The Effect of Multi-Years Reclaimed Water Irrigation on Dryland Carbon Sequestration in the North China Plain

Reclaimed water is an alternative water source which could alleviate the shortage of water resources in agricultural systems. Many researchers have studied the effect of reclaimed water on soil environment, crop yield, etc. However, carbon sequestration in reclaimed water irrigated agricultural systems is less studied. This study investigates methane uptake and photosynthesis in reclaimed water irrigation systems contributing to carbon sequestration estimation and analyzes the important factors impacting them. The results show that CH4 uptake is related to soil water-filled pore space (WFPS) with a quadratic and it has the highest uptake when WFPS is between 40 and 50%. Long-term reclaimed water irrigation could significantly decrease (p < 0.05) CH4 uptake and macroaggregate stability in the topsoil. However, reclaimed water had no significant impact on photosynthesis in comparison. The type of fertilizer is an important factor which impacts CH4 emission from soil; urea had a lower CH4 uptake and a higher CO2 emission than slow-released fertilizer. Overall, reclaimed water irrigation could effectively decrease soil carbon sequestration. A soil wetted proportion level of 40–50% was recommended in this study for favorable methane oxidation. Slow-released fertilizer in reclaimed water irrigated agriculture could better control soil carbon emission and soil carbon absorption.

Risk of Secondary Soil Salinization under Mixed Irrigation Using Brackish Water and Reclaimed Water

The use of unconventional water resources is an effective way to alleviate the scarcity of freshwater resources, especially in areas where freshwater is scarce, but reclaimed water is abundant. To explore the reasonable utilization of brackish water and reclaimed water, a pot experiment was carried out to study the risk of secondary soil salinization. The experiment set two salinity levels of brackish water, four mixed irrigation ratios of brackish water and reclaimed water, and freshwater irrigation as the control. The results showed that: (1) Soil moisture content, salt content, pH, ESP, and SAR decreased with the increase in the proportion of reclaimed water in the mixture. (2) Soil exchangeable Ca2+ content under mixed irrigation was higher than that of brackish water irrigation and reclaimed water irrigation. The content was especially significantly higher under the 1:2 mixed irrigation with brackish-reclaimed water. With the increase of the proportion of reclaimed water in the mixture, soil exchangeable Na+ content decreased, and a significant difference was found between treatments. The soil exchangeable K+ decreased at first and then increased, while the soil exchangeable Ca2+ increased at first and then decreased. The trend of the change of soil exchangeable Mg2+ content was similar to that of soil exchangeable Ca2+ content. (3) Based on the soil pH value, there was no risk of soil alkalization in all treatments. Based on ESP, ESP was less than 15% under freshwater irrigation, brackish (3 g/L)-reclaimed water 1:2 mixed irrigation, and reclaimed water irrigation, indicating no risk of alkalization. However, other treatments may cause soil alkalization. (4) At 3 g/L of brackish water, there was a salinization risk when the proportion of reclaimed water in the mixture was less than 1/2, but there was no salinization risk when the proportion was greater than 1/2. At 5 g/L of brackish water, there was a salinization risk under mixed irrigation. Therefore, the mixed irrigation of brackish water and reclaimed water had the risk of secondary soil salinization, and the appropriate salinity and mixing ratio should be selected.

Essential oil and linalool contents in basil (Ocimum basilicum) irrigated with reclaimed water

Essential oils (EO) are volatile compounds with complex chemical compositions that are derived from the secondary metabolism of aromatic herbs. There are several applications of EO in the industrial and medical sectors. Basil (Ocimum sp.) is one of the most important EO-producing aromatic herbs. In this study, EO content (EOC) and linalool content (LC) in basil irrigated with reclaimed water were investigated. Plant development parameters, nutrient absorption and crude protein (CP) content were also evaluated. The experiment was conducted in a greenhouse, with five different treatments and five repetitions each. Compared with treatments only using water, the results of those with reclaimed water irrigation showed higher nutrient absorption, CP contents (in their foliar tissue), length of plant branches, foliar biomass weights, and EOC and LC. EOC reached up to 0.58% of the dry biomass and LC was up to 5.84% of EO mass. In practice, it is estimated that around 5.8 kg of EO and 0.34 kg of linalool can be obtained from one ton of dry basil biomass.

Effects of Reclaimed Water Irrigation On The Soil Characteristics And Microbial Populations of Plant Rhizosphere

In this paper, the effects of irrigation with different water quality on the soil characteristics of 8 kinds of garden plants were analyzed. The results showed that soil pH (ranging at 7.76–8.73) had no significant difference in different soils compared with the contrast treatment. Under the reclaimed water irrigation, the content of soil total salinity, chloride ions and water soluble sodium in soil of most plants was averagely 160.3%, 83.3% and 67.5% higher than that of tap water, respectively. The influences of reclaimed water irrigation on soil nutrients were changed with the types of plants. The content of soil organic matter and the available potassium showed no significant differences in most plants. Compared with the tap water irrigation, the content of alkaline nitrogen in in 5 plants increased (averagely 25.8%) after 5-year irrigation with reclaimed water. In terms of soil microorganism, the increase of soil microbial population, including bacteria, fungus and Actinomycetes, has been promoted by different levels of reclaimed water irrigation, showing increasing trend with the increasing content of reclaimed water from 0%, 50–100%. Moreover, the number of bacteria and fugus is closely related with the content of soil organic matter, available potassium and effective phosphorus. However, the number of Actinomycetes is determined by the content of available potassium.

Characterizing the Variation of Dissolvable PAHs in Receiving Water in a Reclaimed Water Irrigation Region

Long-term wastewater and reclaimed water irrigation systems constitute the major processes in local water circulation, which concomitantly introduce plenty of undesirable substances that can threaten water quality, ecosystem functions and human health. At the Southeast Reclaimed Water Irrigation Region (SRWIR) of Beijing, wastewater irrigation was adopted from 1969 to 2002, and second-treated effluents (reclaimed water) has been used thereafter. Polycyclic aromatic hydrocarbons (PAHs) were the most ubiquitously detected contaminant in wastewater and reclaimed water and are reported to be carcinogenic. Hence, we measured the concentrations of dissolved sixteen United States Environmental Protection Agency (USEPA) priority PAHs in surface water and groundwater at the SRWIR to characterize their spatial and temporal variations, and to clarify the role of reclaimed water to natural water. The concentration of 16 individual PAHs in reclaimed water, rivers and groundwater varied from 339.4 to 636.2 ng/L, 359.1 to 3,435.0 ng/L and 216.5 to 488,205.2 ng/L, respectively. The lower aromatic rings of PAHs prevailed in aquatic environments rather than the higher ones. Thereinto, naphthalene was the predominant isomer within the highest concentration reached to 486,600 µg/L. The groundwater samples had higher PAHs concentrations at Tongzhou district which attributed to the higher vulnerability of aquifer. Additionally, strong correlations between PAHs and total nitrogen, nitrate, dissolved oxygen and electrical conductivity suggested those potential factors affecting the photo degradation and/or biodegradation of PAHs. The relationship identified between PAHs concentrations and physical and chemical indices would help us to enhance the understanding migration and transformation of PAHs spatially and temporally, enable us to assess the potential risks of the environmental pollutants to aquatic organisms and human water supplies.