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ALGAL SUCCESSION IN THE TRINITY RIVER UNDER SUMMER AND AUTUMN EFFLUENT DOMINATED CONDITIONS

Prepared by the Trinity River Authority of Texas in cooperation with the Texas Commission on Environmental Quality 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.

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TABLE OF CONTENTS Introduction Materials and Methods Results Conclusions TABLES Table 1. Monitoring Stations Table 2. Water Quality Variables Table 3. Summary Statistics for East Fork Water Quality Variables Table 4. Genera Associated with the High Order Assemblage FIGURES Figure 1. Algal Community Composition in Eagle Mountain Lake Figure 2. Algal Community Composition in Joe Pool Lake Figure 3. Maps of Sampling Stations 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 Figure 7. Total Suspended Solids Concentrations in the Main Stem Figure 8. Nitrate Plus Nitrite Concentrations in the Main Stem Figure 9. Total Kjeldahl Concentrations in the Main Stem Figure 10. Relationships of Water Quality Variables and Hydrologic Order Figure 11. Relationships of Algal Genera Figure 12. Relative Abundance of Pandorina vs. Total Phosphorus Figure 13. Relative Abundance of Pediastrum vs. Total Phosphorus Figure 14. Relationships of Algal Groups Figure 15. Relative Abundance of Large Motile Green Colonies vs. Total Phosphorus Figure 16. Relative Abundance of Dinoflagelates vs. Total Phosphorus Figure 17. Relative Abundance of Aphanocapsa vs. Hydrologic Order Figure 18. Relative Abundance of Navicula vs. Hydrologic Order Figure 19. Relative Abundance of Small Centric Diatoms vs. Hydrologic Order Figure 20. Relative Abundance of Small Non-motile Green Algae vs. Hydrologic Order Figure 21. Relative Abundance of Large Non-motile Green Algae vs. Hydrologic Order Figure 22. Relative Abundance of Heterocystous Filamentous Bluegreen Algae vs. Hydrologic Order Figure 23. Relative Abundance of Small Motile Green Algae vs. Hydrologic Order Figure 24. Turbidity vs. Hydrologic Order in the Main Stem APENDICES Appendix 1. Sample Results of Algal Enumeration and Identification Analysis 4 4 6 9 9 9 10 10 10 11 12 13 13 13 14 14 14 14 15 15 16 16 16 18 7 8 11 15 3 5 8 16

2

INTRODUCTION

The Trinity River runs through Central 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 portions of the basin averages around 33 inches, most of which occurs in a relatively few number of storm events with little or no precipitation during summer months. These climatic 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 approximately five and a half million. Cumulative wastewater discharges into the river from the Dallas-Fort Worth area averages approximately 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 significantly elevated over background conditions. Although conventional wisdom holds that algal abundance is directly related to nutrient concentrations, recent observations suggest that algal populations are smaller immediately downstream of wastewater treatment plants despite the corresponding rise in nutrient concentrations. There are several 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, representing a many-fold dilution. Another explanation is that the surface to volume ratio decreases 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 decreases in algal concentrations, then the community should rebound and, taking advantage of the abundant nutrients downstream from the municipal point source, increase respective 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 question then becomes one of looking at spatial changes in algal community structures, or algal succession. "Succession" and "periodicity" are major themes in the ecological study of algal communities (Reynolds 1984). The term succession refers to changes over time, or in this case distance, in the abundance of populations in different taxonomic groups, while the term periodicity highlights that these changes are often reproducible over annual seasonal cycles. Algal succession is particularly well studied in natural lakes of the temperate zone (Sommer et al. 1986), where the algal biota is often dominated by small flagellated 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 diverse populations depending in part on lake trophic status. Eutrophic lakes often experience dominance by large colonial cyanobacteria, often mixed with large dinoflagellates, while oligotrophic lakes maintain a diverse summer community of many algal types. Autumn 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-

