Green Roof Substrate Research Articles

Preparation of growth substrate to improve runoff quality from green roofs: physico-chemical characterization, sorption and plant-support experiments

Growth substrate plays an important role in determining the quality of runoff from green roofs. However, no systematic research has been conducted to design a substrate to improve runoff quality. Hence, the present study aimed at designing and developing a green roof substrate using low-cost and environmentally-benign materials. The inorganic fraction of the substrate includes purosil, vermiculite, sand and light-weight clay aggregates (LECA); whereas the organic fraction includes coco-peat and Sargassum wightii. Through factorial design, 13 different substrate mixes were prepared and the optimum mix (20% purosil, 30% vermiculite, 10% sand, 20% LECA, 10% coco-peat and 10% S. wightii) was found to have high water holding capacity (67.6%), air filled porosity (21%), hydraulic conductivity (5524 mm/h) and low bulk density (495 kg/m3). The substrate also provided maximum support for the growth of Portulaca oleracea. Experiments with metal-contaminated influent from the down-flow of a packed reactor revealed that the green roof substrate possesses a high sorption capacity towards various metal ions.

Removal of Polycyclic Aromatic Hydrocarbons by Extensive Green Roofs

In this study,four pilot-scale extensive green roof facilities with different substrate compositions were developed. In 8 rainfall events, concentrations of 16 kinds of polycyclic aromatic hydrocarbons (PAHs) in effluent of these facilities were investigated and compared with effluents of asphalt roofing, the blank control roof and rain water. Average PAHs concentrations in the effluent of these four facilities, asphalt roofing and blank control facilities were 145, 166, 151, 160, 900, 270 ng·L-1, respectively. The PAHs mass concentrations discharged by four simulation facilities were significantly lower than asphalt roofing and blank control roof. From the perspective of the mass loading control, all four simulation facilities could effectively control roof runoff PAHs load with an average load reduction rate of 71.76% compared with the blank control roof. Interception and adsorption by green roof substrates was the main removal way for PAHs. Facilities' PAHs removal efficiency could be improved by increasing the substrate thickness with the same substrate composition. Transforming traditional asphalt roofing into extensive green roof was an effective way to control PAHs emissions from roof runoff.

Plant species richness enhances nitrogen retention in green roof plots.

Vegetated (green) roofs have become common in many cities and are projected to continue to increase in coverage, but little is known about the ecological properties of these engineered ecosystems. In this study, we tested the biodiversity-ecosystem function hypothesis using commercially available green roof trays as replicated plots with varying levels of plant species richness (0, 1, 3, or 6 common green roof species per plot, using plants with different functional characteristics). We estimated accumulated plant biomass near the peak of the first full growing season (July 2013) and measured runoff volume after nearly every rain event from September 2012 to September 2013 (33 events) and runoff fluxes of inorganic nutrients ammonium, nitrate, and phosphate from a subset of 10 events. We found that (1) total plant biomass increased with increasing species richness, (2) green roof plots were effective at reducing storm runoff, with vegetation increasing water retention more than soil-like substrate alone, but there was no significant effect of plant species identity or richness on runoff volume, (3) green roof substrate was a significant source of phosphate, regardless of presence/absence of plants, and (4) dissolved inorganic nitrogen (DIN = nitrate + ammonium) runoff fluxes were different among plant species and decreased significantly with increasing plant species richness. The variation in N retention was positively related to variation in plant biomass. Notably, the increased biomass and N retention with species richness in this engineered ecosystem are similar to patterns observed in published studies from grasslands and other well-studied ecosystems. We suggest that more diverse plantings on vegetated roofs may enhance the retention capacity for reactive nitrogen. This is of importance for the sustained health of vegetated roof ecosystems, which over time often experience nitrogen limitation, and is also relevant for water quality in receiving waters downstream of green roofs.

