Modeling the effect of forest moss cover patterns on runoff and sediment components under different slopes (A laboratory study using a rainfall erosion simulator)

Introduction
Today, one of the major problems in the watersheds is soil erosion and sediment production, which threatens the sustainable development in these areas. Erosion not only leads to soil degradation and decreasing fertility, but also to pollution of Water Resources and decreased water quality. One of the methods to prevent the loss of water and soil resources is the usage of biological conditioners to control erosion and soil conservation. Organic conditioners can play the more effective role in reducing runoff and sediment. As an organic conditioner, especially in forest areas, Moss is a suitable conservation cover that reduces runoff and soil loss by directly Collision of rainfall droplets. The present study aimed to examination the conservation effects of moss as a type of biological soil conditioner with two planting pattern forms, compared to a plot without conditioner (control) at different slopes (20%, 30% and 40%) with three replications at the plot scale under a rainfall of 120 mm h-1 using a rainfall simulator.
 
Materials and Methods
In order to control erosion in forest areas, natural mulch that is native to the region should be used because the usage of non-native materials such as chemical mulch, including polymers and polyacrylamide, which are long-lasting, if lost, does not play the role in soil enrichment and can even pollute the environment and cause the disrupting natural habitats. In this study, the effects of forest moss on runoff and sediment components were investigated in the rainfall simulator laboratory of the Faculty of Natural Resources, Sari Agricultural and Natural Resources Sciences University. The studied soil in this research was collected from the Darabkola forest located in Mazandaran Province. The transported soil was dried and passed through a 4 mm-sieve for relative stability of soil aggregates. In the present study, two types of soil cultivation patterns were used under laboratory conditions to investigation the conservation effects of moss on runoff and sediment. The conservation treatments including moss cover with planting patterns of clumped, strip and control treatment (without cover) on three different slopes of 20%, 30%, and 40% under intensity of 120 mm h-1 and with three replications in plot scale with dimensions of 1 × 0.5 m2 in depth of 0.2 m. Then, runoff and sediment samples were collected for duration of 10 min for each experiment. The collected sediment samples, after being left to settle for 24 h were dried at 1050C for 24 h, and finally their weight was measured.
 
Results and Discussion
A total of 27 rainfall simulation experiments were conducted. Compared with the control treatment, runoff volume was reduced by 20.24% and 33.83% under the clumped and strip planting patterns, respectively, on the 20% slope. At the 30% slope, runoff volume decreased by 19.56% and 33.46%, while corresponding reductions on the 40% slope were 13.30% and 31.05%, respectively. Soil loss decreased under both planting patterns. The clumped and strip patterns reduced, in slop of 20 percent measured with rates of 28.35% and 51.33% (for planting patterns of clumped and strip); 36.67% and 53.33% (for slope of 30 percent); 2984% and 46.40% (for slope of 40 percent), respectively. Sediment concentration also decreased under both planting patterns. The clumped and strip patterns reduced sediment concentration by 14.35% and 23.13% at the 20% slope, 17.53% and 26.78% at the 30% slope, and 19.12% and 23.62% at the 40% slope, respectively. Likewise, soil loss was substantially reduced under both planting patterns, with the strip arrangement consistently providing greater protection than the clumped pattern. Statistical analysis indicated that moss planting pattern had a highly significant effect (P < 0.01) on runoff volume, soil loss and sediment concentration. Also the separately effect of slope on runoff and soil loss was significant on at level of 99 percent. However, the interaction effects between slope and planting pattern were not significant for all measured variables.
 
Conclusion
In general, the results of the present study showed that the usage of cultivation patterns of clumped and strips significantly reduced the runoff volume and sediment and prevents soil loss. In other words, moss with reducing the flow velocity, caused to increasing infiltration and reduced the separation of soil particles by raindrops. Moss are very effective in increasing water retention capacity at soil, and in fact, the moss surface is like a soft, porous sponge, and rainfall quickly is absorbed by moss, and this conservation treatment traps the caused soil particles by water erosion. So the moss cover is one of the important factors in the management and conservation of water and soil Resources. Given the importance of water and soil conservation and the high cost and environmental inappropriate impacts of mechanical methods over biological methods of water and soil conservation, the application of this conservation cover can be useful in the programs development of soil erosion control.