Evapotranspiration of Residential Lawns Across the United States

Despite interest in the contribution of evapotranspiration (ET) of residential turfgrass lawns to household and municipal water budgets across the United States, the spatial and temporal variability of residential lawn ET across large scales is highly uncertain. We measured instantaneous ET (ETinst) of lawns in 79 residential yards in six metropolitan areas: Baltimore, Boston, Miami, Minneapolis-St. Paul (mesic climates), Los Angeles and Phoenix (arid climates). Each yard had one of four landscape types and management practices: traditional lawn-dominated yards with high or low fertilizer input, yards with water-conserving features, and yards with wildlife-friendly features. We measured ETinst in situ during the growing season using portable chambers and identified environmental and anthropogenic factors controlling ET in residential lawns. For each household, we used ETinst to estimate daily ET of the lawn (ETdaily) and multiplied ETdaily by the lawn area to estimate the total volume of water lost through ET of the lawn (ETvol). ETdaily varied from 0.9 ± 0.4 mm d1 in mesic cities to 2.9 ± 0.7 mm d−1 in arid cities. Neither ETinst nor ETdaily was significantly influenced by yard landscape types and ETinst patterns indicated that lawns may be largely decoupled from regional rain-driven climate patterns. ETvol ranged from ∼0 L d−1 to over 2,000 L d−1, proportionally increasing with lawn area. Current irrigation and lawn management practices did not necessarily result in different ETinst or ETdaily among traditional, water-conserving, or wildlife-friendly yards, but smaller lawn areas in water-conserving and wildlife-friendly yards resulted in lower ETvol

Contribution of Leaf Litter to Nutrient Export during Winter Months in an Urban Residential Watershed

Identification of nonpoint sources of nitrogen (N) and phosphorus (P) in urban systems is imperative to improving water quality and better managing eutrophication. Winter contributions and sources of annual N and P loads from urban watersheds are poorly characterized in northern cities because monitoring is often limited to warm-weather periods. To determine the winter export of N and P, we monitored stormwater outflow in a residential watershed in Saint Paul, Minnesota during 2012–2014. Our data demonstrate that winter melt events contribute a high percentage of annual N and P export (50%). We hypothesized that overwintering leaf litter that is not removed by fall street sweeping could be an important source to winter loads of N and P. We estimated contributions of this source by studying decomposition in lawns, street gutters, and catch basins during two winters. Rates of mass and N loss were negligible during both winters. However, P was quickly solubilized from decomposing leaves. Using mass balances and estimates of P leaching losses, we estimated that leaf litter could contribute 80% of winter total dissolved phosphorus (TDP) loading in this watershed (∼40% of annual TDP loading). Our work indicates that urban trees adjacent to streets likely represent a major source of P pollution in northern cities. Management that targets important winter sources such as tree leaves could be highly effective for reducing P loading and may mitigate eutrophication in urban lakes and streams in developed cities

Assessment of Regional Variation in Streamflow Responses to Urbanization and the Persistence of Physiography

Aquatic ecosystems are sensitive to the modification of hydrologic regimes, experiencing declines in stream health as the streamflow regime is altered during urbanization. This study uses streamflow records to quantify the type and magnitude of hydrologic changes across urbanization gradients in nine U.S. cities (Atlanta, GA, Baltimore, MD, Boston, MA, Detroit, MI, Raleigh, NC, St. Paul, MN, Pittsburgh, PA, Phoenix, AZ, and Portland, OR) in two physiographic settings. Results indicate similar development trajectories among urbanization gradients, but heterogeneity in the type and magnitude of hydrologic responses to this apparently uniform urban pattern. Similar urban patterns did not confer similar hydrologic function. Study watersheds in landscapes with level slopes and high soil permeability had less frequent high-flow events, longer high-flow durations, lower flashiness response, and lower flow maxima compared to similarly developed watersheds in landscape with steep slopes and low soil permeability. Our results suggest that physical characteristics associated with level topography and high water-storage capacity buffer the severity of hydrologic changes associated with urbanization. Urbanization overlain upon a diverse set of physical templates creates multiple pathways toward hydrologic impairment; therefore, we caution against the use of the urban homogenization framework in examining geophysically dominated processes