Ecological Engineering最新文献

The degradation of temperate desert type rangeland leads to decreased vegetation diversity and soil nutrients levels. Grazing prohibition and artificial revegetation are common strategies for vegetation restoration. However, it is currently unknown the duration of grazing prohibition and artificial revegetation affect soil microorganisms. Therefore, experiments on grazing prohibition duration and artificial revegetation were conducted to explore the response of soil microorganisms to these measures. Field experiments were conducted during the peak plant growth season in Guide County, China, to evaluate methods involving grazing prohibition and artificial revegetation. We established six experimental sites, which were grazing prohibition for fifteen years (P15), grazing land located near P15 (P15-CK), grazing prohibition for eight years (P8), grazing land located near P8 (P8-CK), artificial revegetation for three years (A3), and wasteland located near A3 (A3-CK). The results showed that artificial revegetation measures decreased the plant diversity, whereas grazing prohibition for eight years increased it. Artificial revegetation and grazing prohibition measures led to an increase in pH and total carbon, and a decrease in total nitrogen and total phosphorus. The amount of total PLFA increased with artificial revegetation, whereas grazing prohibition resulted in a decrease of total PLFA. Artificial revegetation and grazing prohibition measures decrease the relative abundance of the Ascomycota phylum and the fungal diversity. In addition, the study found that fungal communities were primarily influenced by soil factors such as ammonium nitrogen, pH, and total carbon, rather than by plants. Vegetation restoration enhances the accumulation of total soil carbon and alters fungal community composition and diversity. The effects of artificial revegetation and grazing prohibition measures on the amount of total PLFA varied. These findings provide important information that vegetation restoration promotes soil nutrient accumulation but reduces fungal diversity, which can inform the restoration of degraded temperate desert type rangeland.

Domestic wastewater plays a critical role in the discharge of microplastics into aquatic ecosystems. Constructed wetland systems are used to treat domestic wastewater in rural areas. This study aimed to determine the microplastic concentrations and morphological properties (shape, size, and color) of microplastics in influent, effluent, and sediment samples taken from horizontal subsurface flow constructed wetland system in Denizli/Türkiye. Also, the microplastic removal efficiency was evaluated in the constructed wetland. Samples were collected during summer and winter to investigate the seasonal variations in microplastic concentrations. The findings revealed that the majority of microplastics collected in this study were fibers (winter: 67.78%, summer: 82.46%) and transparent-white colored microplastics in both periods (winter: 88%, summer: 72%). In addition, the most abundant microplastic size was obtained as 100–500 μm (winter: 92%, summer: 82%). Suspected microplastics were identified by ATR-FTIR as PES, PET, and PEVA. PEVA is the most frequently encountered type of polymer. The average removal efficiency of microplastics in summer was determined as 87.43% and in winter was 97.27%. Daily microplastic discharge from the constructed wetland was calculated as 1.365 × 10⁷ MP/day for the summer season, and 2.918 × 10⁷ MP/day for the winter season. The findings obtained in this study suggest that although the constructed wetland system adequately removes microplastics, there is a high release of microplastics in the effluent. All the data suggest that constructed wetlands are a crucial source of the release of microplastics.

Floating treatment wetlands (FTW) are an emerging Nature Based Solution that have exhibited promising nitrogen removal under different range of effluents pollutant concentrations. Despite the notable increase in the number of FTW studies in the last years, nitrogen (N) removal mechanisms within FTW have not been fully assessed. The present study aims to understand N removal in FTW and investigate their microbial biofilm activity through a pilot scale experiment for agri-food tertiary wastewater treatment. A conventional and a modified (with added cellular concrete (CC)) FTW were monitored over 7 months with respect to two control lagoons (conventional lagoons with or without CC hanging in the water column). Experimental results revealed that the best TN removal was achieved by the lagoon equipped with the modified FTW (20% mean removal increase compared to the conventional lagoon). Biofilm denitrification activity potential was up to 6.7–9.0 times higher within pilot lagoons equipped with FTW than that in control lagoon (LC without FTW), while nitrification activity potential was prominent in biofilms within the control pilot lagoons (exhibiting high dissolved oxygen (DO) concentration). Biofilms from plant roots exhibited the highest overall dissolved inorganic nitrogen treatment followed by the biofilms from sediments and CC material. Plant root biofilms exhibited both significant nitrification and denitrification activity potentials despite the overall low DO and COD concentrations within FTW pilot lagoons' water column. This suggests the existence of micro sites in the roots network which provide adequate aerobic conditions and access to organic carbon most probably through root exudates. Overall, N accumulation in the sediment was a minor removal mechanism for all pilot lagoons. Plant accumulation (accounting for one third of TN removal), nitrification and enhanced denitrification appeared to be the main removal mechanisms in pilot lagoons equipped with FTWs (with or without CC) while nitrification, algal assimilation and NH₄-N volatilization may hav-èe been the major processes driving TN removal in the control pilot lagoons. Hence, FTW could be an interesting retrofit of existing lagoons to promote nitrogen removal through denitrification and plant assimilation, especially in the case of receiving bodies highly sensitive to nitrate input. Further research should address optimizing FTW design to guarantee stable N removal under changing water temperature and mitigate seasonal variations as well as investigate biofilm species for in-depth understanding of N cycle within FTWs.

