[미국] 빗물정원의 여과지와 식물 종류 실험

노스캘롤라이나 주립대학교의 연구원은 빗물정원이 도시 폭우 배출로 야기되는 수질 문제를 개선하는 하나의 방법이라고 밝혔다. 빗물정원은 움푹 파인곳에 우수를 저장하고 미생물 활성, 여과, 흡수, 식물의 흡수를 통해 오염원을 제거할 수 있다. 전형적으로 정원은 여과지와 함께 파지거나 식물과 함께 다시 메워져서 오염원 제거를 돕는다.

HorScinece에서 출간되 연구의 주요 필자인 Helen Kraus는 "여과지는 빗물정화의 기본이고 오염원을 제고하고 식물이 성장하도록 돕는다."고 설명했다. Kraus와 동료들은 세 가지 다른 여과지를 통해 영양분 제거와 식물 성장에 어떤 차이가 있는지 알아보기 위해 실험을 설계했다.

연구팀은 3개의 여과지 중 하나를 갖는 12개의 빗물 정원을 건설했다. 빗물 정원은 16개 종의 식물이 심어지고 우수로 관개됐다. 실험에 사용된 모래 베이스의 기질은 80% 젖은 모래, 15% 진흙과 세이토, 5% 소나무 껍질로 구성된다. 한편 흙 베이스의 기질은 50% 사양토, 50% 소나무 껍질로 구성되며 슬레이트 베이스 기질은 80% 슬레이트와 20% 소나무껄질로 구성된다.

실험 결과 모래는 질소를 제외한 오염원의 잔류에 전체적으로 좋았으며 흙은 인의 개선에 제일 낮은 효과를 갖으며 질소 제거 효율은 슬라이트와 비슷했다. 슬라이트는 질소와 인의 잔류에 최고 효율성을 보였다.

Researchers from North Carolina State University are looking to rain gardens as one way to remediate the water quality concerns caused by urban stormwater runoff. Rain gardens -- also known as bioretention cells -- are depressions in the landscape that trap stormwater runoff so microbial activity, filtration/adsorption and plant uptake can remove pollutants. Typically, the gardens are excavated, backfilled with a filter bed substrate, then planted with vegetation that helps to remove pollutants.

"The filter bed substrate is the foundation of the rain garden and gives it the ability to infiltrate runoff, slow drainage, support plant growth, and remove pollutants," explained Helen Kraus, lead author of a study published in HortScience. Kraus and her colleagues designed experiments to assess three different filter bed substrates for their effectiveness in nutrient removal and supporting plant growth.

The research team constructed 12 rain gardens filled with one of three filter bed substrates. The gardens were planted with 16 plant species and then irrigated with stormwater. The substrates used in the experiments included a sand-based substrate (sand) composed of 80% washed sand, 15% clay and silt fines, and 5% pine bark; a soil-based substrate (soil) composed of 50% sandy loam soil and 50% pine bark; and a slate-based substrate (slate) composed of 80% expanded slate and 20% pine bark.

The substrates differed in infiltration and drainage rates as well as chemical composition. Further, diverse plant species that included trees, shrubs, herbaceous perennials, a grass, and a rush were selected to allow the researchers to evaluate the performance of a wide range of evergreen, deciduous, woody, and herbaceous plants.

Results showed that sand had good overall retention of pollutants except nitrogen. Soil had the lowest remediation of phosphorus and highest concentration of phosphorus in its effluent and was similar in nitrogen removal efficiency to slate. Slate had the best retention of nitrogen and phosphorus. "Overall, all three substrates functioned in reducing the quantity of pollutants in urban stormwater runoff," the authors noted. They added that the impact of substrate on remediation appeared to lessen by the second season of the study; as the plants grew, root growth impacted infiltration, and nutrient uptake by the plants increased.

The researchers determined that 11 of the 16 species used in the experiments grew well in the rain gardens. Betula nigra (river birch), Betula nigra 'Duraheat', Magnolia virginiana (sweet bay magnolia), Magnolia virginiana 'Sweet Thing', Itea virginica (Virginia sweetspire), Itea virginica 'Henry's Garnet', Panicum virgatum 'Shenandoah', Juncus effuses 'Frenzy', Helianthus angustifolius (swamp sunflower), Helianthus angustfolius 'First Light', and Eupatorium purpureum subsp. maculatum (Joe pye weed) performed well in the experiments and could be used as rain garden plants, according to the authors.

[출처 = Water World / 2014년 7월 21일]