G. Milton Ward

Effects of food quality on growth of a stream detritivore, Paratendipes albimanus (MEIGEN) (Diptera : Chironomidae)

Laboratory-determined larval growth rates of the detritivore (collector-gatherer) Par- atendipes albimanus (Chironomidae) responded proportionally to the microbial densities of 4 food sources. Substrates with higher microbial activities and biomasses produced greater growth rates in the order: pignut hickory (Carya glabra) leaves > white oak (Quercus alba) > insect feces > natural stream detritus. Laboratory growth rates of P. albimanus were linearly related to quantitative esti- mates of food quality based on substrate adenosine triphosphate (ATP) and respiration rates but were not statistically related to total N or C. Although P. albimanus is univoltine in Augusta Creek, Michigan, an experimental laboratory population of first-instar larvae completed a 2nd generation during the summer when fed detritus generated from hickory leaves. A second experimental popu- lation failed to develop past the first instar when fed natural detritus. The natural growth pattern of P. albimanus involves the interaction of temperature and food quality.

Direct and Indirect Effects of Geology on the Distribution, Biomass, and Production of the Freshwater Snail Elimia

We studied the relationship between geology and lotic secondary production by analyzing geographical patterns of the distribution, biomass, and production of the freshwater snail Elimia (Pleuroceridae) in Alabama. Nine streams were selected for study, three each in three physiographically distinct regions of uniform climate but contrasting lithology. Our objectives were to assess: 1) the production and biomass of Elimia among streams with contrasting alkalinities due to differences in regional geology--sandstone (5.7 mg/L as CaCo3) < phyllite (19.4) < carbonate (103.4); p < 0.05--and 2) geologically mediated variation in thermal regime as an alternative factor contributing to the widely observed correlation between alkalinity and productivity. Although conspicuous in phyllite and carbonate streams, Elimia was absent from sandstone streams. Biomass (B) and annual production (P) of Elimia were significantly lower (p ≤ 0.03) in streams draining phyllite (B = 1102 mg/m2, P = 1565 mg/m2) compared with carbonate catchments (B = 2990 mg/m2, P = 2501 mg/m2). However, whereas the correlation between biomass and alkalinity was consistent throughout the year, the correlation between production and alkalinity was not. Production did not differ significantly during the summer months (April-October, p = 0.41), and differences in annual production between regions were attributable to near cessation of production in phyllite streams during the winter months (October-April, p = 0.04). Although mean annual stream temperature was not significantly different between regions (p = 0.51), a simulation showed that the low winter temperatures of phyllite streams (⪡10°C) should cause the cessation of production and high net losses of snail biomass and result in insufficient post-winter biomass for rapid compounding of production during spring and summer. Consequently, biomass should be regulated at relatively lower levels in phyllite than in carbonate streams where production occurs year-round because of a more moderate thermal regime (e.g., winter minima ∼10°C).

Lignin and Cellulose Content of Benthic Fine Particulate Organic Matter (FPOM) in Oregon Cascade Mountain Streams

Compared to leaf litter, benthic fine particulate organic matter (FPOM) is considered very refractory. FPOM exhibits high carbon to nitrogen ratios, low respiratory rates, and is a relatively poor food source for invertebrates. However, little more is known of the qualitative nature of benthic FPOM, the nature of FPOM processing, or the relationship between benthic FPOM chemical composition and sources of organic matter to a stream system. In this study, qualitative characteristics of benthic FPOM were compared at three sites in the Oregon Cascade Mountains that received either conifer litter, alder leaves, or herbaceous and algal inputs. FPOM from these streams contained approximately 45% lignin and 10-15% cellulose (ash-free dry weight). Lignin content of particles >1 mm was almost 60% whereas in those <0.01 mm it was 30-40%. Based on qualitative differences between known organic matter inputs to these streams, lignin content in FPOM at the conifer site was predicted to be greater than that at the alder site, and to be least at the open site. No seasonal or site related patterns in FPOM lignin or cellulose content were found regardless of the type of canopy cover or aerial allochthonous inputs. FPOM respiration rates were predicted to follow the reverse pattern, highest at the open site and lowest at the conifer site. Respiratory rates at the open site were usually greater than those at the forested sites; but rates were not consistently lowest at the conifer site. Similarities in FPOM lignin and cellulose content and respiration rates among sites suggest that the qualitative characteristics of FPOM are not necessarily regulated by the qualitative characteristics of canopy inputs alone. Additional and as yet unquantified inputs of high lignin-containing allochthonous FPOM, such as soil or wood, may override differences of leaf litter inputs among these three sites.

