Urban wetlands can provide countless ecosystem services (e.g., flood control, nutrient processing, habitat) to an otherwise degraded environment. Anthropogenic stressors in the upslope landscape, such as road salt, erosion, and excess nutrients, can hinder wetland development and provisioning of ecosystem services. Such stressors may have differential effects on the wetlands depending on the routing of water to the wetland by overland runoff or groundwater flow paths. A better understanding of the hydrology in mediating these anthropogenic effects is needed to assess the ecological impacts and effectiveness of wetland restoration. To this end, monitoring of two restored, riparian wetlands underlain by limestone in Louisville, KY, has been underway since August, 2017, when the restoration occurred. Point sampling at both wetlands with a YSI Pro-DSS for turbidity (FNU), pH, temperature (deg C), specific conductance (μS/cm), and nitrate (mg/L) accompanied measurement of alkalinity (mg/L CaCO3) using a Hach colorimetric kit. Additionally, in one wetland, a continuously recording Solinst LTC pressure transducer was used to measure barometrically compensated water level, specific conductance, and temperature. Paired t-tests were used to compare the water quality of the two wetlands.
Results/Conclusions
Mean alkalinity indicated significantly (p=0.008) lower groundwater contributions to Wetland 1 (194.5 mg/L CaCO3, SD 71.5) than Wetland 2 (248.5 mg/L CaCO3, SD 62.4) only 60m away. The sporadic activation of a groundwater spring at Wetland 2 suggested temporally variable groundwater-flow systems that could alter habitat stability for aquatic organisms. Furthermore, phreatophytic interception of groundwater that contained ionic compounds, such as roadway deicing salts, was apparent in the continuous data record at Wetland 2, as evidenced by diurnal fluctuations in specific conductance and wetland water levels. High loading of dissolved material to over 1000 μS/cm may be of concern, particularly to the establishment and persistence of herpetofauna. Lastly, greater nitrate loading to spring-fed Wetland 2 (1.98 mg/L, SD 0.74) likely led to algae production that was not observed in the predominantly runoff-fed Wetland 1 (1.81 mg/L, SD 0.78). This high degree of primary production may provide organic matter to initially support rapid soil development but could lead to diurnal dissolved oxygen fluctuations, limiting macroinvertebrate assemblages to more tolerant organisms. These results illustrate hydroecological influences on wetland restoration in urban environments, and suggest that restoration expectations take into account differential hydrology, particularly where hydrogeology is complex.