Evaluation of the effect of municipal solid waste disposal site activity on the quality of adjacent soil- Case study- Saravan Rasht dumpsite

One of the most important results of population growth, urbanization, and industrialization is the increase of urban waste. Accumulation of municipal solid waste produces toxic leachate that can transfer contaminants to the soil and alter its quality, especially in vulnerable forest ecosystems. This study was carried out to determine the properties of the soil of the Saravan municipal solid waste disposal site that is located in a part of the Hyrcanian forests, Rasht, Guilan province, which have been affected by the activity of the open dumpsite; Determining the minimum data set (MDS) and evaluating the quality adjacent soil to the dumpsite, the route affected by leachate and downstream lands, through soil quality indices such as simple integrated quality index (IQISA), weighted integrated quality index (IQIW) and Nemoro quality index using total data set (TDS) and MDS, and comparing them with each other.

Based on the distance from the disposal site, slope, height, and the route of leachate, from 32 sampling points with the same vegetation, a total of 32 composite samples were prepared in plots 10×10 from (five sub-samples from four heads and the middle by a polyethylene hand auger) a depth of 0-15 cm in June 2019.The soil properties including pH, clay, silt, sand, available phosphorus (Pava), copper (Cuav), zinc (Znav), and iron (Feav), total nitrogen (N), cation exchange capacity (CEC), electrical conductivity (EC), organic carbon (OC), basal respiration (BR), microbial biomass carbon (MBC), the metabolic quotient (qCO2) and enzymatic activities of Urease (UR) and alkaline phosphatase (ALP) were measured. One-way analysis of variance (ANOVA) and independent comparison tests was used to compare the results of the soil samples in areas exposed to dumpsite activities and control. Six properties were selected as MDS using principal component analysis (PCA). The models of the simple integrated quality index (IQIsa), weighted integrated quality index (IQIW), and the Nemoro index were used to determine soil quality. One-way ANOVA and Duncan’s multiple range tests were used to compare the mean soil quality indices in the areas around the disposal site, leachate-affected route, and downstream lands. The possible relationship between chemical, physical and biological properties was investigated by calculating Pearson’s correlation coefficients.

The results showed that the value of soil properties including Feav, EC, Pav, N, Znav, Cuav, OC, BR, MBC, the enzymatic activities of UR and ALP is significantly different from the control (p < 0.01). The properties of Pav, Cuav, EC, clay, silt and MBC were selected as MDS, which can describe 73% of changes in the soil quality. Evaluation of the soil quality through Nemoro index, using MDS and TDS (IV and III, respectively) at different distances from the dumpsite was the same as the control. The values of IQIsa and IQIw using MDS did not show any significant difference with the control in all routes exposed to the activity of the disposal site, except around the dumpsite. However, the degree of soil quality through the overall average IQIsa and IQIw, using MDS in all areas exposed to the dumpsite was the same as the control. The results of IQIsa and IQIw, using TDS were so different so that the values of IQIsa and IQIw, using TDS in the path of leachate and lands downstream of the disposal site showed a significant difference with the control (p < 0.01). Also, the quality degree through the overall mean value of IQIsa and IQIw, using TDS (III and IV, respectively), around the disposal site and the path of leachate were different from the control (II and III, respectively).The Saravan municipal waste disposal site is located in an area, with a Mediterranean climate, with high relative humidity and rainfall. It has increased the possibility of leachate production. On the other hand, with the leachate flowing along the sloping path of 15%, especially after each rainfall in the area, the soil is contaminated by leachate and transfer downstream. Also, Leachate is discharged from the disposal site downstream, into the river, which is used to irrigate agricultural land downstream of the dumpsite. The results of changes in IQIsa and IQIw by TDS can indicate the possible consequence of the leachate effect from the disposal site on the path to the soil of downstream farms.

According to the objectives of the research, it seems that soil properties including Feav, Pav, EC, N, BR, MBC, and the enzymatic activities of UR and AIP have been affected by the activity Saravan solid waste disposal site. Investigating the results of the quality indices using MDS and TDS showed that IQIsa and IQIw, using TDS can better represent the effect of waste disposal site activity on soil quality. Significant differences of the IQIsa and IQIw, in the leachate route and downstream agricultural lands with the control can probably be due to the effect of leachate and leaching of soil around the leachate route and its transfer downstream. Considering the same quality results in the area exposed to the activity of the disposal site with the control through the Nemoro index, using MDS, TDS, it can be concluded that Nemoro index does not have the required sensitivity to describe the effect of waste disposal activity on the quality adjacent soil. This study showed that the change of use of the forest area to waste disposal site affected its soil quality in the path of leachate and downstream lands. Therefore, to protect the areas of Hyrcanian forests in the Saravan region and to prevent the reduction of soil quality in the region, taking the necessary measures to separate the municipal solid waste from the origin, to establish leachate collection systems and treatment of leachate before flowing in the forest areas should be carried out.