1
ALGAL SUCCESSION IN THE TRINITY RIVER UN-DER SUMMER AND AUTUMN EFFLUENT
DOMINATED CONDITIONS
Prepared by the Trinity River Authority of Texas in cooperation with the Texas Commission on Environmental Qual-ity with the Assistance of Dr. James Grover, University of Texas at Arlington.
The preparation of this report was financed through grants from the Texas Commission on Environmental Quality under the Clean Rivers Program.
2
TABLE OF CONTENTS
Introduction 3 Materials and Methods 5 Results 8 Conclusions 16 TABLES Table 1. Monitoring Stations 7 Table 2. Water Quality Variables 8 Table 3. Summary Statistics for East Fork Water Quality Variables 11 Table 4. Genera Associated with the High Order Assemblage 15 FIGURES Figure 1. Algal Community Composition in Eagle Mountain Lake 4 Figure 2. Algal Community Composition in Joe Pool Lake 4 Figure 3. Maps of Sampling Stations 6 Figure 4. Chlorophyll a Concentrations in the Main Stem 9 Figure 5. Orthophosphate Concentrations in the Main Stem 9 Figure 6. Dissolved Oxygen Concentrations in the Main Stem 9 Figure 7. Total Suspended Solids Concentrations in the Main Stem 10 Figure 8. Nitrate Plus Nitrite Concentrations in the Main Stem 10 Figure 9. Total Kjeldahl Concentrations in the Main Stem 10 Figure 10. Relationships of Water Quality Variables and Hydrologic Order 11 Figure 11. Relationships of Algal Genera 12 Figure 12. Relative Abundance of Pandorina vs. Total Phosphorus 13 Figure 13. Relative Abundance of Pediastrum vs. Total Phosphorus 13 Figure 14. Relationships of Algal Groups 13 Figure 15. Relative Abundance of Large Motile Green Colonies vs. Total Phosphorus 14 Figure 16. Relative Abundance of Dinoflagelates vs. Total Phosphorus 14 Figure 17. Relative Abundance of Aphanocapsa vs. Hydrologic Order 14 Figure 18. Relative Abundance of Navicula vs. Hydrologic Order 14 Figure 19. Relative Abundance of Small Centric Diatoms vs. Hydrologic Order 15 Figure 20. Relative Abundance of Small Non-motile Green Algae vs. Hydrologic Order 15 Figure 21. Relative Abundance of Large Non-motile Green Algae vs. Hydrologic Order 16 Figure 22. Relative Abundance of Heterocystous Filamentous Bluegreen Algae vs. Hydrologic Order 16 Figure 23. Relative Abundance of Small Motile Green Algae vs. Hydrologic Order 16 Figure 24. Turbidity vs. Hydrologic Order in the Main Stem 18 APENDICES Appendix 1. Sample Results of Algal Enumeration and Identification Analysis
3
The Trinity River runs through Cen-tral Texas from its origins of four forks near the Red River and the Oklahoma State Line to Trinity Bay where it empties into the Gulf of Mexico. Annual rainfall in the upper por-tions of the basin averages around 33 inches, most of which occurs in a relatively few number of storm events with little or no pre-cipitation during summer months. These cli-matic conditions have established a seasonal pattern of summertime low flows over much of the basin. Located at the junction of three of the river’s four forks is the Dallas-Fort Worth metropolitan area, with a population of ap-proximately five and a half million. Cumula-tive wastewater discharges into the river from the Dallas-Fort Worth area averages ap-proximately 450 million gallons per day. During periods of low flows, which typically occur during the summer but can occur at any time of the year, the river is effluent dominated. Under such conditions nutrient concentrations within the river are signifi-cantly elevated over background conditions. Although conventional wisdom holds that algal abundance is directly related to nu-trient concentrations, recent observations suggest that algal populations are smaller immediately downstream of wastewater treatment plants despite the corresponding rise in nutrient concentrations. There are sev-eral intuitive and satisfactory explanations for this phenomenon. First, the influx of wastewater, which in most cases is devoid of algae, provides an immediate dilution effect. This effect in some cases is dramatic, repre-senting a many-fold dilution. Another expla-nation is that the surface to volume ratio de-creases as more water is added. This often limits the photic zone to the top of the water column, severely limiting the amount of light available for algae to use. In this scenario,
