Home Abstract Introduction Study Area Collection and Processing of Water Samples Determining Trends in Water Quality Analysis of Water-Quality Trends Summary References PDF Version

Statistical summaries and spatial and temporal trends of selected major inorganic constituents and physical characteristics; pH and dissolved oxygen; suspended sediment; nitrogen, phosphorus, and carbon species; trace metals; and bacteriological and biological characteristics were determined for the Miami and Tamiami Canal stations. Statistical summaries presented in tables 3 and 4 include the number of observations, mean, minimum, maximum, median (50th percentile), and interquartile range (25th and 75th percentiles). A log probability regression of concentration values on normal quartiles is used to predict the magnitude of values for constituents with censored data values. The mean, median, and 25th and 75th percentiles are then estimated from predicted values in place of censored values (Schertz and others, 1991, p. 31). Median concentrations of selected constituents also are compared to the Florida Department of Environmental Protection Class III freshwater standards for recreation, propagation, and maintenance of a healthy, well balanced population of fish and wildlife (Florida Department of Environmental Protection, 1993).

Water-quality trends were based on the seasonal definition and the resultant flow/concentration pairs or concentration values selected within that seasonal definition. The trend slope is presented as change in original units per year and as percent per year for each constituent. The trend slope in percent per year is expressed as a percentage of the mean concentration by dividing the slope by the mean and then multiplying by 100 (Schertz and others, 1991, p. 19). In tables 3 and 4, statistically significant values (marked in red) are represented by p-values less than 0.10. The p-value is the attained significance level or probability of rejecting the null hypothesis of no trend when there actually is a trend. ESTREND allows for the use of high p-values (0.10 or higher) when removing flow-related variability (Schertz and others, 1991, p. 24). However, even though no flow adjustment was performed for trends at the Miami Canal station due to the human influence on discharge, a p-value of 0.10 also was used for consistency. Those trends that would not be statistically significant at a p-value of 0.05 are mentioned in the text and noted in tables 3 and 4. The best trends also are represented as to whether they are based on unadjusted or flow-adjusted concentrations (table 2).

Statistically significant and nonsignificant trends are reported at the Miami and Tamiami Canal stations for each constituent during its entire period of record. For most constituents, the time period is 1966-94 for the Miami Canal station or 1967-93 for the Tamiami Canal station (tables 3 and 4). However, because trends are dependent on the period of record for which they originally were determined, trends of selected water-quality constituents (dissolved solids, dissolved oxygen, suspended sediment, total nitrogen, total phosphorus, fecal coliform, and fecal streptococcus) are presented for two or three time periods each at the Miami and Tamiami Canal stations. The additional data sets for the above constituents help provide further understanding of trends at these stations during different time periods (tables 3 and 4). Because of changes in program emphasis over time, some constituents span shorter time periods; whereas others, such as the major inorganic constituents and nutrients, span longer time periods. This accounts for the fact that some trends are for shorter periods than others. Additionally, for constituents spanning the entire period of record, trends are determined for various time periods, but always compared to water-quality data existing at the end of the program.

Water-quality trend analysis is defined as estimating the change in water quality over time (Schertz and others, 1994, p. 1). The trends presented here for a particular constituent over a specific time period represent the overall trend that has occurred during that period. However, trend slopes present the rate of change in original units per year and as a percentage of the mean, but give no indication of how a particular trend has occurred. Trends may have occurred as gradual changes over time, abrupt changes, step changes, or reversals over the period of record. Therefore, those constituents where a statistically significant (p-value less than 0.10) trend has occurred, plots of LOWESS lines have been generated to illustrate the nonlinear variations in the data for the specific period of record. Table 5 provides the number of statistically significant trends for selected constituents at the Miami and Tamiami Canal stations. Table 6 summarizes temporal trends as indicators of improvement or deterioration in water quality over time.

Plots were generated to depict the LOWESS lines of concentration as a function of discharge for dissolved solids, suspended sediment, total nitrogen, and total phosphorus at the Miami and Tamiami Canal stations. LOWESS minimizes the influence of outliers on the smoothed line. A smoothness factor (F) of 0.5 was used for the plots shown in figures 7 and 8. The smoothness factor is the fraction of observations used in fitting the data to the line, and usually ranges from 0.3 to 0.7 (Schertz and others, 1991, p. 24).

