Colbert E. Cushing

BIOENERGETICS OF LOTIC FILTER-FEEDING INSECTS SIMULIUM SPP. (DIPTERA) AND HYDROPSYCHE OCCIDENTALIS (TRICHOPTERA) AND THEIR FUNCTION IN CONTROLLING ORGANIC TRANSPORT IN STREAMS'

This study derives a set of bioenergetic parameters for the blackfly Simulium spp. (Diptera: Simuliidae) and the caddisfly Hydropsyche occidentalis (Trichoptera: Hydropsychidae) and evaluates the impact of these filter feeders on the lotic environment. In addition, comparison is made between field- and laboratory-derived estimates of ingestion and between 2 methods of calculating assimilation rate. Digestion (gut-clearance) time for Simulium ranged between 0.33 and 1.25 h compared to 1.54 to 2.63 h for Hydropsyche. Mean ingestion rate for Simulium in a series of experiments ranged from 1.36 to 54.74 jig DW/mg DW/h. The mean assimilation efficiency for diatoms was about 55% as measured by the dual-label technique. Mean ingestion rates of diatoms for Hydropsyche in 3 exper- iments were 31.3, 31.0 and 29.2 ,ug DW/mg DW/h, respectively; low values (3 ,ug DW/mg DW/h) from a 4th experiment were associated with high concentrations of green algae. An assimilation rate for diatoms of 7.5 ,ug AFDW/mg DW/h was derived for Hydropsyche. Measurements of growth rates of Hydropsyche under natural conditions were 3.6 to 4.4 ,ug DW/mg DW/h. Respiration rate of Hydro- psyche for water a62% 02 saturation was about 2.3 ul 02/mg DW/h at 20?C. The results of this research in combination with literature derived values, yielded the following mean energy budgets for Simulium and Hydropsyche, respectively (J/mg/h): ingestion (C) 0.318, 0.393; respiration (R) 0.092, 0.042; growth (G) 0.092, 0.100; assimilation (A) (as C x AE) 0.182, 0.192; (as G + R) 0.184, 0.142 (values times 0.239 = cal/mg/h). The role of these filter feeders is discussed in terms of their processing of suspended organic material and in directing energy to higher trophic levels. Simulium and Hydropsyche (with net growth efficiencies of 49.5 and 69.6%, respectively) are shown to be comparable to bacteria in terms of metabolic removal of organic C from food sources. During the months in which they were present, the mean biomass and density of Hydropsyche occidentalis in Deep Creek (station 2), Idaho, were 2.45 g DW/m2 and 1786/M2 and of Simulium were 0.22 g DW/m2 and 1699/M2. Based on all 12 monthly samples, Hydropsyche comprised 44% of the total invertebrate standing crop biomass of 4.84 g DW/ mi2. From mean biomasses and numbers of invertebrates in riffles of Deep Creek and mean ingestion rates for Simulium and Hydropsyche (30.5 and 80 ,ug/mg/h, respectively) it was calculated that the filter-feeders remove 1% of the seston flowing over them each day. The filter-feeders also are an important energy base for feeding by carnivorous insects and fish in Deep Creek.

Physical factors influencing fine organic particle transport and deposition in streams

The influence of physical factors on the transport and deposition of fine particulate organic matter (FPOM, 53–106 μm) in streams was investigated using 14C-labeled natural detritus. Field estimates of mean FPOM transport distance (SP) were calculated as the inverse of the longitudinal loss rate (kP) of particles. Deposition was determined by standardizing kP for depth and velocity and expressed as the mass transfer coefficient, vdep. SP varied by orders of magnitude (7–1000 m) within and among streams. As expected, vdep behaved more conservatively than SP but still varied by a factor of 18 (0.06–1.10 mm/s). Field-estimated deposition velocities were always less than the quiescent water fall velocity (vfall) but no consistent relationship existed between the 2 (r = 0.26, p = 0.53). Variability in SP was strongly associated with the cross-sectional area of the transient storage zone (AS; r = 0.93, p < 0.01) and the uptake length of water (SW; r = 0.84, p = 0.01). The transfer coefficient was highest in the 2 smallest streams (Q < 15 L/s) but was similar, and unrelated to stream size, among 6 experiments conducted in stream segments where Q exceeded 100 L/s. Variability in FPOM vdep was less related to physical characteristics than SP, although a significant, positive correlation was detected between vdep and AS/A. Evidence from this study suggests that the mechanisms assumed to govern particle transport in gravitational/hydrodynamic models may not be solely responsible for FPOM deposition in streams and that alternative processes, such as hyporheic filtration and biotic retention, may be important.