Steady-state and transient thermal measurements of green roof substrates

There has been growing interest in using extensive green roofs for commercial and residential buildings in urban areas. Green roofs provide many benefits, including adding an additional insulation layer. The potential of this benefit depends on many factors, including the thermal properties of the green roof substrate. Thermal conductivity values of three substrates comprised primarily of scoria, crushed roof tile and bottom-ash were measured with steady-state and transient techniques under three moisture conditions. Specific heat capacities of the green roof substrates were also measured with a transient technique. Steady-state measurements were performed with a “k-Matic” apparatus while transient measurements with KD2 Pro needles. In general, the steady-state measurements showed more consistency than transient measurements. Thermal conductivity differed among the three substrates: crushed roof tile had the highest conductivity values across all moisture contents. Substrate moisture content consistently increased thermal conductivity across all substrates, but this was significantly greater for the crushed roof tile substrate. Steady-state thermal conductivity curves were fitted using the thermal conductivity model for green roof substrates adopted by Sailor (2011). The coefficients obtained are presented and can be used in green roof models to quantify the thermal performance of green roofs and building energy savings.

Green roof substrates: Effect of recycled crushed porcelain and foamed glass on plant growth and water retention

A study was conducted in a controlled environment greenhouse to examine the potential of recycled crushed porcelain and foamed glass for use as a component of green roof substrates. Porcelain and foamed glass substrates were compared to heat-expanded shale which served as the control. Each finished substrate was analyzed per German FLL guidelines to determine granulometric distribution, bulk density, total porosity, water-holding capacity, saturated hydraulic conductivity, pH, soluble salts, organic matter content, and cation exchange capacity. Both substrates met FLL Guidelines except the porcelain substrate contained a greater percentage of larger particles and its maximum water holding capacity was lower than recommended. Two plant species were used in the study, Sedum album (stonecrop) and Ocinum x citriodolum (lemon basil). Data collected included substrate volumetric moisture content (VMC), plant growth, biomass accumulation, and plant stress as measured by chlorophyll fluorescence. Substrate VMC was generally greater in shale than in foamed glass or porcelain. At the end of the study plant growth index was greatest for stonecrop growing in shale, but there was no difference among the substrates for basil. However, plants of both basil and stonecrop accumulated the most total biomass when grown in shale. It is probable that water retention could be improved for both recycled crushed porcelain and foamed glass if more attention was paid to reducing particle size during processing. If so, then they may perform equal to heat expanded shale when incorporated into green roof substrates. In the case of porcelain, its use could divert some waste from landfills and greatly reduce the embodied energy required to construct a green roof.

Green roof ageing or Isolatic Technosol’s pedogenesis?

Purpose Green roofs (GR) offer a way to improve several ecosystem services in cities. However, the performances of GR are basically considered as steady over time whereas they are living media subject to ageing that are rarely managed by their owners. This study transposes a pedological approach to evaluate changes in GR physical structure and chemical composition over time. Materials and methods A full-scale experimental plot with various vegetation cover was studied. A dedicated sampling strategy was implemented to monitor substrate’s evolution over 4 years. Then, physical and chemical characterisation (carbon and nitrogen contents, particle size distribution, porosity, soil water retention) was conducted and compared to results on the original substrate. Results and discussion The upper layer of the substrate (0 to 5 cm depth) contained a large amount of fine and short roots whereas the root density was much smaller in the lower layer of the substrate (5 to 10 cm depth). There was a global drop of the organic carbon content from 5 % in the initial substrate to 2 % in the 4-year-old substrate. On the contrary, the nitrogen concentration has increased by 0.4 % during the same period. The mesoporosity decreased drastically from 0.11 to 0.02 cm3 cm−3. On the whole substrate, the <2-mm particles fraction was smaller after 4 years (12.5 %) than in the initial substrate (18.2 %) which was especially obvious in the upper horizon (9.5 %). Additionally, the monitored properties also varied significantly as a function of soil cover (sedum, moss and bare soil). Evidences of an early pedogenesis were highlighted such as poral evolution and fine particles eluviation. Conclusions: In conclusion, the study demonstrated the effects of time, climate and vegetation on physical and chemical properties of green roof substrate. They are not only classified as Isolatic Technosols due to their composition and implementation; they also exhibit one of the major characteristic of young Technosols: a fast and intense pedogenesis.