light and not nutrients is limiting. Little is known however, of what happens as the water progresses downstream. If the dilution effect is the only cause for de-creases in algal concentrations, then the com-munity should rebound and, taking advantage of the abundant nutrients downstream from the municipal point source, increase respec-tive to their upstream concentrations. If on the other hand physio-morpholocigal factors are limiting their growth, then a rebound of the algae found upstream is not likely. Should algal populations rebound, the ques-tion then becomes one of looking at spatial changes in algal community structures, or al-gal succession. “Succession” and “periodicity” are major themes in the ecological study of algal communities (Reynolds 1984). The term suc-cession refers to changes over time, or in this case distance, in the abundance of popula-tions in different taxonomic groups, while the term periodicity highlights that these changes are often reproducible over annual seasonal cycles. Algal succession is particu-larly well studied in natural lakes of the tem-perate zone (Sommer et al. 1986), where the algal biota is often dominated by small flag-ellated organisms in winter, giving way to a bloom of fast-growing diatoms in spring, a clear-water phase of low algal density in late spring, with subsequent development of di-verse populations depending in part on lake trophic status. Eutrophic lakes often experi-ence dominance by large colonial cyanobac-teria, often mixed with large dinoflagellates, while oligotrophic lakes maintain a diverse summer community of many algal types. Au-tumn can bring dominance by diatoms or cyanobacteria, giving way to the winter flora of small flagellates. In general, such seasonal patterns are forced by events that affect light and nutrient supply, such as thermal stratifi-
INTRODUCTION
4
feeding animals. Gelatinous coatings that re-duce digestibility protect many species of green algae, making them poorer food. Should a river become dominated by cyano-bacteria, its capacity to support a food web
should be even lower, due to the generally
cation and destratification, and by activities of zooplankton grazers and the fish that prey on them. Reservoirs (i.e. manmade impound-ments) have occasionally been studied. At least superficially, they appear to have succes-sional patterns that re-semble those of natural lakes (Figures 1 and 2), although the driving mechanisms are not as well supported. Much less is known about al-gal succession in flow-ing-water systems; riv-ers are especially poorly studied, despite the development of substantial planktonic algae in many main-stem, large-channel riv-ers (Reynolds 1990). One of the few studies available, that of the River Seine in France (Garnier et al. 1995), shows a clear succession from diatoms early in the growing season to green algae later. Shifts in nu-trient supply, namely a seasonal reduction in silicon supply relative to nitrogen and phosphorus, were suggested as one factor underlying this succession. Such major shifts in algal composition in a river could have implica-tions for its possible uses. Diatoms (and some groups of flagellated algae) are generally an excellent food source for benthic and suspended filter
Figure 1. Eagle Mountain Lake
0%
20%
40%
60%
80%
100%
1 5 9 13 17 21 25 29 33 37 41 45 49
Sample
Rel
ativ
e B
iom
ass
Other
Cryptophyte
Chrysophyte
Euglenoid
Dinoflagellate
Diatom
Bluegreen
Green
Figure 2. Joe Pool Lake
0%
20%
40%
60%
80%
100%
1 6 11 16 21 26 31 36 41 46 51
Sample
Rel
ativ
e B
iom
ass
Other
Cryptophyte
Chrysophyte
Euglenoid
Dinoflagellate
Diatom
Bluegreen
Green
Figure 2. Algal succession in Joe Pool Lake, a Trinity basin reservoir. Samples were collected from March 1998 to October 2000 (Grover and Chrzanowski, un-publ.). Joe Pool Lake has been identified by the TCEQ as having one of the most limited algal populations, as measured by concentrations of chlorophyll a, in the State relative to other Texas reservoirs.
Figure 1. Algal succession in Eagle Mountain Lake, a Trinity basin reservoir. Sam-ples were collected from March 1998 to October 2000 (Grover and Chrzanowski, unpubl.). There are concerns that Eagle Mountain Reservoir may have unhealthy concentrations of algae.
