Hydrology, water quality, and restoration potential for the Upper Big Darby Creek, Central Ohio (1).

Zhang, Li ; Mitsch, William J. ; Fink, Daniel F. 等

ABSTRACT. The restoration of riparian buffers as well as the creation and restoration of wetlands along streams are practices that can be used to control point and non-point source pollution. Our study provides hydrology and water quality data from 2000-2002 in anticipation of recommending restoration of the headwaters of the Big Darby Creek Watershed in central Ohio. One tributary of concern in the headwaters, Flat Branch, contributed 11% of the total river flow during April 2002 flooding and 56 and 88% of the flow in the headwater study area during non-growing (winter and early spring) and growing (summer and early fall) seasons, respectively. There were significant differences in water chemistry, both temporally and spatially, at each sampling station within the upper watershed. Flat Branch was seasonally or continuously higher in temperature, pH, and turbidity, and lower in dissolved ions and oxygen than Darby Creek. Low dissolved oxygen at dawn during the summer months caused by diurnal metabolism in the water column is also a concern in Darby Creek. We propose the creation/restoration of riparian wetlands at the confluence of the Big Darby and Flat Branch as one solution to degrading water quality in the upper Big Darby watershed. Flood pulses, particularly from the Flat Branch, could be directed to riparian wetlands, which would minimize downstream erosion and capture the water exactly when several pollutants (sediments, nitrates, and so forth) are in higher concentrations. The restoration area could have flood control, habitat, and ecotourism values as well.

OHIO J SCI 105(3):46-56, 2005

INTRODUCTION

Riparian forests and wetlands enhance stream ecosystems and their water quality (Odum 1981; Naiman and Decamp 1997; Ward 1998; Mitsch and Gosselink 2000; Sweeney and others 2002; Mitsch and Jorgensen 2004). Restoration of riparian buffers and wetlands along streams stabilize stream channel morphology in addition to controlling non-point source pollution coming from the landscape. They also provide refuge for a great variety of wildlife and some fish species associated with the streams and rivers. If overbank flooding occurs from the stream and river into the riparian forests and wetlands, sediments can be deposited on the floodplain from the river while particulate organic matter can be exported to support detrital food chains in the stream.

A number of research projects around the world have shown how the functions gained from riparian restoration can benefit both nature and humans (Kadlec and Hey 1994; Jacks and others 1994; Moustafa 1999; Nairn and Mitsch 2000; Spieles and Mitsch 2000; Hoagland and others 2001; Mitsch and others 2001, 2002; Henry and others 2002). Peterjohn and Correll (1984) and Lowrance and others (1984) demonstrated that riparian forests of coastal plain agricultural watersheds can be nutrient sinks that buffer the nutrient discharge from surrounding agroecosystems. They also showed that nutrient uptake and removal by soil and vegetation in the riparian ecosystem prevented agricultural upland outputs from reaching stream channels. Most recently, Mitsch and Jorgensen (2004) concluded from a review of many studies that, because chemical and biological conditions will respond accordingly if the proper hydrologic conditions are developed, riparian restoration can lead to both short- and long-term water quality benefits. However, there are still very few techniques to assess the viability of riparian restoration to an entire watershed. Successful stream restoration depends not only on understanding the physical and biological processes that influence ecosystems at the watershed scale, but also in the proximity of the restoration effort to the sources of disturbance (Goodwin and others 1997; Tein and others 1999; Ward and others 1999; Poudevigne and others 2002; Mitsch and Jorgensen 2004).

Our study investigates the potential of restoring the headwaters of the Big Darby Creek Watershed in central Ohio. Big Darby Creek is a stream of relatively high water quality and biological diversity, but recent upstream developments (industrial and agricultural) have raised concerns about pollution effects downstream. Properties adjacent to the creek in the upstream reaches were purchased by the Ohio Chapter of The Nature Conservancy in the 1990s and early 2000s, leading to discussions on the restoration of stream channels, wetlands, and/or riparian ecosystems in this watershed to improve water quality, ameliorate flood peaks, provide habitat, and improve/maintain the biological character of the creek. Any such project would need both pre- and post-restoration monitoring to determine the effectiveness of the restoration. The creation of any wetland/riparian system would require complete data on stream hydrology for example. Because the ability of wetlands to trap or transform nutrients generally increases as the water retention time increases, our study emphasizes understanding the hydrology and water chemistry dynamics temporally and spatially within the upper watershed network. The main goal of this study is to assess the quality of the streams in the vicinity of the potential restoration sites and to provide assistance on the siting and design of riparian restoration in the study area.

