Showing 3 results for Ecosystem
M. Riahi , F. Raiesi,
Volume 16, Issue 59 (4-2012)
Abstract
Mountainous landscapes in Central Zagros are mainly used as grazing rangelands to feed animals and are heavily degraded. Overgrazing may impose a negative effect on rangeland productivity and sustainability through significant changes in soil properties. Soil nitrogen (N) mineralization is one of the key biological processes that might be affected by biotic and abiotic factors including range grazing regime or intensity. The primary objective of this study was to assess the effects of rangeland management (grazing and ungrazing regimes) on soil N mineralization in natural rangelands of Chaharmahal VA Bakhtiyari province. Three range management regimes including a) long-term ungrazed, b) controlled grazed and c) freely- (over)-grazed plots in a close vicinity were selected in three regions consisting of SabzKouh (protected from grazing for 18 years), Boroujen (protected from grazing for 23 years) and Sheida (protected from grazing for 2 years), and soil samples were collected from 0-15 cm depth for some physical and chemical properties. Soil N mineralization was measured under standard laboratory conditions. At SabzKouh, the effect of range management on the cumulative N mineralization and the proportion of N mineralized (%) was significant (P<0.05) and ungrazing regime resulted in 89% and 96% increases in soil N mineralization in ungrazed rangelands compared with controlled grazed and freely- grazed rangelands, respectively. Similarly, soil N mineralization was significantly greater (P<0.05) in ungrazed rangelands (3.3- to 3.5-folds) than in controlled grazed and freely-grazed rangelands at Boroujen site. However, at Sheida site with short-term ungrazing period and cropping history there were no significant and considerable differences in soil N mineralization among the three grazing regimes. Briefly, degraded rangelands at SabzKouh and Boroujen sites seem to recover rather quickly from long-term overgrazing with a proper grazing management, while rangeland ecosystems at Sheida site need a much longer period for steady-state conditions and for improvements in soil quality and fertility after long-term soil degradation and disturbance.
Mahin Karami, Majid Afyuni, Amir Hossein Khoshgoftarmanesh, Mohammad Ali Hajabbasi, Hossien Khademi, Ali Abdi,
Volume 17, Issue 64 (9-2013)
Abstract
Zinc (Zn) is an essential trace element for plants as well as for animals and humans. There is a significant relationship between soils, plants and humans Zn status in a certain agro-ecosystem. The objectives of this study were to assess Zn status of soils in 3 arid and semiarid provinces of Iran and to model the relationship between wheat grain Zn and agro-ecosystem parameters. About 137 soil and wheat samples were collected randomly from the agricultural soils of Fars, Isfahan and Qom and were analysed in laboratory. Modeling the relationship between wheat grain Zn and agro-ecosystem parameters was done using least square based and robust methods. The results indicated that total Zn concentration of soils (range, 21-149 mg kg-1 mean, 75.2 mg kg-1) was in normal ranges. The DTPA-extractable Zn concentrations were below the critical level (0.8 mg kg-1) in 16% of the surveyed fields. The Zn concentration in 80% of wheat grains was sufficient (more than 24 mg kg-1) with respect to plant nutrition (range, 11.7-64 mg kg-1 mean, 31.6 mg kg-1). However, Zn bioavailability for consumers was generally low in more than 75% of the samples. This is because of high phytic acid to Zn molar ratio (more than 15). Soil DTPA-extractable Zn and available P were entered in to most of regression models significantly. Regression analysis showed that most of models fitted to wheat grain Zn concentration and soil Zn and influenced by agro-ecosystem parameters had a weak prediction power, despite their high determination coefficient. This means that factors other than those considered here have a strong influence on the uptake of Zn by wheat in these soils.
E. Ebrahimi, M. Zare Shahraki, O. Farhadian, Y. Keivany,
Volume 23, Issue 4 (2-2020)
Abstract
Benthos play an important role in the transmission of primary production and organic material (detritus) accumulation of the substrate in the water ecosystems to the higher levels of food chain. Also, they are used as biological indicators to evaluate the effect of pollutants caused by human activities on water ecosystems. To evaluate the benthic communities of Zayanderood Dam Lake, 4 sampling stations were selected on the lake; then, during the year 2014, seasonal sampling at each station was performed. The sampling was carried out by using the sediment sampler instrument with the dimensions of (20 cm × 20 cm). The average temperature of surface and deep water in the Zayanderood Dam Lake during the study was estimated to be 15.6 ± 2.4 and 8.9 ± 1.8°C, respectively. The average concentration of dissolved oxygen in the surface and deep water was varied from 10.3 ± 0.6 to 8.1 ± 0.7 mg/L, respectively. Totally, 2165 samples of benthos were collected and identified in the Zayanderood Dam Lake, belonging to 3 classes, 6 orders and 5 families. The maximum number of samples belonged to Tubifex, Naididae and Chironomidae genera. The dominant genus was Tubifex in all stages. According to this study, therefore, it seems that the structure of substrate, the amount of nutrients, grazing pressure and hydrostatic pressure are the most important environmental factors that can affect benthic community in the Zayanderood Dam Lake.
