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Article

Biochar Addition and the Runoff Quality of Newly Constructed Green Roofs: A Field Study

by
Weiwei Xiong
1,2,
Juan Li
1,2,
Hankun Wang
1,2,
Yongbo Wu
1,2,
Dongchang Li
1,2 and
Jianhui Xue
1,2,3,*
1
College of Biology and the Environment, Nanjing Forestry University, Nanjing 210037, China
2
Co-Innovation Center for Sustainable Forestry in Southern China, Nanjing Forestry University, Nanjing 210037, China
3
Institute of Botany, Jiangsu Province and Chinese Academy of Sciences, Nanjing 210014, China
*
Author to whom correspondence should be addressed.
Sustainability 2023, 15(5), 4081; https://doi.org/10.3390/su15054081
Submission received: 26 December 2022 / Revised: 1 February 2023 / Accepted: 20 February 2023 / Published: 23 February 2023
Browse Figures
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Abstract

:
Extensive nutrient leaching has been a major concern in the establishing stage of green roofs. Although an addition of biochar to the green roof substrates has been increasingly recommended, the extent to which this addition can affect the runoff quality is still largely unknown. Using biochars made from maize straws (MSB) and rice husks (RHB), this study investigated the effects of biochar addition rates (0%, 10%, 15%, and 20% biochar, v/v) on the runoff quality of new green roofs over 6 months. Our results show that the addition of biochar significantly affected the runoff quality. With an increasing biochar addition rate (10∼20%), the mean total nitrogen (TN) concentration in the runoff decreased from 103.68 mg L − 1 (CK) to 26.21∼52.77 mg L − 1 (RHB) and 10.12∼3.97 mg L − 1 (MSB), the mean dissolved organic carbon (DOC) concentration decreased from 94.47 mg L − 1 (CK) to 101.76∼59.41 mg L − 1 (RHB) and 52.45∼26.73 mg L − 1 (MSB), and the mean pH increased from 7.15 (CK) to 7.42∼7.50 (RHB) and 7.49∼7.71 (MSB). However, the mean total phosphorus (TP) concentration increased from 0.27 mg L − 1 (CK) to 0.22∼0.57 mg L − 1 (RHB) and 0.58∼1.07 mg L − 1 (MSB). Generally, the N and DOC concentrations were lower in the treatment with added MSB than RHB, but the P concentrations and pH were higher. The N concentration was significantly negatively correlated with the single rainfall and cumulative rainfall in the CK- and RHB-added treatments but not in the MSB-added treatments, suggesting that the addition of MSB affected the process of N leaching from the substrate. Overall, we recommend adding 10% maize straw biochar to the green roof substrate to reduce the initial nutrient leaching from the new green roof and improve the runoff water quality.