MATERIAL AND METHODS

Study Site

Our study watershed, with an area of 127 [km.sup.2], is the headwaters of Big Darby Creek in Logan, Union, and Champaign counties in central Ohio (Fig. 1). Big Darby Creek eventually flows into the Scioto River, a major tributary of the Ohio River. The geology of the Big Darby Creek watershed was defined during the glacial advances and retreats of the Wisconsin glaciation dating back 15,500 to 17,000 years before present. The uppermost bedrock units are Silurian-Devonian limestone and dolomite. The average slope of the upper Big Darby is 6.5%, where the terrain is flat to gently rolling with more than 90% of the land having slopes less than 6%. Soils are silty clay loams with moderately slow to slow subsoil permeability and low to moderate erosion hazards (US EPA 1996; Yu and Schwartz 1999). Prior to European/ American settlement, the Big Darby Creek watershed consisted primarily of wet prairies in the flat and upland regions and mixed oak forests and savannahs on its gently sloping knolls (The Nature Conservancy Ohio 1999). Wetlands made up a significant part of the original Upper Big Darby watershed. Bear Swamp, also known as Flat Woods, was a large, well-developed wetland in the headwaters of the Big Darby (Ohio Historical Society 2001).

[FIGURE 1 OMITTED]

The first permanent settlers came to Union County in 1798 (Ohio Historical Society 2001). Since then, the Big Darby Creek watershed has been drained, and today more than 90% of its wetlands have been converted to agricultural fields and other development (The Nature Conservancy Ohio 1999). Presently, the upper watershed of the Big Darby is a productive agricultural area with a diverse range of land uses including corn-soybean crop rotation, livestock pasturing, forest and woodlot management, and urban/residential use (The Nature Conservancy Ohio 1999). Significant industrial development occurred in the Upper Big Darby Creek watershed in the 1970s and 1980s with the establishment of an industrial park for manufacturing Honda motorcycles and automobiles. Currently, that activity takes up about 24% of the Upper Big Darby watershed, with much of the drainage from that development concentrated in a stream known locally as Flat Branch (see Station 3 on Fig. 1).

Aquatic Surveys

Aquatic surveys of the Upper Big Darby watershed taken by the Ohio EPA prior to our study show a general increase in the number of invertebrate taxa sampled per unit effort from the low order headwaters of the Big Darby to the end of the study reach (Table 1). But there are some signs of invertebrate diversity impact below the confluence of Big Darby with Flat Branch. A maximum of 86 taxa occur in the Big Darby north of the confluence with Flat Branch; this decreases to 73 taxa downstream of Flat Branch. The Invertebrate Community Index (Ohio EPA 1989) and Qualitative EPT richness index (the sum of the number of Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies) taxa present) are high both upstream and downstream of the Flat Branch. Fish count data were provided from the Ohio EPA for a 3.9-km stretch of the Upper Big Darby only upstream of its confluence with the Flat Branch for 1997, 1999, and 2000 (Table 2). The number of species present changed both from year to year and from upstream to downstream, but was always highest near our Station 2a, immediately upstream of the Big Darby confluence with Flat Branch. No fish data were available for Flat Branch or downstream of Flat Branch.

Hydrologic Measurements

Stream stage gage stations with Ott Thalimedes data loggers were installed at 4 locations (Stations 1, 2, 3 and 5 in Fig. 1) in the Upper Big Darby watershed. Streamflow was calibrated to stage with the assistance of the US Geological Survey (USGS) for Flat Branch Creek (Station 3) and Big Darby Creek (Station 5). The resulting rating curves (relation between stage and discharge) were fit to polynomial relationships (Table 3) and significant correlation relationships (R2 >0.999) between observed and simulated discharge were observed for Stations 3 and 5. Annual mean historical streamflow data at the downstream end of the Big Darby Creek Basin during the period of 1922 to 2001 were obtained from USGS hydrological station 3230500. Precipitation data were made available from Honda Inc. at their facility in the watershed.