3

cation and destratification, and by activities feeding animals. Gelatinous coatings that reof zooplankton grazers and the fish that prey duce digestibility protect many species of on them. green algae, making them poorer food. Reservoirs (i.e. manmade impoundShould a river become dominated by cyanoments) have occasionally been studied. At bacteria, its capacity to support a food web least superficially, they appear to have succesFigure 1. Eagle Mountain Lake sional patterns that resemble those of natural 100% lakes (Figures 1 and 2), Other although the driving Cryptophyte 80% mechanisms are not as Chrysophyte 60% well supported. Much Euglenoid less is known about alDinoflagellate 40% gal succession in flowDiatom ing-water systems; riv20% Bluegreen ers are especially Green 0% poorly studied, despite the development of Sample substantial planktonic algae in many mainstem, large-channel riv- Figure 1. Algal succession in Eagle Mountain Lake, a Trinity basin reservoir. Samples were collected from March 1998 to October 2000 (Grover and Chrzanowski, ers (Reynolds 1990). One of the few studies unpubl.). There are concerns that Eagle Mountain Reservoir may have unhealthy concentrations of algae. available, that of the River Seine in France Figure 2. Joe Pool Lake (Garnier et al. 1995), shows a clear succession 100% from diatoms early in the Other growing season to green 80% Cryptophyte algae later. Shifts in nu60% Chrysophyte trient supply, namely a seasonal reduction in Euglenoid 40% silicon supply relative to Dinoflagellate nitrogen and phosphorus, 20% Diatom were suggested as one Bluegreen 0% factor underlying this Green succession. Sample Such major shifts in algal composition in a river could have implica- Figure 2. Algal succession in Joe Pool Lake, a Trinity basin reservoir. Samples were collected from March 1998 to October 2000 (Grover and Chrzanowski, untions for its possible uses. publ.). Joe Pool Lake has been identified by the TCEQ as having one of the most Diatoms (and some groups limited algal populations, as measured by concentrations of chlorophyll a, in the of flagellated algae) are State relative to other Texas reservoirs. generally an excellent food source for benthic and suspended filter should be even lower, due to the generally

Relative Biomass 13 17 21 25 29 33 37 41 45 Relative Biomass 11 16 21 26 31 36 41 46 51 1 6 49 1 5 9

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poor digestibility and frequent toxicity of these algae. Because relative supplies of nitrogen, phosphorus and silicon could influence succession among different algal types in rivers, wastewater discharges could alter or induce algal succession. Wastewater typically supplies 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 undertaken to provide some initial understanding of spatial algal succession in the Trinity River and a preliminary assessment of possible 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 provide samples from the river representing a progression of effluent dominance. The uppermost site was located above all major point sources. Successive sites downstream included one or more sample sites between each major point source through the DallasFort Worth area. Additional samples were included to provide information on how water 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 sample event at each site. The results of this sampling indicated two reaches along the mainstem of the river which experience significant 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 sample sites along with ancillary information, including the dates and phases during which each was sampled. At each site, during both phases, water samples were collected and analyzed for conventional water chemistry parameters (table 2). All samples were collected just below 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 samples 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 placing an aliquot of defined volume from the algal 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.

5

Rowlett Creek Plant (25 MGD) DALLAS

17160 10938

( ( ! ! ( !

Fo Vil rt Wo WW lage rth (16 TP Cree k 9M GD )

10929

( !

EAS

Fort Wort

11085

( !

T FO

10937 11079 ! ! ( ( ! ( ( 11087 ! SS1 11081

( ! ( !

11084

( !

RK

17161 10934

Duck Creek Plant (30 MGD) South Mesquite Creek Plant (25 MGD)

( !

Figure 3. Map of upper and middle Trinity River basin with study sites and locations of major wastewater discharges. Discharges listed in parentheses are permitted limits and therefore do not reflect actual discharges.

TRA Central WWTP \(162 MGD)

Dallas Central WWTP (200 MGD)

10987

Dallas Southside WWTP (110 MGD) 6

10925

( !

