Investigating linkages between the compositions of suspended (seston) and benthic particulate matter is important to the understanding of organic matter (OM) cycling and nutrient retention in aquatic systems. We compared the quantity and quality of the truly suspended (TS) and settleable (SB) fractions of seston as well as benthic particulate matter in the tidal freshwater James River, Virginia. The mass of seston and OM was consistently higher in the TS fraction compared to the SB fraction. OM was preferentially retained in the TS fraction relative to seston. The proportional contribution of OM constituents (chlorophyll a, particulate organic carbon and nitrogen) to the two fractions was consistent across observed concentrations whereas increases in seston concentration resulted in decreased proportions in the TS fraction. Benthic constituent reservoirs were large relative to the SB fraction but the higher proportion of OM in the SB fraction suggests that the settleable material was more labile.

<p>Aquatic macroinvertebrates of channelized headwater streams in agricultural landscapes are exposed to alterations in chemistry and physical characteristics of benthic sediments. These habitat alterations are known to influence communities of aquatic macroinvertebrates. Benthic sediments can have a wide range of impacts and influences on aquatic macroinvertebrates. I hypothesized that sediments would play a significant role in determining macroinvertebrate community structure within agriculturally dominated headwater streams. I evaluated the influences of sediment chemistry characteristics and physical characteristics on aquatic macroinvertebrate communities in Cedar Creek, Indiana and Michigan, and the Upper Big Walnut Creek, Ohio, during 2017 and 2018. Macroinvertebrates were collected twice per year using artificial substrate and leaf pack samplers and identified to the family level. Sediments were sampled two times per year and analyzed for seven physical characteristics and twenty sediment chemistry characteristics. Principle component analyses were used to create axes that are indicators of gradients of sediment chemistry and physical characteristics that occur among the samples. Macroinvertebrate community metrics used in the analyses included abundance, Shannon Diversity Index, Hilsenhoff Biotic Index scores, Invertebrate Community Index scores, percentage of collector-filters, percentage of scrapers, percentage of Chironomidae and a Berger-Parker Reciprocal Index of dominance. Linear Mixed Effect Model analyses revealed that both sediment chemistry and physical characteristics influence macroinvertebrate community metrics. Aquatic macroinvertebrate abundance was negatively correlated with increasing concentrations of simazine and decreasing concentrations of calcium. Percentages of Chironomidae were positively correlated with increasing percentages of sand and decreasing percentages of clay and decreasing diversity of sediment particle sizes. My data supported the hypothesis that benthic sediments play an important role in determining aquatic macroinvertebrate community structure in headwater streams of agriculturally dominated landscapes. Gradients of chemical characteristics containing simazine and calcium were observed to be negatively correlated with macroinvertebrate abundance. Gradients of physical characteristics including percentages of sand and clay along with the diversity of particle sizes were observed to be positively correlated with percentage of chironomids. My research increases the knowledge that benthic sediments, chemically and physically, can lead to alterations in aquatic macroinvertebrate communities within Midwestern headwater streams. </p>

Water from Mantua reservoir has, during some years, exhibited reddish-brown staining when used by Brigham City for irrigation. I propose that seasonal fluctuations in the reservoir chemistry create an environment conducive to dissolving iron from the iron-rich sediments, which subsequently precipitate during irrigation, resulting in a staining event. These conditions are produced by chemical and biological decomposition of organic matter, coupled with isolation of the hypolimnetic waters, which results in seasonal low concentrations of dissolved oxygen in these waters. Under these specific circumstances, anaerobic conditions develop creating a geochemical environment that causes iron and manganese reduction from Fe(III) to Fe(II) and Mn(IV) to Mn(II), respectively. These reducing conditions facilitate reduction-oxidation (redox) chemical reactions that convert insoluble forms of iron and manganese found in the reservoir sediments into more soluble forms. Consequently, relatively high amounts of dissolved iron and manganese are generated in the bottom waters immediately adjacent to the benthic sediments of the reservoir. Water withdrawn from a bottom intake pipe during these periods introduces iron-rich water into the distribution system. When this water is exposed to oxygen, reoxidation shifts redox equilibrium causing precipitation of soluble Fe(II) and Mn(III) back to highly insoluble Fe(III) and Mn(IV). The precipitant appears on contact surfaces as the aforementioned ferric stain. This research focuses specifically on the iron chemistry involved and evaluates this hypothesis using various measurements and models including field data collection, computer simulations, and bench-scale testing to validate the processes proposed.