| An intensive green roof study measured water retention and quality during small-scale irrigation events. Medium retention was promising with 32 to 65 percent of irrigation water retained at irrigation rates ranging from 1.8 to 12.5 cm/hr. Total Kjeldahl nitrogen (TKN), phosphorus (TP) and dissolved solids (TDS) discharge concentrations increased by 77%, 21% and 27%, respectively, compared to irrigation water. Although concentrations increased, nutrient mass exported from the roof was, generally less than the mass loading rate. TKN and TP mass varied by treatment, adding up to 113% or removing up to 63% of mass to discharge, while TDS mass reduced as much as 55%. Concerns regarding water quality, as measured by concentration, obscure the fact that the total mass of nutrients exported from the roof generally decrease. Obtaining reproducible results of full-scale green roof performance from applied treatments remains elusive, largely due to the variable quality of green roof media. |
