Nitrification, the microbial conversion of ammonium to nitrate, is an important transformation in aquatic nitrogen cycle, but factors regulating nitrification rates freshwater ecosystems are poorly understood. We investigated effects organic carbon quantity and quality on stream sediments. First, we hypothesized that when environmental C: N ratios high, heterotrophic bacteria subject limitation will outcompete nitrifying for available NH 4 + , thereby reducing rates. In laboratory...

We evaluated patterns of denitrification and factors effecting in the upper Mississippi River. Measurements were taken over 2 years, during which river discharge ranged from record flooding to base flow conditions. Over period study, average enzyme activity was highest backwater lakes lowest main channel. Throughout study reach, occurred fall winter. Rates spring floods (2001) only slightly higher than preceding Mean unamended rates 0.02 (fall 2001 backwaters) 0.40 µg N·cm –2 ·h –1 (spring...

1. Microbial decomposition of dissolved organic carbon (DOC) contributes to overall stream metabolism and can influence many processes in the nitrogen cycle, including nitrification. Little is known, however, about relative rates different DOC sources their subsequent effect on 2. In this study, labile fraction microbial were measured for leaf leachates from 18 temperate forest tree species. Between 61 82% (mean, 75%) was metabolized 24 days. Significant differences among found ( P <...

We investigated the response in nitrification to organic carbon (C) availability, interactive effects of C: nitrogen (N) ratio and N differing pH sediments from several streams upper midwestern United States. In addition, we surveyed 36 assess variability sediment rates. Labile dissolved (DOC) additions 30 mg C·L –1 (as acetate) stream reduced rates (P < 0.003), but lower concentration or dilution ambient DOC had no effect on nitrification. C:N availability strongly interacted affect...

Direct counting techniques, first developed for aquatic samples, can be used to enumerate bacteria in soil and groundwater sediments. Two fluorescent dyes, 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) actively respiring 4(prm1),6-diamidino-2-phenylindole (DAPI) total bacteria, were tested their usefulness epifluorescent direct bacterial enumeration soil. Both dyes the same sample without affecting results. Staining 8 h with CTC 40 min DAPI resulted maximum numbers of stained cells. The...

We measured nitrification rates in sediment samples collected from a variety of aquatic habitats Navigation Pool 8 the Upper Mississippi River (UMR) 7 times between May 2000 and October 2001. also conducted nutrient-enrichment experiments analyzed vertical profiles to determine factors regulating nitrification. Nitrification were relatively high compared other ecosystems (ranging 0–8.25 μg N cm−2 h−1) exhibited significant temporal spatial patterns. greatest during summer spring autumn...

Abstract Physical, chemical, hydrologic, and biologic factors affecting nitrate (NO 3 − ) removal were evaluated in three agricultural streams draining orchard/dairy row crop settings. Using 3‐d “snapshots” during biotically active periods, we estimated reach‐level NO sources, mass balance, in‐stream processing (nitrification, denitrification, uptake), retention potential associated with surface water transport ground discharge. Ground contributed 5 to 11% stream discharge along the study...

The use of personal response systems, or clickers, is increasingly common in college classrooms. Although clickers can increase student engagement and discussion, their benefits also be overstated. A practice to ask the class a question, display responses, allow students discuss then collect responses second time. In an introductory biology course, we asked whether showing question biased response. Some sections course displayed bar graph others served as control group which discussion...

1. Although it is well known that sediments can be hot spots for nitrogen transformation in streams, many previous studies have confined measurements of denitrification and nitrate retention to shallow (<5 cm deep). We determined the extent processing deeper a sand plains stream (Emmons Creek) by measuring core sections depth 25 assessing vertical profiles, with peepers piezometers, 70 cm. 2. Denitrification rates sediment slurries based on acetylene block were higher shallower sections....

Abstract We investigated the frequency of p53 mutations in 47 pediatric brain tumors various histologic subtypes that were collected over a period 5 years. The specimens included 15 primitive neuroectodermal (PNETs), 17 low grade astrocytomas, one anaplastic astrocytoma, three glioblastomas (GBMs), mixed glial tumor, eight ependymomas, choroid plexus carcinoma, and gangliocytoma/ganglioneuroma. Mutations identified by single strand conformation polymorphism analysis exons 4–8 verified...

Zebra mussels (Dreissena polymorpha) have altered the structure of invaded ecosystems and exhibit characteristics that suggest they may influence ecosystem processes such as nitrogen (N) cycling. We measured denitrification rates seasonally on sediments underlying zebra mussel beds collected from impounded zone Navigation Pool 8 Upper Mississippi River. Denitrification assays were amended with nutrients to characterize variation in nutrient limitation presence or absence mussels. at sites...

Restored riparian wetlands in the Upper Mississippi River basin have potential to remove sediment and nutrients from tributaries before they flow into River. For 3 yr we calculated retention efficiencies of a marsh complex, which consisted restored an adjacent natural that were connected Halfway Creek, small tributary Mississippi. We measured sediment, N, P removal through mass balance budget approach, N denitrification, mechanical soil excavation. The complex had average rates approximately...

Abstract Nitrogen (N) has been linked to increasing eutrophication in the Gulf of Mexico and as a result there is increased interest managing improving water quality Mississippi River system. Water level reductions, or ‘drawdowns’, are being used more frequently large river impoundments improve vegetation growth sediment compaction. We selected two areas Upper system (Navigation Pool 8 Swan Lake) examine effects drawdown on N dynamics. Navigation experienced summer drawdowns 2001 2002....

Sediments in the backwaters of Upper Mississippi River (UMR) are highly organic and provide an optimal environment for N removal. We monitored 8.6-ha UMR backwater site near La Crosse, Wisconsin, nearly 3 y to assess temporal variability, seasonal trends, factors regulating denitrification. measured rates unamended denitrification (DEN) enzyme activity (DEA) at ambient temperature DEA 30°C (DEA30). Seasonal mean (±1 SE) DEN ranged from 0.041 ± 0.015 0.47 0.23 μg cm−2 h−1 were highest winter...

Eutrophic and hypoxic coastal waters are often associated with high nutrient inputs from riverine systems. For example, nitrogen (N) export the Mississippi River into Gulf of Mexico has been identified as an important factor causing eutrophication seasonal hypoxia. Modelling studies N flux in large rivers, including River, suggest that much enters rivers remains solution is exported downstream. However, patterns cycling complex vary according to habitat type season. Here we use spatial data...

Abstract Although floodplains are thought to serve as important buffers against nitrogen (N) transport aquatic systems, frequent flooding and high levels of nutrient availability also make these systems prone invasion by exotic plant species. Invasive plants could modify the cycling nutrients within floodplains, with effects that feedback promote persistence invasive species impact N export riverine coastal areas. We examined effect on soil properties at a floodplain site in Pool 8 Upper...

Selective feeding and differential nutrient excretion by aquatic invertebrates plays a substantial role in recycling. Grazing larvae of the caddisfly Glossosoma intermedium construct portable case for protection that also serves as good substrate periphyton colonization because it is constantly fertilized larval excreta. We tested whether was enriched compared to streambed selective on facilitates P remineralization. measured total N, P, N∶P stream water cobble 3 western Wisconsin streams....