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Rain gardens play a key role in urban non-point source pollution control. The drainage type affects the infiltration processes of runoff pollutants. The soil properties and microbial community structures were studied to reveal the stability of the ecosystem in rain gardens with different drainage types under long-term operation. The results showed that the soil water content and total organic carbon in the drained rain gardens were always higher than that of the infiltrated ones. With the increase in running time, the contents of heavy metals in rain gardens showed significant accumulation phenomena, especially the contents of Zn and Pb in drained rain gardens were higher than that in infiltrated ones. The accumulation of pollutants resulted in lower microbial diversity in drained rain gardens than in infiltrated rain gardens, but the microbial community structures were the same in all rain gardens. The effects of drainage type on microbial community evolution were not significant, only the accumulation of heavy metals led to changes in the abundance of dominant microorganisms. There were differences in the soil environment of rain gardens with different drainage types. The long-term operation of rain gardens led to fluctuations in the soil ecosystem, while the internal micro-ecosystems of the drained rain gardens were in unstable states. [ABSTRACT FROM AUTHOR]

As the bioretention facilities have been extensively built in the construction of "Sponge City" in China, urban non-point source pollutants could be effectively controlled. The influences on microbial community in three bioretention facilities with different underlying types/built times at field scale were studied. The results showed that nutrient loads in road runoff were 1.1–3 times higher than of roof. Compared with the other two rain gardens, the bioretention tank (BT) was relatively stable and showed >90% nutrient load reduction rates. The nutrients brought by the stormwater runoff changed the original habitat in the soil. Nutrient removal led to the deterioration of the living environment of microorganisms, and then the number of microorganisms and diversity changed. Ten dominant bacteria species were found in the facilities, and Proteobacteria were the most dominant bacteria phyla, with the relative abundances all >30%. Suspended solids were found to be the most important factor and had a high correlation to the most dominant microorganisms. With the increased operation period, the microorganism species tended to be concentrated on Proteobacteria , resulting in decreases of other functional microorganisms. The bioretention facility with the road underlying had the lowest microbial diversity, and the built time was the factor that had the greatest impact on microbial diversity. Based on these results, the future design and construction of bioretention facilities should consider the risk after nutrients entered the bioretention facility and the changes in microbial diversity. [Display omitted] • The nutrient removal effects of bioretention facilities with different underlying types/built time were monitored. • The changes of TOC and nutrients (N and P) contents were studied. • The evolutions of the microbial communities were explored. • The relationship between soil nutrient contents and microorganisms was built. • The influences of different design types on the microbial diversity were determined. [ABSTRACT FROM AUTHOR]

Urban waterlogging and nonpoint source (NPS) pollution caused by urbanization have considerably increased, and their control effects are affected by many factors. This study established a distribution model to analyze the influences of different rainfall conditions and rain garden layouts on runoff output and NPS pollution. Simulation results showed that (a) the reduction rates of the runoff and pollution load decreased from 45% to 23% and from 57% to 23% with increasing rainfall duration (1–24 hr). The flow and concentration peaks, total discharge amount and load increased, and the reduction rates of the runoff and pollution load decreased from 47% to 32% and from 60% to 21%, respectively, with increasing recurrence period (1–50 annual). The changes in the rain peak coefficient had minimal reduction effect on water quantity and quality. (b) Under different rain garden layouts, the reduction rates of the runoff and pollution load were 37%–52% and 13%–57%, respectively. The reduction effects of the runoff and pollution load improved, whereas amplitudes decreased with increasing rain garden layouts (0%–4%). (c) Rainfall duration and rain garden proportion greatly influenced the runoff and load reductions, respectively. Practitioner points: The reduction effects of runoff and pollution load under different rainfall conditions were simulated and analyzed.The reduction effects of runoff and pollution load under different setting proportions of rain garden were simulated and analyzed.The influence degrees of different design conditions on water quantity and quality reduction rates were evaluated. [ABSTRACT FROM AUTHOR]

• Field performance data were obtained for four typical LID facilities. • Exceedance probabilities of effluent concentration is reduced obviously. • The weighted annual load reduction is more than 60% and stable. • An estimation method for LID extent and cost in urban built-up areas is proposed. Field studies are valuable because of the insufficient number of field performance data in low-impact development (LID)-related research. Four typical LID facilities in northwest China were built and monitored. These facilities differ in their impervious/pervious bottom, inflow underlying surface, media types, and combinations. The water volume reduction of impervious rain garden filled with native loess decreases by approximately 20% when the total daily rainfall levels gradually increase from light to heavy. Several technical measures, such as media modification, setting internal storage area, reducing drainage area, and increasing media thickness, have been taken to improve the runoff regulation effect. The volume reduction rate in light and medium-sized rainfall (daily rainfall totals < 25 mm) is above 68.2% for two improved facilities, namely, mixed media rain garden and layered media bioswale. For impervious native loess rain garden, mixed media rain garden, and layered media bioswale, the median values of inflow total suspended solid (TSS) event mean concentrations (EMC) are reduced from 43.5 to 68.5 mg/L to 22.4–24.3 mg/L. In accordance with the Class IV limits of Surface Water Environmental Quality Standards (total nitrogen (TN) = 1.5 mg/L; total phosphorus (TP) = 0.3 mg/L), the probabilities of the effluent TN concentration exceeding the IV limit are 32.7%, 42.3%, and 19.8% for the three facilities. The exceedance probabilities for TP are 18.5%, 6.5%, and 8.9%. The weighted results indicate that the annual load reduction rate is more stable than the fluctuating concentration removal, which is above 60%. An approach to estimate the total scale of LID construction was established on the basis of rainfall level proportion, land use types, and monitored data. When native loess and mixed media rain garden are applied in building areas and layered media bioswale is applied in road area, the LID implementation cost is approximately 36.0 billion CNY until 2030 for Xi'an City. [ABSTRACT FROM AUTHOR]