Water Quality Sampling

We manually monitored temperature, dissolved oxygen, conductivity, pH, and reduction potential at 4 instrumented sampling stations and at 3 manual sampling stations on a weekly basis with a YSI 610XL sonde. Manual grab samples were also taken weekly for nutrient analyses. A YSI 610XL water quality sonde was installed at station 5 late in our study to investigate stream temperature, dissolved oxygen, conductivity, and pH at 30-min intervals for one month in summer 2002.

Lab Analysis

Manual water samples were taken to the laboratory and preserved according to standard methods (US EPA 1983; APHA 1996). They were analyzed for soluble reactive phosphorus, total phosphorus, and nitrate-nitrogen using a Lachat QuickChem FIA+ 2000 series in The Ohio State University Ecosystem Analytical Laboratory. Samples taken from the auto samplers were used to estimate water quality during flooding events. These samples were measured for the following: conductivity, nitrate, and turbidity. Monthly samples were analyzed at the STAR laboratory at The Ohio State campus in Wooster for major and trace elemental analysis by ICP emission spectrometry.

Land Use Analysis

We developed a data storage system with ArcView 3.2 (ESRI 2000) that displays prominent land-use features and other aspects of the watershed that contribute to the water quality of Big Darby Creek.

RESULTS AND DISCUSSION

Hydrologic Influence of Flat Branch on the Upper Big Darby Watershed

Three of the five wettest years from the period 1922 to 2001 have occurred since 1990 in the Darby Creek watershed, while there has been no dry year since 1987 (Fig. 2). For the Upper Big Darby Creek, April 2002 was the wettest month during our study period of 2000-2002 (Fig. 3). The Flat Branch contributed a significant part of the flow to Big Darby Creek. When compared to flow downstream at Station 5 on the Big Darby, Flat Branch Creek contributed 56% of the Big Darby Creek flow during flood periods and 88% of the flow during normal flow periods (Table 4). When comparing the contribution of flooding events to the downstream USGS station on Big Darby Creek at Darbyville well below our Upper Big Darby study area, our study showed that Flat Branch contributed 11% of the total river flow during April 2002 flooding. Flat Branch contributes more flow to the overall Darby Creek ecosystem than had been suspected by us or other investigators. This is significant because hydrological dynamics is a driving force in river/stream ecosystems (Allan 1995; Poff 1997; Richter 1998). Streamflow controls nutrient and chemical loading rates, affects the exchanges of organisms and energy patterns in time and space, and also affects physical attributes such as channel morphology (Whitton 1975; Allan 1995; Ward and Stanford 1995; Richter 1998; Mitsch and Jorgensen 2004). Thus, the high contribution of flow to the Big Darby Creek from the Flat Branch has significant implications on the ecosystem health in Big Darby Creek itself.

[FIGURES 2-3 OMITTED]

Water Quality

Conductivity is higher in the growing season than in the wetter non-growing season in the Big Darby upstream of its confluence with Flat Branch and drops about 100 [micro]mhos/cm (20%) downstream of Flat Branch, illustrating the distinct difference in water sources of the two streams when they meet (Fig. 4). Flat Branch is much more dominated by low-ionic surface flow resulting from runoff than by groundwater flow that heavily influences the upper reaches of the Big Darby. The Upper Big Darby is significantly higher in turbidity after it passes the confluence with the Flat Branch (Fig. 4). Turbidity in the Big Darby Creek doubles from 20 to 40 NTU in the growing season and more than doubles from 5 to 12 NTU in the non-growing season below the confluence. Phosphorus increases significantly between Stations 2 and 2a in Darby Creek. We believe this effect is due to a small Logan County treatment plant which discharges into the Big Darby Creek upstream of its confluence with Flat Branch. Nitrate-nitrogen does not increase in Big Darby Creek due to Flat Branch and concentrations are, not unexpectedly, quite variable especially in the non-growing season (error bar is 3.0 mg-N/L) compared to the growing season (error bar is generally less than 1.0 mgN/L). Significant differences of nitrate-nitrogen concentrations were detected during a winter flooding event in 2001 when auto-sampling showed a doubling in nitrate-nitrogen from about 0.8 mg-N/L to about 1.6 mgN/L in one hour during the flood event.

