essential in the establishment and early development of marsh plantings. 

 Another and perhaps more important reason is the role that marshes 

 and marsh plants play in the storing and recycling of nutrients, and 

 in serving as nutrient sinks to reduce the polluting effect of excess 

 nutrient supplies in estuaries. Data relating to some of these func- 

 tions were discussed by Woodhouse, Seneca, and Broome (l974). The 

 data in this section are largely supplemental to the coverage in the 

 earlier report. 



a. Effect of 4 Years of Fertilization on a Young Natural Stand 



of Sparti-na altevniflora at Ocracoke, North Carolina . This experiment 

 was established in 1971 on a young natural stand of Spartina ditevni- 

 flova growing on a sandy substrate near Hatteras Inlet. The regular 

 lunar tidal range is about 30 centimeters at this site but may be 

 increased to 1 meter or more by wind setup. A factorial design was 

 used with two rates of phosphorus and four rates of nitrogen. Phos- 

 phorus was applied as concentrated superphosphate and nitrogen as 

 ammonium sulfate. The fertilizer was broadcast on the soil surface 

 during low water. The applications were split, one-third late April 

 or early May, one-third June, and one-third late July or early August. 

 Aerial growth was harvested with a sickle-bar mower in September of 

 each year. 



Total growth and response to nitrogen increased in the fourth year, 

 over the previous year, in the presence of applied phosphorus (Table 

 17). In the absence of applied phosphorus, nitrogen had a slight de- 

 pressing effect. Both nitrogen and phosphorus were sharply limiting 

 factors at this stage. 



This fourth-year response is of interest in demonstrating the 

 capacity of this vegetation to withstand and benefit from a rather 

 high input of nutrients on a continuing basis. 



b. Effect of 5 Years of Fertilization on the Short and Tall Forms 

 of Spartina alt erni flora . The fertilizer treatments and the design of 

 this experiment, begun on Oak Island in 1972, are the same as in the 

 1971 Ocracoke experiment. The Oak Island marsh differs from the Ocra- 

 coke marsh in several ways. The tidal range is greater, the substrate 

 is finer textured, the marsh is much older, and the drainage pattern is 

 better developed. The tall form of Spartina alterniflora occupies the 

 tidal creek banks; the plots at Oak Island include both the short and 

 tall form. 



Growth of the short form of Spartina alterniflora was increased by 

 the application of nitrogen without the addition of phosphorus. There 

 was a further significant increase at the higher rates of nitrogen 

 when phosphorus was applied (Table 18) . The finer sediments of the Oak 

 Island marsh supply more phosphorus than the sandy Ocracoke substrate. 



Growth of the tall form of Spartina alterniflora was increased 

 significantly by phosphorus application in this experiment in 1974 



63 



