بررسی توزیع جانبی و عمودی کربنات کلسیم در خاک با استفاده از زمین آمار و توابع اسپلاین

نوع مقاله: مقاله پژوهشی

نویسندگان

1 عضو هیئت علمی

2 گروه مرتع و آبخیزداری، دانشکده محیط زیست و منابع طبیعی، دانشگاه صنعتی خاتم الانبیاء بهبهان، بهبهان

3 گروه مهندسی علوم خاک، پردیش کشاورزی و منابع طبیعی، دانشگاه تهران

4 گروه خاکشناسی، دانشکده کشاورزی، دانشگاه شهرکرد

چکیده

در بیشتر مطالعات انجام‌شده روی توزیع کربن خاک، به توزیع سه‌بعدی کربن معدنی کمتر توجه شده است. کربنات کلسیم شکل غالب کربناتها در خاکهای مناطق خشک و نیمه‌خشک است که دانستن توزیع سه‌بعدی آن برای شناسایی عوامل موثر بر توزیع آن، پیش‌بینی برخی رفتارهای مهم و مدیریت بهتر خاک اهمیت دارد. این پژوهش با هدف بررسی توزیع سه‌بعدی کربنات کلسیم خاک در منطقه‌ای به وسعت 3600 هکتار در دشت سیلاخور (استان لرستان) انجام گرفت. برای این منظور، تابع اسپلاین با سطح برابر به داده‌های کربنات کلسیم به‌دست‌آمده از 103 مکان تا عمق یک متری برازش داده شد و مقادیر کربنات کلسیم در پنج عمق استاندارد پروژه جهانی نقشه‌برداری رقومی برآورد گردید. سپس از کریجینگ معمولی برای تهیه نقشه پیوسته تغییرات جانبی کربنات کلسیم در همه عمق‌ها استفاده شد. بررسی‌های زمین‌آماری نشان داد که در همه عمق‌ها مدل کروی بهترین مدل برای نشان دادن ساختار تغییرات مکانی کربنات کلسیم بود. نسبت اثر قطعه‌ای به آستانه واریوگرام برای همه عمق‌ها کمتر از 25 درصد بود که بیانگر پیوستگی مکانی قوی کربنات کلسیم بود. بررسی ناهمسانگردی بیانگر بیشتر بودن دامنه واریوگرام‌ها در امتداد دشت نسبت به امتداد عمود بر آن بود که نشان‌دهنده پیوستگی مکانی بیشتر در این امتداد به دلیل یکنواختی بیشتر مواد مادری، کاربری اراضی و شیب بود. نتایج برازش توابع اسپلاین بیانگر کارآیی خوب آنها در تخمین تغییرات عمودی کربنات کلسیم (88/0=R2 و 99/0=RMSE) بود. نقشه‌های توزیع جانبی و توابع اسپلاین هر دو بیانگر روند افزایشی کربنات کلسیم با عمق بودند. در بخش‌های شرقی و جنوبی منطقه به دلیل زهکشی ضعیف و در نتیجه کاهش آبشویی، مقدار کربنات کلسیم در خاکها بالا و روند افزایشی آن با عمق زیاد محسوس نبود. به‌طورکلی نتایج نشان داد که کاربرد همزمان توابع اسپلاین با روش‌های زمین‌آماری، رویکرد امیدوارکننده‌ای در بررسی تغییرات سه‌بعدی خواص خاک و برطرف کردن برخی مشکلات نقشه‌های سنتی است.

کلیدواژه‌ها


عنوان مقاله [English]

Study of lateral and vertical distribution of soil calcium carbonate using geostatistics and spline functions

چکیده [English]

In most studies on the distribution of soil carbon, three-dimensional distributions of soil inorganic carbon were neglected. Calcium carbonate is the most common carbonate in arid and semi-arid soils. Information on its spatial three-dimensional distribution is very important to determine factors controlling its distribution, to predict soil behavior and to improve soil management practice. This study aimed to map three-dimensional distributions of soil calcium carbonate (SCC) in an area of 3600 ha located in Silakhor plain (Lorestan province). An equal-area spline depth function (ESDF) was fitted to the measured SCC data of 103 pedons and the amounts of SCC at the five standard depths of the global soil map project were estimated.Then, ordinary kriging was employed to map the lateral distribution of SCC at all specified depths. Geostatistical analysis showed that spherical model was the best model representing spatial structure of calcium carbonate in all depths. All experimental variograms had a nugget to sill ratio less than 25 % which indicated strong spatial dependence for SCC. Anisotropy analysis indicated that ranges of variograms for all specified depths in the northwest-southeast direction were more than perpendicular direction. It indicated that SCC had more spatial dependence along Silakhor plain due to small variations in land use, slope and parent materials along the plain. Spline functions showed good performance in predicting vertical distribution of SCC (R2=0.88, RMSE=0.99). Both lateral continuous maps and spline functions indicated an increasing trend in SCC with increasing depth. In the eastern and southern parts, due to poor drainage and low leaching, SCC was high and its increasing trend with depths was not significant. Generally, results indicated that the combination of spline functions and geostatistical method is a promising approach to map three-dimensional distribution of SCC and to deal with some of the problem arising from legacy soil maps.

کلیدواژه‌ها [English]

  • Continuous soil map
  • Silakhor plain
  • spline functions
  • three-dimensional soil mapping
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