Laserfiche WebLink
<br />Ground-water pumping can affect not only <br />water supply for human consumption but also the <br />maintenance of instream-flow requirements for <br />fish habitat and other environmental needs. Long- <br />term red uctions in streamflow can affect vegeta- <br />tion along streams (riparian zones) that serve <br /> <br /> <br />-l <br /> <br /> <br />critical roles in maintaining wildlife habitat and in <br />enhancing the quality of surface water. Pumping- <br />induced changes in the flow direction to and from <br />streams may affect temperature, oxygen levels, <br />and nutrient concentrations in the stream, which <br />may in turn affect aquatic life in the stream. <br /> <br /> <br />Perennial streams, springs, and wetlands in the Southwestern United States are highly valued as <br />a source of water for humans and for the plant and animal species they support. Development of <br />ground-water resources since the late 1800's has resulted in the elimination or alteration of many <br />perennial stream reaches, wetlands, and associated riparian ecosystems. As an example, a 1942 photo- <br />graph of a reach of the Santa Cruz River south of Tucson, Ariz., at Martinez Hill shows stands of <br />mesquite and cottonwood trees along the river (left photograph). A replicate photograph of the same <br />site in 1989 shows that the riparian trees have largely disappeared (right photograph). Data from two <br />nearby wells indicate that the water table has declined more than 100 feet due to pumping, and this <br />pumping appears to be the principal reason for the decrease in vegetation. (Photographs provided by <br />Robert H. Webb, U.S. Geological Survey.) <br /> <br />34 <br />