4 – GULF COAST RIVERS OF THE SOUTHEASTERN UNITED STATES

The river basins of the eastern Gulf Coast lie west of the Atlantic slope and east of the Mississippi River. The region has abundant water resources, including seven major rivers that arise and flow through five physiographic provinces in five states to empty into the Gulf of Mexico. These rivers vary widely in size, hydrology, geomorphology, and water chemistry, but experience a similar climate and exhibit many biological similarities. The dominant physiographic province through which the rivers flow is the coastal plain, more specifically, the sections named the eastern Gulf Coastal Plain and the Floridan. There are five freshwater ecoregions within the eastern Gulf of Mexico region, arranged by longitude. These include portions of the Mississippi Embayment and Florida ecoregions, all of the Mobile Bay and Apalachicola ecoregions, and much of the Florida Gulf ecoregion. Two of these, the Mobile Bay and the Apalachicola, follow watershed boundaries of the Mobile and Apalachicola river basins, whereas the remaining three ecoregions include multiple river basins. All rivers in this region flow from north to south into the Gulf of Mexico, and all are located between 84°W and 91°W longitude and 30°N and 35°N latitude. The eastern Gulf Coast rivers encompass a rich variety of aquatic habitats and resources. This diversity is most evident in the fishes, mollusks, crayfishes, and caddisflies.

Geological Mediation of Stream Flow and Sediment and Solute Loading to Stream Ecosystems Due to Climate Change

The effects of global warming and predicted widespread changes in climate within the next century caused by the “greenhouse effect” have been the subject of much scientific debate. Research based on instrument records and indirect effects of climatic change, e.g., sea levels and ice cores, indicate that millennial changes in global temperatures fall roughly within an interval of ±1°C. However, “greenhouse models” responding to the doubling of CO2 (0.06%), which is predicted to occur within the next century, indicate that global temperatures may increase by approximately 3°C (Hansen et al., 1981; Mearns et al., 1990). The “greenhouse models” have been severely criticized for emphasizing positive feedbacks (warming phenomena) within the atmospheric-oceanic system at the expense of negative feedbacks (cooling phenomena) (Reifsnyder, 1989; Lindzen, 1990). Despite these criticisms, the reality of significant anthropogenic influence on atmospheric chemistry such as the documented increases in CO2 levels (e.g., Bascatow and Bjorkstrom, 1981) as well as the possibility for climatic changes related to “greenhouse gas” increases have initiated a high level of concern.

Ecology of Pectinatella magnifica (Bryozoa) in an Alabama oxbow lake: colony growth and association with algae

Colonies of the bryozoan Pectinatella magnifica commonly occur on submersed substrata in an oxbow lake (Touson Lake) in the floodplain of the Black Warrior River, Alabama. Seasonal growth patterns, substratum preference, and potential effects of bryozoan colonies on algal assemblages attached to artificial and natural substrata were determined. Colony growth on artificial substrata (pine sticks) and natural ones (dead cypress twigs and aquatic plants) was monitored at biweekly intervals from the appearance of bryozoans during early autumn to the loss of colonies from substrata in late December. Maximum colony growth occurred during late September and early October. Some colonies reached up to 65 cm in length and 10 cm in diameter. Colonies showed no preference among the substrata examined, but young colonies always developed first on the shaded side of the substratum. The presence of bryozoan colonies affected the composition of attached algae. Blue-green algae (90%) dominated on surfaces enclosed by the colonies and also within the gelatinous colony matrix, whereas surfaces uncolonized by Bryozoa developed mixed communities of diatoms (78%), blue-green algae (12%), and green algae (11%).

