Environmental impact assessment of salt harvesting from the salt lakes

Urmia Saline Lake, USL which is registered as an international park by the United Nations, has suffered hypersalinity and serious dryness in recent years. Increasing the dryness trend has been led to a great tendency, especially by private sectors to harvest salt from different parts of the bed sediments. During this study the four- step process was used for environmental impact assessment of such a large scale salt harvesting activities with specialized Folchi matrix and enriched by data on heavy metal concentrations in the limited number of sediment samples. Impact analysis using matrix showed that the most significant impacts were on environmental components, namely “land use”, “gradient and topography of the lake bed” and “hydrology and lake water quality” with score values of 73.22, 73.21 and 72.45, respectively. The mean concentrations of As, Cd, Cr, Hg, Pb, Ni and Zn in salt and sediment samples were 15.2±8.8, 0.05±0.047, 15±8.2, 0.54±0.3, 11.9±6.28, 15.4±9.56 and 22.3±13.66 mg/kg, respectively. The higher concentration of arsenic and lead in comparison with earth crust averages, warns that dispersion of salt particles from storage piles may affect local people’s health. This study provides readers and authorities with environmental impacts of salt harvesting from unique saline Lake of Iran, presents effective management options such as stopping any unlicensed and unrestrained salt harvesting activities on the USL bed, avoiding deep excavations, minimizing accumulation of piles to prevent the diffusion of salt particles etc. and also specialized the Folchi matrix for application in similar projects.

Keywords: Surface mining, Environmental consequences, Folchi matrix, Heavy metals, Iran

Introduction

The exploitation of natural resources and mines has its environmental aspects that can lead to irreversible degradation of the environment, without observing the principles of sustainable development. This issue becomes even more significant when the mining area is considered environmentally important and vulnerable. Problems associated with mining operations include destruction of landscapes, agricultural and forest lands; air and water pollution; noise, ground vibrations from blasting, and air blast; transport; reclamation; waste utilization; and subsidence etc. [1].

Salt after iron ore is the most widely utilized non-energy mineral. The chemical sector (chlor alkali, soda ash, etc.), de-icing, human consumption, animal feedstuffs, water treatment, and industrial applications are the main consumers of salt. Total world production of salt is about 300 million tons which China (68 million), the United States (42 million), India (29 million), Germany (13 million), Canada (13 million) and Australia (12 million) are the top six salt producers in the world [2]. There are three basic salt production methods in the world including: seawater solar evaporation or inland brines, brine extracted through solution mining, and mined rock salt. More than a third of the world’s salt production comes from evaporation of sea water by solar energy [3]. However, there is a less known and irregular method for salt production; direct salt harvesting from surface sediments of saline lakes. Desiccation of saline lakes and surface mining on the dried bed of these lakes can be economically feasible. However, a major problem with this kind of salt harvesting is its unknown environmental and health impacts. These lakes represent 44% of the volume and 23% of the area of all lakes on earth and are among the most important natural resources in the world with considerable aesthetics, economic, recreational, ecological, scientific and cultural values [4]. During recent years, these lakes and their surrounding ecosystems have been damaged by some of the natural processes and human activities. Harvesting of minerals such as halite, trona, calcite, gypsum, borax, lithium and uranium requires various surface mining activities, including the construction of causeways, evaporation ponds, barriers, equipment and storage sites for tailing materials and other physical structures and heavy vehicles commute, may cause great environmental discomforts in the region [5, 6] and destroy a core part of lakes aesthetic appearance [7]. The mining damages are rarely rehabilitated after mining has ceased, so the lake surface becomes disfigured forever [8].

To avoid environmental degradation, EIA -as an environmental management and decision making tool- is necessary to predict, assess and reduce adverse environmental and social consequences of mining projects in the ecosystem of saline lakes [9]. Various methods are used for assessment of environmental impacts including Adhoc method, checklists, matrices, networks, overlays, environmental index using factor analysis, cost/benefit analysis, and predictive or simulation methods [10]. Among these methods, matrices provide some advantages such as ease of use, flexibility in matrix dimensions and consideration of both project activities as well as environmental components. Because of these features, the matrices are of the popular methods used in the EIA [11].

