Partitioning of selected micronutrients and trace elements and distribution of clay minerals in the substrate of one artificial and three natural marshes

Abstract

Dredged sediments from the Gulf Intracoastal Waterway near Galveston, Texas were used as a substrate in the construction of an artificial marsh. Substrate chemical and physical properties (total Kjeldahl nitrogen, ammonium, nitrate, cation exchange capacity, pH, extractable phosphorus, particle size distribution, organic matter) were monitored for 2 1/2 years following construction of the marsh site. Low concentrations of clay, organic matter and nutrients were determined during the initial characterization. Increases of 3 to 10 fold in total Kjeldahl nitrogen, ammonium, organic matter, extractable phosphorus, cation exchange capacity, and clay content were observed in the artificial marsh over the study period. The artificial marsh and three natural marshes were compared at the conclusion of the study. Concentrations of total Kjeldahl nitrogen, ammonium, and organic matter for the natural marshes were much higher (2 to 3 times) than in the artificial marsh. Extractable phosphorus and clay concentrations of the artificial marsh fell within the range of values determined for samples from the natural marshes. Concentrations of substrate parameters increased with decreasing site elevation. Substrate samples taken from the artificial and natural marsh sites were fractionated to determine the distribution of Cu, Ni, Cr, Zn, Mn, and Fe. Substrates from the artificial and natural marshes contained low concentrations of Cu, Ni, Cr, Zn, Mn, and Fe. Large percentages, of total elemental concentrations, were fixed or associated with the organic + sulfide fraction, Mn and Fe hydrous oxides, and the residual phase. Only Zn and Mn were detected in the exchangeable + water soluble fraction. Under stable conditions the metals associated with the exchangeable + water soluble fraction were considered to be plant available.