[FIGURE 4 OMITTED]

We statistically compared Station 2 water quality (Darby Creek upstream of Flat Branch) and Station 5 water quality (downstream of Flat Branch) with Flat Branch (Table 5). There were significant differences in turbidity during the growing (non-flooding) and non-growing (flooding) seasons and significant differences in dissolved oxygen and conductivity during the growing season between Flat Branch and both Darby Creek stations. Water from Flat Branch is more turbid, lower in dissolved ions, and lower in dissolved oxygen than is water in Darby Creek in lower flow conditions of the summer and fall. During these low-flow conditions, Flat Branch is also statistically warmer and has higher pH compared to the upstream station 2. No statistical differences were seen between the Big Darby and Flat Branch for the three nutrient parameters analyzed.

Significant diurnal changes occur in temperature dissolved oxygen, pH, and conductivity in the summer in Upper Big Darby Creek at Station 5 (Fig. 5). These patterns are driven by aquatic metabolism (primary productivity and respiration) in the water column that is particularly significant during low-flow summer conditions. This photosynthesis and respiration, in turn, is caused by high nutrients in the water column. When storm pulses (floods) occur, as on 20 July, 27 July, and 6 August, diurnal patterns are dampened (Fig. 5). After these pulses, the diurnal patterns reestablish themselves in a few days. These high-frequency data also illustrate that dissolved oxygen in the Big Darby dropped to almost 3.0 mg/L at dawn on several days in late July and early August, levels that are threatening to aquatic ecosystem health. Sampling the river manually would never have revealed these potentially threatening low levels. Flood pulses, when they occur, temporarily remove the low dawn dissolved oxygen conditions until aquatic metabolism increases to the point where dissolved oxygen at dawn again decreases below 3.0-4.0 mg/L.

[FIGURE 5 OMITTED]

Specific dissolved ions and trace metals showed some differences between Flat Branch (Station 3) and three other Darby Creek stations (Tables 6, 7). Flat Branch had higher concentration of two significant metals (A1 and Fe) than any of the three other sampling stations on the Darby. Aluminum, a chemical that can threaten aquatic communities at concentrations seen in the Flat Branch, remains high in the Darby downstream of Flat Branch (93 [micro]g/L downstream vs 39 [micro]g/L upstream). Chronic effects on fish growth at A1 concentrations as low as 100 [micro]g/L have been detected in the poorly buffered lakes affected by acid deposition in the Adirondacks of northeastern USA (Cronan and Schofield 1979). Flat Branch also was significantly higher in arsenic (As) than Station 2 in Darby Creek. Arsenic average concentrations at all Darby Creek and Flat Branch stations (average = 44 [micro]/L at Station 1; 75 [micro]g/L at Station 5) are above the US EPA (1980, 1981) 24-hr maximum criteria recommended for the protection of freshwater aquatic life of 40 [micro]/L. But the As averages in Table 6 should be viewed with some caution; the level of detection was 50 [micro]g/L for As, so our protocol then used 25 [micro]g/L of all such numbers below the level of detection for calculating averages. Conversely, Flat Branch had lower concentrations of sulfur and barium than did two and three Darby Creek stations respectively and, as would be expected from conductivity data described above, lower concentrations of the major dissolved ions calcium and magnesium than most of the Darby Creek sampling stations (Table 7). The high concentrations of aluminum and arsenic in Flat Branch give some concern for that stream contributing to the degradation of aquatic communities in Big Darby Creek downstream of Flat Branch.