1. Introduction

The rapidly increasing urban area and the consequent increase in impervious surfaces have led to environmental issues such as urban flooding and decreased stormwater runoff quality [1]. Although cities are equipped with supporting drainage facilities, reducing green areas due to urbanization also increases the possibility of flooding. In addition, many stormwater management technologies require additional land space and maintenance costs [2]. Roofs may account for half of the impervious surfaces in urban areas [3], and establishing green roofs may have great potential for stormwater management while not occupying additional land [4,5]. Thus, as one of the typical low-impact development practices [6], green roofs have become a more and more popular method of mitigating stormwater problems and combating climate change [7,8]. As research progressed, it was discovered that green roofs also have many benefits, such as reducing building energy consumption, extending the life of the roof, reducing pollution, and buffering acidic rain [9,10,11,12,13].
However, there are still concerns about nutrient leaching from green roofs [14]. This is especially an issue for extensive green roofs (also the dominant green roof type), which often lack well-developed runoff recycling facilities [9]. Therefore, to date, there have been debates on the runoff quality of green roofs [15,16]. For example, Gong et al. [6] showed that extensive green roofs with different substrates were all sinks of NH 4 + , NO 3 − , TN, and TP, but also sources of chemical oxygen demand (COD). On the contrary, Kuoppamäki and Lehvävirta argued that the P and N concentrations in runoff from green roofs were much higher than those from nearby non-vegetated asphalt and tin roofs in their investigations in southern Finland [17]. Similarly, a number of studies found that new green roofs have the highest nutrient leaching concentrations and that the composition of a substrate is critical to runoff quality [9,15].Therefore, developing and utilizing more sustainable green roofing substrate materials has become the goal of many scholars’ research [18,19,20].
Biochar is a stable product produced by pyrolysis of biomass [21,22], such as straw and rice husk, and its use as a soil amendment for reducing nutrient leaching and improving soil’s physical properties has been proven [23,24,25,26]. The successful use of biochar in agriculture and horticulture in recent years has led to it being suggested as a component of green roof substrate, and it has been proven to have a positive effect on green roofs [27]. Chen et al. [28] demonstrated that adding biochar to natural soil substrates could improve the substrate’s physicochemical properties, change the microbial community structure, and promote plant growth by lowering the substrate temperature and increasing the substrate moisture. Cao et al. [29] confirmed that adding biochar to green roof substrates can reduce the substrate’s bulk density and improve the hydrological performance of green roofs, in addition to extending the number of days for plants to reach their permanent wilting points.
However, few studies have quantified the effect of biochar application on green roof runoff quality based on replicated experiments, especially in newly constructed green roofs. Qiu et al. [30] measured the runoff nutrient content of four outdoor green roof modules during the rainy season and confirmed that rice husk biochar reduced the leaching of N from the green roof substrate. Beck et al. [27] found that the addition of biochar made from plant husks and waste tires to green roof soil significantly reduced the nutrient content in the runoff through indoor rainfall experiments. We are not aware of any studies quantifying the effect of biochar’s addition on green roof runoff quality on the basis of replicated experiments. Therefore, it is necessary to evaluate the effect of biochar on the runoff quality of newly constructed green roofs. To fulfill these purposes, we built green roofs with four gradients of biochar additions and conducted runoff quality monitoring in a field environment for four months. The runoff quality indicators included concentrations of TN, nitrate (NO 3 − ), TP, orthophosphate , DOC, and pH in the runoff.

2. Materials and Methods

2.1. Study Area and Experimental Design

This experiment was conducted on the roof of a teaching building at Nanjing Forestry University in China. The region has a subtropical monsoon climate with an average annual precipitation of 1106.5 mm and relative humidity of 76%. The spring season is from April to May,summer is from June to September, autumn is from October to November, and winter is from December to March. The experimental period was from 28 March to 1 October 2022, with most of the local precipitation and heavy rainfall events occurring within this period. Altogether, six precipitation events resulted in runoff that could be monitored (Figure 1).
Referring to Chen et al. [21] and Kuoppamäki et al. [31], and taking into account the fire risk and load requirements of the building, we set up seven treatments of local soil, perlite, and vermiculite (CK) and mixed them with 10%, 15%, and 20% rice husk biochar or maize straw biochar (RH10, RH15, and RH20 as well as MS10, MS15, and MS20, respectively), as detailed in (Table 1), and the physicochemical properties of these components are shown in (Table 2). A total of 21 extensive green roof modules (0.4 m × 0.8 m × 0.15 m) with seven treatments and three replications were installed on angle brackets on an open flat roof and placed at a slope of 2 ∘ . Runoff was collected in a 25 L PVC container connected to the modules’ front hole (Figure 2). The natural soil was obtained from old fields in Xiashu, Zhenjiang, and Jiangsu, China, a yellow-brown soil widely distributed in southern China. These soils were air-dried and passed through a 5 mm sieve to remove stones and plant and animal debris. Commercial biochar (Nanjing Qinfeng Straw Treatment Company) was produced from maize straw and rice husk in a rotational kiln. The pyrolysis temperature was in a range of 450∼650 ∘ C, with 2 h of slow pyrolysis. Before mixing, only biochar in the particle size range of 0.5∼2 mm was retained.
The green roof modules included the plant layer, substrate layer, filter layer, drainage layer, and waterproof layer. The substrate depth was set to 10 cm, and Sedum lineare was selected as the plant layer, which is widely adopted in extensive green roof settings. The substrate material was mixed well and poured into the modules on 27 March 2022, and cuttings were subsequently taken at a density of 100 plants/m 2 with just enough water to support plant growth. Throughout the trial, we did not apply fertilizer or perform any nurturing management practices, as is usually performed by most managers of extensive green roofs [17].

