Longitudinal survey of the upper Ohio River with implications on the impact of tributaries.

摘要

The Ohio River system was extensively sampled every 8 km within the main stem and in 34 major tributaries from Pittsburgh, PA, to Rising Sun, IN. This study used data from that sampling to characterize Ohio River chemical, physical, and biological attributes; and determine any longitudinal changes along this continuum. The objectives were to determine: (1) if tributaries were different than the main stem due to effects from predominant land use (ie: agriculture, forested, urban); (2) if discharge from distinct tributaries alter the river main stem; (3) which factors control algal biomass through experimentation; and (4) how algal communities of tributaries and the main stem differ with respect to land use practices in the tributary watershed. In situ measurements of temperature, dissolved oxygen, pH, conductivity, turbidity, and water samples were collected and analyzed for dissolved inorganic nitrogen (DIN), soluble reactive phosphorus (SRP), total phosphorus (TP), and chlorophyll. Whole water samples were collected and preserved with Lugol's iodine for algal community analysis. The Ohio River was significantly different from its tributaries in light penetration, conductivity, total phosphorus, and chlorophyll. Longitudinally, the cumulative effluent from tributaries not only increased the Ohio River discharge but some nutrients (DIN, SRP, TP) also gradually increased downriver. The flooding Kanawha River tributary had a significant impact on the Ohio River that persisted for several miles downriver (ANOVA p 0.05). A series of controlled experiments showed that light penetration was the most important factor affecting chlorophyll (ANOVA p 0.05). Tributaries with agriculture-dominated land use within their watershed had much higher levels of nutrients and chlorophyll, which separated from other tributaries by DCA. Tributaries had significantly higher algal densities, and some had a dominant taxon that comprised more than 40% of the community. Canonical Correspondence Analysis showed a significant, dominating gradient that determined the relationship between taxa and the environment (CCA axis 1 p = 0.020). Site scores separated along these axes in relation to their land use and underlying geology.