WATER QUALITY DEGRADATION IN URBAN STREAMS OF THE ...

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International Symposium on Urban Storm Runoff (University of Kentucky, Lexington, Kentucky-July 23·26, 1979)

WATER QUALITY DEGRADATION IN URBAN STREAMS OF THE SOUTHEAST: WILL NON-POINT SOURCE CONTROLS MAKE ANY DIFFERENCE?* by

Alfred M. Duda, Hydrologist David R. Lenat, Biologist

David Penrose, Biologist

North Carolina Department of Natural Resources

Division of Environmental Management

Raleigh. North Carolina 27611

Abstract. Amethodology is presented for using aquatic biolog­ ical monitoring to assess whether the water quality impact of urban stormwater runoff is severe enough to warrant abatement. Sampling was conducted in seven urban streams in four North Carolina cities. Biological communities indicative of grossly degraded water quality were found in each urban stream reach compared to up­ stream or adjacent rural control stations. Traditional measure­ ments of water chemistry were compared to the biological results. Observations were made concerning the sources of water pollution in the seven urban watersheds. While no major point sources were known to exist. numerous unrecorded sources of pollution - other than urban washoff - may have contributed to the problem. Three general types of urban streams were identified: the inner city stream, the suburban stream, and the receiving stream. If enough funding was expended, biological integrity might be restored to suburban and receiving streams. However, the cost of discovering unrecorded urban sources of pollution through monitoring and the economic (and political) costs of requiring pollution abatement may make the restoration of biological integrity an unattainable goal in inner city urban streams. Introduction

that the water chemistry problem is severe enough to warrant abatement. Without a measure of the impact of these pollutants on aquatic life. information on urban stormwater chemistry alone may result only in recommendations for continued study. rather than abatement of pollution.

Federal legislation enacted during the 1970's focused water pollution abatement efforts on point source problems. During this time, extensive studies of non-point sources were being conducted. Now that many of these investigations are complete, it is becoming increasingly evident that urban stormwater runoff is a significant contributor to our nation's water quality problem.

The objective of this paper is to share some of the problems we have encountered in North Carolina in monitoring water quality in urban streams. To deal with these problems, a meUodol­ ogy is presented that util izas the monitoring of aquatic invertebrate communities to determine whether the impact of urban stormwater runoff is severe enough to warrant abatement. The results of this biological sampling are contrasted with traditional chemical water quality measurements made in several cities in North Carolina.

The goal of many of these studies was to collect data for calibrating stormwater quality models. The urban watersheds were treated as unit source areas of pollutants that washed off streets, roofs, and lawns. While this "black box" approach may be sufficient for Simulating historical data, it may be inadequate for predicting the impact of abatement measures because the actual sources of pollutants were not identified. Decision makers may be hesitant to spend the taxpayers' money on pollution control if the sources have not ade­ quately been identified or if they are not sure

The Environmental Setting The Southeast, extending from Maryland to Alabama, is characterized by three distinct physi­ ographic provinces: the Appalachian mountains, the Piedmont plateau, and the Coastal Plain. In the western part of the region, rugged topography limited the extent of urban areas and confined development to the valleys. In the flat Coastal

*The work reported herein was financed through an EPA Wastewater Treatment Management Planning Grant (IIP004l980l 0) . 151

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sewered system had numerous cross-connecti ons and bleeders joined to storm sewers that contributed raw sewage during all flow regimes.

C: ~I

APPALACHIAN MOUNTAINS

D

PIEDMONT PLATEAU

Ragan et al. examined water quality in eight urban. subur~and rural streams i"7Maryland adjacent to the District of Columbia. No trend in BODS was found except for large values in three streams known to have illegal sewage connections to storm sewers or overloaded sewers that overflowed at the slightest rainfall. No trends in dissolved oxygen or nutrients were found, perhaps because the biweekly sampling missed stormflows.

COASTAL PLAIN

Figure 1. Location of physiographic regions and several cities in North Carolina.