The suitability of crushed porcelain and foamed glass as alternatives to heat-expanded shale in green roof substrates: An assessment of plant growth, substrate moisture, and thermal regulation

The suitability of two materials, foamed glass and crushed porcelain, as substrates for single course extensive green roofs was investigated. Both of these materials were produced from bulk waste intended for disposal in a landfill. The candidate materials were compared to a commercially available substrate made from heat-expanded shale by evaluating commonly measured physical properties, plant development, substrate moisture, and subsurface temperature. Physical properties were measured in a lab setting and all other metrics were taken from outdoor green roof platforms. Total plant coverage in both porcelain and foamed glass was equivalent to expanded shale on 5 of the 6 dates measured over two growing seasons. Substrate moisture and temperature were observed during the second season. Moisture content of both the porcelain and foamed glass was either equivalent to or greater than that of the expanded shale throughout the season. Subsurface temperatures were cooler in the porcelain and foamed glass than the expanded shale during the daytime for the majority of the second season. Variation in daily temperatures in the porcelain was significantly lower than the expanded shale when plant coverage was below 50%. Overall, both candidate materials were found to be suitable for use in extensive green roof applications.

Steady-state thermal measurement of moist granular earthen materials

A technique based on the heat flow meter method is proposed for measuring the thermal conductivity of moist earthen and granular loose-fill materials. Although transient methods have become popular, this steady-state approach offers an uncertainty that can be reliably estimated and a test method that is widely accepted for building certification purposes. Variations to the standard method are proposed, including the use of a rigid holding frame with stiff base and silicone sponge buffer sheets, in conjunction with difference measurement to factor out the contributions from base, buffers and contact resistance. Using this approach, results are presented for green-roof substrates based on scoria, terracotta and furnace-ash at different moisture contents. Thermal conductivity ranged from 0.13 to 0.80 W/m K and fitted well to linear regression plots against moisture content. Further comparative measurements of a single specimen showed that direct measurement was less consistent than difference measurement and thus indicated that thermal resistance was higher by 0.023 m2 K/W, attributable to the presence of contact resistance.

Mitigating nutrient leaching from green roofs with biochar

Green roofs may have great potential for managing urban runoff but their effects on the quality of infiltrating water are highly variable. At worst, it can contain high concentrations of nutrient pollutants, especially phosphorus. We made a survey in southern Finland and found much higher concentrations of phosphorus and nitrogen in runoff from existing green roofs than nearby non-vegetated bituminous and tin roofs. However, metal concentrations in runoff generally exhibited an opposite pattern. Media mixtures with aggregates, such as biochar, have been suggested as a means of retaining nutrients in green roof substrate. Thus, we set up a green roof platform experiment in order to study the amendment of biochar in a substrate consisting of mainly recycled crushed brick, by using two vegetation establishment methods: pre-grown mats and planting with seeds and plug plants. We monitored the effect of biochar on runoff during one year across all four seasons, including winter with periods of freezing and thawing. At the beginning of the experiment we found negligible impacts of biochar, but when the systems had matured for less than one year, biochar retained nutrients. The total annual loads of both nutrients were significantly reduced by biochar amendment in both green roof types. Efficient solutions are needed if urban greening, such as green roofs, is to be applied in a way that does not produce ecosystem disservices like nutrient pollution. According to our results, amending green roof substrates with biochar could be a partial solution to the nutrient pollution problem.

The use of reactive material for limiting P-leaching from green roof substrate.

The aim of the study is to assess the influence of drainage layer made of reactive material Polonite(®) on the water retention and P-PO(4) concentration in runoff. A column experiment was performed for extensive substrate underlined by 2 cm of Polonite(®) layer (SP) and the same substrate without supporting layer as a reference (S). The leakage phosphorus concentration ranged from 0.001 to 0.082 mg P-PO(4)·L(-1), with average value 0.025 P-PO(4)·L(-1) of S experiment and 0.000-0.004 P-PO(4)·L(-1) and 0.001 P-PO(4)·L(-1) of SP experiment, respectively. The 2 cm layer of Polonite(®) was efficient in reducing P outflow from green roof substrate by 96%. The average effluent volumes from S and SP experiments amounted 61.1 mL (5.8-543.3 mL) and 46.4 mL (3.3-473.3 mL) with the average irrigation rate of 175.5 mL (6.3-758.0 mL). The substrate retention ability of S and SP experiments was 65% and 74%, respectively. Provided with reactive materials, green roof layers implemented in urban areas for rain water retention and delaying runoff also work for protection of water quality.

