SUMMARY1. A review is presented of the literature on riparian vegetated buffCT strips (VBS) for use in stream-water-quality restoration and limitations associated with their use are discussed. The results are also presented of recent investigations on the effectiveness of a forested and a grass vegetated buffer strip for reducing shallow subsurface inputs of nutrients from agriculture to a stream in central Illinois, U.S.A. 2. Because riparian zones link the stream with its terrestrial catchment, they can modify, incorporate, dilute, or concentrate substances before they enter a lotic system. In small to mid-size streams forested riparian zones can moderate temperatures, reduce sediment inputs, provide important sources of organic matter, and stabilize stream banks. 3. Several questions on the utility and efficiency of vegetated buffer strips for stream restoration still remain unanswered, including: what types (grass v forest) are most efficient; do they become nutrient saturated; are they only temporary sinks; how does species composition influence effectiveness; and, what is the optimal width of buffer to facilitate nutrient reduction under different conditions? 4. Water samples were collected (1989-90) from lysimeters located at three depths (60, 120, and > 120 cm) in an upland area planted in conventional row crops (com and soybean) and in three adjacent riparian buffer treatments, a 39 m wide grass buffer, a 16 m wide mature forested buffer, and a buffer planted in row-crops to the stream bank. Concentrations of dissolved and total phosphorus and nitrate-N in each sample were determined following major precipitation events over a seventeen month period. 5. Both the forested and grass VBS reduced nitrate-N concentrations in shallow groundwater (up to 90% reduction). On an annual basis the forested VBS was more effective at reducing concentrations of nitrate-N than was the grass VBS, but was less efficient at retaining total and dissolved P. 6. During the dormant season, both grass and forested buffer strips released dissolved and total P to the groundwater. The VBS apparently acted as a nutrient sink for much of the year, but also released accumulated nutrients during the remaining portion of the year. Periodic harvesting of plant biomass may reduce the amount of P released during the dormant season. 7. VBSs are not as effective in agriculture areas with tile drained fields. Alternative restoration practices such as discharging drain tiles into wetlands constructed parallel to the stream channel may prove to be a more effective means of controlling non-point-source agricultural inputs of nutrients in such areas. 243244 L.L. Osborne and D.A. Kovacic

We found a significant and positive relationship between fish species richness and four measures of stream size (drainage area, stream order, link magnitude, and downstream link) in three Illinois drainage basins. Downstream link (incorporating both stream size and size of stream at the next downstream confluence) explained the greatest portion of the variance. This suggests that downstream processes significantly influence the structure of fish communities inhabiting warmwater streams. Significantly higher numbers of fish species were collected from tributary streams (< 259 km2 drainage area) located lower in a drainage network and connected to a main channel system than from similarly sized streams located in the headwaters of a drainage network. The difference in species richness among station treatments was not due to a difference in the number of individuals collected among treatments. We were unable to accept or reject the hypothesis that differences in fish species richness were due to differences in physical habitat. The immigration–extinction hypothesis appears to provide a plausible explanation for the observed pattern in fish community structure within a drainage. The location of a stream channel within a network may provide a general template for fish community structure in warmwater drainages by regulating potential species richness.

The largescale structure of an agriculturally developed prairie river system in central Illinois was examined and compared with predictions from current stream ecosystem theory. High rates of primary productivity (> 15 g carbon∙m−2∙d−1) were characteristic of the watershed, although longitudinal patterns in riparian vegetation, stream temperature, and primary productivity were inverted relative to typical streams in forested uplands. Empirical models of gross primary production and community respiration were developed. Light availability, mediated by both channel shading and turbidity, appeared to be the principal factor limiting primary productivity. Both nitrate and orthophosphorus were found in high concentrations throughout the watershed. Largescale patterns in nutrient availability suggest that landuse patterns, and particularly urbanization, strongly affected spatial and temporal distributions of both nutrients. Differences between prairie river systems and "prototype" structures envisioned by the River Continuum Concept (RCC) derive from the descriptive nature of the RCC, and its inability to incorporate nonstandard distributions of key driving variables. The use of empirical modelling in stream ecosystem studies is discussed.

/ 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 longterm 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 riverfloodplain 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.Rivers with floodplains differ from rivers and streams with constrained channels and narrow riparian zones. Differences include flooding patterns, relative importance of lateral versus upstream-downstream linkages in nutrient cycling (or spiraling), fluxes of organic matter, and the adaptation of many biota to transient aquatic-terrestrial environments (Junk and others 1989). These differences govern how we understand disturbance and how we design monitoring programs, manage and regulate water quality and quantity, and restore degraded riverfloodplain systems.The fact that all large rivers in the temperate zone

Factors limiting periphyton accrual in east-central Illinois agricultural streams were investigated. Nutrient-diffusing substrata were used to examine periphyton macronutrient limitation in streams in two agricultural watersheds. Substrata consisted of sand-agar mixtures with one of six experimental treatments. Macronutrients included carbon, nitrate, phosphate and combinations of the three. Substrata were collected after a 5 and 9 day period and analyzed for chlorophyll a. None of the treatments were significantly greater than the controls at any of the seven stations, thus we conclude that periphyton in these streams was not nutrient limited. Highest periphyton colonization/growth rates were associated with the smaller upstream reaches, while lower rates occurred in the larger downstream reaches. Multiple regression showed that most of the variance in the rate of chlorophyll a accrual after five days was explained through water temperature and turbidity (13 = 0.91); whereas, stream nitrate and phosphate concentrations accounted for no significant portion of the variance. We conclude that instream primary production in agricultural streams of central Illinois is limited by temperature and light.