northern estuaries presently "treating" 

 secondarily treated sewage discharged 

 into estuarine waters. 



Major differences between our study 

 and that of Valiela et al. in Massachu- 

 setts were (1) their study of the re- 

 sponse of a salt marsh to sewage enrich- 

 ment was carried out over several years, 

 had controls of inorganic nutrient fer- 

 tilization as well as nonfertilization 

 and measured more marsh processes and 

 (2) they used commercially prepared sew- 

 age fertilizer which had been amended 

 with inorganic fertilizer. We used sew- 

 age sludge from an Athens, Georgia, 

 treatment plant, air dried the sludge, 

 and then ran it through a grinder to 

 make it into a crumbly powder. Our sew- 

 age sludge was from an anaerobic diges- 

 tion process, but at times a significant 

 fraction may have been only primarily 

 treated. 



We applied the dry sludge at the 

 rate of 25 g/m 2 per week at biweekly 

 intervals, which was equivalent to Teal 

 and Valiela's high rate of fertiliza- 

 tion. They also tested a lower rate of 

 about 8 g/m 2 per week. During our 1-yr 

 study, a total of 1.2 kg/m 2 was applied. 

 We compared our fertilized short Spar- 

 tina marsh with a tall Spartina creek- 

 bank marsh and with a separate unfertil- 

 ized short Spartina marsh as a control. 



In the first year the Massachusetts 

 group did not report any increase in 

 plant biomass (Valiela et al. 1975). 

 After comparing their high frequency of 

 sewage sludge fertilization with fertil- 

 ization with urea only, they concluded 

 that it was the nitrogen in sewage 

 sludge that resulted in increased plant 

 growth. Phosphorus fertilizer did not 

 increase the standing plant biomass in 

 either the low or high marsh. The sewage 

 sludge and urea-enriched plots, which 

 had the same nitrogen content applied, 

 showed two- to three-fold increases in 

 plant biomass (Valiela et al. 1975). 

 Plants in a Massachusetts high marsh 

 tended also to become morphologically 

 more like plants in the low marsh during 

 the sewage enrichment study. 



In the first year of sludge fertil- 

 ization of our experimental plots, the 

 aboveground live S partina biomass in- 

 creased about a third over our control 

 Spartina biomass (Figure 1). In some 

 months of the year our experimental 



plots had almost as much live Spartin a 

 biomass as the tall plants by the creek, 

 which was the more productive area of 

 the marsh. On the other hand, the dead 

 Spartina biomass in our fertilized plots 

 did not increase significantly above the 

 control during the course of the experi- 

 ment. One might expect that as the ex- 

 perimental live plant biomass died off 

 in the winter, there would be a corres- 

 ponding increase in the dead material, 

 but so far this effect has not become 

 apparent. 



We also attempted to monitor the 

 response of belowground plant biomass to 

 enrichment. Measuring live belowground 

 plant biomass was difficult in these 

 marshes because: (1) there was so much 

 dead matter and (2) the clay sediments 

 clung to the roots so tightly that it 

 was very difficult to accurately sepa- 

 rate the live plant roots and rhizomes 

 from dead roots and rhizomes. As a 

 crude indication of belowground plant 

 growth, we measured the total macro- 

 organic matter (MOM), i.e., the organic 

 material larger than 2 mm (0.08 inch) in 

 our three plot areas. 



A seasonal comparison of the total 

 belowground MOM to a depth of 30 cm in 

 our three plots showed much variation 

 (Figure 2). The trend during the course 

 of the experiment was a slight increase 

 in the belowground MOM in our experi- 

 mentally enriched plots compared to the 

 control plots. A rather drastic. drop in 

 the amount of MOM in the tall Spartina 

 (creekbank) marsh sites was also noted. 

 The data also indicate that organic mat- 

 ter is mineralized more rapidly in the 

 low marsh sediments, which could explain 

 in part the rapid disappearance of the 

 creekbank soil MOM. 



Valiela et al. (1976) separated the 

 live roots and rhizomes from the total 

 dead belowground MOM by visual observa- 

 tion and staining procedures. They 

 found very little live root and rhizome 

 material in comparison to the total 

 amount of dead matter. The dry weight 

 of live roots in their Spartina marsh 

 was much less than the dry weight of the 

 rhizomes. Sewage fertilization appeared 

 to decrease the standing crop of roots 

 in the marsh. Valiela et al. (1976) 

 speculated that the enriched plants re- 

 quired fewer roots because they had a 

 relatively higher standing stock of 



149 