2.2. Sampling and Measurements

Rainfall data were collected using the Davis Vantagepro2 weather station, which was mounted on the roof near the angle brackets. The container with a capacity of 25 L was always able to receive all of the event runoff. Therefore, the average water quality of the whole precipitation event could be assessed.
At the end of each rainfall event, we checked the rainfall reported by the weather station and checked for possible runoff. If runoff was collected in the containers, then we sampled it when it was no longer flowing from the pipes. Before taking each sample, we shook the container vigorously and brought the water sample back to the laboratory in a 500 mL polyethylene bottle. All of the samples were stored at 4 ∘ C and measured within 48 h. The runoff quality indicators included TN, NO 3 − , TP, orthophosphate, pH, and DOC, which were measured following Chinese national standards [32].
The pH values of the water samples were determined using a portable pH meter. The TN and TP samples were first oxidized by adding potassium persulfate and then heated in an autoclave at 120 ∘ C for 30 min and analyzed spectrophotometrically. The orthophosphate samples and DOC samples were analyzed spectrophotometrically and with a Shimadzu TOC analyzer after passing through a 0.45 μm PTFE membrane filter, respectively. The NO 3 − samples were analyzed spectrophotometrically after the addition of sulfamic acid.

2.3. Data Analysis

Two-way repeated measures ANOVA (two-way RM-ANOVA) was employed to investigate the main effects of time and treatment and their interaction (time × treatment) over the study period. After using a Kolmogorov–Smirnov test to examine the normality and homogeneity of variance, Mauchly’s sphericity test was employed, and if the sphericity assumption was violated, then we used Greenhouse–Geisser Correction to correct the result. Regression analysis was used to determine the possible relationship between the runoff quality indicators and rainfall characteristics (single rainfall depth and cumulative rainfall depth). All analyses were performed using R programming (Version 4.1.2) [33].

3. Result

3.1. Runoff pH

The addition of biochar significantly increased the pH of the runoff (F = 16.77), but time had a greater effect (F = 53.51), with lower pH levels at the beginning of the experiment. There was an interaction between time and treatment (Table 3). Specifically, the runoff pH of the CK treatment increased significantly and became constant on 23 June, while the biochar-added treatment advanced this process to 28 April. Different biochar types and different addition rates did not result in significant differences (Figure 3a).

3.2. Runoff TN and NO 3 − Concentrations

There were significant effects from both time and treatment on the TN and NO 3 − concentrations in the runoff, and there was an interaction effect (Table 3). During the whole observation period, there was a significant decrease in the TN and NO 3 − concentrations in the runoff with the addition of MSB but no significant difference between the high (MS20) and low (MS10) addition rates (Figure 3b,c). At the same addition rate, the concentrations of TN and NO 3 − in the runoff with MSB were always lower than those of RHB (p < 0.05). The treatment with RHB also yielded less TN and NO 3 − leaching at the beginning of the trial but significantly higher TN and NO 3 − concentrations in the RH20 runoff than CK at the end. All treatments exhibited the same temporal pattern, with maximum TN and NO 3 − leaching at the beginning of the trial, followed by a sharp decline in June and a subsequent increase.

3.3. Runoff TP and Orthophosphate Concentrations

As shown in Figure 3c,d, the TP and orthophosphate concentrations in the runoff were significantly influenced by the time and treatment (Table 3). The addition of both MSB and RHB significantly increased the TP and orthophosphate concentrations in the runoff, with increasing addition rates for all rainfall events during the observation period. The TP and orthophosphate concentrations in the runoff were always higher for the MS treatment than for the RH treatment at the same addition rate. The runoff TP and orthophosphate concentrations showed a trend of increasing and then decreasing, but the effect of time was low and was only observed in the treatments with RHB’s addition.