A literature review reveled that in spite of salt production from seawater or saline lakes in different parts of world, researchers have not treated the environmental impacts of such activities in more details. One of the studies is related to Great Salt Lake (Utah, USA) which is the fourth largest terminal saline lake in the world and about 2 million tons salt from this lake is harvested annually [12, 13]. The environmental impacts of the proposed “Great Salt Lake Solar Evaporation Ponds Expansion” project which was intended to expand the size of its operations to 119 mile 2 with construction of vast dike systems were evaluated in 2008. As reported, this project would result in the loss of too many acres of waters of the US and thereby imperils; the health of the ecosystem and the survivability of the organisms and wildlife. In sum, disturbance of natural values under the proposal due to adverse impacts on navigation and recreation purposes, increasing evaporation from lake with unknown effects on water quality, and cumulative impacts from other current development projects, has been immense recognized. [14]. The applicant for the proposed project withdrew their application in 2015.

In the other study in Kenya, environmental issues and socio-economic problems emanating from salt mining at Magarini District, was investigated. The process was consisted of the capturing seawater in shallow ponds where the solar evaporates most of the water. During the study, 120 households and 12 institutions were selected and then, a questionnaire by interviews and focus group discussions was completed. The findings revealed several environmental impacts including corrosion of iron sheets, the freshwater salinization, temperature rising, deforestation, loss of pasture, air pollution, reduction of rainfall in the area, land degradation, and increased dustiness in the area [15].

The other EIA study regarding salt production activities has been conducted for new solar salt production facility at the Cape Cross Salt Pan, Namibia. The project involved the mining of natural rock-salt and the establishment of salt crystallization pans for salt production by solar evaporation.

According to the EIA report, the majority of the project’s potential negative impacts were of medium to low significance and mitigation strategies have been recommended. However, a number of impacts from the full project scope including loss of sandy gravel plain ecotone habitat and reduction in Cape Cross lagoon water levels were noted as potentially high significance impacts. To proceed project in an environmentally responsible manner, Phase 2 limited to a single grouping of crystallizer ponds up to a maximum extent of 100 ha on the alluvial fan. Full project scope (phases 3 and 4) which are related to construction & operation of additional groupings of crystallizers on the alluvial fan and accessory works were not recommended for environmental clearance due to the information uncertainties. Once the recommended studies have been completed to enable impact assessment with a higher degree of confidence, it may be appropriate for Gecko Salt to reapply for environmental clearance for the full project scope. Nevertheless, the proposed project has significant positive socio-economic impacts which contribute direct, indirect and induced economic benefits to the local and regional economy [16–19].

Direct salt harvesting from surface sediments is a usual activity in USL as the second largest saltwater lake in the world and the largest lake in Iran [20], which has experienced a dramatic shrinking of water level in recent years [21]. The USL contains an estimated eight billion tons of salt and is considered as a potential source of minerals with substantial amounts of magnesium, lithium and potassium [22]. Although, it seems that the harvesting and utilization of salt in USL can be a great opportunity for creating jobs and growing the economy of the region, but similar to other methods that have been used to mine minerals, is connected to the environmental concerns obviously. Salt mining projects in unique saline Lake of Iran are not subject to stringent environmental impact assessment. Until recently, there has been no reliable evidence about the environmental consequences of this project. Only one study has attempted to investigate the “Environmental Impacts of the Industrial Utilization Projects from Lake Urmia”, which was carried out by Geological Survey and Mineral Explorations Department of Iran [23]. The study only reviewed the relevant laws and regulations, health and environmental standards and description of the existing status of the environment in the study area. Our field surveys followed by local reports showed that digging the lake’s bed with loaders has changed the topography of the region and may disturb the natural flow of water and accelerate the lake’s desiccation. So, the present case study seeks to explain the environmental impacts of salt harvesting at USL. The major objective was to develop a specialized matrix for EIA of direct salt harvesting from salt lakes’ bed and sediments. Application of this method was evaluated about USL and determined how were close the predictions of method to the actual impacts of these activities. Also, this research was aimed to address the most significant impacts of project and also, to quantify those impacts. The findings should make an important contribution to the field of EIA for similar projects.

Materials and methods

Study area

The USL is located in the northwest of Iran between the provinces of East Azerbaijan and West Azerbaijan. There are three fields for salt extraction from deposits of USL bed, including Aq Gonbad, Gamichi and Pesyan (Fig. 1 ). In the present study, the environmental impacts associated with salt harvesting from mentioned fields were studied. These fields are considered as excellent salt source due to the remarkable thickness of sediments.