Water quality in the Dickinson Bayou watershed (Texas, Gulf of Mexico) and health issues

Marine Pollution Bulletin 58 (2009) 896–904

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Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul

Water quality in the Dickinson Bayou watershed (Texas, Gulf of Mexico) and health issues Antonietta Quigg a,b,*, Linda Broach c,1, Winston Denton d,2, Roger Miranda e,3 a

Department of Marine Biology, Texas A&M University at Galveston, 5007 Avenue U, Galveston, TX 77551, United States Department of Oceanography, Texas A&M University, 3146 TAMU, College Station, TX 77843, United States c Texas Commission on Environmental Quality, 5425 Polk Avenue, Suite H, Houston, TX 77023, United States d Coastal Fisheries Division, Texas Parks and Wildlife Dickinson Department, 1502 FM 517 East, Dickinson, TX 77539, United States e Texas Commission on Environmental Quality, 1200 Park 35 Circle, Austin, TX 78711, United States b

a r t i c l e

i n f o

Keywords: Bacteria Ecosystem management Environmental monitoring Eutrophication Low dissolved oxygen Nitrogen Nutrients

a b s t r a c t The Dickinson Bayou watershed (near Houston, Texas, Gulf of Mexico) provides habitat for numerous coastally influenced communities of wildlife, including scores of birds and fish. Encroaching development and impervious surfaces are altering the habitat and degrading water quality. Herein we have defined the current health of the bayou using water quality data collected between 2000 and 2006. Elevated bacteria (fecal coliform, Escherichia coli and Enterococcus) and depressed dissolved oxygen concentrations (often <3 mg l1) are the two major impairments to this ecosystem. While nutrient ratios indicate primary productivity may be nitrogen limited, concerns of eutrophication persist because the bayou has a low intrinsic flushing rate. Consistent with this is the magnitude of algal blooms (ca. 100 lg chl l1) which often occur in spring/summer. The findings of this study will assist with the understanding of the influence of urban development on small watersheds. Published by Elsevier Ltd.

1. Introduction The interaction between ecosystem function and human use means that coastal zones are the most complex ‘multiple use’ areas in the world (Griffis and Kimball, 1996). These are also the most challenging and problematic areas in which to develop ecosystem sustainability management plans. Coastal areas in the US and worldwide are experiencing rapid population growth. The population in Texas for example, is expected to double between 2000 and 2050, growing from 21 million to 46 million (TWDB, 2007). Most of this development will occur along the coastline, significantly impacting its 7 major estuaries. Increased development is highly correlated with increased land-derived nitrogen loads near urbanized areas. Major sources of anthropogenic nitrogen are fertilizer application, wastewater disposal and atmospheric deposition (Carpenter et al., 1998; Bowen and Valiela, 2001; Howarth and Marino, 2006). Knowledge of the pollution sources and impacts on ecosystems is important not only for a better understanding on the ecosystem

* Corresponding author. Tel.: +1 409 740 4990; fax: +1 409 740 5001. E-mail addresses: [email protected] (A. Quigg), [email protected] (L. Broach), [email protected] (W. Denton), [email protected] (R. Miranda). 1 Tel.: +1 713 767 3579. 2 Tel.: +1 281 534 0138. 3 Tel.: +1 512 239 6278. 0025-326X/$ - see front matter Published by Elsevier Ltd. doi:10.1016/j.marpolbul.2009.01.012