Restoring Upper Big Darby Creek

Big Darby Creek is a stream of great importance in Ohio because of its status as an Ohio Scenic River. Its aquatic life is threatened by a combination of altered hydrology and a deterioration of water quality that includes high turbidity, nutrients, and some trace metals. The high nutrients in turn cause high diurnal patterns of dissolved oxygen in the Darby, a condition that also threatens aquatic life when dawn dissolved oxygen goes below 5.0 mg/L. Increased low-ion surface runoff in the Flat Branch, compared to groundwater flow which dominates much of the rest of the Upper Darby, is an indicator that Flat Branch water is polluted from a combination of non-point sources including parking lot and industrial runoff and drained agriculture land. Increased flow, particularly during flood events, has caused tributaries and the creek itself to change its erosion-sedimentation patterns, also increasing turbidity.

The sources of the pollutants to the Upper Big Darby are many and come from agriculture, highway runoff, and industries. They are mostly non-point pollution sources that are difficult to regulate or control. It would be difficult to identify specific sources of nutrient, sediment, and trace element pollution in the Upper Big Darby or to control specific pollution sources beyond what is already being done. Based on the data presented in this paper and on the interest for some restoration in the Upper Big Darby by The Nature Conservancy and other agencies and NGOs, we believe that creation of a riparian wetland system, if properly located near the confluence of the Upper Big Darby and the Flat Branch, could contribute significantly to water quality improvement in the Upper Big Darby.

Restoring and creating wetlands could enhance water quality, flooding control, and ecosystem function in the Upper Big Darby Creek. The importance of long-term restoration has been emphasized by Richardson and Vaithiyanathan (1995); Costanza and others (1997); Mitsch and Gosselink (2000); Mitsch and others (2001); Poudevigne and others (2002); and Whigham and others (2002). Storm events are often the main mechanism for transporting pollutants, causing biological degradation downstream but, because of the logistics of manual sampling, these measurements are often not taken. In the Upper Big Darby, N[O.sub.3], Al, Fe, P, and Si increased with storm flows. The flood pulsing and water quality coming from the Flat Branch tributary of the Big Darby is of particular concern. This tributary is turbid and has higher concentrations of several pollutants than do the upstream reaches of Big Darby Creek. Controlling pollution in the Flat Branch is particularly significant as it contributes 56% of the flow of the Big Darby Creek during flood events and 88% of the flow during normal flow.

Most of the pollutants seen in this study can be controlled through riparian restoration projects. If the river is permitted to flood its riparian zone with greater frequency, then the effects of sediment and nutrient pollutants downstream, particularly during storm events, could be minimized. Creation and restoration of wetlands will also provide important ecological functions within the headwater watershed. Vegetation is productive and a portion is exported during seasonal flood pulses; exported organic carbon is an important food resource for aquatic communities (Dosskey and Bertsch 1994).

We propose an investigation into the creation/ restoration of riparian bottomlands at the confluence of the Big Darby and Flat Branch as one solution to the problem (Fig. 6). Flood pulses, particularly from the Flat Branch, could be directed to riparian wetlands, capturing the flood pulse, thus minimizing downstream erosion as well as pollutant transport and capturing the water exactly when several chemicals (sediments, nitrates, and so forth) are in higher concentrations. The value of such an effort would be three-fold:

1. water quality of the Big Darby could be improved particularly if the Flat Branch is the focus of the flood pulse capture;

2. an array of biologically diverse forested and wetland habitats would develop in land already purchased by The Nature Conservancy. Terrestrial and wetland fauna and flora would flourish in such an environment; and

3. wetlands at this location could also be designed to treat the minor flow coming from the Logan County wastewater treatment plant located adjacent to this proposed wetland restoration site.

[FIGURE 6 OMITTED]

The wetland/riparian area, which could be called something like the Upper Big Darby Creek Wetland Demonstration Park, could also become an ecotourism destination with signs from adjacent and heavily used US Route 33 and could be a good example of public and private partnership to improve the Darby Creek watershed. It could be modeled after the successful 12-ha Olentangy River Wetland Research Park at The Ohio State University (Mitsch and others 1998; Mitsch and Jorgensen 2004) and could also be eligible for Federal and state support as well as private development. Additional stream and riparian restoration approaches should also be investigated in this basin, but the initial focus should be on restoring the Flat Branch.

