Daniel E. Canfield

Volunteer Lake Monitoring: Testing the Reliability of Data Collected by the Florida LAKEWATCH Program

ABSTRACT Because the use of volunteer samplers is a very cost-effective way to collect large amounts of information on lakes over space and time, we studied the reliability of the protocols used by the Florida LAKEWATCH program. We found that chlorophyll extractions with hot ethanol gave values that were no different from those obtained with the standard method of grinding with acetone. In a comparative study of 125 lakes we found the data collected by volunteers were comparable to those collected by professionals. Mean Secchi disk depth, TP, TN, and chlorophyll values obtained by the citizens were strongly correlated (r > 0.99) to the mean values obtained by the professionals. To determine if freezing was a valid means of preserving water samples prior to analysis, we compared estimates of chlorophyll, TP, TN, pH, total alkalinity, and specific conductance obtained from fresh samples with estimates obtained from samples frozen up to 150 days. For most lakes there was little difference in chemical measurements made in samples preserved by freezing for different lengths of time, and various statistical tests indicated that freezing was a valid means of preserving lake water samples prior to analysis. Water quality data produced by volunteer samplers following the LAKEWATCH protocols were just as good as those from samples collected by professional biologists and handled using standard methods of sample preservation. The fact that volunteers can collect credible data means that lake management agencies could amplify their limited budgets by using volunteer monitoring, to sample more lakes and to sample them more frequently.

The Potential For Wave Disturbance in Shallow Florida Lakes

ABSTRACT We applied wave theory to calculate the extent and frequency that we would expect wave-driven surface water movements to disturb the sediments in 36 Florida lakes covering a broad range of surface areas and mean depths. The calculated per cent of the lakebed subject to wave disturbance at one time or another ranged from 6 to 100% and the per cent of the time 50% of the lakebed was disturbed ranged from 0 to 65%. The large Florida lakes, Apopka, Okeechobee, and Istokpoga showed high levels of calculated wave disturbance, which was consistent with the conclusions of previous investigations. Historic water level fluctuations in Lake Apopka were calculated to have major effects on wave disturbance in that lake. The dynamic ratio (the square root of lake surface area in square kilometers divided by the mean depth in meters) was significantly related to various measures of wave disturbance in our sample lakes. For lakes with ratio values above about 0.8 the entire lakebed was subject to wave disturbance at least some of the time. The dynamic ratio was also related to lake water quality. We found that increases in the dynamic ratio were significantly related to decreases in water quality as measured by total phosphorus, total nitrogen, chlorophyll, and Secchi disk depth. Calculations of wind disturbance by waves need to be modified in lakes with extensive beds of macrophytes, where water levels change and in periods where climatic fluctuations result in changes in wind regimes.

The Eutrophication of Lake Okeechobee

ABSTRACT Average annual total phosphorus concentrations in Lake Okeechobee increased from 0.049 mg/L in 1973 to 0.098 mg/L in 1984. The increases in total phosphorus concentrations were not correlated to external phosphorus inputs, but to changes in lake water levels. It is proposed that the flooding of marshes and exposed lake bottom primarily caused increased total phosphorus concentrations, but that the resuspension of bottom sediments by wind action may also be a major factor influencing in-lake total phosphorus concentrations. Reducing phosphorus inputs by 40 percent as proposed by the Lake Okeechobee Technical Advisory Committee (LOTAC) will not significantly improve water quality in Lake Okeechobee. Average total phosphorus concentrations will not decline significantly. Chlorophyll a concentrations and Secchi transparencies are not correlated to total phosphorus concentrations so massive expenditures of public funds to reduce nutrient inputs will not protect long-term water quality at Lake Okeechobee.

An Index of Biotic Integrity: A Test with Limnological and Fish Data from Sixty Florida Lakes

Abstract An index of biotic integrity (IBI) that used eight fish assemblage metrics was examined for effectiveness in estimating anthropogenic impacts to 60 Florida lakes ranging in size from 2 ha to more than 12,400 ha. The lakes ranged in trophic status from oligotrophic to hypereutrophic and had aquatic macrophyte abundances (percent lake volume infested) ranging from less than 1% to 100%. Fish species were classified by trophic feeding guild and tolerance to increases in turbidity or warming and decreases in dissolved oxygen concentration. Fish assemblage metrics tested were as follows: Number of fish species, number of native fish species, number of Lepomis species, number of piscivorous species, number of generalist species, number of invertivore species, number of species intolerant of increased turbidity or warming and decreased dissolved oxygen concentration, and number of species tolerant of increased turbidity or warming and decreased dissolved oxygen concentration. The total IBI scores and the...

Regional Geology and the Chemical and Trophic State Characteristics of Florida Lakes

ABSTRACT A limnological survey of 165 Florida lakes was conducted between September 1979 and August 1980 to determine their chemical and trophic state characteristics. A wide range of limnological conditions was documented. Average lake pH values ranged from 4.1 to 9.2 and average total alkalinity concentrations ranged from 0 to 204 mg/L as calcium carbonate (CaCO3). Average specific conductance values ranged from 11 to over 5600 μS/cm at 25° C. Mean total nitrogen concentrations ranged from 0.063 to 4.6 mg/L and mean total phosphorus concentrations ranged from 3 to 834 mg/m3. Although lake trophic states ranged from oligotrophic to hypereutrophic, Florida lakes as a group can be characterized as productive, softwater lakes. Over 75 percent of the sampled lakes had total alkalinity concentrations below 40 mg/L as calcium carbonate and total hardness concentrations below 75 mg/L as calcium carbonate. Most of the sampled lakes were either mesotrophic (52 percent) or eutrophic (35 percent) because total phos...