responses to pollutants but also to formulate prevention measures. The main objective of this study was to examine recent water quality data collected by a number of state agencies in Texas between 2000 and 2006 in the Dickinson Bayou watershed (near Houston, Texas, Gulf of Mexico) (Fig. 1). This meta-analysis of salinity, dissolved oxygen (DO) concentration, chlorophyll, nutrient, and bacterial indicator (fecal coliform, Escherichia coli and Enterococcus) data provides the key to examining the systems response to watershed alternations. We hypothesize that persistent low DO concentrations during the summer and elevated bacterial counts are a result of the combination of nutrient loading and long residence times. Coastal bayous (small, slow-moving coastal streams or creeks) such as Dickinson Bayou are especially susceptible to anthropogenic contamination associated with encroaching development and impervious surfaces because they have intrinsically low flushing rates. In order to develop a process based understanding of the influence of urban development on small watersheds, studies benefit from considering a board range of water quality parameters to evaluate a systems response to natural versus anthropogenic perturbations. 1.1. Study area The Dickinson Bayou watershed (DBW) is located within Galveston Bay, Texas as shown in Fig. 1. This small urban watershed is approximately 275 km2. Water leaving this watershed makes

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Fig. 1. The Dickinson Bayou watershed is located within the San Jacinto–Brazos Coastal Basin at 29°290 N, 95°140 W, 45 km southeast of Houston, Texas.

its way into Dickinson Bay, a secondary bay of the larger Galveston Bay complex which is protected by an US EPA National Estuary Program (http://www.gbep.state.tx.us/). The bayou, running west to east, receives runoff from seven major tributaries on the north side and 5 on the south side (Fig. 1). Most of the tributaries carry only rainfall runoff with the notable exception of Gum Bayou (see Table 1) which also receives wastewater from a major treatment facility. The watershed has experienced vast changes in the last few decades, especially from agriculture, drainage channels, residential and commercial development, and groundwater withdrawals (H-GAC, 2006). After the permanent alterations caused by development, invasive plant and animal species are perhaps the most significant threat to the native habitat in this watershed, concurrent with water quality degradation.

DBW is divided into two hydroscapes. The above tidal segment is approx. 11 km long, narrow and shallow (average 0.5 m), much like a small coastal prairie freshwater stream. Limited access and intermittent flows preclude regular sampling at many locations in this part of the bayou. The tidal segment is 24 km long, significantly wider (100’s m in places) and deeper (up to 6 m in places) with sluggish waters that often become hypoxic or anoxic in the summer, especially near the bottom, as a result of a halocline that can extend from Dickinson Bay upstream 19.7 km to Cemetery Road (Table 1). This halocline is more common in the summer months, and may be absent in the winter months or after a large rainfall event (East and Hogan, 2003; H-GAC, 2006). Both segments have been on the EPA and State of Texas Clean Water Act Section 303(d) list of impaired water bodies since 1986. While both

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Table 1 Summary of sampling sites visited on a regular basis between 2000 and 2006. The distances inland were calculated relative to Dickinson Bay at SHI46 (see Fig. 1). Segment, latitude, longitude, and a brief description are included for reference. Tributaries are in italics. Distance from Dickinson Bay (km)

Segment

Station

Latitude

Longitude

Location description

0 5.8 6.4 7.4 10.4 11.8 11.9 12.4

1103 1103 1103 1103 1103 1103 1103 1103

11455 11436 16979 16679 11460 11461 16471 18650

29.46.000 29.46.944 29.46.350 29.45.822 29.45.611 29.45.556 29.45.750 29.45.536

94.97.417 95.01.334 95.01.614 95.01.803 95.04.778 95.05.750 95.05.778 95.06.173

13 13.4 14.2 15.6

1103 1103 1103 1103

16470 16469 11462 18649

29.45.500 29.45.194 29.44.500 29.43.985

95.06.750 95.07.195 95.07.361 95.08.200

19.7 21.3 22.4 26.2

1103 1103 1104 1104

11464 11434 11465 11467

29.42.917 29.43.861 29.42.917 29.43.583

95.11.500 95.13.583 95.13.944 95.16.972

SH 146 bridge Gum Bayou at FM 517 Upstream of Gum Bayou Mariners Mooring road SH 3 bridge Benson Bayou confluence Benson Bayou Magnolia Bayou at Paul Hopkins County Park Geisler Bayou at FM 517 Bordens Gulley at FM 517 IH 45 bridge Between IH 45 bridge and county ditch no. 9 Cemetery Rd Cedar Creek at FM517 W End of Jack Beaver road FM517Eof Alvin