3.4. Runoff DOC Concentration

The DOC concentration in the runoff was significantly affected by treatment and time, and the interaction was significant (Table 3). MSB and RHB additions significantly reduced the DOC concentrations in the runoff in the early part of the experiment (Figure 3f). In contrast, higher runoff DOC concentrations were observed in RH10 and MS10 than in CK in the later part of the experiment. The effects of the two biochars also differed, with MSB reducing the runoff’s DOC concentrations more than RHB in the early part of the experiment and showing no significant difference between high and low addition rates, and in the late part of the experiment, MS10 and CK were not significantly different, but they were significantly lower than MS15 and MS20, while RH10 showed no significant difference or significant increase in DOC concentration due to CK.

3.5. Response Relationship between Nutrient Leaching and Rainfall Characteristics

Regression analysis showed that the TN concentration in the runoff decreased with increasing single and cumulative rainfall depths, and these changes occurred in the CK- and RHB-added treatments. The correlation between the TP concentration and cumulative rainfall was low, but an increase with an increasing single rainfall depth was observed in the RHB-added treatments. No correlation was found between the DOC concentrations in the runoff and rainfall conditions (Figure 4).

4. Discussion

4.1. The Effects of Biochar Application on Runoff pH

Acid rain has become a major environmental problem [34]. Large amounts of energy consumption and vehicle emissions make urban areas more prone to acid rain [35]. Correspondingly, most green roofs are built in urban areas, and therefore the mitigation of acid rain in urban areas has become one of the critical ecological services of green roofs. Rainwater passing through green roofs forms alkaline or weakly alkaline runoff, which helps prevent the acidification of urban drainage systems.
In our study, the pH of all runoff samples was significantly higher than local rainwater (5.5∼6.5), which is consistent with previous studies [36], probably because we used alkaline soil (Table 2). The addition of biochar further increased the pH of the runoff, either because the ash contained in the biochar was leached out or the biochar raised the pH of the substrate [37,38].
As with the results of Zhang et al. [39], we observed a major effect from time on the runoff pH, with the runoff pH generally low at the beginning of the experiment and then increasing and becoming constant (Figure 3), which Zhang et al. attributed to acid leaching from the substrate. Notably, the addition of biochar not only increased the pH of the runoff but also shortened the time it took for the pH of the runoff to increase and stabilize, suggesting that the addition of biochar may have reduced the leaching of acid from the substrate, further increasing the green roof’s ability to regulate stormwater’s pH.

4.2. The Effects of Biochar Application on the Runoff’s N Concentration

The results showed significant TN and NO 3 − leaching in the early stages of new green roofs, especially for CK, validating previous results showing that green roofs are a source rather than a sink for nutrient pollutants (Figure 1a,b), at least in regard to new green roofs [40]. In addition, the TN and NO 3 − concentrations in the runoff showed a consistent trend, which is the same as the conclusion of Gong et al. [6] and proves that most of the N in the runoff exists in the form of NO 3 − . Such high TN and NO 3 − leaching levels were possible since the soil we used came from agricultural land and had a high nitrogen content. The substrate of higher nutrient contents would leach more nutrients [1]. Adding only 10% biochar in the soil can significantly reduce the TN concentration in the runoff, similar to the conclusions of Beck et al. [27]. These results were likely explained by the enhanced adsorption of these ions and the promotion of plant uptake of N from the substrate by biochar [21,41].
In this study, the effects of the two types of biochar on the TN and NO 3 − concentrations in the runoff were significantly different, with the biochar made from maize straw showing a better ability to reduce N leaching, which may be due to the different physicochemical properties of the biochar [42]. In addition, it is noteworthy that neither biochar type performed better at higher addition rates (RH20 and MS20) and even increased N leaching, probably because a 10% volumetric addition is already a very high dose. Therefore, continuing to increase the amount of biochar application may not yield better results.
The effect of adding RHB and MSB on reducing the TN and NO 3 − concentrations in the runoff were significant in the first rainfall, which may also be related to the timing of the rainfall. Nguyen et al. [43] concluded that soil inorganic N would be significantly reduced about one month after adding biochar, and the timing of our initial rainfall was just about one month after setting up the experiment. Furthermore, our additions were made at a volumetric ratio, which reduced the amount of soil and thus enhanced the effect of the biochar.
The specific analysis in Figure 4a,b shows that the TN and NO 3 − concentrations in the runoff gradually decreased with increasing single rainfall and cumulative rainfall depths. The physical nature of NO 3 − may be responsible for these results, as it is highly mobile and leachable in the soil, resulting in a gradual decrease of N in the substrate with increasing single and cumulative rainfall depths. Moreover, the addition of biochar significantly inhibited the dissolution of N from the substrate in stormwater, thus reducing the concentration of N in the runoff. However, this does not explain the increase in the TN and NO 3 − concentrations in the runoff that we observed on 29 July and 1 August. Gong et al. [15] observed similar results and suggested that this was related to seasonal and rainfall conditions. We suggest that their results may also be related to plant growth. The Sedum lineare grown in this experiment and that of Gong et al. [15] flowered from April to May and fruited from June to July, and NO 3 − was taken up heavily as a nutrient required for plant growth, thus reducing N leaching. Meanwhile, in July, plant growth slowed down, leading to an increase in N leaching from the substrate. This may also explain the increase in NO 3 − concentration in the winter snowmelt runoff observed in other experiments [9].

