ارزیابی اثرات تلقیح غلظت‌های مختلف سیانوباکتری بر محتوای ماده آلی و نیتروژن بسترهای خشک‌شده تالاب‌های فصلی

Introduction and Goal
Healthy ecosystems are vital for sustainable development, serving as the foundation for food security and biodiversity while providing essential resources and services for survival and well-being. Weaknesses in implementating sustainable development plans lead to increased exploitation of resources and instability of ecosystems, particularly in water and soil management. Furthermore, unsustainable practices have led to the formation of new and fragile landscapes. Permanent or seasonal dryness of wetlands, due to unsustainable water consumption, is one of the negative consequences of improper exploitation of water resources, turning their beds into sources of dust. Despite extensive efforts to stabilize and enhance the sustainability of beds, the durability and effectiveness of conventional solutions for controlling wind erosion in these beds have faced challenges due to the periodic flooding of wetlands. Recently, the approach of inoculating cyanobacteria aimed at stabilizing erosion-sensitive beds has gained attention; however, its effectiveness under dry-flooding conditions of wetlands has not been examined. Furthermore, direct measurement of wind erosion resulting from bed stabilization efforts, as well as the use of indicators determining soil erosion sensitivity, such as organic matter content and total nitrogen from the components of soil biological richness, is also common. Therefore, this study was conducted to evaluate the effects of inoculating different concentrations of native cyanobacteria on the organic matter content and nitrogen in the soil under conditions of complete dryness and dry-flooding.
Materials and Methods
For this research, the international Kobi Baba Ali Wetland, in West Azerbaijan Province in northwestern Iran was selected. This 500-hectare wetland is known as the Ramsar Convention. The mentioned wetland is subject to seasonal cycles of dryness and flooding due to decreased rainfall and unsustainable water use upstream. Volume soil samples from the dried bed of the wetland were collected and transferred for preparation into small erosion trays. Simultaneously, native cyanobacteria for soil conservation of the dried-up wetland bed were extracted, identified, purified, and propagated. From the obtained Cyanobacterial (Nostoc sp. and Oscillatoria sp.) four concentrations of 0, 1.5, 3, and 6 g m^-2 were prepared. Then, the prepared cyanobacteria were water-inoculated on prepared trays based on the defined treatments in four replicates. The penetration depth of the inoculation solution was at least one cm. Then, the treated trays were placed under two conditions: completely dry (representing a permanently dried wetland) for 134 days, and dry-dewatering (representing a seasonal wetland experiencing cycles of dryness in the warm seasons and flooding during the rainy seasons) with a total of 60 days of dryness, 60 days of flooding, and 14 days of dryness (a total of 134 days). A total of 32 experiments were conducted (16 experiments under complete dryness conditions and 16 experiments under dry-flooding conditions). The study was conducted in the from of a completely randomized experimental design from July to November 2022. After the completion of the experiments, the measurements of organic matter and total nitrogen in the soil were determined using the Walkley-Black and Kjeldahl methods, respectively. Finally, statistical analysis of the results was conducted using one-way and two-way analysis of variance and independent t-tests.
Results and Discussion
The findings showed that the effects of cyanobacteria inoculation treatments (concentrations of 0, 1.5, 3, and 6 g m^-2) on nitrogen content at depths of 0 to 1 cm were significant (at the 1% probability level) under both complete dryness and dry-flooding conditions. The effects of the inoculation treatments on nitrogen content under dry-flooding conditions at depths of 0 to 5 cm were also significant (at the 1% probability level). The effect of inoculation treatments on soil organic matter content was significant (at the 5% probability level) at both depths of 0 to 1 and 0 to 5 cm and under both complete drought and drought-waterlogging conditions. Nitrogen content increased by 26% and 39% under complete dryness conditions with the inoculation of medium (3 g m^-2) and high (6 g m^-2) concentrations of cyanobacteria, and by 28% and 44% under dry-flooding conditions, respectively. Organic matter also increased by 65% and 72% under complete dryness conditions with the inoculation of 3 and 6 g m^-2, and by 49%, 54%, and 63% with the inoculation of 1.5, 3, and 6 g m^-2 under dry-flooding conditions, respectively. The interaction effects of moisture conditions (dry vs. dry-dewatering) and cyanobacterial inoculation on soil nitrogen and organic matter content were not insignificant (at the 5% probability level). The performance of inoculating low concentrations of cyanobacteria (1.5 g m⁻²) in improving the examined components was not acceptable.
Conclusion and Suggestions
The results of this study indicated that the effects of the annual natural flooding of the wetland on improving soil organic matter and nitrogen content, and in other words, on the expansion of the soil biological crust in dry beds, were not positive. Therefore, the implementation of other measures, such as the inoculation of cyanobacteria, is essential for improving organic matter and nitrogen as components of soil sustainability. The findings showed that when cyanobacteria were inoculated into the soil under dry-flooding conditions, they both survived and grew, similar to complete dryness conditions, increasing the measurements of organic matter and nitrogen. While the inoculation of cyanobacteria is effective in improving soil sustainability components against erosive factors, there are also concerns about their negative effects on wetlands as an invasive species, especially on a large scale, which requires further investigation. The inoculation of cyanobacterial, especially at a concentration of at least of 3 g m^-2 is a rapid and environmentally friendly method for stabilizing the substrates of dried wetlands, particularly for wetlands with alternating flooding and dryness conditions. It is recommended that complementary studies be conducted on a desert scale with conditions of alternating dryness and natural dry-flooding, along with field measurements of wind erosion.