well as equivalent thermal resistance of the complete green roof system during winter conditions in southern Finland. Three experimental green roof platforms (1 m x 2 m) with heated boxes and three identical bare roof platforms (without substrate, vegetation and other green roof layers) were equipped with thermocouples that continuously measured a vertical temperature profile through the roofs. A steady-state heat transfer analysis was performed to assess the functioning and relative thermal performance of the green roof systems. Layer analysis at various intensities of frost penetration showed that the thermal conductivity of each layer decreased when penetrated by frost. In particular, thermal conductivity of the substrate and vegetation layers decreased from 0.41 Wm(-1)K(-1) and 0.34 Wm(-1) K-1 prior to freezing, to 0.12 Wm(-1) K-1 and 0.10 Wm(-1) K-1 after freezing, respectively. This phenomenon is explained by a reduction in bridge-water connectivity during freezing and a volumetric water content that was below the critical threshold value. Overall, a frost depth that extended through the complete green roof yielded the greatest equivalent thermal resistance. During times of snow cover, snow acted as an insulator and reduced the relative energy saving benefits achieved by green roofs. These results provide information for designing the substrate and vegetation layers of green roofs for optimal insulation. (C) 2017 Elsevier Ltd. All rights reserved.Peer reviewe

Alkaline habitat for vegetated roofs? Ecosystem dynamics in a vegetated roof with crushed concrete-based substrate

Using local and recycled materials is a sustainable way to establish a vegetated roof. In order to understand how the roof ecosystem functions and returns ecosystem services, it is important to study vegetation, soil organisms and runoff quality. We established a vegetated roof experiment based on a substrate containing lightweight crushed concrete, an alkaline side product from a concrete factory, mixed with compost. This five-year experiment in southern Finland tested how planting method (pre-grown vegetation mats vs. pot planting), compost content (20% vs. 40%, fresh volume), and substrate depth affect the cover and diversity of plants, the abundance of soil animals and the quality of runoff. Although the substrate had a high pH (7.3–11.8), many vascular plants were able to survive and establish viable populations. The planting method had a strong effect on plant diversity and the cover of individual species because the vegetation mats became dominated by the invasive, non-native Phedimus hybridus. Establishment with pot plants in turn provided bare ground that was colonised by spontaneous non-invasive species. This resulted in higher diversity, and a more even distribution of species. The amount of compost had only a weak impact on vegetation, whereas high pH generally reduced plant abundance and diversity. The concentrations of total phosphorus and total nitrogen in runoff were low as compared to values reported from many other vegetated roofs, were not affected by compost content and decreased over time. In summary, the high-pH substrate based on recycled materials is an environmentally responsible choice, suitable for a wide variety of plants, even rare and endangered species.Peer reviewe

Antiepileptic drugs and prostate cancer risk in the Finnish Randomized Study of Screening for Prostate Cancer

Antiepileptic drugs (AEDs) with histone deacetylase (HDAC) inhibitor properties decrease prostate cancer (PCa) cell proliferation in vitro. A population-based cohort of 78 615 men was used to evaluate the risk of PCa among users of AEDs. Study population was linked to the Finnish national prescription database to obtain information on individual medication reimbursements in 1996 to 2015. Cox regression with antiepileptic medication use as a time-dependent variable was used to analyze PCa risk overall, and low, medium and high-risk PCa separately. The analysis was adjusted for age, screening trial arm, and other drugs in use, including statins, antidiabetic drugs, antihypertensive drugs, aspirin, and nonsteroidal anti-inflammatory drugs. Compared to the nonusers of AEDs, overall PCa risk was decreased among AED users (hazard ratio [HR] = 0.86, 95% confidence interval [CI] = 0.76-0.96). A similar PCa risk decrease was observed among users of HDACi AEDs (HR = 0.87, 95% CI = 0.76-1.01), but no risk difference was found when comparing HDACi AED users to users of other AEDs (HR = 0.98, 95% CI = 0.76-1.27). Our study showed a decrease in overall PCa risk among men using AEDs compared to nonusers. The risk associations were similar for HDAC inhibitors as for AEDs in general.Peer reviewe

Response of boreal lakes to episodic weather-induced events

Weather-induced episodic mixing events in lake ecosystems are often unpredictable, and their impacts are therefore poorly known. The impacts can be short-lived, including changes in water temperature and stratification, but long-lasting effects on the lake’s biology may also occur. In this study we used automated water quality monitoring (AWQM) data from 8 boreal lakes to examine how the episodic weather-induced mixing events influenced thermal structure, hypolimnetic dissolved oxygen (DO), fluorometric chlorophyll estimates (Chl-a), and lake metabolism and how these events varied in frequency and magnitude in lakes with different characteristics. Rise in wind speed alone had an effect on the lakes with the weakest thermal stability, but a decrease in air temperature together with strong wind induced mixing events in all lakes. The return period of these mixing events varied widely (from 20 to 92 d) and was dependent on the magnitude of change in weather. In lakes with strong stability, thermal structure and hypolimnetic DO concentration were only slightly affected. Weather-induced mixing in the upper water column diluted the surface water Chl-a repeatedly, whereas seasonal maximum occurred in late summer on each lake. Although Finnish lakes have been characterized with stable stratification during summer, we observed many substantial mixing events of relatively short return periods relevant to both chemical and biological properties of the lakes