Sediment and Nutrient Losses from Prairie and Turfgrass Buffer Strips during Establishment

Abstract

The increase in impervious surface areas associated with urban development has created a more efficient water conveyance system leading to heightened surface water runoff flows and volumes. There is public concern about the continued degradation of bodies of water through increased sediment and nutrient loading, and the effects that urban vegetation may have on these receiving waters. We conducted a study focusing on the qualitative and quantitative characteristics of surface water runoff from urban landscapes. Turfgrass and prairie landscapes were compared for their use as buffer strips in reducing nutrient- and sediment-rich runoff from urban areas. Three impervious to pervious surface ratios (1:1, 1:2, 1:4) were studied to obtain information for improved design of urban landscapes to control runoff. Runoff events from natural precipitation were monitored continuously for 24 months following seeding of vegetated buffer strips downslope from pavement. All water samples were analyzed for phosphorus (P) as total phosphorus, bioavailable phosphorus, soluble phosphorus, organic soluble phosphorus, and for sediment concentration. The majority (>75%) of runoff, nutrient, and sediment loading occurred during frozen soil conditions. A 2:1 or 4:1 buffer:pavement ratio reduced runoff and nutrient loading only during nonfrozen soil conditions. Prairie vegetation had 46% and 119% more total runoff volume than turfgrass vegetation during the first two years of establishment, respectively (p = 0.08). Sediment losses from prairie were two to five times greater than from turf (p < 0.05) during non-frozen soil conditions, and decreased in both systems from year one to year two. Total phosphorus loads averaged 0.18 kg ha -1 and 0.08 kg ha -1 from native prairie, compared to 0.07 kg ha -1 and 0.02 kg ha -1 from turfgrass buffers during nonfrozen soil conditions during the first and second years of establishment, respectively (p < 0.05). Total annual P and sediment losses from prairie and turf were similar, however, because runoff during frozen soil conditions was significantly greater than runoff from nonfrozen soil. Although not an intended focus of the study, the high proportion of forbs (broadleaf prairie herbs) relative to prairie grasses in the commercial seed mixtures recommended for urban plantings may not truly represent prairies which existed prior to European colonization. Since only a small portion of runoff occurred from either of the vegetated surface types during the growing season, surface water quality in temperate regions may benefit best from urban stormwater management practices aimed at controlling runoff during the winter months.