ACKNOWLEDGMENTS. We appreciate the assistance of students and staff at the Olentangy River Wetland Research Park (ORWRP) for helping with field sampling and laboratory analysis, particularly intern Emily Resch and site engineer Michelle Guthrie. The Ohio EPA (Marc Smith) kindly provided invertebrate and fish data from recent collections in the region. The USGS was able to develop rating curves for two of the stream stations under a subcontract; we appreciate the help of Steve Hindall, Harold Shindel, and Sandy Coen. We especially appreciate the assistance of Laura Belleville of The Nature Conservancy, Central Ohio Office, in making this project happen. Funding support was provided from the Huntington District of the US Army Corps of Engineers under contract DACW69-01-P-0198. John McDonald, YSI Inc., kindly installed a YSI water quality sonde in the Big Darby at the end of our study that enabled us to obtain diurnal data reported in this study. Clyde F. Morrow Sr., Honda of America, kindly provided meteorological data. Olentangy River Wetland Research Publication 05-005.

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LI ZHANG (2), WILLIAM J. MITSCH, AND DANIEL F. FINK, Olentangy River Wetland Research Park, School of Natural Resources and Environmental Science Graduate Program, 352 W. Dodridge Street, The Ohio State University, Columbus, OH 43202

(1) Manuscript received 8 March 2004 and in revised form 15 December 2004 (#04-06).

(2) Corresponding Author: Email: zhang.326@osu.edu; Fax: 614/ 292-9773

TABLE 1
Macroinvertebrate distribution in the Upper Big Darby
Creek during 1997. Data provided by Ohio EPA.

Closest Sampling Station * 0 1 2 2 a 6

River Mile 83.2 82.5 81.5 79.3 69.4
No Quantitative Taxa 39 33 39 62 42
No Qualitative Taxa 44 33 38 54 59
Total Taxa 70 54 58 86 73
No Organisms 1378 1130 1558 1558 1600
ICI 48 40 38 52 54
Qual EPT 16 7 5 16 22

ICI = Ohio EPA Invertebrate Community Index
Qual EPT = Sum number of taxa of Ephemeroptera (mayflies),
Plecoptera (stoneflies), and Trichoptera (caddisflies).

* See Figure 1.

TABLE 2
Size and distribution of fish in the Upper Big Darby in 1997,
1999, and 2000. Sample stations are sites chosen by Ohio EPA.

Closest Sampling Station * 0 1 2 2 a

2000
 River Mile 82.6 81.5 80.8
 Total Fish 1666 815 364
 Relative Number 2499 1287 575
 Relative Weight 6.34 1.2 7.93
 No Species 12 12 13

1999
 River Mile 83.2 82.6 81.5 80.8
 Total Fish 714 2556 809 1523
 Relative Number 1428 2270 1213 1216
 Relative Weight 3.57 3.39 14.22
 No Species 14 17 16 21

1997
 River Mile 83.2 82.6 81.5 80.8
 Total Fish 1144 1553 1985 1210
 Relative Number 1072 1456 1861 682
 Relative Weight 5.22 2.94 8.48 9.18
 No Species 11 13 18 21

* See Figure 1.

TABLE 3
Relationship between streamflow (Q) and staff gage readings (X)
for Flat Branch (Station 3) and Upper Big Darby Creek
(Station 5) as shown in Figure 1.

 Parameters

Stream a b c d [R.sup.2]

Flat Branch
 0.11<X<=0.36 2.099 7.502 9.067 3.684 0.9999
 0.36<X<1.22 2.924 14.013 30.690 29.857 0.9992
 1.22<=X<1.92 0.677 61.376 -294.187 860.749 0.9990
Darby Creek
 downstream of
 Flat Branch 1.118 1.387 -0.802 -0.312 0.9998

log Q = a + b log X + c [(log X).sup.2] + d [(log X).sup.3]
X: staff gage reading, m
Q: streamflow, [m.sup.3]/s

TABLE 4
Streamflow (average [+ or -] std. Error (# of events)) of Flat Branch
(Station 3) as a percent of Darby Creek streamflow at Station 5, 9
March-22 August 2002.

