Freshwater Forum, Vol 28 (2010)

Coarse organic matter dynamics in urbanised tributaries of the St. Johns River, Florida

Michael Chadwick, Alexander Huryn, Arthur Benke, Dean Dobberfuhl

Abstract

Urbanisation can impact stream ecosystems by altering hydrology, channel geomorphology and riparian conditions. In this case study of four streams in the vicinity of Jacksonville, Florida, USA, we investigated how inputs, exports and within-channel storage of organic matter vary with differing urban–rural land use. Inputs ranged from 600 to 1000 g ash free dry mass (AFDM) m-2 y-1. Decreased riparian cover did result in significantly lower coarse particulate organic matter (CPOM) input. Export, estimated using leaf analogues, increased with urban land use. It appeared that estimated export was mostly influenced by stream hydrology and the extent of retentive structures. Monthly CPOM biomass ranged from 50 to 2000 g AFDM m-2. Streams shaded by riparian cover showed little seasonal pattern in CPOM biomass. However, the stream that lacked riparian shading had peak CPOM biomass in summer due to macrophyte production. This case study demonstrates how urbanisation can affect stream ecosystems at multiple spatial scales and highlights the importance of riparian vegetation management in urban settings.

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