FRESHWATER STREAM INVERTEBRATES: RESPONSE TO WATER QUALITY IMPAIRMENT AND PHYSICAL HABITAT ALTERATION

Transcription

1 Technical Paper #0508 FRESHWATER STREAM INVERTEBRATES: RESPONSE TO WATER QUALITY IMPAIRMENT AND PHYSICAL HABITAT ALTERATION Prepared by: Bill Isham Weston Solutions, Inc. (WESTON ) For Presentation at: StormCon 2005 July 18-21, 2005 JW Marriott Grande Lakes Orlando, FL, USA 05P

2 FRESHWATER STREAM INVERTEBRATES: RESPONSE TO PHYSICAL HABITAT ALTERATION AND WATER QUALITY IMPAIRMENT IN SOUTHERN CALIFORNIA Bill Isham, Weston Solutions, Inc., Carlsbad, CA INTRODUCTION Preservation of the biological integrity of freshwater stream habitats and nearshore marine receiving waters is the primary goal of coastal water quality management programs. While studies of nearshore marine biological resources have been conducted for decades, such studies have only recently been initiated in coastal southern California freshwater streams. Biomonitoring of benthic macroinvertebrates has become an increasingly widespread tool in the measurement of ecological response to urban runoff. Heavy urbanization in southern California in close proximity to the Pacific Ocean has created great challenges to control non-point source pollution. Physical alteration of natural drainages in the form of impervious surfaces and flood control channels has compounded the issues of biomonitoring, as storm flows lack the benefit of the natural retention times evident in non-channelized drainages, and the degraded physical habitats are not ideal for biological uses. Interpretation of biomonitoring results in watersheds with physically altered habitats becomes complicated when water quality and physical habitat quality must be weighed to determine realistic use attainability by the benthic macroinvertebrate community. The Regional Water Quality Control Boards in southern California have included requirements for biomonitoring of benthic macroinvertebrates within municipal NPDES permits. In Los Angeles County, the permitted agency is the Los Angeles Department of Public Works. In Orange County, the permitted agency is the County of Orange Resources and Development Management Department, and in San Diego County, the San Diego County Municipal Copermittees. Each county agency developed a monitoring plan to assess watershed-scale impacts of urban runoff, with biomonitoring stations strategically located throughout the various watersheds (Figure 1). Ideally, each watershed should contain a monitoring site in the lower reaches of a watershed, and another site located in the mid to upper reaches of the watershed, although in some cases a watershed of special concern contained more monitoring sites. Additionally, each of the three regional studies included three sites designated as reference sites, with little or no urban runoff. This paper presents the results of biomonitoring surveys in Los Angeles, Orange, and San Diego counties with two primary goals: to present a large-scale overview of the application of a recently developed Index of Biotic Integrity, and to assess the relationship between benthic community quality and physical habitat quality. All of the studies were conducted by the same team of biologists using identical methods. 1

3 Figure 1. Project Study Area. 2

4 METHODS There are several methods for the sampling and analysis of benthic macroinvertebrates that are being used in California, and analyses have indicated that all yield statistically similar results. For the three studies discussed here, all employed the California Stream Bioassessment Procedure (Harrington 1999). This protocol was developed by the California Department of Fish and Game (CDFG) and gives detailed procedural information for the field collection, laboratory processing, and data analysis of benthic macroinvertebrate samples. To summarize the protocol, the field survey includes the collection of three composite samples taken from wadable riffle habitat, each representing 6 ft 2 of benthic habitat, as well as a rapid quantified physical habitat assessment. Laboratory sample processing involves the random removal of 300 benthic macroinvertebrates from each sample and taxonomic identification to standard levels of effort; Genus level for most insects, Family or Order level for most non-insects. Benthic macroinvertebrate data analysis consists of the calculation of a variety of biological metrics, as well as a multi-metric Index of Biotic Integrity (IBI). The IBI, specific for southern California, was developed by the CDFG in 2003, and provides a numerical and qualitative rating system for biomonitoring sites. The IBI score is the sum of seven metrics (Table 1). The metrics were selected based on the ability to show a consistent (linear) dose response to ecological disturbance gradients and on a lack of correlation to other metrics. Additionally, to assess the relationship between benthic community quality and physical habitat quality, a scatter plot correlating IBI scores and physical habitat scores was created. Table 1. Index of Biotic Integrity Parameters and Scoring Ranges. % CF+CG % Non- Insect % Tolerant Number Coleoptera Number Predator % Intolerant Individuals Number EPT Parameter Metric Score >5 > > , Total IBI Scoring Ranges 0-13 Very Poor Poor Fair Good Very Good Physical habitat quality analysis performed in the field included the assessment of 10 parameters. Each parameter was scored on a scale of 0 to 20 and summed, thus 200 was the highest possible physical habitat score for a monitoring reach. The parameters are gauged in a qualitative manner, but the scoring ranges are well defined and the assessment has a high degree of repeatability. Physical habitat 3