 Flat Branch Darby Creek
 (Station 3) (Station 5)

Flood Conditions 14.6 [+ or -] (2) 26.2 [+ or -] 0.9 (2)
mean ([m.sup.3]/s) 0.56
ratio

Low Flow 0.7 [+ or -] 1 (22) 0.8 [+ or -] 0.9 (19)
mean ([m.sup.3]/s) 0.88
ratio

TABLE 5
Paired sample comparison of water quality at stations 2 and 5
with water quality at station 3 (Flat Branch) for growing season
(non-flooding period) and non-growing season (flooding period).
Statistics is t-test (95% Confidence Interval of the Difference).

 Paired t-test, p-value

Parameter Station 2 Station 5

1. Growing season (fewer floods)
 Temperature 0.000 nd
 DO 0.000 0.000
 pH 0.000 nd
 Conductivity 0.000 0.003
 Turbidity 0.000 0.000
 Soluble Reactive P nd nd
 Total P nd nd
 N[O.sub.3]+N[O.sub.2] nd nd

2. Non-growing season (period of floods)
 Temperature nd nd
 DO nd 0.004
 pH nd nd
 Conductivity nd nd
 Turbidity 0.003 0.001
 Soluble Reactive P -- --
 Total P -- --
 N[O.sub.3]+N[O.sub.2] nd nd

nd = no significant difference at a = 0.05

TABLE 6
Selected major ions and metals form normal flow and one storm event
during the period June 2001-June 2002 for Upper Big Darby Creek.
Station numbers are located on Figure 1. Data in bold for Station 3
(Flat Branch) indicate where that tributary is statistically different
than at least one of the other Darby Creek stations (see Table 7).

 Station 1

 Mean Max Min Storm

Major Elements, mg/L

Ca 77 [+ or -] 0.0 100 43 43
K 2 [+ or -] 3.0 6 1 6
Mg 36 [+ or -] 0.0 44 17 17
Na 14 [+ or -] 0.0 43 5 5
S 25 [+ or -] 4.3 62 8 8
Si 2.3 [+ or -] 0.3 4 1 3
Fe 0.1 [+ or -] 0.0 0 <0.01 0.4

Other Elements, [micro]g/L

Ag 19 [+ or -] 4.54 50 <5 25
Al 41 [+ or -] 21 251 <40 251
As 44 [+ or -] 12 127 <50 62
B 36 [+ or -] 7 62 <10 62
Ba 51 [+ or -] 4 76 26 45
Be 2 [+ or -] 1 7 <2 7
Cd 2 [+ or -] 1 10 <2 10
Co 6 [+ or -] 1 15 <10 15
Cr 3 [+ or -] 1 12 <5 12
Cu 6 [+ or -] 1 13 <10 13
Mn 2 [+ or -] 1 10 <2 10
Mo 7 [+ or -] 1 18 <10 18
Ni 5 [+ or -] 0 <10 <10 <10
Ph 10 [+ or -] 0 <20 <20 <20
Se 67 [+ or -] 12 173 <100 109
V 5 [+ or -] 2 10 <10 <10
Zn 8 [+ or -] 2.31 22 <5 13

 Station 2

 Mean Max Min Storm

Major Elements, mg/L

Ca 70 [+ or -] 0.0 91 41 41
K 3 [+ or -] 2.4 6 1 6
Mg 31 [+ or -] 0.0 42 15 17
Na 15 [+ or -] 3.4 46 7 5
S 21 [+ or -] 2 .0 32 11 8
Si 2.6 [+ or -] 0.2 3 1 3
Fe 0.1 [+ or -] 0.0 0 <0.01 0.40

Other Elements, [micro]g/L

Ag 19 [+ or -] 5 50 <5 25
Al 39 [+ or -] 16 191 <40 46
As 50 [+ or -] 14 138 <50 23
B 29 [+ or -] 4 46 <10 46
Ba 52 [+ or -] 5 80 29 36
Be 1 [+ or -] 0 <2 <2 <2
Cd 1 [+ or -] 0 2 <2 <2
Co 5 [+ or -] 0 <10 <10 <10
Cr 3 [+ or -] 0 <5 <5 <5
Cu 6 [+ or -] 1 5 <10 5
Mn 2 [+ or -] 0 5 <2 2
Mo 5 [+ or -] 0 <10 <10 <10
Ni 5 [+ or -] 0 <10 <10 <10
Ph 10 [+ or -] 0 <20 <20 <20
Se 56 [+ or -] 6 114 <100 50
V 7 [+ or -] 5 22 <10 <10
Zn 11 [+ or -] 6 72 <5 9

