Chlorophyll a concentrations in Lake Pearl, Florida, increased as the percentage of the lake's total volume infested with aquatic macrophytes decreased. Using data from 32 Florida lakes having a wide range of limnological characteristics, we demonstrated that predictions of chlorophyll a concentrations could be improved by including a term for the percentage of the lake's total volume infested with macrophytes in existing nutrient–chlorophyll models. Our best-fit multivariate regression equation was[Formula: see text]where CHLA is the chlorophyll a concentration (milligrams per cubic metre), TN is the total nitrogen concentration (milligrams per cubic metre), TP is the total phosphorus concentration (milligrams per cubic metre), and PVI is the percentage of the lake's total volume infested with macrophytes. By use of this equation, we assessed the potential effect of aquatic macrophytes on chlorophyll yields and Secchi disc transparencies in lakes of different trophic status.

No abstract

No abstract

The relation between reservoir hydrology and recruitment of black crappies Pomoxis nigromaculatus and white crappies P. annularis was examined in 11 reservoirs throughout Alabama from 1990 to 1996. Estimates of recruitment were derived from catch rates of age‐1 fish in the fall with trap nets and from residuals associated with catch‐curve regressions of age 3–7 fish captured in the spring with electrofishing gear. Reservoirs were separated into three hydrologic categories: (1) eight reservoirs with short retention (volume/discharge) times (2–9 d) that fluctuated less than 1 m/year; (2) two reservoirs with longer retention times (44–55 d) that generally fluctuated 1.8 and 4.6 m/year; and (3) one reservoir that fluctuated 1.8 m/year with a relatively short retention time of 15 d. In the reservoirs with low retention times and stable water levels, greater year‐class production was related to low winter (January–March) retention before crappie spawning and to higher postwinter (April–December) retention when these fish were age 0. These variables explained about 60% of the variation in crappie year‐class abundance. Higher production of young crappies was nearly always associated with both winter retention of 6 d or less and postwinter retention greater than 11 d. In these reservoirs, cyclic crappie recruitment appeared to be influenced by climatic conditions. In the three reservoirs that fluctuated 1.8 m or more per year, short winter retention and higher water levels in winter before crappie spawning were both associated with greater year‐class abundance; hydrologic conditions during and after crappie spawning were not related to crappie recruitment. In these reservoirs, maintenance of higher water levels in the winter before crappie spawning may enhance reproductive success.

Artificial fluctuations in stream flow caused by hydroelectric power dams can degrade fish habitat and reduce the abundance and diversity of riverine fish faunas. Increased minimum water releases and reduced fluctuations in discharge may mitigate these effects. In this study, we compared shoreline fish abundance and diversity before and after an enhanced flow regime was implemented on the Tallapoosa River (Alabama) downstream of a hydroelectric dam. Before the minimum-flow regime, only eight species of fish were collected 3 km downstream from the dam, and all were classified as macrohabitat generalises. After the minimum flow was initiated, species richness 3 km below the dam more than doubled, and over half of the species collected were classified as fluvial specialists. Fish community response to the enhanced flow was not as great at a site 37 km downstream from the dam, where species richness was similar between the two periods. However, more species classified as fluvial specialists were collected after the minimum flow regime than before enhanced flows at this site. Additionally, relative abundance of species classified as fluvial specialists increased from less than 40% of fish collected before enhanced flows to over 80% after minimum flows began. Our results suggest that the enhanced flow regime provided conditions supporting a relatively abundant and diverse fish assemblage more reflective of a riverine system.