Use of water-retention additives to improve performance of green roof substrates

Green roofs provide an opportunity to make our cities more liveable by reducing the impact of urban stormwater runoff through the combined effects of substrates (growing media) absorbing rainfall and plants using water. Stormwater retention is determined by substrate s ability to absorb and store water (water holding capacity; WHC) and supply it to plants (plant available water; PAW). As green roof substrates are largely mineral-based with minimal organic matter, water-retention additives might provide improved stormwater and plant performance. We evaluated the effects of adding biochar, silicates and hydrogels on WHC, PAW, permanent wilting point and bulk density of a scoria-based green roof substrate. Permanent wilting and PAW was assessed in two drought experiments with wheat growing in substrate with and without water retention additives. Hydrogel and silicates were added at 0.01 and 1% v/v, respectively, whereas biochar was added at 10, 20, 30 and 40% v/v. Although hydrogel and silicates increased WHC, only hydrogel increased PAW, but this did not delay permanent wilting. Biochar addition greatly increased WHC and PAW, and reduced bulk density, with greater rates of addition resulting in lighter substrates which also held more water. The onset of permanent wilting was delayed by up to 2 days (30 and 40% biochar). When modelled for Melbourne conditions, a green roof installed with scoria and 40% biochar substrate would retain 12% more annual rainfall from runoff and reduce potential water deficit conditions by 77% compared with un-amended scoria substrate. This has significant implications for green roof performance in terms of stormwater water management and plant survival. As green roof substrates are similar to other designed containerised substrates these findings also have wider applicability to urban horticulture.

A green roof segment for monitoring the hydrological and thermal behaviour of anthropogenic soil systems

Jelinkova V., Dohnal M., Picek T. (2015): A green roof segment for monitoring the hydrological and thermal behav iour of anthropogenic soil systems. Soil & Water Res., 10: 262–270. Green roofs and similar anthropogenic soil-plant systems in conurbations have a high relevance for society, especially in a changing climate. Understanding the hydrological performance of green roof substrates is a significant task in the framework of sustainable urban planning and water/energy management in urban areas. Potential retention and detention capabilities of anthropogenic, light weight, highly permeable soil systems and their continued performance over time are of major importance. A green roof test segment was designed to investigate the benefits of such anthropogenic systems. This adaptable low-cost system allows for long-term monitoring of preferred characteristics. Temperature and water balance measurements complemented with me teorological observations and studies of physical properties of substrates provide a basis for a detailed analysis of thermal and hydrological regime in green roof systems. The very first results obtained from the test segment have confirmed the green roof systems benefits. Reduced temperature fluctuations as well as rainfall runoff were attained compared to the traditional roof systems. Depending on numerous factors including the substrate material or vegetation cover, in the green roof tested the temperature amplitude for a selected period of nonfreezing days (with minimum ambient air temperature of 2.8°C) was suppressed by about 6.5 °C o n average. The

Biochar amendment in the green roof substrate affects runoff quality and quantity