5
poor digestibility and frequent toxicity of these algae. Because relative supplies of nitrogen, phosphorus and silicon could influence suc-cession among different algal types in rivers, wastewater discharges could alter or induce algal succession. Wastewater typically sup-plies little silicon, while supplying abundant nitrogen and phosphorus at a relatively low N:P ratio. By itself, this nutrient spectrum could be expected to stimulate dominance by cyanobacteria (Smith 1983), possibly leading to impaired uses downstream. The study herein detailed was under-taken to provide some initial understanding of spatial algal succession in the Trinity River and a preliminary assessment of possi-ble wastewater influences. MATERIALS AND METHODS A series of nineteen sampling sites were selected from the Beach Street bridge over the West Fork of the Trinity in Tarrant County to the HWY 7 bridge over the Main Stem near the city of Crockett in Houston County (figure 3). Sites were selected to pro-vide samples from the river representing a progression of effluent dominance. The up-permost site was located above all major point sources. Successive sites downstream included one or more sample sites between each major point source through the Dallas-Fort Worth area. Additional samples were included to provide information on how wa-ter chemistry and algal communities change in a downstream fashion below Dallas and additional significant point-source inputs. An additional site was included on the East Fork of the Trinity. This site differs from the others in that it is not on the Main Stem and therefore is not in series with them. The site was included to provide information on water chemistry and algal community composition in the East Fork, which empties
into the Main Stem below Dallas. The study was undertaken in two phases, both of which were conducted under low flow conditions during the summer and autumn of 2002. Phase one consisted of a single sam-ple event at each site. The results of this sam-pling indicated two reaches along the main-stem of the river which experience signifi-cant changes in algal community structure. Phase two sampling targeted these two reaches as well as the East Fork site. During the second phase, three sample runs were conducted at each of these reaches. Each of the main-stem reaches including three sites. Table 1 contains a complete list of the sam-ple sites along with ancillary information, in-cluding the dates and phases during which each was sampled. At each site, during both phases, wa-ter samples were collected and analyzed for conventional water chemistry parameters (table 2). All samples were collected just be-low the waters surface and were analyzed by the TRA CRWS laboratory. 100 ml samples for algae identification and enumeration were also collected. Upon collection, these sam-ples were preserved with formalin-Lugol’s solution, and delivered to Dr. James Grover at the University of Texas at Arlington. An attempt to measure irradiance was also made at each site, however this proved impractical since most samples were collected from high bridges, leading to significant complications from strong winds and swift river currents. Ultimately, irradiance measures were deemed to be of little use. The inverted microscope method was utilized to identify and enumerate algae (Margalef 1969). This method involves plac-ing an aliquot of defined volume from the al-gal sample in a sedimentation chamber so that cells and colonies sink to the bottom, which consists of a thin glass plate that can be viewed with an inverted microscope.
6
!(
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!( !( !(
10920
10922
10924
10925
10987
10929
10934
17161
10937
SS111079
11081
11084
11087
17160
1108510938
TRA
Central W
WTP
\(162 MG
D)
Dallas C
entral W
WTP (200 M
GD
)
Fort
Wor
th
Villa
ge C
reek
WW
TP
(169
MGD
)
Dallas Southside
WW
TP (110 MG
D)
Figure 3. Map of upper and middle Trinity River basin with study sites and loca-tions of major wastewater discharges. Discharges listed in parentheses are permit-ted limits and therefore do not reflect actual discharges.
South Mesquite Creek Plant (25 MGD)
Duck Creek Plant (30 MGD)
Rowlett Creek Plant (25 MGD)
MAIN STEM
EA
ST F
OR
K
DALLAS
Fort Wort
7
SITE DESCRIPTION SITE ID PHASES SAMPLED
CUMULATIVE DISTANCE (mi)
CUMULATIVE TRAVEL TIME (hrs—estimated)
DATES SAMPLED
HYDO ORDER
Immediately Below Beach Street Impoundment on West Fork in Fort Worth
10938 I 0 0 7/29/02 1
Precinct Line Road 11085 I 12 180 7/29/02 2
Bedford Arlington Road 17160 I and II 15.1 236 7/29/02 9/5/02 9/26/02 10/1/02
3
FM 157 11087 I 19.5 242.5 7/29/02 4
HWY 360 11084 I and II 24.5 251.1 7/29/02 9/5/02 9/26/02 10/1/02
5
Belt Line Road 11081 I 31 260.6 7/29/02 6
Immediately upstream of TRA Central WWTP Outfall
11079 I and II 36.75 267.3 7/29/02 9/5/02 9/26/02 10/1/02
7
Main Stem below Singleton BLVD at location of Old Sin-gleton Road bridge
SS1 I 38.25 269.3 7/29/02 8
Mockingbird 10937 I 41.25 273.3 7/29/02 9
Immediately upstream of Dal-las Central WWTP Outfall
17161 I 50.25 285.3 7/29/02 10
South Loop 12 10934 I 54.5 289.6 7/3002 11
Malloy Bridge 10929 I and II 71.5 311.6 7/30/02 9/5/02 9/26/02 10/1/02
12
HWY 34 near Rosser 10925 I and II 93.5 340.6 7/30/02 9/5/02 9/26/02 10/1/02
13
HWY 85 10924 I 112.5 371 7/3002 14
HWY 31 near Trinidad 10922 I and II 152.1 427.1 7/3002 9/5/02 9/26/02 10/1/02
15
HWY 287 near Cayuga 10920 I 170.1 455.1 7/3002 16
HWY 79 near Oakwood 10919 I 229.6 538.6 7/3002 17
HWY 7 10918 I 276.6 607.5 7/3002 18
East Fork at Valley Ranch 10987 I and II NA NA 7/31/02 NA
Table 2. Study Sites, Phases, Distances, Travel Times, Dates Sampled and Hydrologic Order
8
Fields or transects of known area on the bot-tom plate are then examined, with all algal specimens identified and enumerated. In this method, the volume of aliquot thus sedi-mented is adjusted based on total density of algae. Experience in Texas reservoirs sug-
gested that 20 ml represented a reasonable volume for initial counts, and this volume was thus utilized. For this study, the “natural units” method was followed, meaning that an indi-vidual unit of algae was the cell for unicellu-lar organisms and the colony for colonial or-ganisms. Count data were entered into Excel spreadsheets for conversion to volumetric density, and for data summary and statistical analysis. A complete identification to species level was not attempted. Instead, coarse cate-gories based on higher taxonomy (algal divi-sions), size, and morphology were enumer-ated. This resolution was sufficient to detect major successional changes in algae. Because the algal units counted cover
a very wide range of size, counts at three magnifications was necessary. At each mag-nification, sufficient fields or transects were examined to count 200-400 units in the dominant category.