The concentration of dissolved solids as a function of discharge at the Miami Canal station (fig. 7) shows no substantial changes with increasing discharge, indicating there is no dilution effect or increase in concentration due to washoff. The dissolved-solids concentration plot for the Tamiami Canal station (fig. 8) illustrates the effect of constituent dilution with increasing discharge. The concentration of suspended sediment as a function of discharge at the Miami Canal station (fig. 7) indicates a slight increase with increasing discharge. A similar suspended-sediment concentration plot for the Tamiami Canal (fig. 8) shows slight dilution followed by an increase in sediment with increased discharge. An initial decrease in suspended sediment concentration with increasing discharge, followed by an increase in constituent concentration with increasing discharge, might reflect initial dilution of a point source followed by washoff of nonpoint source contaminants. The concentrations of total nitrogen and total phosphorus as a function of discharge at the Miami Canal station indicate the effects of dilution and washoff (fig. 7). The total nitrogen and total phosphorus plots (fig. 8) for the Tamiami Canal station show only initial dilution at lower discharges.

Major inorganic constituents and physical characteristics were analyzed to determine water-quality trends at the Miami and Tamiami Canal stations during the period of record (1966-94) or other selected time periods. Upward trends of some major dissolved ions (chloride, magnesium, potassium, and sodium), specific conductance, and dissolved solids were detected at both stations; upward trends of silica and sulfate also were detected at the Miami Canal station. Downward trends of turbidity and fluoride were detected at the Miami and Tamiami Canal stations, respectively. Plots were generated to show the LOWESS lines of selected major inorganic constituents and other characteristics as a function of time at the Miami and Tamiami Canal stations (figs. 9 and 10).

Major inorganic constituents, as discussed in this report, include those cations (positively charged ions) and anions (negatively charged ions) that constitute the bulk of the dissolved solids and that commonly occur in concentrations exceeding 1.0 mg/L (milligram per liter). The major dissolved cations generally are calcium, magnesium, sodium, and potassium; the major anions are sulfate, chloride, fluoride, and those constituents contributing to alkalinity, which primarily are carbonate and bicarbonate (Hem, 1985). These charged species in solution contribute to the water’s specific conductance, defined as the ability to conduct an electric current. Both dissolved solids and specific conductance are dependent on the degree of mineralization of the water and generally are indicators of inorganic water quality. Silicon, which is nonionic, contributes to the dissolved solids and is usually reported as silica.

The highest rate of increase for the cations was determined for potassium (3.35 percent per year) at the Miami Canal station during 1966-94. The LOWESS line of potassium shows an overall increase during the period of record, with a rather abrupt rate of increase beginning in about 1980 (fig. 9). The rate of increase for potassium was 1.34 percent per year at the Tamiami Canal station (table 4). The rates of increase for sodium were 1.54 percent per year at the Miami Canal station (1966-94) and 1.45 percent per year at the Tamiami Canal station (1967-93); the rates for magnesium were 1.20 percent per year at the Miami Canal station (1966-94) and 1.48 percent per year at the Tamiami Canal station (1967-93). However, the LOWESS lines for sodium and magnesium at the Miami Canal station shows decreasing trends for the last several years of record (fig. 9). The cations potassium, sodium, and magnesium occur in fertilizers, and upward trends of these constituents may be related to fertilizer usage. Median concentrations of potassium, sodium, magnesium, and other cations were determined at the Miami and Tamiami Canal stations. Median concentrations of all these cations were higher at the Miami Canal station than at the Tamiami Canal station (tables 3 and 4).

The highest rate of increase for anions was determined for sulfate (4.74 percent per year) at the Miami Canal station in 1966-94 (table 3). Results also indicate rates of increase for chloride at the Miami Canal station (1.23 percent per year) and the Tamiami Canal station (1.07 percent per year) as presented in tables 3 and 4, respectively. However, trends for chloride at both stations are relatively flat for the last few years of record. An upward trend in chloride at the Miami Canal station (fig. 9) might be due to increased urban or agricultural activities, whereas the upward trend for this anion at the Tamiami Canal station might be due to discharge of more highly mineralized water from Water Conservation Areas 3A and 3B through structures S-343A, S-343B, and S-344 (fig. 1). An upward trend in sulfate at the Miami Canal station might be due to increased urban or agricultural activities, as well as sulfur-emitting discharges in atmospheric deposition. Smith and others (1987, p. 8), however, concluded that sources of sulfate in NASQAN stations across the Nation were more likely to be terrestial (rather than atmospheric) in origin because of the higher frequency of trends in basins where the statistical association between the ratio of atmospheric deposition to aquatic yield of sulfur is low. The LOWESS lines for sulfate and chloride at the Miami Canal station and for chloride at the Tamiami Canal station are shown in figures 9 and 10. The fluoride trend for the Tamiami Canal station shows an overall downward trend; however, there seems to be no trend for about the last 15 years of record (fig. 10).

