The effect of the Zayandeh Rood Dam on the water quality and abundance of macroinvertebrates on the bottom of the Zayandeh Rood River

Master's Thesis of Fisheries Aquatic Ecology

Abstract

Rivers, as one of the most important water resources, are very vulnerable to human activities. Creating reservoirs and dams is one of the oldest forms of human intervention in aquatic ecosystems. Despite the many benefits (hydroelectric energy production, flood control and water level regulation), dams also have the potential to change the population of aquatic organisms. The construction of dams causes important changes in the flow regime, transport and transfer of suspended particles, river morphology, water temperature and chemical conditions, especially in the downstream of rivers. Large benthic animals are affected by the changes made in the habitat. The effect of dams on benthic communities is very important because of the role they play in the functioning of the river ecosystem. Zayandeh Rood River is one of the largest rivers of Iran and the most important river flowing in the central plateau of Iran, whose flow regime is influenced by the Zayandeh Rood Dam. In order to evaluate the ecological effect caused by the construction of the Zayandeh Rood Dam on the biological communities and water quality of the Zayandeh Rood River, the number of 6 stations (Khorsonek and Oregan stations before the dam, Chadegan station near the downstream of the dam, and Hojatabad, Markadeh and Horeh stations downstream of the dam) were selected and the quality of water and sediments of the river were quantitatively examined from July 2012 to June 2013. Sampling of water and sediments of the river was done in each station with 3 repetitions and in time intervals of 45 days (twice in each season). The parameters of temperature, dissolved oxygen, nitrate, phosphate, BOD5, COD, EC and pH of water samples were measured by standard method. Biological indices including taxon richness, BMWP and ASPT as well as Shannon, Simpson and Margalef diversity indices were calculated for benthic communities. The results showed that the physical and chemical characteristics of the river water (except temperature) between the upstream and downstream areas were not affected by the dam structure and were mostly affected by seasonal changes. Also, the diversity indices including Ghan, Shannon, Margalf and Simpson diversity indices showed a significant decrease, especially in the station downstream of the dam, and a significant decrease in the stations downstream of the dam, which can be influenced by the dam structure. The density of many Kafzian families in the dam station showed a significant decrease. In the stations downstream of the dam, in addition to reducing the density, the types of organisms also changed and were replaced with specimens adapted to the new conditions. Also, BMWP and ASPT biological indicators respectively showed the water quality status in the station below the dam similar to polluted and suspected to moderately polluted waters. This decrease in quality is not caused by organic pollution and is more due to the change in the density and diversity of aquatic families.

Key words: Dam, Zaindarud, biological indicators, large aquatic organisms, water quality.

Running waters or rivers are one of the most important water sources that play an important role in providing water needed for various agricultural, industrial, drinking and electricity production activities. Knowledge of the quantity and quality of water resources is one of the important needs in planning and developing water resources, its protection and control. It is obvious that in order to know the quality of water sources and to produce comprehensive and complete information, permanent monitoring should be done. Because having comprehensive, correct and reliable information with appropriate time periods can be an important factor in decisions and policies [13].

Rivers carry not only water, but also a lot of sediment, soluble minerals, and plants rich in food from the waste of living and dead plants and animals downstream. The changes of a river are not only dependent on the different lands it passes through, but also related to seasonal changes and the difference between dry and wet years. The annual and seasonal changes in the volume of water, sediments and nutrients washed into a watershed may be very large, especially in dry areas where a large part of the annual precipitation falls in several storms [24].Today, the introduction of all kinds of industrial, urban, domestic and agricultural wastewaters and their unprincipled disposal on the one hand and the creation of dams, changing the course of rivers and transferring water between water basins on the other hand cause many problems in watersheds, which include the death of aquatic animals, contamination of underground water sources, and pollution of rivers and lakes [28, 58]. Exploitation of natural resources to the extent that the environment can bear does not cause irreparable damage to the ecosystem [34], but it leads to certain changes in it [34].

The vastness of the country, the diversity of climatic conditions, the inappropriate distribution of areas of residence and activity, the physical view of the country's decision-makers towards the phenomena, the tendency of public attention to short-term benefits and the like, all joined hands to convince managers and public opinion that the only way to fight drought and water scarcity is to build dams. It is numerous on all the water streams of the country. The creation of reservoir dams and other water structures is one of the activities that, despite economic and social benefits, can cause irreparable damage to biological resources and water ecosystems [59]. Since every river is a special and unique phenomenon due to its specific flow pattern, the land it flows in, and the species that depend on it, the design and pattern of dam exploitation as well as its consequences on the river and the ecosystems connected to it It is also special and unique. A large number of large dams, as well as all major dams in the world, have been completed in the last 6 decades, while the environmental consequences of a dam may not emerge until hundreds of years after its construction [24]. A dam can be considered a large, irreversible and uncontrolled environmental experiment. A dam breaks all the interconnected network of life in the river valley. Dams are the most important cause of the endangerment or extinction of a fifth of the world's freshwater fish. Dams endanger the lives of fish, amphibians, snails, insects, waterfowl and other river and wetland wildlife [79]. The dam as an obstacle in the riverbed affects the physical and chemical characteristics of the sediment. The construction of the dam as an obstacle to the movement and passage of floating objects has caused a disturbance in the natural regime of the river and effects such as the accumulation of sediments in the reservoir, the effect on underground water resources, the drying up of wetlands and swamps, the creation of high waves and dangerous floods due to the release of the flow, the creation of induced earthquakes, the accumulation of nutrients in the lake water and the phenomenon of nutrient enrichment of water, thermal layering and so on. follows [9]. The most important consequence among the thousands of complex and interconnected environmental disturbances of dams is that they scatter and fragment the river ecosystem, isolate the species population upstream and downstream of the dam, stop the migration of fish or the movement of other species [60] and undoubtedly reduce the number of species in the watershed. The reduction of benefits caused by the transport of nutrients due to flooding of rivers may be the single biggest harmful ecological consequence of a dam [24]. The creation of dams, through the influence on the water regime and flow bed in the area downstream of the dam, causes dramatic changes in the concentration of nutrients, the load of organic and mineral substances carried by the river, the amount of dissolved oxygen, changes in temperature conditions, and so on. creates and in this way affects the diversity of biological communities and species richness and sometimes causes irreparable damage to the river ecosystem [54]. Changes in habitat parameters such as slope, bed type, water flow speed, water temperature and climate changes can change the quantity and quality of biological communities in a flowing water ecosystem, evaluating the changes made in the population characteristics of these organisms can clarify the effect of each of the above parameters [40, 68]. The water is flowing. Although more than half of the world's large river systems are affected by dam construction, there are very few biological studies that compare the river system before and after dam construction[80].