Hydrology and aquatic habitat characteristics of a riverine swamp: I. Influence of flow on water temperature and chemistry

Abstract

We monitored water temperature, air temperature, hydrologic characteristics, and chemical variables for 25 months in a 254-km2 portion of the Atchafalaya Basin, Louisiana, USA, a distributary swamp of the Mississippi River. We related observed trends in thermal and chemical variables to characteristics of the flood pulse, available channel types, and paths of water flow within the study area. Dissolved oxygen (range 0.05–13.05 mg L−1), percent oxygen saturation (range 0.6–142.4%), and pH (range 6.31–8.52) increased as river stages decreased, and water temperatures (range 4.75–32.25°C), specific conductance (range 207.8–931.5 μmhos), and the top–bottom difference in dissolved oxygen (−7.5–12.05 mg L−1) increased as air temperatures rose. The maximum variance observed for all chemical and thermal habitat characteristics occurred during periods when air temperatures exceeded, and river stages were less than, their respective medians observed during the study. At any point in time, thermal and chemical variables varied most among stations in water courses with no visible water turbulence (low-energy channels), and these channels consistently had lower dissolved oxygen, percent oxygen saturation, and pH than turbulent water courses (high-energy channels) or lakes contained. Water was directed from the river into one region of the study area from two opposing directions, thereby impeding water flow through the region. Low-energy channels in this region consistently exhibited lower dissolved oxygen concentrations, percent oxygen saturation, and pH than was observed in low-energy channels of regions where water flow was unimpeded. The quantity and quality of aquatic habitat characteristics in riverine swamps can be manipulated by controlling the timing and magnitude of the flood pulse, relative availability of different water courses, and internal paths of water flow through the swamp. Copyright © 1999 John Wiley & Sons, Ltd.