Nitrogen isotope ratios of ammonium and nitrate ions from soil and water samples can be analyzed reproducibly with an experimental error of approximately +/-1 parts per thousand (ppt). Two isotopic ranges of soil nitrate are found in the soils of southern Runnels County, Texas. Nitrate from the decomposition of animal waste nitrogen has a dN15 of +10 ppt to +22 ppt. The isotopic ratio is controlled by the volatilization of isotopically light ammonia gas during the decomposition of urea in urine.

Change, both natural and man-induced, is a significant and defining element of the Coastal Zone. Man-induced change, by definition, can be controlled if desired. The work of nature, however, is altered and modified with much more difficulty, if at all, and attempts to do so commonly lead to unintended results. Prudent use and adequate management of the Coastal Zone must consider natural changes.

The Houston-Galveston Area Council of Governments (HGAC) encompasses over 12,000 square miles of southeast Texas (fig. 1). It is an area undergoing rapid development and population growth due to the presence of vast agricultural, mineral, and energy resources, expanding industrial activity, and diverse recreational areas. Planning is particularly critical in the HGAC to ensure orderly development.