A Report to the
Ten Towns Great Swamp Management Committee

January, 2006

As a broad generalization, 2005 macroinvertebrate (MIV) community quality slipped in poorer sites, but held steady or improved in better ones.  Among the 17 sampling sites, 3822 individuals representing a total of 122 species were observed – a decline from the high of 138 species observed in 2004.  For the most part, B-IBI values in 2005 lie within the mean +/- 1 standard deviation range.  Only GB2 and PR1 fell at or below these limits, while GB3, PB1, PR2 and PR3 exceed them.  Over the past six years, the higher quality streams within the Great Swamp watershed, i.e., Primrose Brook, the upper Passaic River, and Indian Grave Brook, have gradually improved with regard to the quality of their MIV communities, while stresses such as sluggish water flow, sedimentation, and resultantly poor substrate conditions at Great, Loantaka, and Black Brooks appear to have limited their capacity to improve. 

Community quality measures show high correlation with most of the various habitat assessments, including Total Habitat scores and the Habitat Values (limited to those features most accurately estimates).  Strong negative correlation is seen between B-IBI measures and total dissolved substances (TDS) (i.e., as TDS increases, B-IBI quality decreases), while the correlation with lack of sediment and substrate embeddedness, bank stability, habitat quality, and stream gradient are all positive.  All of the sites characterized by high mean temperatures (GB5, LB2, GB3, BB1, and PR1) are located just below impoundments and all such sites fall in the "poor" to "very poor" categories of community quality.  The relationship between mean B-IBI value and mean total dissolved substances shows a clear threshold at ca 200 ppm, below which community quality varies from poor to good, but above which, all communities are in the worst categories.  The relationship between mean community quality and mean pH shows that between ca.  7.3 and 7.6 units, community quality varies widely and thus is controlled by other variables.  The three sites that show higher average pH (i.e., LB2, GB3, and GB5) are all associated with plant-productive impoundments.  Relatively high community quality at PR1 and PR2 seem to mismatch their modest habitat quality.  The fact that they are downstream sites in a very high quality stream suggests the importance of upstream sites as potential sources of input for downstream communities.  GB3's low community quality despite a higher habitat quality highlights the long recovery that this community is experiencing following a major dredging operation just upstream (at Silver Lake) a few years back.

Refer to Stream Summaries at the end of this document for more details.

In Figure 05-2, B-IBI values from 2005 samples are compared to samples from 2000-2005.  For reference, the mean scores for each site are shown (horizontal bars) as are scores from 2005 and indications of the high and low range of scores as indicated by 1 standard deviation above and below the mean.  For the most part, B-IBI values in 2005 lie within the mean +/- 1 standard deviation range.  Only GB2 and PR1 fell at or below these limits, while GB3, PB1, PR2 and PR3 exceed them.  Fig. 05-3 shows that despite these comparatively positive results in 2005, B-IBI values were mostly at or below the exceptionally high values observed in 2004.  In Table 05-4, components comprising B-IBI scores are compared for 2005 and 2004.  Declines at GB2 and PR1 mentioned above are joined by a steep fall in community quality at LB3.  In the latter case, this "slip" represents a return to more typical results from this highly stressed site just below the Morris Township sewage treatment plant.  The surprisingly high score at LB3 in 2004 proved to be a "too good to be (lastingly) true" circumstance.  Along with LB3, GB2 hosted about one half the number of species in 2005 that were found in 2004.  At GB2, species reduction included the absence of all representatives of the most stress-sensitive groups (i.e., Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies).  GB2 was swamped by amphipod crustaceans (133 of 209 specimens), while LB3 had high numbers of hydropsychid caddisfly larvae (161 of 204 specimens). 

While one-year comparisons between B-IBI scores for the current and preceding years have been the primary focus of analysis in past reports, a valuable larger perspective on B-IBI community quality scores is available in viewing B-IBI scores over the past 6 years of these surveys, as shown in Figs.  05-4a-e.  These figures permit us to distinguish single year anomalies from overall patterns in site-by-site comparisons over time.  Interpretations of these results will be incorporated into the Stream Summaries section below.  In general, it may be said that over the past six years, the higher quality streams within the Great Swamp watershed, i.e., Primrose Brook, the upper Passaic River, and Indian Grave Brook, have gradually improved with regard to the quality of their MIV communities, while stresses such as sluggish water flow, sedimentation, and resultantly poor substrate conditions at Great, Loantaka, and Black Brooks appear to have limited their capacity to improve.

Even though labeling categories of "very poor", "poor", "fair", and "good" (e.g., see Fig. 05-3) have been assigned in somewhat arbitrary fashion to the numeric B-IBI scale, they have been consistently applied to this study over the years.  In 2005, the communities at PB1 and PR2 rose to join the four sample sites (PB2, PB3, PR3, IG1) in the "good" category for the first time.  However, a slip in community quality at PR1 to "poor" left the "fair" category empty in 2005.  All three stressed streams supported "very poor" communities, with only LB2, GB3, and GB5 inching into the "poor" range. 