 Station 3

 Mean Max Min Storm

Major Elements, mg/L

Ca 44 [+ or -] 0.0* 72* 24* 24*
K 16 [+ or -] 1.7 39 5 7
Mg 15 [+ or -] 0.0* 25* 7* 7*
Na 33 [+ or -] 8.5 100 5 5
S 17 [+ or -] 2.3* 29* 6* 6*
Si 1.7 [+ or -] 0.3* 3* 0* 3*
Fe 1 [+ or -] 0.1 1 <0.01 0.5

Other Elements, [micro]g/L

Ag 25 [+ or -] 5 50 <5 25
Al 152 [+ or -] 51* 473* <40* 473*
As 60 [+ or -] 20* 183* <50* 23*
B 31 [+ or -] 3 45 <10 33
Ba 39 [+ or -] 6* 75* 22* 24*
Be 1 [+ or -] 0 <2 <2 <2
Cd 2 [+ or -] 0 2 <2 2
Co 5 [+ or -] 0 <10 <10 <10
Cr 3 [+ or -] 0 <5 <5 <5
Cu 5 [+ or -] 0 <10 <10 <10
Mn 4 [+ or -] 2 26 <2 6
Mo 8 [+ or -] 2 19 <10 <10
Ni 5 [+ or -] 0 <10 <10 <10
Ph 10 [+ or -] 0 <20 <20 <20
Se 63 [+ or -] 9 128 <100 50
V 5 [+ or -] 0 <10 <10 <10
Zn 11 [+ or -] 4 50 <5 18

 Station 5

 Mean Max Min Storm

Major Elements, mg/L

Ca 60 [+ or -] 0.0 84 32 32
K 8 [+ or -] 3.3 25 3 8
Mg 25 [+ or -] 0.0 37 10 10
Na 18 [+ or -] 5.8 52 5 5
S 16 [+ or -] 2.2 26 7 7
Si 2.1 [+ or -] 0.33 0 3
Fe 0.1 [+ or -] 0.1 0 <0.01 0.4

Other Elements, [micro]g/L

Ag 20 [+ or -] 6 50 <5 <5
Al 93 [+ or -] 33 300 <40 300
As 75 [+ or -] 26 201 <50 23
B 29 [+ or -] 4 43 <10 40
Ba 52 [+ or -] 6 82 30 34
Be 1 [+ or -] 0 <2 <2 <2
Cd 2 [+ or -] 0 3 <2 <2
Co 5 [+ or -] 0 <10 <10 <10
Cr 3 [+ or -] 0 <5 <5 <5
Cu 6 [+ or -] 1 10 <10 10
Mn 1 [+ or -] 0 3 <2 3
Mo 7 [+ or -] 1 13 <10 <10
Ni 5 [+ or -] 0 <10 <10 <10
Ph 13 [+ or -] 3 <20 <20 <20
Se 57 [+ or -] 7 109 <100 109
V 7 [+ or -] 4 15 <10 <10
Zn 7 [+ or -] 2 13 <5 8

Number of samples = 11 (Stations 1, 2, and 3) and 8 (Station 5).
When a reading is reported as being below the level of detection,
detection level/2 was used as estimate for determining averages.

Note: Data in bold for Station 3 (Flat Branch) indicate where that
tributary is statistically different than at least one of the other
Darby Creek stations (see Table 7) indicated with *.

TABLE 7
Statistical comparison of Big Darby Creek sampling stations
with Flat Branch sampling station 3 (t-test, at 95%
confidence interval of difference).

Element Paired t-test, p-value

 Station 1 Station 2 Station 5

Ca 0.024 0.002 nd
Mg 0.002 0.000 0.023
S nd 0.000 0.013
Al 0.015 0.031 nd
Ba 0.036 0.010 0.018
Si nd nd 0.014

nd = no significant difference at a = 0.05