Effects of enhanced freshwater mussel populations on water quality in a novel urban habitat of the Schuylkill River, Philadelphia, Pennsylvania

Lance Butler

doi:10.17918/00011432

Urban aquatic systems are often characterized by altered hydrology, degraded water quality, and reduced ecological function, limiting their capacity to support biologically diverse communities. While traditional management approaches rely heavily on engineered and landscape-based controls, increasing attention has been directed toward nature-based solutions that leverage biological processes to improve water quality and ecosystem resilience. Among these approaches, freshwater mussels (Family Unionidae) represent a potentially powerful yet underutilized component of urban aquatic restoration. This research integrates physiological, ecological, and modeling approaches to evaluate the capacity of freshwater mussels to persist and function within urban aquatic systems. Laboratory and field studies quantified species-specific physiological rates, including clearance rate (CR), filtration rate (FR), and net absorption rate (NAR), and evaluated their variability across environmental conditions. Seasonal variation strongly influenced all physiological processes, with peak filtration and assimilation rates occurring in fall in response to elevated particulate concentrations. When scaled to the mussel-bed level, these processes resulted in substantial material fluxes, with particulate matter removal exceeding 10,000 kg·yr⁻¹·ha⁻¹ and particulate nitrogen removal ranging from approximately 37 to over 150 kg N·ha⁻¹·yr⁻¹, driven primarily by dominant taxa (Utterbackiana implicata and Elliptio complanata). To assess feasibility within a novel urban habitat, controlled introductions were conducted in the Manayunk Canal using a Before–After, Control–Impact–Repeated Measures (BACIR) design. Hydrologic reconnection of the canal resulted in improved water quality and habitat conditions, including increased dissolved oxygen, reduced organic loading, and decreased sediment accumulation. Within this transformed system, freshwater mussels exhibited high survivorship, sustained growth, and stable condition across sites and cohorts. Survival remained comparable to a riverine reference, indicating that the canal did not function as a demographic sink, while growth and condition responses demonstrated that hydrologic restoration did not impose chronic physiological stress. Scenario-based modeling was then used to scale organism-level processes to system-level function under varying stocking densities. Modeled outcomes indicated that mussel assemblages could process up to approximately 30% of canal baseflow and remove between 200 and 7,500 kg·yr⁻¹·ha⁻¹ of particulate matter, with net absorption rates reaching 2,700 kg·yr⁻¹·ha⁻¹. Gross particulate nitrogen removal increased proportionally with density, exceeding 200 kg N·yr⁻¹·ha⁻¹ under high-density scenarios. These results establish a quantitative linkage between organismal physiology and ecosystem-scale water quality processes. Overall, these findings demonstrate that subadult freshwater mussels can persist, maintain physiological function, and contribute to measurable ecosystem services within urban aquatic systems. By linking organism-level processes with population structure and environmental context, this work supports the integration of freshwater mussel assemblages as a form of nature-based technology capable of augmenting traditional water quality management strategies through in situ particulate and nutrient processing.

Effects of enhanced freshwater mussel populations on water quality in a novel urban habitat of the Schuylkill River, Philadelphia, Pennsylvania

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Effects of enhanced freshwater mussel populations on water quality in a novel urban habitat of the Schuylkill River, Philadelphia, Pennsylvania

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