Constructed Wetlands for Water Quality Improvement: A Synthesis on Nutrient Reduction from Agricultural Effluents

Excess nutrients from agricultural settings contribute to surface water and groundwater impairment. Constructed wetlands have been widely used for water quality protection in various agricultural systems. We used a synthesis approach to document the performance of constructed wetlands for nutrient removal from a range of landscapes and geographic regions with the following objectives: (1) review the current use of constructed wetlands in agricultural applications, (2) summarize the nutrient removal efficiency of constructed wetlands, and (3) identify the geographic usage and costs associated with constructed wetlands. We reviewed over 130 publications and reports to characterize nutrient removal performance for the following types of agricultural effluents: cropland surface and subsurface drainage, and wastewater from livestock production, greenhouse, aquaculture, and hydroponic systems. Data from the reviewed studies indicate that constructed wetlands are efficient in protecting water quality in agricultural production settings. However, differences in constructed wetland characteristics reported by the studies suggest that standards are needed to ensure nutrient removal goals are met based on wetland design. Researchers should consider including basic performance parameters for constructed wetlands in published reports, including influent and effluent concentrations, hydraulic retention time, hydraulic loading rate, watershed to treatment wetland ratios, and plant species and relative cover. Future studies are needed to explore cost-benefit analyses to assess the feasibility and potential promotion of wetland incentive programs in various geographic regions and watershed nonpoint-source pollution goals for using these systems in agricultural settings. Keywords: Agricultural wastewater, Agricultural water quality, Aquaculture, Cropland runoff, Greenhouse, Hydroponic, Livestock, Review, Subsurface, Treatment wetland.

Evaluation of Different Methods to Assess the Hydraulic Behavior in Horizontal Treatment Wetlands

While there have been numerous studies on the rate and development of clogging in horizontal subsurface treatment wetlands (HSTWs) and, consequently, the effects on its hydraulic characteristics, research has not shown a clear understanding of the processes. The existing methods for measuring the impact of clogging provide limited information on the extension and degree of the phenomenon. This study aimed to evaluate the capacity of various measurement techniques to assess the degree and variation in space and time of clogging in HSTWs. Hydraulic conductivity at saturation (Ks) measurements were conducted using a newly implemented scheme, the drainage equation method, and traditional tracer tests, which were carried out in a full-scale HSTW system, located in Sicily, Italy, during 2019. After five years of operation, the results highlighted a severe decrease in Ks (<1000 m day−1) in the inlet zone (despite the fact that the filter gravel was replaced in 2017), a very high reduction of Ks along the central path inside the bed, a nonuniform flow through the HSTW, the presence of stagnant zones, and a reduction of the porosity of the bed gravel. Nonetheless, the mean values of the physical–chemical and bacteriological parameters at the hybrid treatment wetland (hybrid TW) outlet indicated that the partial clogging had no significant effect on the quality of the discharged water. Moreover, the results obtained using the different measurement techniques (in terms of both the Ks values and the flow distribution inside the bed) were consistent with each other and with results obtained previously for the same system. Finally, the most efficient combination of methods to assess clogging in HSTWs was identified.

Application of geophysical methods for the subsurface treatment of the Piekary highway junction in shallow mining terrain

The study presents the application of geophysical methods in the subsurface treatment of the A-1 highway in the area of the Piekary junction in the terrain of historic zinc and lead ore mining, in the northern part of the Upper Silesian Coal Basin in Poland (USCB). The study area was under threat of discontinuous deformations, mainly sinkholes. This threat resulted from the shallow exploitation of zinc and lead ores, as well as contemporary exploitation of coal seams at greater depths. An original methodology of subsurface treatment has been developed as an adaptation to the geophysical measurement results. The methodology uses the gravimetric method at the initial and final control stages, as well as the seismic and borehole georadar methods during the detailed evaluation stage. The results of the study allowed different categories of sinkhole hazard to be determined in the area of the Piekary junction. The scope of the liquidation works was selected to match the hazard levels. Blasting of varying intensities and the borehole injection of the filling material were performed. The combination of substrate treatment methodologies and highway construction protection systems have proved to be effective.

THE EXPEDIENCY OF APPLICATION OF HERBICIDES IN SEVAH SPRING WHEAT ON DIFFERENT BACKGROUNDS OF CHEMICALS WHILE MINIMIZING THE AUTUMN TREATMENT