Relationships between Zooplankton Abundance and Chlorophyll a Concentrations in Florida Lakes

ABSTRACT Data collected during a limnological survey of 165 Florida lakes were used to examine statistical relations between chlorophyll a concentrations and the abundance of total zooplankton, cladocerans, copepods, crustaceans, and rotifers. Abundances of the different groupings of zooplankton were positively correlated with chlorophyll a concentrations, but all correlation coefficients were less than 0.72. Rotifers were most strongly correlated with chlorophyll a concentrations during the summer (r=0.71). No major changes in community composition could be demonstrated with increasing chlorophyll levels. Empirical models derived from regression analyses were developed to predict zooplankton abundance from measures of chlorophyll a concentrations.

Limnological Factors Influencing Bird Abundance and Species Richness on Florida Lakes

ABSTRACT Forty-six bird species were observed on 33 Florida lakes with some species occurring on only one lake and others on as many as 26 lakes. Average annual bird abundance ranged from seven to 750 bird/km2 and total species richness ranged from two to 30 species per lake. Regression analyses were used to examine the effects of lake trophic status, aquatic macrophyte abundance, and lake morphology on average annual bird abundance and total species richness. All trophic state parameters (total phosphorus, total chlorophyll a, etc.) accounted for significant portions of the variance in average annual bird abundance, but total chlorophyll a concentrations (μg/L) accounted for the highest percentage (47 percent) of the variance. The best fit regression equation was: Log Bird Abundance = 1.35 + 0.56 Log Total Chlorophyll a . Lake area, shoreline length, and all trophic state parameters accounted for significant portions of the variance in total species richness. Multiple regression analyses indicated that l...

A Management Alternative for Lake Apopka

ABSTRACT We examine the idea that whenever high levels of planktonic algae impair a lake, nutrient control is the first step to be taken regardless of what other management actions might be contemplated. Our example is Lake Apopka, a 12,500 ha, shallow (1.7 m), polymictic lake in central Florida. Prior to 1947, the lake was dominated by macrophytes, was reputed to have clear waters, and had a national reputation for its largemouth bass fishery. Following a hurricane in 1947, the lake switched to a turbid, algal state and the bass fishery is all but gone. For over 30 years, it was either implied or stated directly that nutrient enrichment from anthropogenic activities, especially farms along the north shore, was to blame for this change and the lack of macrophyte recovery. The current management plan is to remove the farm nutrient supply by purchasing the farms under the theory that this will lower the total phosphorus concentration in the water and thus restore the lake. We have developed the most probable phosphorus budgets for the lake based on the studies of others and have determined that a fluid mud layer that is frequently resuspended by the wind will lead to high internal loading and slow the drop in phosphorus concentration. The equilibrium phosphorus concentration will lie between 52 and 88 mg·m−3, so the lake will remain in its eutrophic state. We propose an alternative management plan using artificial reefs that will focus on restoring the largemouth bass fishery in the immediate future. This idea is attractive because bass fishing was the dominant use of this lake in the past, it can be accomplished without waiting for a change in trophic state, and it can produce results in a relatively short period of time.

Seasonal Patterns of Chlorophyll, Nutrient Concentrations and Secchi Disk Transparency in Florida Lakes

ABSTRACT Florida lakes as a group exhibited a distinct seasonal pattern in the concentration of algal chlorophylls. This conclusion was based on an analysis of data from the Florida LAKEWATCH 1994 database containing 416 lake-years of observations from 209 lakes. For oligotrophic, mesotrophic, and eutrophic lakes, monthly chlorophyll concentrations were typically lower than the annual mean chlorophyll concentration from December to May and were higher from August to October. Hypereutrophic lakes (annual mean chlorophyll > 40 μg·L−1) tend to have high fluctuating levels of algal chlorophyll for most of the year except for low levels in December, January, and February. Maximum chlorophyll concentrations tended to occur most frequently from August to October, however the maximum or minimum level in any given lake can occur at any time of the year. The variance (s2) in monthly chlorophyll concentrations over the course of a year increased with increasing annual mean chlorophyll for Florida lakes. There was al...

Training Grass Carp to Respond to Sound for Potential Lake Management Uses

Abstract Future use of triploid grass carp Ctenopharyngodon idella as a control agent for aquatic macrophytes could be enhanced by efficient methods of removing the fish from stocked waters. In laboratory trials, we evaluated the ability to train triploid grass carp to move to a specific area for potential recapture by coupling low-frequency sounds (i.e., 1,000, 800, and 600 Hz) and grass carp feeding sounds with a food reward. Repeated-measures analysis of variance (ANOVA) indicated that grass carp response times to sound stimuli declined over training sessions for all low-frequency sounds tested. Percent return rates averaged 94, 94, 88, and 71% for low-frequency sounds of 600, 800, and 1,000 Hz and grass carp feeding sounds, respectively. Our results suggest that sound can be used to attract triploid grass carp to a central area where they potentially can be removed.