Nutrient Removal in Rain Garden Lysimeters with Different Soil Types

Abstract

Rain gardens are increasingly used to control stormwater because they are effective at both volume removal and pollutant control. Nutrients carried in stormwater are a major concern for many watersheds because uncontrolled nutrients can lead to eutrophication, harmful algal blooms, fish kills, degradation of habitat quality, and an overall alteration to local ecosystems in receiving water bodies. Nutrients are removed by several mechanisms: filtration, adsorption, sedimentation, ion exchange, chemical precipitation, biological decomposition, and plant uptake. Much of the existing research on nutrient removal has focused on sandy soils. This study used discrete-weighing lysimeters as rain garden replicas to quantify nutrient reduction and constituent transport properties for five different soil types and flow patterns. Batch adsorption isotherm and column test experiments were also performed to support interpretation of the lysimeter results and place the results into context. The results indicate that rain gardens are effective at treating phosphorus, regardless of soil type. Nitrogen retention occurred, but not as effectively as phosphorus retention, and was not dependent on soil type. The implication for design is that native soils can effectively be used in rain gardens as long as volume removal goals are achieved.