segments do not meet bacterial standards, the tidal portion also does not meet DO standards (Texas Commission on Environmental Quality (TCEQ) 303(d) list; www.tceq.state.tx.us). Of concern is that the tidal section is used by local residents for recreational boating, fishing, water skiing, canoeing, and other activities. Increasing demand for these ecological ‘‘services” concurrent with development is leading watershed managers and scientists to develop strategies to protect this system. 2. Methods To assess the current health of the DBW, we performed a metaanalysis of key water quality parameters (salinity, DO, chlorophyll, nutrients, bacteria) collected by state agencies between 2000 and 2006. They were measured at 11 stations on the main stem (2 above tidal, 9 in tidal) and at 5 tributary stations (Table 1). Processing of samples followed standard TCEQ methods (TCEQ, 2003) that were checked against requirements of a Quality Assurance Project Plan which were based on the mandates by the US Environmental Protection Agency (1986, 1998, 2002). Briefly, salinity and DO were measured using calibrated multi-probe water quality meters, typically Hydrolab sondes. Water samples for nutrient (ammonia, nitrite, nitrate, total phosphorus), chlorophyll and indicator bacteria (fecal coliform, E. coli and Enterococcus) were collected in acid washed containers, returned to the laboratory within 8 h of collection for analysis. Chlorophyll concentrations were calculated as chlorophyll a plus phaeophytin for the purpose of this meta-analysis. Temperature and rainfall data were obtained from the nearest National Weather Service station located in League City (Houston NWS HGX; http://www.srh.noaa.gov/hgx/climate/hgx.htm). Not all water quality parameters were measured at every station on each sampling trip conducted between 2000 and 2006 due to logistical and funding constraints. For example, more data is available for salinity and DO than for nutrients or bacteria. Many more stations were visited than listed in Table 1. For the purpose of this analysis however, we only included a station if at least 20 samples were taken over at least 2 different years between 2000 and 2006, and if both summer and winter seasons were covered for the parameter in question. The only exceptions made were for the nutrient and bacterial data, in which case a minimum of 12 samples was considered. Given the nature of the data collection process there is insufficient data to produce a time series in which we could have assessed trends; hence findings are presented as pooled data (months and/or years). Statistical analyses were performed with SPSS version 15.0 (SPSS Inc, Chicago, Illinois).

3. Results 3.1. Air temperature and rainfall Air temperatures in the DBW followed seasonal oscillations with warmest temperatures in August (28 °C ± 0.5) and coolest in December (12 °C ± 1.2) (Fig. 2A). From May to September 2000 to 2006, average temperatures were 26.5 °C (±1.5) (Fig. 2A). These months are herein defined as warm months. All others (October to April) were designated as cool, with an average of 16.3 °C (±3.9). These designations were used to examine the seasonal shifts below. As with other non-arid subtropical environments, the DBW receives its greatest rainfall in the summer months, on average 17.7 cm (±1.7). The least amount of rain (<10 cm) fell between January and April each year (Fig. 2B), with July and December receiving slightly (but not significantly) more rain – 12.3 cm (±1). Tropical storms and hurricanes can be used to account for the large error bars associated with the rainfall data. Of all those that hit during the study period, tropical storm Allison (June 5–9, 2001) had the largest impact on the watershed, introducing 44 cm of rain over a 5 day period. Average annual DBW rainfall was 160 cm (Fig. 2C); 2005 was the driest (106 cm) and 2002 was the wettest (207 cm) year. 3.2. Salinity and dissolved oxygen concentrations Salinity in the DBW varied from 0 ‰ (freshwater) in the above tidal portion to up to 25 ‰ (estuarine) at its entrance near Dickinson Bay (Fig. 3). Salinities presented in Fig. 3 were calculated as the water column average and then log transformed to show the range at each location. There were no seasonal salinity patterns (p > 0.05) during the study period; rather the range (min and max bars) reflects the interplay between freshwater inputs and a halocline that typically extended most of the way up the bayou. DO concentrations are often used as a measure of water quality and aquatic health. The DO 24 h average for healthy waterways is set at 4 mg l1 (TCEQ, 2003). Surface waters (61 m) in the bayou had average DO concentrations of 6.1 mg l-1 between 2000 and 2006 (Fig. 4A), with minimums as low as 0.6 mg l1 (at IH 45, 14.2 km) and maximums as high as 14.3 mg l1 (at SH 3, 10.4 km). Waters deeper than 1 m were generally lower in DO (Fig. 4B), with a mean DO of 3.5 mg l1. Low values between 0.2 and 1 mg l1 in bottom waters were not uncommon upstream of Gum Bayou (6.4 km), all the way to Cemetery Rd (19.7 km). This