The utilisation of ecosystem services has been suggested as one solution to manage urban environmental problems, one of which is the excessive quantity or poor quality stormwater. As roofs contribute significantly to the amount of runoff, vegetated, i.e. green roofs have become an increasingly popular way to manage urban water in densely built areas. However, green roofs may introduce a new source of water pollution evidenced as higher concentrations of nutrients, especially phosphorus, in runoff compared to that in precipitation inputs. In two controlled, replicated experiments, one in the field for 7 months and another in the laboratory for 6 weeks, the amendment of biochar to green roof substrates was studied for its potential to mitigate the leaching of nutrients from newly installed pre-grown green roof Sedum and meadow mats. Nutrient concentrations were an order of magnitude higher in runoff from green roofs than in rain water. In the field experiment, biochar reduced the cumulative leaching of nutrients, even though biochar did not significantly reduce nutrient concentrations. These results can be interpreted as a combined impact of biochar on both the quantity and quality of runoff over time, the quantitative effect being apparently stronger than the qualitative. In the laboratory experiment, one type of biochar reduced nutrient concentrations and load in runoff while another type had an opposite effect. As the properties of biochar can vary considerably, careful studies are necessary before large-scale implementation of biochar amendment in green roofs are considered, to avoid unintended consequences.

Determination of the Physical, Chemical, and Hydraulic Characteristics of Locally Available Materials for Formulating Extensive Green Roof Substrates

Several locally available materials were tested to create an optimized growth substrate for arid and semiarid Mediterranean extensive green roofs. The study involved a four-step screening procedure. At the first step, 10 different materials were tested including pumice (Pum), crushed tiles grade 1–2 mm (T1–2), 2–4 mm (T2–4), 5–8 mm (T5–8), 5–16 mm (T5–16), and 4–22 mm (T4–22); crushed bricks of either 2–4 mm (B2–4) or 2–8 mm (B2–8); a thermally treated clay (TC); and zeolite (Zeo). All materials were tested for their particle size distribution, pH, and electrical conductivity (EC). The results were compared for compliance with existing guidelines for extensive green roof construction. From the first step, the most promising materials were shown to include Pum, Zeo, T5–8, T5–16, and TC, which were then used at the second stage to develop mixtures between them. Tests at the second stage included particle size distribution and moisture potential curves. Pumice mixed with TC provided the best compliance with existing guidelines in relation to particle size distribution, and it significantly increased moisture content compared with the mixes of Pum with T5–8 and T5–16. As a result, from the second screening step, the best performing substrate was Pum mixed with TC and Zeo. The third stage involved the selection of the most appropriate organic amendment of the growing substrate. Three composts having different composition and sphagnum peat were analyzed for their chemical and physical characteristics. The composts were a) garden waste compost (GWC), b) olive (Olea europaea L.) mill waste compost (OMWC), and c) grape (Vitis vinifera L.) marc compost (GMC). It was found that the peat-amended substrate retained increased moisture content compared with the compost-amended substrates. The fourth and final stage involved the evaluation of the environmental impact of the final mix with the four different organic amendments based on their first flush nitrate nitrogen (NO3−-N) leaching potential. It was found that GWC and OMWC exhibited increased NO3−-N leaching that initially reached 160 and 92 mg·L−1 of NO3−-N for OMWC and GWC, respectively. By contrast, peat and GMC exhibited minimal NO3−-N leaching that was slightly above the maximum contaminant level of 10 mg·L−1 of NO3−-N (17.3 and 14.6 mg·L−1 of NO3−N for peat and GMC, respectively). The latter was very brief and lasted only for the first 100 and 50 mL of effluent volume for peat and GMC, respectively.

Determining Thermal Specifications for Vegetated GREEN Roofs in Moderate Winter Climates

