One of the three great seas of historic Armenia, Lake Sevan is a unique high-altitude freshwater lake, the most important natural resource and national treasure of present-day Armenia. While largely important from ecological, economic, and cultural perspectives, Sevan had been taken for granted and mercilessly exploited for many decades. The alarming trend of water level reduction forced the authorities to partially redirect two of the nearby rivers to the lake through tunnel projects in 1981 and 2004. Level stabilization alone, however, could not prevent continued ecological deterioration of the Lake Sevan. In July of 2018, an excessive algal bloom caused greenish discoloration of Sevan waters, alerting experts of yet another serious problem with water quality. The SevaMod project was initiated with a vision to provide solid, scientifically substantiated solution to this issue. We talked to the SevaMod project coordinator, German scientist Dr. Martin Schultze about the project, its initial results, and future outlook.
Text : IBiS Photo : UFZ
The Project “Development of a Model for Lake Sevan for the Improvement of the Understanding of its Ecology and as Instrument for the Sustainable Management and Use of its Natural Resources” (SevaMod) was operated from June 2017 to May 2019 by the Helmholtz Centre for Environmental Research – UFZ in partnership with the Institute of Hydroecology and Ichthyology of the National Academy of Sciences of RA and the Environmental Monitoring and Information Center of the Ministry of Nature Protection of RA (now Ministry of Environment). The project consisted of several components, but the core idea was to develop a long-term scientific instrument able to predict water quality dynamics for management purposes so that the bodies responsible for the lake management could make decisions based on scientific data. “The world began to realize that we cannot only make use of natural resources, but we also have to take care of them, so that the generations to follow will have a chance to experience it,” says Dr. Schultze.
Taking sediment cores
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After the initial surveys by the German scientists, year-round monitoring of water quality started through the monthly sampling of Lake Sevan waters. Temperature and oxygen concentration sensors were placed in the lake. These operations brought much deeper insight and understanding of the temporal and spatial dynamics of the lake’s physics and chemistry. The implementing team collaborated with the regional players, the administration of Sevan National Park and the Foundation for Restoration of Sevan Trout Stocks and Development for Aquaculture. The representatives of various EU projects, state officials, and the Embassy of the Federal Republic of Germany in Armenia also largely supported the project.
To build up the limnological characterization of Lake Sevan, the SevaMod project started with developing a one-dimensional (1D) physical model for Lake Sevan, which would describe the surface stratification and mixing processes of the lake, including heat distribution in both Big Sevan, which has a relatively shallow maximum depth of 35 meters, and the Small Sevan, which reaches down to 80 meters. The vertical temperature distribution is especially important in summer months due to the heating at the surface and insufficient exchange between shallow and deep layers resulting in a stable density stratification that prevents exchange between bottom and surface waters.
In science terms, this phenomenon is called thermal stratification, or layering. The warmer water, which is lighter, stays above the heavier colder water. Absence of substantial circulation and mixing prevents replenishment of deeper layers with much-needed oxygen, and all the organisms living there have to survive with the amount of oxygen that remains since the previous period of uniform temperatures and circulation. The sedimentation is another natural process correlated with stratification. Anything that enters the lake and grows or dies there eventually falls to the bottom and undergoes decay mediated by bacteria. As long as there is enough oxygen at the sediment-water interface, only a small flux of phosphorus, which is released by mineralization, gets back into the water body. Once the oxygen is depleted, large amounts of absorbed phosphorus are released from the sediment due to reductive conditions and spread into the whole water body when mixing resumes in winter. In the next spring, these nutrients induce massive growth in the well-lit surface waters and cause what is called algal blooming.
Measurements in sediment core
Theoretically, a three-dimensional (3D) model of the lake basin would collect much more information, but it would be exceedingly complex, resource-intensive, and very difficult to manage and sustain. Therefore, a 1D model was pursued since it would provide sufficiently reliable data, gain understanding and guide lake management in the right direction while fitting within the budget, timeframe, and scope of SevaMod. This model is also the cornerstone of providing projections for the effects of climate warming on Lake Sevan.