Comparison of corn pollen and natural fine particulate matter transport in streams: can pollen be used as a seston surrogate?

The transport of fine particulate organic matter (FPOM) in streams is an important process that links stream reaches, but until recently little was known about the distances traveled by fine particles in streams or the mechanisms governing their transport, deposition, and resuspension. Within the past decade, a number of studies have measured FPOM transport distances using either natural stream particles or a variety of artificial particles as FPOM surrogates. The purpose of our study was to compare estimates of FPOM transport distances in streams using: 1) radioactively labeled natural FPOM, and 2) corn pollen as an FPOM surrogate. We compared the particle types with simultaneous releases at 3 locations in Bloomington Creek, Idaho, and in a streamside flume in Pennsylvania. Mean transport distances in the stream and in the flume ranged from 49 to 637 m for corn pollen, compared with 23 to 1164 m for natural FPOM. Particle deposition velocities, which adjust for the effects of water depth and velocity on transport distance, had narrower ranges: 0.094 to 0.31 mm/s for pollen and 0.051 to 0.25 mm/s for natural FPOM. Pollen and FPOM transport distances were not significantly different at 2 of the stream sites, whereas corn pollen transport was significantly shorter at the 3rd stream site and significantly longer in the flume. We conclude that corn pollen, although not an exact mimic of natural particles, provides estimates of FPOM transport that are well within the limits of precision obtained with other methods. Corn pollen and other seston surrogates can serve as useful standard particles for comparing FPOM dynamics in streams with a variety of geomorphic and hydraulic characteristics.

Seston Removal by Filter‐Feeders

ity. For long-term studies in large areas we suggest a bilateral approach. We have used an extensive network (26 sites in 260 kM2) of simple max-min thermometers visited monthly (Thorp and Hinds 1977), and a much smaller number of strategically placed continuous recorders. We deduced microclimatic associations within the broad study area covered by the max-min thermometers by cluster analysis (Rotenberry et al. 1976). A single thermograph appropriately located then serves to calibrate a larger number of the simpler stations.

Ecology: The Structure and Function of Riverine Ecosystems

This chapter illustrates how riverine ecosystems reflect the integration of the physical, chemical, and biological factors. It also describes the interrelationships among the energy sources produced within the stream as well as terrestrially derived primary production, and how these energy sources are utilized by different functional groups of organisms within the stream. This is a generalization of what is going on at a particular place in a stream; however, it captures the essential processes and players. The river, located in a forest drainage basin has its headwaters flowing through a heavily shaded forest; it then flows into more open country, and eventually becomes a large, deep, heavily silted river. The river is broken into three general regions—the headwaters, the mid-reaches, and the lower reaches. Stream habitats and communities exist in differing scales, from those existing on a single grain of sand or rock to those characteristics of the entire stream reach. The study of these habitats is called patch dynamics, and it is important to consider these when describing the animal communities and their interactions. Another important relationship in the river and stream ecosystems is the interaction and exchanges that occur between the stream and its floodplain. This has been termed the flood-pulse concept and describes the exchange of nutrients, organisms, and organic material that occurs when a stream or river floods and then recedes.

Chapter 9 – Warm-water Rivers of the Midwest

This chapter explores the small streams and rivers of Americas heartland, most of which originate at low altitude and have low gradients. Long runs and pools predominate, but shallow, gravelly riffles can be found where the geology and gradient combine appropriately. Cascades, waterfalls, and boulders are rare. Substrate varies from place to place; however, often includes sand, silt, and mud. Water temperatures are cold in the north; however they grade into cool and warm waters as one proceeds south. This chapter begins by describing the setting, which is always more complex and heterogeneous than our mental image. It takes a look at the River Continuum Concept, because the understanding of the functioning of forested headwater streams has been greatly advanced by studies in this region. In addition, for those whose vision of a stream is a cold, stonybottom trout stream, it may be interesting to contrast warmer, slower streams that often have sandy and muddy bottoms. Finally, rivers of this region have been greatly modified by human activities. This chapter concludes with a lesson on river history and an examination of the threats and opportunities that confront the mankind today.