Median concentrations of chloride, sulfate, and other anions were determined at the Miami and Tamiami Canal stations. Median chloride concentrations were higher at the Miami Canal station (70 mg/L) than at the Tamiami Canal station (17 mg/L). During periods of backpumping in the northern Everglades, highly mineralized connate ground water is drawn into the canals, which might account for the higher chloride concentrations (Parker and others, 1955, p. 733).

Median concentrations of sulfate were 5.8 mg/L at the Miami Canal station and 1.0 mg/L at the Tamiami Canal station. Caution is in order in the interpretation of the sulfate trend at the Miami Canal station (fig. 9); a known positive bias in sulfate concentrations was discovered in 1989 based on a turbidimetric method in laboratory use since 1982 (Schertz and others, 1994, p. 35). This bias was generally evident in water samples where sulfate concentrations were less than 75 mg/L and median concentrations were less than 20 mg/L, which correlated with the data from the Miami and Tamiami Canal stations (tables 3 and 4). Additionally, color values greater than 20 Pt-Co units (platinum-cobalt units) may also have contributed to the positive bias (tables 3 and 4). The LOWESS line for sulfate indicates an overall upward trend in sulfate over time (fig. 9), which coincides with the upward trends for other ions. What effect this bias may have had on the overall trend remains unknown.

Results indicate upward trends for silica and dissolved solids at the Miami Canal station (fig. 9), and a general upward trend for dissolved solids at the Tamiami Canal station (fig. 10). The rate of increase for silica was 0.82 percent per year at the Miami Canal station during 1966-94. The rates of increase for dissolved solids were 0.41 percent per year at the Miami Canal station during 1966-94 (table 3), and 0.78 percent per year at the Tamiami Canal station during 1967-93 (table 4). A slightly downward trend for dissolved solids occurred at the Tamiami Canal station during the last few years of record (fig. 10). There also were upward trends at the Miami Canal station during 1976-94 (0.38 percent per year) and 1987-94 (0.83 percent per year). The trend for dissolved solids in 1987-94 would not have been statistically significant at an alpha level of 0.05 as noted in table 3. Median concentrations of silica and dissolved solids were higher at the Miami Canal station than at the Tamiami Canal station (tables 3 and 4), indicating greater mineralization. Upward trends in silica and dissolved solids tend to indicate an overall deterioration in water quality. High concentrations also can be detrimental to aquatic organisms.

Trends were determined for physical characteristics that include color, turbidity, and specific conductance. No upward or downward trends were determined for color; however, median values were 50 Pt-Co units at the Miami Canal station (table 3) and 30 Pt-Co units at the Tamiami Canal station (table 4), indicating higher concentrations of organic material in the Miami Canal water. This might be due to the organic peat soils found in the water-conservation and agricultural areas through which water in the Miami Canal flows as compared to the marls or sands prevalent in the Big Cypress National Preserve. A statistically significant downward trend for turbidity was detected at the Miami Canal station (fig. 9), with a rate of decrease of -2.37 percent per year during 1970-78 (table 3). This trend would not have been statistically significant at an alpha level of 0.05 as noted in table 3. The median turbidity value of 1.0 NTU (nephelometric turbidity unit) was the same at both stations (tables 3 and 4) and was well below the State freshwater standard (Florida Department of Environmental Protection, 1993) of less than or equal to 29 NTU above natural background conditions. The maximum turbidity values for the Miami and Tamiami Canal stations were 11 and 4.5 NTU, respectively. As for specific conductance, an upward trend was detected at both the Miami and Tamiami Canal stations during the period of record, with rates of increase of 0.88 and 1.22 percent per year, respectively, (tables 3 and 4). A downward trend for specific conductance was apparent at the Tamiami Canal station, but only during the last few years of record (fig. 10). Whereas median specific conductance values of 640 µS/cm (microsiemens per centimeter) at the Miami Canal station and 352 µS/cm at the Tamiami Canal station were below the State freshwater standard of 1,275 µS/cm (Florida Department of Environmental Protection, 1993), a maximum specific conductance of 1,350 µS/cm detected at the Miami Canal station did exceed the State standard. The upward trend in specific conductance indicates that an increase in dissolved solids occurred in both canals over time, which might be a result of natural phenomena or anthropogenic activities.

