Year IV of Post Restoration Monitoring at Shiawassee National Wildlife Refuge

Abstract

Our research took place at Shiawassee National Wildlife Refuge (SNWR) where recent hydrologic reconnection has restored a large area of floodplain wetland in the Shiawassee Flats region, where four major rivers meet before flowing into the Saginaw Bay. In this fourth and final year of post-restoration monitoring, our project team sought to assess the ecological health of the recently restored wetlands in comparison to reference conditions and previous years. Through a partnership with the U.S. Fish and Wildlife Service and U.S. Geological Survey, we were able to effectively carry out four months of ecological research monitoring centered around the study of four indicators of overall wetland health: water quality, vegetation, aquatic macroinvertebrates, and fish. Our goals for 2022 were to evaluate ecological conditions indicative of the wetland’s overall ecosystem health shortly after restoration in order to demonstrate the impact and value of SNWR’s restoration investment. By collecting and analyzing a robust set of ecological data along with comparing conditions across years, our team is able to provide recommendations to refuge managers and provide the data to support this refuge’s standing as a wetland restoration model for the Great Lakes region. Water Quality: We analyzed five key water quality parameters: average temperature, average pH, average conductivity, average turbidity, and average dissolved oxygen, for variation across months, wetland management unit, and vegetation type. Additionally, we analyzed nutrient samples to characterize the relationship between turbidity and dissolved Nitrogen and Phosphorus concentrations throughout SNWR. Finally, we visually compared water quality and nutrient levels across all four years of post-restoration monitoring. ● We found consistent trends in water quality across 2019-2022; conductivity is higher in the Shiawassee River (SHR) and Pool 1A (P1A) than in Maankiki units, and Maankiki South (MS) consistently holds the lowest dissolved oxygen levels. ● In 2022, water quality varied significantly across season, management unit, and vegetation type which in turn impacts community assemblages and seasonal movements of invertebrates and fish which impact higher trophic levels. ● Dissolved oxygen (DO) is possibly the most salient determinant of species guilds among our five parameters and limits the range of more sensitive taxa within the refuge making preservation of areas of higher DO important to preserving overall species diversity. ● We found a significant correlation between pH and dissolved oxygen which is related to rates of autotrophy and heterotrophy. 2 ● Turbidity still cannot be used as a reliable predictor for Phosphorus and Nitrogen concentrations, but in the future, using flow data as another predictor variable may help elucidate the relationship between Lake Huron seiche dynamics and upstream nutrient levels, or conversely the impact of upstream river water on nutrients at SNWR. ● Recommendations for management include increased sampling of water quality in certain vegetation types to better assess spatial heterogeneity, incorporating flow data into nutrient analysis, as well as preserving areas of high dissolved oxygen that are correlated with specific vegetation types. Vegetation: We surveyed and identified the plant community at SNWR with the goal of describing the vegetative structure of each of the four wetland management units, as well as the overall ecological health of the vegetative community within the sampled area. We performed 190 individual quadrat samples, collecting between 35 and 55 sample points in each wetland management unit, and performed a variety of statistical analyses in order to compare and contrast biotic indices in the wetland management units amongst dominant vegetation zones, individual units, and among overall sampling years (2019-2021). We found that: ● The ecological health of SNWR’s 4 wetland management units, while relatively low when compared with pristine pre-colonial reference conditions, is fairly high in the context of regional wetland quality. ● Indices of Biotic Integrity (IBI) scores have decreased since 2021 as a result of interannual discrepancies in data analysis and interpretation. ● Maankiki Center (MC), the most recently connected wetland management unit, had the lowest IBI assessment, and its 2022 metrics differed greatly from analysis performed in 2021. ● Floristic Quality Analysis (FQA) and Floristic Quality Index (FQI) scores have increased in every unit since the 2021 sampling season. ● Based on our data and results, we provide future recommendations for the management ՟of these wetland management units, including the prioritization of invasive species management via removal and intentional flooding. Aquatic Macroinvertebrates: We describe variations in macroinvertebrate abundance and community composition in SNWR and compare our findings to previous monitoring seasons, 2019-2021. Data is analyzed by unit, month, and vegetation zones of sampling. ● We collected macroinvertebrates from 55 sites and obtained fewer total individuals than previous years but maintained similar taxa richness. 3 ● The month of sampling contributed to the total abundance of macroinvertebrates collected, likely due to seasonal changes in the environment that trigger transitions in life-cycle stage. ● P1A, the ‘reference’ unit, had a community composition different than that of the Maankiki Marsh units, which is likely attributable to invertebrate dispersal ability and time-since-reconnection (as it is the oldest restored unit). ● Vegetation type had little impact on macroinvertebrate abundance or composition across all units. ● When calculating macroinvertebrate IBIs, all wetland management units were considered “mildly impacted.” This represents an increase in IBI values from the previous sampling season (2021). Fish: We monitored and surveyed wetland management units to characterize how fish populations are influenced by seasonal variation and interaction of other biotic and abiotic factors. Our research goals include assessing wetland health with IBI scores across wetland management units over the months of May, June, July, August, and October of 2022. Two gear types, fyke netting and electrofishing, were used to sample a wide variety of habitats within the wetlands, spanning various vegetation zones and water depths. There were a total of 108 fyke nets set and 31 electrofishing sites surveyed during the summer 2022 field season. We conducted statistical analysis to determine the implications of the data collected from monitoring. Statistical analysis allowed for an in-depth look at fish species abundance, community composition, and an assessment of the ecological wetland health. ● Despite dynamic filters that constrain the species pools of SNWR, the restored wetlands have recovered relatively quickly. ● The most recently restored wetland management unit, MC, is still more similar to SHR showing that there is a stage of colonization where species must compete to establish in the previously inaccessible habitat. ● IBI score assesses overall health of wetland management units based on species composition which ranged from moderately impacted (>45-50) to degraded (<36). Over the past four years, fish IBI has generally improved in the wetland management units. ● We surmise that the high fish abundance and various assemblages that we found support complex trophic interactions and high-quality ecosystem services. Trophic interactions between vegetation and macroinvertebrates are important factors in determining species composition and abundance. ● Island biogeography theory plays an important role in understanding the importance of unit connectivity and explains ecological variation by collective time of unit connection. 4 In the final year of post-restoration monitoring, our team was able to incorporate past years’ data alongside data from 2022 to comprehensively characterize ecological conditions shortly after restoration. Overall, our findings suggest a successful response of biotic communities to hydrologic reconnection and enable us to make recommendations that support further habitat improvements and biodiversity.