Studies conducted in 1996-2017. on the black soil leaching-locenih forest-steppe of the Ob region in multi-factor stationary field experiment in Sibnica. Crops were cultivated in 4-full rotation: from 1996 to 2006 «steam-winter rye-wheat-wheat”; since 2007 winter rye was replaced with wheat:”steam - wheat - wheat - wheat». The mechanical treatment of soil in fields of crop rotations: 1) plowing in a couple of 25-27 cm, under the wheat (the second and third culture after pairing) is 20-22 cm; 2) subsurface treatment stands, Cibima in a couple of 25-27 cm, under a wheat - 20 to 22 cm; 3) minimum tillage cultivator «Step-UC» to a depth of 10-12 cm for all crops; 4) no autumn treatment. SASO of-attorney of the crops studied in the three backgrounds of chemicals - extensive, low-intensive and intensive. The high efficiency of herbicide treatment of spring wheat with a tank mixture of Puma-super and Elant - premium against the main types of weed vegetation is shown. Against the background of the use of herbicides for all years of research, there were no significant differences in the number of weeds in the variants with fertilizers and without fertilizers, as well as in the contamination of different variants of the main tillage. The average contamination of spring wheat crops in the grain-fallow crop turnover for 20 years of research on an intensive and low-intensity background in all variants of the experiment did not exceed the threshold of harmfulness. On the background without herbicides the number of weeds was steadily higher than in the horn of harmfulness in all embodiments, the main processing of the soil. The maximum of weeds has always been noted in the variant without fall tillage - from 12.6 % in the first crop rotation to 35.3 % in the third, and the minimum - for plowing (from 7.1 to 21.8 %). The maximum biological and economic efficiency of herbicide treatment was observed on an intensive background in the tillering phase of spring wheat (92.5 %). It is shown that the use of herbicides on spring wheat without fertilizers and fungicides in the conditions in Western Siberia is advisable only for grain predecessors with a planned yield of at least 15 t/ha.

A soil column study to evaluate treatment of trace elements from saline industrial wastewater

Industrial wastewater from the flue gas desulfurization (FGD) process is characterized by the presence of trace elements of concern, such as selenium (Se) and boron (B) and relatively high salinity. To simulate treatment that FGD wastewater undergoes during transport through soils in subsurface treatment systems, a column study (140-d duration) was conducted with native Kansas soil and saline FGD wastewater, containing high Se and B concentrations (170 μg/L Se and 5.3 mg/L B) and negligible arsenic (As) concentration (∼1.2 μg/L As). Se, B, and As, and dissolved organic carbon concentrations and organic matter spectroscopic properties were measured in the influent and outflow. Influent Se concentrations were reduced by only ∼half in all treatments, and results suggest that Se sorption was inhibited by high salinity of the FGD wastewater. By contrast, relative concentrations (C/Co) of B in the outflow were typically &lt;10%, suggesting that B sequestration may have been enhanced by higher salinity. Unexpected elevated As concentrations in the outflow (at &gt;150 μg/L in the treatment with labile organic carbon addition) suggest that soils not previously known to be geogenic arsenic sources have the potential to release As to groundwater in the presence of high salinity wastewater and under reducing conditions.

Influence of receptions of the main processing of the soil, fertilizers and means of protection of plants on a contamination, agrophysical properties of the soil and efficiency of barley

The field experiments with barley of multiserial Vakula variety were conducted on gray forest soil of Kama region of theRepublic of Tatarstan. This experiment was carried out to identify the responsiveness of barley for fertilizers, methods of the basic soil cultivation and plant protection products. On average over three years of our research, the highest yield of barley (3.95 tons per hectare) was obtained in the flattered soil tillage and carrying out the calculated fertilizernorm in the way, when we used the seed protectant Stinger for pre- treatment of the soil. The yield was a little lower (3.88 tons per hectare), when we used Binoram for pre-sowing seed treatment, Albit was in the third place (3.80 tons per hectare), the fourth - Rizoagrin (3.65 tons per hectare), and the fifth - control (3.42 tons per hectare). The lowest barley yield (2.46 tons per hectare) were obtained on the background when not fertilized subsoiling tillage without the use of plant protection products. The use of seeds for incrustation, treated by Stinger chemical fungicide, increased the yield to 4.0 centner per hectare, compared with the control. When we used moldboard plowing, the yield declined in control to 4.7 centner per hectare and at fertilizered background to 4.9 centner per hectare, and at KSN soil treatment to3-5.3 centner per hectare. In arid 2010 the highest barley harvest was obtained at KSN-3 soil treating, on the second place is subsurface treatment and the third is plowing. Modern energy-saving methods of the basic soil cultivation, treating the calculated norms of fertilizers and use of plant protection products contribute to the production of planned productivity, saving fuel and lubricants, but they are unable to maintain phytosanitary conditions in barley fields within economic threshold. Taking inro account above-mentioned and the current state of agriculture in the steppe of the Volga region, it is necessary to alternate basic soil treatment methods, application of calculated norms of fertilizers and use protectants and biofungicides for pre-sowing treatment, considering fitoekzamination of seeds.

Influence of groundwater composition on subsurface iron and arsenic removal

Subsurface arsenic and iron removal (SAR/SIR) is a novel technology to remove arsenic, iron and other groundwater components by using the subsoil. This research project investigated the influence of the groundwater composition on subsurface treatment. In anoxic sand column experiments, with synthetic groundwater and virgin sand, it was found that several dissolved substances in groundwater compete for adsorption sites with arsenic and iron. The presence of 0.01 mmol L−1 phosphate, 0.2 mmol L−1 silicate, and 1 mmol L−1 nitrate greatly reduced the efficiency of SAR, illustrating the vulnerability of this technology in diverse geochemical settings. SIR was not as sensitive to other inorganic groundwater compounds, though iron retardation was limited by 1.2 mmol L−1 calcium and 0.06 mmol L−1 manganese.