RESULTS
Water Quality Variables Examination of the measured water quality parameters indicates a strong, incre-mental influence on certain variables by the four major wastewater dischargers. This phe-nomenon is clearly displayed in figures 5 and 8, which show concentrations of the dis-solved nutrients otrhophosphate and nitrate plus nitrite. Concentrations of these parame-ter increase dramatically after each input of reclaimed water and then slowly decrease be-fore the next point source. Although not shown, total phoshporus followed a similar pattern. Concentrations of chlorophyll a steadily increased downstream, peaking at Highway 287 near Cayuga before dropping sharply. An exception to this trend was seen at the two uppermost sites, 17160 and 11084. These sites, sampled only during phase one in July of 2002, had relatively high concen-trations of chlorophyll a and by extension al-gae. Total suspended solids showed a pat-tern of increasing concentrations down-stream. Conversely to dissolve nutrients however, TSS concentrations were seen to decrease with each input of reclaimed water, and slowly increase with distance from the point source. Dissolved oxygen concentrations, while highly variable at the FM 157 site, were otherwise fairly consistent, increasing slightly in a downstream manner. It should be noted however that samples further down-stream were collected later in the day. It is
PARAMETER UNITS
Dissolved Oxygen mg/L
pH Standard Units
Water Temperature Degrees C
Air Temperature Degrees C
Specific Conductivity Micro siemen
NO2/NO3 mg/L
TKN mg/L
NH3 mg/L
OP-O4 mg/L
NO3 mg/L
Total Phosphorus mg/L
Chlorophyll a ug/L
E. coli MPN
Total Suspended Solids mg/L
Table 2. Water quality variables analyzed.
9
R2 = 0.622
R2 = 0.8361
0
10
20
30
40
50
60
Hydro log ic Order
7-Jul
5-Sep
26-Sep
1-Oct
Linear (5-Sep)
Linear (26-Sep)
0
0.5
1
1.5
2
2.5
H y d r o l o g i c O r d e r
7-Jul
5-Sep
26-Sep
1-Oct
R2 = 0.6136
0
1
2
3
4
5
6
7
8
9
10
H y d r o l o g i c O r d e r
7-Jul
5-Sep
26-Sep
1-Oct
Linear (7-Jul)
Vill
age
Cre
ek
WW
TP
Dal
las C
en-
tral W
WTP
TRA
Cen
tral
WW
TP
Dal
las S
outh
Si
de W
WTP
Figure 4. Chlorophyll a concentrations in the Main Stem.
Figure 5. Orthophosphate concentrations in the Main Stem.
Figure 6. Dissolved oxygen concentrations in the Main Stem.
10
Dal
las S
outh
Si
de W
WTP
0
20
40
60
80
100
120
0 2 4 6 8 10 12 14 16 18 20
Hydrologic Order
TSS(
mg/
L)
7-Jul
5-Sep
26-Sep
1-Oct
0
2
4
6
8
10
12
14
16
0 2 4 6 8 10 12 14 16 18 20
Hydrologic Order
NO
2NO
3(m
g/L)
7-Jul
5-Sep
26-Sep
1-Oct
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0 2 4 6 8 10 12 14 16 18 20
Hydrologic Order
TKN
(mg/
L)
7-Jul
5-Sep
26-Sep
1-Oct
Figure 7. Total suspended sediment concentrations in the Main Stem.
Figure 8. Nitrate plus nitrite concentrations in the Main Stem.
Vill
age
Cre
ek
WW
TP
TRA
Cen
tral
WW
TP
Dal
las C
en-
tral W
WTP
Figure 9. Total Kjeldahl nitrogen concentrations in the Main Stem.
