Richard E. Sparks

Need for Ecosystem Management of Large Rivers and Their Floodplains These phenomenally productive ecosystems produce fish and wildlife and preserve species

Most of the 79 large river floodplain ecosystems in the world have been altered by human activities and the rest are likely to be altered soon. Ecosystem management works to guide rather than thwart, natural processes. This article describes briefly the history of floodplain and flood plain management and then focuses on the importance of large river-floodplain ecosystems and some of the consequences of altering the natural river processes, functions, and connectivity. The species-focused management system typically employed by natural resource agencies is contrasted to the ecosystem approach to river-flood plain management. Ecological management is defined as working with the natural driving forces and variability of the ecosystems with the goal of maintaining or recovering biological integrity. Flood-pulses are also a focus because they drive the system and the great floods on several continents in the last years. 88 refs., 10 figs.

Disturbance and recovery of large floodplain rivers

Disturbance in a river-floodplain system is defined as an unpredictable event that disrupts structure or function at the ecosystem, community, or population level. Disturbance can result in species replacements or losses, or shifts of ecosystems from one persistent condition to another. A disturbance can be a discrete event or a graded change in a controlling factor that eventually exceeds a critical threshold.The annual flood is the major driving variable that facilitates lateral exchanges of nutrients, organic matter, and organisms. The annual flood is not normally considered a disturbance unless its timing or magnitude is “atypical.” The record flood of 1973 had little effect on the biota at a long-term study site on the Mississippi River, but the absence of a flood during the 1976–1977 Midwestern drought caused short- and long-term changes. Body burdens of contaminants increased temporarily in key species, because of increased concentration resulting from reduced dilution. Reduced runoff and sediment input improved light penetration and increased the depth at which aquatic macrophytes could grow. Developing plant beds exerted a high degree of biotic control and were able to persist, despite the resumption of normal floods and turbidity in subsequent years.In contrast to the discrete event that disturbed the Mississippi River, a major confluent, the Illinois River, has been degraded by a gradual increase in sediment input and sediment resuspension. From 1958 to 1961 formerly productive backwaters and lakes along a 320-km reach of the Illinois River changed from clear, vegetated areas to turbid, barren basins. The change to a system largely controlled by abiotic factors was rapid and the degraded condition persists.Traditional approaches to experimental design are poorly suited for detecting control mechanisms and for determining the critical thresholds in large river-floodplains. Large river-floodplain systems cannot be manipulated or sampled as easily as small streams, and greater use should be made of man-made or natural disturbances and environmental restoration as opportunistic experiments to measure thresholds and monitor the recovery process.

Nutrient dynamics of large river floodplains

A range of river floodplain sites in North America and Europe were investigated, to determine what factors were determining nutrient richness and productivity. A principal component analysis revealed that phosphorus richness of the soil and plant growth were strongly associated with the size of the river and the position of the site, both in relation to the distance to the source of the river and to the river channel. N mineralisation and available P were significantly correlated with river water quality. A phytometer experiment revealed that a large amount of the stress experienced by plants growing on the floodplain was due to other than soil factors, and fertiliser experiments showed that at several of the sites, production was not limited by nutrients. Climatic factors (temperature, latitude) also determine plant production. The hydrological regime that a floodplain is subjected to is a vital factor for determining both nutrient dynamics and plant production, but it is not straightforward to characterise due to the complex and variable nature of the flood pulse.

Effects of hydroperiod and predation on a Mississippi River floodplain invertebrate community

Abstract The objective of this study was to determine if pond permanence and vertebrate predation (by fish and waterfowl) affect invertebrate community structure in the mudflat habitat of floodplain ponds. Invertebrate communities were studied for 1 year in four Mississippi River floodplain ponds with different hydroperiods. Pond 1 experienced five dry periods, pond 2 experienced four, pond 3 dried once, and standing water remained in pond 4 for the entire year. Vertebrate predator exclusion treatments (all access, no access, small-fish access and cage controls) were placed in all ponds. As pond duration increased, predatory invertebrate richness and abundance increased while overall invertebrate richness and abundance decreased. With the exception of the cladoceran Diaphanosoma, all commonly encountered taxa were strongly affected by pond permanence in terms of abundance, biomass and, generally, individual biomass. Taxa were nearly early divided between those that were more abundant in less permanent ponds and those that were more abundant in longer-duration ponds. Invertebrate taxa richness, abundance, and total biomass were lower in the all-access treatment than in the treatments that restricted predator access, and these effects were stronger in the more permanent ponds. In general, there were no significant differences in responses to the treatments with small-fish access and no access. These results support models that predict relatively weak effects of predation in frequently disturbed habitats.

Seston quality controls zebra mussel (Dreissena polymorpha ) energetics in turbid rivers

Abstract Feeding processes and energetic balance of zebra mussels were both related to the quantity and quality of natural seston. Filtration rate and pseudofeces production increased while clearance rate remained constant with increasing seston concentration. Ingestion rate, assimilation efficiency, and assimilation rate all increased with increasing food quality, measured as the ratio of organic to inorganic material in the seston. Respiration rate did not change with either food quantity or quality. As a result, scope for growth declined with decreasing food quality, and fell below 0 cal mg−1 h−1 at an organic:inorganic ratio of 0.5. The association between feeding processes and food quality appears related to a breakdown in the ability of zebra mussels to selectively ingest high-quality organic particles when the organic content of the seston is low. Ingestion, assimilation efficiency, assimilation rate and scope for growth were all higher when seston was amended with an addition of a natural assemblage of algae. Food quality may be a better indicator of environmental conditions suitable for growth than food quantity. These results suggest that the conditions of high suspended inorganic sediment concentrations in large turbid rivers represent a difficult growth environment for the zebra mussel.

