Matt R. Whiles

Quantification of the Nitrogen Cycle in a Prairie Stream

Nitrogen (N) was added for 35 days in the form of 15NH4Cl to Kings Creek on Konza Prairie, Kansas. Standing stocks of N in key compartments (that is, nutrients, detritus, organisms) were quantified, and the amount of labeled N entering the compartments was analyzed. These data were used to calculate turnover and flux rates of N cycling through the food web, as well as nutrient transformation rates. Inorganic N pools turned over much more rapidly in the water column of this stream than in pelagic systems where comparable measurements have been made. As with other systems, the mass of ammonium was low but it was the key compartment mediating nutrient flux through the ecosystem, whereas dissolved organic N, the primary component of N flux through the system, is not actively cycled. Nitrification was also a significant flux of N in the stream, with rates in the water column and surface of benthos accounting for approximately 10% of the total ammonium uptake. Primary consumers assimilated 67% of the inorganic N that entered benthic algae and microbes. Predators acquired 23% of the N that consumers obtained. Invertebrate collectors, omnivorous crayfish (Orconectes spp.), and invertebrate shredders dominated the N flux associated with primary consumers. Mass balance calculations indicated that at least 23% of the 309 mg of 15N added during the 35 days of release was retained within the 210-m stream reach during the release. Overall, the rates of turnover of N in organisms and organic substrata were significantly greater when C:N was low. This ratio may be a surrogate for biological activity with regard to N flux in streams.

HYDROLOGIC INFLUENCES ON INSECT EMERGENCE PRODUCTION FROM CENTRAL PLATTE RIVER WETLANDS

The physical template of freshwater ecosystems has a pervasive influence on biological communities and processes. To examine the influence of hydrology on wetland insect communities, we quantified insect emergence from five riparian sloughs in the central Platte River valley. Annual hydroperiods of the wetlands ranged from 94 to 365 d/yr, and frequency and magnitude of drying events were inversely proportional to hydroperiod length. Three emergence traps were placed in each wetland from April through November 1997. Most insects collected in traps were identified to genus, and individual dry mass (DM) also was determined. Abundance of emerging insects (24 124 individuals/m2) and emergence production (5.1 g DM·m−2·yr−1) were highest from the site with an intermediate hydroperiod of 296 d. Sites with longer and shorter hydroperiods had lower emergence abundance and production. Emergence production from the perennial site, which contained fish year-round, was only 0.26 g DM·m−2·yr−1. Diptera generally dominated emergence trap catches. Chironomidae, Culicidae, and Ceratopogonidae were among the dominant contributors to abundance, whereas Sciomyzidae and Muscidae were important contributors to biomass at most sites. Quadratic equations best described relationships between taxa richness and annual hydroperiod (r2 = 0.78, P < 0.05) or number of drying events/yr (r2 = 0.81, P < 0.05), reflecting a peak in richness at intermediate levels of both. These relationships followed predictions of the intermediate disturbance hypothesis, but specific mechanisms underlying patterns were difficult to discern. Like emergence production, taxa richness was also highest at intermediate hydroperiods. Hence, insect diversity (measured as richness) and emergence production were positively correlated (r2 = 0.85, P < 0.05). Results indicate that the hydrology of central Platte River wetlands exerts a strong influence on insect species richness and emergence production, and that intermittent sites harbor the highest insect diversity and produce more emergent insect biomass. However, trends in seasonal emergence patterns and taxonomic shifts across the hydrologic gradient in this study suggest that a landscape containing a mosaic of hydrologically distinct wetlands will maximize aquatic insect diversity and productivity at larger spatial and temporal scales.

Aboveground Invertebrate Responses to Land Management Differences in a Central Kansas Grassland