11
Water quality variables from all sites were examined statisti-
cally to determine rela-tionships between vari-ables, including hydro-logic order (figure 10) Algal Community Structure Appendix A con-tains results of algae
identification and enumeration. These data were analyzed by genera to determine poten-tial relationships between water quality vari-ables and presence of genera. Through this analysis of genera, several relationships were identified as seen in figure 11 and as de-scribed below: A phylogenetically diverse group of genera were found to be associated with high TP, DO, & NO2. These genera included Au-lacoseira, Chlamydomonas, Chlorogonium, Eudorina, Pandorina, Lagerheimia, Pedias-trium, Cryptomonas, Rhodomonas, Euglena and Phacus. Conversely, two genera of green algal, Ankistrodesmus and Crucigenia, were associ-ated with lower concentrations of TP, DO, & NO2. Genera associated with low hydrologi-cal order, high conductivity and high nitrite plus nitrate include the cyanobacteria Aphanocapsa, Cylindrospermum, “Oscillatoria”, Planktolyngbya, Raphidiopsis and Spirulina. Others genera found to be asso-ciated with lower hydrologic order were Di-nobryon, Cymbella and Navicula. The latter two are pennate diatoms commonly living in benthic habitats. There association with low order is not surprising. It is also plausible that some of the filamentous cyanobacteria, in-cluding Oscillatoria and Planktolyngbya
therefore likely that the observed increase in dissolved oxygen concentrations is a function of sample times and corresponding levels of photosynthetic activities. Analysis of East Fork data in terms of hydrologic order was not performed, as there was only one sample station in that reach. Like the Main Stem, the East Fork is effluent dominated, and demonstrated water quality characteristics consistent with this fact. Key variables are summarized in table 3.
Table 3. Average, minimum and maximum concentrations of key water quality variables at the East Fork site.
PARAMETER AVERAGE CONCEN-TRATION
MINIMUM MAXIMUM
Orthophosphate 2.6 (mg/L) 2.1 4.4
Nitrate/Nitrite 10.3 (mg/L) 9.0 11.8
TKN 1.0 (mg/L) 0.7 1.5
Chlorophyll a 30.6 (ug/L) 8.7 51.7
Dissolved Oxygen 10.2 (mg/L) 8.7 11.5
TSS 88.3 (mg/L) 65 103
-0.2 0.8
-1.0
0.4
Hydrolog
Cond
DO
pH
TSS
NH3
NO2
TKN
NO2/NO3
TP
OP-D
Chloroph
Figure 10. Relationships of quality variables and hydrologic order are shown in relation to two axes.
Axis 1
Axis 2
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and cyanobacteria, associated with lower order reaches that tend to have higher nitrite and low conductivity.
3. “Reservoir assemblage” consisting of primarily green algae and diatoms that are also common in reser-voirs and are associated with higher order reaches. High TP Assemblage The “high TP assemblage” characterizes only two samples, both of which were from the East Fork Valley Ranch site near Cran-dall, and both were collected in autumn. Thus the high TP assem-blage was found only rarely. This assemblage appears to be prob-lematic, and is highly influenced by a single sample. That sample had a concentration of 4.37mg/L which was the highest TP re-corded during the course of the study by a factor of two. Five genera were identi-fied in five or fewer samples. For
these, their relative abundance in the high TP sample was high, gen-erating a strong correlation driven
by a single influential point. Figure 12, a plot of Pandorina vs. TP illustrates this problem. Six other genera, Pandorina, Chlorogonium, Eudorina, Lagerheimia, and Phacus, were included in the TP assemblage based on similar abundance patterns. Given the relative rarity of these genera, confidence in their identification as species associated with high TP conditions is low. The remaining genera associated with high TP concentrations occur in 16 to 37 samples, however their association with TP is weak (correlations from -0.02 to 0.43), and again is a result of the single high TP sample. Figure 13 is a plot of Pediastrum, which had
originate from benthic habitats, however most of the other genera in this group are be-lieved to be considered planktonic. Genera associated with high hydro-
logical order, low conductivity, and low ni-trite plus nitrate are mostly green algae com-mon to reservoirs. These include Chlamydo-monas, Chlorella, Coelastrum, Crucigenia, Oocystis and Selenastrum. Unicellular cen-tric diatoms (Cyclotella, Stephanodiscus) also common in reservoirs, were likewise in-cluded in this group . To summarize the patterns in algae, three potential assemblages were identified:
1. “High TP assemblage” consisting of diverse taxa associated with high TP.
2. “Blue-green & benthic assemblage” consisting of benthic pennate diatoms
-0.4 1.0
-0.6
0.8
Achnanth
ActinastAnabaenaAnkistro
Aphanizo
Aphanoca
Aulacose
Carteria
Chamaesi
Chlamydo
Chlorell
Chlorogo
Chroococ
Closteri
Closteri
Coelastr
Cosmariu
Crucigen
Cryptomo
Cyclotel
CylindroCymbella
Dactyloc
Dictyosp
Dinobryo
EudorinaEuglenaGyrosigm
Kirchner
Lagerhei
Large flMallomon
Merismop
MicractiMicrocys
Monoraph
Navicula
Nitzschi
.Oscilla
Oocystis
Pandorin
Pediastr
Peridini
Phacus
Planktol
Raphidio
Rhodomon
Scenedes
Schroede
Selenast
Small fl
Sphaerel
Sphaeroc
Spirulin
Spondylo
Staurast
Stephano
Synedra
Tetraedr
TetrastrTreubari
Figure 11. Algal genera relationships are shown in relation to axes. Figure 10 defines the relationship of the axes to the water quality variables. Axis one (horizontal) was found to be associated most closely with the parameter group of TP, DO and NO2. Axis two (vertical) is most closely associated with hydrologic order.