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Average Temperature (°C)

A

30 25 20 15 10 5 0 Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Jul

Aug

Sep

Oct

Nov

Dec

Month

B

40

Average Rainfall (cm)

35 30 25 20 15 10 5 0

Jan

Feb

Mar

Apr

May

Jun Month

C

250

Total Rainfall (cm)

200 150 100 50 0 2000

2001

2002

2003

2004

2005

2006

Year Fig. 2. Average monthly (A) air temperature (°C) and (B) rainfall (cm) in the DBW between 2000 and 2006. Error bars represent standard deviations. (C) Annual rainfall (cm) is subject to cyclic patterns and perturbations due to tropical storms.

30

Salinity (‰)

25 20 15 10 5 0 0.0

6.4

7.4

10.4

11.8

14.2

19.7

22.4

26.2

Distance from Dickinson Bayou at IH46 (km) Fig. 3. Average water column salinities (‰) measured between 2000 and 2006 from Dickinson Bay (0 km; SH I46) to the upper reach of the tidal portion of Dickinson Bayou. The averages are presented with minimums (lower bars) and maximums (higher bars). A log scale was used to show the range across the bayou.

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20

-1

Dissolved Oxygen (mg l )

A

16 12 8 4 0 0.0

6.4

7.4

10.4

11.8

14.2

19.7

22.4

26.2

19.7

22.4

26.2

19.7

22.4

Distance from Dickinson Bayou at IH46 (km)

-1

Dissolved Oxygen (mg l )

B

20 16 12 8 4 0 0.0

6.4

7.4

10.4

11.8

14.2

Distance from Dickinson Bayou at IH46 (km)

C

70

% Exceedances

60 50 40 30 20 10 0 0.0

6.4

7.4

10.4

11.8

14.2

26.2

Distance from Dickinson Bayou at SH I46 (km) Fig. 4. Average (24 h) DO concentrations (mg l1) measured between 2000 and 2006 from Dickinson Bay (0 km; SH I46) to the upper reach of the tidal portion of Dickinson Bayou. (A) Surface DO was typically 6.1 mg l1 along the length of the bayou with minimum DO’s (bottom bar) ranging from 0.6-2.8 mg l1 and maximums (top bar) from 7.9–19 mg l1. (B) DO at >1 m depth was typically 3.5 mg l1 in the bayou with minimums (bottom bar) ranging from 0.1–1.0 mg l1 and maximums (top bar) from 8.2– 9.8 mg l1. (C) Exceedances refer to the measurement of instantaneous DO concentrations of 63 mg l1. The fraction of exceedances in surface (61 m) waters (white bars) was less than those in deep (>1 m) waters (black bars). The greatest fraction of exceedances occurred in the tidal segment of the bayou between Gum Bayou (6.4 km) and Cemetery Road (19.7 km).

