9.0  Motts Creek

   Motts Creek near River Road has been classified by the State of North Carolina as a Natural Heritage Site because of the area’s biological attributes.  These include the pure stand wetland communities, including a well-developed sawgrass community and unusually large flats dominated by Lilaeopsis chinensis and spider lily, with large cypress in the swamp forest.  Thus, it is important that these attributes should be protected from land and water-disturbing activities.  UNCW scientists sampled Motts Creek at the River Road bridge (Fig. 9.1).  A large residential development is scheduled for construction upstream of the sampling site between Motts and Barnards Creeks.  In recent years extensive commercial development has occurred along Carolina Beach Road near its junction with Highway 421.

Dissolved oxygen concentrations were below 5.0 mg/L from May through September (range 3.6-4.9 mg/L) similar to previous years (Mallin et al. 2003; 2004).  Unlike previous years, neither turbidity nor suspended solids were problematic in 2004.  Fecal coliform contamination was a problem in Motts Creek, with the geometric mean of 272 CFU/100 mL exceeding the State standard of 200 CFU/100 mL, and samples exceeding this standard on five of seven occasions (Appendix B).  Fecal coliform contamination was similar to previous years.  Total nitrogen, ammonium, and total phosphorus levels decreased over the previous year’s study, but chlorophyll a concentrations generally increased, with one major and one minor bloom (Table 9.1).  BOD5 was sampled on seven occasions in 2004, yielding a mean value of 1.7 mg/L and a median value of 1.2 mg/L, which was lower than the previous years (Mallin et al. 2003; 2004).  Thus, this creek showed mixed water quality, with algal blooms increasing but BOD and turbidity decreasing, and dissolved oxygen and fecal coliform counts staying relatively similar to last year.  Cessation of the commercial development activities near the headwaters upstream may have contributed to the decrease in BOD and nutrient loading in the creek at River Road.

Table 9.1.  Selected water quality parameters at a station (MOT-RR) draining Motts Creek watershed before entering the Cape Fear Estuary, as mean (standard deviation) and range, January-September 2004.  Fecal coliforms as geometric mean / range.
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Parameter                                                           MOT-RR
                                                            Mean (SD)                 Range
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Salinity (ppt)                                      2.8 (4.6)                      0.1-21.3

TSS (mg/L)                                        9.7 (4.6)                     5.0-19.0 

Turbidity (NTU)                                 13 (6)                          8-25  

DO (mg/L)                                          5.3 (2.4)                     3.6-10.0     

Nitrate (mg/L)                                    0.110 (0.119)            0.030-0.350

Ammonium (mg/L)                            0.041 (0.018)            0.005-0.060

Total nitrogen (mg/L)                       1.103 (0.170)             0.780-1.290

Orthophosphate (mg/L)                   0.014 (0.010)            0.005-0.030

Total phosphorus (mg/L)                 0.060 (0.015)             0.040-0.080

Mean N/P ratio                                  32.3                     
Median                                               24.4                   

Chlor a (mg/L)                                    11.3 (15.5)                 1.8-41.1   

BOD5 (mg/L)                                     1.7 (1.1)                     0.8-3.7

BOD20                                               5.9 (3.3)                      1.8-11.5

Fecal coliforms (CFU/100 mL)       272                               90-900
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