Water hardness is reported as an equivalent amount of calcium carbonate (CaCO₃) and is dependent primarily on calcium and magnesium. No Federal or State standards exist for hardness, but waters are classified as soft from 0-60 mg/L, moderately hard from 61-120 mg/L, hard from 121-180 mg/L, and very hard at greater than 180 mg/L (Hem, 1985, p. 159). Based on median concentrations, water is very hard (230 mg/L) at the Miami Canal station and is hard (150 mg/L) at the Tamiami Canal station (tables 3 and 4). Limestone present in the surficial aquifer system and Big Cypress National Preserve, where the stations are situated, is a natural source of calcium and magnesium, which affect hardness.

Trend determinations were made for the time-dependent constituents pH and dissolved oxygen. The characteristics of pH and dissolved oxygen are related through the process of photosynthesis, which results in the uptake of carbon dioxide and the manufacture of dissolved oxygen by aquatic plants. Both pH and dissolved oxygen may exhibit diel variations, and together may be positively correlated to be higher during day-light hours because of photosynthetic activity and lower during night-time hours because of plant respiration. For this study, dissolved-oxygen concentrations were determined only in the daytime, and thus, represent concentrations that occurred during photosynthetic activity. However, the downward trends in pH at the Miami Canal station (fig. 9) and dissolved oxygen at the Tamiami Canal station (fig. 10) did not correlate with an accompanying statistically significant trend in either dissolved oxygen at the Miami Canal station (table 3) nor pH at the Tamiami Canal station (table 4), which would be expected if the trends were dependent on photosynthetic activity alone.

Results indicate downward trends in pH (-0.17 percent per year) at the Miami Canal station during 1966-94 (fig. 9 and table 3) and in dissolved oxygen (-2.59 percent per year) at the Tamiami Canal station during 1967-93 (figs. 9 and 10; tables 4 and 5). There were, however, no statistically significant trends in dissolved oxygen at the Tamiami Canal station for the 1976-93 and 1987-93 periods. A downward trend in dissolved oxygen usually results from an increase in oxygen-demanding materials (most likely organic) in water, and generally is indicative of increased anthropogenic activities and deteriorating water-quality conditions. Median pH values were 7.6 at the Miami Canal station during 1966-94 and 7.5 at the Tamiami Canal station during 1967-93, which were well within the range (6.0-8.5) established by the Florida Department of Environmental Protection (1993) for freshwater standards. The median concentrations of dissolved oxygen were 3.3 mg/L (1987-94) and 2.7 mg/L (1967-93) at the Miami and Tamiami Canal stations, respectively, which were below the FDEP standard.

Suspended sediment is material that is maintained in suspension in a water column due to the upward components of turbulent currents or material that exists in suspension as a colloid. This solid material may result from the disintegration of rocks and may include chemical and biochemical precipitates, as well as decomposed organic material. The concentration of suspended sediment in a stream is closely related to environmental and land-use factors (both urban and agricultural), intensity and volume of precipitation, geology and soil types, and physical characteristics of the stream. Suspended-sediment concentrations in southern Florida streams tend to be lower than those in other areas across the Nation, especially the western areas, which probably is due to the abundant vegetative cover that limits soil bank erosion. High suspended-sediment concentrations may adversely affect stream water quality by increasing turbidity, and thus, inhibiting photosynthetic activity. Suspended material, highly organic in nature, may increase the water column oxygen demand, resulting in hypoxic conditions. Additionally, high concentrations of suspended sediment may adversely affect aquatic life. Smith and others (1987, p. 13) found a close association between increasing trends in suspended sediment and basins in which land use results in high rates of soil erosion.

Results indicate a statistically significant upward trend (3.56 percent per year) in suspended sediment at the Miami Canal station during 1974-94, a statistically significant upward trend (4.08 percent per year) at the Tamiami Canal station during 1976-93 (but no detectable trend during 1987-93), and a statistically significant downward trend (-14.44 percent per year) at the Miami Canal station during 1987-94 (tables 3 and 4). The upward trends indicate some deterioration of water quality. At the Miami Canal station, the downward trend is an indication of improvement in water quality over the last few years of the period of record. Median concentrations of suspended sediment at the Miami and Tamiami Canal stations were 3.0 and 4.0 mg/L, respectively. The suspended sediment trends at the Miami Canal station during 1974-94 and 1987-94 were not statistically significant at an alpha level of 0.05 as noted in table 3.