( MA ! IN ST EM

10924

( !

10922

10920

( !

Table 2. Study Sites, Phases, Distances, Travel Times, Dates Sampled and Hydrologic Order

SITE DESCRIPTION SITE ID PHASES CUMULATIVE CUMULATIVE DATES SAMPLED DISTANCE TRAVEL TIME SAMPLED (mi) (hrs-- estimated)

10938 HYDO ORDER

Immediately Below Beach Street Impoundment on West Fork in Fort Worth Precinct Line Road Bedford Arlington Road

I

0

0

7/29/02

1

11085 17160

I I and II

12 15.1

180 236

7/29/02 7/29/02 9/5/02 9/26/02 10/1/02 7/29/02 7/29/02 9/5/02 9/26/02 10/1/02 7/29/02 7/29/02 9/5/02 9/26/02 10/1/02 7/29/02

2 3

FM 157 HWY 360

11087 11084

I I and II

19.5 24.5

242.5 251.1

4 5

Belt Line Road

11081

I I and II

31 36.75

260.6 267.3

6 7

Immediately upstream of TRA 11079 Central WWTP Outfall

Main Stem below Singleton SS1 BLVD at location of Old Singleton Road bridge Mockingbird 10937

I

38.25

269.3

8

I I I I and II

41.25 50.25 54.5 71.5

273.3 285.3 289.6 311.6

7/29/02 7/29/02 7/3002 7/30/02 9/5/02 9/26/02 10/1/02 7/30/02 9/5/02 9/26/02 10/1/02 7/3002 7/3002 9/5/02 9/26/02 10/1/02 7/3002 7/3002 7/3002 7/31/02

9 10 11 12

Immediately upstream of Dal- 17161 las Central WWTP Outfall South Loop 12 Malloy Bridge 10934 10929

HWY 34 near Rosser

10925

I and II

93.5

340.6

13

HWY 85 HWY 31 near Trinidad

10924 10922

I I and II

112.5 152.1

371 427.1

14 15

HWY 287 near Cayuga HWY 79 near Oakwood HWY 7 East Fork at Valley Ranch

10920 10919 10918 10987

I I I I and II

170.1 229.6 276.6 NA 7

455.1 538.6 607.5 NA

16 17 18 NA

Fields or transects of known area on the bottom plate are then examined, with all algal specimens identified and enumerated. In this method, the volume of aliquot thus sedimented is adjusted based on total density of algae. Experience in Texas reservoirs sugTable 2. Water quality variables analyzed. PARAMETER Dissolved Oxygen pH Water Temperature Air Temperature Specific Conductivity NO2/NO3 TKN NH3 OP-O4 NO3 Total Phosphorus Chlorophyll a E. coli mg/L Standard Units Degrees C Degrees C Micro siemen mg/L mg/L mg/L mg/L mg/L mg/L ug/L MPN UNITS

a very wide range of size, counts at three magnifications was necessary. At each magnification, 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, incremental influence on certain variables by the four major wastewater dischargers. This phenomenon is clearly displayed in figures 5 and 8, which show concentrations of the dissolved nutrients otrhophosphate and nitrate plus nitrite. Concentrations of these parameter increase dramatically after each input of reclaimed water and then slowly decrease before 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 concentrations of chlorophyll a and by extension algae. Total suspended solids showed a pattern of increasing concentrations downstream. 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 downstream were collected later in the day. It is

Total Suspended Solids mg/L

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 individual unit of algae was the cell for unicellular organisms and the colony for colonial organisms. 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 categories based on higher taxonomy (algal divisions), size, and morphology were enumerated. This resolution was sufficient to detect major successional changes in algae. Because the algal units counted cover

8

60

7-Jul 5-Sep 26-Sep

50

1-Oct Linear (5-Sep) Linear (26-Sep)

40

30 R = 0.622 R2 = 0.8361 20

2

10

0 Hydrologic Order

Figure 4. Chlorophyll a concentrations in the Main Stem.

