Urban wastewater includes stormwater runoff and sewage. Increases in stormwater occur concurrently with high levels of impervious surface and changes in land use associated with development. In older cities, including Wilmington, outdated, combined sewer and stormwater infrastructure can result in sewage flows into streams and rivers, and problems with sewage backup during flooding events. Efforts to address these issues are being made, but projects are costly. 

Delaware has a long legacy of industrial pollution. Currently, 17 sites in Delaware are on the U.S. EPA’s National Priority List (EPA 2025).  

With respect to toxic substances that affect Delaware’s water resources, the Division of Waste and Hazardous Substances and the Division of Watershed Stewardship have developed a Watershed Approach to Toxics Assessment and Restoration (WATAR). WATAR is a holistic (watershed scale), integrated, and systematic approach to the evaluation of contaminant sources, transport pathways, and receptors, and a mechanism to implement restoration actions based upon site prioritization. 

Nutrients from agriculture and development are a problem for aquatic systems, especially in the Inland Bays watershed. Nitrate concentrations on the Coastal Plain can exceed 10mg/L in agricultural areas, ranging as high as 41.5 mg/L (Soroka et al. 2024). Delaware NEMO (Nonpoint Education for Municipal Officials), coordinated by the University of Delaware’s Delaware Sea Grant Program, is an educational program for local decision makers that addresses the relationship between land use and natural resource protection, with a focus on watersheds. The Chesapeake Bay Watershed is also designated a Critical Conservation Area (CCA) by the NRCS Regional Conservation Partnership Program (RCPP), with the goal of addressing issues related to inadequate habitat and water quality degradation. 

Pesticides, including fungicides and insecticides, present an issue for many invertebrate SGCN. Recent research on declines of Honeybees (Apis mellifera) implicates both insecticides and fungicides in bee declines (Pettis et al. 2013, Fairbrother et al. 2014), and these results are likely applicable more broadly to other native bee species, especially bumblebees (Bombus sp.). Studies indicate that foraging bees are acquiring pesticides not just from foraging on the flowers of treated crops, but also from non-crop species at field margins and other areas within agroecoystems that may be subject to overspray. Widespread use of neonicotinoid insecticides, such as imidacloprid, in agricultural systems represents a threat to non-target invertebrates (reviewed by Pisa et al. 2015), including SGCN, as well as a potential threat to vertebrate SGCN via both direct and indirect impacts (reviewed by Gibbons et al. 2015).   

Widespread use of non-selective herbicides to treat weeds in herbicide-tolerant (e.g., Roundup Ready®) crops reduces diversity of native plants in the vicinity of field margins and may lead to increased herbicide resistance of some plant species (VanGessel 2001), potentially including invasives. 

In residential settings, pesticide use continues to occur at a large scale. The recent popularity of private backyard mosquito control treatments, especially those utilizing adulticides as barrier sprays, has the potential for negative impacts on native invertebrate species, including SGCN bees, butterflies, and moths.  Coordination, information dissemination, and technical assistance with the landscaping and pest control industries are important in minimizing impacts to non-target wildlife and water quality.  

Excess Energy 

Thermal, Noise and Light Pollution 

Thermal pollution of the Delaware Estuary from cooling water discharges at industrial complexes along the Delaware River and Bay is a potential issue for aquatic SGCN, especially since river temperatures are already rising globally as a result of climate change (Kaushal 2010, Van Vliet et al. 2011) and thermal impacts of discharges may contribute to local exacerbation of these effects (Coulter et al. 2014). 

Studies indicate that there are negative effects from noise pollution on breeding birds (Ortega 2012, Schroeder et al. 2012) and these effects are more pronounced in insectivorous species and species with lower frequency vocalizations that overlap to a greater extent with ambient noise frequencies from highways, air traffic, and other sources (Francis 2015). Delaware’s extensive road transportation network and location within the flight paths of several major airports are sources of excess noise. In-water noise (such as from pile driving, excavation, drilling, etc.) can create an impediment to upstream migration for anadromous fish species. American Shad (Alosa sapidissima), Blueback Herring (Alosa aestivalis), and Alewife (Alosa pseudoharengus) are especially sensitive to changes in their natural environment and noise and vibrations can interrupt their upstream migration to spawning areas. Marine noise also has detrimental effects on marine mammal SGCN. The National Oceanic and Atmospheric Administration (NOAA) has developed acoustic guidance for assessing the effects of anthropogenic sound on marine mammal species under their jurisdiction (NOAA 2024). 

Light pollution is one of the most common forms of excess energy in the Northeast. Beachfront lighting has long been known to disorient sea turtle hatchlings. Excessive nighttime lighting has similar disconcerting effects on migrating birds and can disrupt their circadian rhythms (Cabrera-Cruz et al. 2018). Bats, including members of the genus Myotis, show mixed responses. They may avoid traveling through areas with artificial lighting and opportunistically forage around light fixtures that are attracting night-flying insects; increased light levels may lead bats to abandon roosting sites and can disrupt circadian rhythms and alter nightly emergence timing (Stone et al. 2015). Nocturnal insects and other invertebrates are also heavily impacted by light pollution (Gaston et al. 2013). Fireflies are of particular interest as lighting may affect this taxonomic group more than other nocturnal insects because it interferes with their bioluminescent communication signals (Firebaugh and Haynes 2016, Owens and Lewis 2018).  

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