Fertilization and cultivation management strongly affect crop productivity, alter soil nutrient availability, and influence microbial communities, leading to substantial stoichiometric imbalances. However, how these practices reflect the potential nutrient limitation of soil microbes in agricultural ecosystems remains unclear. Herein, soil samples (0–10 and 10–20 cm) from a maize crop subjected to a 15-year long-term field experiment considering five different treatments (no fertilizer + downslope cultivation, combined manure and mineral fertilizers + downslope cultivation, mineral fertilizer alone + downslope cultivation, 1.5-fold mineral fertilizer + downslope cultivation and mineral fertilizer + contour cultivation representing CK, T1, T2, T3 and T4, respectively) were deployed on a 15° purple soil sloping farmland to explore the potential microbial resource limitation using various extracellular enzyme stoichiometry (EES) approaches. Our results revealed that fertilization practices (i.e., T1, T2, T3, and T4) significantly influenced extracellular enzyme activity (EEA), particularly in T1 and T3 at the 0–10 and 10–20 cm soil depths. The mean natural logarithms of the EES ratio across the treatments were 1.23:1.34:1.00 at 0–10 cm and 1.23:1.32:1.00 at 10–20 cm depths, deviating from the overall global mean of 1:1:1, suggesting an imbalance in microbial resources. Based on the calculations of threshold elemental ratio (TER) and available resource ratios (R_C:N – TER_C:N > 0), scatter plots of EES (below the 1:1 line) and vector angle (<45°) revealed that fertilization and cultivation management alleviated microbial N limitation. Furthermore, a strong homeostasis analysis of N:P and a significant increase in the N:P stoichiometry imbalance also synthetically supported N limitation from soil microbes. Heatmap correlation and random forest analysis showed that C:N, EES_C:N and N:P stoichiometry imbalances were the main factors influencing microbial N limitation. Based on partial least squares path modeling (PLS-PM), soil EEA was the driving factor that induced microbial N limitation. These findings enable greater comprehension of the status of microbial resource limitation by considering the EEA stoichiometry approach under fertilization and cultivation management and provide insight into regulating soil nutrient cycling (i.e., N cycle) mediated by soil ecological processes and adjusting their management in similar intense agroecosystems worldwide.

This study investigates the suitability of Phragmites australis (reed) biomass deriving from a surface flow constructed wetland (CW) to produce three compost types: reed (RC), reed mixed + potato cuttings (PC) and reed + liquid anaerobic digestate (DC), to promote both resource circularity and soil carbon sequestration. The composts were tested over 60 days on lettuce at two levels in combination or not with NH₄NO₃ (at the same kg N ha⁻¹ loading), along with NH₄NO₃ reference (Chem) and an unamended control (Ctrl). The plant tissue dry weight and N load was determined, and the N relative efficiency (N-RAE %) was calculated. On pot soil, total and labile carbon (TOC, C_L), along with the carbon management index (CMI) and δ¹³C were evaluated. Pot test showed that PC₁₀₀ yielded the best (g pot⁻¹) lettuce biomass (3.0) > DC₁₀₀ and RC₁₀₀ (2.5 and 1.6) ≈ chemical reference (3.8). A similar pattern was detected at 50% (g pot⁻¹): PC₅₀ (2.9) > DC₅₀ (2.7) > RC₅₀ (2.4). N-RAE (%) reflected this pattern: PC₁₀₀ (60) > DC₁₀₀ (21) > RC₁₀₀ (10) and PC₅₀ (76) > DC₅₀ (53) > RC₅₀ (52). Pot soil analyses showed composts well performed in TOC and CMI, in comparison to Ctrl (+42% and +13%), suggesting a positive impact on soil C amelioration. No significant differences were observed for δ¹³C distribution, suggesting the composts did not influence the microbic metabolism differently. These results indicated that the biomass harvested from the CWs can represent an interesting material for composting, combining carbon sequestration and nutrients recycling potential of these system, in addition to their wastewater treatment capacity.

