Substrate Characterization of an Experimental Marsh and Three Natural Marshes

Abstract

Abstract Dredge material from the Gulf Intracoastal Waterway near Galveston, Tex., was used as a substrate material in the construction of an experimental intertidal salt marsh. Chemical and physical properties of dredge substrate samples at 270 sites were monitored over a 16‐month period. Cation exchange capacity (CEC), extractable phosphorus (P), total Kjeldahl nitrogen (TKN), NH 4 ‐N, and organic matter increased from 3.0 to 7.4 meq/100 g, 24 to 96 µg P/g, 85 to 296 µg N/g, 3.0 to 9.9 µg N/g, and 0.2 to 0.5%, respectively. No significant increases in N and P were observed in the substrate due to fertilization. A separate study comparing substrate properties of the experimental marsh to three natural marshes demonstrated that organic matter, TKN, and NH 4 ‐N concentrations in the experimental marsh were lower. Organic matter, TKN, and NH 4 ‐N in the experimental marsh substrate averaged 0.6%, 260 µg N/g, and 5.4 µg N/g compared to 2.3%, 650 µg N/g, and 12.1 µg N/g, respectively, for the three natural marshes. Within each of the four marsh sites extreme spatial heterogeneity of chemical and physical properties was apparent.