5 parameters assessed included Instream Habitat Cover, Substrate Embeddedness, Velocity/Depth Regimes, Sediment Deposition, Channel Flow Status, Channel Alteration, Riffle Frequency, Bank Stability, Vegetative Protection, and Riparian Zone Width The scope and goals of each of the three regional monitoring programs varied somewhat. In Los Angeles County, a total of 14 monitoring sites were sampled, with a focus on the Los Angeles River and Malibu Creek watersheds. In Orange County, 15 monitoring sites were sampled within a relatively small geographical area, including four sites in the 303d listed Aliso Creek watershed. In San Diego County, 23 sites were monitored and were co-located with 10 mass loading/stormwater monitoring stations throughout the region. RESULTS The IBI scores for each monitoring reach are presented in Figure 2, separated by county. For each county program, the majority of the monitoring sites receiving urban runoff (test sites) were rated Poor and Very Poor. One reference site in the Los Angeles River watershed was rated Very Poor, and, based on visual observations of surrounding land uses, the field sampling biologists questioned the validity of the reference designation for the site. All other reference sites were rated in the Fair and Good ranges, and were the highest rated sites in each county program. 60 Very Good 50 Reference Site Good Test Site 40 Fair Los Angeles County Orange County San Diego County Poor 10 Very Poor REF-AT2 REF-SVC REF-CS CC-CR TC-AP LC-133 SD-AP SJC-74 TC-DO AC-ACP SJC-CC AC-CCR AC-PPD SC-MB EC-MD REF-DLC3 REF-DLC REF-SC SMR-CP SMR-WGR AHC-ECR MB-RC SD-DDH SDR-MT CC-FB BVR-CB CCC-805 TC-TCNP ESC-EF GVC-WB AHC-MR LPC-CCR SR-WS SLRR-BR SR-94 ESC-HRB SLRR-MR SDR-1 Figure 2. Index of Biotic Integrity Scores. Fall

6 Although not quantified for this paper, the estimated amount of urban runoff as a factor of area of impervious surfaces and urbanization appeared to have a strong relationship to IBI scores. The extent of urbanization was estimated through examination of aerial photographs and GIS maps, and it is the goal of these investigators to quantify this information in the future. In Los Angeles County, the three highest rated test sites were located in zones of the watersheds where cumulative urban runoff was considerably less than the remaining test sites. The three lowest sites were located in the Los Angeles River watershed. The same trend was observed in Orange County, where the highest rated test site is a borderline reference site, with almost no urban runoff. As IBI scores decreased, the estimated amount of developed watershed areas increased. In San Diego County, the two highest rated test sites were in the least developed watershed. A large number of the test sites in the San Diego County program had very similar IBI scores, with correspondingly similar levels of estimated urbanization. To assess the relationship between benthic macroinvertebrate community quality and physical habitat quality, scatter plots correlating IBI score and physical habitat score were created (Figure 3). One analysis included the reference sites, and one excluded the reference sites. When the reference sites are included, R 2 (correlation coefficient) is 0.29, indicating a poor relationship between macroinvertebrate quality and physical habitat quality. It should be noted that approximately one-third of the test sites had physical habitat quality scores within the range of the reference site scores. All but one of the reference sites were in a cluster well outside of the test sites, with IBI scores of 30 and above. When the reference sites were excluded from the correlation analysis, the R 2 was This indicates that there was virtually no relationship between macroinvertebrate community quality and physical habitat quality in the presence of urban runoff. SUMMARY IBI Values IBI Values Reference Site Test Site R 2 = Physical Habitat Test Site R 2 = Physical Habitat Figure 3. Relationship of Index of Biotic Integrity Scores to Physical Habitat Quality Scores. Results of three large-scale regional benthic macroinvertebrate monitoring programs from Los Angeles, Orange, and San Diego counties were analyzed. Benthic community quality was quantified using a southern California IBI and was compared to the physical habitat quality scores of each monitoring reach. The purpose of the comparison was to determine if physical habitat quality was a limiting factor in the colonization potential of benthic macroinvertebrates. Over the coastal southern California region, nearly all monitoring sites receiving urban runoff had IBI scores rated Poor and Very Poor. While most 5

7 sites with very poor physical habitat quality had poor quality macroinvertebrate assemblages, many sites that had very good physical habitat quality also had poor quality macroinvertebrate assemblages. Regression analysis indicated that sites receiving substantial urban runoff showed almost no correlation between habitat quality and benthic macroinvertebrate community quality. Analysis of estimated amount of urbanization in watersheds above the monitoring sites indicated that the area of urbanization likely had a much greater effect on benthic macroinvertebrate community quality. Future quantification of the area of urbanization, impervious surfaces, and land use types and their relationship to benthic macroinvertebrate community quality is necessary to confirm this premise. LITERATURE CITED Harrington, J.M California stream bioassessment procedures. California Department of Fish and Game, Water Pollution Control Laboratory. Rancho Cordova, CA. 6