A severe problem with sediment was found in streams of this portion of the Maryland Piedmont. While rapid development caused large sediment loads during the 1950's. most of the present sedi­ ment load stems from streambank erosion. The additional impervious area caused by urbanization has resulted in dramatic increases in peak flows of urban stormwater and has caused severe channel erosion. Stream channels that were 9-10 feet wide in 1948 are now 35-40 feet wide. Severe degra­ dation of fish populations was also noted in these streams. 7

Plain. urbanization was limited by swamps. floods, mosquitoes, and the agrarian nature of the area. It is in the Piedmont portion of the Southeast that conditions were most favorable for urbanization. Figure 1 illustrates the location of these three physiographic regions in North Carolina. Urban areas were established in the Piedmont because of the abundant supply of water that attracted industry. As a result. many medium size cities (populations of 30,000 to 150.000) sprang up along rivers. Most of these communities have separate sewer systems for sewage and stormwater. The older central business districts. served by underground storm sewers. are normally surrounded by older residential areas with open channeled streams. Rapidly developing suburban areas may be found outside of the older inner cities.

Urban Stream Sampling Problems Characterization of the magnitude and impor­ tance of the urban stormwater quality problem is not an easy task. In many instances, it may be difficult to document the real source of the pollu­ tion problem. It may be non-point source in origin: washout of air pollution; washoff of urban land; garbage near streams; polluted groundwater; leaking or broken sanitary sewers; cross connections (bleeders or bypasses) between sanitary and storm sewers; or overflow of overloaded sanitary sewers. It may also be pOint source in origin, primarily benthic resuspension of regulated (and unregulated) point sources or small (seemingly unimportant) or intermittent pOint sources. In all likelihood, the pollution problem in urban streams of the Southeast is caused by a mixture of these sources, each with very different strategies for abatement.

Previous Water Quality Studies Numerous water quality studies have been undertaken in the Southeast to investigate the impact of urban stormwater runoff. In the late 1960'S. researchers at Duke University began to monitor the quality of urban runoff in Durham, North Carolina. The study demonstrated that large quantities of sediment. bacteria, metals. and oxygen-demanding substances can reac~ streams draining urban areas.l Colston contlnued the early investigations in a widely publicized study for the Environmental Protection Agency.2 More recently. Rimer and others reported the results of water quality sampling near Raleigh, North Carolina. 3 Significant loads of pollutants came from central business district or commercial areas compared to residential or rural areas. The dissolved oxygen in receiving streams was depressed an average of one mg/l by urban stormwater runoff.

Once an assumption is made concerning the sources of pollution in urban areas. the next prob­ lem involves the choice of sampling strategy. Grab or random sampling is not sufficient in many cases. Expensive automated samplers are necessary for taking samples during storm event~. ~his instru­ mentation often breaks down. leavlng lncomplete records upon which to base annual yields. The equipment is costly, making the installati?n of many stations cost prohibitive. and extenslve man­ power must be devoted to preventative maintenance.

In Northern Virginia, Randall et al. investi­ gated the water quality in runoff from an urban­ izing watershed. 4 While highly significant loads of solids, organic matter, and nutrients came from the mixed urban watershed. smaller amounts came from recently developed residential areas. A con­ tinuation of the study found that the degree of imperviousness of urban watersheds had the greatest influence on pollutant loading. 5

The suite of water quality parameters to be analyzed is often limited by the cost of laboratory determinations as well as limited number of samples that can be taken by automated units. Consequently, some pollutants which may cause aquatic bi?logical degradation are never monitored. Many tOX1C sub­ stances are not routinely monitored because the laboratory cannot measure them. In the past. water quality was considered to be degraded when a physical or chemical measurement exceeded the water quality standard. These stand­ ards were primarily developed for controlling point source discharges, and they may be ineffective in controlling non-point source pollutants in urban

In Maryland. disease causing pathogens and bacteria were found in urban stormwater runoff from the Baltimore area. 6 Recovery of these organisms was not correlated with season. rainfall amount. time since last rain, or streamflow. The authors concluded that the old (65 year old) separately 152