Winter Habitats Used by Largemouth Bass in the Illinois River, a Large River-Floodplain Ecosystem

Abstract During the winter of 1993–1994, we characterized habitats used by 17 radio-tagged largemouth bass Micropterus salmoides in La Grange Reach of the Illinois River, a large river–floodplain ecosystem that has been significantly altered from its natural state. Radio-tagged largemouth bass wintered in backwaters, off-channel coves, ditches, and marinas from November through February. Electrofishing mean catch rates were higher in the study areas during winter than in other seasons, indicating fish were more concentrated in these areas during winter. Five of nine study areas received thermal inputs from springs or power plants, but water temperatures in all nine areas were warmer than the main channel during winter. Current velocities averaged 2 cm/s in the study areas and 19 cm/s in the main channel. We did not document movement of radio-tagged fish into the main channel during winter. River levels played a major role in determining the suitability of wintering habitats. When river levels declined, te...

Notes: Largemouth Bass Size Distributions under Varying Annual Hydrological Regimes in the Illinois River

Abstract Little is known about the population dynamics of largemouth bass Micropterus salmoides in temperate large river–floodplain ecosystems. However, the hydrological regimes in these systems are often similar to those of large reservoirs where fluctuating water levels during spawning have been shown to affect largemouth bass population dynamics. Most backwater lakes of the Illinois River have soft, silty substrates. These substrates are not conducive to nest building, so spawning centrarchids may use annual spring floods to access inundated terrestrial vegetation and previously dry, compacted substrates on the floodplain. We used electrofishing catch data from La Grange Reach of the Illinois River (1990–1995) to assess how spring and early-summer river levels influence the cohort strength of largemouth bass. Strong cohorts were produced during years with high spring floods (1990, 1993, and 1995) when largemouth bass could access the floodplain for spawning and nursery habitat. In both 1990 and 1993, f...

Evidence of Grass Carp (Ctenopharyngodon idella) Reproduction in the Illinois and Upper Mississippi Rivers

Abstract Grass carp (Ctenopharyngodon idella) is an exotic species which was imported into the United States in 1963 to control aquatic vegetation. Individuals escaped from ponds and subsequently spread into streams in the Mississippi River basin. We have been collecting grass carp in the Illinois River since 1990, and some of our associates have also collected grass carp in other portions of the upper Mississippi River system. The presence of juveniles (some less than 20 mm long) and adults (some diploid) in our collections leads us to believe that grass carp are reproducing in the Illinois River, and their larvae are finding suitable nursery areas in backwaters. Naturalized, reproducing grass carp populations probably exist as far north as 209 km into the Illinois River. Collections of juveniles by other researchers indicate reproduction and recruitment may also be occurring in upper Mississippi River Reaches 25, 26 and the Open River Reach below Lock and Dam 27.

RAPID ASSESSMENT OF WATER QUALITY, USING THE FINGERNAIL CLAM, MUSCULIUM TRANSVERSUM

An apparatus for testing the effects of drugs on the ciliary beating rate of clam gills has been modified to rapidly (15 min to 1 h) assess the effects of water quality factors on a sensitive organism, the fingernail clam, Musculium transversum. The gill and adductor muscles of the clam are excised and placed in a petri dish through which a continuous flow of molluscan Ringers solution or a test solution can be maintained. Normal ciliary activity of the gill preparation can be maintained for at least eight days. The ciliary beating rate is determined by synchronizing the rate of flashing of the sub-stage lamp of a microscope, with the rate of beating of the cilia. Synchronization is achieved when the metachronal ciliary wave appears to stand still. The first water quality factor selected for testing by the rapid method was potassium, because potassium concentrations are higher in the Illinois River where fingernail clams have largely died out, than in the Mississippi River where the clams are still abundant. The apparatus provided statistically reliable results in a short period of time. There are significant differences in the responses of large (7 to 11 mm) and small (1 to 5 mm) clams to: (a) removal and subsequent addition of potassium, (b) variation of maintenance dosage of potassium in the washing solution, and (c) lag period of response to a specific dose. The results suggest that an intracellular trans-membrane potential change (surface effect) is necessary to activate ciliated cells of small clams. This latter change in small clams would account for the relatively short lag period for potassium activation. Potassium levels required for maintenance of a basal ciliary beating rate are 10 - 3 M (39.1 mg/litre) for small clams and 10 - 6 M (0.039 mg/litre) for large clams. Greater concentrations are cilioinhibitory. Lesser concentrations are generally cilioexcitatory, but concentrations less than 10 - 8 M (0.00039 mg/litre) and 10 - 9 M (0.000039 mg/litre) are insufficient to sustain basal rates in large and small clams, respectively. Potassium concentrations in certain rivers, such as the Illinois and Mississippi, are high enough to cause cilioinhibition in gill preparations from large fingernail clams. Inhibition of ciliary activity in intact clams would impair feeding and respiration. The effects of potassium on the survival, growth, and reproduction of intact fingernail clams are currently being determined and will be related to the effects observed by means of the rapid method.

Establishment of Daphnia lumholtzi (an Exotic Zooplankter) in the Illinois River

Abstract Daphnia lumholtzi, an exotic zooplankter, recently has become established in the Illinois River. This species was first detected at Illinois River Mile (IRM) 121.1 near Havana, Illinois in June of 1995, and exhibited a peak abundance of 22.5/L in August. Population trends and densities in the Illinois River resemble those reported in lakes and reservoirs of the southeastern United States, suggesting D. lumholtzi is adaptable to lotic as well as lentic systems. Individuals were found at sampling sites as far upriver as IRM 195.9.