24 



MISCELLANEOUS PUBLICATION NO. 10 65, U.S. DEPARTMENT OF AGRICULTURE 



the vicious raids of Mongols led by Hulagu Khan 

 in A.D. 1258. But recent evidence indicates that 

 Hulagu and his horsemen found nothing but deso- 

 lation when they invaded the region. Archeologists 

 Jacobsen and Adams (60) found that by the 12th 

 century the natural phenomena delivering sedi- 

 ment into the irrigation waters had caused far 

 greater devastation to the irrigated land, and thus 

 to the food supply of the cities, than any invading 

 hordes could have inflicted. 



These bits of history leave no doubt that sedi- 

 ment in water can adversely affect agriculture. 



The sediment burden in streams may come from 

 many different sources through the erosion proc- 

 ess. It arises from forested lands that have been 

 devastated by fire, construction of forest roads and 

 other forest improvements, certain logging prac- 

 tices, overgrazing and trailing of animals on 

 rangelands, cultivated lands that are inadequately 

 protected, industrial construction sites, highway 

 construction, unprotected roadside cuts, suburban 

 development projects, spoil banks from strip min- 

 ing and other mining activities, unstabilized 

 stream banks, and geologic erosion of such areas 

 as the Badlands of South Dakota. The land is 

 robbed and the water despoiled. 



The material is entrained by water in motion, 

 transported by moving water, and deposited by 

 relatively quiet or still waters. 



Aside from filling stream channels, irrigation 

 canals, farm ponds, and reservoirs used for irri- 

 gation, recreation, fishing, and farmstead water 

 use, sediment in water increases the expense of 

 clarification of the water used on the farmstead or 

 in sprinkler irrigation systems. Suspended sedi- 

 ment impairs the dissolved oxygen balance in water 

 and thereby slows amelioration of other oxygen- 

 demanding wastes. Reduced oxygen supply hurts 

 fish life. Fish population is also reduced by the 

 sediment blanketing fish nests, spawn, and food 

 supplies. The thousands of farmers using farm 

 ponds to sell fishing rights are much concerned 

 with the deterioration of water quality by sedi- 

 ment burden. 



Recreational interest in water in the ponds of 

 farms and ranches varies inversely with muddiness 

 of the water. 



The useful life of many farm ponds is surpris- 

 ingly short because of sediment accumulation. 

 Surveys on 30 farm ponds in the Iowa and Mis- 



souri Deep Loess Hills land resource area showed 

 that, on an average, they would be completely 

 filled with sediment in 20 years. However, the 

 ponds will have been rendered essentially useless, 

 and many will have become a nuisance, long before 

 their original water storage capacities have been 

 replaced by sediment. 



The adverse effect of waterborne sediment upon 

 agriculture is by no means limited to losses asso- 

 ciated with recreational use of farm and ranch 

 ponds. Damage to agricultural land resources 

 from overwash of infertile materials, impairment 

 of natural drainage, and swamping and increased 

 flooding because of sediment accumulations in 

 stream channels are also aspects of the silt problem 

 having a direct bearing on farmers and ranchers. 

 Irrigation canals and waste water disposal ditches 

 are also subject to costly maintenance because of 

 silt deposited from muddy water. 



Ford (43) estimated that sediment damages in 

 upstream watersheds come to about $87 million 

 annually. The damages from this particular re- 

 source waste are over and above those caused by 

 gully erosion, flood plain scour, and streambank 

 erosion and by impairment of water quality from 

 sediment in farm ponds and farm water supplies. 



In the nearly 4 billion tons of sediment that are 

 delivered to our waterways each year, the equiva- 

 lent of 4 million acres of topsoil are transported. 

 We can validly assume that at least 75 percent of 

 this mass is derived from agricultural and forested 

 lands and that it will have an average analysis of 

 0.10 percent nitrogen, 0.15 percent P 2 5 , and 1.50 

 percent K 2 0. This means that more than 50 million 

 tons of primary nutrients are lost from our agri- 

 cultural and forested lands each year through 

 sediment delivery. 



The adverse effects of sediment in streams on 

 agriculture and forestry is indeed a Texas-size 

 problem. 



Plant Nutrients 



Plant nutrients in the soil are a must for food on 

 the table. Volumes of benign words have been 

 written on the essentiality of fertile soils to meet 

 one of the basic needs of mankind. But when these 

 nutrients become resources out of place in ground 

 water and surface water, they are serious pollut- 

 ants. There are about 150 species of algae and other 

 aquatic plants that grow in farm ponds, woodland 