13
ing a vector graph. The group analysis again suggested a high TP assemblage. These groups, closely and positively correlated to axis one, con-sists of dinoflagelates, filamentous centric diatoms (Aulacoseria), euglenoids, large mo-tile green colonies and Microcystis. Of these, large motile green colonies had the most con-vincing correlation (figure 15). Two of the genera included in this group, (dinoflagelates and filamentous centric diatoms) disagreed with the previously established positive rela-tionship between TP and abundance, show-ing a negative relationship to that parameter. Figure 16 shows this negatively relationship for dinoflagelates. Comparing the relative abundance of high TP groups identified during the group analysis again demonstrated the influence of the single exceptionally high TP sample were obvious. This fact ultimately calls into ques-tion the validity of the high TP assemblage, which could be nothing more than an artifact created by the single aberrant sample.
the strongest correlation to TP (0.43). The remaining genera in the high TP assemblage have similar patterns, in that they reach a fairly high relative abundance in the high TP sample, but have no obvious relationship
with TP in the remaining samples. Additional statistical analyses were then performed, focusing on inter-species correlations (i.e. group analysis). Fig-ure 14 shows the results of this analysis us-
Figure 13. Pediastrum abundance vs. TP.
Pandorina
TP
0 1 2 3 4 5
Rel
ativ
e Ab
unda
nce
0.00000
0.00005
0.00010
0.00015
0.00020
0.00025
TP July vs Pandorina July TP Early Sep vs Pandorina Early Sep TP Late Sep vs Pandorina Late Sep TP Oct vs Pandorina Oct
Figure 12. Pandorina abundance vs. TP concentra-tions.
Pediastrum
TP
0 1 2 3 4 5
Rel
ativ
e Ab
unda
nce
0.0000
0.0002
0.0004
0.0006
0.0008
0.0010
TP July vs Pediastrum July TP Early Sep vs Pediastrum Early Sep TP Late Sep vs Pediastrum Late Sep TP Oct vs Pediastrum Oct
Figure 13. Pediastrum abundance vs. TP con-centrations.
-0.4 1.0
-0.8
0.6
LgNMGrnC
LgMGrnCoEuglenoiDino
LgUniDes
FilCentD Microcys
NHFilBG
HFilBG
PennDiat
SmCentDi
SmNMGrn SmMGrn
Crypto
SmFlag
SmCoccBG
Figure 14. Vector graph of group correlations.
14
Blue-green And Benthic Assemblage This assemblage consists primarily of blue-green and benthic algae, and was found to be associated with sites in the low order portion of the study reach. This is seen in the negative relationship these species demon-strated with axis 2, (figure 11) which was as-
sociated with decreasing hydrologic order (figure 10). Two genera in particular, Aphano-capsa, a small-celled coccoid bluegreen al-gae and Navicula, a benthic pennate dia-tom, showed good correlations to hydro-logic order (figures 17 and 18) in all sample runs. Five additional genera in this as-semblage including Cylindrospermum, Raphidiopsis, Spirulina, Dinobryon and
Aphanocapsa
Hydrological Order
0 2 4 6 8 10 12 14 16 18 20
Rel
ativ
e Ab
unda
nce
0.0
0.1
0.2
0.3
0.4
0.5
0.6
Order July vs Aphanocapsa July Order Early Sep vs Aphanocapsa Early Sep Order Late Sep vs Aphanocapsa Late Sep Order Oct vs Aphanocapsa Oct
Figure 17. Aphanocapsa abundance in relation to hydrologic order
Navicula
Hydrological Order
0 2 4 6 8 10 12 14 16 18 20
Rel
ativ
e Ab
unda
nce
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
Order July vs Navicula July Order Early Sep vs Navicula Early Sep Order Late Sep vs Navicula Late Sep Order Oct vs Navicula Oct
Figure 18. Navicula abundance in relation to hy-drologic order
Dinoflagellates
TP
0 1 2 3 4 5
Rel
ativ
e Ab
unda
nce
0.00000
0.00005
0.00010
0.00015
0.00020
0.00025
0.00030
TP July vs Dino July TP Early Sep vs Dino Early Sep TP Late Sep vs DinoLate Sep TP Oct vs Dino Oct
Figure 16. This graph of Dinoflagelate abundance vs. TP suggests dinoflagelates respond negatively to increasing concentrations of total phosphorus.