Influence of particle shapes and size distributions on fine particulate organic matter surface area in streams

The objective of this study was to determine whether fine particulate organic matter (FPOM) from different sources would have similar surface areas. Individual FPOM particles collected from Grasshopper Creek (clear-cut), Mack Creek (old-growth coniferous forest), and Quartz Creek (second-growth) in Oregon were photographed using scanning electron microscopy, and their surface area was calculated by assuming spherical or cylindrical shapes. In Grasshopper Creek, FPOM cylinders (n = 326) represented 89% of the total surface area (124.9 m2) and 68% of the total FPOM numbers. In Mack Creek, FPOM cylinders (n = 231) contributed 77% of the total surface area (114.2 m2) even though they represented only 55% of the total numbers. In Quartz Creek, FPOM cylinders (n = 185) represented 79% of the total surface area (61.8 m2) and 60% of the total numbers. There was a significant difference in the distribution of particle sizes and shapes from the different streams, particularly between Mack Creek and the other two streams. These differences are likely due to the differences in riparian vegetation. The importance of FPOM surface area to physical, chemical, and biological processes in aquatic ecosystems is usually overlooked in favor of more easily measured FPOM mass.

The dynamic nature of land-water interfaces: changes in structure and productivity along a water depth gradient in the Talladega Wetland Ecosystem

Hydrologic factors sueh as water depth, hydroperiod, and residenee time largely deterrnine the strueture and funetion of wetlands by modifying physieoehemistry and influeneing speeies eomposition and riehness (MrrscH & GossELINK 2007). Generally, produetivity is depressed by stagnant, flooded eonditions but enhaneed by flow and pulsing hydroperiods. When wetlands are impounded, flooding leads to anaerobiosis, low soil redox potential, redueed nutrient availability, deereased species riehness, and eonsequently, redueed primary produetion (MrrscH et al. 1991 ). Conversely, flood pulsing eontributes to higher primary produetivity by providing adequate water, subsidizing nutrients, oxygenating the rhizosphere, and flushing waste produets (JUNK et al. 1989). Variation in water depth ereates a diversity o f mierohabitats for plants that support different mierobial and invertebrate eommunities. Wetlands, and in partieular beaver impounded wetlands, are not permanent features ofthe landseape. Extent and volume of these wetland habitats vary as a funetion o f hydrologie change as beavers maintained impoundrnents are created and lost. During 15 years of study at the Talladega Wetland Eeosystem, pond habitats were ereated by new impoundrnents and lost when beavers failed to maintain or repair breaehed dams at existing ponds. Seeondary sueeession following a dam breaeh in a 50+ year-old pond provided an interesting seientifie perspeetive on habitat permanenee and the dynarnism ofwetland landseapes. We deseribe differenees in the strueture and funetion of different zones of a beaver-impounded wetland in the southeastem United States as a site for understanding how wetlands respond following the loss of a beaver dam.

Diurnal variability of stage in a wetland pond in the southeastern United States

The specific effects of water heighr on werland characterisrics an d rhe influence o f hydrologic regimes o n inundarion pattern have been a relarively recent focus of werland research acrivities. The hydrologic regime is one of rhe mosr imporranr driving variables rhat derermines biological variabiliry in werlands (Luco er al. 1990a). Because werlands are shallow water environmenrs, small changes in warer volume over time can result in significanr changes in areal extent ofinundation. Hydroperiodiciry of a werland, i.e. water depth, duration and frequency, can elicit major changes in werland arrribures such as vegetation composition and biomass, decomposirion rares, aquaric macrophyte root metabolism, nirrogen cycle processes, plant production, invertebrate abundance and biomass, warer budgets, and emission of gases such as CO, and CH,.