As we speculated last June (Pollock, 2004), in June 2004 we saw 12 of 17 sites in the Great Swamp watershed at their best.  We approach the 2006 sampling period with concern for GB2 and PR1 sites where MIV community quality fell in 2005.  Six year results suggest that our better streams continue to reflect in MIV community quality improvement their protected environmental status.  However, our more challenged streams continue with poor MIV communities that show no little sign of significant improvement.

In Table 05-5, I have used a box and bold type to highlight statistically significant correlations (coefficients > +/- 0.482 at df = 15, p<0.05) between the two biotic indexes calculated here, Beck and B-IBI, and environmental variables monitored on June 11, 2005. 

First, it is reassuring that the metrics, B-IBI and Beck Index, continue to be highly correlated with one another (r = 0.948).  These community quality measures show high correlation with changes in most of the various habitat assessments, including Total Habitat scores and the Habitat Values (limited to components easiest to estimate with consistency).  Strong negative correlation is also seen between B-IBI measures and total dissolved substances (TDS) (i.e., as TDS increases, B-IBI quality decreases), while the correlation with lack of sediment and substrate embeddedness, bank stability, habitat quality, and stream gradient are all positive.  Several variables show strong correlation with one another.  For example, it is clear that the percent riffle habitat and the gradient (i.e., slope) of stream sites correlate strongly with most other variables. 

Over the years, one-shot measurements of environmental variables and of MIV community quality taken on a single date during the sampling period, e.g., Table 05-1, have proved useful.  However, a more comprehensive picture that smooths out annual variability can be obtained by repeating the correlation analysis using mean values for B-IBI and for variables averaged from six years of available data, 2000-2005.  Mean values for most variables correlate even more strongly with mean B-IBI community measures using this averaged data.  It is possible to fit an optimal regression line between pairs of such variables and calculate R2 statistic – the coefficient of variation, that displays the degree to which values for a dependent variable (in this case community quality or B-IBI) at each site can be predicted by examining values of an independent variable (in these cases, environmental factors) at these same sites.  An R2 value of 0.792 between habitat values and B-IBI, for example, says that 79.2% of the variability in community quality can be predicted by variations in habitat value – a strong indication that favorable habitat characteristics are related to the composition of resultant communities.  Table 05-6 displays R2 coefficients of variation between mean B-IBI values (i.e., community quality) and various environmental variables.  These determinations are made by generating a mathematical equation that best fits the two sets of data being compared.  Such an equation may take the form of a straight line (linear) regression or it may use a more complex curvilinear (polynomial) equation to make such comparisons.  Remembering that the higher the R2 value, the more closely the two variables appear to be related, it is clear that pH and turbidity have little to do with shaping community quality directly, but all the other variables reveal high levels of correlation with community quality.  It is important to keep in mind that correlation does not necessarily reflect causation.  Both variables may be comparably influenced by some third (unidentified) variable.

This comparative approach may help us to understand better the potential influences over MIV community quality in the Great Swamp watershed.  Graphic depictions of these comparisons (Figs.  05-5a-f) serve to illustrate relationships between mean B-IBI estimates of community quality (i.e., the degree of stress reflected in community composition) and mean values for various key environmental parameters.  In each case, symbols distinguish each of the five stream sites and particularly noteworthy sites are identified specifically.  There is a clear contrast between the distinctly better conditions associated with high community quality Passaic River and Primrose Brook sites versus the more stressed streams, Great Brook, Loantaka Brook, and Black Brook.  In Fig. 05-5a, site-wise B-IBI values are compared to mean temperatures occurring at each site.  Note that all of the sites characterized by high mean temperatures (GB5, LB2, GB3, BB1, and PR1) are located just below impoundments and that all such sites fall in the "poor" to "very poor" categories of community quality.  All sites ranking "fair" or "good" in quality occur at mean mid-June temperatures less than 21 degrees centigrade.  The relationship between mean B-IBI value and mean mid-June total dissolved substances, in Fig. 05-5b, shows a clear threshold at ca 200 ppm, below which community quality at all but one site varies from fair to good, but above which, all communities are in the worst categories.  Only two sites appear to be exceptional in terms of mean B-IBI vs.  mean dissolved oxygen, Fig. 05-5c.  PR1 shows higher community quality (i.e., B-IBI score) than one might expect from its low mean dissolved oxygen – likely the result of its location below a warm impoundment.  In contrast, the effectiveness of the Chatham Sewage Treatment plant in releasing water of high oxygen content can be seen in the case of the BB2 – a site of poor community quality.  The relationship between mean community quality and mean mid-June pH, in Fig. 05-5d, shows that between ca.  7.3 and 7.6 units, community quality varies widely and thus is controlled by other variables.  The three sites that show relatively high average pH (i.e., LB2, GB3, and GB5) are all associated with plant-productive impoundments.  In contrast, three sites (i.e., LB3, BB2, and PR1) include two (the first two) at which the pH is probably influenced by sewage treatment protocols.  A survey of mean mid-June turbidity vs.  mean B-IBI, shown in Fig. 05-5e, highlights two sites with poor quality but very low turbidity, and two of surprisingly high quality despite high turbidity.  In the former instance, these sites also reflect the effectiveness of sewage treatment on waste water clarity.  In the latter case, both PR2 and PB1 possess decent substrate conditions, but they lie just downstream from major roadways (I-287 and Lee's Mill Road respectively), and perhaps other sources of siltation.  All the "good" quality sites are found at mean turbidity less than 2 FTU.  And finally, mean community quality is compared to mean habitat quality in Fig. 05-5f.  Relatively high community quality at PR1 and PR2 seem to mismatch their modest habitat quality.  The fact that they are downstream sites in a very high quality stream suggests the importance of upstream sites as potential sources for downstream communities.  GB3's low community quality despite a higher habitat quality highlights the long recovery that this community is experiencing following a major dredging operation just upstream (at Silver Lake) a few years back.