4.3. The Effects of Biochar Application on the Runoff’s P Concentration

The TP and orthophosphate concentrations in the runoff were low in CK, while the TP and orthophosphate concentrations in the runoff increased significantly with the addition of biochar, a result that supports the conclusions of Bu et al. [44] and Kuoppamäki et al. [17]. Furthermore, the TP and orthophosphate concentrations were minimally affected by time and were not significantly correlated with the cumulative rainfall or single rainfall depths (Figure 4c,d and Table 3). These results may be explained by most of the TP in the runoff being present in the form of orthophosphate in our study, and orthophosphate has less mobility in most soil [45], leaving the P from the substrate difficult to dissolve in rainwater. At the same time, adding biochar increased the P content in the soil and changed the form to available P [46], thus increasing the P leaching (Figure 3d,e).
The results were not as positive as those of Beck et al. [27], who concluded from two simulations of artificial rainfall that adding biochar could consistently reduce the TP concentrations in the runoff. Our experiments show that this leads to a significant increase in the TP and orthophosphate concentrations. Although biochar addition may reduce TP and orthophosphate loading by increasing the water holding capacity of the substrate [47]. This effect has an almost negligible impact on extensive green roofs in the case of heavy or stormy rainfall. The results of column leaching experiments by Yao et al. [42] showed that adding biochar made from different materials to the soil caused other nutrient leaching behavior, with Brazilian pepperwood biochar reducing orthophosphate leaching and peanut shell biochar having the opposite effect. We note that Beck et al. [27] used biochar made from rice husks, nut shells, coconut shells, and car tires, while we used maize straw and rice husk as a feedstock, which may be the main reason for our different results.
Our negative results for the TP and orthophosphate concentrations in the runoff demonstrate the importance of selecting the correct type of biochar for green roof substrates. In the future, more types of biochar could be tested for their effect on runoff quality, such as animal resolution, sludge, and wood. In addition, biochar modification is a possible option, and it has been documented that iron-modified or magnesium-modified biochar can remove P from aqueous solutions [48,49].

