James F. Saunders

Ecological Determinism on the Orinoco Floodplain

ll oo dplains of l a r ge rivers are among the most produ ctive of eco s ys tem s ; they are also among the f i rst to be altered by econ omic devel opm ent and population growth.Floodplains are vulnerable not only to direct agents of change, such as agriculture and settlement, but also to changes in the hydrology or quality of water in the rivers to wh i ch they are con n ected . Thu s , even floodplains not yet clear ed or diked may show drastic ecological change caused by shifts in flo oding regime, sediment transport, or n utrient budgets as a result of human activities upstream. Because the floodplains of large rivers are vulnerable to a diverse array of anthropogenic influences, their natural functions cannot be obse rved or documented in an y region of dense population or where natural resources and a gri c u l tu ral po ten tial have been ex p l oi ted ex ten s ively. Nearly all of the major floodplain rivers in the Northern Hemisphere,and many in the Southern Hemisphere,have been le veed or impounded f or na vigation, agriculture, power g eneration, or flo od c ontrol (P ower et al. 1995, Vitousek et al.1997).Only large rivers of the far north and in some parts of the tropics now offer a view of large floodplains as they existed b efore human intervention (Cushing and Cummings 1995). Information on the ecological characteristics o f these few floodplains is the only practical means of understanding the natural functioning of floodplains, and is p robably the most useful basis for planning the restoration or protection of floodplains. All large floodplains give the impression of great ecological complexity. The combination of constant physical change, which is driven by the rise and fall of the river, spatial heterogeneity of vegetation reflecting varied depth and duration of inundation, and longitudinal gradients of f l oodplains proj ects intract a ble mu l ti d i m en s i on a l i ty. Closer inspection shows, however, a sur prising degree o f order and repetition in the physical and chemical environment, which in turn suggests the possibility of order and predictability in the biotic components of the system. The most feasible candidate for a test of this idea is a large floodplain whose physical characteristics remain essentially natural.

Uncertainty in the Estimation of Stream Metabolism from Open-Channel Oxygen Concentrations

The open-channel oxygen method for estimating stream metabolism avoids many of the problems associated with chamber techniques, but its uncertainty has not been rigorously quantified. Uncertainty in open-channel estimates of photosynthesis (P) and respiration (R) can be estimated by use of a Monte Carlo approach incorporating uncertainty in each of the terms (reaeration rate coefficient, range of temperature oscillation, midpoint temperature, travel time, metabolic rate, and precision of instrument calibration) affecting error in estimates of P and R. The distributions derived from the Monte Carlo simulations provide confidence limits for estimates of P and R. Use of this approach along with simulation of a range of stream conditions indicates that: 1) given equivalent metabolic rates and physical conditions, estimates of R are subject to greater uncertainty than are estimates of P, especially in high-gradient streams, and 2) uncertainty can be minimized by special attention to the precision of measurement for factors affecting the saturation concentration of oxygen. Reasonable confidence limits (95% CL within 30% of mean) can be achieved for estimates of P where daily photosynthetic rates exceed L-1d-1, but in turbulent streams (k20⚬=100/d), rates of R must be nearly 15 mg L-1d-1 to achieve similar precision.

Effects of Invasive Tissue Collection on Rainbow Trout, Razorback Sucker, and Bonytail Chub

Abstract Histological examination and biochemical assays of fish tissues are used for disease detection, genetic characterizations, contaminant analyses, and the detection of stable isotopes. However, tissue sampling usually requires invasive sampling procedures that may harm or kill an organism under investigation. For this reason, invasive procedures are rarely used with threatened, endangered, or other sensitive species. If invasive tissue sampling could be performed with little harm, a wide array of sophisticated techniques could be employed to assist in protection and management of species in decline. We subjected rainbow trout Oncorhynchus mykiss to nonlethal invasive sampling of fin, muscle, and liver tissue. Techniques first developed for trout were applied to two endangered fishes, razorback sucker Xyrauchen texanus and bonytail chub Gila elegans. Acute (mortality) and chronic (suppression of growth rate) effects of tissue removal were evaluated in a hatchery for control and treatment groups of e...

Application of a nutrient-saturation concept to the control of algal growth in lakes

Abstract Either phosphorus or nitrogen can be responsible for nutrient limitation of algae in lakes. Nitrogen limitation can be defeated by heterocystous cyanobacteria through nitrogen fixation, but no comparable mechanism exists for P. Therefore, P is considered the predominant factor limiting phytoplankton biomass in lakes. Even so, increasing numbers of studies show that many lakes are limited by N deficiency because heterocystous cyanobacteria do not become sufficiently abundant to offset N deficiency. Where N limitation prevails, P control over phytoplankton populations can be achieved only if P concentrations are first reduced to a saturation threshold that is determined by the amount of available N. The extent of this reduction, which will typically occur without any suppression of phytoplankton biomass, can be estimated from nutrient chemistry, nutrient enrichment experiments, and information on the stoi-chiometry of phytoplankton, as illustrated with data for a Colorado reservoir in which a reduction of N of about 50% would be necessary to induce P limitation. Analysis based on stoichiometry could allow managers of water quality in lakes to anticipate the implications of N limitation for P-based management of water quality.

Movements of Young Colorado Pikeminnow and Razorback Sucker in Response to Water Flow and Light Level

ABSTRACT We studied the effects of three flow regimes on the activity patterns and movements of one-, three-, six-, and 36-week old Colorado pikeminnows (Ptychocheilus lucius) and two-week old razorback suckers (Xyrauchen texanus) in an experimental tank under light and dark conditions. The seven-chambered tank simulated a system of backwater habitats, which are used by the young fishes in nature. Water flows through the tank were slow, and velocities were discernable only in the vicinity of surface ports that connected each chamber. Fish movements were related to light or dark condition and activity tended to increase with age. Larvae, relatively active in daylight, moved little at night with no flow, but flow stimulated night activity and downstream movement. Older fish also had a diminished response to flow direction during daylight, but responded at night. The tendency for night movement may be a predator avoidance mechanism, but the tendency to move downstream with flow is likely a response to life in backwater habitat. With inflow and backwater filling “downstream” larval movements would access expanding habitat. With outflow and backwater draining, downstream movement would avoid stranding and potential death in a shrinking habitat.