Survey and Assessment of cyro Critical Urban Wetlands: City of Aurora December 2020 CNHP’s mission is to advance the conservation of Colorado's native species and ecosystems through science, planning, and education for the benefit of current and future generations. Report Prepared by: Colorado Natural Heritage Program Warner College of Natural Resources Colorado State University 1475 Campus Delivery Fort Collins, CO 80523-1475 (970) 491-1150 Report Prepared for: City of Aurora 15151 E. Alameda Parkway Aurora, CO 80012 U.S. Environmental Protection Agency, Region 8 1595 Wynkoop St. Denver, CO 80202 Recommended Citation: Gilligan, L., G. Doyle, G. Smith, J. Lemly, B. Lambert, and J. Handwerk. 2020. Survey and Assessment of Critical Urban Wetlands: City of Aurora. Colorado Natural Heritage Program, Colorado State University, Fort Collins, Colorado. Front Cover: Wetlands at the Sand Creek Riparian Preserve in north central Aurora. Survey and Assessment of Critical Urban Wetlands: City of Aurora Laurie Gilligan, Georgia Doyle, Gabrielle Smith, Joanna Lemly, Brad Lambert, and Jill Handwerk Colorado Natural Heritage Program Warner College of Natural Resources Colorado State University Fort Collins, Colorado 80523-1475 December 2020 EXECUTIVE SUMMARY The city of Aurora, located within the South Platte River Basin, is the third most populous city in Colorado, and is rapidly expanding its developed land area. Wetlands in dense urban centers differ from natural systems due to their modified hydrology, geomorphology, and increased non-native plant species, but they perform critical functions such as reducing flood risk, improving water quality, and providing wildlife habitat. Prior to this study, knowledge of the wetland extent for much of the city was outdated and coarse, much of it based on 1980’s mapping. Information was needed on the status and trends of extant wetlands throughout the City of Aurora. This study provides specific data on wetland locations and the condition of important wetlands in the City of Aurora. This information can be used for strategic urban planning, from prioritizing development projects to have the least impact to critical resources, to identifying the most important resources to protect and restore, and their management needs. To assess the extent and types of wetlands in Aurora, existing National Wetland Inventory (NWI) maps were updated with new imagery and ancillary spatial data layers. To assess the condition of important Aurora wetlands, Ecological Integrity Assessment (EIA) and Functional Assessment of Colorado Wetlands (FACWet) methods were used in 20 targeted wetlands selected for management priority, size, vegetated buffer, and likelihood of higher function within Aurora. Other Aurora wetlands, waterbodies, and riparian areas are viewable with their updated NWI mapping on the USFWS Wetlands Mapper: http://www.fws.gov/Wetlands/Data/Mapper.html. The wetland mapping results indicate that wetlands and riparian areas (including waterbodies) are uncommon in Aurora and account for 2.5% of the land area. The majority of acres mapped in the National Wetland Inventory (NWI) are large, constructed water storage reservoirs, water conveyance canals, and natural rivers that dot the landscape. These waterbodies provide surface water storage, sediment retention, groundwater recharge, and aquatic habitat. Vegetated wetlands and small ponds represent only 0.7% of the land area, but they provide nutrient cycling, shoreline stabilization, support biodiversity and native plant establishment, and terrestrial habitat function. The EIA and FACWet scores indicate the 20 targeted wetlands are in good to poor condition. One wetland assessment area (AA) rated B, 10 rated C, and 9 rated D with the EIA method. It should be noted that the EIA and FACWet methods evaluate wetlands relative to wetlands of the same type that are in “reference” condition, that is with no or minimal human impact. Urban wetlands are not expected to score high on such a scale. The wetlands with the highest ecological condition scores were generally located in the eastern, less developed part of the city. The wetlands with the lowest ecological condition score were generally located within the urban core –however, these truly urban wetlands scored the highest on a social rating scale indicating their importance for valued recreation and green space benefits. Historical aerial photographs indicate the streams along the Front Range were previously wide sandy washes with flashy flood flows. Many factors associated with urbanization including an increase in paved surfaces creating increased stormwater runoff, and flow constrictions from impoundments, road crossings, and culverts creating ponding, have changed the character of the Survey and