&lt;p class="zhengwen"&gt;Because local weather conditions in moderate climates are changing constantly, heat transfer specifications of substrate and vegetation in vegetated green roofs also change accordingly. Nevertheless, it is assumed that vegetated green roofs can have a positive effect on the thermal performance of construction in winter conditions. Is there proof from scientific research and field testing for this assumption? To answer this question, research is conducted with the main research question: Which parameters defining thermal performance for vegetated green-roof construction for a moderate winter climate like that in the Netherlands can be determined from existing literature, and how do these parameters influence thermal performance? Literature research was executed on monitoring and testing of thermal specifications of vegetated green roofs. Models with physical parameters on vegetated green roofs were studied and compared. The first goal was to make a list of all physical parameters and corresponding variables valid in the Dutch moderate-winter climate. None of the models that were found in the literature seemed to cover all physical processes. These models use parameters and variables to calculate the overall u-value of substrate and vegetation. Nevertheless, one nearly complete model was used for a sensitivity test on variables. Maximum and minimum values of variables were calculated in the model to determine the influence on the outcome in terms of u-value. From this analysis, a distinction could be made between variables influencing the u-value strongly and other variables influencing the outcome weakly.&lt;/p&gt;&lt;p class="zhengwen"&gt;The modelling showed that three variables were influencing the model calculations moderately strongly and therefore the thermal performance of the vegetated green-roof substrate and vegetation. These variables are not consistent with parameters modeling or calculating u-value in constructions. This finding means that contribution to thermal insulation by extensive vegetated green-roof substrate and vegetation in terms of u-value would be negligible. Only a small theoretical contribution to thermal insulation can be argued from weak variables. To be sure about this small theoretical contribution to the u-value of the roof construction, this u-value was used as input for energy-use calculations for residential buildings. These calculations show that such a small increase of the u-value leads to no visible reduction in energy use for heating in winter conditions. The contribution is negligible compared to the influence of the u-value from extra insulation under the roof.&lt;/p&gt;For vegetated green roofs in such moderate winter climates as in the Netherlands, additional u-value will have to be proven specifically, because the modelling shows that, in general, no contribution to thermal insulation can be expected.

The inorganic component of green roof substrates impacts the growth of Mediterranean plant species as well as the C and N sequestration potential

Extensive green roofs substrates should meet a list of physicochemical and biochemical requirements to be used as a basis for plant growth: high water holding capacity, good aeration, low bulk density, and proper drainage are some of them. In recent years, the impact of different organic matter doses and the substrate depth on the subsequent plant growth have been deeply studied. By contrast, there are not many publications about the effect of the inorganic component of these substrates on plant development and C and N sequestration potential by the green roof system, and even more under semi-arid Mediterranean conditions. Four substrates were made by mixing the same compost, at 10% by volume, with different inorganic materials: CsB (compost, silica sand, and crushed bricks; 1:1:8), CB (compost and crushed bricks; 1:9), CSB (compost, clay-loam soil, and crushed bricks; 1:1:8), and CsS (compost, silica sand, and clay-loam soil; 1:1:8). These were placed, a depth of 10cm, on “cultivation tables” in an experimental farm located in the SE of Spain. Two native species were sown in each substrate: Lotus creticus and Asteriscus maritimus. Physicochemical, nutritional, and biochemical properties of the substrates as well as the plant development were evaluated during a 10-month experiment. The CsB and CSB mixtures had good physicochemical properties (high porosity and acceptable water holding capacity) although the levels of C, N, and humic substances were higher in the soil-containing substrates than in the CB and CsB mixtures. The hydrolytic enzyme activity was also promoted in these mixtures. The plant growth pattern showed differences regarding the inorganic composition of the substrate; L. creticus had superior development in the CsB substrate and A. maritimus was able to grow in all tested substrate mixtures, although its cover was low, being a more versatile candidate to establish a green roof cover. The greatest C and N sequestration potential was achieved by the CsS mixture, reaching 1.06kgTCm−2 of green roof substrate. Therefore, substrate composition impacts the growth of native plant species as well as the C and N sequestration by the green roof system.

Impact of the Properties of a Green Roof Substrate on its Hydraulic and Thermal Behavior

Green roofs integrate vegetation into infrastructures to reach benefits that minimize negative impacts of the urbanization. Green roofs use artificial soils (substrates) that have an improved performance compared to natural soils. In this work, we characterized four substrates in terms of their hydraulic and thermal properties, and performed numerical simulations of heat and fluid flow to study the effect of these properties on green roof performance. Simulation results show that the green roof behavior strongly depends on substrate properties and on moisture content prior to a rainstorm, highlighting the need of dynamic biophysical models for design/maintenance of green roofs.