section of the bayou was previously described as impaired. DO was generally within the acceptable range (>4 mg l1) in the tributaries (data not shown). Instantaneous measurements of DO should be P3 mg l1 to sustain aquatic life (US EPA 1986; TCEQ, 2003). Values not meeting this standard are referred to as exceedances. During 2000–2006, the fraction of exceedances in surface (61 m) waters (white bars) was significantly less than those in deeper (>1 m) waters (black bars; Fig. 4C). Three out of 9 surface stations had exceedances which occur >20% of the time compared with 5 out of 5 deep stations (Fig. 4C). The greatest fraction of these exceedances occurred in the impaired section of the tidal segment. Gulf coast bayous typically exhibit seasonal variations in DO. During the warm months, lowest DO concentrations were measured in the bayou (Fig. 5A and B), in particular in waters >1 m

(Fig. 5B). Differences between seasons were as little as 10% at a number of stations in surface waters (Upstream of Gum Bayou to SH 3) to as much as 58% at Cemetery Rd (19.7 km in Fig. 5A). The difference in the DO content of the water between cool and warm months in deeper waters was as much as 76% (Fig. 5B). 3.3. Chlorophyll and nutrients With the large range in measured chlorophyll values, we reported findings as medians and included the range. Chlorophyll values were highest (16.8 lg l1) at SH 3 (10.4 km) and generally lower, but not significantly (p > 0.05) upstream (Table 2). Chlorophyll values > 19.2 lg l1 are considered high for Texas tidal bayous (TCEQ, 2003). Although most readings (80%) were below the screening level between 2000 and 2006 (Table 2), the bayou

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Dissolved Oxygen (mg l -1)

10 8 6 4 2 0 0.0

6.4

7.4

10.4

11.8

14 . 2

19.7

22.4

26 . 2

Distance from Dickinson Bayou at IH46 (km)

Dissolved Oxygen (mg l -1)

10 8 6 4 2 0 0 .0

6.4

7. 4

1 0.4

11 .8

14 .2

1 9.7

2 2.4

26 .2

Distance from Dickinson Bayou at IH46 (km) Fig. 5. Seasonal patterns in DO concentrations varied as a function of water depth. Surface waters were those at 61 m (A) while deep waters were those at >1 m (B). October to April represent the cool months (white bars) while May to September are the warm months (black bars), respectively.

Table 2 Average chlorophyll concentrations (lg l1) measured between 2000 and 2006 from Dickinson Bay to the upper reach of the tidal region. No data is available for above the tidal reach. Values presented here are the median chlorophyll concentrations (i.e., chl a plus phaeophytin). The range and number of samples (N) examined is also included. Tributaries are in italics. Distance from Dickinson Bay (km)

Total chlorophyll (lg l1) Median

N

(min–max) 5.8 10.4 12.4 15.6 19.7

13.4 (2.241.5) 16.8 (2.0108.4) 10.7 (2.043.8) 9.4 (2.045.4) 5.0 (2.097.8)

27 34 27 27 29

did experience occasional algal blooms in the late spring/summer at SH 3 (108 lg chl l1) and at Cemetery Road (98 lg chl l1) which are located 10.4 km and 19.7 km upstream of Dickinson Bay, respectively (Fig. 1; Table 1). Unfortunately, there is no information on the phytoplankton species responsible for these blooms. Nutrient concentrations measured in the DBW are relatively low; average total inorganic nitrogen (ammonia, nitrite and nitrate) concentrations ranged from 0.08 to 0.51 mg l1 while mean total phosphorus values ranged from 0.09 to 0.25 mg l1 (Table 3). Highest nitrogen values were recorded at Cemetery Road (19.7 km) and the highest orthophosphate was measured at SH I46 (0 km). Ratios of N:P of <15 are indicative of N-limitation (Howarth and Marino, 2006). Given this ratio was close to 1 (Table 3), primary productivity in this system is likely to be frequently N lim-

