Hooffs Run Watershed Special Threats or Challenges

The main threat to the Hooffs Run watershed is runoff extremes due to the highly urbanized nature of the City of Alexandria. The prevalence of impervious surfaces, and absence of a residential storm water management strategy implemented by private home owners to complement the city’s storm water management system, results in localized flooding and possibly the flow of toxins in to the Potomac River. Urbanization and the road network may also be leading to non-native plant invasion within the Hooffs Run Watershed based on a 2017 study.

According to an article in the ‘Biological Invasions journal’ authored by Dennis Skultety and Jeffrey Matthews, “Human modification of the landscape, including urbanization and road construction, has facilitated the spread and establishment of non-native plant species” (Skultety & Matthews, 2017).

The authors further conclude that heavily urbanized areas have a “combination of factors making them susceptible to invasion” and the “impacts of urbanization can subsequently change factors such as native community diversity, resource availability…which can increase susceptibility of local communities to invasion” (Skultety & Matthews, 2017).

The City of Alexandria is highly urbanized as evidenced in these images of the Del Ray and Old Town neighborhoods (source: Google Maps). It would be reasonable to conclude that based on the research undertaken by Skultety and Mathews, the Hooffs Run watershed is likely susceptible to non-native plant invasion and nutrient run off.

Furthermore, according to a paper by the American Geophysical Union, “urbanization impacts ecosystem functions and services by fundamentally altering the balances between precipitation, water yield, and evapotranspiration in watersheds” (Li et al., 2020). The paper goes on to note rapid urbanization poses “serious stresses” to watershed ecosystem structure, function, and services.

In order to mitigate the amount of water run off from private homes in to the storm water system, and reduce stresses to the watershed, residents within the Hooffs Run watershed could help by undertaking one simple measure.

Homeowners should consider a revised approach to lawns, noting they are a significant contributor to hazardous materials running off from private properties. Specifically, during rain and localized flooding, fertilizers and other lawn treatments (such as mosquito sprays) will eventually run off through the Hooffs Run watershed in to the Potomac River. The image below highlights a typical residential dwelling with a large lawn area that could be partially replaced by native grasses and sedges (source: Google Maps).

To reduce the impact of this hazard, home owners could easily replace 50% or more of their front and back laws with hearty native grasses and sedges that do not need fertilizer to survive and need minimal watering. If planted on mass throughout the watershed, it is possible there could also be a positive impact on improving evapotranspiration since native plants and sedges probably have more surface area than traditional urban lawns. While not certain, it is possible that native plants and grasses planted on mass throughout the Hooffs Run watershed could reduce the likelihood of invasive species taking hold. As in general terms, balanced ecosystems can be more successful in out-competing introduced species.

Sources: 

 

Li, C., Sun, G., Caldwell, P. V., Cohen, E., Fang, Y., Zhang, Y., . . . Meentemeyer, R. K. (2020). Impacts of Urbanization on Watershed Water Balances Across the Conterminous United States. Water Resources Research, 56(7). doi:10.1029/2019WR026574

Skultety, D., & Matthews, J. W. (2017). Urbanization and roads drive non-native plant invasion in the Chicago Metropolitan region. Biological Invasions, 19(9), 2553-2566. doi:10.1007/s10530-017-1464-7