2.5 7-Jul 5-Sep 26-Sep 1-Oct 2

1.5

1

0.5

0

Hydrologic Order

Figure 5. Orthophosphate concentrations in the Main Stem.

10

9

8

R 2 = 0.6136

7

6

5

4

3 7-Jul 2 5-Sep 26-Sep 1 1-Oct 0 Linear (7-Jul)

Hydrologic Order

Figure 6. Dissolved oxygen concentrations in the Main Stem.

Village Creek WWTP

TRA Central WWTP

9

Dallas South Side WWTP

Dallas Central WWTP

120

7-Jul 5-Sep 26-Sep

100

1-Oct

80

TSS(mg/L)

60

40

20

0

0

2

4

6

8

10

12

14

16

18

Hydrologic Order

Figure 7. Total suspended sediment concentrations in the Main Stem.

16 7-Jul 5-Sep 14 26-Sep 1-Oct 12

10

NO2NO3(mg/L)

8

6

4

2

0

0

2

4

6

8

10

12

14

16

18

Figure 8. Nitrate plus nitrite concentrations in the Main Stem.

1.8 7-Jul 5-Sep 1.6 26-Sep 1-Oct 1.4

Hydrologic Order

1.2

TKN(mg/L)

1

0.8

0.6

0.4

0.2

0

0

2

4

6

8

10

12

14

16

18

20

20

Hydrologic Order

Figure 9. Total Kjeldahl nitrogen concentrations in the Main Stem.

TRA Central WWTP

10

Dallas South Side WWTP

Dallas Central WWTP

Village Creek WWTP

20

Table 3. Average, minimum and maximum concentrations of key water quality variables at the East Fork site.

PARAMETER Orthophosphate Nitrate/Nitrite TKN Chlorophyll a Dissolved Oxygen TSS

0.4

Cond NO2/NO3

AVERAGE CONCENTRATION 2.6 (mg/L) 10.3 (mg/L) 1.0 (mg/L) 30.6 (ug/L) 10.2 (mg/L) 88.3 (mg/L)

Water quality variables from all sites were examined statistiMINIMUM MAXIMUM cally to determine relationships between vari2.1 4.4 ables, including hydro9.0 11.8 logic order (figure 10)

0.7 8.7 8.7 65 1.5 51.7 11.5

Algal Community Structure

TKN

Axis 1

NH3 TP DO Chloroph TSS pH

NO2

OP-D

Hydrolog

-0.2

0.8

Figure 10. Relationships of quality variables and hydrologic order are shown in relation to two axes.

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.

Appendix A contains results of algae identification and enumeration. These data were analyzed by genera to determine potential relationships between water quality variables and presence of genera. Through this analysis of genera, several relationships were identified as seen in figure 11 and as described below: A phylogenetically diverse group of genera were found to be associated with high TP, DO, & NO2. These genera included Aulacoseira, Chlamydomonas, Chlorogonium, Eudorina, Pandorina, Lagerheimia, Pediastrium, Cryptomonas, Rhodomonas, Euglena and Phacus. Conversely, two genera of green algal, Ankistrodesmus and Crucigenia, were associated with lower concentrations of TP, DO, & NO2. Genera associated with low hydrological order, high conductivity and high nitrite plus nitrate include the cyanobacteria Aphanocapsa, Cylindrospermum, "Oscillatoria", Planktolyngbya, Raphidiopsis and Spirulina. Others genera found to be associated with lower hydrologic order were Dinobryon, 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, including Oscillatoria and Planktolyngbya

103

Axis 2

-1.0

11

originate from benthic habitats, however most of the other genera in this group are believed to be considered planktonic. Genera associated with high hydro0.8

.Oscilla Aphanoca Planktol Raphidio Spirulin Dinobryo Cylindro Cymbella Navicula Closteri Synedra Staurast Achnanth Nitzschi

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 reservoirs and are associated with higher order reaches. High TP Assemblage

