Ecological Engineering最新文献

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.

Sediment deposition in coastal wetlands is key to maintaining marsh elevation during periods of sea level rise. Deposition occurs naturally during storms to increase marsh elevation or when dredged sediments are intentionally introduced during restoration to build elevation capital. The deposition of sediments containing iron sulfide compounds (FeS and FeS₂) under natural or managed scenarios alters biogeochemical cycles, including the potential to induce dramatic declines in soil pH under prolonged oxidizing conditions. This 20-week mesocosm study investigated FeS and FeS₂ dynamics under continuously flooded, tidal, and drought treatments following a simulated natural or restoration deposition event by placing hyposulfidic sediment onto the marsh soil surface. The introduced FeS and FeS₂ rapidly oxidized (< 21 days) after sediment deposition across all treatments, followed by declining oxidation reduction potentials, increasing dissolved Fe concentrations, and subsequent FeS and FeS₂ re-precipitation in flooded and tidal treatments. Nominal pH declines occurred in flooded and tidal treatments due to re-precipitation of FeS and FeS₂ minerals. Conversely, pH decreased 1–2 units under simulated drought conditions. Observational and modeling results indicate that S⁻² generation limited the rate of FeS and FeS₂ formation following sediment deposition in alignment with previous field studies. Results suggest that the deposition of hyposulfidic sediments during storms and restoration events pose minimal risk of acidification when prolonged saturated conditions are present. However, short term FeS and FeS₂ oxidation and re-precipitation likely occur following both natural (over wash) and managed (restoration) scenarios as the deposited sediments achieve new dynamic biogeochemical equilibria. Coastal resource managers can use these results to ensure restoration projects maximize positive restoration outcomes while minimizing the risk of soil acidification through the informed management of FeS and FeS₂ minerals.

Microplastic pollution represents a global challenge that threatens ecosystems and human health. Because of this, there has been an increased interest in evaluating the use of phytotechnologies as a natural alternative for the removal of microplastics in water bodies. This study assessed the microplastic removal by Floating Treatment Wetlands (FTWs) consisting of linear arrays planted with Cyperus papyrus and Pontederia sagittata, installed in two urban ponds (“Pond 1” and “Pond 4”) located in the center of the city of Xalapa, Veracruz, Mexico. The results indicated that the two linear arrays of FTWs in Pond 1 (FTW1 and FTW2) efficiently removed microplastics in water column and sediments, with total removal rates of 82.4% and 81.1% respectively, despite having a high initial microplastic concentration. On the other hand, the effectiveness of the two FTWs in Pond 4 was mainly attributed to the first line of plants (FTW3), where the highest removal rates were observed, showing 61.6% in water column and 72.6% in sediments. However, the total removal of the two lines was 64.6% in water and 48.8% in sediments. C. papyrus and P. sagittata plants strongly retained microplastics in their roots, with concentrations of 16.4 and 11.9 mg/g respectively for FTW1 and FTW2 in Pond 1, and 2.1 and 6 mg/g for FTW3 and FTW 4 in Pond 4. These results suggest that the main removal microplastic mechanism was root retention, which facilitates microplastic removal from the aquatic environment by periodical root harvesting. Therefore, the crucial role of roots in the stabilization and reduction of these pollutants is highlighted. This study represents the first report in Mexico on the efficiency of FTWs in removing microplastics in urban water bodies.

Green infrastructure (GI) systems have been employed as an environmentally sustainable alternative to treat stormwater in urban areas, and many previous studies indicated GI practices are effective at reducing stormwater runoff flows to watersheds by rerouting flows through vegetation and soil. However, little is known about the effects of maintenance on GI performance. This study evaluated the maintenance efficiency for four GI designs (bioretention, grass channel, compost-amended grass channel, and bioswale) receiving the same weather conditions and pollutants along Lorton Road, Fairfax County, VA, USA., based on water-quality performance and economic costs. Seven regular maintenance events and a forebay restoration were monitored from 2018 to 2022. Stormwater quality performance among these four GI practices before and after these in-field maintenance activities was assessed on the load reduction of dissolved organic carbon (DOC), total dissolved nitrogen (TDN), total suspended solids (TSS), and runoff over four years. The average runoff reductions over all monitored storms were 74%, 85%,63%, and 68% for bioretention, grass channel, compost-amended grass channel, and bioswale, respectively. Over these maintenance events, the mean runoff reduction of all monitored GI designs improved by 3% after maintenance, DOC mass load reduction increased by 41%, TDN mass load reduction improved by 21%, and TSS mass load reduction increased by 2%. All the pollutant and runoff reductions for swales improved after spring maintenance events, and monitored GI systems generally performed better after spring maintenance events, potentially due more to the vegetation growth than the maintenance work. Bioretention and compost-amended grass channel DOC load reductions were the only statistically significant GI performance improvements attributable to maintenance.