4.4. The Effects of Biochar Application on the Runoff DOC Concentration of Green Roofs

Although biochar is commonly applied to increase soil carbon stocks, there are still concerns about potential negative impacts associated with its application, such as additional leaching and mineralization due to the organic carbon contained in the biochar [50].
In the early stages of the experiment, we observed that CK had the highest DOC leaching, being significantly higher than the biochar-added treatments except for RH10, which supports the findings of Lei et al. [51]. This result indicates that biochar can reduce the DOC concentration in runoff [52]. However, the opposite effect was obtained by Liu et al. [53], which might be due to the C-rich soil (Table 2) in our study and the C-poor soil (1.4 g kg − 1 ) in the study of [53] Barnes et al. [54] observed that adding biochar to C-rich soils reduced DOC leaching, while the opposite was found for C-poor soils.
By the later part of the experiment, the DOC concentrations in the runoff were significantly higher, especially in the treatments with added biochar, which is consistent with the seasonal pattern of DOC concentrations observed in much of the literature [51] and may be related to plant growth and microbial activity. Root secretions and biomass were the main input source of soil DOC [55], and the biomass of Sedum lineare gradually increasing may have resulted in more DOC input and thus higher DOC concentrations in the runoff. In addition, microbial activity in the substrate may also facilitate the conversion of unstable C to DOC in biochar [56]. We suggest that biochar may have contributed to the microbial activity, thus creating a “priming effect” that resulted in higher DOC concentrations in the runoff.
Overall, we suggest that adding biochar has both negative and positive effects on runoff’s DOC concentrations. On the one hand, the adsorption of biochar can reduce the leaching of DOC [52,57], which explains the significant decrease in the runoff’s DOC concentration we observed with increasing biochar addition rates. Meanwhile, the addition of biochar promotes plant growth and microbial activity [55,58], leading to more DOC input and thus increasing the DOC concentration in the runoff, which explains why MS10 and RH10 did not significantly reduce the runoff’s DOC concentration in the later part of the experiment and even increased instead.
Undoubtedly, in the long term, DOC in the substrate will gradually leach out with increasing cumulative rainfall, thus reducing the DOC concentration in the runoff. However, from our experimental results, this is not the case in the short term. Therefore, it is still necessary to evaluate the long-term impact of biochar on runoff DOC concentrations. In addition, it is worth noting that most of the previous studies have focused on N and P leaching, and fewer have reported on DOC concentrations in green roof runoff. Although our study showed a positive effect of added biochar on reducing DOC leaching, this was still much higher than the DOC concentrations in rainfall, demonstrating that green roofs are a source rather than a sink for DOC.

5. Conclusions

We found that adding biochar had both positive and negative effects on green roof runoff quality. The positive effects included lowering the N and DOC concentrations in the runoff and increasing the runoff’s pH level, while the negative effects were mainly in the form of higher P concentrations in the runoff. Considering the impact of biochar’s addition rate on runoff quality, we suggest adding 10% maize straw biochar by volume to the green roof substrates to improve the water quality of new green roof runoff. Our results emphasize that adding biochar interacts with the duration of green roof use. Thus, further long-term monitoring of green roof runoff quality with added biochar is still necessary.

Author Contributions

Conceptualization, W.X.; investigation, W.X. and J.L.; data curation, W.X.; writing—original draft preparation, W.X.; writing—review and editing, W.X., H.W., D.L., Y.W. and J.X.; visualization, W.X.; supervision, J.X.; project administration, J.X.; funding acquisition, J.X. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by Major State Basic Research Development Program of China (grant no. 2016YFC0502605) and Forestry Science and Technology Innovation and Extension Program of Jiangsu Province (grant no. LYKJ(2022)02), and it was a project funded by Priority Academic Program Development of Jiangsu Higher Education Institutions (grant no. PAPD).