The "high TP assemblage" characterizes only two samples, Monoraph Micracti Aulacose Treubari Sphaerel both of which were from the East Gyrosigm Tetrastr Microcys Phacus Lagerhei Eudorina Euglena Cosmariu Pandorin Fork Valley Ranch site near CranDictyosp ActinastSchroedeTetraedr Peridini Ankistro dall, and both were collected in Anabaena Chlorogo Chamaesi Pediastr Rhodomon autumn. Thus the high TP assemSphaeroc Spondylo Merismop Chroococ blage was found only rarely. This Aphanizo Mallomon Carteria assemblage appears to be probClosteri Large fl Cryptomo Kirchner Scenedes Dactyloc lematic, and is highly influenced Selenast by a single sample. That sample Chlamydo Crucigen Stephano had a concentration of 4.37mg/L Coelastr which was the highest TP reChlorell Cyclotel Oocystis corded during the course of the -0.4 1.0 study by a factor of two. Figure 11. Algal genera relationships are shown in relation to axes. Five genera were identiFigure 10 defines the relationship of the axes to the water quality fied in five or fewer samples. For variables. Axis one (horizontal) was found to be associated most these, their relative abundance in closely with the parameter group of TP, DO and NO2. Axis two the high TP sample was high, gen(vertical) is most closely associated with hydrologic order. erating a strong correlation driven logical order, low conductivity, and low niby a single influential point. Figure 12, a plot trite plus nitrate are mostly green algae com- of Pandorina vs. TP illustrates this problem. mon to reservoirs. These include ChlamydoSix other genera, Pandorina, monas, Chlorella, Coelastrum, Crucigenia, Chlorogonium, Eudorina, Lagerheimia, and Oocystis and Selenastrum. Unicellular cenPhacus, were included in the TP assemblage tric diatoms (Cyclotella, Stephanodiscus) based on similar abundance patterns. Given also common in reservoirs, were likewise in- the relative rarity of these genera, confidence cluded in this group . in their identification as species associated To summarize the patterns in algae, with high TP conditions is low. three potential assemblages were identified: The remaining genera associated with high TP concentrations occur in 16 to 37 1. "High TP assemblage" consisting of samples, however their association with TP diverse taxa associated with high TP. is weak (correlations from -0.02 to 0.43), and 2. "Blue-green & benthic assemblage" again is a result of the single high TP sample. consisting of benthic pennate diatoms Figure 13 is a plot of Pediastrum, which had

Small fl

-0.6

12

Pandorina

0.00025

0.00020

0.00015

0.00010

0.00005

0.00000 0 1 2 3 4 5

TP

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 concentraFigure 13. Pediastrum abundance vs. TP. tions.

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

Pediastrum

0.0010

ing a vector graph. The group analysis again suggested a high TP assemblage. These groups, closely and positively correlated to axis one, consists of dinoflagelates, filamentous centric diatoms (Aulacoseria), euglenoids, large motile green colonies and Microcystis. Of these, large motile green colonies had the most convincing correlation (figure 15). Two of the genera included in this group, (dinoflagelates and filamentous centric diatoms) disagreed with the previously established positive relationship between TP and abundance, showing 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 question the validity of the high TP assemblage, which could be nothing more than an artifact created by the single aberrant sample.

Relative Abundance

0.6

0.0008

Relative Abundance

NHFilBG SmCoccBG LgUniDes PennDiat

0.0006

0.0004

Dino

0.0002

FilCentD Euglenoi

Microcys LgMGrnCo

SmFlag

0.0000 0 1 2 3 4 5

HFilBG

TP

TP July vs Pediastrum July TP Early Sep vs Pediastrum Early Sep TP Late Sep vs Pediastrum Late Sep TP Oct vs Pediastrum Oct

Crypto SmNMGrn LgNMGrnC SmMGrn

with TP in the remaining samples. -0.4 Additional statistical analyses Figure 14. Vector graph of group correlations. were then performed, focusing on interspecies correlations (i.e. group analysis). Figure 14 shows the results of this analysis us13

-0.8

Figure 13. Pediastrum abundance vs. TP concentrations.