Experimental Characterization of Green Roof Components

Green roofs are known for their beneficial aspects on the buildings energy consumption and the environment quality. However, the lack of precise knowledge of thermal, water, botanic characteristics is an obstacle to predict theirs efficiencies in the case of construction projects. In this study, three of the main physical properties of green roofs were experimentally investigated to determine some of the key green roof modeling parameters. First, the thermo-physical properties of green roofs were characterized by correlating the thermal conductivity of the substrate with the water content for different maximum water capacities. Also, the thermal resistance of green roof was evaluated in controlled weather conditions using a low speed wind tunnel. Next, the moisture storage was characterized using the dynamic vapor sorption technique to determine both of sorption and desorption isotherms as well as the moisture buffer capacity. Third, the microstructural properties of green roof substrate were characterized using mercury intrusion porosimetry to measure the porosity range of green roof substrate. The experimental results were used to estimate the parameters used as input data in the developed green roof model to evaluate the energy performance of a building.

The composition and depth of green roof substrates affect the growth of Silene vulgaris and Lagurus ovatus species and the C and N sequestration under two irrigation conditions

Extensive green roofs are used to increase the surface area covered by vegetation in big cities, thereby reducing the urban heat-island effect, promoting CO2 sequestration, and increasing biodiversity and urban-wildlife habitats. In Mediterranean semi-arid regions, the deficiency of water necessitates the use in these roofs of overall native plants which are more adapted to drought than other species. However, such endemic plants have been used scarcely in green roofs. For this purpose, we tested two different substrates with two depths (5 and 10 cm), in order to study their suitability with regard to adequate plant development under Mediterranean conditions. A compost-soil-bricks (CSB) (1:1:3; v:v:v) mixture and another made up of compost and bricks (CB) (1:4; v:v) were arranged in two depths (5 and 10 cm), in cultivation tables. Silene vulgaris (Moench) Garcke and Lagurus ovatus L. seeds were sown in each substrate. These experimental units were subjected, on the one hand, to irrigation at 40% of the registered evapotranspiration values (ET0) and, on the other, to drought conditions, during a nine-month trial. Physichochemical and microbiological substrate characteristics were studied, along with the physiological and nutritional status of the plants. We obtained significantly greater plant coverage in CSB at 10 cm, especially for L. ovatus (80–90%), as well as a better physiological status, especially in S. vulgaris (SPAD values of 50–60), under irrigation, whereas neither species could grow in the absence of water. The carbon and nitrogen fixation by the substrate and the aboveground biomass were also higher in CSB at 10 cm, especially under L. ovatus – in which 1.32 kg C m−2 and 209 g N m−2 were fixed throughout the experiment. Besides, the enzymatic and biochemical parameters assayed showed that microbial activity and nutrient cycling, which fulfill a key role for plant development, were higher in CSB. Therefore, irrigation of 40% can maintain an adequate plant cover of both endemic species, particularly in a deeper and soil-containing substrate.

Application of seaweed as substrate additive in green roofs: Enhancement of water retention and sorption capacity

Green roof substrates are usually designed to achieve desirable characteristics such as low bulk density, preparation cost, high water holding capacity (WHC), hydraulic conductivity (HC) and airfilled porosity (AFP). However, no importance is given to sorption capacity or leaching potential of substrate. Thus, in the present study, novel attempt was made to incorporate a brown-seaweed (Turbinaria conoides) in growth substrate to enhance the runoff quality from green roofs. The green roof substrate, prepared using 30% perlite, 20% vermiculite, 10% sand, 20% crushed brick, 10% cocopeat and 10% T. conoides, was found to have favourable characteristics such as low bulk density (477.7kg/m3), high WHC (49.5%), AFP (20.5%) and HC (4210mm/h). With the aid of down-flow fixed column, sorption capacity of green roof substrate towards various metal ions (Na, K, Ca, Mg, Al, Fe, Cd, Cu, Cr, Ni, Pb and Zn) was examined and results indicated that the column was able to operate for 1440min at a flow rate of 5mL/min before outlet Ni concentration reached the inlet. Green roof experiments were performed using pilot-scale assemblies with Portulaca grandiflora as vegetation. Under rainfall simulations, it was observed that vegetated-green roof assemblies acted as a sink for various metal ions and produced better runoff. In addition, green roofs buffered acidic rain and delayed runoff generation.