ited (Table 4). We did not find any significant seasonal patterns in nutrient concentrations across the bayou (p > 0.05). 3.4. Bacteria Three bacterial indicators were used in Dickinson Bayou between 2000 and 2006: fecal coliform, E. coli and Enterococcus. These were used as proxies for the presence of human and/or animal waste (US EPA, 1986; TCEQ, 2003). While these bacteria themselves do not typically cause illness in humans, their presence indicates that other disease-causing microbes may be present (NRDC, 2006). Fecal coliform has been used as the test organism for contact recreation safety (activities that bring humans in contact with surface water, e.g. swimming, skiing, etc.) for over 30 years. Values higher than the standard have been associated with greater risks of gastrointestinal illness in swimmers (Viessman and Hammer, 1985; NRDC, 2006). In the DBW, fecal coliform levels (Table 4; Fig. 6 – white bars) were found to be high (i.e., exceeding screening levels) in about 37% of samples collected. Tributaries in general, had higher than acceptable fecal coliform numbers (49% of samples) than did the main stem (26%) (Fig. 6). E. coli and Enterococcus are also used as bacterial indicators; the relationship between these and the rates of illness in swimmers are clearer than those for fecal coliform (US EPA, 1986). Enterococcus was used in tidal waters which in our study included everything from Dickinson Bay to Cedar Creek. Enterococcus was only high in 12% of the samples (Table 4). E. coli was used in freshwater settings and found to be elevated in 23% of the samples. Seasonal distribution of fecal coliform bacteria and E. coli have been shown previously (e.g., East and Hogan, 2003); we did not have sufficient data to make a similar analysis.

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Table 3 Total nutrient concentrations (mg l1) in the water column of Dickinson Bayou, based on a sample size (N), collected between 2000 and 2006. The range (min–max) was included to show the variability. Tributaries are in italics. Distance from Dickinson Bay (km) 0 5.8 6.4 7.4 10.4 11.9 12.4 13 13.4 14.2 19.7 21.3 22.4 26.4

Nitrogen mean (min–max)

N

Phosphorus mean (min–max)

0.19 (0.060.52) 0.17 (0.040.40) 0.42 (0.070.84) 0.27 (0.070.93) 0.34 (0.040.77) 0.08 (0.040.51) 0.22 (0.060.58) 0.22 (0.050.56) 0.31 (0.040.85) 0.27 (0.080.66) 0.51 (0.070.94) 0.20 (0.080.82) 0.18 (0.070.36) 0.19 (0.070.79)

28 24 22 21 55 22 28 28 27 49 26 16 20 30

N:P ratio N

0.25 (0.080.98) 0.19 (0.070.32) 0.09 (0.040.15) 0.19 (0.070.38) 0.19 (0.040.56)

12 12 22 12 66 <12 12 12 12 <12 <12 16 <12 <12

0.20 (0.080.35) 0.22 (0.080.39) 0.21 (0.070.45)

0.09 (0.020.22)

0.77 0.88 4.9 1.4 1.8 1.1 1.0 1.5

2.2

Table 4 Bacterial counts in the surface waters of Dickinson Bayou. Minimum and maximum values generally (but not always) reflect the lower and upper detection limits for these tests and so were not included. Rather the % of samples that exceeded the criteria (%E) were included as well as the number of samples (N) measured. Fecal coliform was measured at all stations while Enterococcus was only measured in the tidal segment and E. coli only in the above tidal segment. Tributaries are in italics. Distance from Dickinson Bay (km)

0 5.8 6.4 7.4 10.4 11.8 12.4 13 13.4 14.3 19.7 21.3 22.4 26.2

Fecal coliform

Enterococcus

Geometric mean

%E

N

Geometric mean

44 775 161 93 214 93 482 518 642

14 33 32 14 30 59 57 52 67 33 28

21 21 22 21 43 21 21 21 21 43 43

29 38

17 21

319

E. coli %E

N

18

9

12

19

10

20

38

18

12

Geometric mean

%E

N

92

16

19

145

29

24

70

Exceedances (%)

60 50 40 30 20 10 0 0.0

5.8

6.4

7.4

10.4

11.8

11.9

13.0

13.4

14.2

19.7

22.4

26.2

Distance from Dickinson Bayou at SH I46 (km) Fig. 6. Percentage exceedances of fecal coliform measured between 2000 and 2006 from Dickinson Bay (0 km; SH I46) to the above tidal portion of Dickinson Bayou. The main stem of the bayou (white bars) in general, had fewer exceedances than the tributaries (black bars).