Chapter 13 – Higher Plants: The Macrophytes

This chapter discusses the larger aquatic plants, those that are easily seen with the naked eye. They are either attached to rocks and stones, freefloating, or rooted on the stream bottom; the latter may be entirely submerged or have emergent plant parts. Collectively, these are called macrophytes . Included in this category are flowering plants, mosses and liverworts, some species of encrusting lichens, and a special group, the Charales. Macrophytes attached to solid objects are usually found in the colder, headwater regions of streams where the largely rocky stream bottom offers sites for attachment. Representatives of this group include bryophytes, some flattened lichens, and two peculiar families of flowering plants found in tropical waterfalls. The mosses and liverworts are the forms most likely to be encountered in the North American streams. Bryophytes, particularly mosses, require high levels of dissolved carbon dioxide; this is one reason for their restricted distribution to areas high in dissolved carbon dioxide, such as headwater springs and turbulent regions. The depth of water also influences the presence or absence of certain species of mosses. Where rocks are rarely submerged, a variety of terrestrial mosses and liverworts can be found in shady places. True aquatic mosses, such as Fontinalis, occur below the water level. Thus, as one looks at a large reach of stream, the presence of a mosaic of species is apparent depending on the amount of light and the depth of the water.

Special Riverine Systems

This chapter characterizes some unique rivers and streams of the United States. Hot springs are generally the result of water flowing through hot rock formations and eventually reaching the surface as fumaroles, geysers, or other outlets. Water temperatures can be extremely hot; the thermal springs in Arkansas flow at a fairly constant temperature of about 64 °C throughout the year. Thermal waters are often highly charged with dissolved minerals due to the dissolving power of hot water and the fact that they are under high pressures underground. Thus, at spring sources, and for varying distances downstream, one may observe deposits of minerals that precipitate out as soon as both pressure and temperature are reduced when exposed to air. Bacteria appear to be the only living organisms existing in water up to 75.5°C Algae are the life-forms most adaptable to existing under high temperatures, and their presence provides the brilliant colors found in many of the large hot pools that form the source of the thermal springs. Cyanobacteria, such as Synechocyetis and Phormidium, have been found flourishing in waters as hot as 60°C. As waters cool to below 40°C, diatoms begin to appear. Protozoa, water mites, and midges are also found near the sources of these springs where the water has cooled to around 50°C As the water further cools downstream, the normal occupants of streams begin to appear—mayflies, stoneflies, and fishes.

Diverse Rivers of the Southeast

The southeastern region of the United States contains a wide diversity of streams. These range from high-gradient, clear-flowing headwater streams which exhibit ecological characteristics in common with similar streams found elsewhere in the country, to low-gradient blackwater streams found on the Coastal Plain region of several southeastern states. Fish diversity in this region is historically low. Thus, evaluating the success of the restoration efforts will not be based so much on recovery of preexisting fish species and numbers, but on overall ecosystem functioning. Restoration will hopefully restore the higher concentrations of dissolved oxygen extant prior to channelization. The model for this uses nutrient cycling, the movement of larvae, juvenile, and adult fishes, and macroinvertebrates. Two groups of birds have been selected to evaluate restoration: waterfowl and waders. Population data, regularity of occurrence, and nesting and feeding activities are considered in the conceptual model developed to evaluate the overall success of the restoration efforts for these animals. Evaluation of the success of the restoration efforts on the structure and function of the Kissimmee River ecosystem depends on the evaluation of several ecosystem components, their connectivity and interactions, and how well they reflect historic conditions. Determining these requires a major, long-term, intensive research effort by a large team of scientists.

Large Rivers of the West

Several large rivers have headwaters in the western United States, including the Columbia, Colorado, Missouri, Yellowstone, Snake, Arkansas, and Rio Grande rivers. This chapter emphasizes the Colorado and Columbia rivers, both well studied and important rivers. Physically, they are similar in length and drainage area. But the mean annual discharge of the Columbia, at 7960 m 3 /s, is more than 10 times greater than that of the Colorado, at 640 m 3 /s. The ecological history of these two rivers can be summed up in a single word—abuse. This abuse largely has been due to the construction of large hydroelectric and storage dams to produce cheap and abundant electrical energy, to supply irrigation water to crops throughout the western United States, and to control floods. The Corps of Engineers and Bureau of Reclamation have held fast to their philosophy that every drop of water that flows to the sea unused is wasted. Fortunately, as public awareness of the ecological harm caused by dams began to grow, the missions of both the Corps and the Bureau evolved from dam-building to other pursuits, including recreation. All in all, the Colorado and Columbia rivers represent severely impacted riverine ecosystems. The Upper Basin of the Colorado remains fairly typical of pristine streams of this region; however, the Colorado River in the Lower Basin and the entire Columbia River within the continental United States are mere ghosts of their former ecosystems. These significant and largely irreversible impacts were initiated during a time when there was little appreciation for the value of unperturbed wilderness or pristine environments.