Nitrogen, phosphorus, and carbon species are needed for the growth and maintenance of all organisms, especially plants. Water bodies that receive increased concentrations of nitrogen and phosphorus tend to have dense plant growth or algal blooms and usually become eutrophic (Hem, 1985, p. 128). Elevated concentrations of nitrogen and phosphorus can be attributed to municipal wastewater, industrial waste-water, or agricultural and urban runoff. Nitrogen occurs in natural waters in the form of organic nitrogen, ammonia, nitrite, and nitrate. Phosphorus also may exist in both organic and inorganic states. Organic carbon can be contributed to a water body through plant and animal waste. Total organic carbon is a measure of the dissolved and suspended organic carbon in a water sample.

Trends were determined for selected nitrogen, phosphorus, and carbon species at the Miami and Tamiami Canal stations. Statistically significant downward trends in total ammonia were detected at both stations (figs. 11 and 12). The rates of decrease for ammonia were -5.63 percent per year at the Miami Canal station during 1971-94, and -4.46 percent per year at the Tamiami Canal station during 1970-92 (tables 4 and 5). The median concentration of total ammonia was 0.1 mg/L at the Tamiami Canal station and 0.2 mg/L at the Miami Canal station, both exceeding the FDEP freshwater standard of 0.02 mg/L (Florida Department of Environmental Protection (1993).

According to Schertz and others (1994, p. 38), a known positive analytical bias occurred between 1980 and 1986 in the analysis of total ammonia and total ammonia plus organic nitrogen (Kjeldahl nitrogen). This bias was introduced by the mercuric chloride tablets used for field preservation of nutrient samples, and was caused by an additional positive matrix effect introduced by the sodium chloride carrier in the tablets. In 1986, the preservation of nutrient samples using the tablets was discontinued, and mercuric chloride ampoules were substituted. This bias, however, did not seem to affect the overall trends of total ammonia at the Miami and Tamiami Canal stations (figs. 11 and 12).

Total nitrite plus nitrate and total phosphorus were the only other species that demonstrated statistically significant downward trends. The rates of decrease were -12.94 percent per year for total phosphorus at the Miami Canal station during 1987-94 (fig. 11 and table 3) and -5.68 percent per year for total nitrite plus nitrate at the Tamiami Canal station during 1975-85 (fig. 12 and table 4). The statistically significant downward trend for total phosphorus (-12.94 percent per year) at the Miami Canal station coincides with the statistically significant downward trend for suspended sediment (-14.44 percent per year) over the same time period (table 3). However, the total phosphorus trend was not statistically significant at an alpha level of 0.05 as noted in table 3. A strong statistical association (p-value less than 0.001) exists between trends in total phosphorus and suspended sediment at NASQAN stations across the Nation (Smith and others, 1987, p. 13). The coexisting downward trends in total phosphorus and suspended sediment may also suggest that the source of total phosphorus was primarily nonpoint in origin over this time period. These decreasing trends indicate a general improvement in water quality, perhaps due to a reduction in agricultural or urban runoff. Median concentrations of the nitrogen species were higher at the Miami Canal station, which may be attributed to flow through the highly urbanized and agricultural areas. Median concentrations of total phosphorus (0.02 mg/L) were the same at both the Miami and Tamiami Canal stations during all time periods.

The only statistically significant upward trend (2.83 percent per year) was reported for total organic carbon at the Miami Canal station during 1970-81 (fig. 11 and table 3). Median concentrations of total organic carbon were 20 mg/L at the Miami Canal station (table 3) and 13 mg/L at the Tamiami Canal station (table 4). The higher concentration at the Miami Canal station probably reflects the influence of the highly organic soils prevalent in the agricultural and water-conservation areas.