SmCentDi

1.0

Large Motile Green Colonies

0.0007

0.0006

Relative Abundance

0.0005

0.0004

0.0003

0.0002

0.0001

sociated with decreasing hydrologic order (figure 10). Two genera in particular, Aphanocapsa, a small-celled coccoid bluegreen algae and Navicula, a benthic pennate diatom, showed good correlations to hydrologic order (figures 17 and 18) in all sample runs. Five additional genera in this assemblage including Cylindrospermum, Raphidiopsis, Spirulina, Dinobryon and

Aphanocapsa

4 5

0.0000 0 1 2 3

TP

0.6

TP July vs LMGC July TP Early Sep vs LMGC Early Sep TP Late Sep vs LMGC Sep TP Oct vs LMGC Oct

0.5

Figure 15. Abundance of large motile green colonies vs. TP.

Dinoflagellates

0.00030

Relative Abundance

0.4

0.3

0.2

0.1

0.00025

0.0

Relative Abundance

0.00020

0

2

4

6

8

10

12

14

16

18

20

Hydrological Order

0.00015

0.00010

Order July vs Aphanocapsa July Order Early Sep vs Aphanocapsa Early Sep Order Late Sep vs Aphanocapsa Late Sep Order Oct vs Aphanocapsa Oct

0.00005

Figure 17. Aphanocapsa abundance in relation to hydrologic order

0 1 2 3 4 5

0.00000

TP

TP July vs Dino July TP Early Sep vs Dino Early Sep TP Late Sep vs DinoLate Sep TP Oct vs Dino Oct

Navicula

0.035

0.030

Relative Abundance

Figure 16. This graph of Dinoflagelate abundance vs. TP suggests dinoflagelates respond negatively to increasing concentrations of total phosphorus.

0.025

0.020

0.015

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 demonstrated with axis 2, (figure 11) which was as-

0.010

0.005

0.000 0 2 4 6 8 10 12 14 16 18 20

Hydrological Order

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 hydrologic order 14

Cymbella occurred in 7 or fewer samples. However when present, these genera were found only in or upstream of Dallas. Nevertheless, the low frequency of occurrence of these genera gives low confidence to their identification as members of this assemblage. Group analysis focusing on interspe-

lationships with hydrologic order. These include small centric diatoms, small non-motile greens and large non-motile green colonies. Figures 19-21 show these relationships. Two other groups, heterocystous filamentous bluegreens and small motile greens also showed a relationship to flow, however this relationship is not as convincing as Table 4. Genera in High Order--Reservoir Assemblage the other groups in this assemblage and correlations to hydrologic order. (figures 22 and 23).

GENUS NO. OCCURRENCES 37 38 22 28 37 36 38 21 CORRELATION WITH HYDRO ORDER 0.26 0.48 0.47 0.42 0.48 0.19 0.58

0.02 0.14 0.12

Chlamydomonas Chlorella Coelastrum Crucigenia Oocystis Selenastrum Cyclotella Stephanodiscus

Small Centric Diatoms

Relative Abundance

0.10

0.08

0.06

0.04

0.49

0.00 0 2 4 6 8 10 12 14 16 18 20

cies correlations identified small coccoid bluegreens, large unicellular desmids, nonheterocystous filamentous bluegreens and pennate diatoms as being included in this assemblage. 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 bottom. Large unicellular desmids and coccoid bluegreens are less clearly benthic in origin.