4. Discussion While many of the sources of aquatic pollution are well known and ubiquitous, new concepts and ideas on environmental pollution are emerging with a corresponding need for an update of the knowledge of environmental responses to perturbations, spe-

cifically the response of small urban watersheds to population increases (Shahidul Islam and Tanaka, 2004). Federal and state agencies across the US and worldwide have amassed large databases of water quality parameters measured over decades in response to the Clean Water Act Section 303(d) and other initiatives to clean and improve the status and health of water bodies

A. Quigg et al. / Marine Pollution Bulletin 58 (2009) 896–904

in across a wide array of environments. Nonetheless, the current status of coastal ecosystems worldwide is cause for great concern (e.g., Shahidul Islam and Tanaka, 2004; Howarth and Marino, 2006). In Texas, the TCEQ recently established partnerships in which scientists, resource managers and the public work together to establish the baseline conditions in watersheds (e.g., Armand Bayou Watershed Plan, 2000; Dickinson Bayou Watershed Plan, 2008) and then prepare remediation plans according to nine key parameters identified by the US EPA to improve water quality and restore ecosystem services. The most pervasive emerging environmental threat in the DBW is elevated bacteria levels, indicating that disease-causing human and/or animal wastes are present in higher concentrations than standards set by the EPA and in this case, TCEQ (US EPA, 1986; TCEQ 2003). H-GAC (2006) had reported that bacterial concentrations, especially E .coli, appear to be increasing in Texas watersheds, and in particular, in the tidal segments of bayous. With this relatively short term data set, we did not see a similar trend. Nonetheless, outfall from a sewage treatment plant, failing septic tanks and pasture lands, waste from agricultural operations, storm water runoff, wild and domestic animal feces, and boat-discharge are all important bacterial sources for Dickinson Bayou. Bacterial standards however do not address the causative agents of rashes, respiratory infections and other symptoms reported by recreational users, nor do they address the nature of protozoan parasites or viruses (NRDC, 2006). Bacterial indicators simply indicate casual agents have an ‘‘unknown origin” and, because these indicators are not representative of these organisms, the causal agents for these diseases remain unknown. This lack of specific information complicates goals for remediation. Nonetheless, they are a first approximation or tool for addressing human health concerns. For the DBW, future studies should improve spatial and temporal coverage of bacterial indicator surveys, as well as examine sediments to measure the persistence of pathogens. Elevated nutrient concentrations remain the greatest issue for ecosystems worldwide (Nixon, 1995; Terrio, 1995; Nixon et al., 2001: Howarth and Marino, 2006). Eutrophication is associated with degradation of water quality and ecosystem function. In addition to external inputs, nutrients are also released from organic matter and/or sediments within aquatic systems. Interestingly, ratios of N:P were < than 16, indicating N limitation of primary productivity between 2000 and 2006 in Dickinson Bayou. Relative to the findings of Kirkpatrick (1986a, b), we found nutrient concentrations to be relatively low. Excessive nitrogen additions to low-nutrient systems, particularly those with low flow, often cause algal blooms (Nixon, 1995; Valiela et al., 1997; Carpenter et al., 1998), which is indeed what is observed in the DBW, particularly in the spring/summer. Algal blooms often develop following high flow or rainfall runoff conditions indicating that this is an important mechanism for nutrient loading. Although nutrient levels were below screening levels (TCEQ, 2003), it is unclear if these standards, based on the 85th percentile of similar water bodies in Texas, are adequate to assess the trophic status of Dickinson Bayou, or for that matter, other systems. Findings for example, from the Neuse estuary in North Carolina (Glasgow and Burkholder, 2000), indicate that significant lowering of nutrient concentrations (below the EPA standards) is ultimately required to achieve noticeable reductions in algal blooms, hypoxia and fish kills. DO levels were frequently below the criteria used to support aquatic life in the tidal segment (Figs. 4 and 5). DO was less than the minimum 27% of the time in surface waters between Interstate 45 and Cemetery Road (14.2 km and 19.7 km respectively upstream of Dickinson Bay as shown in Fig. 1), and almost half the time (48%) at >1 m between 2000 and 2006 (Fig. 4). Aside from decaying blooms, oxygen demand increases in the summer due