Large Motile Green Colonies
TP
0 1 2 3 4 5
Rel
ativ
e Ab
unda
nce
0.0000
0.0001
0.0002
0.0003
0.0004
0.0005
0.0006
0.0007
TP July vs LMGC July TP Early Sep vs LMGC Early Sep TP Late Sep vs LMGC Sep TP Oct vs LMGC Oct
Figure 15. Abundance of large motile green colo-nies vs. TP.
15
lationships with hydrologic order. These in-clude small centric diatoms, small non-motile greens and large non-motile green colonies. Figures 19-21 show these relationships. Two other groups, heterocystous fila-mentous bluegreens and small motile greens also showed a relationship to flow, however
this relationship is not as convincing as the other groups in this assemblage (figures 22 and 23).
Cymbella occurred in 7 or fewer samples. However when present, these genera were found only in or upstream of Dallas. Never-theless, the low frequency of occurrence of these genera gives low confidence to their identification as members of this assemblage. Group analysis focusing on interspe-
cies correlations identified small coccoid bluegreens, large unicellular desmids, non-heterocystous filamentous bluegreens and pennate diatoms as being included in this as-semblage. The latter two are associated with benthic habitats, so it is possible that this “low order assemblage” is being influenced by benthic species suspended from the bot-tom. Large unicellular desmids and coccoid bluegreens are less clearly benthic in origin. High Order—Reservoir Assemblage Eight genera identified with this group had high frequency of occurrence and moderately strong correlations with hydro-logic order (table 4). This assemblage con-tains many genera which are commonly found in north and east Texas reservoirs. Group analysis of this assemblage found three algal groups with convincing re-
Small Centric Diatoms
Hydrological Order
0 2 4 6 8 10 12 14 16 18 20
Rel
ativ
e Ab
unda
nce
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
Order July vs Sm centrics July Order Early Sep vs Sm centrics Early Sep Order Late Sep vs Sm centrics Late Sep Order Oct vs Sm centrics Oct
Figure 19. Relative abundance of small centric diatoms plotted against hydrologic order.
Small Non-motile Greens
Hydrological Order
0 2 4 6 8 10 12 14 16 18 20
Rel
ativ
e Ab
unda
nce
0.0
0.1
0.2
0.3
0.4
0.5
Order July vs SmNM greens July Order Early Sep vs SmNM greens Early Sep Order Late Sep vs SmNM greens Late Sep Order Oct vs SmNM greens Oct
Figure 20. Relative abundance of small non-motile green algae plotted against hydrologic order.
Table 4. Genera in High Order—Reservoir Assemblage and correlations to hydrologic order.
GENUS NO. OCCUR-RENCES
CORRELATION WITH HYDRO ORDER
Chlamydomonas 37 0.26
Chlorella 38 0.48
Coelastrum 22 0.47
Crucigenia 28 0.42
Oocystis 37 0.48
Selenastrum 36 0.19
Cyclotella 38 0.58
Stephanodiscus 21 0.49
16
confidence that hydrological order and some associated environmental variables (e.g. NO2/NO3 and conductivity) are related to changes in algal composition. Hydrological order appears to be the most important vari-able influencing many of the physical and chemical characteristics of the river. Algal assemblage associated with high order sites contained many genera that are common in reservoirs in north and east Texas. Although the high order sites are deeper, they are substantially more turbid (figure 21). Accordingly, conditions at those sites do not necessarily resemble those in reservoirs making the selective mechanisms for this assemblage less intuitive. In terms of abundance, small non-motile green algae dominated this assem-blage. These algae are believed to be a good food source for planktavores. Large non-motile green colonies, although not pre-dominant in terms of abundance, can due to their size constitute a majority of algal bio-mass. Unlike the small greens, these algae are believed to be a poor food source. Al-though the prevalence of this algal group
CONCLUSIONS Both genera and group analyses yielded similar results, identifying three dis-tinct algal assemblages. However only the two assemblages correlated with hydrologi-cal order, the “low order—bluegreen & ben-thic” and “high order—reservoir algae” as-semblages are defined on the basis of multi-ple samples and genera with high frequen-cies of occurrence. As such, there is more
Small Motile Greens
Hydrological Order
0 2 4 6 8 10 12 14 16 18 20
Rel
ativ
e Ab
unda
nce
0.00
0.05
0.10
0.15
0.20
0.25
Order July vs SmM greens July Order Early Sep vs SmM greens Early Sep Order Late Sep vs SmM greens Late Sep Order Oct vs SmM greens Oct
Figure 23. Relative abundance of heterocystous filamentous bluegreen algae to hydrologic order. Heterocystous Filamentous Bluegreens
Hydrological Order
0 2 4 6 8 10 12 14 16 18 20
Rel
ativ
e Ab
unda
nce
0.0000
0.0005
0.0010
0.0015
0.0020
0.0025
0.0030
0.0035
Order July vs HFBG July Order Early Sep vs HFBG Early Sep Order Late Sep vs HFBG Late Sep Order Oct vs HFBG Oct
Figure 22. Relative abundance of heterocystous filamentous bluegreen algae to hydrologic order.
