The Effects of Rainfall Runoff on Suburban Wetland Water Quality

Abstract

Wetlands within the boundaries of suburbs can be adversely affected by rainfall runoff and storm water inputs. These wetlands may need to be monitored more frequently and drainage patterns modified to protect the wetlands from excessive exposure to potentially toxic runoff entering the wetland waters. This is especially true if more suburban development with its associated construction of buildings, roads, lawns, and loss of natural landscapes occurs around the wetlands. Suburban nature preserve workers noted less frog calling in the past few years in two suburban wetlands. There was concern about the water quality of these wetlands, especially since an expansive new lawn had been added adjacent to one of the wetlands within the past few years. It is speculated that an increase in lawn runoff has adversely changed the quality of the wetland water and that this should be more evident after significant rainfalls. During the summer and autumn of 2014, and the spring of 2015, water samples were taken from these two wetlands and tested for pH, nitrates, and phosphates and compared to the amounts of precipitation during the 24 hour period of the sampling date. It is anticipated that wetland phosphate and nitrate levels would increase, and pH levels would decrease with increasing amounts of precipitation. Macroinvertebrate sampling was also done in the late autumn of 2014 to assess for species diversity and richness as bioindicators of wetland health. Results showed that the pH did decrease with increasing amounts of precipitation at the wetland with the newly added adjacent lawn, but not at the other wetland. However, the mean pH values at both wetlands were not statistically different. The phosphate levels were abnormally high at both wetlands being 1.0 ppm. However after a rainfall of ~5 inches the phosphate levels increased at one wetland but decreased at the other wetland. The nitrate levels were within the healthy range at both wetlands throughout the study. Macroinvertebrate sampling results lacked biodiversity showing a predominance of scrapers at both sites.