Cylindrical Bristle Clusters (CBCs) provide a multi-species fish passage solution at sloped weirs. Configurations trialled to date (min. diagonal spacing between CBCs up to 0.17 m) were designed to facilitate passage of relatively small (e.g. < 30 cm) potamodromous species and may hamper the movements of larger bodied (e.g. > 40 cm) fishes, such as adult anadromous salmonids. Therefore, in this study, the hydraulic conditions created by an array of large diameter (0.13 m) CBCs positioned farther apart than in previous studies (min. diagonal spacing 0.29 m) was assessed to determine whether conditions would be suitable for facilitating the passage of small-bodied fish while also providing sufficient space for larger individuals to manoeuvre. Two experiments were conducted in an open channel flume. Experiment 1 quantified the hydraulic conditions created by a model Crump weir when unmodified and with CBCs installed in supercritical flow (Fr 1.23–3.01) on the 1:5 downstream sloping face under a low (0.08 m³ s⁻¹) and high (0.23 m³ s⁻¹) discharge. Patches of low water velocity were created in the wake of the CBCs, and the median (time and space averaged) velocity was reduced under both low (30.1%) and high (22.3%) discharge. Based on estimated burst swimming speeds of two common European species, the roach (Rutilus rutilus) and brown trout (Salmo trutta) (0.16 m long, swimming at 15.1 °C), this reduction in velocity would facilitate upstream passage. Experiment 2 documented the vertical velocity profile and shear stress characteristics (a measure of turbulence) within the CBC array. Unlike in Experiment 1, the CBCs were installed on the flat base of the flume and under subcritical flow (Fr = 0.31) to generate sufficient water depth. The velocity was reduced (up to 22.5%) at depths that did not exceed (> 2 cm above) the height of the bristles. Above these depths, velocity was (up to 14.6%) higher compared to open channel conditions upstream of the CBC array and a vertical shear layer was evident. As the main hydraulic benefits of CBCs occur at depths that do not exceed the bristles, their height should be tailored to site specific conditions (e.g. size of target fish species and/or depth of water at infrastructure). Field-based research is needed to determine velocity reduction at longer weirs and under a wider range of flows than can be tested under flume conditions. How the hydraulic characteristics of submerged CBCs differ from those described here with those that occur in the field when installed on a steep sloping weir under supercritical flow should be further investigated.

In face of sea-level rise and increasing risks for storm impacts on shorelines, there is a growing demand for developing nature-based flood defenses, for example by restoring or creating salt marshes in front of engineered structures such as dikes. However, salt marshes can only optimally provide flood defense if their sediment beds are erosion resistant, even under very high flow velocities. It remains unknown how fast sediment strength develops in marshes restored or created for nature-based flood defense. Therefore, this study investigated how 1) sediment type, 2) tidal drainage depth and duration, and 3) pioneer vegetation species drive the development rate of sediment strength. A controlled experiment was set up with pots filled with two sediment types, which were either left bare or planted with Spartina anglica or Scirpus maritimus, two dominant salt marsh pioneers in NW Europe. All treatments were subjected to four different tidal regimes with different tidal drainage depth and duration. The results showed that sandy mud (with a 37% silt and clay fraction) led to much stronger sediments than fine mud (with a 77% silt and clay fraction). Sediment strength was higher in the treatments with deeper tidal drainage depth and longer drainage duration. The presence of vegetation increased sediment strength and this effect was stronger with Scirpus maritimus than with Spartina anglica. Plant roots increased sediment strength directly, and the presence of vegetation also seemed to increase sediment strength through enhanced evaporation and transpiration. From these results it can be concluded that to restore or create erosion resistant salt marshes for flood defense, it is essential to ensure that marshes can form at relatively high elevations from well-draining sand-mud mixtures, thereby also ensuring vegetation growth.

