ارزیابی کارکرد زیست‌محیطی پخش‌سیلاب از نظر ترسیب کربن در خاک و گیاه

ارزیابی نقش آبخوان داری در ترسیب دی اکسید کربن موجود در هوا به شکل کربن آلی، هدف این پژوهش بود. با نمونه برداری از خاک و گیاهان در کاربری های جنگل دست کاشت اوکالیپتوس با و بدون پخش سیلاب و جنگل دست کاشت آکاسیا همراه با پخش سیلاب، مرتع بدون پخش سیلاب و مرتع با پخش سیلاب، مقدار کربن آلی اندازه گیری گردید و در نهایت کل ترسیب کربن محاسبه شد. داده ها، در قالب طرح بلوک های کامل تصادفی با استفاده از نرم افزار sas تجزیه و تحلیل آماری شد و میانگین ها با آزمون دانکن در سطح 5 درصد مقایسه شدند. نتایج نشان داد که تاثیر کاربری های مختلف بر مقدار کربن آلی و ترسیب کربن در خاک و گیاه در سطح یک درصد معنی دار شد. جنگل کاری با اوکالیپتوس کامالدولنسیس همراه با پخش سیلاب، میزان کربن آلی خاک را از 0.51 درصد در شاهد (اوکالیپتوس بدون پخش سیلاب) به 1.68 درصد در نوار اول جنگل اوکالیپتوس افزایش داد (3.29 برابر). با محاسبه ی میانگین عرصه هایی که در آن ها اوکالیپتوس کاشته شده بود، مشخص شد بیشترین کربن به میزان 121.84 تن در هکتار در این کاربری در درختان، لاشبرگ و در خاک (تا عمق 30 سانتی متر) زیر پوشش آن ها ذخیره شده است. با توجه به این که هر تن کربن، معادل 3.67 تن دی اکسید کربن است، می توان نتیجه گرفت که هر هکتار از جنگل اوکالیپتوس 447.15 تن دی اکسید کربن هوا را به صورت ماده ی آلی ذخیره کرده است. ارزش اقتصادی مقدار کربن ذخیره شده معادل 3.76 میلیارد ریال در هکتار محاسبه گردید.

Assessment of Environmental Performance of Flood Spreading with Respect to Carbon Sequestration in Soil and Plant

Introduction: Carbon sequestration (CS) by forests, pastures, afforested stands and soils is the most appropriate way to reduce atmospheric carbon. A combination of all these activities can help balance the global warming process by reducing the concentration of atmospheric CO2. The amount of CS and quality of carbon storage in the soil depends on the interaction between climate, soil, tree species, litter chemical composition and their management. The results of Dinakaran and Krishnayya (2008) research showed that the type of vegetation cover has a significant effect on soil carbon storage. So that the amount of carbon storage in the soil depends on the amount of carbon entering the soil through plant debris and carbon loss through decomposition. To increase carbon in the soil, management activities such as increasing the amount of carbon entering the soil by adding litter and crop residues as well as reducing the rate of decomposition of soil organic matter should be done. Decomposition rate of soil organic matter is affected by soil condition (humidity, temperature and access to oxygen), sequestration of organic matter, placement of organic matter in the soil profile and the degree of physical protection by aggregates. Evaluating the role of aquifer management in reducing via storing the atmospheric CO2, to organic carbon (O.C) is the aim of this study. Materials and Methods: The studied land uses were as follows: 1Rangelandwithout flood spreadingwith grazing (control), 2 Range without grazingwithout flood spreading, 3 Six rangelands stripeswith grazingwith flood spreading, 4 RangelandAtriplex plantationwith spreading of flood, 5 Eucalyptus control forestwithout flood spreading, 6 Eucalyptus forestfirst stripwith flood spreadingBisheZard 4 (BZ4), 7 Eucalyptus forestsecond stripwith flood spreading(BZ4), 8 Eucalyptus forestthird stripwith flood spreading(BZ4), 9 Acacia forestwith flood spreading(BZ4). Soil and plant were sampled from each land use type. Then, the amount of O.C was measured in the laboratory and CS was calculated. The economicenvironmental value of carbon stored in the soil is based on Rivers’ proposal, which declares a carbon tax rate of $200 per tonne of CO2. The dollar is equal to 42,000 Iranian rials. Data were analyzed using randomized complete block design and Duncan test (at p < 0.05 ) was used to compare mean values using the SAS software. Results and Discussion: The analysis of variance showed that the effect of different land uses on the bulk density (BD), %O.C and the CS in the soil was significant at the level of 1%. Comparison of the mean of BD in various land uses showed that the eucalyptus forest (third strip) had the lowest BD compared to others, and the difference between this land use and other land uses was statistically significant. The first strip of Eucalyptus forest had the highest %O.C and the highest amount of CS in the soil, and the statistical difference between these two indices in this land use with other land uses was significant. Among the studied land uses, the lowest amounts of CS were related to the control range and range without grazingwithout flood spreading. The interaction of plant to plant species on plant dry weight and plant carbon storage showed that the rangeland species of Heliantemum lippii and Dendrostellera lessertii in the range with flood spreading have the highest dryweight and the species of Helianthomus has the highest amount of carbon storage. This indicates that the impacts of flood spreading on plant biomass production and carbon storage have been greater than the impact of no grazing on these indicators. In all uses, Artemisia sieberi showed the lowest dry weight and carbon storage. Planting of Eucalyptus camaldulensis irrigated with flood water spreading increased the soil O.C from 0.51% in the control to 1.68% in the first strip of eucalyptus forest (3.29 times). By calculating the mean of the three strips in which the eucalyptus was planted, it was found that the highest carbon content of 121.84 ton/ha was stored in the plant, litter and soil of this land use. Given that, each tonne of carbon is equivalent to 3.67 tons of CO2 gas, it can be concluded that 447.15 tonnes of CO2 gas from the air is stored as organic matter. The economicenvironmental value of this CS is 3.76 billion rials ($89523.81) per hectare. Conclusion: The studied land that was irrigated with flood spreading, especially the eucalyptus forested area at Kowsar station, captured significant amounts of CO2 from the air and stored it as organic matter in the root and shoot of plants and in the soil. Also, this may lead to the release of a large amount of oxygen gas to the environment which play an important role in reducing air pollution. Considering the economicenvironmental value of the carbon stored in the eucalyptus plantation forest areas, the development of this method in flood prone areas is quite economically justifiable. Due to the high potential of tree species in improving soil carbon storage, it seems that increasing the percentage of woody species and their physiological diversity have increased the carbon storage capacity of these species. Therefore, in order to improve the carbon storage capacity of flood distribution systems, it is suggested that the planting of native and perennial compatible species in these systems should be considered.