Field

areas. Water quality standards normally do not provide for synergistic or antagonistic effects between pollutants that can degrade biological populations. Slug doses of toxics or chemicals. accidentally or intentionally dumped several times a year in urban areas, can totally decimate the aquatic biota. It is clear that a technique is needed for integrating the water quality effect of unrecorded sources of pollutants and for over­ coming the inadequacies of water quality standards, instrumentation problems. and measurements of water chemistry. This direct approach involves the monitoring of aquatic macroinvertebrate communities. Bio1ogica~nitorin9

Sam~ling Methodolo~

Samples were collected by the "kick" method. A net is positioned upright on the streambed, while an upstream area of one square meter is physically disturbed for a specified time. The use of arti­ fical substrate samplers was avoided because this technique may not reflect the effects of natural substrate changes. Kinney et a1. found that the kick technique was t~perior~oth Surber and artifical samplers. At each station a minimum of two replicate samples are collected. Samples are preserved in ethanol and returned to the laboratory. where the organisms are sorted and specimens are keyed to the lowest possible tax­ onomic level with the use of microscopes.

Strate9X

Why Benthic Macroinvertegrates?

Data

Benthic macroinvertebrates are bottom­ dwelling organisms that live in streams. riVers, and lakes. Being an important part of the biolog­ ical food chain. they serve as a source of food for many species of fish. They are useful biolog­ ical monitors because they are found in all aquatic habitats, they are less mobile than many other aquatic organisms, and they are large enough to be easily collected. While short-time critical events or slugs of pollutants may often be missed with chemical sampling. the macro invertebrates reflect both long and short term conditions. Since most species in a macroinvertebrate community have life cycles of a year or more, the effects of a short-term pollutant will generally not be over­ come until the following generation appears.

The North Carolina Division of Environmental Management has developed a series of analysiS techniques which may be used to relate information on the benthic macroinvertebrate commu~\ty to environmental stress (water pollution). Use of this analysis system is intended to determine both the degree of stress as well as the probable stress factors. Level I analysiS concentrates on changes in Density (N), Taxa richness (S), Shannon-Weiner Diversity (H) and a modified Biotic Index (BI). Comparisons are made either with an upstream "control" site or with a series of control data sets generated from studies of unpolluted streams and rivers throughout North Carolina. Level II analysis summarizes data for various taxonomic groups, especially the various orders of the class Insecta. Finally, Level III analysis examines data for indi­ vidual taxa. preferably at the species level. based on the known tolerance (from the literature) of benthic invertebrates to various pollutants.

The use of benthic macroinvertebrates for monitoring water quality is not new. Richardson used them fifty years ago to demonstrate that water Quality was degraded by discharges of domestic sewage~ However, very few biological studies have monitored the impact of urban runoff. In most of the investigations (such as Harrell and Duplechin or Campbell), the impact of sewage discharges has been superimposed over the effects of urban storm­ water runoff. 9,lO

Ana1xsisMethodoJ~

Biological

Monitori!l93~~!Il!;~~yrban

Streams

During 1977 and 1978. the benthic macroin­ vertebrate communities of seven urban streams were sampled. The monitoring occurred in four cities across North Carolina: Asheville, Charlotte, Winston-Salem, and Raleigh. Five streams were sampled extensively each season for at least one year, while two other streams were only occasionally sampled. Predominant urban land use. location !nd drainage area of these streams are included in Table 1. For the sake of hrevi ty, only a cursory

In Massachusetts, urban runoff was found to degrade the macro invertebrate community in a small river. ll However. the organisms were collected on artificial samplers, which may selectively collect only certain types of organisms rather than those that are representative of what is living in the water.12 In Virginia, Lorenz monitored metals accumulations in certain types of macroinvertebrates in an urban reach of a small river. but he did not sample the entire community.13 In Georgia, macroinvertebrates found in an organically polluted urban stream were compared to those in a stream draining a suburban residential area. 14