Abstract Macroinvertebrate communities in a central Kansas grassland were examined to assess their responses to differences in land management and explore their viability for biological assessment of grasslands. Canopy (drop-trap) and ground-dwelling (pitfall traps) communities were quantitatively sampled from June-September 1998 and 1999. The responses of the whole arthropod community and two focal groups, Coleopteran families and Orthopteran species, to three land use types (brome fields, old fields, and native prairies) were examined. Vegetation analyses reflected clear differences among land use types. Bromus inermis Leyss, an exotic grass, and Andropogon gerardii Vitman, a native grass, dominated brome fields and native prairie sites, respectively. Old fields were composed of a mixture of native and exotic plant species. Coleopteran family richness and diversity were significantly greater in native prairies than brome fields (P < 0.05), whereas orthopteran species richness and diversity peaked in brome fields. Diversity and richness of all arthropod groups examined were significantly, positively correlated with plant species diversity and richness in drop-trap samples (P < 0.05). Coleopteran family diversity and richness in pitfall samples were positively correlated with abundance of native plants, but orthopteran species diversity and richness were negatively correlated with native plant abundance. Coleopteran and orthopteran responses to land use appeared linked to differences in management practices. Whereas coleopterans appeared most influenced by plant community composition, orthopterans showed sensitivity to mechanical disturbance associated with haying on native prairie. Plant and arthropod group diversities were not consistently correlated, demonstrating that arthropod groups can reflect differences in a landscape that may not be apparent from examining plant communities alone.

Feeding ecology and emergence production of annual cicadas (Homoptera: Cicadidae) in tallgrass prairie

Abstract The emergence phenology and feeding ecology of annual cicadas in tallgrass prairie are poorly documented. However, these large insects are abundant, and their annual emergence represents a potentially important flux of energy and nutrients from belowground to aboveground. We conducted a study at Konza Prairie Research Natural Area in eastern Kansas to characterize and quantify cicada emergence and associated energy and nutrient fluxes. We established emergence trap transects in three habitat types (upland prairie, lowland prairie, and riparian forest), and collected cicadas every 3 days from May to September. A subset of trapped cicadas was used for species- and sex-specific mass, nutrient, and stable isotope analyses. Five species were trapped during the study, of which three were dominant. Cicadetta calliope and Tibicen aurifera exhibited significantly higher emergence production in upland prairie than in lowland prairie, and were not captured in forested sites at all. T. dorsata emerged from all three habitat types, and though not significant, showed a trend of greater abundance in lowland grasslands. Two less abundant species, T. pruinosa and T. lyricen, emerged exclusively from forested habitats. Nitrogen fluxes associated with total cicada emergence were estimated to be ∼4 kg N ha–1 year–1 in both grassland habitats, and 1.01 kg N ha–1 year–1 in forested sites. Results of stable isotope analyses showed clear patterns of resource partitioning among dominant cicada species emerging from grassland sites. T. aurifera and C. calliope had δ13C and δ15N signatures indicative of feeding on shallowly rooted C4 plants such as the warm-season grasses dominant in tallgrass prairie ecosystems, whereas T. dorsata signatures suggested preferential feeding on more deeply rooted C3 plants.

Life history and production of a semi-terrestrial limnephilid caddisfly in an intermittent Platte River wetland

The life history and ecosystem significance of a recently discovered species of Ironoquia (Trichoptera:Limnephilidae) were examined in a riparian slough of the central Platte River, Nebraska, USA. Monthly benthic samples were collected for 1 y and adult emergence was monitored to examine I. plattensis life history in this harsh, intermittent habitat. Ecosystem significance of this caddisfly was assessed by estimating larval secondary production and consumption of coarse particulate organic matter (CPOM), biomass exported from the slough during larval migration onto land, and adult emergence production from the riparian prairie where pupation occurred. The life cycle of I. plattensis appeared intimately linked to the hydroperiod, with larval migration to land and adult emergence coinciding with drying and inundation of the slough, respectively. Total larval production in a 20-m reach of slough, adjusted for average wetted area during sampling intervals, was 429-536 g ash-free dry mass (AFDM)/y, depending upon the method of calculation. Biomass that left the slough via larval migration to land was estimated at 109 g AFDM (∼23% of larval production), and total adult emergence was 69 g AFDM (∼16% of larval production). Turnover rate of larval biomass was 10-12/y. CPOM consumption estimates indicated that larvae in the study site consumed 8690 g AFDM/y, ∼13% of the annual average CPOM standing stock in the site. Results demonstrate that this leaf-shredding trichopteran is a productive component of this prairie wetland system, representing an abundant invertebrate food resource for aquatic and terrestrial predators and facilitating decomposition processes. However, its distribution along the central Platte River may be limited because of habitat destruction and its adaptation to a specific hydrologic regime.

