T. Wells Shartle
Published: 2012
Total Pages: 260
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The Richland Creek WMA constructed wetland for water reuse, located 40 km southeast of Corsicana, Texas, was designed by Tarrant Regional Water District (TRWD) and is operated jointly with Texas Parks and Wildlife Department (TPWD). TRWD's perspicacity to supply the regions rapidly growing population with an additional secure water source, and the desire of TPWD to enhance migratory and indigenous wildlife habitat, as well as providing outdoor recreational opportunities to the public, led to the joint venture. The constructed wetland operates on water from the Trinity River (TR), from which the wetland reduces water nutrient and metal concentrations and thereby improves water quality. The purpose of this study was to assess the first seven years of operation of the field-scale wetland's nutrient removal efficiency, primarily addressing the fate of phosphorus (P). For the field study, conducted during a period of moist-soil management (MSM), soil/sediment samples were collected from the sedimentation basin (SB), Cell 1, Cell 3, and a reference wetland (RW) with a similar soil series that is inundated only during overbank flooding from the TR. Soil samples were tested for Mehlich 3 P (M3P), water extractable P (WEP), total P (TP), a P sorption index (PSI), and pH. The field study results indicated that soil P is more concentrated in the SB and cell 1 of the wetland system than in cell 3 or the RW. M3P concentration was nearly double the threshold for no additional fertilizer recommendations for agriculture of 60 mg kg−1 in the SB and cell 1. WEP concentrations are highest in the SB and cell 1. TP concentrations are comparable to other treatment wetland systems that receive high quantities of P from the water column. The PSI identified the SB and cell 1, the areas with consistently higher soil P concentrations, as the areas with the least potential P fixing capacity remaining. Hydrologic data collected by TRWD from the summer of 2003 through the winter of 2010, was analyzed and provided some insight regarding nutrient loading that has occurred in the constructed wetland. The results indicated that the wetlands efficiency at removing nutrients from the water was linked to the nutrient accumulation in soils of the wetland. The wetland cells with the higher estimated TSS loading, also had a higher soil P concentrations. An ex situ and in situ tillage simulation was completed in order to determine a potential solution to prolong the effectiveness of the wetland system and avoid hydrologic burnout. The no-till, 10-cm, and 20-cm tillage groups, underwent a three phase water column study and then the soil was tested for M3P, TP, and a PSI. The water column study indicated the tillage treated soils released less P, were more efficient at removing P from a 2 mg P L−1 solution, and just as efficient at removing P from a 75 mg P L−1 solution as the no-till soil. The soil core experiment indicated tillage may provide plants during MSM more readily available P for enhanced growth, while also improving efficiency at removing P from the water column. The ex situ soil P data indicated that a deeper tillage depth has potential to distribute P more deeply in the soil column.