In support of the project, the Armenian partners collected all available water quality data from previous studies and state monitoring archives to understand longer-term trends observed before, and to assure the project team of the applicability of scientific approaches commonly used for other lakes. Another important step was the examination of samples of Lake Sevan sediment. None of the prior research projects focused on the concentration and the geochemical form of phosphorus in the sediments. Thus, the SevaMod team took Lake Sevan research to a new level never attained before and collected new data that can be used today but will also serve as a baseline for future comparisons. In Dr. Schultze’s words, “Our task is not only to do good science but to develop applicable solutions which can be transformed into technical and political actions to manage natural resources.”
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After preliminary analysis, the results of the Lake Sevan health assessment are concerning. Last July, when the bloom in the lake was quite extensive, a simple “white disk” test was carried out to quantify the general water quality of the lake. A white disk is lowered into the lake to the depth where it is no longer visible. In contrast to clear water that offers 10-meter visibility, surface waters of Lake Sevan allowed visibility at only 4.5-2.5 meters, which is considered problematic. During our interview, Dr. Schultze brought the example of Lake Constance in Germany, which is similar to Lake Sevan in size and had also experienced excessive amounts of phosphorus. A lake restoration programme implemented by the German, Swiss and Austrian governments in the 1970s took about 25 years to return the lake to its original condition. The volume of Lake Constance is naturally exchanged every five years by the inflow of rivers, but it takes three times longer to wash out all the phosphorus and all other contaminants. The residence time, which is time to exchange all the water in Sevan, is in the range of 25-40 years, which means that it needs much longer than Lake Constance to get rid of its “bad matters.” If the interpretations of the SevaMod project scientists are right, it may take over 125 years to restore water quality if Lake Sevan is turned into a fully polluted system; this is why it is crucial to have a good understanding of how to manage the lake successfully and to make predictions for a long run.
Thermistor chain ready for implementation
“To implement new tools to predict the future development of Lake Sevan, i.e. a fully coupled physical-ecological lake model, will be an effective instrument but not the only one,” Dr. Schultze says, “We need not only good technical approaches developed by scientists and engineers for solving or avoiding problems but we also need the right legislative framework and the acceptance of the local people. Otherwise, we will not be able to implement developed technical measures. In that sense, we want to contribute one piece of the system that is needed: developing a model that can reliably predict the development of Lake Sevan.”
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The SevaMod team is working on manuscripts of a special issue of an international scientific journal focusing primarily on Lake Sevan. The scientists plan to have the edition in print by the end of 2019. They already received positive feedback from several journals that are interested in publishing such a special issue. The majority of previous publications on Lake Sevan by Armenian and Soviet scientists were in Russian, remaining largely unknown to the international limnological community. The expected special issue will make Lake Sevan data available to all specialists around the globe. However, the team does not mean to wait until the data are published. In late April, a one-day workshop was organized for specialists and officials responsible for Lake Sevan management. The event was highly successful as it communicated scientific data and forecasts and resulted in continued constructive discussions on the issue.
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The coordinator of the project Martin Schultze indicated that the currently developed physical model is only a basic component of a complex model necessary for the sustainable development of the lake. The future model should be able to simulate the ecological behavior of the lake depending on all foreseeable circumstances. However, such an undertaking is well beyond the scope of SevaMod project. Should SevaMod continue into another phase, it would implement more sophisticated monitoring to populate the model with the appropriate amount and types of data. Dr. Schultze says, “We need to be sure that the instrument we are constructing and plan to hand over to the managers is beneficial and not misleading and thus resulting in wrong decisions. Otherwise, it will be irresponsible.”
Measuring with multi parameter probe
The project gets funding in its second phase, and it is planned to develop the ecological part of the model and also design a 3D physical lake model of Sevan reflecting the lake basin in detail and showing local details of mixing processes. The 3D model will enable to quantify the influence of the lake’s large size and the complicated bottom, as it can only be accomplished via comparing the monitoring results with the simulation. However, at this stage, the team will provide the 1D model of the lake and the results of the sediment investigation, as well as the summary and evaluation of the existing data.