Table 1. Biological Sampling in Urban Streams Drainage Predominant Stream Area {mi2) Land Use ~~______ Ex tens i .Y_~J,L?~P red:T91r.:T9!~--- Pigeonhouse Br. 2.4 CBD-Commercia1 Raleigh , Raleigh Rocky Br. 1.1 Commerc i a 1 Tar Branch .4 CBD Winston-Salem Salem Cr. 31. 7 Below CBD Winston-Salem 5.2 Within Sween ten Cr. Comm./lndust. Ashevill e

Several conclusions can be drawn from these studies. Physical-chemical sampling underestimates the actual environmental impact of urban pollutants. A reduction in taxa richness (the number of different types of macroinvertebrates) is the most reliable indicator of stress (water pollution). The total numbers of macroinvertebrates are normally increased by organiC pollution and decreased by toxic pollutants. The benthic communities in areas affected by urban runoff are characterized by pollution tolerant types of macroinvertebrates: 01igochaeta (worms) and Chironomidae (midge larvae).

Nasty Br. Stewart's Cr.

153

1.2 CBD-Commercial 5.4 Comm./lndust.

Ashevill e

Charlotte

analysis of the data ;s presented here. Detailed analyses and species lists are available else­ where.15, 16

of the city. This pattern suggests that a slug of toxic material from a spill or intermittent dis­ charge may have occurred prior to the sampling.

Specific Results: Sweeten Creek

The Level II analysis of the data substan­ tiates that severe degradation occurs in the benthic community 1n the urban reach. The more sensitive groups (Ephemeroptera, Plecoptera, Trichoptera) are almost completely eliminated and are replaced with pollution tolerant organisms, especially 01igo­ chaeta (Limnodri1us hoffmeisteri, L. udekamianus, I1¥odri1us tem letonT:-Nais communis) and ch ronomidae { hironomus spp. and Cricotopus spp.).

The adverse impact that unrecorded urban of pollution can have on aquatic life was illustrated by the sampling that was conducted on Sweeten Creek in the mountains of North Carolina. Sweeten Creek begins in the hills surrounding Asheville. North Carolina (population 60.000), and flows through a commercial section of the city. A control station was located upstream of the city and a downstream station was located about one stream mile into the commercial section. The drai~age area was about 5.2 square miles at this pOint, and no significant point source discharges were known to exist. sour~es

t

Genera1 Resul ts Considerable differences in macroinvertebrate communities were expected in the five extensively sampled urban streams because different cities and different physiographic provinces were involved. However, the results were remarkable uniform. In each of the five urban streams, an average sample had only 6-13 taxa (types of macroinvertebrates) compared to the 35-44 taxa expected from the control data. This reduction greatly exceeds the 50 percent reduction criterion for severe stress which has been adopted in North Caro1ina. 15

Table 2. Analysis of Macroinvertebrate Communities Monitored in Sweeten Creek* Level lAnallsi s Parameter Ave. Ave. Ave. Ave. Group

Station 1 (control)

Density (N) 197 Taxa Richness (S) 35.3 Diversity (H) 3.5 Biotic Index (BI) 1.8 Level II Analxsis Taxa Parameter: Richness Station:

Station 2 (urban)

As indicated earlier. a high percentage of Oligochaeta (worms) and pollution tolerant Chironomidae (midge larvae) indicates poor water quality. Figure 2 demonstrates that for each of the five regularly sampled urban streams. these pollu­ tion tolerant groups comprised more than 90 percent of the total organisms that were collected. The macroinvertebrate groups that cannot live in polluted water (mayflies. stonef1ies. caddlsflies. and beetles) were not just reduced in numbers in urban streams. they were usually absent.

564 10.3 1.5 3.8 Density

(% of total)

,

2

2

III

Ephemeroptera (Mayflies Plecoptera (Stonefli es) Trichoptera (Caddisfl ies) Diptera (true fl ies) 01itchaeta worms} "Other" Total

5.5

0.0

17

0

5.5

0.5

36

0

6.3

0.5

27

0

9.8

5.5

13

10

1.0 7.2

3.0 0.8

2

35.3 10.3

100

~ "­ ~

III