As noted last year (Pollock, 2004), three major habitat modifiers that appear to most adversely influence immediately downstream sites within the Great Swamp watershed, are sewage treatment plants (impact BB2 and LB3), impoundments (impact BB1, LB2, GB3, GB5, PB3, and PR1), and parking lot runoff/detention ponds (impact LB4, GB4).  There is a clear distinction between B-IBI assessed macroinvertebrate community quality at struggling Black, Loantaka, and Great Brooks and much higher quality at Primrose Brook and Passaic River sites.  From the distribution of the three habitat modifiers, it is clear that nearly all sites in poorer quality streams experience one of these sources of stress. 

1. Monitoring of these 17 sampling sites should be continued.  Time-trend graphs illustrate the value of looking at multi-year patterns in addition to single year changes in MIV community quality.  I will submit a proposal for the extension of this monitoring program to the Ten Towns Great Swamp Watershed Management Committee.
    
2. The MIV community at GB2 (just above the Great Brook Stream Flow Monitoring Station) fell to an all-survey low this year.  Species richness was only one-half that of 2004 and included the absence of Ephemeroptera, Plecoptera, and Trichoptera.  No comparable decline in environmental conditions occurred there.  This site bears watching in 2006.
    
3. Overall habitat limitations and heavy siltation continue to plague Loantaka and Great Brooks.  Efforts to reduce run-off flow into these streams and to stabilize their banks would likely improve in-stream conditions substantially.

Barbour, M.T., J.Gerritsen, B.D.Snyder, and J.B.Stribling.  1999.  Rapid Bioassessment Protocols for Use in Streams and Wadeable Rivers: Periphyton, Benthic Macroinvertebrates and Fish, Second Edition.  (EPA 841-B-99-002).  U.S.  Environmental Protection Agency; Office of Water; Washington, D.C.

Pollock, L.W.  2000.  The Macroinvertebrate Communities of the Great Swamp Watershed.  A Report to the Ten Towns Great Swamp Management Committee.  General Introduction and Methods: 2000 and Subsequent.  12 pp., Tables & Figures.

Pollock, L.W.  2004.  The Macroinvertebrate Communities of the Great Swamp Watershed, June, 2004: Results.  A Report to the Ten Towns Great Swamp Management Committee.  11 pp, 6 Tables, 6 Figures.

Figure 05-2.  B-IBI values for 17 sampling sites within the Great Swamp watershed for June, 2005 & June, 2003 compared with the mean and range of values from 2000-2005.

Figure 05-3.  Mean B-IBI vs. mean habitat values for data from 2000-2005.

Figure 05-4a.  Six-year trends (2000-2005) in B-IBI values for Black Brook sites.

Figure 05-4b.  Six-year trends (2000-2005) in B-IBI values for Loantaka Brook sites.

Figure 05-4c.  Six-year trends (2000-2005) in B-IBI values for Great Brook sites.

Figure 05-4d.  Six-year trends (2000-2005) in B-IBI values for Primrose Brook sites.

Figure 05-4e.  Six-year trends (2000-2005) in B-IBI values for Passaic River and Indian Grave Brook sites.

Figure 05-5a.  Mean B-IBI vs. mean temperature (2000-2005). Noteworthy sites are labeled (see text).

Figure 05-5b.  Mean B-IBI vs. mean total dissolved substances (2000-2005). Noteworthy sites are labeled (see text).

Figure 05-5c.  Mean B-IBI vs. mean dissolved oxygen (2000-2005). Noteworthy sites are labeled (see text).

Figure 05-5d.  Mean B-IBI vs. mean pH for data from 2000-2005

Figure 05-5e.  Mean B-IBI vs. mean turbidity (2000-2005). Noteworthy sites are labeled (see text).

Figure 05-5f.  Mean B-IBI vs. mean habitat value (2000-2005). Noteworthy sites are labeled (see text).

All Figures.     All Tables.     Appendix 1.