Hydrology and Physiography of Wetland Habitats

This chapter discusses the hydrology and physiography of wetland habitats. Hydrologic regimes of wetlands can range from highly variable to fairly constant. Hydrologic regime forms probably the most important abiotic template that influences wetland ecology. Important characteristics include permanence, predictability, and seasonality. On a larger scale, diversity of hydrologic regimes among individual wetlands in a region can greatly influence wetland communities through the process of cyclic colonization. Wetlands can be coarsely divided into coastal and inland systems. There are four broad geomorphic classifications of wetlands including riverine, depressional, coastal, and peatlands. Coastal wetlands can be heavily influenced by tides, whereas the hydrology of riparian wetlands is influenced by rivers. Depressional wetlands can be influenced solely by local precipitation or various combinations of precipitation and surface and groundwater inputs. Hydrology has a pervasive influence on wetland processes and communities. Biotic interactions such as predation are generally more important in wetlands with long hydroperiods.

Lakes and Reservoirs

This chapter focuses on the physiography of lakes and reservoirs. A variety of processes form lake basins, including tectonic, glacial, fluvial, volcanic, and damming processes. Lake basin morphology is described with various parameters, including mean depth, area, maximum depth, volume, shoreline development (DL), and watershed area relative to lake surface area. Shallow lakes with large watersheds and highly dissected shorelines are generally the most productive. Reservoirs are unique habitats that have characteristics of both streams and lakes. Reservoirs can have profound impacts on upstream and downstream habitats and communities depending upon how they are constructed and managed. Stratification can alter the water circulation in lakes and thus alter biogeochemical, ecosystem, and community properties. Mixing can occur often (polymictic), once a year (monomictic), twice a year (dimictic), or rarely (amictic or meromictic), depending on climate and type of stratification. High concentrations of dissolved substances can also lead to stratified layers in lakes. Movement of wind is generally the main cause of waves across lakes, although motorboat activity can cause significant wave action.

Lakes and Reservoirs: Physiography

This chapter focuses on the physiography of lakes and reservoirs. A variety of processes form lake basins, including tectonic, glacial, fluvial, volcanic, and damming processes. Lake basin morphology is described with various parameters, including mean depth, area, maximum depth, volume, shoreline development (DL), and watershed area relative to lake surface area. Shallow lakes with large watersheds and highly dissected shorelines are generally the most productive. Reservoirs are unique habitats that have characteristics of both streams and lakes. Reservoirs can have profound impacts on upstream and downstream habitats and communities depending upon how they are constructed and managed. Stratification can alter the water circulation in lakes and thus alter biogeochemical, ecosystem, and community properties. Mixing can occur often (polymictic), once a year (monomictic), twice a year (dimictic), or rarely (amictic or meromictic), depending on climate and type of stratification. High concentrations of dissolved substances can also lead to stratified layers in lakes. Movement of wind is generally the main cause of waves across lakes, although motorboat activity can cause significant wave action.

Properties of Water

This chapter discusses the properties of water. One of the many unusual properties of water is that it exists in liquid form at the normal atmospheric temperatures and pressures encountered on the surface of earth. The density of liquid water, which is influenced by temperature and dissolved ions, can control the physical behavior of water in wetlands, groundwater, lakes, reservoirs, rivers, and oceans. Density also influences water flow and viscosity. Differences in density are important because less dense water floats on top of water with greater density. Such density differences can maintain stable layers. Formation of distinct stable layers is called stratification. Many aspects of life in aquatic environments can be discussed conveniently using the Reynolds number (Re). This number can quantify spatial- and velocity-related effects on viscosity and inertia. Small organisms have low values of Re and little inertia relative to the viscous forces they experience; the opposite is true for larger organisms. Biological activities, such as swimming, filter and suspension feeding, and sinking and many other aspects of aquatic ecology are constrained by properties of water that can be described by Re.

Fish Ecology and Fisheries

This chapter discusses the biogeography of fish communities and factors that influence growth, survival, and reproduction of fishes. Biodiversity of fish is related to factors that operate at a variety of temporal and spatial scales. In general, fish communities are more diverse in tropical areas, in large drainage basins, in areas with high terrestrial productivity, where greater habitat diversity exists, and where more prey species exist. Much of the economic impetus behind protecting freshwaters is related to the maintenance of productive sport and commercial fisheries. Fishes dominate many freshwater food webs as the top predator in streams and lakes. Fishes are good indicators of water quality and model organisms for physiological and behavioral research. Knowledge of fish ecology and traits is essential to fish conservation.