Assessment of Critical Urban Wetlands: City of Aurora i streams. Hydrologic alteration is compounded by the fact that local watersheds receive additional water above their natural flow through transbasin diversions. Irrigation of lawns and parks may infiltrate into the soil and drain to local streams, increasing their base flow and further altering their character. Condition alone is not the full measure of wetland value. Functioning urban wetlands perform numerous ecosystem services that are acutely needed in highly developed watersheds, such as improving water quality, maintaining base flows, attenuating flood waters, providing habitat for plants, animals, and pollinators, as well as offering recreational and educational opportunities. Although water draining to urban wetlands contains high pollutant loads, wetlands filter some of those pollutants and provide cleaner water to downstream flows. While urban wetlands contain high cover of non-native species, their very presence in the developed landscape provides vital habitat where it is scare. Equally important, natural and green spaces within urban areas provide recreational and therapeutic opportunities for all residents, including children and families, to connect with nature. These ecosystem services are essential to watershed health and provide major economic benefits to society. However, degraded conditions impact a wetland’s functional capacity. Maintaining or improving the condition of urban wetlands can enhance their ability to provide these essential services. A balanced assessment of urban wetlands must consider both perspectives. First, it is important to document the condition of wetland resources and the stressors they face in order to recommend practical management actions to improve condition. Second, the assessment must consider the enormous benefit wetland ecosystems provide to urban residents and prioritize their conservation and management for current and future generations. This study of critical wetlands in the City of Aurora addresses both perspectives. While impacted by historic and current land use, all the wetlands surveyed in this project provide important wetland functions and are worthy of protection and restoration, even the lowest condition wetlands. Recommended management efforts for protecting and improving Aurora’s urban wetlands include protecting existing wetland and riparian buffers, minimizing construction activities impacts near wetlands and riparian areas, planning for watershed friendly trails, and limiting chemicals in weed treatment. In some areas streams have become disconnected from their floodplains due to stream entrenchment; reconnecting these streams to their floodplains and facilitating structural diversity would improve or restore a variety of wetland functions to Aurora wetlands. Additionally, the possibility of controlling non-native invasive bullfrogs that threaten the existing population of northern leopard frog, a Tier 1 species of greatest conservation need in Colorado should be investigated. The 20 wetland sites chosen for on-the-ground survey were chosen based on review of aerial photography with input from the stakeholder group. Wetlands that appeared to have the highest potential to be a natural feature, to be a functioning wetland, and/or with the presence of a vegetated buffer were chosen for on-the-ground survey. Most of the selected wetlands were in existing City of Aurora Natural Areas or Parks indicating Aurora has been proactive in protecting their wetlands. ii Colorado Natural Heritage Program © 2020 SUMMARY OF FINDINGS Wetland Mapping National Wetland Inventory (NWI) maps were updated for the City of Aurora using multiple sources of updated imagery. 2,568 acres or 2.5% of the City of Aurora is mapped as wetlands, waterbodies and riparian areas. 34% of the mapped acres (867 acres) are lakes and reservoirs and 13% (331 acres) are rivers, streams and canals. 26% of mapped acres (680 acres) are vegetated wetlands and ponds. Of these, herbaceous wetlands and ponds were the most common. The remaining 27% of mapped acres (690 acres) are non-wetland riparian areas. Wetland Condition Assessment Ecological Integrity Assessments (EIA) and surveys for critical biological resources were conducted at 20 targeted assessment areas that together covered 380 acres. The 20 wetlands surveyed ranged from good to poor condition. One wetland rated a B EIA score; 50% rated as C, and 45% rated as D. The condition of surveyed Aurora wetlands rated higher on average than the critical wetlands surveyed in the city of Denver and lower on average than the randomly sampled wetlands throughout the Lower South Platte River Basin. Five of the nine wetlands with D (poor) EIA condition scores had a very high or high social