Trace metals commonly occur in concentrations less than 1.0 mg/L (Hem, 1985, p. 129), and in small amounts, some may be toxic to plants, animals, and humans. Many trace metals occur naturally in the environment, but some may be present as a result of urban, agricultural, or atmospheric sources. Trace metals can adsorb to the bottom sediments and re-enter the water column due to changes in the oxidation/reduction potential. Trend determinations were made for dissolved barium, copper, iron, manganese, nickel, strontium, and zinc. Most samples were analyzed using the Seasonal Kendall censored procedure, which does not provide for removal of flow-related variability. Where censored data consist of greater than 5 percent of the total data values for a specific trace metal, the trend slopes might not be reliable, thus, the results were not recorded. Data sets for many of the water samples were too highly censored to make definitive trend analyses for the trace metals at the Miami and Tamiami Canal stations.

Results indicated statistically significant downward trends in barium and iron at the Miami Canal station (fig. 13 and table 3) and in barium at the Tamiami Canal station (fig. 14 and table 4). The downward trend in iron at the Miami Canal station was not statistically significant at an alpha level of 0.05 as noted in table 3. A weak trend also was detected for strontium at the Tamiami Canal station (fig. 14 and table 4), with a median concentration of 230 µg/L (micrograms per liter). The rates of decrease for barium were -3.86 percent per year at the Miami Canal station and -8.55 percent per year at the Tamiami Canal station. The concentration of barium in natural water is controlled by barium sulfate solubility, which usually limits the concentration of barium to a narrow range. Median concentrations of barium were 31 and 19.5 µg/L at the Miami and Tamiami Canal stations, respectively; these concentrations are not considered to be toxic to aquatic life.

The rate of decrease for iron was -2.43 percent per year at the Miami Canal station (table 3). The median iron concentration was 100 µg/L, which is well below the FDEP freshwater standard of 1,000 µg/L (Florida Department of Environmental Protection, 1993). The solubility of iron in water depends on several factors including the oxidation/reduction potential and the pH of the natural system (Hem, 1985, p. 76).

Bacteriological determinations were made for two types of indicator bacteria, fecal coliform and fecal streptococcus, at the Miami and Tamiami Canal stations. The presence of these bacteria might be a signal that pathogenic disease-producing bacteria or viruses exist in the specific water body. There is a close association between fecal coliform density and Salmonella contamination, with a sharp increase in Salmonella detection when fecal coliform colonies exceed 200 colonies per 100 mL (milliliters) according to the U.S. Environmental Protection Agency (1976). Contamination with both types of bacteria may come from industrial/municipal and urban/agricultural runoff.

At the Miami Canal station, results indicate a statistically significant downward trend in fecal coliform (-3.84 percent per year) during 1976-94, but no detectable trend during 1987-94. A statistically significant upward trend in fecal streptococcus (45.86 percent per year) also was found at the Miami Canal station during 1987-94 (table 3). The downward trend in fecal coliform may indicate an improvement in water quality over time (1976-94), whereas the upward trend in fecal streptococcus may indicate a deterioration in water quality during the last few years of the period of record (fig. 15). Additionally, the trends for fecal coliform during 1976-94 and for fecal streptococcus during 1987-94 are not statistically significant at an alpha level of 0.05 as noted in table 3. The deterioration in water quality may be due to inadequately treated sewage or runoff from urban or agricultural areas. There were no statistically significant upward or downward trends in bacteriological characteristics at the Tamiami Canal station (table 4). Median concentrations of fecal coliform and fecal streptococcus were higher at the Miami Canal station than at the Tamiami Canal station (tables 3 and 4). This probably is because the Miami Canal traverses areas that are influenced more by urban and agricultural activities.

Biological determinations were made for phytoplankton at the Miami and Tamiami Canal stations. Phytoplankton consist of microscopic free-floating plants that are mostly blue-green algae, diatoms, or green algae. Their movements are dependent on the prevailing current within the water column, and their growth is dependent on solar radiation and nutrient concentrations within the water body. Heavy nutrient loads (especially phosphorus) to a stream, lake, or estuary may cause the water body to become eutrophic, with an increase in phytoplankton growth or algal blooms and the development of hypoxic or anoxic conditions, resulting in fish kills. Heavy phytoplankton growth might also result in undesirable aesthetic effects, manifested in unpleasant color and odor problems. Conversely, low phytoplankton growth might be an indication that a water body is oligotrophic or poorly nourished with respect to nutrients. Results indicate no statistically significant upward or downward trends in phytoplankton at the Miami and Tamiami Canal stations for the period of record (tables 3 and 4). Median concentrations of phytoplankton were 840 and 1,800 cells/mL (cells per milliliter) at the Miami and Tamiami Canal stations, respectively.