Relative Abundance

Hydrological Order

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

0.5

0.4

High Order--Reservoir Assemblage Eight genera identified with this group had high frequency of occurrence and moderately strong correlations with hydrologic order (table 4). This assemblage contains many genera which are commonly found in north and east Texas reservoirs. Group analysis of this assemblage found three algal groups with convincing re-

0.3

0.2

0.1

0.0 0 2 4 6 8 10 12 14 16 18 20

Hydrological Order

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. 15

Large Non-motile Green Colonies

Small Motile Greens

0.20 0.18 0.16

0.25

Relative Abundance

0.14 0.12 0.10 0.08 0.06 0.04 0.02 0.00 0 2 4 6 8 10 12 14 16 18 20

0.20

Relative Abundance

Hydrological Order

Order July vs LNMGC July Order Early Sep vs LNMGC Early Sep Order Late Sep vs LNMGC Late Sep Order Oct vs LNMGC Oct

0.15

0.10

0.05

0.00 0 2 4 6 8 10 12 14 16 18 20

Hydrological Order

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 21. Relative abundance of large green algae colonies plotted against hydrologic order.

Heterocystous Filamentous Bluegreens

0.0035

Figure 23. Relative abundance of heterocystous filamentous bluegreen algae to hydrologic order.

0.0030

Relative Abundance

0.0025

0.0020

0.0015

0.0010

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 variable 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 nonmotile green algae dominated this assemblage. These algae are believed to be a good food source for planktavores. Large nonmotile green colonies, although not predominant in terms of abundance, can due to their size constitute a majority of algal biomass. Unlike the small greens, these algae are believed to be a poor food source. Although the prevalence of this algal group

0.0005

0.0000 0 2 4 6 8 10 12 14 16 18 20

Hydrological Order

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.

CONCLUSIONS Both genera and group analyses yielded similar results, identifying three distinct algal assemblages. However only the two assemblages correlated with hydrological order, the "low order--bluegreen & benthic" and "high order--reservoir algae" assemblages are defined on the basis of multiple samples and genera with high frequencies of occurrence. As such, there is more

16

was observed to be perhaps larger than noted in the literature, it is not believed to be unusually so and is therefore probably not problematic. 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 related 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 filamentous bluegreens which are known to have representatives that live in benthic or periphytic 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 substantial benthic communities than the higher order sites. Pennate diatoms were the most dominant algal type associated with this assemblage, representing what is believed to be a healthy situation. The increase in pennate diatoms downstream from the Village Creek Wastewater Treatment Plant could be evidence that the clear, nutrient rich water from that discharge is stimulating benthic algal growth. Also associated with this assemblage

are large unicellular green algae, which due to their size and protective coatings, are less suitable for food. These algae however represent a very small percentage of algal abundance 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 believed to be a concern. There is much less confidence in the assemblage identified with high TP conditions. The analysis of environmental variables suggests that TP and some other nutrients vary somewhat independently of hydrological order, and it is plausible that some differentiation of algal composition could occur in response to this variation. Moreover, some of the genera in the "high TP" assemblage are large colonial forms known or suspected 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 refutation of this assemblage will require more samples with higher than usual TP. The assemblages found during the course of this study represent what is believed to be a relatively healthy system. There was evidence that the numerous and significant municipal point sources discharging to the river are impacting algal biomass. Specifically, it is likely that the resultant increases in nutrient concentrations are allowing the river to support a larger algal population. However, no compelling evidence was found to suggest that the community composition would be significantly different in the absence of these point sources.

17

35 July August September October

30

25

20

15

10

Figure 24. Turbidity in the Main Stem increases as one moves downstream. Although this pattern might be considered normal underhigh flow conditions, it is somewhat counterintuitive for low flow situations. Data for this figure were collected as part of TR Clean Rivers Program routine monitoring during A July, August September and October of 2002.

Clarity as Secchi Tube Depth (cm)

18

Beltline 11081 Loop 12 10934 Mockingbird 10937

5

0

Rosser 10925

Trinidad 10922

Oakwood 10919

First Street 17662

Monitoring Station

APPENDIX A

ALGAL ENUMERATION AND IDENTIFICATION DATA

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JULY 29

SAMPLE RUN

20

SEPTEMBER 5

SAMPLE RUN

21

SEPTEMBER 26

SAMPLE RUN

22

OCTOBER 1

SAMPLE RUN

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Information

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