Sediment supply downstream of dams through control techniques of reservoir sedimentation is attracting attention for promoting both sustainable water use and river ecosystem restoration. Sediment sluicing is a sediment control technique expected to recover natural sediment regimes because it allows sediment from an upstream reservoir to pass through a downstream dam during high flows. However, only a few studies have evaluated the restorative effects of sediment sluicing. We evaluated the restoration effects of sediment sluicing on macroinvertebrate assemblages in a dammed river using a before–after control–impact design. After sediment sluicing operations, the taxa richness of macroinvertebrates increased at sites downstream of the dam under free-flow conditions, where the reservoir was completely lotic and large amounts of sediment were transported. Meanwhile, there were few changes in macroinvertebrate richness and composition at sites downstream of the dam without sluicing operations and at the dam where sluicing was operational but did not achieve free flow. The increase in taxa richness was probably due to sediment supply from sluicing operations. As most taxa that increased in response to sluicing operations were grazers, sediment supply could provide benefits through indirect impacts via food resources. Negative impacts were observed on macroinvertebrates because of the first flush of excess sediment supply during the first sluicing; however, the extent of impact was spatiotemporally limited. Sluicing operation would be better than other sediment control techniques. This study suggests that sediment sluicing is an effective restoration method for not only macroinvertebrate assemblages but also for ecosystem functions.

Water infiltration plays an important role in water hydrological processes, especially in precipitation-limited drylands. Biocrusts are ubiquitous in drylands which had significant influence on soil water infiltration in most cases, while grazing may affect water infiltration by the disturbance of biocrusts. Toward this end, the effects of grazing on surface land cover characteristics, soil physical attributes, and water infiltration rates were measured at non-grazed area (NG) and five intensities grazing slope grasslands (G1, 2.2 goat·hm⁻²; G2, 3.0 goat·hm⁻²; G3, 4.2 goat·hm⁻²; G4, 6.7 goat·hm⁻²; G5, 16.7 goat·hm⁻²) by conducting a fenced grazing experiment. Results showed that surface cover characteristics and soil physical properties changed significantly after grazing, especially at the G5 grazing intensity. Grazing decreased the vegetation coverage and biocrust thickness, while it increased biocrust coverage, bare soil coverage, surface roughness, and splitting index (SPLIT) of biocrust, and the influence was related to grazing intensities. Consequently, there was an increase in the water infiltration rate of 24%–47% after G1-G2 grazing, and the stable infiltration rate and average infiltration rate increased about 56% and 33% at G1, respectively when compared with non-grazed area. The infiltration rate decreased sharply when the grazing intensity was below G3, and infiltration rates remained stable when the grazing intensity was over G3. Improvement of soil infiltration under light grazing after one year was due to the changes of soil surface characteristics and biocrusts characteristics. Among them, disturbance, biocrusts thickness, soil surface roughness together explained the increase of initial infiltration rate, and 0–5 cm soil bulk density, biocrust coverage and its thickness together affected the stable infiltration rate. This link points to the possible use of grazing on the slope grassland with widespread biocrusts and their potential use for the management of soil water in drylands ecosystems.

Green roofs provide several ecosystem services that may aid cities in locally adapting to climate change such as the regulation of local air temperatures by evaporative cooling and the limitation of stormwater damage by retention of precipitation water in the green roof substrate. In the past, water storage levels in green roofs have often been inferred from substrate moisture measurements. Here, we test the applicability of recession analysis to quantify water storage levels from the temporal decrease in evapotranspiration during dry periods using latent heat flux densities measured by the eddy covariance (EC) method over the time period of 2015–2020. We found water storage levels to vary between 0.1 and 35.8 mm (median of 4.2 mm). The water storage capacity of 35.8 mm was larger by a factor of ≥27 compared to modelled values for paved urban surfaces (1–1.3 mm). Seasonal variation of water storage levels inferred by EC was characterised by an energy-limited evapotranspiration regime in winter and water limitation during summer. The increase in the green roof vegetation coverage over time resulted in a slight increase in the capacity of the green roof to store water. Water storage levels calculated from in-situ substrate moisture sensors found very similar results compared to the EC recession analysis. Multi-year eddy covariance observations prove a useful tool to quantify and monitor variation of water storage levels in an extensive green roof, as long as evapotranspiration is not limited by available energy.