Geology topics

W.F. James

Publications and source records attributed to W.F. James.

5 recordsLinked to original sources

USGS2008

Effects of residence time on summer nitrate uptake in Mississippi River flow-regulated backwaters

Nitrate uptake may be improved in regulated floodplain rivers by increasing hydrological connectivity to backwaters. We examined summer nitrate uptake in a series of morphologically similar backwaters on the Upper Mississippi River receiving flow-regulated nitrate loads via gated culverts. Flows into individual backwaters were held constant over a summer period but varied in the summers of 2003 and 2004 to provide a range of hydraulic loads and residence times (??). The objectives were to determine optimum loading and ?? for maximum summer uptake. Higher flow adjustment led to increased loading but lower ?? and contact time for uptake. For highest flows, ?? was less than 1 day resulting in lower uptake rates (Unet, < 300 mg m-2 day-1), low uptake efficiency (U% < 20%) and a long uptake length (Snet > 4000 m). For low flows, ?? was greater than 5 days and U% approached 100%, but Unet was 200 mg m-2 day-1. Snet was < half the length of the backwaters under these conditions indicating that most of the load was assimilated in the upper reaches, leading to limited delivery to lower portions. Unet was maximal (384-629 mg m-2 day-1) for intermediate flows and ?? ranging between 1 and 1.5 days. Longer Snet (2000-4000 m) and lower U% (20-40%) reflected limitation of uptake in upper reaches by contact time, leading to transport to lower reaches for additional uptake. Uptake by ???10 000 ha of reconnected backwaters along the Upper Mississippi River (13% of the total backwater surface area) at a Unet of ???630 mg m-2 day-1 would be the equivalent of ???40% of the summer nitrate load (155 mg day-1) discharged from Lock and Dam 4. These results indicate that backwater nitrate uptake can play an important role in reducing nitrate loading to the Gulf of Mexico. Copyright ?? 2008 John Wiley & Sons, Ltd.

River Research and Applications↗

USGS1996

Phosphorus dynamics in Delavan Lake Inlet, southeastern Wisconsin, 1994

Removal of rough fish from Delavan Lake Inlet in southeastern Wisconsin transformed the inlet from a shallow, turbid-water system with few macrophytes to a clear-water system with an abundance of macrophytes and increased phosphorus concentrations. To understand the changes in the phosphorus dynamics, the U.S. Geological Survey and the U.S. Army Corps of Engineers, in cooperation with the Town of Delavan, constructed a detailed phosphorus budget for the inlet for April through September 1994. The budget included inputs from the drainage basin, atmosphere, sediments (as a function of pH and the fraction of the day under anoxic conditions), and ground water. Laboratory studies estimated phosphorus flux rates under various conditions. Field studies documented ambient conditions in the inlet and fluxes of phosphorus into and out of the inlet. Phosphorus released from the sediments was estimated by coupling the flux rates, estimated in the laboratory, with ambient conditions in the inlet. The detailed phosphorus budget indicated that the increase in phosphorus concentrations was caused primarily by elevated pH resulting from increased photosynthetic activity of the macrophytes and a high release of phosphorus from the sediments. The release of phosphorus from the sediments was the largest source of phosphorus to the inlet in the spring and summer of 1994 and in other years of low to near normal runoff; however, in years of high runoff, phosphorus input from the inlet's drainage basin was the largest source of phosphorus. A less-detailed phosphorus budget constructed for the period from February 1993 to September 1994 demonstrated that, over the entire year, runoff from the drainage basin was the dominant source in the phosphorus budget. During April-September 1994, the input of phosphorus from the inlet may especially affect the summer productivity in Delavan Lake because almost 80 percent of the phosphorus loading during this time was in the form of dissolved orthophosphate.

Wisconsin↗

USGS1996

Phosphorus mobilization from littoral sediments of an inlet region in Lake Delavan, Wisconsin

Rates of P release from littoral sediments of the inlet region of Lake Delavan, Wisconsin, were examined in the laboratory under different redox and pH regimes using sediment systems and also in situ using sediment peppers. In the laboratory, rates of P release from sediments increased about two-fold (i.e., to 7 mg m-2 d-1) under oxic conditions as a result of adjusting the pH of the overlying water from 8.5 to about 9.0. Laboratory rates increased to a maximum of 23 mg m-2 d-1 under anoxic conditions. Both in situ pH and dissolved oxygen (DO) exhibited marked seasonal fluctuations due, primarily, to metabolism by submersed macrophytes, which occupied over 50% of the inlet region. Using continuous records of in situ pH and DO and ranges in rates of P release measured in the laboratory, we estimated an overall mean rate of P release of 5.7 mg m-2 d-1 from the littoral sediments during the summer (April-September) of 1994. Rates of P release estimated from Fickean diffusional fluxes were similar to rates estimated from pH and DO. Our results suggest that aquatic macrophyte communities of the inlet region enhance the mobilization of P from littoral sediment by regulating pH and DO in the surrounding environment.

Archiv fur Hydrobiologie↗

USGS1993

Analysis of summer phosphorus fluxes within the pelagic zone of Eau Galle Reservoir, Wisconsin

Major phosphorus (P) fluxes to and from the pelagic zone (i.e., open water region including epilimnion, metalimnion, and hypolimnion) were estimated from data collected over a 6 year period during the summer in Eau Galle Reservoir, Wisconsin. P inputs to the pelagic zone included profundal sediments, the watershed, groundwater, and transport of P from the littoral zone. P outputs from the pelagic zone included discharge from the reservoir, deposition, and transport of P to the littoral zone. Nighttime convective circulation was assumed to be the dominant mechanism of P exchange between the littoral and pelagic zones. Littoral P inputs, often neglected from budgetary analyses, accounted for 15% of the total measured P input and 25% of the internal P input to the pelagic zone. External P inputs were greatest, accounting for 42% of the total measured P input to the pelagic zone. These results emphasize the need for control of various sources of P inputs in the development of lake and reservoir management strategies.

Lake and Reservoir Management↗

USGS1993

Sediment resuspension, redeposition, and focusing in a small dimictic reservoir

Rates of seston (dry mass) sedimentation, estimated from sediment traps (ST rates) and sediment cores (SC rates), were determined at four water depths to examine seasonal and annual sedimentation patterns in Eau Galle Reservoir, Wisconsin (USA). Annual ST rates overestimated annual SC rates at water depths less-than-or-equal-to 4 m, suggesting that sediment resuspension and redeposition in relatively shallow regions of the reservoir caused the overestimate. In contrast, annual ST and SC rates were similar at depths >4 m, suggesting minimal sediment resuspension and redeposition in deeper regions of the reservoir. Using variations in daily ST rates estimated during the autumn overturn of 1987, we developed a conceptual framework for estimating sediment resuspension, redeposition, and focusing. Resuspension of shallow sediments during this particular period accounted for over 50% of the annual ST rate at depths less-than-or-equal-to 4 m. At the same time, focusing of resuspended shallow sediments to deeper regions accounted for about 20% of the annual ST rate at depths >4 m. Our results indicate that during autumn overturn in this reservoir, peaks in sedimentation in the deep, profundal region, estimated from sediment traps, may reflect sediment focused from shallow regions rather than sediment resuspended from the profundal region.

Canadian Journal of Fisheries and Aquatic Sciences↗