اثرپذیری محتوای ماده آلی و نیتروژن بسترهای خشک‌شده تالاب‌های فصلی از تلقیح سطوح مختلف سیانوباکتریایی

Introduction and Goal
Healthy ecosystems are vital for sustainable development, serving as the foundation for food security and biodiversity while also providing essential resources and ecosystem services. Weak implementation of sustainable development plans, particularly in water and soil management, has led to increased resource exploitation and ecosystem instability, resulting in the formation of fragile landscapes. Unsustainable water use can cause permanent or seasonal dryness in wetlands, transforming them into sources of dust. Despite extensive efforts to stabilize these beds and enhance their resilience, the durability and effectiveness of conventional solutions for controlling wind erosion have been challenged by the periodic dewatering of wetlands. The use of cyanobacteria to stabilize erosion-prone areas has gained attention, but their effectiveness under dry and dewatering wetland conditions remains largely unexplored. This study investigates the impact of inoculating soil with varying concentrations of native cyanobacterial biomass on soil organic matter and nitrogen content, key components of biological soil crusts, under dry and dry-dewatering conditions. The aim is to assess how these cyanobacteria influence the soil’s susceptibility to wind erosion, which is commonly evaluated using indicators such as organic matter and nitrogen content.
Materials and Methods
The Kobi Baba Ali International Wetland, a 500-hectare site in West Azerbaijan Province, Iran, is the focus of a study due to its vulnerability to drought and dewatering. This Ramsar-recognized wetland experiences these fluctuations due to reduced rainfall and excessive upstream water usage, according to a wetland report. Bulk soil samples were collected from the dried wetland bed and transferred into small erosion trays for preparation. At the same time, native cyanobacteria from the dried-up bed of study wetland and effective in soil conservation were extracted, identified, purified, and propagated. Cyanobacterial strains (Nostoc sp. and Oscillatoria sp.) were prepared at four concentrations: 0, 1.5, 3, and 6 g m-2. The inocula were then applied in hidro-seeding method to prepared trays under controlled conditions, with four replicates per treatment. The inoculum was incorporated to a minimum depth of one centimeter to ensure consistent soil contact. Then, the treated trays were subjected to two conditions: completely dry (representing a permanently dried wetland) for 134 days and dry-dewatering (representing a seasonal wetland experiencing alternating drought in the warm seasons and dewatering in the rainy seasons of the year) for 60 days of dry, 60 days of dewatering, and 14 days of dry (a total of 134 days). The study involved 32 soil samples: 16 under dry conditions and 16 under dry-dewatering conditions. The study was conducted in a completely randomized experimental design from June to November 2022. Soil organic matter and total nitrogen were measured after the experiments using the Walkley-Black and Kjeldahl methods, respectively. The data was then analyzed using one- and two-way ANOVA and an independent t-test.
Results and Discussion
The study found that cyanobacteria inoculation significantly affected nitrogen content in both dry and dry-dewatering conditions at a soil depth of 0-1 cm. The different inoculation concentrations (0, 1.5, 3, and 6 g m-2) had a statistically significant impact on nitrogen levels (p<0.01). Inoculation treatments significantly influenced both soil nitrogen and organic matter content under dry-dewatering conditions. Specifically, inoculation significantly increased nitrogen content at a depth of 0-5 cm (p<0.01) and organic matter content at both 0-1 cm and 0-5 cm depths, under both complete dry and dry-dewatering conditions (p<0.05). Overall, both nitrogen content and organic matter were significantly enhanced by cyanobacterial inoculation under dry and dry-dewatering conditions. Nitrogen content increased by 26% and 39% under dry conditions, and by 28% and 44% under dry-dewatering conditions, with moderate (3 g m-2) and high (6 g m-2) cyanobacterial biomass concentrations, respectively. Organic matter increased by 65% and 72% under dry conditions with 3 and 6 g m-2 inoculations, respectively, and by 49%, 54%, and 63% under dry-dewatering conditions with 1.5, 3, and 6 g m-2 inoculations, respectively. The interaction effects of moisture conditions (dry vs. dry-dewatering) and cyanobacterial inoculation on soil nitrogen and organic matter content were statistically insignificant (p>0.05). Inoculation with low concentrations of cyanobacteria (1.5 g m⁻²) did not significantly improve soil properties.
Conclusion and Suggestions
This study suggests that annually draining a natural wetland does not improve soil organic matter and nitrogen content in the dry beds. Instead, alternative methods such as cyanobacterial inoculation are recommended to enhance these soil components, which are vital for biological soil crust development and, consequently, soil stability. The research revealed that cyanobacteria, when introduced into soil under dry-dewatering conditions, not only persisted but also thrived, increasing both organic matter and nitrogen content, similar to their performance under completely dry conditions. While cyanobacterial inoculation can enhance soil resistance to erosion, it also poses risks as a potential invasive species in wetland ecosystems, particularly with large-scale applications, necessitating further study of its impacts on aquatic life. Cyanobacterial inoculation, particularly at concentrations of 3 g m-2 or higher, can be a highly effective and eco-friendly approach for stabilizing dry wetland substrates, especially in areas experiencing fluctuating wet and dry conditions. It is recommended that future research on wind erosion be expanded to include field-scale studies simulating both drought and natural dry-dewatering conditions, alongside laboratory and field-based measurements of erosion dynamics.