Large Non-motile Green Colonies
Hydrological Order
0 2 4 6 8 10 12 14 16 18 20
Rel
ativ
e Ab
unda
nce
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0.20
Order July vs LNMGC July Order Early Sep vs LNMGC Early Sep Order Late Sep vs LNMGC Late Sep Order Oct vs LNMGC Oct
Figure 21. Relative abundance of large green al-gae colonies plotted against hydrologic order.
17
are large unicellular green algae, which due to their size and protective coatings, are less suitable for food. These algae however repre-sent a very small percentage of algal abun-dance in the low order reach. Also present were filamentous blue-greens, which are not favorable. These algae however were not overly abundant and are therefore not be-lieved to be a concern. There is much less confidence in the assemblage identified with high TP condi-tions. The analysis of environmental vari-ables suggests that TP and some other nutri-ents vary somewhat independently of hydro-logical order, and it is plausible that some differentiation of algal composition could oc-cur in response to this variation. Moreover, some of the genera in the “high TP” assem-blage are large colonial forms known or sus-pected to have high nutrient requirements. Despite the plausibility of this assemblage, its support in the data is weak, and is based on a single sample with the highest TP and a somewhat unusual composition that includes several rare genera. Confirmation or refuta-tion of this assemblage will require more samples with higher than usual TP. The assemblages found during the course of this study represent what is be-lieved to be a relatively healthy system. There was evidence that the numerous and significant municipal point sources discharg-ing to the river are impacting algal biomass. Specifically, it is likely that the resultant in-creases in nutrient concentrations are allow-ing the river to support a larger algal popula-tion. However, no compelling evidence was found to suggest that the community compo-sition would be significantly different in the absence of these point sources.
was observed to be perhaps larger than noted in the literature, it is not believed to be un-usually so and is therefore probably not prob-lematic. The small centric diatoms that were also closely associated with this assemblage represent a small percentage of algae in terms of relative abundance however like the large green colonial algae, their large size offsets this in terms of their contribution to the overall algal biomass. The prevalence of these algae is believed to represent a healthy situation and the increase of this group re-lated to increasing hydrologic order is well supported by the literature. Heterocystous filamentous bluegreens can be associated with taste and odor and toxicity issues. However their association with the high-order assemblage was weak, and their abundance sufficiently low to keep them from being a concern. The algal assemblage associated with low order sites is less well supported by the data than that associated with high order sites, but is supported by the fact that it is biologically plausible. Many of the genera in this assemblage are pennate diatoms or fila-mentous bluegreens which are known to have representatives that live in benthic or pe-riphytic habitats of streams and rivers. Since the river is both shallower and less turbid at lower order sites, it makes sense that this stretch is more likely to have more substan-tial benthic communities than the higher or-der sites. Pennate diatoms were the most domi-nant algal type associated with this assem-blage, representing what is believed to be a healthy situation. The increase in pennate diatoms downstream from the Village Creek Wastewater Treatment Plant could be evi-dence that the clear, nutrient rich water from that discharge is stimulating benthic algal growth. Also associated with this assemblage
18
05101520253035
First Street 17662
Beltline 11081
Mockingbird 10937
Loop 12 10934
Rosser 10925
Trinidad 10922
Oakwood 10919
Mon
itorin
g St
atio
n
Clarity as Secchi Tube Depth (cm)
July
Augu
st
Sept
embe
r
Oct
ober
Figu
re 2
4. T
urbi
dity
in th
e M
ain
Stem
incr
ease
s as o
ne m
oves
dow
nstre
am. A
lthou
gh th
is pa
ttern
mig
ht b
e co
nsid
ered
nor
mal
und
er hi
gh fl
ow c
ondi
tions
, it
is so
mew
hat c
ount
erin
tuiti
ve fo
r low
flow
situ
atio
ns. D
ata
for t
his f
igur
e we
re c
olle
cted
as p
art o
f TRA
Cle
an R
iver
s Pro
gram
rout
ine
mon
itorin
g du
ring
July
, Aug
ust S
epte
mbe
r and
Oct
ober
of 2
002.
19
APPENDIX A
ALGAL ENUMERATION AND IDENTIFICATION DATA
20
JULY 29
SAMPLE RUN
21
SEPTEMBER 5
SAMPLE RUN
22
SEPTEMBER 26
SAMPLE RUN
23
OCTOBER 1
SAMPLE RUN
