Ecosystem Dynamics and a Phosphorus Budget of an Alluvial Cypress Swamp in Southern Illinois

Abstract

Annual patterns in hydrology, phosphorus circulation, and sediment dynamics were studies in a southern Illinois, USA floodplain swamp dominated by bald cypress (Taxodium disyichum) and swamp tupelo (Nyssa aquatica). The study emphasized the swamp's interactions with the adjacent river. For the year, major inputs of water to the swamp were throughfall (74.3 cm) and runoff (69.4 cm) with minor contributions due to groundwater (21.6 cm). Outflows were by evapo—transpiration (72.3 cm), surface outflow (56.5 cm), and groundwater (21.0 cm), with the latter two draining primarily to the river. A flood occurred during the study period, passing 1.6 x 107m3 of river water over the swamp and depositing 0.06 cm of sediments. An annual phosphorus budget was developed for the swamp from field measurements. The greatest input of phosphorus to the swamp was 3.6 g P.m—2.yr—1, due to deposition of high—phorsphorus sediments during the flood. This was 10 times greater than the outflow of phosphorus to the river, 0.34 g P.m—2.yr—1, and 26 times greater than the throughfall input of 0.14 g P.m—2.yr—1. Total tree uptake from sediments was estimated to be 0.87 g P.m—2.yr—1 of which 0.77 g P.m—2.yr—1 returns as litterfall to the swamp sediments. Duckweed productivity was estimated to take 3.3 g P.m—2.yr—1 from the water column and deposit this in the sediments during die—off. For the period 1937—1967, cypress growth, based on tree ring analyses, was closely correlated with several measurements of flooding frequencies and magnitude, all obtained from past river data. Three ring data prior to 1937 showed poor correlation with flooding, probably because of logging activity. Cypress growth has decreased dramatically in recent years, corresponding to the rise in water level caused by beaver activity.