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to higher temperatures and lower flow rates. We found the area of lowest DO consistently to be in the widest, deepest and most sluggish section of the bayou. Unfortunately, this area is also the location of the waste water treatment facility. Fish kill events are often observed in this section, primarily associated with phytoplankton blooms and low water column DO, particularly in the summer. The most often affected fish is Brevoortia patronus (Gulf menhaden). B. patronus is the fish species most often reported in fish kills along the Texas coast (Thronson and Quigg, 2008). It is also often reported in fish kill events at nearby bayous (McInnes and Quigg, submitted for publication) as well as along the gulf coast states (Lowe et al., 1991). Bayous, particularly those in coastal states, are under threat from rapid development and urbanization. With this kind of growth there is a concurrent increase in the spread of impervious surfaces and a channelizing and directing of water directly into watersheds with such landscape modifications. Large rainfall events are no longer dispersed across wide land areas but now move more directly into watersheds, altering the natural hydrodynamics, increasing bacterial and nutrient loading. Relative to the nearby Armand Bayou and other local bayous along the Texas gulf coast, the DBW median concentrations for nutrients (nitrogen and phosphorus) were generally lower, with highest recorded in Armand Bayou which also had very high chlorophyll concentrations (median and individual) indicative of more frequent and persistent algal blooms (Armand Bayou Watershed Plan, 2000; East and Hogan, 2003). Non point source pollution which is either not regulated or difficult to regulate because its point of origin is hard to identify, has a clearer mechanism to enter watersheds under urbanization. Bayous are especially susceptible to this kind of encroaching development and contamination due to their inherent nature; they have sluggish water masses and low flushing rates with limited freshwater inflow. The purpose of this study was to determine the current health status of the DBW, within the border context of the DBW Partnership. While bacterial counts are high, and DO is frequently too low, chlorophyll and nutrient concentrations are not be the main issue threatening this system. Our findings are contrary to perceptions by scientists and the public on the state of the watershed. Hence, the criteria currently set to evaluate eutrophication may not be appropriate for this bayou. The disparity is well recognized and there are efforts underway to develop more appropriate assessments for bayous and coastal ecosystems across Texas and worldwide. The data in this paper will be used, along with that collected on habitat, land use, flood and storm water management and recreational uses to set goals to sustain and restore the health and overall quality of the DBW. In addition to examining standards, we propose within the constructs of the partnership, to direct efforts to outreach and public education. Programs such as the DBW Partnership are therefore important for bringing together scientists, managers and the public to ‘‘protect, preserve and enhance the ecological integrity of the watershed while improving the quality of life for communities.” In addition, they provide a mechanism for scientists and resource managers to come together and evaluate, and in some cases, re-evaluate ecosystems which may not be considered by larger programs. It is important that the impact of urban develop on small urban watersheds be better studied. Acknowledgements We are indebted to the numerous personal that conducted hours of field work and sample analyses from 2000 to 2006. We thank M. Cunningham (Penreco), S. Johnston (Galveston Bay Estuary Program, TCEQ), J. Wright (H-GAC), B. Solmonsson and S. Benner (Texas A&M University & Texas Cooperative Extension Program) for participating with the authors on the water quality committee established as part of the Dickinson Bayou Partnership Program.

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