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Rainfall data during the test period. Blue bars indicate the rainfall that did not produce runoff, red bars indicate the rainfall that resulted in runoff, and black lines indicate cumulative rainfall depth.
Figure 1. Rainfall data during the test period. Blue bars indicate the rainfall that did not produce runoff, red bars indicate the rainfall that resulted in runoff, and black lines indicate cumulative rainfall depth.
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Figure 2. Experimental area’s vertical layout. Plant layer: Sedum lineare Thunb.; substrate layer: mixture with a thickness of 10 cm; filter layer: geotextile with 150 g/m 2 ; egg carton-like water storage and drainage layer: 25 mm thick molded polystyrene.
Figure 2. Experimental area’s vertical layout. Plant layer: Sedum lineare Thunb.; substrate layer: mixture with a thickness of 10 cm; filter layer: geotextile with 150 g/m 2 ; egg carton-like water storage and drainage layer: 25 mm thick molded polystyrene.
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Figure 3. Runoff quality indicators for different treatments. The different capital letters (A–F) indicate the statistical difference between different sampling times for the same treatment, and the different lowercase letters (a–e) indicate the statistical difference between different treatments at the same sampling time: (a) = pH, (b) = TN concentration, (c) = NO 3 − concentration, (d) = TP concentration, (e) = orthophosphate concentration, and (f) = DOC concentration.
Figure 3. Runoff quality indicators for different treatments. The different capital letters (A–F) indicate the statistical difference between different sampling times for the same treatment, and the different lowercase letters (a–e) indicate the statistical difference between different treatments at the same sampling time: (a) = pH, (b) = TN concentration, (c) = NO 3 − concentration, (d) = TP concentration, (e) = orthophosphate concentration, and (f) = DOC concentration.
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Figure 4. Response relationship between the nutrient leaching and rainfall characteristics. (a,c,e) Relationship between TN concentration, TP concentration, DOC concentration, and cumulative rainfall depth. (b,d,f) Relationship between TN concentration, TP concentration, DOC concentration, and single rainfall depth.
Figure 4. Response relationship between the nutrient leaching and rainfall characteristics. (a,c,e) Relationship between TN concentration, TP concentration, DOC concentration, and cumulative rainfall depth. (b,d,f) Relationship between TN concentration, TP concentration, DOC concentration, and single rainfall depth.
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Table
Table 1. The proportion of each component in the substrate (v/v).
Table 1. The proportion of each component in the substrate (v/v).
TreatmentSoilBiocharPerliteVermiculite
CK70%015%15%
MS1060%10%15%15%
MS1555%15%15%15%
MS2050%20%15%15%
RH1060%10%15%15%
RH1555%15%15%15%
RH2050%20%15%15%
MS = treatment with the addition of corn straw biochar; RH = treatment with the addition of rice husk charcoal; numbers after abbreviation = addition rate.
Table
Table 2. Chemical properties of the components (“-” means below the detection limit).
Table 2. Chemical properties of the components (“-” means below the detection limit).
ComponentpHTC (g kg − 1 )TN (g kg − 1 )TP (g kg − 1 )
Soil8.012.12.11.5
MSB10.4470.412.012.7
RHB8.5390.19.91.4
Perlite7.0---
Vermiculite7.0---
RHB = rice husk biochar; MSB = maize straw biochar.
Table
Table 3. Results of two-way repeat measures ANOVA.
Table 3. Results of two-way repeat measures ANOVA.
IndicatorspHTNNO 3 − TPOrthophosphate DOC
Fp η p 2 Fp η p 2 Fp η p 2 Fp η p 2 Fp η p 2 Fp η p 2
Treatment16.76<0.0010.88104.05<0.0010.98121.05<0.0010.98127.33<0.0010.98445.30<0.0010.99105.90<0.0010.98
Time53.51<0.0010.79271.15<0.0010.95268.09<0.0010.954.020.030.2211.50<0.0010.4573.25<0.0010.80
Interaction3.74<0.0010.6250.73<0.0010.9650.36<0.0010.961.650.130.4110.01<0.0010.8116.17<0.0010.87
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Xiong, W.; Li, J.; Wang, H.; Wu, Y.; Li, D.; Xue, J. Biochar Addition and the Runoff Quality of Newly Constructed Green Roofs: A Field Study. Sustainability 2023, 15, 4081. https://doi.org/10.3390/su15054081

AMA Style

Xiong W, Li J, Wang H, Wu Y, Li D, Xue J. Biochar Addition and the Runoff Quality of Newly Constructed Green Roofs: A Field Study. Sustainability. 2023; 15(5):4081. https://doi.org/10.3390/su15054081

Chicago/Turabian Style

Xiong, Weiwei, Juan Li, Hankun Wang, Yongbo Wu, Dongchang Li, and Jianhui Xue. 2023. "Biochar Addition and the Runoff Quality of Newly Constructed Green Roofs: A Field Study" Sustainability 15, no. 5: 4081. https://doi.org/10.3390/su15054081

APA Style

Xiong, W., Li, J., Wang, H., Wu, Y., Li, D., & Xue, J. (2023). Biochar Addition and the Runoff Quality of Newly Constructed Green Roofs: A Field Study. Sustainability, 15(5), 4081. https://doi.org/10.3390/su15054081

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