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Florida Lake Management Society Annual Conference, Naples, Florida, June 4 – 7, 2007

INVERTEBRATE COMMUNITY PATTERNS ASSOCIATED WITH LAND USE INFLUENCED CHANGES IN ORGANIC MATTER LOADING IN TRIBUTARIES OF THE LOWER ST. JOHNS RIVER.

Dean R. Dobberfuhl St. Johns River Water Management District Palatka, FL. Michael A. Chadwick, Alex D. Hury and Arthur C. Benke University of Alabama Tuscaloosa, AL

Introduction

Organic matter, primarily in the form of detritus, serves as the resource base for invertebrates in many small streams (Wallace et al. 1997). However, urban development reduces organic matter inputs and can potentially alter stream ecosystems through a suite of possible mechanisms (Meyer et al. 2005, Walsh et al. 2005). These changes have been shown to alter stream function in northeast Florida streams (Chadwick et al. 2006). One important finding was that increased urbanization changes the character of the organic matter loading by increasing the relative proportion of labile OC. It was hypothesized that increasing labile organic carbon in the system would improve detrital food quality and result in greater secondary productivity. A two- year study was undertaken to examine the effects of urbanization on low-order streams in the lower St. Johns River basin. The prediction that increased labile carbon would produce greater macroinvertebrate biomass was tested.

Methods

Eighteen watersheds were selected representing a range of total impervious area from 0- 66%. Water quality samples were collected monthly from streams draining those watersheds and analyzed for standard field and chemical parameters. Macroinvertebrate samples were collected from a subset of seven streams, representing various levels of urbanization with 0-51% impervious surface. Macroinvertebrates were sampled quarterly or monthly in triplicate at five random sites within a 100-m reach. Samples were sorted, counted, and measured for biomass estimation. Analyses were performed using Systat®.

Results and Discussion

Sites were significantly different with respect to all measured forms of OM. Factor analysis indicated that most of the variance among sites was explained by differences in seston, labile OM, and refractory OM. There was no relationship between benthic organic matter (CPOM) or seston (FPOM) and total impervious area (TIA). The only apparent effect of impervious surface on OM constituents was an exponential decline in TOC and a significant increase in the relative proportion of labile TOC with increasing TIA. Thus, it appears that increasing TIA in watersheds (i.e., urbanizing) not only reduces the total loading of OM but also

Session 9 – Page 2

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