9.0  Motts Creek 

Mott’s 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 Mott’s Creek at the River Road bridge (Fig. 9.1).  A large residential development is scheduled for construction upstream of the sampling site and between Mott’s and Barnard’s Creeks.  Recently, extensive commercial development has occurred along Carolina Beach Road near its junction with Highway 421.

Dissolved oxygen concentrations were below 5.0 mg/L on 45% of the occasions sampled, a lower compliance rate than during the 2001-2002 sampling (Mallin et al. 2003).  Turbidity was occasionally a problem, exceeding the state brackish water standard of 25 NTU on three of 11 occasions.  This station also maintained some of the higher suspended solids levels in the system.  Fecal coliform contamination was a problem in Mott’s Creek, with the geometric mean of 530 CFU/100 mL well exceeding the state standard of 200 CFU/100 mL, and monthly samples exceeding this standard on seven of 11 occasions (Appendix B).  Fecal coliform contamination worsened from the previous year.  Total nitrogen levels increased over the previous year’s study, but chlorophyll a concentrations remained below standard at all times, an improvement over the previous year (Table 9.1).  BOD5 was sampled on 11 occasions in 2002-2003, yielding a mean value of 1.9 mg/L and a median value of 1.9 mg/L, which was lower than the previous year (Mallin et al. 2003).  Thus, this creek showed mixed water quality, with algal blooms and BOD decreasing but dissolved oxygen and fecal coliform counts getting worse.  Cessation of the commercial development activities near the headwaters upstream may have contributed to the decrease in BOD and algal blooms 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) / range,
August 2002-September 2003.  Fecal coliforms as geometric mean / range.
_____________________________________________________________________
Parameter                                          MOT-RR
_____________________________________________________________________
Salinity (ppt)                                      2.5 (6.3)
                                                           0.1-21.3

TSS (mg/L)                                        26.3 (27.0)             
                                                            7.8-97.0

Turbidity (NTU)                                  37 (34)         
                                                            6-123       

DO (mg/L)                                          5.5 (1.9)         
                                                            3.4-9.7                               

Nitrate (mg/L)                                     0.092 (0.069)     
                                                            0.015-0.220        

Ammonium (mg/L)                             0.091 (0.057)     
                                                            0.005-0.210 

Total nitrogen (mg/L)                        1.188 (0.432)
                                                            0.838-2.133       

Phosphate (mg/L)                              0.037 (0.040)
                                                            0.005-0.135        

Total phosphorus (mg/L)                   0.490 (1.360)
                                                            0.020-4.590 

Mean N/P ratio                                  18.7                     
Median                                               15.9                     

Chlor a (mg/L)                                    6.6 (4.9)         
                                                            1.2-17.0 

Fecal coliforms (CFU/100 mL)        530          
                                                            24-6000